GLOSSARY

Fluid Transport is fluid movement during uptake or distribution, with its exact meaning defined by site and process.

Leaving the stomach is not the same as entering circulation: gastric emptying and intestinal absorption are separate stages. Remaining volume, beverage energy, exercise intensity and individual tolerance influence delivery. Fullness is not an exact measure of gastric volume. Rehearse portions and drink composition under actual training conditions rather than relying only on a package's implied absorption speed or assuming swallowed fluid is immediately available.

Much water absorption occurs in the intestine, following solute transport and osmotic gradients. Sodium and glucose can contribute, but plain water is also absorbed; every sip does not require added sugar. Intestinal uptake, distribution among body compartments and renal retention are connected yet distinct processes. A claim about one stage should not automatically be interpreted as proof of a better whole-body hydration outcome.

Diluting or concentrating powder changes nutrients and particles per mouthful. Combining several powders or gels in one bottle can make a concentrated, poorly tolerated mixture. Match the label to actual water volume and rehearse the final formulation during training. Combining individually useful products does not necessarily create a better drink, and concentrated fuel does not remove the need to consider water separately.

Osmosis is net water movement across a water-permeable barrier in response to differences in solute effects. Particle count alone is insufficient: membrane permeability to each solute matters. Freely crossing particles have different sustained effects on cell volume from confined particles. This explains why measuring a solution's total particle concentration is not always enough to predict cellular swelling or shrinking.

Aquaporins are membrane proteins facilitating water passage, not energy-consuming pumps forcing water in a chosen direction. Regulating some of these channels in the kidney supports water reabsorption. The mechanism does not create a need to ingest water channels or purchase a special supplement. Nutrition decisions should follow intake, losses and bodily responses rather than a protein name used in a product claim.

During exercise, coordinate drinking opportunities and fueling with estimated losses and gut tolerance. Replacing every drop of sweat immediately is not compulsory, and gaining mass from excessive drinking is undesirable. The strategy should adapt to weather and intensity. When access is constrained, rehearsing its practical execution matters as much as calculating volumes. A plan supports decisions rather than forcing intake despite changing conditions.