Speed Endurance Training to Improve Performance

ABSTRACT

In many sports, the physical dimension plays a crucial role in determining athletic performance. This review provides insights into the effectiveness of speed endurance training (SET), that is, exercise training performed at intensities higher than that eliciting maximum oxygen uptake (V̇O₂‐max), on performance across different sports and event durations, that is, lasting 20–60 s, 1–10 min, and 10–60 min, as well as repeated intense exercise, as found in sports like football and basketball. Only studies with trained subjects and athletes are reviewed. For each event, the description is divided into the effect of SET, either alone or in combination with aerobic training or power/resistance training. We highlight that SET enhances performance across all event durations, even when training volume is markedly reduced. The performance enhancements arise despite no changes in V̇O₂‐max and are typically associated with improved exercise economy and a greater capacity to handle muscle ionic shifts and counter exercise‐induced reductions in pH. Thus, athletes can benefit from periods with SET—either performed alone or in combination with other training modalities.

1. Introduction

In elite sports, the difference between winning and missing the podium can be remarkably tight, with mere fractions of a second separating athletes at the highest level of competition. A few examples from Olympic running events illustrate this. In the 2016 Rio Olympics men's 400‐m Final, Wayde van Niekerk of South Africa broke the world record with a time of 43.03 s, but the competition was fierce, with the top four runners separated by just 0.36 s. In the 1984 Los Angeles Olympics women's 800‐m final, Nawal El Moutawakel became the first Moroccan woman to win Olympic gold, but the top four finishers were separated by only 0.54 s. Such narrow margins of victory are not confined to shorter races; even in longer distances, differences can be minuscule. In the 2012 London Olympics men's 10 000‐m final, Mo Farah's first Olympic gold came in a race where the top four were separated by just 0.71 s. These examples highlight the importance of effective training strategies to optimize performance.

In recent years, speed endurance training (SET) has gained attention due to its effectiveness to improve sports performance in a time‐efficient manner. SET encompasses interval training performed at intensities above that corresponding to maximum oxygen uptake (V̇O₂‐max) and is hence dominated by contributions from anaerobic energy systems [1]. It has to be recognized that V̇O₂‐max often is reached at intensities below 20% of maximal intensity. For example, an individual may reach V̇O₂‐max during cycling at an external load of 200 W, while being capable of achieving a peak power output over 1000 W, for example, during a maximal effort sprint, and even more than 1500 W during an explosive action such as a high jump. Therefore, for most individuals, SET encounters more than 80% of all exercise intensities. SET is divided into “production training” (SET‐P), which focuses on high anaerobic, primarily glycolytic, ATP turnover during repeated short intervals (10–40 s) with relatively long recovery periods, for example, 30‐s intervals separated by 3 min of recovery, and “maintenance training” (SET‐M) with exercise periods lasting 5–120 s with shorter recovery periods to develop fatigue during repeated bouts, for example, 1‐min intervals separated by 1 min of recovery, thereby increasing exercise tolerance. It is well established that energy turnover and substrate utilization during SET are influenced by exercise intensity and duration, as well as the duration of the recovery periods between repeated bouts. For instance, during a maximal 6‐s bout, muscle anaerobic ATP production derives from around 10% net ATP degradation, 50% from phosphocreatine (PCr) utilization, and 40% from glycolysis [2], whereas during 30 s of maximal exercise, these contributions shift to around 1%, 29%, and 70%, respectively [2]. Additionally, when maximal bouts are repeated, total work decreases, and the rate of glycolysis is lowered, likely due to low muscle pH and progressive higher aerobic energy contribution [2, 3, 4]. Therefore, when interpreting the data obtained in the studies presented, these factors should be considered.

In this review, we discuss the impact of SET, alone or in combination with other training forms, on performance across different sports and event durations in already well‐trained individuals and athletes. Specifically, we cover events lasting 20–60 s, such as the 400‐m run and 50‐m swimming; 1–10 min, like the 800‐m and 1500‐m runs, 4‐min track cycling, and 2000‐m rowing; 10–60 min, such as the 5000 and 10 000‐m runs, as well as longer events (> 60 min) such as marathons and triathlons. Furthermore, we address performance in sports requiring repeated intense actions, such as football, basketball, team handball, and Madison cycling. By examining these diverse contexts, we provide insights into the effectiveness of SET in a range of sports and competitive environments. It should be emphasized that most SET interventions utilized running or cycling, and not all studies used a sport‐specific field test.

Article search for this review was conducted using keywords such as training intervention, high‐intensity interval training, speed endurance training, sprint interval training, trained individuals, and athletes in the PubMed database and Google Scholar. Relevant articles were screened, and only studies dealing with SET where the subjects were categorized as trained, well‐trained, or athletes with a V̇O₂‐max higher than 45 mL kg⁻¹ min⁻¹ for females and 50 mL kg⁻¹ min⁻¹ for males were included. Thus, it should be emphasized that some articles with sport‐specific training and testing are not included, such as the study by Papandreou et al. [5], which did not meet the inclusion criteria due to participants' V̇O₂‐max levels being below the defined thresholds. In that study, national‐class kayakists completed 8 weeks of training consisting of eight bouts of 30‐s paddling at an intensity corresponding to 120% V̇O₂‐max, separated by 1 min recovery, three times per week. Despite the intervention comprising approximately 15 times less training volume, improvements were observed in 200‐m time trial performance and paddling economy at submaximal speed [5]. Additionally, only statistically significant (p < 0.05) or near‐significant (p < 0.1) changes with training are presented. It is important to note, however, that lack of statistically significant changes in a study does not necessarily imply that an intervention cannot benefit elite athletes. In elite sport, even a single athlete gaining an advantage from an intervention can be meaningful.

Each section begins by presenting examples of sports events that fall within the specified time frame. The aim is also to provide insights into the physiological responses to SET training. Thus, when discussing individual studies, the physiologically significant changes are highlighted and summarized at the end of each section to offer a potential mechanistic basis for the performance improvements. For further exploration of these topics, see previous publications [6, 7].

2. Short Events (20–60 s)

There are a number of sports events lasting 20–60 s, such as 200‐m sprint canoeing (male: ~38 s; female: ~45 s) or kayaking (~33 s; ~38 s), 400‐m run (~43 s; ~48 s) or hurdles (~45 s; ~51 s), 500‐m speed skating (~34 s; ~36 s) and 500‐m time trial cycling (~29 s; ~33 s). To test the effect of SET on events lasting 10–60 s, the running distance in 30 s or time of a 200‐m run as well as mean power during a Wingate test (maximal effort in 30 s) are often used in interventions with running and cycling.

2.1. Speed Endurance Training (Table 1)

TABLE 1.

Effect of speed endurance training (SET) on performance during exercise (10 s to 60 min) and physiological adaptations in well‐tained individuals.

