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Tennis is a sport that is played indoors and outdoors but more typically outdoors. Conditions are usually hot and humid which can be strenuous on the body. This requires the makeup of a tennis player's team to be able to understand the effects temperature and hydration can have on the player's performance and overall health. Hypohydration and hyperthermia caused by exercise has been shown to decrease optimum performance (magal et al 2003). More research needs to be done on what causes this and what can be done to prevent players from feeling the effects on hypohydration and hyperthermia.
As conditions are so hot and humid players sweat at higher rates to help regulate their body temperatures. Studies have shown that players can sweat a estimated 2.5l-h (hour) to sweat levels higher than 3.0l-h (Bergeon 2003). Trying to keep hydrated at the sweat rates of these players is physically demanding. Tennis players that take in more than 1.25l-h can cause players feeling discomfort in the gastrointestinal tract (Montain 1992). Another study found that players they studied were consuming an estimated 1.0l-h (Bergeon 1995). This may have been due to the discomfort that consuming more than 1.0l-h causes.
There is evidence that shows optimum performance levels decreases when a players is hypohydrated to as small as 2% of body mass. A deficit of 5% can lower performance vy around 30% (Costill 1990). During physical activity the scale of hypohydration gets higher, also the core temperature increases from between 0.10°c and 0.40°c for each percentage that is lost in body weight (Wall 2000). The objective when picking ergogenic aids, designing training programmes and the appropriate time to recover is to make the most of training time while limiting the effects a increase in body temperature and hypohydration can have on performance.
The aim of this physiological review is to help highlight the most important information on hydration and temperature regulation, to help teams to prepare their tennis players for optimum performance.
Thirst and body water status
Thirst does not show the full scale of body water levels and is not an acceptable catalyst in preventing a high amount of body water loss caused by the hot environment during physical activity (Wilmore and Costill 2004). Tennis players drinking when they feel the need to regularly leads to unintentional dehydration. One case for unintentional dehydration is that before thirst is even felt there could be a decrease of 1.5l in body water (Wilmore and Costill 2004). The environment of the tennis players and the rate they sweat at, are very important factors in leading to hypohydration. On the court the pattern that fluid is taken is also vital.
As there is an increase in the amount of sweat that is produced, plasma osmotality also increases (higher solute concentration). This causes the need for fluid intake to aid the partial plasma retention of NA+. Due to the osmotic gradient increasing, the rate at which the intravascular albumin is transported gets higher (Nayashima 1999). Fluid levels is then controlled from the intracellular compartment to keep the level of the extracellular fluid volume (Nayashima et al 1999). As the fluid has been moved from the cells it lowers an essential catalyst for thirst. Research has shown that the thirst felt by the tennis player post match and body weight percentage change have no link between them (Bergeon 1995). This supports the theory that thirst is not quick enough in identifying the body water levels or in preventing a high amount of body water loss during exercise at high degrees of heat.
Less than 3% in body weight that is loss because of dehydration brought on by anaerobic exercise has been shown to have a detrimental effect on 5m and 10m sprint times In tennis players (Magal et al 2003). One study has shown that a reduction in performance due to hypohydration could be down to the player's lack of ability to maintain adequate central nervous system drive to the muscles that are being worked (Montain et al 1998). This is down to the research that has shown that there is a 14% decrease in muscular endurance in players when in a hypohydrated state (Montain et al 1998).
The effects of temperature regulation on tennis performance
Tennis is a variegated sport due to the stop and start nature of it and not having a set time for the length of matches (longest match lasting 11 hours 5 minutes). Most points in tennis matches last less than 10 seconds with rest periods lasting no more than 25 seconds (Kovacs 2004). This high intensity form of exercise can cause body temperature to fluctuate but does provide time for the players to take on fluids.
During a tennis match the metabolic rate of the players dramatically increases compared to the rate when resting. Only a small amount of energy from the player contributes to hitting the tennis ball or their movement as 80% is released as heat (Bergeron 1995). The most productive system during the match is thermoregulation which occurs through heat loss being evaporated through sweat. As the temperature of most court surfaces is hotter than the players skin temperature, it causes the players body temperature to increase due to conductive heat transfer. Other forms of heat exchange that are looked at are radiative heat exchange and convective heat exchange. Radiative heat exchange is the non contact transfer of electromagnetic energy, while connective heat exchange is heat transfer due to gas or fluid motion. Research has found that evaporative cooling is more beneficial for maintaining the right body temperature compared to convective cooling (Bergeron 1995).
If fluid levels is not sustained the role of thermoregulation is decreased (Jung et al 2005). There is a difference between males and females body water levels. As females have less lean body mass than the male players they hold less body water. Per hour, depending on the area they are playing in, the intensity level of the game, fitness levels, hydration status and gender male and female players could lose between 0.5l and 3.0l of water (Bergeron 2003).
When playing in hotter conditions heart rates are higher, as the body has to replace the large amount of fluid lost through sweating from the blood. Also the heart rate increases to help lower body temperature (Mcord and Minson 2005). As a result of these functions central blood volume is decreased, which decreases the stroke volume (Powers and Howley 2001). A higher heart rate is then required to sustain the required amount of blood flow.
Some research has suggested that to maintain cardiovascular stability, thermoregulation is abandoned. This proposal has been made with the assumption that a tennis player who is dehydrated will stop playing and move to an environment which is lower in temperature (Sawka 1992). This plan would not be effective for a tennis player in a competitive match as the main values of all winning athletes is to try and push through physiological barriers.
Electrolyte balance and dehydration
Electrolyte balance is an important factor in helping tennis players perform at optimum level, it helps in limiting fatigue, dehydration and the potential for muscle cramping. For a player who is acclimatised to the hot conditions, there sweat will have low levels of potassium () and magnesium (Mg) (Bergeron et al 1995). Evidence suggests that does not cause muscle cramp but rather a decrease in extracellular Na+ causes muscle cramps when playing in hot conditions (Bergeron et al 1995).
Due to the quick succession of matches in tennis tournaments, it is important that Na+ is ingested daily through diet as many days of tennis may lead to low extracellular Na+. This is what causes many players to start having muscle cramps later on in the tournament. There are studies that suggest that the psychological stress of the tournament could also contribute in causing muscle cramps (Jung et al 2005). This would show that it's not just down to dehydration and electrolyte loss.
While players are in there matches it is essential that players take on an adequate amount of fluids to maintain optimum performance. To do this some research has suggested that 200ml of fluid every 15 minutes is the appropriate amount to have in sustaining body fluid balance in warm conditions (Maclaren 1998). Carbohydrate supplement drinks is also another ergogenic aid that tennis players take during matches. Studies have shown that there is no benefit to tennis performance lasting less than 4 hours (Ferrauti et al 1997) in contrast to the ACSM guidelines who suggest taking 30-60g of carbohydrate supplemented drinks for exercise lasting longer than a hour (ACSM). It is important to maintain glucose levels. Gluscoe levels tend to decrease between the 1st and 2nd match during a tournament situation (Ferrauti 2003). The study showed that it had no effect on competitiveness but in conditions where it is highly competitive, it could have a large effect on the player being in the right frame of mind to perform at the highest level (Ferrauti et al 2003).