In animals, exposure to stressors results in the stress reaction, and this reaction includes a series of hormonal and neuronal changes. In particular, adrenaline and cortisol are released, and this increases alertness as well as the supply of energy for activity. Exercise is considered a form of stress to all animals, because physical exertion results in the stress reaction. Stress is generally considered detrimental to the health and so one could be forgiven to questioning the benefits of exercise stress to health. However, stress is often misunderstood because stressors are beneficial if they are presented to the individual in a manageable quantity, and if adequate rest is provided in order to allow recuperation. Under such circumstances adaptation to the stressor occurs and this makes the individual more able to cope with future exposure to stressors of that nature. This is the basis of increased fitness due to training through exposure to exercise. In other words, that which does not kill me makes me stronger.
Exercise is therefore a double edged sword. No physical activity whatsoever is detrimental, because we are organisms that require activity to maintain our skeletal, muscular and vascular systems. However, too much activity stresses these systems and ultimately leads to a disruption of homeostasis through hormonal and neuronal dysfunction. As with all things, balance is therefore the key ingredient with exercise, with the benefits of regular exercising only being obtained by also adopting adequate recuperation times between periods of exertion. Exercise itself has insulin sensitising effects which are its real benefit in weight loss. Following exercise glucose is more readily transported into skeletal muscle where it can be used to resynthesise glycogen or can be oxidised as a fuel, and this lowers blood glucose levels. Those with insulin resistance therefore benefit greatly from exercise. However, too much exercise is detrimental because it ultimately causes deterioration of the organism through excessive stress.
Using exercise to cause weight loss is controversial because few people understand the nuances of the art. Weight gain is caused by insulin resistance, and in order to cause weight loss, this insulin resistance must be reversed. Most people who are overweight and desire to lose weight consider exercise a process by which energy is ‘burnt’ and therefore the more exercise they perform the more weight they lose. Many trainers also fall into this trap. However, the role of exercise in weight loss is one of causing insulin sensitivity to increase, thus reversing the metabolic dysfunction that has caused the weight gain. In this regard hours of running or cycling do not benefit weight loss in the obese because they provide additional metabolic disruption in the form of stress to an already existing disease state. Instead moderate activity that minimises the exposure of the individual to excessive stress, while providing insulin sensitising effects, should be considered the best strategy to cause reductions in body fat.
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