Table 2.

Characteristics of the included studies.

Author, Year, Country, Study Design	Sample Characteristics N of Subjects_ M/F_ Mean Age	Probiotics Daily Intake Intervention Length	Type of Performance/Physical Condition Variables Studied	Main Results
Harnett, 2020 Australia -double-blind randomised controlled trial	Elite male rugby union players Probiotic group (n = 9) 27.0 ± 3.2 years Placebo group (n = 10) 26.6 ± 2.9 years	genera Lactobacillus, Bifiodbacterium and Streptococcus (during international competition) Dose: 60 bilion SBFloractivTM (Bioceuticals, Australia AustL# 285024) containing 250 mg of the yeast Saccharomyces boulardii was added to the probiotic regime during the international travel −17 weeks	Muscle soreness rated on a 1–5 scale: 5 = non-existent, 4 = fine, no dramas let’s get on with it, 3 = there’s some, but after normal warm-up, I’ll be fine, 2 = pretty ordinary, my movements are stiff and sore, and1 = severe, I need to alert the physio or doctor. Leg heaviness on a 1–10 Likert scale	Muscle soreness was ∼0.5 units lower (F(1, 343) = 42.646, p < 0.0001) and leg heaviness scores∼0.7 units lower (F(1, 334) = 28.990, p < 0.0001) in the probiotic group compared to the placebo group. Across both groups, as self-reported muscle soreness scores and salivary CRP (C-reactive protein) concentrations increased, sleep quantity, quality and motivation scores decreased. Conversely, as muscle soreness scores and CRP decreased, sleep quantity and quality, and motivation scores improved.
Ching Huang, 2019 Taiwan -double-blind experimental design	Triathletes 18 subjects for Study I 16 subjects for study II Probiotic group (n = 9) STUDY I 20.2 ± 0.7 years STUDY II 22.3 ± 1.2 years Placebo group (n = 9) STUDY I 21.1± 1.5 years STUDY II 20.1 ± 0.3 years	Lyophilized L. plantarum PS128 Dose: twice capsules per day (3 × 1010 CFU/day) −4 weeks (STUDY I) −3 weeks (STUDY II)	Body composition evaluated using DEXA (dual-energy X-ray absorptiometer). Anaerobic and aerobic capacities evaluated using a 30-s Wingate anaerobic kinetic Test and VO2 max endurance test. Muscle damage evaluated using Biochemical Indices, such as CK, LDH, protein carbonyl, myioglobin. Muscle fatigue evaluated using Biochemical Indices, such as Ammonia, Lactate and FFA.	L. plantarum PS128 supplementation, combined with training, can significantly alleviate oxidative stress (such as creatine kinase, Thioredoxin, and Myeloperoxidase indices) after a triathlon (p < 0.05). This effect is possibly regulated by a 6–13% decrease of indicated pro-inflammation (TNF-α, interleukin-6, and interleukin-8) cytokines (p < 0.05) and 55% increase in anti-inflammation (interleukin-10) cytokines (p < 0.05) after intensive exercise stimulation. In addition, L. plantarum PS128 can also substantially increase 24–69% of plasma-branched amino acids (p < 0.05) and elevate exercise performance, as compared to the placebo group (p < 0.05). There was no significant difference in body composition between the probiotic group and placebo group pre- and post-supplementation (p ≤ 0.05).
Ching Huang, 2020 Taiwan -double-blind experimental design	Male Triathletes Probiotic group (n = 10) 21.9 ± 1.4 years Placebo group (n = 10) 21.6 ± 1.3 years	L. plantarum PS128 Dose: a single capsule twice per day, equivalent to 3 × 1010 CFU/day −4 weeks	Maximal oxygen consumption and exercise performance evaluated using a treadmill (Pulsar, h/p/cosmos, Germany) and an auto respiratory analyzer K4b2 (Cosmed, Concord, CA, USA). Body composition evaluated using DEXA (dual-energy X-ray absorptiometer).	L. plantarum PS128 supplementation was associated with an improvement in endurance running performance through microbiota modulation and related metabolites, but not in maximal oxygen uptake. The probiotic group could significantly elevate endurance performance by the treadmill exercise protocol; the performance could increase by about 130% as compared to the placebo group (p = 0.0035). However, at the end of the study, the VO2 max and body composition (bone, fat, and lean percentage) demonstrated no significant difference between groups in the gas and DEXA analysis.
