Introduction

Exercise in later life has often been a contentious issue, and a major consideration is a diminished tolerance to heat stress in older members of the community. Given that Australia is by and large a hot, humid country with an aging population it is important to understand the implications associated with exercising and staying fit in the heat for the elderly.

First, the belief that the elderly are less able to cope with thermal stress than their younger counterparts is not supported by the scientific research. Indeed, older people with similar fitness levels are capable of exercising in the heat just as well as their younger counterparts. They also acclimatize to heat stress over a period of time in a similar manner to younger people.

There are, however, subtle changes that occur as people age which effect exercise tolerance in the heat.

One involves skin blood flow characteristics. When exercising, only 25% of energy produced results in muscular contraction, the remain­ing energy simply produces heat within the muscle. This heat must be dissipated if exercise is to continue and that occurs primarily in two ways: (i) There is an increase in blood flow to the skin; and (ii) sweat is evaporated from the skin which cools the blood flowing directly below the skin’s surface.

Older people show a 25% to 40% decrease in skin blood during exercise. This is largely due to altered characteristics of the skin which inhibit the opening of the small blood vessels close to the skin's surface. This loss of blood flow appears to be somewhat negated, providing the individual remains active throughout life.

Additionally, the normal lowering of sweat production which commonly occurs with age can be offset by ongoing partici­pation in aerobic exercise. On the other hand, if people allow themselves to lose a degree of aerobic-fitness, this may be accompanied by lowered sweat production and skin blood flow which will certainly decrease an individual's ability to cope with heat whilst exercising.

Research has also shown that older people have a lower perception of the need to consume fluids than their younger counterparts. In other words, with age, it appears that the sensitivity of the thirst mechanism (which is already a poor indicator of fluid needs even in the young), is further blunted. This results in an even lower voluntary consumption of fluids which can have dire effects on the individual's ability to exercise in the heat as the internal temperature starts to rise. Therefore, while aggressive fluid con­sumption over and above what a person 'feels' he or she needs is important, the importance of this practice is further compounded in the elderly. Like others, the elderly are best served by consuming a sports drink during extended exercise periods of 60 minutes or more.

Research suggests that it isn't the aging process so much that inhibits an older persons ability to exercise in the heat. Rather, it is a combination of factors includ­ing lowered aerobic fitness, incomplete acclimatization, chronic dehydration and low carbohydrate diets. These are far more important and predispose the elderly to thermal strain in hot environments rather than the aging process per se.

Eldery Age Heat Stress Variables

The variables that decrease a person’s ability to exer­cise in the heat as they age include:

• Lower maximal oxygen uptake capacities
• Sedentary lifestyles
• Increased levels of body fat
• Chronic dehydration as a result of less sensitive thirst mechanisms lowering fluid intake and/or increased fluid excretion
• Higher incidences of chronic diseases (such as heart disease)
• An increased usage of prescription drugs for the treatment of chronic diseases (like diuretic use in the treatment of hyperten­sion).

Therefore, the average older person is probably at a greater risk of heat stress than the average younger person, but available information suggests that fit, healthy older people are at no greater disadvantage when exercising in the heat than a comparable 25 year old. Provided a number of guidelines based on commonsense are fol­lowed, the elderly needn't avoid exercising in hot environments to any greater extent than younger individuals.

Guidelines For Heat Stress and the Elderly

The guidelines suggested are:

• Hydrate. Pay particular attention to fluid when exercising in the heat. Drink as much fluid as is tolerable 30 to 45 minutes prior to exercise (ideally a sports drink as the electrolyte content of such beverages will help to maintain hydration status better than water alone), and a further cupful every 15 minutes whilst exercising. When you finish exercising drink more than is necessary to quench your thirst over the subsequent two hours. Eat meals with a high fluid content (like fruit and vegetables) and consume a sports drink to best meet fluid and electro­lyte requirements.
• Use commonsense. If you think that it's too hot to exercise during the day, it probably is. Choose cooler times of the day to exercise (morning or evening), or swim during the hotter periods.
• Maintain aerobic fitness. Cardiovascular fit individuals cope with thermal stress flu-better than others.
• Learn about heat stress. The signs and symptoms need to be understood so it can be avoided or effectively treated if sustained.
• Pay attention to your health status and/or the use of prescription drugs.   Viral infections increase fluid losses considerably leading to dehydration. Couple this with trying to maintain normal exercise habits and the consequences can be catastrophic. Like­wise, if you are taking any form of medication, consult your doctor to ensure your fluid requirements and/or body responses to exercise haven't been altered in any way.

Exercise should be fun. Staying fit and healthy should be a lifetime quest in an attempt to maximize the quality of life. By being attentive to the changes our bodies undergoes as we age, the benefits of exercise won't just be the dominion of the young.