Few topics in sports nutrition cause as much confusion as creatine. Some people avoid it because they think it damages the kidneys, some take it without knowing why, and some give up after a few weeks because they didn't feel any different. The problem isn't creatine — it's that most of what circulates about it doesn't come from where it should. Creatine is, by a wide margin, the most researched supplement in the history of exercise science, backed by decades of studies and thousands of trial participants. It's worth separating what the research actually shows from what's just gym folklore.
What creatine actually does inside the muscle
Creatine is a molecule your body already produces, mainly in the liver and kidneys, and also gets from meat and fish. About 95% of it is stored in skeletal muscle as phosphocreatine, acting as a fast-access energy reserve. When you do a short, intense effort — a heavy squat set, a sprint, an explosive lift — your body taps the ATP-phosphocreatine system to regenerate energy almost instantly, before glycolysis or aerobic respiration even kick in.
Supplementing with creatine raises the muscle's phosphocreatine stores beyond what diet alone can sustain. In practice, that means more available energy for an extra rep, a slightly heavier load, or a faster sprint, set after set. The effect doesn't show up after a single workout: it builds over weeks, as muscle stores saturate and your body adapts to the training volume that extra energy lets you sustain.
What the research shows about strength and muscle mass
A systematic review with meta-analysis published in 2024 pooled 23 studies and 509 participants under age 50 to compare creatine combined with resistance training against a placebo paired with the same training. The result: the creatine group gained, on average, 4.43 kg more upper-body strength and 11.35 kg more lower-body strength than the placebo group over the same training period. That's not creatine acting alone — it's creatine stacked on top of the training stimulus, which is exactly how it works: it doesn't build strength without training behind it.
Source: PubMed
The same pattern shows up in reviews covering other populations, including older adults and people in rehabilitation: the strength and lean-mass gains disappear when you compare creatine alone against training without supplementation, but they show up consistently when creatine is paired with ongoing resistance training. In other words, it amplifies a stimulus that already needs to exist — it doesn't replace it — and the effect depends on consistency, not a single dose before a big session.