Athlete Conditioning, Adaptation, and Age

The human body has wonderful adaptive mechanisms, and the ability to adapt to higher or lower glucose concentrations and faster or slower rates of fluid ingestion is no exception. It seems clear that athletes can train to enhance their potential for achieving optimal hydration. Therefore, each athlete should start with general recommendations for fluid intake to maintain hydration state, then make modifications that are best suited to them.

Heat tolerance is highly influenced by physical fitness: Poor physical fitness dramatically increases the risk of heat illness similarly in both men and women. However, this improved heat tolerance is the result of an enhanced sweat rate. Since children have fewer sweat glands and each gland produces less sweat, child athletes have a lower potential for adaptation to heat and are generally considered to have a lower heat tolerance than well-conditioned adults.³¹ Poorly conditioned athletes with higherbody fat levels also have lower heat tolerance. Put simply, fat deters heat loss. In summary, well-conditioned adult athletes with low body fat levels must develop strategies for constantly increasing fluid intakes as their conditioning improves because sweat rates increase with better conditioning. Children and adults with higher body fat are likely to have a lower heat tolerance, making maintenance of adequate hydration even more critical for these individuals.

Table 3.5 Body Adjustments During Acclimatization

• Plasma volume expands to increase total blood volume.
• The heart is then able to pump more blood per beat.
• More blood flows to muscles and skin.
• Less muscle glycogen is used as an energy source during exercise.
• Sweat glands hypertrophy and produce 30% more sweat.
• Salt in sweat decreases by about 60% to conserve electrolytes.
• Sweating starts at a lower core temperature.
• Core temperature will not rise as high or as rapidly as in unacclimatized state.
• Psychological feeling of stress is reduced at a given exercise rate.

Intestinal Absorption

Fluid-Related Problems