Proper nutrition can contribute in the delay of fatigue. The most common type of fatigue that players experience are due to the improper balance between the fuels intake and expense.
As tennis is mainly moderate to high intensity sport, it’s important to understand which type of fuels are the most needed for the athlete, and that should be the first step to the successful nutrition and delaying the onset of fatigue. By nutritional researches from the past, it is well known that tennis is in demand of the muscle glycogen as the main fuel source for working muscles. The second step in successful delay of the fatigue would be a proper muscle glycogen stores regeneration and understanding that the athlete is in need to start the practice or competition with the high levels of glycogen, otherwise the consequence would be lack of energy fuels and fatigue. At the exercise intensity of around 55-60% of VO2 max, glucose utilization by skeletal muscle are around 80-85% of the WHOLE BODY disposal and at the intensities even higher then 60% of VO2 max, the skeletal muscles are expressing even higher needs.
When muscle glycogen is depleted due to inadequate pre-event fuel intake, the athlete reduces the exercise intensity or just stops exercising due to acidity generation (both sign of fatigue). At this point, the muscle turns to fat or blood glucose to respond to the energy demands of the stress applied, so the maintaining of the glucose level in the blood is dependent on the liver and its glycogen stores. Knowing that 80% of total carbohydrate is stored in skeletal muscle and about 14% is stored in the liver (6% in the blood in the form of glucose), it’s understandable the importance of the fully fueled athlete to delay the onset of fatigue.
Due to the glycogen stores depletion, the muscles do not have enough fuel to continue with the higher intensity exercise, and brain gets extremely sensitive to shortfalls in glucose delivery. These shortfalls have as a consequence central nervous system fatigue and symptoms such are dizziness, mental confusion, feeling of heaviness, sleepiness and overall tiredness.
The athlete should consume complex carbohydrates such are whole grains and plant based carbohydrates. Complex carbohydrates, in contrast to the simple ones, take longer time to break down to get absorbed by the bloodstream, therefore providing the energy to the body more slowly. Simple carbohydrates can increase the fatigue as they have immediate energy burst but followed by the fast crash.Potassium (avocado, spinach, sweet potato, banana etc) is a vital mineral to protect against fatigue. It’s an important mineral which contributes to the fluid balance.
Rising levels of dehydration influences the perception of the play and decrease the physical and mental levels of performance. Decrements in hydration as low as 2% have been shown to impair performance. Losses in excess of 5% of body weight can decrease the performance capacity by about 30%. At the highest level, even smallest decrement in physiological or psychological readiness can influence the outcome.
The main reasons why dehydrated athlete experience decrease in performance are lower blood flow volume, lack of oxygen reaching to the body tissues, decreased sweat rate and skin blood flow and increase in core temperature and muscle glycogen usage. All these symptoms contribute to the athlete’s perception of the fatigue.
Dehydration causes decreased blood volume which increases the blood thickness (viscosity) and lowers the central venous pressure which reduces the venues return of blood to the heart. Due to these reductions, at the stage when the heart is relaxed and trying to fill with blood before the next contraction, the filling decreases reducing the stroke volume and cardiac output (for working muscles in the case of physical fatigue).
Dehydration reduces the body sweat rate and skin blood flow which limits the body ability to lose heat due to reduced sweating response. This makes the body temperature rise faster and as core temperature rises towards around 39.5° C (103° F), sensations of fatigue occur. If the athletes are dehydrated, they reach this critical temperature much faster.
Rise in core temperature during exercise due to the dehydration lead to increased rate of glycogen breakdown in the muscles, which directly contributes to the early signs of fatigue.
Hypo hydration, as opposite, has been shown to increase blood cortisol (hormone that helps the body respond to the stress and successfully break down the carbohydrates, lipids and proteins) concentration and perception of efforts (RPE), which would be a sign of greater mental and physical response by the athlete to the training stress.