Table 2.

Studies (n = 8) examining the impact of HIIT-based running programs on physiological, metabolic, neuromuscular, and biomechanics measurements in recreationally trained endurance runners (intervention studies).

Study	Subject description	Training program (treatment and control groups)	Outcome measure	Result
Bangsbo et al. (2009)33	n = 17 M 34 ± 2 years 74 ± 2 kg 182 ± 2 cm VO2max 63 ± 2 mL/kg/min - Moderately trained male endurance athletes (running 4–5 day/week)	- Intervention period: for a 6- to 9-week period - Groups: speed endurance group (SIT, n = 12) and control group (CG, n = 5) - Training:  - SET: 25% ↓ in the weekly training but including SIT (2–3 time/week, 8–12 running bouts repeated 30 s at 95% of maximal speed with 3 min passive recovery), HIIT (4 × 4 min running at ~85% of HRmax separated by 2 min of passive recovery), and 1–2 sessions of CR (75%–85% of HRmax)  - CG: continued the endurance training (~55 km/week)	Physiological measurements: - VO2max and RER - HR and blood samples (BLa and K+) - Muscle analysis: ion transport proteins and enzymes Performance measurements: - Incremental test - Repeated sprint test - 3 and 10 km	- The inclusion of SIT and HIIT with ↓ in training volume not only resulted in ↑ short-term work capacity but also ↑ 3 and 10 km performance in endurance runners - The improvements were associated with an ~70% higher expression of Na+-K+ pump and lower plasma K+ concentrations during exhaustive running
Denadai et al. (2006)36	n = 17 M 37 ± 4 years 63 ± 4 kg 166 ± 5 cm VO2max 59 ± 6 mL/kg/min - Trained endurance runners training a mean weekly volume of ~80 km divided into 6 training sessions	- Intervention period: for 4 weeks - Groups: 95% or 100%vVO2max groups - Training: 2 HIIT sessions per week (at 95%–100%vVO2max), 1 session at VLTP (2 × 20 min with 5 min of rest at 60% vVO2max) and 3 CR (45–60 min at 60%–70%vVO2max)  - 95%vVO2max: 4 intervals (60%Tlim at 95%vVO2max; recovery = 30%Tlim at 50% vVO2max)  - 100%vVO2max group: 5 intervals (identical to previous, but according to 100%vVO2max)	Physiological measurements: - VO2max and RER - HR and BLa Performance measurements: - Incremental test - Submaximal test - 1.5 and 5 km time trials	- vVO2max, RE, and performance (1.5 and 5 km) can be ↑ using a 4-week training program consisting of 2 HIIT sessions at 100%vVO2max and 4 submaximal run sessions per week (95%vVO2max) - CG did not present significant improvement on the vVO2max, RE, and 1.5 km running performance
Esfarjani and Laursen (2007)37	n = 17 M 19 ± 2 years 73 ± 3 kg 172 ± 4 cm VO2max 51 ± 2 mL/kg/min - Moderately trained male runners with 2–3 years of run training	- Intervention period: for 10 weeks - Groups: 2 intervention groups (HIIT-based, EG1 and EG2) and 1 control group (CR-based, CG) - Training:  - HIIT groups (EG1, and EG2): 2 HIIT sessions and 2 CR (60 min at 75%vVO2max) each week EG1: 5–8 intervals at vVO2max for a duration equal to 60%Tlim, with a 1:1 work–rest ratio EG2: 7–12 × 30 s bouts at 130%vVO2max with 4.5 min of recovery  - CG: 4 × 60 min CR (75%vVO2max) per week	Physiological measurements: - VO2max and RER - HR and BLa Performance measurements: - Incremental test - 3000 m time trial	- HIIT-based running plan ↑ 3 km running performance time (−7.3%), concomitant with ↑VO2max (+9.1%), vVO2max (+6.4%), Tlim (+35%), and VLT (+11.7%). - SIT improved 3 km performance (−3.4%) with simultaneous ↑ in VO2max (+6.2%), vVO2max (+7.8%), and Tlim (+32%), but not VLT (+4.7%) - ↑ performance and physiological variables tended to be greater using more prolonged HIIT at vVO2max when compared with SIT
