Exercise for good health

Physical activity is essential for maintaining good health. But it can also do more harm than good. Tiago Villanueva and Karim Khan explain

For the hunter-gatherer society, daily physical activity was a prerequisite for survival.w1 Activities such as hunting, tool making, butchering and other food preparation, preparing clothing, carrying firewood and water, and moving to new campsites all needed physical labour.

Nowadays, as most modern societies have predominantly sedentary jobs, people spend about 38% of the caloric expenditure per unit body mass compared with late paleolithic stone agers. We tend to be physically active for recreational purposes and to get fit or maintain their fitness.^w1 Regular physical activity leads to numerous health improving effects. But just how much physical activity is necessary to achieve the benefits, and can exercising too much do harm?

Definitions

Physical activity, exercise, and sport are not quite the same thing. Physical activity is an umbrella term meaning any bodily movement produced by skeletal muscles that results in expenditure of energy above the basal level (includes work and leisure).^w2 Examples include walking, cycling, housework, cleaning the house, and climbing the stairs. Exercise is a subcategory of physical activity that is planned, structured, repetitive and purposive in the sense that improvement of or maintenance of one or more components of physical fitness is the objective.w2 Examples include brisk walking, aerobic dancing, and some active hobbies, such as gardening. Sport is physical activity in structured competitive situations governed by rules.^w3

Benefits of physical activity

Because the human genome has not changed much for the past 10000 years, some researchers think that it has always been programmed for a physically active lifestyle.^{w4 w5} The current levels of physical inactivity might alter the normal expression of genes and lead to an altered pattern of protein expression paving the way for the emergence of clinical disorders.^w6

Evidence indicates that physical inactivity leads to increased incidences of cardiovascular disease (heart disease,^w7 hypertension,^w8 stroke,^w9 intermittent claudication,^w10 platelet adhesion and aggregation,^w11 metabolic diseases (type 2 diabetes,^w12 obesity,^w13 dyslipidemia,^w14 and gallstones^w15), cancer (breast,^w16 colon,^w17 prostate,^w18 pancreatic,^w19 and melanoma^w20), immune dysfunction,^w21 and neurological disorders (cognitive impairment, Alzheimer’s disease, and dementia).^w22 Evidence also indicates that physical inactivity worsens asthma and accelerates bone loss.^{w23 w24}

The effects of physical activity on mental health and psychological wellbeing are relevant.^w25 Regular physical activity seems to promote psychological wellbeing-that is, self esteem, mood, and self perceptions, such as body image and physical self worth)-therefore improving health related quality of life. Physical activity also appears to improve reaction to stress, the quality and length of sleep, aspects of cognitive function (such as planning, short term memory, and decision making) and to reduce anxiety, symptoms of depression, and feelings of loneliness.^{w26 w27}

Getting most people to adopt an active lifestyle may mean finding a compromise between a level of activity which is beneficial and one which is accessible. The most recent recommendations call for 30 minutes at a time of moderate intensity-for example, brisk walking-sessions of physical activity, in most or all days of the week.^{w28 w29}

Overdoing it

Just as the health benefits increase as we progress from active living to training for sport, so do the associated risks and harms, such as sports injuries and sudden cardiac arrest. Elite sport, which requires high training volumes, carries the greatest amount of risks and harms for the health in the physical activity spectrum.

The primary goal of an élite athlete’s training is to improve performance and to peak at the right moment. They need to do relatively high amounts of intensive exercise to perform at their upper limit.

But how much training is necessary to achieve peak performance? The answer is not straightforward. Researchers studied the effect of increasing the training volume on performance capacity in swimmers. Doubling the training volume for six weeks did not lead to any increase in performance indexes.^w30

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Too much exercise affects your fashion sense

Others have demonstrated a curvilinear relationship between training load and cycling performance showing saturation characteristics.^w31 Yet another study showed a 3-6% decrease in performance during the period of the highest training load.^w32

These studies suggest that there is an optimal level of training, which is difficult to quantify. The relatively scarce data available suggests an inverted U shaped relationship between training volume and increase in performance: training at levels higher than the top of the curve can result in overtraining.

The generally used training model is based on the idea that physical exercise disturbs the cellular homeostasis.^{w4 w33 w34} Changes induced by exercise trigger physiological mechanisms that aim to put homeostasis back in place and induce training adaptations.

More than 60% of distance runners experience the consequences of overtraining at least once during their career.^w35 Overtraining is an imbalance where too much training and competition is coupled with too little time for regeneration.

Overtraining can be divided in two phases: incomplete recovery or over-reaching, and overtraining syndrome, burnout, or staleness.^w36 Over-reaching may occur after some days of hard training, and is associated with muscle fatigue, possibly due to insufficient metabolic recovery and a decrease in the amount of energy rich phosphates.^w37

The transition from over-reaching to overtraining syndrome is gradual. The overtraining syndrome probably occurs when there is an imbalance between stress and the athlete’s ability to cope. (The hypothalamus provides the instructions the body needs to deal with every threat to the integrity of the organism. This is channelled through the endocrine system, the autonomic nervous system, and behaviour.^w38) Consequently, neuroendocrine dysfunction occurs as well as eventual changes in behaviour.^w39

The syndrome includes persistent poor performance, extreme fatigue, altered mood, emotional instability, decreased motivation, increased infections, and low libido.^w40

Conclusion

Too little or too much physical activity can take its toll on our health. For most people, moderate regular physical activity and exercise helps to maintain physical and mental health. According to Horace, "in medio stat virtus", which means "virtue stands in the middle." Virtue is the moderate not the extreme position. Old wisdom never seemed so contemporary.

Tiago Villanueva, Clegg scholar BMJ and intercalating medical student, University of Lisbon
Email: tvillanueva@netcabo.pt

Karim Khan, North American editor British Journal of Sports Medicine, BMJ Publishing Group
Email: karim.khan@familymed.ubc.ca


studentBMJ 2004;12:265-308 July ISSN 0966-6494

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Responses published this month Articles Responses EDITORIALS Exercise for good health       Tiago Villanueva and Karim Khan (July 2004) dilip yadav (June 29, 2004) Read this response EDITORIALS Exercise for good health       Tiago Villanueva and Karim Khan (July 2004) Caroline Mann (July 27, 2004) Read this response EDITORIALS Exercise for good health       Tiago Villanueva and Karim Khan (July 2004) dilip yadav(June 29, 2003)       MBBS 2nd year kathmandu dilipk@iom.edu.np good finding to aware those who might think excessive exercise might good enough for their health. EDITORIALS Exercise for good health       Tiago Villanueva and Karim Khan (July 2004) Caroline Mann(July 27, 2003)       4th year medical student, University of Birmingham 'Undertraining in Medical Students': As a long distance runner, I have myself experienced overtraining, or more often under-recovery. However, the majority of medical students rarely even manage moderate exercise, let alone overtraining. Even those of us who are members of gyms seem to rarely use them. The excuse is generally that we are too busy, but we can always make time for other activities that we perceive as important, such as drinking, socializing and watching TV. Over the years, the UK population has led a more and more sedentary lifestyle, with the prevalence of obesity and other diseases related to a lack of exercise increasing rapidly. As medical students we have all seen patients so obese that they can only be moved by hoists, or suffering from repeated MIs and strokes. The health benefits of exercise are well known, but surely future doctors with first hand knowledge of the health risks of inactivity should be amongst the more active of the population?