Introduction
Proposed ergogenic mechanisms
Dose, timing, and safety
Study | Participants | Dose (C-M ratio) and Timing | Experimental design | Functional Measure/test | Resistance Exercise Protocol* | Resistance Performance Outcomes | Other measures |
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Bendahan et al. (2002) | Sedentary males symptomatic of fatigue (n = 18) Age: 31 ± 9 years | CM: 2 g ingested 3 × per-day (6 g) for 15 days | Single group treatment for 15 days | Dynamic finger flexions using slide weight and displacement transducer – power (w) 31P magnetic resonance spectroscopy | Finger flexions performed at 1.5 s intervals lifting a 6 kg weight for 3 min Performed: 2 × before ingestion CM 3 × during ingestion CM 1 × after ingestion CM | Power (w) ↑ during CM ingestion CM when compared with before ingestion (2.0 + 0.1 vs. 1.7 ± 0.1) | Delta change in pH per unit of power ↓ during CM ingestion compared with before ingestion (0.24 ± 0.02 vs. 0.29 ± 0.03) Rate of oxidative ATP production (%EC) ↑ during CM ingestion (74 ± 4 vs. 54 ± 12) Rate of PCr resynthesis (mmol/min) ↑ during CM ingestion (24.2 ± 3.2 vs. 16.9 ± 2.9) |
Perez-Guisado et al. (2010) | Resistance trained males (n = 41) Age: 30 ± 8 years | CM: 8 g PLA: 10 g sugar and 60 mg sodium saccharine Single dose 1-h prior | Randomized, double-blind, cross-over design 7-day wash out | Dynamic concentric and eccentric muscular endurance/strength using barbell | 4 sets at 80% 1RM until failure before and then again after a pectoral training workout 1-min rest between sets Barbell bench press | Bench press: total reps ↑ in CM vs. PLA before workout: Set 3 (8.2 ± 1.6 vs.7.4 ± 1.6) Set 4 (7.1 ± 1.7 vs. 6.0 ± 1.6) Total reps ↑ in CM vs. PLA after workout: Set 1 (10.3 ± 1.8 vs. 9.2 ± 2.1) Set 2 (8.4 ± 1.8 vs. 6.9 ± 2.0) Set 3 (6.9 ± 1.7 vs. 5.1 ± 1.8) Set 4 (5.5 ± 1.5 vs. 3.6 ± 1.4) | Muscle soreness following 24-h ↓ 39.7% in CM vs. PLA 48-h ↓41.8% in CM vs. PLA |
Wax et al. (2015) | Resistance trained males (n = 12) Age: 22 ± 1 years | CM: 8 g PLA: Maltodextrin and aspartame Single dose 1-h prior | Randomized, double-blind, counter-balanced, cross-over design 7-day wash out | Dynamic concentric and eccentric muscular endurance using machines | 5 sets at 60% 1RM until failure 3-min rest between sets Leg press Hack squat Leg extension | Leg press: total reps ↑ in set 5 in CM vs. PLA Hack squat: total reps ↑ in sets 4 and 5 in CM vs. PLA Leg extension: total reps ↑ in set 5 in CM vs. PLA (mean data not reported) | Blood lactate ↔ HR ↔ Blood pressure: Systolic ↔ Diastolic ↔ |
Wax et al. (2016) | Resistance trained males (n = 14) Age: 23 ± 2 years | CM: 8 g PLA: Maltodextrin and aspartame Single dose 1-h prior | Randomized, double-blind, counter-balanced, cross-over design 7-day wash out | Dynamic concentric and eccentric muscular endurance using body weight exercises | 3 sets until failure 3-min rest between sets Chin-up Reverse chin-up Push-up | Chin-up: total reps: ↑ in CM vs. PLA (32.2 ± 5.6 vs. 28.4 ± 7.1) Reverse chin-up total reps ↑ in CM vs. PLA (32.1 ± 7.1 vs. 26.6 ± 5.6) Push-up total reps: ↑ in CM vs. PLA (97.7 ± 36.1 vs. 89.1 ± 37.4) | Blood lactate: ↔ HR: ↔ Blood pressure Systolic: ↔ Diastolic: ↓ |
Glenn et al. (2017) | Resistance trained females (n = 15) Age 23 ± 3 years | CM: 8 g + 8 g dextrose PLA: 8 g dextrose Single dose 1-h prior | Randomized, double-blind, cross-over design 7-day wash out | Dynamic concentric and eccentric muscular endurance/strength using barbell and plate loaded leg press | 6 sets at 80% 1RM until failure 1-min rest between sets Bench press Leg press | Bench press: total reps ↑ in CM vs. PLA (34.1 + 5.7 vs. 32.9 + 6.0) Leg press: total reps ↑ in CM vs. PLA (66.7 ± 30.5 vs. 55.1 ± 20.6) | Bench press RPE: ↓ Leg press RPE: ↔ Bench press HR: ↔ Leg Press HR: ↔ |