Study	Subjects (no., M/F, age, intervention)	V̇O2‐max	Intervention (duration, sets/reps, work/rest, frequency, Δ% volume)	Performance, V̇O2‐max and RE	Effect (Δ%)	Adaptations	Effect (Δ%)
Bickham et al. (2006)	7 M runners Age: 28 years SET‐P: n = 7	58.0	SET‐P: 6 weeks of 14–30 × 40–100 m of near maximal sprint (90%–100%); 5 min rest. 3/week	Intense exercise (~2.5 min)	+11	Type II fibers	+6
						MCT1	+50
Dawson et al. (1998)	9 M trained Age: 22 years SET‐P: n = 9	57.0	SET‐P: 6 weeks of 3–5 set of 4–8 × 40–100 m of near maximal sprint (90%–100%); 2–4 min rest. 3/week	Repeated sprint Intense exercise (~1 min)	+2	Phosphorylase activity	+40
					+11	CS activity	−36
Fischer et al. (2023) + Jeppesen et al. (2022)	12 M elite ice hockey players Age: 18 years SET‐P: n = 12 CON: n = 12	53.0	SET‐P: 4 weeks of 6–10 × 20‐s skating bouts > 95% of maximal skating speed; 2 min rest, 3/week + regular on‐ice training 30–40 min pr training session	YoYo‐IR1‐IH test (on ice)	+14	Stroke volume	+10
				Incremental test time exhaustion	+6.5	Left atrial end‐diastolic	+23
				V̇O2‐max	+4.7	Left atrial end‐systolic	+42
						Circumferential strain	+0.9
			CON: 4‐weeks of regular on‐ice training ~60‐min duration, 3/week
Gunnarsson et al. (2012)	7 M football players Age: 23 years SET‐P	60.0	SET‐P: 5 weeks of 5–9 × 30‐s all‐out; 3 min rest, 1/week +11% training volume	Intermittent running (Yo‐Yo 2)	+11	MCT1	+9
						Na+–K+ subunit β1	−13
Hov et al. (2022)	21 M trained Age: 23 years SET‐P: n = 9 SET‐M: n = 12 HIIT: n = 10	63.0	SET‐P: 8 weeks of 10 × 30‐s all‐out; 3.5 min active rest, 3/week	3‐km (~11 min)	+2.2	—	—
				300‐m sprint (~45)	+3.3
			SET‐M: 8 weeks of ~8 × 20‐s all‐out; 10‐s passive rest. Aiming to exhaust the subject during eighth or nineth interval. 3/week	V̇O2‐max	+3.3
				3‐km (~11 min)	+4.1
				300‐m sprint (~45‐s)	+4.4
				Stroke volume	+3.8
Iaia et al. (2008)	15/16 M runners Age: 33 years SET‐P: n = 8/9 CON: n = 7	56.0	SET‐P: 4 weeks of 8–12 × 30‐s all‐out; 3 min rest, 3–4/week −64% training volume	Intermittent running (Yo‐Yo 2)	+19	Na+–K+ subunit α1	+29
				Intense exercise (~1½ min)	+27	Na+–K+ subunit α2	(+16)
				30‐s all‐out	+7	NKCC1	(+14)
						NHE1	+30
			CON: continued with normal training habits on a weekly distance of ~45 km
Iaia et al. (2017)	19 M football players Age: 17 years SET‐M: n = 9 SET‐P: n = 10 CON: n = 10	—	SET‐M: 5 weeks of 1–3 set of 6 × 5‐s sprint; 15‐s rest. 2 min rest. 1–2/week with 8 training sessions in total	200‐m sprint (~30‐s)	+2
				Intermittent running (Yo‐Yo 2)	+11.4
				Repeated sprint ability	+2.6
				Submaximal test		Blood lactate	−17
			SET‐P: 5 weeks of 1–3 set of 6 × 5‐s sprint; 30‐s rest. 2 min rest. 1–2/week with 8 training sessions in total	Intermittent running (Yo‐Yo 2)	(+6.5)
				Repeated sprint ability	+3.6
				Submaximal test		Blood lactate	−18
Jeppesen et al. (2024)	24 M cyclists Age: 25 years SET‐M—Low: n = 8 SET‐M—High: n = 8 CON: n = 8	68.3	SET‐M—Low: 6 weeks of 6 × 30‐s all‐out; 1 min rest, 2/week −30% training volume	4‐min time trial	+3.8
			SET‐M—High: 6 weeks of 12 × 30‐s all‐out; 1 min rest, 2/week −30% training volume			PFK	+20
						Na+–K+ subunit α1	+50
						Na+–K+ subunit α2	+19
						Na+–K+ subunit β1	+24
						FXYD1	+42
Nyberg et al. (2016)	13 M football players Age: 24 years SET‐M: n = 13	—	SET‐M: 9 weeks of 2–3 sets of 8–10 × 5‐s all out sprint; 10‐s rest. 1.5/week	Intermittent running	+12	HAD	−8
						COX IV	−9
						OXPHOS	−16
						Capillarization	−15
Puype et al. (2013)	29 M trained Age: 25 years SET‐P normoxia: n = 9 SET‐P hypoxia: n = 10 CON: n = 10	53.0	SET‐P normoxia: 6 weeks of 4–9 sets of 30‐s all out; 270‐s rest. 3/week			PFK	+17
						MCT1	+70
			CON: maintained normal traning	—	—
Shepley et al. (1992)	9 M runners Age: 23 years SET‐P: n = 9	67.0	SET‐P: 1 week of 1–5 × ~70‐s all out; 6–12 min rest. 5/week −91% training volume	Intense exercise (~5 min)	+22	CS	~+18
						Blood volume	~+13
						Red cell volume	~+9
						Muscle glycogen	~+15
Skovgaard et al. (2017)	14 M/4 F runners Age: 28 years SET‐P—HF: n = 11, 8 M/3 F SET‐P—LF: n = 7, 7 M/1 F	57.3	FAM: 40 days of 10 SET sessions of 10 × 30‐s all‐out; 3.5‐min rest + 10 sessions of AMI training −32%–38% training volume	10 km (~40–44 min)	+3.5	NHE1	+75
				Repeated running test	+18	PFK	+30
				RE	+2
			HF: 40 days of 20 SET sessions of 8–12 × 30‐s all‐out; 3.5‐min rest + 20 sessions of AMI training −38% training volume	Repeated running test	+12	Na+–K+ subunit β1	+39
						FXYD1	+57
						SERCA I	+24
						CS	(+15)
			LF: 80 days of 20 SET sessions of 10 × 30‐s all‐out; 3.5 min rest + 20 sessions of AMI training −32% training volume	Repeated running test	+16	Na+–K+ subunit β1	+58
						SERCA II	−33
						CS	(+12)
Skovgaard et al. (2018)	8 M runners Age: 28 years SET‐P	59.3	40 days × 2 (P1 + P2) separated by 80 days of normal training P1 + P2: 40 days of 10 SET sessions of 6–10 × 30‐s all‐out; 3.5‐min rest + 10 sessions of AMI training −33% training volume	P1: V̇O2‐max	+2.1	—	—
				P1: 10 km (~40–42 min)	+2.9
				P1: RE at 60% vV̇O2‐max	+1.9
				P1: RE at v10‐km	+1.6
				P2: V̇O2‐max	+2.6	—	—
				P2: 10 km (~40–42 min)	+2.3
				P2: RE at 60% vV̇O2‐max	+1.8
				P2: RE at v10‐km	+2.0
				P2: Repeated running test	+20.3
				P2: 30 s sprint distance	+4.9
Skovgaard et al. (2018)	14 M/6 F runners Age: 28 years SET‐P	56.4	40 days of 10 SET sessions of 5–10 × 30‐s all‐out; 3.5‐min rest + 10 sessions of AMI training −36% training volume	10 km (~45–48 min)	+1.7	SERCA II	+20
				RE at v 10‐km	+2.1	CS	+11
				RE at 60% vV̇O2‐max	+2	HAD	+9
						PFK	+23
						ST single fiber
						Muscle dystrophin	+41
						UCP3	−25
						FT single fiber: MHCIIa	+19
Purkhus et al. (2016)	25 F elite volleyball players Age: 19 years SET‐P: n = 13 CON: n = 12	—	SET‐P: 4 weeks of 6–10 × 30‐s all‐out; 3 min rest, 3/week + normal team training and games	Repeated sprint	+4.3	—	—
				Intermittent running (Yo‐Yo 2)	+12.6
				Intermittent running (Yo‐Yo 1)	+18.3
				Arrow agility test (~20 s)	+2.3
			CON: normal team training and games
Ørtenblad et al. (2000)	15 M trained Age: 24 years SET‐P: n = 9 CON: n = 6	61.0	SET‐P: 5 weeks of 20 × 10‐s all out; 50‐s rest. 3/week	Repeated sprint	+12	Ca2+ release	+9
						SERCA I	+41
						SERCA II	+55
						RyR1	+48
			CON: maintained normal training habits

Note: The relative effect size for performance and muscle changes from each study is presented only for statistical measures with significance (p ≤ 0.05) or for those that are trending towards significance (p = 0.05–0.10), indicated in parentheses.

