For those who engage in regular exercise, keeping hydrated is key to maximising performance, writes GILES WARRINGTON.
CONSUMPTION OF water is vital for supporting life, regulating key bodily functions and maintaining good health.
The human body is 60-65 per cent water, which is a key component of the various cells, muscle and other tissues within the body. While the human body can exist without food for extended periods, we can only survive without water for a matter of days.
Importance of good hydration
Good hydration practices are critical for maintaining normal physiological and cognitive function and optimising performance during participation in sport and exercise. Adequate hydration before, during and after exercise is, therefore, essential.
Despite this, hydration and maintaining fluid levels is a factor often overlooked in training and competition. It is important to be aware that good hydration practices do not just apply to serious athletes, but to anyone engaging in regular physical activity and exercise.
During exercise, the body breaks down food to create energy necessary to fuel the working muscles. Exercise leads to a dramatic increase in energy turnover which, in turn, results in a rapid elevation in inner (core) body temperature.
This accumulating heat must in some way be removed from the body to prevent overheating. Unless appropriately regulated, core body temperature will continue to rise, leading to fatigue and, in extreme cases, heat exhaustion and, worse still, heat stress.
The body’s main defence mechanism for regulating temperature during exercise is through the evaporation of sweat, which accounts for about 80 per cent of all heat loss. This will result in significant losses in body water which must be replaced to avoid dehydration.
In this regard, a fundamental difference between the diet of someone who is physically active and that of the general sedentary population are that those in training require additional fluid to cover losses through sweating in order to regulate body temperature.
Daily fluid needs
For the average healthy person under normal conditions, daily fluid requirements will typically be in the region of two to three litres, which includes the water content in foods consumed.
For those engaging in regular physical activity, fluid intake needs will be greater and should match body water losses through sweating. Scientific evidence across a range of activities suggests that sweat rates can vary considerably and can be affected by a number of factors including age, gender, fitness levels, exercise intensity and duration as well as environmental conditions.
Typical sweat losses during sport participation and exercise will be in the region of 0.5 to two litres per hour, which equates to a 0.5-2kg loss in body weight. For the average 70kg individual who sweats heavily, this may result in a fall in body weight of between 2 and 3 per cent during a training session lasting around 60 minutes!
Avoiding dehydration
Dehydration is a condition in which the body contains an insufficient volume of water to meet its various needs.
If you train even in a mildly dehydrated state, your body has to work that much harder to regulate body temperature. As a result, your sub-maximal heart rate and perception of effort during exercise will be higher than normal, indicating increased physical stress. Not only will physiological and cognitive function be negatively affected, but work capacity and performance will decrease.
Research has shown that fluid losses as little as 2 per cent of body weight, which are commonly experienced, can have a marked negative impact on endurance, performance, concentration and decision-making. This may have significant implications for those involved in prolonged activities or events with a high skill component.
The bottom line is that, for those engaging in physical training, you should create a plan to get into the habit of making sure that you are well hydrated before commencing exercise, as well as drinking enough fluid during and after exercise to balance potential water losses.
Next week we will look at simple ways to monitor your hydration status as well as practical fluid intake guidelines for those involved sport and exercise.
- Dr Giles Warrington is a sport and exercise physiologist and lecturer in the School of Health and Human Performance at DCU.