Supplements
Evidence-based reviews of common training supplements — creatine, beta-alanine, citrulline, caffeine, ashwagandha, and pre-sleep protein.
Creatine Supplementation
Supplements
Is creatine safe to take long-term?
About this study
Max dose tested
30 g/day
Longest follow-up
5 years
Official ISSN consensus statement synthesizing decades of trials across populations from infants and children to elite athletes, healthy older adults, and clinical patients with neurodegenerative disease, diabetes, osteoarthritis, and other conditions.
The finding
Creatine monohydrate is the most thoroughly studied supplement in sports nutrition. Decades of trials show no safety concerns at the doses people typically use, and benefits stretch from high-intensity performance to rehabilitation and aging.
The answer
30 g/day for 5 years (safe)
Performance dose: 3–5 g/day · Loading option: 20 g/day × 5–7 days
The position stand reviewed creatine intake up to 30 g/day for 5 years and found no major safety issues across populations spanning infants to seniors. Practical dosing is much lower: 3-5 g of creatine monohydrate daily, with an optional 5-7 day loading phase at 20 g/day to saturate muscle stores faster. No need for cycling or off-periods.
Supplements
Who actually benefits most from creatine?
About this study
Studies pooled
14 RCTs
People
523 adults
Adults aged 19-69 (mostly male) across multiple training backgrounds. Researchers pooled creatine-vs-placebo strength trials and applied robust statistical methods to handle multiple strength tests per study.
The finding
Creatine reliably boosts strength, but the size of the boost depends a lot on who's taking it and how. Untrained people gain three times as much as trained lifters, and lower doses work as well as or better than higher ones.
The answer
3× bigger gains (untrained)
Untrained SMD 1.06 · Trained SMD 0.32 · Low dose (3-5g) beats high dose (20g)
An untrained adult adding creatine sees roughly 3× the strength bump a trained lifter does (SMD 1.06 vs 0.32). Counterintuitively, low-dose protocols (3-5 g/day) produced larger pooled effects than high-dose loading (SMD 0.88 vs 0.24). Pairs best with moderate-to-high intensity training (>75% 1RM). If you're already a trained lifter, expect a modest single-digit-percent strength gain over a typical training cycle.
Supplements
How much extra strength does creatine add to lifting?
About this study
RCTs pooled
23 trials
People
509 adults
Predominantly male adults (88%; mostly trained or recreational lifters) across 23 trials lasting 4-12 weeks at 2-5 sessions/week. Loading 15-25 g/day for ≤7 days followed by 2-10 g/day maintenance.
The finding
Creatine plus resistance training adds measurable strength on top of training alone — about 4 kg extra to upper-body and 11 kg extra to lower-body lifts over 4-12 weeks. The effect was clearest in men; the small pooled female sample showed no significant upper-body benefit.
The answer
+4 / +11 kg upper / lower (men)
Upper WMD 4.43 kg · Lower WMD 11.35 kg · Female upper-body: no significant gain
Over 4-12 weeks of resistance training, men adding creatine gained an extra 4.43 kg on upper-body lifts and 11.35 kg on lower-body lifts versus placebo. The female sample was small (40 women across 2 studies) and showed no significant upper-body benefit — could be a real sex difference or a power-limited finding. Most men can expect this to translate to faster strength progression on compound lifts.
Supplements
Does creatine make muscles measurably bigger?
About this study
RCTs pooled
10 trials
Study duration
6–52 weeks
Mostly untrained young (mean age 23.5) and older adults (mean age 61.6). Researchers used direct imaging — MRI, CT, or ultrasound — to measure cross-sectional area changes in elbow and knee flexors/extensors after resistance training with or without creatine.
The finding
Creatine adds a small, consistent boost to muscle size when combined with training, but the effect is genuinely small — well under a centimeter of regional cross-sectional area, and any single region's confidence interval crosses zero.
The answer
~1 mm extra CSA (very small)
Pooled ES = 0.11 · Individual regions: 0.10–0.16 cm with credible intervals crossing zero
Across 10 imaging-based trials, adding creatine produced muscle-size gains around 0.10-0.16 cm in elbow and knee muscles — a very small effect that's directionally positive but isn't statistically clean for any single region. Translation: creatine is a strength supplement first and a hypertrophy supplement only barely. If you're chasing visible muscle gain, expect strength-mediated progress, not direct mass.
Supplements
How big are the strength and power gains from creatine?
About this study
RCTs pooled
69 trials
People
1,937 adults
Largest creatine meta-analysis to date. Researchers separated outcomes by exercise type (bench, squat, vertical jump, Wingate) and stratified by age, sex, and intervention length. Doses ranged from low (≤8 g/day) to high (>8 g/day, with loading).
The finding
Creatine adds a small-to-moderate kick to all the explosive outputs that matter for sport — vertical jump, Wingate power, lower-body strength. Upper-body strength gains are real but smaller. The clearest beneficiaries are younger men in long-duration (≥8 week) protocols.
The answer
+5.6 / +1.5 kg squat / cm jump
Bench +1.43 kg · Squat +5.64 kg · Vertical jump +1.48 cm · Wingate peak +48 W
In the largest creatine analysis to date, squat strength rose ~5.64 kg, vertical jump ~1.48 cm, and Wingate peak power ~48 watts versus placebo. Bench press gains were smaller (~1.43 kg). The effects were noticeably bigger in younger males running ≥8-week protocols; older adults and women saw minimal improvements on most measures. For under-30 men chasing power output, this is the most reliable supplement in the kitchen.
Caffeine & Ergogenic Aids
Supplements
How much caffeine actually helps performance?
About this study
Effective dose
3–6 mg/kg
Timing
~60 min pre-exercise
Official International Society of Sports Nutrition consensus statement synthesizing decades of caffeine-and-performance research across athletes, trained and untrained adults.