Abbreviations: CON, control; COX IV, cytochrome c oxidase subunit IV; CS, citrate synthase; FXYD1, FXYD domain‐containing ion transport regulator 1; HAD, hydroxyacyl‐CoA dehydrogenase; HF, high frequency; LF, low frequency; MCT1, monocarboxylate transporter; MHCIIa, myosin heavy chain isoform IIa; NHE1, Na⁺−H⁺ exchanger isoform 1; NKCC1, Na⁺−K⁺−2Cl⁻ channel isoform 1; OXPHOS, oxidative phosphorylation complex; PFK, phosphofructokinase; RE, running economy; SERCA I + II, sarcoplasmic reticulum Ca²⁺ ATPase isoform I and II; SET‐M, speed endurance training—maintenance training; SET‐P, speed endurance training—production training; UCP3, mitochondrial uncoupling protein 3; V̇O₂‐max, maximum oxygen consumption (mL kg⁻¹ min⁻¹).

In studies where SET was the only intervention, either in addition to normal training [8] or with a significant reduction in habitual weekly training volume [9, 10], improvements in performance in events lasting 20–40 s have been observed (Figure 1A; Table 1). In the study by Iaia et al. [8] football players performed 5 weeks of 1–3 sets of 6 × 5‐s sprints separated by 15‐s rest periods 1–2 times per week and found that performance in a 200‐m run was improved by 2% [8]. Similarly, when runners were conducting 8–12 × 30‐s all‐out sprints separated by 3‐min rest period 3–4 times a week for 4 weeks, with 64% reduction in training volume, performance in the 30‐s sprint was elevated by 7% [9], and Skovgaard et al. [10] found a 5% improvement 30‐s sprint performance after runners during a 40‐day period performed 10 SET sessions consisting of 6–10 × 30‐s all‐out bouts with a 33% lowered training volume [10]. Likewise, well‐trained runners improved 300‐m performance by 4% and 3% after 8 weeks with SET three times a week consisting of 8 × 20‐s intervals at an intensity corresponding to around 150% of MAS (maximal aerobic speed) separated by 10‐s rest periods (SET‐M) and 10 × 30‐s at about 175% of MAS with 3.5‐min recovery periods (SET‐P), respectively [11]. In the study by Iaia et al. [9], improved performance was associated with higher expression of muscle Na⁺–K⁺ subunits α₁ and Na⁺–H⁺ exchanger isoform 1 (NHE1).

FIGURE 1.

Effect of speed endurance training (SET) on performance during exercise. Performance during exercise: (A) 10–60 s, (B) 1–10 min, (C) 10–60 min, (D) repeated sprint performance, and (E) intermittent running performance. The studies are categorized based on the effect of either; SET performed by itself (red; dark red = SET‐maintenance, red = SET‐production), SET and aerobic high‐intensity training (blue), SET during aerobic moderate‐intensity training (green), or SET and power (resistance) training (yellow). Data are presented as the percentage change (Δ) observed in the specific study. Studies marked with "(#)" indicate a training intervention with a reduced training volume. The filled bars represent a significant effect (p ≤ 0.05), whereas the scaled bars indicate a trend towards a significant change (p ≤ 0.09).

2.2. Speed Endurance and Aerobic High‐Intensity Training (Table 2)

TABLE 2.

Effect of speed endurance training (SET) and aerobic high intensity (AHI) training on performance during exercise (10 s to 60 min) and physiological adaptations in well‐trained individuals.

Study	Subjects (no., M/F, age, intervention)	V̇O2‐max	Intervention (duration, sets/reps, work/rest, frequency, Δ% volume)	Performance, V̇O2‐max and RE	Effect (Δ%)	Adaptations	Effect (Δ%)
Christensen et al. (2023)	18 M cyclists Age: 28 years SET‐P—Low + AHI: n = 8 SET‐P + AHI: n = 10	71.0	SET‐P—Low: 7 weeks of 12 × 30‐s uphill sprints; 5 min rest, 1/week + AHI: 5 × 4‐min intervals at highest possible intensity; 3 min rest, 2/week −33% training volume	400‐kcal time trial without preload (~20 min)	+3	PFK	+22
				Repeated sprint fatigue resistance	+10
				Repeated sprint MPO during preload (2 × 20‐s)	+6
			SET‐P: 7 weeks of 12 × 30‐s uphill sprints; 5 min rest, 1/week + AHI: 5 × 4‐min intervals at highest possible intensity; 3 min rest, 2/week Maintained normal exercise volume	400‐kcal time trial without preload (~20 min)	+2	HAD	(+4.7)
				Repeated sprint fatigue resistance	+3
				30‐s sprint test (PPO)	+2.5
Bangsbo et al. (2009)	17 M runners Age: 35 SET‐P + AHI: n = 12 CON: n = 5	63.0	SET‐P: 6–9 weeks of 8–12 × 30‐s all‐out; 3 min rest, 2–3/week + AHI: 4 × 4 min at ~95% of maximal aerobic speed; 3 min rest, 1–2/week −30% training volume	Intense exercise (~2 min)	+36	Na+–K+ subunit α2	+68
				30‐s all out	+5.7	Na+–K+ subunit β1	(+10)
				3 km (~10 min)	+3.3
				10 km (~36–38 min)	+3.1
				Incremental – time to exhaustion	+9
				RE at v12‐km	+3
			CON: 4–5 days/week with an average weekly distance of ~55 km
Gunnarsson et al. (2013); Thomassen et al. (2016)	8 M cyclists Age: 33 years SET‐P + AHI	59.0	SET‐P: 7 weeks of 10–12 × 30‐s all‐out; 4.5 min rest, 2–3/week + AHI: 4–5 × 3–4 min at 90%–95% peak aerobic power output, 1–2/week −70% training volume	Repeated sprint	+4	In vivo buffering	+18
				Intense exercise (~4 min)	+18	CS	−16
						COX IV	−11
						KIR2.1	(+18)
						KIR6.2	−14
						NHE1	(+30)
						FXYD1	+30
						FYXD1‐phos	+40
						PLN	+16
						PLN‐phos	+42
						CaMKII	+25
						CaMKII‐phos	+300
Nevill et al. (1989)	8 M/8 F runners Age: 30 years SET‐P + AHI: n = 4 M/4 F CON: n = 4 M/4 F	55.0	SET‐P + AHI: 8 weeks of 2 × 30‐s all out; 10 min rest + 6–10 × 6‐s all out; 54‐s rest + 2–5 × 2 min all out; 5 min rest 3–4/week	30‐s all out	+6	Anaerobic glycolytic ATP production rate	+14
						In vivo buffering capacity	+44
			CON: maintained normal running with an average weekly distance of ~32 km
Thomassen et al. (2010); Christensen et al. (2011)	7 M football players Age: 23 years SET‐P + AHI: n = 7 CON (inactive): n = 11	55	SET‐P: 2 weeks of 10–12 × 30‐s all‐out; 3 min rest, 2–3/week + AHI: 8 × 2 min soccer exercise; 1 min rest, 2–3/week −30% training volume	Repeated sprint	+2	Na+–K+ subunit α2	+15
				Intermittent running (Yo‐Yo 2)	(+6)	FXYD1‐phos	+27
						MCT1	(+13)
						PDH	+17
			CON: inactivity

Note: The relative effect size for performance and muscle changes from each study is presented only for statistical measures with significance (p ≤ 0.05) or for those that are trending towards significance (p = 0.05–0.10), indicated in parentheses.

Abbreviations: CaMKII, Ca²⁺‐calmodulin‐dependent protein kinase II; CON, control; COX IV, cytochrome c oxidase subunit IV; CS, citrate synthase; FXYD1, FXYD domain‐containing ion transport regulator 1; HAD, hydroxyacyl‐CoA dehydrogenase; K_IR2.1, K⁺ inward rectifier channel 2.1; K_IR6.2, K⁺ inward rectifier channel 6.2; MCT1, monocarboxylate transporter; MPO, mean power output; PDH, pyruvate dehydrogenase; PFK, phosphofructokinase; PPO, peak power output; SET‐P, speed endurance training—production training; V̇O₂‐max, maximum oxygen consumption (mL kg⁻¹ min⁻¹).

