5. Limitations
whole-body loss [
FLUID RETENTION
The study was limited by including males only in a controlled laboratory setting for an 8.5 h period using non-invasive methods (body weight and urine excretion), and it compared commercially available products to manipulate beverage Na and CHO concentrations. Participants were asked to not exercise during the 24 h period prior to each experiment and were interviewed to confirm this at the start of each trial. By standardizing their diet and physical activity prior to studies, we assumed but did not verify that for each trial, participants had similar muscle glycogen levels and insulin responsiveness, which could influence Na retention [Using the change in body mass to establish the change in hydration status has been criticized as inexact [The use of commercial products prevented isolated comparisons of single functional ingredients, and not all ingredients were compared. The ORS contained only glucose at 2.5%, which would favor osmolality and energy density for fast absorption, whereas the 6% CHO sports drink contained sucrose and glucose that upon hydrolysis would be 50:50 glucose:fructose and, hence, have a higher energy density and be hyperosmotic. The ORS also had three times the chloride and over six times the potassium compared to the sports drink. Chloride might be important for fluid retention given that it resides in the extracellular space with sodium, but its rehydration potential is unclear [The methodology to quantify sweat Na losses had several limitations. A single-site collection may under-represent all losses, but the forearm site has been shown to correlate highly with whole-body loss [