A short burst of creatine helped women gain lean mass, but when paired with resistance training, the benefits plateaued. Could timing, dose, or hydration hold the key to unlocking creatine’s full potential?

Study: The Effect of Creatine Supplementation on Lean Body Mass with and Without Resistance Training. Image Credit: BongkarnGraphic / Shutterstock

In a recent study published in the journal Nutrients, researchers investigated whether creatine monohydrate (CrM) supplementation alone and in combination with resistance training (RT) influenced lean body mass (LBM).

They found that a CrM ‘wash-in’ period of seven days increased LBM, particularly in females and mainly in the trunk region, where gains may be linked to water retention. However, CrM, when combined with RT, did not lead to significantly greater LBM growth than RT alone overall. The 7-day wash-in meant that participants took 5 grams of creatine daily for one week without resistance training to see how creatine alone affected lean body mass. 

The authors suggest a higher daily maintenance dose than five grams may be needed to sustain LBM increases when CrM is used long-term with RT.

Background

Increasing LBM has many health benefits, such as lowering the risk of death, improving bone strength, and enhancing blood sugar control. RT is the most effective way to build LBM, typically leading to a gain of about 1.5 kilograms during a three-to-four-month period.

Researchers have found that CrM supplementation enhances LBM growth when combined with RT, possibly by increasing training capacity. However, there is little evidence that CrM effectively boosts muscle protein synthesis.

Supplementation usually follows a two-phase approach: a short-term “loading” phase with high doses (20–25 grams a day) and a lower “maintenance” dose (2–5 grams a day). While the maintenance phase can still increase muscle creatine levels, its effects on LBM without prior loading are unclear.

Some studies suggest that CrM may temporarily increase body water content, potentially affecting LBM measurements. Limited research has examined how CrM alone (without RT) influences LBM. A short-term study found that CrM increased total body water and fat-free mass, suggesting that its impact on LBM may not be entirely due to muscle growth. More research is needed to determine if CrM alone significantly contributes to LBM gains.

About the study

This study aimed to determine whether a seven-day CrM supplementation period (without exercise) affected LBM measurements in healthy, inactive adults. The research was a component of a larger trial on gut microbiota and LBM growth, with a planned sample size of 33 per group.

Researchers also examined whether this initial increase in LBM influenced later changes in LBM during a 12-week RT program. Participants were randomly assigned to either a CrM supplementation group (five grams a day) or a control group.

The study lasted 13 weeks and included three assessment points: baseline, after the seven-day CrM phase, and after 12 weeks of RT. Participants were required to fast for eight hours before each assessment and avoid exercise for 12 hours. LBM and fat mass were measured using dual-energy X-ray absorptiometry (DXA). Participants also recorded their diet and physical activity levels throughout the study.

After the seven-day supplementation phase, both groups followed the same supervised RT program, consisting of three full-body workouts per week, including upper and lower-body exercises. Training intensity was adjusted based on perceived exertion to ensure consistent effort across participants.

The research team analyzed the data using statistical comparisons and regression modeling. Sex-disaggregated analysis was also conducted.

Findings

After the initial assessment, one participant from the supplement group withdrew, and nine others, including four from receiving the CrM supplements, left following the second assessment. However, their reasons were not related to the research program. No adverse effects were reported.

The research team found that adherence was high at 95%, session attendance at 91.92%, and exercise compliance at 99.91%. At baseline, the control group reported higher carbohydrate intake, but overall dietary intake was similar between groups.

During the seven-day supplement-only phase, the supplement group gained significantly more total LBM than the control group. However, researchers found no differences in LBM changes in the arms or legs. The supplement group also had greater trunk LBM gains. Fat mass changes did not significantly differ between groups.

After 12 weeks of RT, both control and supplement groups gained around two kg of LBM, with no significant differences between them. This confirmed that RT alone was effective in promoting LBM gains. Similar results were observed when analyzing by sex. However, female participants in the supplement group showed statistically significant greater gains in total and trunk LBM, particularly over the entire study period. CrM supplementation did not increase LBM in males at any time point. No significant differences were observed between groups or by sex in terms of changes in fat mass.

Conclusions

This study found that taking five grams per day of CrM for seven days increased LBM without RT. However, when CrM was taken for 12 weeks alongside RT, it did not enhance LBM gains beyond RT alone. A wash-in phase before RT helped isolate CrM’s effects.

The study also found that CrM increased LBM in females, especially in the trunk region, which may be due to changes in total body water not distinguishable by DXA. Sex-disaggregated results suggest that only females responded to CrM with LBM gains, and this was not observed in males.

Limitations included a lack of menstrual cycle tracking and hydration measurement, which may influence body water distribution and, therefore, LBM assessments.

Although dietary intake was monitored, self-reported data may underestimate true intake. In addition, creatine ingestion was not supervised, and water consumption was neither controlled nor recorded.

Future research should explore different dosing strategies and incorporate hydration tracking and menstrual cycle data to determine whether changes in LBM are linked to fluid shifts.