When SET was combined with aerobic high‐intensity training performed as 8–12 × 30‐s all‐out bouts 2–3 times per week and 4 × 4 min at ~95% of maximal aerobic speed 1–2 times per week for 6–9 weeks, respectively, with 30% reduced training volume, performance during a 30‐s run was improved and muscle Na⁺–K⁺ subunit α₂ was 68% higher [12]. Similarly, when combining the two training types 3–4 times per week for 8 weeks, performance in a 30‐s maximal test was elevated by 6%, and the in vivo muscle glycolytic ATP production and buffer capacity were higher [13].

2.3. Summary

Taken together, it appears that studies implementing SET led to enhanced performance during events lasting 10–60 s. It may not be surprising, as the intervals during training in most studies are lasting 20–40 s, but it must be recognized that the training volume was markedly reduced in most of the studies. The reasons for the improvements in short‐term intense performance are not clear. Higher levels of muscle glycolytic enzymes (PFK) (Figure 4A) and ion transporters, such as Na⁺–K⁺ subunits (Figure 2A–D), NHE1, and SERCA I (Figure 3A,C), may have contributed as maximal exercise for a duration of 10–60 s led to marked changes in ion distribution and membrane potential (see also below).

FIGURE 4.

Effect of speed endurance training on muscular adaptation in the PFK, LDH, CS, OXPHOS, COXIV and HAD. Changes in either expression or maximal activity of muscle (A) phosphofructokinase (PFK), (B) lactate dehydrogenase (LDH), (C) citrate synthase (CS), (D) oxidative phosphorylation complex (OXPHOS I–V), (E) cytochrome c oxidase subunit IV (COX IV) and (F) hydroxyacyl‐coenzyme A dehydrogenase (HAD). Studies are categorized based on the effect of either; SET performed by itself (SET‐production), SET and aerobic high‐intensity training (blue), SET during aerobic moderate‐intensity training (green), or SET and power (resistance) training (yellow). Data are presented as the percentage change (Δ) observed in the specific study. Studies marked with "(#)" indicate a training intervention with a reduced training volume. The filled bars represent a significant effect (p ≤ 0.05), whereas the scaled bars indicate a trend towards a significant change (p ≤ 0.09).

FIGURE 2.

Effect of speed endurance training on muscular adaptations in Na⁺–K⁺ subunits and FXYD. Changes in (A) Na⁺–K⁺ subunit α₁, (B) Na⁺–K⁺ subunit α₂, (C) Na⁺–K⁺ subunit β₁, (D) Na⁺–K⁺ subunit β₂ and (E) FXYD domain‐containing ion transport. Studies are categorized based on the effect of either; SET performed by itself (SET‐production), SET and aerobic high‐intensity training (blue), SET during aerobic moderate‐intensity training (green), or SET and power (resistance) training (yellow). Data are presented as the percentage change (Δ) observed in the specific study. Studies marked with "(#)" indicate a training intervention with a reduced training volume.  The filled bars represent a significant effect (p ≤ 0.05), whereas the scaled bars indicate a trend towards a significant change (p ≤ 0.09).

FIGURE 3.

Effects of speed endurance training on muscular adaptations of the NHE1, MCT1 and SERCA pumps. Changes in (A) Na⁺–H⁺ exchanger isoform 1 (NHE1), (B) muscle monocarboxylate transporter 1 (MCT1), (C) muscle sarcoplasmic reticulum Ca²⁺ ATPase isoform I (SERCA I), and (D) muscle sarcoplasmic reticulum Ca²⁺ ATPase isoform II (SERCA II). Studies are categorized based on the effect of either; SET performed by itself (SET‐production), SET combined with aerobic high‐intensity training (blue), SET combined with aerobic moderate‐intensity training (green), or SET combined with power (resistance) training (yellow). Data are presented as the percentage change (Δ) observed in the specific study. Studies marked with "(#)" indicate a training intervention with a reduced training volume. The filled bars represent a significant effect (p ≤ 0.05), whereas the scaled bars indicate a trend towards a significant change (p ≤ 0.09).

3. Events Lasting 1–10 min

In some sports lasting 1–10 min the athletes reach rapidly the target intensity (or higher), either at or higher than that eliciting V̇O₂‐max, and are aiming at maintaining the intensity often to finish with a maximal effort (sprint). These include, among others, 2000‐m rowing single sculls (~5:50; ~7:00 min:s), 500‐m or 1000‐m canoeing (~1:45; ~2:05 and ~ 3:45; ~4:05 min:s) or kayaking (~1:35; ~1:50 and ~ 3:25; ~3:50 min:s), 800‐m (~1:45; ~1:55 min:s) and 1500‐m (~3:30; ~3:55 min:s) run, 1000‐m speed skating (~1:05; ~1:15 min:s) and 1000‐m (~60 s; ~1:02 min:s) or 4000‐m track cycling—team pursuit (~3:45; ~4:10 min:s). To examine the effect of an intervention period with SET field tests, such as a 1500‐m run, or laboratory tests, such as runs on a treadmill to exhaustion or time trials on a cycle ergometer, are often used.

3.1. Speed Endurance Training (Table 1)

In the early 1990's, Shepley et al. [14] studied nine male middle‐distance runners with V̇O₂‐max of 67 mL kg⁻¹ min⁻¹ during a week with a reduced training volume (referred to as tapering) but including 70‐s SET intervals five times during the week. Performance was measured as treadmill run to fatigue at a velocity equivalent to each subject's best 1500‐m time (~4 min), and performance was increased by 22% during the week (Figure 1B). The group increased muscle glycogen concentration, citrate synthase (CS) activity (Figure 4C), and total blood volume, but had no change in V̇O₂‐max [14]. Likewise, Dawson et al. [15] found an improvement in short‐term performance (duration ~1 min), along with a 40% increase in phosphorylase activity after a 6‐week SET intervention consisting of 3–5 sets of 4–8 × 40–100‐m near maximal sprints, interpersed of 2–4 min rest, three times per week. On the other hand, they observed a decrease in muscle maximal CS activity. Later, Iaia et al. [9] studied runners, and the effect of SET conducted 3–4 times a week for 4 weeks, with a reduction in training volume of 64%, and found improvements of 19%–27% in performance during exhaustive treadmill running lasting 1–3 min. Notably, these changes were accompanied by increases in muscle monocarboxylate transporter 1 (MCT1), NHE1 (Figure 3A,B) and Na⁺–K⁺ subunit α₁ (Figure 2A), as well as improved running economy without a change in V̇O₂‐max. Several studies have observed similar effects on performance of a period of SET. Bickham et al. [16] found that well‐trained runners (V̇O₂‐max: 58 mL kg⁻¹ min⁻¹) experienced an 11% improvement in intense exercise (~2.5 min), along with a 50% upregulation in MCT1 expression, after undergoing a 6‐week training intervention with SET three times per week [16]. Aditionally, Puype et al. [17] reported an increase in MCT1 expression of up to 70% after 6 weeks of SET performed three times per week [17].

More recently, Skovgaard et al. [18] subjected runners with a V̇O₂‐max around 58 mL kg⁻¹ min⁻¹ to SET every fourth day during a 40‐day period, in which they also lowered their weekly training volume by 30%–40%. Despite the marked reduction in training volume, the introduction of SET improved their time to exhaustion at 90% vV̇O₂‐max (4–6 min) by 20% (Figure 1B) and running economy while V̇O₂‐max remained unchaged. In muscle homogenates, the intervention led to higher abundance of NHE1 (Figure 3A) and maximal PFK activity (Figure 4A). When SET was continued with the same frequency for another 80 days or with the frequency increased to perform SET every second day, performance at 90% vV̇O₂‐max was further elevated by 12% and 16%, respectively [18]. In the second period, both groups showed increased muscle expression of Na⁺–K⁺ subunit β₁ (Figure 2C), whereas maximal activity of CS and PFK, running economy, and V̇O₂‐max did not change. Additionally, muscle expression of FXYD domain‐containing ion transport regulator 1 (FXYD1) (Figure 2E), SERCA I (Figure 3C), and FXYD1 activity increased in the high‐frequency group, whereas muscle expression of SERCA II decreased in the low‐frequency group. When Jeppesen et al. [19] studied cyclists doing 6 or 12 repetitions of 30‐s maximal sprints performed twice per week during 6 weeks with a 30% reduction in training volume, they found that the group performing six repetitions had a significant improvement (4%) in a 4‐min time‐trial with no significant change in the group performing 12 repetitions. On the other hand, only the latter group exhibited elevated levels of muscle Na⁺–K⁺ subunits, FXYD1 (Figure 2) and maximal PFK activity (Figure 4A). Thus, a period of SET can elicit substantial performance gains despite a lowering of training volume in already well‐trained individuals.

