Monday, January 7, 2013

Heat, Dehydration and Injury Risk

Soccer players are often asked to train or play matches on hot, humid days. It is well known that these conditions cause excessive sweat and considerable fluid loss. If fluids are not replaced, dehydration occurs which in turn negatively affects performance. Research shows that fluid losses equal to 1-3% of body weight can decrease speed, power as well as technical abilities. Fluid losses greater than 3% can lead to health problems. A new study from the Human Performance Laboratory at the University of Connecticut finds that dehydration may have other consequences. It appears that heat and dehydration may also affect neuromuscular control and raise the risk of joint injuries.

The investigators (Distefano et al., 2012) examined the effects of heat and hydration on balance and movement. The subjects were asked to exercise for 90 minutes on four different occasions. For two of the sessions, the environmental temperature was elevated (34°C or 93°F) from control (18°C or 64°F). Once at each temperature, subjects reported to the laboratory in a slightly dehydrated state (hypohydrated) and received no fluid during exercise. On the other two occasions, they were asked to drink fluids before session and given drinks during exercise. Before and after each exercise session, balance and joint angles were measured during series of stationary activities (e.g. standing on one leg) and dynamic movements (e.g. jumping and landing).

The researchers found that under the condition of heat and dehydration, post-exercise measures of balance and movement skill were negatively affected. When standing on one leg, dehydration resulted in more sway and unwanted hip, knee and ankle movements. When lading from a jump, the investigators also found poor landing technique.

It is important to note that under with heat and dehydration, the subjects lost nearly 6% of their body weight and had much higher exercising and recovery heart rates. This is a somewhat extreme condition, one that clearly posed a tremendous physiological stress. Thus, the loss of movement control could simply be a function of fatigue rather than heat and dehydration alone. In fact, several studies show that fatigue can negatively affect neuromuscular control and raise injury risk.

Why is neuromuscular control important? Loss of neuromuscular control can result in poor balance and poor sport-specific technique. And, balance and movement technique are critical components issues in joint injury. Muscles work with ligaments and other connective tissues to stabilize joints. Proper technique insures that abnormal stresses are not applied that might lead to ligament sprains or ruptures. For example, a lack of neuromuscular control can result in a player landing with his or her knees in a knock-kneed position (called valgus collapse) rather than with the knee over the foot. It can also reduce the ability of the hamstrings to help stabilize the knee. These conditions can stress the ACL and raise the risk of ligament rupture. Thus, if heat and dehydration reduce balance and lead to a loss of neuromuscular control and landing technique, the risk of knee and ankle injury could be substantially increased.

Is this dehydration a problem a problem in young players? A second study focused on young players during a 5-day soccer camp. The results show that many players arrive at training in a hypohydrated state (Arnaoutis et al., 2012). That is, they are not be dehydrated, but their hydration status is often less than optimal for the conditions. Add to that, players do not drink enough during or after training to replenish lost fluids. Thus, dehydration typically persists over the course of the soccer camp. Given the physical demands of a soccer camp (multiple training session each day) and changes in eating and drinking habits it is likely that many of the players studied were not performing their best. Also, a loss of neuromuscular control associated with heat and dehydration may have placed them at risk of injury.

A similar situation could easily arise during a weekend soccer tournament played in a hot climate. Without proper hydration, playing multiple matches in 3-day period could easily result in dehydration, performance loss and more importantly, increased risk of injury. Thus, it is important to hydrate before and to re-hydrate after training or matches. Players should drink plenty of fluids in the days leading up to the tournament to lessen the risk of dehydration. They should also strive to replenish 1.5 times the amount of fluid lost each match (The amount of fluid lost can be estimated by body weight lost, 1kg = 1L or 1lb = 1 pint / 16 oz).

Please note that the focus of this post is on injury risk associated with dehydration. However, remember that dehydration can result in serious heat-related medical conditions ranging from mild discomfort to stroke and death. Players who are suspected of being dehydrated should stop play immediately, move to a cool environment and be attended to by a qualified medical professional.

Over the past years, we have discussed factors that raise an athlete’s risk of joint injury and advocated neuromuscular training program designed to reduce injury risk. These two studies add another simple strategy – proper hydration. By being well hydrated before matches or training, drinking during stoppages in play and rehydrating afterwards, dehydration can be avoided. As a result, injury risk may be lessened and, as a bonus performance maintained throughout the match.

To learn more about how to avoid dehydration when playing in the heat, enroll in our e-learning course, “Soccer Diet: The Simplest Way to Improve Your Team’s Performance”.  CLICK HERE for more info.

References

Arnaoutis G, Kavouras SA, Kotsis YP, Tsekouras YE, Makrillos M, Bardis CN (2012) Ad libitum fluid intake does not prevent dehydration in sub-optimally hydrated young soccer players during a training session of a summer camp. International Journal of Sport Nutrition and Exercise Metabolism, in press.

Distefano LJ, Casa DJ, Vansumeren MM, Karslo RL, Huggins RA, Demartini JK, Stearns RL, Armstrong LE, Maresh CM (2012) Hypohydration and hyperthermia impair neuromuscular control after exercise. Medicine and Science in Sports and Exercise, doi: 10.1249/MSS.0b013e3182805b83