Gliemann et al. (2015)35	n = 160 HIIT group: n = 132 (58 M, 74 F) 49 ± 1 years 73.7 ± 1.1 kg VO2max 52 ± 1 mL/kg/min CG: n = 28 (15 M, 13 F) 46 ± 2 years 73.7 ± 2.5 kg VO2max 52 ± 4 mL/kg/min - Recreational >2-year training (>3 session/week)	- Intervention period: for 8 weeks - Groups: CG and HIIT group (replacing 2 of 3 weekly sessions with 10–20–30 training) - Training  - CG: same plan (CR-based, HR between 75% and 85% of HRmax)  - HIIT group: 1 × CR + 2 × 10–20–30 training per week. (10–20–30: 3–4 × 5 min running periods interspersed by 2 min of rest; each 5 min running period consisted of 5 consecutive 1 min intervals divided into 30, 20, and 10 s at an intensity corresponding to ∼30%, ∼60%, and ∼90%–100% of maximal running speed	Physiological measurements: - VO2max and RER - Blood pressure - HR and BLa - Blood variables: glucose, cholesterol, insulin, cortisol - Muscle morphology Performance measurements: - Test to exhaustion - 5000 m time trial	- 8 weeks of 10–20–30 training was effective in improving VO2max and 5 km performance (–38 s) and lowering blood pressure (∼5 mmHg) - Muscle fiber area, fiber type, and capillarization were not changed after 10–20–30 training
Gunnarsson and Bangsbo (2012)34	n = 18 (12 M, 6 F) 34 ± 2 years 75 ± 4 kg 179 ± 2 cm VO2max 52 ± 1 mL/kg/min - Moderately trained runners (3–4 weekly running sessions, ~30 km/week)	- Intervention period: for 7 weeks - Groups: CG and HIIT (10–20–30 training) - Training: 10–20–30 training concept (identical to the previous)  - CG: continued with their regular endurance training (CR-based)  - HIIT: all regular training sessions were replaced with 3 weekly 10–20–30 training sessions. In the first 4 weeks, 10–20–30 conducted 3 × 5 min intervals and, in the remaining 3 weeks, 4 × 5 min intervals per session	Physiological measurements: - VO2max and RER - Blood pressure, HR, BLa - Blood variables: glucose, cholesterol, insulin, cortisol - Muscle morphology Performance measurements: - Incremental test - 1.5  and 5 km trials	- After 7 weeks of 10–20–30 training, with a ~50% ↓ in training volume, VO2max ↑ by 4% and performance in a 1.5 km and a 5 km run ↑ by 21 s and 48 s, respectively. - Fasting blood and plasma values = CG, while HIIT group ↓ values at post-test in cholesterol and LDL - Resting HR remained unchanged in both groups, but blood pressure was reduced in the HIIT group after intervention - Muscle morphology equal in both groups; same occurred in BLa
Smith et al. (2003)38	n = 27 M 25 ± 1 years 72 ± 2 kg 179 ± 2 cm VO2max 61 ± 1 mL/kg/min - Well-trained male endurance runners	- Intervention period: for 4 weeks - Groups: CG (n = 9), HIIT1 (60%Tmax, n = 9) and HIIT2 (70%Tmax, n = 9) - Training: HIIT groups completed 2 HIIT session/week at vVO2max and their respective Tmax duration; work–rest ratio of 1:2 was used during HIIT; HIIT groups performed 1 CR (30 min at 60%vVO2max) per week  - HIIT1: 6 intervals per HIIT session  - HIIT2: 5 intervals per HIIT session  - CG: Maintained current training level (low intensity, long duration training)	Physiological measurements: - VO2max, RER, VT, and RE - HR and BLa Subjective ratings: - sleep, fatigue, stress, and muscle soreness Performance measurements: - Treadmill test - 3 and 5 km	- HIIT1 showed a 17 s improvement in 3 km, compared to a 7 s improvement of HIIT2; this change in HIIT1 was related to changes in VO2max and RE, and these runners improved in VT (6.8%) and Tmax (50 s) compared to 1.7% and 16 s improvements in HIIT2
