How full are your muscles?

Constants used

• Baseline muscle creatine (men): 120 mmol/kg dry muscle, roughly 75–80% of maximum.
• Baseline (women): about 10% higher than men at rest.
• Maximum saturation: ~160 mmol/kg dry muscle.
• Daily breakdown rate: ~1.7% of the muscle pool per day (range 1–2%).
• Loading dose (weight-scaled): 0.3 g/kg/day.
• Optimised maintenance dose: 0.1 g/kg/day.
• Brain dose: 10 g/day flat, scaled to 0.1 g/kg/day if body weight exceeds 100 kg.

Saturation curve

Each curve uses a first-order saturation model:

S(t) = S∞ − (S∞ − S₀) · e−k·t

where S₀ is your starting % saturation, S∞ is the steady state your dose holds, and k is the uptake rate constant fitted to research saturation timelines:

• Loading (0.3 g/kg/day): full saturation in ~6 days, k ≈ 0.54/day.
• 10 g/day (70 kg adult): full saturation in ~11 days, k ≈ 0.29/day.
• 5 g/day (70 kg adult): full saturation in ~25 days, k ≈ 0.13/day.
• 3 g/day (70 kg adult): full saturation in ~32 days, k ≈ 0.10/day.

Other dose values are interpolated linearly in dose-per-kg space, which mirrors how the SLC6A8 transporter behaves at typical doses. Heavier people on a fixed dose like 5 g/day saturate slightly slower than lighter people on the same fixed dose, because the dose-per-kg ratio drops.

Missed-dose decay

When dosing stops, the elevated portion above baseline decays exponentially at the daily breakdown rate:

S(t) = S_baseline + (S_start − S_baseline) · e−0.017·t

This gives the 4–6 week washout period reported in the literature.

Sources

• Hultman, E. et al. (1996). Muscle creatine loading in men. J Appl Physiol 81(1), 232–237.
• Harris, R.C. et al. (1992). Elevation of creatine in resting and exercised muscle. Clin Sci 83(3), 367–374.
• Kreider, R.B. et al. (2017). ISSN position stand: safety & efficacy of creatine supplementation. JISSN 14:18.
• Candow, D.G. & Forbes, S.C. (2024). Creatine for brain & bone health. Adv Exerc Health Sci.
• Smith-Ryan, A.E. et al. (2021). Creatine supplementation in women's health. Nutrients 13(3), 877.
• Forbes, S.C. et al. (2022). Effects of creatine supplementation on brain function and health. Nutrients 14(5), 921.
• Roschel, H. et al. (2021). Creatine supplementation and brain health. Nutrients 13(2), 586.

Built from the kinetic data summarised in the Fitness Etc. internal research brief (Apr 2026). Full citation chain available on request.

Your muscles can only hold so much creatine — about 160 mmol per kg of dry muscle. Most people walk around at 75–80% of that ceiling. Supplementing fills the rest of the tank.

Loading just means using a high dose for a week to fill the tank fast. After that, a smaller daily dose keeps it topped up. There's no magic to loading — you can skip it and take 5–10 g/day, but it'll take 3–4 weeks to reach the same level.

Once your tank is full, performance benefits are the same no matter how you got there.