3.2. Speed Endurance and Aerobic High‐Intensity Training (Table 2)

SET combined with aerobic high‐intensity training has also been shown effective for increasing short‐term performance. In well‐trained runners, Bangsbo et al. [12] found a 36% improvement in performance during a ~2‐min running bout (Figure 1B) after 6–9 weeks with SET and aerobic high intensity training, and ~30% reduction in the amount of training. Likewise, in trained cyclists, Gunnarsson et al. [20] observed an 18% increase in performance during a cycle bout lasting ~4‐min after 7 weeks with SET and aerobic high intensity training, with 70% lowered training volume. In the study by Bangsbo et al. [12], the changes were associated with a marked increase (68%) in muscle Na⁺–K⁺ subunit α₁, and in the latter study, elevated expression of muscle FXYD1 (30%) (Figure 2A,E) and a tendency for increase in muscle NHE1 (30%) (Figure 3A) but decrease in expression and activity of muscle oxidative enzymes like CS and cytochrome c oxidase subunit IV (COX IV) (Figure 4C,E) [21]. This indicates that the upregulation of Na⁺–K⁺ subunits, NHE1 and FYXD1 may be among the underlying mechanisms responsible for the improvement short‐term performance.

3.3. Speed Endurance Training During Aerobic Moderate Intensity Training (Table 3)

TABLE 3.

Effect of speed endurance training (SET) during aerobic low/moderate intensity training (LIT/MIT) on performance during exercise (10 s to 60 min) and physiological adaptations in well‐trained individuals.

Study	Subjects (no., M/F, age, intervention)	V̇O2‐max	Intervention (duration, sets/reps, work/rest, frequency, Δ% volume)	Performance, V̇O2‐max and RE	Effect (Δ%)	Adaptations	Effect (Δ%)
Almquist et al. (2020)	16 M cyclists Age: 22 years SET‐P: n = 7 CON: n = 9	72.0	SET‐P: 3 weeks of SET during 90 min cycling on 60% V̇O2‐max (LIT) including 3 sets of 3 × 30‐s maximal sprints; 4‐min active rest, 1/week + LIT sessions 2/week −60% training volume	Repeated 30‐s sprint	+8
			CON: 3 weeks of LIT, 3/week −60% training volume				—
Almquist et al. (2021)	18 M cyclists Age: 21 years SET‐P: n = 9 CON: n = 9	75.2	SET‐P: 2 weeks of SET during 4‐h LIT session including 4 sets of 3 × 30‐s maximal sprints; 4‐min active rest, 5 sessions in total +48% training volume Followed by 2 weeks “recovery” −55% training volume	Repeated 30‐s sprint	+4	PFK	−14
				5 min time trial	+4
			CON: 2 weeks of distance matched LIT without sprints (control exercise), 5 sessions in total +48% training volume Followed by 2 weeks “recovery” −55% training volume
Gliemann et al. (2014)	18 M/F runners Age: 40 years 10–20–30: n = 11 M/2 F CON: n = 5	52.3	10–20–30: 8 weeks of 5 × 10–20–30 × 3–4 sets: 4‐min rest btw sets, 2/week + AMI: 5–10 km constant running 1/week	V̇O2‐max	+3
			CON: maintained normal running routines ~27 km/week, distributed 3/week			—	—
Gunnarsson and Bangsbo (2012)	18 M/F moderate trained Age: 34 years 10–20–30: n = 10 CON: n = 8	52.2	10–20–30: 7 weeks of 5 × 10–20–30 × 3–4 sets: 2‐min rest btw sets. 3/week −54% training volume	V̇O2‐max	+4
				1500 m running (~6 min)	+6
				5 km running (~23 min)	+4
			CON: maintained normal running routines ~25 km/week, distributed 2–4/week			—	—
Gunnarsson et al. (2019)	13 M team sports or endurance trained Age: 25 years ST: n = 6 CON: n = 7	53.5	ST: 8 weeks of ST during 60 min continuous cycling on ~60% V̇O2‐max including 6 sets of 30‐s sprints every 10 min, 3/week Matched workload between groups	45 min time‐trial	+4	COX IV	+25
				Incremental—time to exhaustion	+3	CS	+21
			CON: 8 weeks of 60 min continuous cycling on 60% V̇O2‐max, 3/week	45‐min time trial	+9
Hostrup et al. (2019)	20 M football players Age: 24 years 10–20–30: n = 12 ST: n = 8	—	10–20–30: 10 weeks of 5 × 10–20–30 × 2–3 sets: 4–min rest btw sets, 3/week −20% training volume	Intermittent running (Yo‐Yo 2)	+18	HADHA	+24
						PDH‐E1α	+40
						OXPHOS	+51
						Na+–K+ subunit α2	+33
						Na+–K+ subunit β2	+27
Skovgaard et al. (2024)	19 M runners Age: 27 years 10–20–30—SUBMAX: n = 11 10–20–30—MAX: n = 8	53.6	SUBMAX: 6 weeks of 5 × 10–20–30 × 2–4 sets; 2–3 min rest btw sets, 3/week	5 km (~21 min)	+3
				V̇O2‐max	+6.4
			MAX: 6 weeks of 6 × 10–20–30 × 2–4 sets; 2–3 min rest btw sets, 3/week	5 km (~21 min)	+2.3	OXPHOS	+17
				V̇O2‐max	+7.5	OXPHOS I	+15
						OXPHOS II	+24
						OXPHOS III	+29
						OXPHOS IV	+9
Taylor et al. (2021)	11 M cyclists Age: 22 years SET‐P: n = 5 CON: n = 6	54.7	SET‐P: 3 weeks of ST during 90 min continuous cycling on ~60% V̇O2‐max including 3 sets of 3 × 30‐s maximal sprints; 4‐min active rest, 1/week + LIT −64% training volume	20 min time trial	+7.3
			CON: 3 weeks of 90 min cycling on 60% V̇O2‐max −64% training volume			—	—

Note: The relative effect size for performance and muscle changes from each study is presented only for statistical measures with significance (p ≤ 0.05) or for those that are trending towards significance (p = 0.05–0.10), indicated in parentheses.

Abbreviations: CON, control; COX IV, cytochrome c oxidase subunit IV; CS, citrate synthase; DHPR, dihydropteridine reductase deficiency; HADHA, hydroxyacyl‐CoA dehydrogenase trifunctional multienzyme complex subunit alpha; LDL, low‐density lipoproteins; OXPHOS I–IV, oxidative phosphorylation complex I–V enzymes; PDH‐E1α, pyruvate dehydrogenase E1 subunit α1; PFK, phosphofructokinase; SET‐P, speed endurance training—production training; ST, speed training; V̇O₂‐max, maximum oxygen consumption (mL kg⁻¹ min⁻¹).

Almquist et al. [22] found in elite cyclists (V̇O₂‐max: 75 mL kg⁻¹ min⁻¹) a 4% better performance in a 5‐min time‐trial (Figure 1B) after 2 weeks of five sessions with SET consisting of 4 × 30‐s sprints during 4 h of aerobic low‐intensity training with a 48% increase in training volume followed by 2 weeks of “recovery” with a reduction in training volume of 55%. In addition, the maximal muscle PFK activity after the first 2 weeks was reduced by 14%. Similarly, Gunnarsson et al. [23] in a group of trained cyclists (V̇O₂‐max: 54 mL kg⁻¹ min⁻¹) observed a 3% increase in performance during an incremental test (lasting ~16 min) after 8 weeks of repeated 6 × 30‐s sprints during moderate intensity exercise three times a week as well as elevated expression of muscle CS and COX IV, without change in V̇O₂‐max.