Komano, 2018 Japan -randomized, placebo-controlled, double-blinded trial	Healthy male athletes Probiotic group (n = 26) 20.8 ± 0.8 years Placebo group (n = 24) 20.5 ± 0.8 years	cells of heat-killed Lactococcus lactis strain plasma Dose: a capsule containing 100 billion cells −13 days	Physical condition, fatigue, articular pain, lassitude, and muscle pain evaluated using a daily questionnaire.	CD86 (Cluster of Differentiation 86) as a maturation marker on pDC (plasmacytoid dendritic cells) was significantly increased in the probiotic group. Moreover, the cumulative days of fatigue were significantly fewer in the probiotic group.
Pugh, 2020 UK -randomized, double-blind, placebo-controlled crossover trial	Trained male cyclists (n = 7) 23 ± 4 years	Active strains Lactobacillus acidophilus (CUL60), Lactobacillus acidophilus (CUL21), Bifidobacterium bifidum (CUL20), and Bifidobacterium animalis subsp. lactis (CUL34; Proven Probiotics, Port Talbot, UK) During exercise, subjects consumed a 10% CHO drink enriched with the stable isotope [U-13C] glucose (CK Isotopes, Ibstock, UK). Maltodextrin (176.4 g; Myprotein Inc., Northwich, UK) and 3.6 g [U-13C] glucose Dose: a capsule containing 25 billion CFU-two, 28-day, periods of supplementation, separated by a 14-day washout period.	Exercise trials made using time trial	Probiotics led to minimal increases in absorption and oxidation of the ingested maltodextrin and small reductions in fat oxidation, whereas having no effect on subsequent time-trial performance. During the 100-kJ time trial, there was no significant difference in the time to complete between placebo group (308 ± 69 s) and probiotic group (301± 74 s; p = 0.714).
Salleh, 2021 Malaysia -randomized, placebo-controlled study	Badminton Players Probiotic group (n = 15) 19.5 ± 1.0 years Placebo group (n = 15) 19.9 ± 1.3 years	Lactobacillus casei Shirota Dose: drink containing 3 × 1010 CFU −6 weeks	Body composition evaluated using the InBody 500 bioelectrical impedance analyser. Aerobic Capacity evaluated using a 20-m multi-stage shuttle run test. Hand strength evaluated using the handgrip test. Leg power assessment measuring the distance of the most extreme point the subject could reach with their arm by jumping. Speed evaluated using a 40-m dash. Agility evaluated using a t-test.	Supplementation of probiotics improved aerobic capacity in probiotic group by 5.9% (p < 0.001) but did not influence the speed, strength, leg power and agility.
Sawadaa, 2019 Japan -randomized, double-blind, and placebo-controlled parallel group study	Male university Ekiden (long-distance relay race) runners Probiotic group (n = 24) 19.8 ± 1.4 years Placebo group (n = 25) 20.1 ± 1.1 years	Heat-inactivated Lactobacillus gasseri CP2305 Dose: 200 mL of beverages containing 1 × 1010 bacterial cells −12 weeks	Fatigue evaluated using Fatigue Scales	Daily CP2305 intake was effective in recovering from fatigue during the vigorous training period. Furthermore, administration of CP2305 improved the richness and evenness of the gut microbial ecosystem and prevented the stress-induced changes in gene expression of peripheral blood leucocytes. No significant difference in physical performance was found between the probiotic group and placebo group.