The finding
Caffeine reliably improves endurance, strength, sprint, and jump performance — but the size of the effect is small to moderate, not transformative. Genetics affect individual response.
The answer
3–6 mg/kg pre-exercise
Endurance: 2–4% gain · Strength: SMD 0.16–0.20 · Endurance: SMD 0.28–0.38
For a bw_70kg adult, that's roughly 210-420 mg of caffeine — about 2-4 cups of coffee — taken 45-60 minutes before training. Doses below 2 mg/kg may not help; doses above 9 mg/kg add side effects (sleep disruption, anxiety) without further performance benefit. Individual response varies with genetics; some people see clean gains, others see jitters. Cycling off periodically helps maintain sensitivity.
Supplements
How big are caffeine's effects across the research?
About this study
Participants
2,463 adults
Meta-analyses pooled
9 reviews
Researchers synthesized 9 prior meta-analyses on caffeine's effect on muscle strength and endurance across 2,463 total participants. The pooled sample was 91%+ male; only 2 reviews specifically examined women.
The finding
Caffeine produces small but consistent gains across both strength and endurance. Endurance effects are larger than strength effects. The female-specific evidence is still thin — most data comes from male athletes.
The answer
0.18 / 0.30 SMD strength / endurance
8 of 9 reviews showed positive effects · Female-specific evidence: limited
Across thousands of participants, caffeine improved strength by SMD 0.18 (small) and endurance by SMD 0.30 (small-to-moderate). Endurance benefits are roughly twice as large as strength benefits. Important caveat: the underlying data is almost all male, so the female response — especially with menstrual-cycle considerations — is still under-studied. For trained women, expect similar but not identical results.
Supplements
What dose of caffeine actually moves the needle?
About this study
RCTs pooled
14 trials
Strength threshold
≥6 mg/kg
14 RCTs in young adults (ages 16-29), mostly males (11 of 14 male-only). Researchers compared acute caffeine doses (2-11 mg/kg) and timings (45-60 min pre-exercise) on strength and endurance outcomes.
The finding
Doses below 6 mg/kg don't significantly help strength. Above 6 mg/kg, caffeine reliably improves strength (especially lower-body) and endurance. Timing matters — 45 minutes pre-exercise outperformed 60 minutes. Men responded more strongly than women.
The answer
≥6 mg/kg for strength (men)
Below 6 mg/kg: no significant strength effect · 45 min beats 60 min pre-exercise
For a bw_70kg man, the threshold dose for strength benefit is about 420 mg of caffeine taken 45 minutes pre-exercise. Lower doses (e.g., a single cup of coffee, ~80 mg) won't move the strength needle. Endurance is more responsive to lower doses. The 14 RCTs included only 3 with female participants — women showed smaller effects, but the female data is too sparse for a confident female-specific dose.
Beta-Alanine Supplementation
Definitive meta-analysis establishing a significant overall effect (ES = 0.18) for beta-alanine on exercise capacity, with exercise duration (60–240 seconds) as the strongest moderator — establishing that beta-alanine is most effective for high-intensity efforts in the 1–4 minute range and provides no benefit for shorter explosive efforts or long endurance events. A total intake of ~179 g over time (≈4–6 weeks at 3–4 g/day) is associated with a 2.85% performance improvement.
Updated 2024 meta-analysis of 18 studies finding a significant effect (ES = 0.39) for beta-alanine on maximal intensity exercise, with the largest benefits at 4–10 min effort durations and higher doses (5.6–6.4 g/day) — validating beta-alanine as the third-tier ergogenic supplement (after creatine and caffeine) for high-volume resistance training, HIIT, and sport-specific intervals.
Citrulline & Pre-Workout Supplements
The first systematic review and meta-analysis on citrulline and endurance performance finding inconsistent results across studies — establishing that citrulline enhances nitric oxide synthesis and ammonia buffering but does not consistently produce meaningful ergogenic effects on endurance performance, providing a balanced evidence-based perspective for app supplement guidance.
Meta-analysis of 13 studies finding citrulline malate (8 g, ~60 min pre-exercise) significantly reduced perceived exertion (RPE) during exercise and muscle soreness 24 hours post-exercise — establishing citrulline's most consistent benefit as a recovery and perceived effort aid rather than a direct performance enhancer.
Ashwagandha & Adaptogens
Bayesian meta-analysis of 12–13 RCTs finding ashwagandha significantly improved 1RM strength, VO2max, blood hemoglobin, muscle fatigue recovery, sleep quality, and reduced cortisol — with KSM-66 standardized extract at 300–600 mg/day being the most studied and consistent form. Establishes ashwagandha as the most evidence-supported adaptogen for stress, recovery, and performance applications.
Meta-analysis of 58 RCTs (3,508 participants) finding that mindfulness and relaxation interventions produce a medium effect (g = 0.282) on cortisol reduction — establishing the physiological basis for stress management features in the app (breathwork, mindfulness integration) as evidence-based cortisol-lowering strategies that directly benefit body composition and recovery.
Pre-Sleep Protein
Systematic review of 9 studies establishing that 20–40 g of casein protein consumed ~30 minutes before sleep stimulates whole-body protein synthesis during overnight recovery, with chronic pre-sleep protein consumption augmenting muscle fiber cross-sectional area, strength, and lean mass after 10–12 weeks of resistance training in younger adults. Validates the app's pre-sleep protein guidance.
Foundational RCT directly demonstrating that casein protein before sleep is effectively digested overnight, increasing whole-body protein synthesis by 22% and shifting net protein balance from negative to positive throughout the night — establishing the mechanistic basis for the "bedtime protein" strategy and validating cottage cheese, Greek yogurt, and casein supplements as targeted pre-sleep nutrition tools.