10–20–30 training is also a form of SET during aerobic moderate‐intensity training as the participants perform low‐intensity exercise for 30 s, moderate‐intensity exercise for 20 s, and then sprint for 10 s [24]. When a group of female and male runners (V̇O₂‐max: 52.2 mL kg⁻¹ min⁻¹) conducted 10–20–30 training consisting of 3–4 sets of 5‐min 10–20–30 training intervals three times a week for 7 weeks, with a reduction in training volume of 54%, they improved the time to complete a 1500‐m run by 21 s (Figure 1B) and increased V̇O₂‐max by 4% [24].

3.4. Speed Endurance and Power Training (Table 4)

TABLE 4.

Effect of speed endurance training (SET) and resistance training on performance during exercise (10 s to 60 min) and physiological adaptations in well‐trained individuals.

Study	Subjects (no., M/F, age, intervention)	V̇O2‐max	Intervention (duration, sets/reps, work/rest, frequency, Δ% volume)	Performance, V̇O2‐max and RE	Effect (Δ%)	Adaptation	Effect (Δ%)
Houston and Thomson (1977)	5 M runners Age: 35 years SET + S + AHI + RT: n = 5	59.0	6 weeks, 4/week of: SET‐M: 3 × 60‐s all out; 120‐s rest + S: 5 × 6‐s all out; 24‐s rest + AHI: 2 × 90‐s all out; 180‐s rest RT: Leg press (15 RM)	Intense exercise (~1 min)	+17	ATP content	+15
				60‐s running distance	+14
				90‐s running distance	+13
Skovgaard et al. (2014)	23 M runners Age: 31 years SET‐P + RT: n = 12 CON: n = 11	59.0	SET‐P: 8 weeks of 4–9 × 30‐s all‐out; 4.5 min rest, 4/week + RT: heavy resistance training, 4/week −42% training volume	1500 m running (~5 min)	+5	NHE1	+35
				10 km running (~42–44 min)	+6	SERCA I	−15
				RE at v12‐km	+3.1
				Intermittent running (Yo‐Yo 2)	+44
			CON: maintained normal running routines ~40 km/week, including ~4 km/week of interval running
Vorup et al. (2016)	16 M runners Age: 38 years SET‐P + RT/AMI/AHI: n = 9 CON: n = 7	60.0	SET‐P: 8 weeks of 4–8 × 30‐s all‐out; 3 min rest, 2/week + RT/AMI/AHI: resistance training/aerobic moderate/high intensity training, 2/week −58% training volume	400 m running (~1 min)	+5	Na+–K+ subunit β1	+15
				Incremental – time to exhaustion	+9	LDH	+17
				Intermittent running (Yo‐Yo 2)	+19
			CON: maintained normal running routines ~45 km/week

Note: The relative effect size for performance and muscle changes from each study is presented only for statistical measures with significance (p ≤ 0.05) or for those that are trending towards significance (p = 0.05–0.10), indicated in parentheses.

Abbreviations: AHI, aerobic high intensity training; AMI, aerobic moderate intensity training; CON, control; LDH, lactate dehydrogenase; NHE1, Na⁺−H⁺ exchanger isoform 1; RE, running economy; RT, resistance training; SERCA I, sarcoplasmic reticulum Ca²⁺ ATPase isoform I; SET‐P, speed endurance training—production training.

When introducing both SET and power training conducted in the same training session in runners with a 42% reduction in training volume for 8 weeks, Skovgaard et al. [25] observed a 5% increase in performance in a 1500‐m run (Figure 1B). The change was accompanied by a 35% increase in muscle NHE1 expression (Figure 3A) and a 15% decrease in SERCA I (Figure 3C). Likewise, Vorup et al. [26] studied SET and power training in separate sessions and observed a 5% reduction in the time required to complete a 400‐m run (~1 min), which was associated with elevated expression of muscle Na⁺–K⁺ subunit β₁ and lactate dehydrogenase (LDH) (Figure 4B). A study by Houston and Thomson [27] investigated the combination of SET, AHI, and power training in runners during a 6‐week intervention period, with four training sessions per week. Performance in the 1–1.5‐min time domain improved by 13%–17%. However, it should be noted, that the study only included five participants.

3.5. Summary

It appears that all interventions with SET either alone or in combinations with other types of training improve performance in exercise lasting 1–10 min. Thus, it is relevant in several sports, such as 1500‐m running, 500‐m canoeing/kayaking, 2000‐m rowing, and 4000‐m track cycling. To understand what is causing the improvement, one must clarify the determining factors during such an exercise. The running speed or cycling intensity that can be maintained is dependent on V̇O₂‐max, the relative contribution of V̇O₂‐max (%V̇O₂‐max) that can be maintained, running/cycling economy (the lower oxygen needed, the better performance), and the capacity to not only produce energy via anaerobic metabolic pathways but also to tolerate the metabolic and ionic perturbations occurring with a progressive reliance on anaerobic metabolism in the muscle.

In less trained individuals, for example, with a V̇O₂‐max of around 55 mL kg⁻¹ min⁻¹ and lower, SET, especially when combined with aerobic high‐intensity training or performed during moderate‐intensity exercise, does increase V̇O₂‐max. However, in well‐trained individuals, an increase in V̇O₂‐max is not observed, suggesting that this is not a contributing factor to the better performance in this population. Some studies have found a better movement economy that contributes to improved performance, but most studies, particularly with cycling as an intervention, have not observed a change in movement economy. There are also no indications of changes in relative work intensity.

Then, the focus should be on factors causing fatigue during this type of intense exercise lasting 1–10 min. Many of the studies showed elevated levels of muscle Na⁺–K⁺ subunits and FXYD1, which may contribute to counter exercise‐related K⁺ shifts, sustain sarcolemmal excitation‐contraction coupling, and delay muscle fatigue [6]. Another common finding is that the muscle expression of NHE1 and MCT1 is elevated after a period with SET, which should promote the release of H⁺ from the muscle cells during exercise; thereby, together with higher muscle buffer capacity, lowering the accumulation of intracellular H⁺ (less reduction of pH), which can also contribute to better performance [6]. See also below for further discussion of the importance of changes in the expression and activation of muscle ion transporters.

4. Events Lasting 10–60 min

Time trials in road cycling, for example, 40‐km time trial (~45; ~50 min), 5‐km (~13; ~15 min) and 10‐km (~27; ~30 min) run, cross‐country skiing with distances of 5‐km (~12; ~14 min) or 10‐km (~20; ~25 min) are examples of sports with high exercise intensity (at or slightly below the intensity eliciting V̇O₂‐max) over 10–60 min. A number of studies have focused on the effect of SET on performance in events lasting 10–60 min typically determined as the time to complete a 5‐ or 10‐km run or a 20‐min time trial during cycling.

4.1. Speed Endurance Training (Table 1)

Studies by Skovgaard et al. observed 2%–4% improvement in 10‐km performance (Figure 1C) after 40 days of SET consisting of 10 SET sessions with ten to twelve 30‐s sprints, with a reduction in training volume of 30%–40% [10, 18, 28]. The improved performance was associated with better running economy, elevated expression of NHE1 (Figure 3A), Na⁺–K⁺ subunit β₁, FXYD1 (Figure 2C,E), and SERCA I, and decreased expression of SERCA II (Figure 3C,D). Jeppesen et al. [19] observed in elite cyclists (V̇O₂‐max: 68 mL kg⁻¹ min⁻¹) conducting 6 weeks of 6 × 30‐s sprints twice a week, with the amount of training being lowered by 30%, an improvement of 6% in a 20‐min time trial, but without changes in the expression of muscle ion transporters. Hov et al. [11] studied well‐trained runners conducting 8 × 20‐s intervals at an intensity corresponding to 150% of MAS separated by 10‐s rest periods (SET_M) and 10 × 30‐s intervals at about 175% of MAS with 3.5 min recovery periods (SET‐P) three times a week and found an increase in 3000‐m performance by 4% and 2%, with only the former group having an increase (3%) in V̇O₂‐max.