Vezzoli et al. (2014)32	n = 20 M CR group: 50 ± 6 years 69 ± 10 kg 174 ± 7 cm HIIT group: 45 ± 8 years 72 ± 9 kg 176 ± 6 cm - National level, 45 km/week	- Intervention period: For 8 weeks - Groups: 2 groups, 3 times nonconsecutively per week: CR-based (n = 10) or HIIT-based (n = 10) - Training: 3 different types of training sessions were scheduled, with the total distance covered in each session being controlled:  - CR: (1) 64.5 min at 70%GET, (2) 58.5 min at 80%GET, and (3) 54 min at 90%GET  - HIIT: (1) 18 × (1 min at 120%GET and 2 min at 65%GET), (2) 18 × (1 min at 130% GET and 2 min at 65%GET), and (3) 18 × (1 min at 140%GET and 2 min at 65%GET)	Physiological measurements: - VO2max, RER, and VT - HR and BLa - Blood pressure Indexes of oxidative stress in blood and urine samples	- CR and HIIT induced similar beneficial effects in master runners, ↓ resting levels of oxidative stress biomarkers - Resting lipid peroxidation levels were ↓ after training both in CR and HIIT - No changes in PC resting values in both CR and HIIT - The data showed ↓ 25% in urinary 8-OH-dG excretion in both CR and HIIT groups - The defences against oxidative damage were lowered only in CR, not in HIIT
Zatoń and Michalik (2015)39	n = 17 (6 F, 11 M) CG: 34 ± 15 years 70 ± 10 kg 174 ± 7 cm EG: 34 ± 9 years 76 ± 7 kg 176 ± 12 cm - Amateur long-distance runners >1 year of experience	- Intervention period: for 8 weeks - Groups: 2 groups completing 8 weeks of CR-based (CG, n = 9) or HIIT-based (EG, n = 8) - Training: CG performed 3–4 CR session/week; EG performed 2 HIIT and 1 CR session/week - CG: continued to train as normal - EG: HIIT, 4 × 20–30 s repetitions of maximal intensity running (covering a distance of 90–200 m); rest between each repetition was based on a 1:2 work–rest ratio and ranged from 40 s to 60 s; number of sets performed ranged from 2 to 4	Physiological measurements: - VO2max - HR - Blood variables during graded exercise test: BLa, pH, partial pressure of O2 and CO2 (pO2 and pCO2) Performance measurements: - Cooper test	- HIIT develops physiological function similar to a CR-based training protocol in amateur long-distance runners - HIIT training ↑ VO2max, minute ventilation, tidal volume, distance covered in the Cooper test, and ↑ postexercise recovery as well as RE - CG ↑ VO2max and tidal volume with a larger ↓ in minute ventilation compared with EG - Relative VO2max and relative HR ↓ in both groups, which suggests improved RE in both groups

Notes: ↑ to increase or to obtain a higher value; ↓ to impair or to obtain a lower value; ~ approximately.

Abbreviations: 8-OH-dG = 8-hydroxy-2-deoxy-guanosine; BLa = blood lactate accumulation; CG= control group; CR = continuous run; EG = experimental group; F = female; GET = gas exchange threshold; HIIT = high-intensity intermittent training; HR = heart rate; HR_max = maximum heart rate; M = male; PC = phosphocreatine; RE = running economy; RER = respiratory exchange ratio;. SET = speed endurance training; SIT = sprint interval training; T_lim = time to exhaustion sustained at VO_2max; T_max = time for which vVO_2max can be maintained; VLTP = velocity associated to lactate turn points; VO_2max = maximal oxygen uptake; vVO_2max = velocity associated to VO_2max; VT = ventilatory threshold; V_LT = velocity associated to lactate threshold.