Schreiber, 2021 Israel-randomized, double-blind, two-arm, placebo-controlled trial design	Male cyclists, ranked elite or category 1 level competitions Probiotic group (n = 11) 25.9 ± 4.6 years Placebo group (n = 16) 29.5 ± 6.2 years	(≥) 4.3×109 CFU Lactobacillus helveticus Lafti L10 (28.6%), ≥4.3 × 109 CFU Bifidobacterium animalis ssp. lactis Lafti B94 (28.6%), ≥3.9 × 109 CFU Enterococcus faecium R0026 (25.7%), ≥2.1 × 109 CFU Bifidobacterium longum R0175 (14.3%) and ≥0.4 × 109 CFU Bacillus subtilis R0179 (2.8%) Dose: 15 billion CFU −90 days	Body composition assessed using Skyndex Electronic Skinfold Caliper (Caldwell, Justiss & Co., Inc., Fayetteville, AR, USA), measuring 4 skinfolds (triceps, biceps, subscapularis, iliac crest) in triplicates and the average of each skin fold was used to calculate body density and percent body fat was calculated using the Siri equation. VO2max measured using Metalyzer 3B (Cortex Biophysik GmbH, Leipzig, Germany) metabolic cart and determined following personalized graded exercise protocol. Fatigue evaluated using Time to fatigue (TTF) test	Mean rate of perceived exertion (RPE) values during the TTF (test and time-to-fatigue) were lower in the probiotic group (ΔRPE: −0.3 ± 0.9 vs. 0.8 ± 1.5, p = 0.04). No significant changes were measured between and within groups in VO2max and TTF values, mean levels of C-reactive protein, interleukin-6 and tumour necrosis factor-alpha values following treatment.
Shing, 2014 Australia -double-blind, cross-over trial	Male runners Probiotic group (n = 5) Placebo group (n = 5) 27 ± 2 years	7.4 billion CFU of Lactobacillus acidophilus, 15.55 billion CFU of L. rhamnosus, 9.45 billion CFU of L. casei, 3.15 billion CFU of L. plantarum, 1.35 billion CFU of L. fermentum, 4.05 billion CFU of Bifidobacterium lactis, 1.35 billion CFU of B. breve, 0.45 billion CFU of B. bifidum and 2.25 billion CFU of Streptococcus thermophilus Dose: 1 capsule/day (45 billion CFU) −4 weeks	VO2 max evaluated using a test involving an incremental treadmill run to fatigue starting at 10 km h−1, 0% gradient with the speed increasing by 1 km h−1 each minute until a speed of 18 km h−1. After 1 min at 18 km h−1, the treadmill gradient was increased by 1% each minute until volitional fatigue. Fatigue evaluated time-to-fatigue run test	Probiotics supplementation significantly increased run time to fatigue (min:s 37:44 ± 2:42 versus 33:00 ± 2:27; p = 0.03, d (Cohen’s effect size) = 0.54).
Smarkusz-Zarzecka, 2020 Poland -randomised, double-blind study	Long-Distance Runners Probiotic group (n female = 14; 37.21 ± 8.09 years); (n male = 20; 40.85 ± 8.32 years) Placebo group (n female = 6; 33.33 ± 8.73 years) (n male = 26; 38.61 ± 8.84 years)	Bifidobacterium lactis W52, Lactobacillus brevis W63, Lactobacillus casei W56, Lactococcus lactis W19, Lactococcus lactis W58, Lactobacillus acidophilus W37, Bifidobacterium bifidum W23 and Lactobacillus salivarius W24 Dose: 2 capsules of the supplement twice a day- A capsule contains 2.5 × 109 CFU/g −3 months	Body Composition evaluated using the InBody770 analyser. Cardiorespiratory Fitness evaluated using the Fitmate MED device and a medical treadmill adapted. The Bruce protocol treadmill test was used.	A statistically significant increase in maximum oxygen uptake VO2max (p = 0.017), minute ventilation (Ve) (p = 0.013), functional capacity (FC) (p = 0.036), breathing reserve (p = 0.020) and exercise capacity (p = 0.036) was observed in the group of men taking the probiotic supplement. In the group of women taking the probiotic supplement, a decrease in body fat (in kilograms and percentages) and visceral fat (VAT) was observed, but the differences were not statistically significant.