4.2. Speed Endurance and Aerobic High‐Intensity Training (Table 2)

When adding not only SET but also aerobic high‐intensity training significant improvements in performance in events lasting more than 10 min were observed (Figure 1C), for example, Bangsbo et al. [12] found in runners that the time for a 10‐km run was lowered from 37.3 to 36.3 min after 6–9 weeks of SET consisting of 8–12 × 30‐s sprint intervals conducted 2–3 times per week and aerobic high intensity training as 4 × 4 min exercise bouts 1–2 times week, with a reduction in training volume of 30%. In addition, the expression of muscle Na⁺–K⁺ subunit α₂ was elevated markedly (Figure 2B). Likewise, Christensen et al. [29] examined elite cyclist (V̇O₂‐max: 71 mL kg⁻¹ min⁻¹) and after 7 weeks of SET (12 × 30‐s sprints) once a week and aerobic high‐intensity training (5 × 4‐min intervals) twice a week, performance in a 400‐kcal time trial lasting ~20 min was improved by 2%–3%, with the same improvement in a group maintaining training volume and another reducing is by 33%. In the latter group, muscle PFK activity was elevated (Figure 4A), but otherwise no significant muscle changes were observed.

4.3. Speed Endurance Training During Moderate‐Intensity Training (Table 3)

When SET is conducted during moderate‐intensity aerobic training, improvements in performance during events lasting longer than 10 min are observed (Figure 1C). A 7% improvement was found in a study by Taylor et al. [30] in which they studied cyclists (V̇O₂‐max: 55 mL kg⁻¹ min⁻¹) doing 3 × 30 s sprints during a 90‐min moderate intensity training session performed once a week for 3 weeks with a 64% reduction in training volume. Similarly, when performing the 10–20–30 training (3–4 × 5‐min sets) during 8 weeks, recreational runners (V̇O₂‐max: 52.2 mL kg⁻¹ min⁻¹) improved the 5‐km time by 48 s [24]. Furthermore, a study by Gliemann et al. [31] found that recreational runners (V̇O₂‐max: 52.3 mL kg⁻¹ min⁻¹) who replaced two of three weekly training sessions with 10–20–30 training improved the 5‐km time by 38 s. This training approach also increased V̇O₂‐max, with no change observed in muscle fiber area, fiber type distribution, or capillarisation. However, the expression of pro‐angiogenic vascular endothelial growth factor (VEGF) was reduced by 22%. Likewise, Gunnarsson et al. [23] observed a 4% increase in performance during a 45‐min time‐trial after 8 weeks of 30‐s all‐out efforts every 10 min during 60 min of moderate intensity cycling three times a week. However, the control group in the same study also improved performance in the time trial (9%) with no difference observed between groups. V̇O₂‐max was unchanged, but the intervention group had significantly higher activity/levels of muscle oxidative enzymes, such as CS and COX IV (Figure 4C,E). Moreover, when 10–20–30 training was done with submaximal effort (80%) during the 10‐s sprints and compared with maximal effort, 5‐km performance and V̇O₂‐max were increased to the same level (3.0% vs. 2.3% and 6.4% vs. 7.5%, respectively), but only the group performing with maximal effort increased expression of muscle OXPHOS I‐V (Figure 4D) [26].

4.4. Speed Endurance and Power Training (Table 4)

In two studies, the effect of performing SET and power training with a reduced training volume in runners (V̇O₂‐max: 59 mL kg⁻¹ min⁻¹) was shown to improve 10‐km run performance [25, 26]. In the study by Skovgaard et al. [25], SET was performed immediately after power training, whereas in the study by Vorup et al. [26], SET was performed on a separate day. Apparently, both forms exhibited a positive effect on the 10‐km performance (Figure 1C). Furthermore, Skovgaard et al. [25] observed an improvement in running economy and higher expression of muscle NHE1 (Figure 3A), whereas SERCA I was reduced (Figure 3C). In the study by Vorup et al. [26], Na⁺–K⁺ subunit β₁ (Figure 2C) and LDH levels were higher after than before the intervention period.

4.5. Summary

Taken together, performance in events lasting 10–60 min is improved by introducing SET independent of whether it was done without other training interventions, and in most cases the training volume was reduced. Some studies showed improved exercise economy, which, to some extent, can explain the improved performance. In some of the studies with moderately trained individuals, SET increased V̇O₂‐max, which contributed to enhanced performance during events lasting 10–60 min, but in studies with well‐trained individuals, no change in V̇O₂‐max was observed. The third important factor is the relative work intensity that the athlete can maintain for a longer period (%V̇O₂‐max). In some studies, blood lactate levels were lower at a given exercise intensity, indicating a higher muscle oxidative capacity and higher fractional use of V̇O₂‐max. However, in studies measuring muscle oxidative enzyme and respiratory capacity, no change was observed, and even in some cases, decreases were observed. Factors pertaining to muscle ion handling capacity and pH regulation likely play a smaller role during longer events. In the study by Jeppesen et al. [19], the group performing SET with 12 repetitions per session did not improve performance in a 20‐min time trial, despite elevated levels of muscle Na⁺–K⁺ subunits α1, α2 and β1 as well as FXYD1. Thus, these changes alone appear not sufficient to improve the performance of well‐trained subjects.

5. Long‐Term (> 60 min)

Few studies have examined the effect of SET on long‐term performance, that is, exercises lasting longer than 60 min, such as marathon running or road cycling.

Jeppesen et al. [19] found in elite cyclists (V̇O₂‐max: 68 mL kg⁻¹ min⁻¹) no change in performance in a 20‐min time trial conducted after 60 min of pre‐load with an intensity corresponding to 60% of V̇O₂‐max, after a 6‐week training intervention of either 6 or 12 repetitions of 30‐s sprints twice a week. In addition, V̇O₂‐max, muscle mitochondrial respiratory capacity, maximal CS activity, fiber type‐specific mitochondrial proteins (complexes I–V), and phosphofructokinase (PFK) content did not change in any of the groups [19]. Similarly, Christensen et al. [29] also studied elite cyclists (V̇O₂‐max: 71 mL kg⁻¹ min⁻¹) and conducted a 400‐kcal time trial (~20 min) after a pre‐load consisting of 120 min of moderate intensity cycling, including repeated 20‐s sprints to simulate physiologic demands during road races, before and after a 7‐week intervention period with SET (30‐s sprint intervals) and aerobic high‐intensity training (4‐min intervals) during the competitive part of the season. After the intervention period, neither of the groups had a change in performance in the time trial, but both groups had conducted more work in the pre‐load, so no firm conclusion can be made regarding the effect on long‐term performance. The muscle oxidative enzyme activity remained unchanged, whereas the glycolytic enzyme PFK increased by 22% in the training group, reducing the training volume by 33%.

In both studies, the training volume was reduced (30% and 33%; respectively), demonstrating that training volume can be markedly reduced when performing a period of SET without having a negative effect on long‐term performance. Nevertheless, whether SET, either alone or in combination with other training forms, can improve long‐term performance should be further elucidated.

6. Intermittent Sports

The effect of SET on intermittent exercise performance has mainly been evaluated by conducting repeated sprints and using the Yo‐Yo intermittent tests relevant for many sports such as football, basketball, and team‐handball.

6.1. Speed Endurance Training (Table 1)

In 2000, Ortenblad et al. [32] studied nine trained subjects conducting 20 × 10‐s sprints three times per week for 5 weeks and found a 12% increase in repeated sprint performance (Figure 1D). The change was associated with increased muscle Ca²⁺ release capacity in vitro and muscle content of SERCA I + II (Figure 3B,C). Similarly, Iaia et al. [9] observed that runners had a 19% improvement in intermittent exercise performance, assessed with the Yo‐Yo intermittent recovery (IR) test level 2, when doing 30‐s sprint intervals 2–3 times per week for 4 weeks, with a 64% decrease in training volume (Figure 1E).

