Exercise And Pituitarytesticular Function Normal Men Exercise Responses

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It is generally accepted that short-term, maximal, and anaerobic-type exercise results in an elevation of the circulating testosterone level (see Table 1 for definitions of exercise-types terminology) (25,28-30). It is still debatable whether this effect results from solely hemoconcentration and reduced metabolic clearance or whether there is also an increase in testosterone production.

Unlike changes during maximal exercise, testosterone responses to submaximal exercise are more variable and are dependent on the duration and intensity of exercise. Progressive increases in testosterone levels during moderate intensity exercise lasting 45 to 90 min have been found (25,31,32). However, 90 min of submaximal moderate intensity exercise has also been reported to produce no change or a slight decrease in testosterone concentrations (25,31). Exercise of a moderate or hard intensity until exhaustion, of more than approx 2 h duration typically lowers testosterone concentrations (25,31,32).

Several explanations for these dissimilar changes during short-term submaximal exercise have been proposed. Initially, hemoconcentration may increase the testosterone concentration; but as exercise continues, testicular testosterone production declines. The latter change may partly result from reduced testicular blood flow (26,27). Hepatic blood flow may also decline, reducing hepatic clearance (26,27). This latter change may be offset by an increased uptake of testosterone by peripheral target tissue (i.e., skeletal muscle) as exercise duration continues, gradually reducing circulating testosterone levels.

Interestingly, these acute effects of a bout of maximal and submaximal exercise on testosterone levels are transient. The changes are typically short lived and corrected during the recovery period (1 to 24 h) (25,33-35).


Research results examining gonadotropin response to maximal and anaerobic-type exercise are contradictory (36,37); however, the majority of the evidence indicates there are small transient increases in the circulating gonadotropins (35,38-44). In addition, the outcomes of these studies and their interpretations are subject to methodological limitations. In many cases, researchers did not obtain blood samples frequently enough to assess the highly pulsatile gonadotropin secretory profile (12,16,24). Resistance-type exercise causes an increase in serum gonadotropin levels in both men and women (43-46).

Likewise, the prolonged (~1-2 h) submaximal exercise responses of the gonadotropins vary considerably for both men and women (25,41,42). Evidence of sig-

Normal Testosterone Blood LevelNormal Testosterone Blood Level

Fig. 1. Factors that influence the level of circulating testosterone in a normal, healthy man at rest and in response to a physical exercise bout. This figure is based on information from refs. 19,22,24,25.

Table 1

Categorization and Definition of Exercise-Intensive and Exercise Type Relative to Exercise Studies of Physically Fit Men

Table 1

Categorization and Definition of Exercise-Intensive and Exercise Type Relative to Exercise Studies of Physically Fit Men







Category Term

(% VÜ2maX)




Light or easy exercise



>30 min


Moderate exercise

>35 <70


>30 min <180 min


Heavy exercise



<120 min


Maximal exercise



<15 min

Maximal or Max

Supramaximal exercise



<1 min

Sprints, power

* In quantifying exercise intensity, it is typical to express it as a relative percentage of an individual's maximal oxygen uptake (VO2max; i.e., maximal aerobic capacity). (Based on ref. 27a.)

* In quantifying exercise intensity, it is typical to express it as a relative percentage of an individual's maximal oxygen uptake (VO2max; i.e., maximal aerobic capacity). (Based on ref. 27a.)

nificant increase, decrease, and no change has been reported (31,35,38,39,41,42). If submaximal exercise is extended for extremely long periods (several hours) or until exhaustion occurs, then gonadotropin levels are suppressed (41,47-49).

These exercise-induced gonadotropin disturbances are transient and last for relatively short periods into the recovery from exercise. The exception to this point is that submaximal exercise of many hours duration can produce disturbances that last several days (48,49).

Other Pituitary Hormone—Prolactin

PRL presents an interesting paradox in reproductive physiological function. In physiological concentrations, it may be necessary for normal testicular function, whereas excessive PRL levels disrupt both central and peripheral aspects of the hypo-thalamic-pituitary-testicular axis (16,50). Circulating PRL concentrations increase during most exercise. The magnitude of the increase is approximately proportional to the intensity of the activity (25,41,51). Short-term, maximal, and anaerobic-type exercise results in increases in PRL (25,41,51-55). Submaximal exercise of 30 to 60 min duration, provided it is intense enough, increases circulating PRL levels as well (25,42,52-55).

Extending the duration of a submaximal exercise bout augments the magnitude of the PRL response (24,42,51,52). There are several factors that further increase the PRL response to prolonged exercise: (1) consumption of a diet rich in fat, (2) fasting for an extended period of time before exercise, (3) performing exercise in conditions promoting an increase in body temperature, and (4) administration of P-adrenergic blocking agents before exercise (25,42,52,55). On the other hand, PRL release is inhibited by a-adrenergic blockade (25,42). Training history (i.e., training type or mode) also has a positive or negative influence on this response to submaximal exercise (25).

PRL changes after maximal exercise or submaximal exercise of 1-2-h duration are short lived and transient in nature (52-54). Interestingly, Hackney and associates have reported that nocturnal PRL levels are two to three times greater after 1.5 h of intensive endurance exercise than when no daytime exercise was performed (38).

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