Source: Scandinavian Journal of Medicine & Science in Sports / PubMed. DOI: 10.1111/sms.70332.
A new PubMed-indexed sports-science study adds nuance to a simple gym question: why do some athletes seem to need more fluid than others?
The paper studied 30 male athletes and used isotope dilution, DXA, MRI/MRS, and body-composition modeling to examine water turnover over one week. The researchers reported that water turnover was associated with total body water, intracellular water, skeletal muscle mass, and ambient temperature. In regularized regression models that tried to reduce mathematical coupling, skeletal muscle mass, intracellular water, and ambient temperature remained predictors, while extracellular water, bone mineral content, muscle glycogen, and relative humidity were not retained.
The practical takeaway is cautious. This is not a new hydration formula and it does not mean muscle mass alone dictates fluid needs. The model performance was modest, and the authors noted that behavior and unmeasured environmental factors probably still matter. But the data support a point coaches already see in the field: hydration targets may need to account for the athlete, the environment, and body composition rather than using one fixed rule.
Why it matters for lifters
For lifters, bodybuilders, and strength athletes, the study is a reminder that larger amounts of lean tissue may change day-to-day fluid turnover. That matters most during hard training blocks, hot gyms, weight cuts, travel, and high-sweat sessions where thirst, scale weight, urine color, and performance trends can all provide useful context.
The finding also argues against overconfident hydration advice. A muscular athlete who trains in heat may need a different plan than a smaller athlete doing the same session in a cooler room, but the answer still depends on sweat rate, sodium losses, food intake, and medical context.
What to watch next
Future work should test larger and more diverse athlete groups, including women, masters athletes, physique competitors, and athletes in different climates. The key next step is whether practical field markers can predict fluid needs well enough to guide training-day decisions without expensive lab methods.
This article is for informational purposes only and is not medical advice. Athletes with kidney disease, heart disease, diabetes, eating disorders, heat illness history, or prescribed fluid restrictions should follow guidance from a qualified clinician or sports dietitian.