Relationship of adaptive capabilities in athletes to the type of reaction of their opioid system to stressful physical exercise

Abstract

Eleven highly skilled skiers are examined during and after prolonged exercising on a bicycle ergometer at a Vo 2 equal to 80% of the maximum. Parameters of mechanical work, Voz, plasma lactate concentration, and activity of 8-type opioid receptor ligands are recorded. The opioid system is found to develop two types of reaction to the exercise: activation in the course of work on the ergometer with a tendency toward normalization in the recovery period (Type A) or inhibition during the exercise (Type B). The reaction of Type B involved a rapid increase in the activity of the opioid system immediately after the exercise in some cases and a further fall in the activity of plasma opioids in others. Skiers with Type B reaction performed a lesser amount of work at a higher energy cost than did those with Type A. It is concluded that the latter type of reaction is more efficient than the former. Key Words: adaptation; opioid system; physical exercise; energy supplyOne important mechanism of adaptation is associated with functioning of the opioid system (OS) which participates both in stress-promoting reactions by mobilizing the appropriate neuroendocrine processes and in stress-limiting reactions by restricting overactivation of adaptation mechanisms. The OS not only wards off damaging effects of stress but also sets up an adaptation reserve of functional capabilities in the body [5].One of the most common stressors is strenuous physical activity and adaptation to it activates physiological mechanisms characteristic of stress. Study of these mechanisms during exercising has several advantages; thus, the parameters of stress are measurable, the work load is gradable, and the results are reproducible.That the OS is involved in body's reactions to stress has been demonstrated in numerous investigations. In particular, plasma concentrations of 13-enResearch Institute of Sports; National Research Center for Mental Health, Russian Academy of Medical Sciences, Moscow dorphin and enkephalins were shown to be elevated in the course of and after intensive and prolonged work [7,10,11], and opioid peptides were found to influence the synthesis and secretion during work of stress-mediating hormones such as catecholamines [10], growth hormone and prolactin [8], corticotropin and cortisol [ 11].The purpose of the present study was to establish how adaptive capabilities of the body relate to the reaction of the OS to stressful exercise. The criteria of adaptation were parameters of mechanical work (its duration and the ability to sustain its present power) and energy supply (oxygen consumption [Vo2] and lactate level in the blood during exercising).