Gonzalez et al. (2018) | Recreational resistance trained males (n = 12) Age: 21 ± 2 years | CM: 8 g PLA: Flavored water Single dose 40-min prior | Randomized, double-blind, placebo-controlled, counter-balanced, cross-over design ~ 7-day wash out | Dynamic concentric and eccentric muscle endurance/Hypertrophy using barbell Dynamic Power measured with linear position transducer | 5 sets × 15 reps at 75% 1RM 2-min rest between sets Barbell bench press | Total reps: ↔ Peak power: ↔ Mean power: ↔ Fatigue index: ↔ | RPE: ↔ Muscle thickness (cm): ↔ Subjective feelings of focus, energy, fatigue, and muscle pump: ↔ |
Chappell et. al. (2018a) | Recreational resistance trained males (n = 11) and females (n = 4) Age: 24 ± 2 years | CM: 8 g (1.11: 1) PLA: 6 g Citric acid Single dose 1-h prior | Randomized, double-blind, placebo-controlled, counter-balanced, cross-over design 7-day wash out | Isokinetic-dynamometer: Isometric force max Concentric force max Eccentric force max | 10 sets × 10 reps 70% of Concentric force max 1-min rest between sets Leg curl – knee extensor and flexor strength | Total Reps: ↔ Isometric force max: ↔ Concentric force max: ↔ Eccentric force max: ↔ | Blood lactate: ↔ Quadriceps muscle soreness: ↑ 25.7%, 41.1%, 37.3% in CM vs. PLA at 24, 48 and 72 h following exercise, respectively |
Chappell et al. (2018b) | Recreational resistance trained males (n = 12) and females (n = 17) Age: 26 ± 8 years | CM: 8 g (1.11: 1) PLA: 6 g Citric acid Single dose 1-h prior | Randomized, double-blind, placebo-controlled, counter-balanced, cross-over design 7-day wash out | Dynamic concentric and eccentric muscular endurance/strength using barbell | 10 sets × 10 reps at 80% 1RM 1-min rest between sets Barbell Curls | Total reps: ↔ | Blood lactate: ↔ Creatine Kinase: ↔ Upper and lower arm muscle soreness: ↓ in CM vs. PLA at 24, 48 and 72 h (individual data not reported) |
Farney et al. (2019) | Recreationally trained males (n = 6) and females (n = 6) Age: 24 ± 4 years | CM: 8 g PLA: 20 oz sugar free water CON: No drink Single dose 1-h prior | Single-blind, balanced, randomized, cross-over design 7-day wash out | Isokinetic-dynamometer Power Fatigue Index | 1 set × 15 reps at 180osec Leg extension | Measured following high intensity exercise body weight session: Total Reps: ↔ Peak torque: ↔ Peak power: ↔ Fatigue index: ↔ | Lactate: ↔ Heart rate: ↔ |
da Silva et al. (2017) | Recreational active males (n = 9) Age: 24 ± 3 years | CM: 6 g PLA: Corn starch Single dose 1-h prior | Double-blind, randomized, crossover design 7-day wash out | Recovery of Dynamic muscular endurance | 1 set at 100% of 10 RM Machine Leg press Machine Hack Squat | Measured into 24, 48, 72 h recovery only following resistance exercise 3 sets at 90% of 10RM (2 min rest): Total no. Reps: ↔ | RPE: ↔ Lactate: ↔ Creatine Kinase: ↔ Muscle soreness: ↔ Lactate: ↔ Testosterone-cortisol: ↔ Electromyography: ↔ |
Trexler et al. (2019a) | Recreationally active men (n = 27) Age: 22 ± 4 years | 8 g dose 2-h prior to exercise | Double-blind, randomized placebo-controlled design | Maximal concentric leg extensions | 5 sets × 30 reps | No performance enhancing effect: ↔ versus placebo | NOx pre or post-exercise: ↔ vs. PLA Blood flow: ↔ vs. PLA Metabolic efficiency: ↔ vs. PLA Hormonal response: ↔ vs. PLA |
Trexler et al. (2019b) | Recreationally active men (n = 27) Age: 22 ± 4 years | 8 g dose 2-h prior to exercise | Double-blind, randomized placebo-controlled design | Submaximal isotonic leg extensions | 25% of maximal voluntary contraction torque | No performance measure | Muscle blood flow: ↔ Oxygen consumption: ↔ Respiratory exchange ratio: ↔ Indirect calorimetry: ↔ |
Resistance trained males (n = 75) Age: 21 ± 2 years | CM = 2 g per day for 8 weeks L-citrulline & glutathione (LG): 200 mg.day of GSH + 2 g.day of L-citrulline PLA: 2.52 g.day of cellulose | Double-blind, randomized placebo-controlled design | Maximal muscular Strength (1RM test) adaptation evaluated over 8 weeks | 1 RM testing: Free weight bench press Angled leg press Performed at baseline, 4 and 8 weeks training | Bench press Baseline: ↔ 4 weeks: ↔ 8 weeks: ↔ Angled leg press Baseline: ↔ 4 weeks: ↔ 8 weeks: ↔ | Body mass: ↔ Fat mass: ↔ Body water: ↔ Lean Mass: ↑ at week 4, but not week 8 in LG vs. PLA |