In addition, athletes who engage in sports with intermittent exercise have been studied. Purkhús et al. [33] found improved repeated sprint ability (4%) (Figure 1D) and Yo‐Yo IR2 performance (17%) (Figure 1E) after 4 weeks of SET consisting of 30‐s sprint intervals three times a week, in addition to normal training during the season. Similarly, Gunnarsson et al. [34] showed that 5 weeks with five to nine 30‐s sprint intervals once a week improved Yo‐Yo IR2 performance by 11% (Figure 1E). These changes were accompanied by an increase in muscle MCT1 expression (Figure 3B) and a decrease in Na⁺–K⁺ subunit β₁ (Figure 2C). Similarly, Iaia et al. [8] observed that 17‐year‐old football players increased performance during a repeated sprint test by 3% and 4% when performing speed endurance production and maintenance training, respectively, for 5 weeks (Figure 1D). In addition, the Yo‐Yo IR2 performance was elevated by 11% and 7%, respectively (Figure 1E), with only the effect of speed endurance production training being significant. Likewise, young elite ice hockey players improved their Yo‐Yo IR1 performance on ice by 14% (Figure 1E) after a 4‐week period of SET three times per week [35]. The improved performance was accompanied by a 5% increase in V̇O₂‐max, which was associated with several cardiac adaptations [36] (Table 1).

6.2. Speed Endurance and Aerobic High‐Intensity Training (Table 2)

The effects of adding both SET and aerobic high‐intensity training on intermittent exercise performance were also studied. Well‐trained cyclists improved (4%) repeated sprints performance (Figure 1D) after a 7‐week period with SET (10–12 × 30‐s all‐out 2–3/week) and aerobic high‐intensity training (4–5 × 3–4‐min intervals 1–2/week) with a 70% reduction in training volume [20]. In vivo muscle buffer capacity and expression of many proteins related to ion transport, such as NHE1 (Figure 3A) and FXYD1 (Figure 2E), were elevated after the intervention period, whereas muscle oxidative enzyme levels were decreased [21]. Furthermore, increased expression of muscle Ca⁺/calmodulin‐dependent protein kinase II (CaMKII) and phospholamban (PLN) as well as increased phosphorylation of CaMKII Thr‐287 were observed. Christensen et al. [29] also studied the effects of combined SET and aerobic high‐intensity training in elite cyclists. The intervention period lasted 7 weeks and consisted of 12 × 30‐s uphill sprints (SET) and 5 × 4‐min intervals (AHI) twice a week. There were two groups: one group had a 33% reduction in training volume, and the other maintained training volume. The former group exhibited a 10% improvement in repeated sprint fatigue resistance, whereas the second group exhibited a non‐significant increase of 3%. The group with a reduced training volume exhibited a higher expression of muscle PFK, with no other muscle changes observed in either group. Furthermore, V̇O₂‐max was also unaltered in both groups [29].

Additionally, Christensen et al. [37] studied semi‐professional football players conducting SET as repeated 30‐s sprints and aerobic high‐intensity training with 2‐min intervals 2–3 times per week in the first 2 weeks after the competitive season with a reduction in training volume of 30%. They observed that repeated sprint performance (2 × 20 s separated by 1 min recovery) was elevated by 2% (Figure 1D), and the players tended to improve (6%) Yo‐Yo IR2 performance (Figure 1E). These changes were accompanied by increases in muscle Na⁺–K⁺ subunit α₂ (Figure 2B), FXYD1 phosphorylation, and pyruvate dehydrogenase (PDH) [38]. Nyberg et al. also found enhanced (12%) performance in the Yo‐Yo IR2 test in semi‐professional football players after a 9‐week period with SET consisting of 8–10 repetitions of 5 s maximal exercise followed by 10 s of rest conducted 2–3 times per session 1.5 times a week for 9 weeks [39]. The improvement was associated with faster oxygen kinetics but reduced expression of muscle oxidative enzymes.

6.3. Speed Endurance Training During Moderate‐Intensity Aerobic Training (Table 3)

In two studies, Almquist et al. [22, 40] examined well‐trained cyclists (V̇O₂‐max: 72–75 mL kg⁻¹ min⁻¹), who conducted SET during aerobic moderate‐intensity training, with more than 40% reduction in training volume, over 2–3 weeks, and in one case with a 2‐week recovery [22]. Performance in repeated 30‐s sprints was improved in both studies (4%–8%) (Figure 1D), and muscle PFK activity was reduced.

When studying football players performing 3 × 5‐min 10–20–30 training sets three times per week for 10 weeks with a 20% reduction in training volume, performance in the Yo‐Yo IR2 test was 18% better (Figure 1E) [41]. In addition, elevated levels of muscle oxidative enzymes, such as pyruvate dehydrogenase E1 subunit α1 (PDH‐E1α) and oxidative phosphorylation complex (OXPHOS) (Figure 4D), as well as muscle ion transporters, that is, Na⁺–K⁺ subunits α₂ and β₂ (Figure 2B,D), were observed.

6.4. Speed Endurance and Power Training (Table 4)

The two studies [25, 26] that examined the effect of combining SET and power training of runners, with a marked reduction in training volume (> 40%), both showed a marked improvement in Yo‐Yo IR2 performance (Figure 1E). One of the studies showed elevated expression of muscle NHE1 (Figure 3A) [25], and the other higher muscle Na⁺–K⁺ subunit β₁ (Figure 2C) [26] after the intervention period.

6.5. Summary

It appears that all studies introducing SET, with or without reducing training volume, showed an improvement in intermittent exercise performance either assessed using repeat sprint tests or one of the intermittent Yo‐Yo tests. The question is what caused these adaptations. The explanation may be that the ability to recover from intense exercise during the resting periods is around 30 s in the repeated sprint tests and 5 or 10 s in the Yo‐Yo tests. A candidate is an increased rate of CP resynthesis, as the creatine kinase reaction is expected to contribute significantly during the short intense exercise bouts used in both the repeated sprint and intermittent Yo‐Yo tests [42]. However, the rate of resynthesis of CP in recovery periods is closely related to the muscle oxidative capacity [43] and in none of the studies, an increase in muscle oxidative enzymes or other respiratory measurements was observed. In fact, one study showed reduced expression of muscle oxidative enzymes. Instead, it may have been caused by a higher rate of oxygen uptake in the initial phase of each exercise bout (oxygen kinetic), as observed in one study, or higher muscle re‐uptake of K⁺ due to elevated activity of the Na⁺–K⁺ pumps, as the muscle content of Na⁺–K⁺ subunits and FXYD1 has been observed to increase in several of the studies (Tables 1, 2, 3, 4). In addition, lower muscle H⁺ accumulation through elevated muscle buffer capacity and capacity for H⁺ efflux due to an increased abundance of muscle NHE1 and MCT1 +4 may have contributed, as muscle pH had been shown to be around 6.6 at the end of the Yo‐Yo IR tests [42]. Improved intracellular Ca²⁺ handling could also be an explanation as the expression of several of the related muscle proteins is higher after a SET‐training period.

7. Synopsis and Perspectives

Multiple studies highlight the effectiveness of performing periods of SET in already well‐trained individuals and athletes. Independent of task duration, at least for events lasting less than 60 min, SET enhances performance—both when introduced by itself or in combination with aerobic moderate‐ and high‐intensity training or power training. The effects of SET are evident regardless of whether the SET has been carried out as production or maintenance training, or whether SET is added to the regular training, with either higher, unchanged, or reduced volume. Actually, it is a significant advantage that the training volume can be reduced, as overloading can be avoided and motivation from the athlete may be greater. Along the line, the finding that SET with 6 repetitions was as effective as 12 repetitions on performance in elite cyclists [19] and SET twice a week was as beneficial as four times when runners were familiarized [18] suggesting that high SET volume is unnecessary for major performance gains.

Regarding injury risk with SET, cycling imposes minimal load on the leg muscles, making injuries rare, while running studies also reported low overuse injury rates. However, to examine the potential risk of injury, studies with a high number of participants are needed (based on a proper power analysis).

A significant number of the studies presented have been conducted with elite athletes, but further studies with top athletes are required. In addition, various combinations of training modalities, as they occur in sports, need to be investigated to determine to what extent the training volume can be reduced and for how long. Lastly, studies on optimizing SET in the weeks leading to competition are also essential.

Conflicts of Interest

The authors declare no conflicts of interest.

Bangsbo J., Kissow J., and Hostrup M., “Speed Endurance Training to Improve Performance,” Scandinavian Journal of Medicine & Science in Sports 35, no. 7 (2025): e70091, 10.1111/sms.70091.

Data Availability Statement

The authors have nothing to report.