Strasser, 2016 Austria -randomized, double-Blinded, placebo-controlled Trial	Trained athletes Probiotic group (n = 14) 25.7 ± 3.5 years Placebo group (n = 15) 26.6 ± 3.5 years	Bifidobacterium bifidum W23, Bifidobacterium lactis W51, Enterococcus faecium W54, Lactobacillus acidophilus W22, Lactobacillus brevis W63, and Lactococcus lactis W58 (Ecologic® Performance, Winclove B.V., Amsterdam, The Netherlands). The total cell count was adjusted to 2.5 × 109 colony-forming units (CFU) per gram Dose: 1 sachet of 4 g per day, which is equivalent to 1 × 1010 CFU/day −3 months	Athletic performance evaluated using n incremental cycle ergometer exercise test until Exhaustion. Body composition evaluated using the bioelectrical impedance analysis (BIA) method (BIA-2000-M, Data Input, Pöcking, Germany).	Data indicate reduced exercise-induced tryptophan degradation rates in the probiotic group. Daily supplementation with probiotics, however, did not benefit athletic performance and body composition. Analysis of training loads indicated that the weekly training of the aerobic system, mainly continuous endurance training at moderate intensity (60% to 80% VO2max), varied significantly between the group: the means were significantly higher in the probiotics group as compared to the placebo (8.0 ± 2.3 and 6.6 ± 4.3 h per week endurance training, respectively).
Toohey, 2018 Tennessee -double-blind, placebo-controlled, randomized study	Female athletes (volleyball, soccer) Probiotic group (n = 11) Placebo group (n = 12) 19.6 ± 1.0 years	DE111 (genome sequenced and clinically tested strain of Bacillus subtilis) Dose: 5 billion CFU/day −10 weeks	Body Composition evaluated using air displacement plethysmography using the BODPOD (COSMED, Rome, Italy), multifrequency bioelectrical impedance analysis (BIA) using the InBody 570 Body Composition Analyzer device (Biospace, Inc., Seoul, Republic of Korea), the 3-compartment water (3C-W) model described by Siri (32). Performance evaluated using: dynamic strength test, isometric strength test, vertical jump test, and pro-agility test.	Significant (p ≤ 0.05) main effects for time were observed for improved squat 1RM (1 repetition maximum), deadlift 1RM, bench press 1RM, vertical jump, RF MT (rectus femoris muscle thickness), and BF% (body fat%). Of these, a significant group 3-time interaction was noted for BF% (p = 0.015), where greater reductions were observed in probiotic group (−2.05 ± 1.38%) compared with placebo group (−0.2 ± 1.6%).
Townsend, 2018 USA -double-blind, placebo-controlled, randomized study	Male baseball athletes Probiotic group n = 13 Placebo group n = 12 20.1 ± 1.5 years	Bacillis subtilis DE111 (Deerland Enzymes, Kennesaw, GA, USA) Dose: a capsule containing 1.2 billion CFU −12 weeks	Body Composition evaluated using air displacement plethysmography using the BODPOD (COSMED, Rome, Italy), multifrequency bioelectrical impedance analysis (BIA) using the InBody 570 Body Composition Analyzer device (Biospace, Inc., Seoul, Republic of Korea), the 3-compartment water (3C-W) model described by Siri (32). Performance evaluated using: dynamic strength test, Ten-Yard Sprint, Pro-Agility Test, Standing Long Jump.	There were no group differences observed between the probiotic group and placebo group for any measure of strength, performance or body composition. Collectively, significant improvements (p < 0.001) were observed in squat 1RM, deadlift 1RM, pro-agility, and standing long jump as a result of 12 weeks of offseason training, while no improvement (p = 0.312) in 10-yard sprint time was found.