7-day creatine “wash-in” increases muscle mass in women, but it's not long-term, research reveals

A short burst of creatine helped women to acquire lean masses, but when combined with resistance training, its benefits were layered. Can timing, dosage, or hydration be key to fully unlocking creatine potential?

study: Effects of creatine supplementation with or without resistance training. Image credit: Bongkarngraphic / Shutterstock

A recent study published in the journal Nutrientsresearchers investigated whether creatine monohydrate (CRM) supplementation alone affected lean body mass (LBM) in combination with resistance training (RT).

They found that the 7-day “wash-in” period of CRM increases in LBM, especially women and mostly trunk areas. However, when combined with RT, RT alone did not increase LBM growth. A seven-day wash-in meant that participants took 5 grams of creatine every day for a week without resistance training to see how creatine alone affected lean body mass.

The authors suggest that if CRM is used for a long period of time at RT, a daily maintenance dose above 5 grams may be required to maintain an increase in LBM.

background

Increased LBM has many health benefits, including lower risk of death, improved bone strength, and enhanced glycemic control. RT is the most effective way to build LBMs, usually leading to a gain of about 1.5 kilograms over 3-4 months.

Researchers found that when combined with RT, CRM supplementation promotes LBM growth, perhaps by increasing training ability. However, there is little evidence that CRM effectively increases muscle protein synthesis.

Supplements usually follow a two-phase approach. Short-term “load” phase with high doses (20-25 grams per day) and low “maintenance” doses (2-5 grams per day). Muscle creatine levels may increase during the maintenance stage, but the effects on LBM without prior loading are unknown.

Several studies suggest that CRM can temporarily increase body water content and affect LBM measurements. Limited studies have investigated how CRM alone (no RT) affects LBM. Short-term studies suggest that CRM increases total water and fat-free masses in the body, suggesting that the effects on LBM are not entirely due to muscle growth. Further research is needed to determine whether CRM alone contributes significantly to the benefits of LBM.

About the research

This study aims to determine whether a 7-day CRM supplementation period (no exercise) affected LBM measurements in healthy, inactive adults. This study was a component of a larger trial of gut microbiota and LBM growth, with a sample size of 33 per group planned.

The researchers also looked into whether this initial increase in LBM had an impact on subsequent changes in LBM during the 12-week RT program. Participants were randomly assigned to either the CRM supplementation group (5 grams per day) or the control group.

The study lasted for 13 weeks and included three assessment points: after a 7-day CRM phase and after a 12-week RT. Participants were required to fast 8 hours prior to each assessment and avoid exercise for 12 hours. LBM and fat mass were measured using dual energy x-ray absorption measurements (DXA). Participants also recorded their diet and physical activity levels throughout the study.

After a 7-day supply phase, both groups followed the same monitored RT program, consisting of three full-body training per week, including upper and lower body exercises. Training intensity was adjusted based on perceived movement to ensure consistent efforts between participants.

The researchers analyzed the data using statistical comparisons and regression modeling. Sexual penetration analysis was also performed.

Survey results

After the initial assessment, one participant from the supplement group left, and nine participants, including four who received the CRM supplement, left following the second assessment. However, their reasons had nothing to do with the research program. No adverse effects have been reported.

The research team found 95% of compliance, 91.92% attendance in the session, and 99.91% athletic compliance. At baseline, the control group reported higher carbohydrate intakes, but overall dietary intakes were similar across groups.

During the 7-day supplement only phase, the supplement group achieved significantly more total LBM than the control group. However, researchers found that there was no difference in the changes in LBM in the arms and legs. The trunk LBM gain has increased in the supplement group. The changes in fat mass did not differ significantly between groups.

After 12 weeks of RT, both the control and supplement groups achieved approximately 2 kg of LBM, but there was no significant difference between them. This confirmed that only RT is effective in promoting LBM benefits. Similar results were observed when analysed by gender. However, female participants in the supplement group showed statistically significant benefits for total and trunk LBM, particularly throughout the study period. CRM supplementation did not increase male LBM at any time. No significant differences were observed between groups or sex in terms of changes in fat mass.

Conclusion

This study found that taking 5 grams of CRM per day for 7 days increased LBM without RT. However, when CRM was collected with RT for 12 weeks, it did not promote LBM gain beyond RT alone. The wash-in phase before RT helped to isolate the effects of CRM.

This study also found that CRM increases LBM in women, particularly in trunk areas. This may be due to changes in total water that cannot be distinguished by DXA. Sexual penetration results suggest that only women who responded to CRM with LBM gain were not observed in men.

Limitations included lack of menstrual cycle follow-up and hydration measurements. This can affect the body's water distribution and therefore has an LBM rating.

Although dietary intake was monitored, self-reported data could underestimate true intake. Furthermore, creatine intake was not supervised, and water consumption was not controlled or recorded.

Future studies should investigate various dosing strategies and incorporate hydration tracing and menstrual cycle data to determine whether changes in LBM are linked to fluid shifts.