Introduction
Growth hormone (GH) and testosteron (T) are anabolic hormones. Heavy resistance exercise is known to lead to acute increases in serum GH and T concentrations and is associated with acute decreases in neuromuscular function. The stress caused by heavy resistance exercise is believed to work as a major stimulus for muscle fiber hypertrophy (e.g., 5, 25, 31). The type of heavy resistance loading may, however, play an important role in the magnitude of the acute anabolic hormonal response. Increases in serum GH appear to be greatest during hypertrophic types of exercise when using rather high numbers of repetitions and sets (7, 18, 20). The load should be near the maximum (e.g., 70–80%), but each set should be performed until the 8– 12 repetition maximum (8–12RM).
The serum T level increases also during strength exercise if the exercise stimulus is sufficient (17, 33). The amount of serum anabolic hormone increases is dependent on the age of the subject, the resting periods during the exercise, the total amount of work, and the amount of activated muscle mass (2, 7, 10, 11, 14, 17, 19–21). In the case of serum T response, the high load exercise (100% 3–6RM) caused a more dramatic increase in serum T than did the moderate load (70%) training protocol (28). Although hormonal changes after heavy resistance exercise have also been observed in women, the acute responses, particularly for T, are generally greater in men than in women (11, 17, 34). Acute metabolic changes may be related to hormonal responses during heavy resistance exercise. Blood lactate has been shown to increase more when the number of repetitions is high with high loads than when loads are lower (1) or the number of repetitions is lower (10).
Women do not seem to be as able as men to aggressively activate the muscles rapidly, and it has been suggested that this is related to their lower T concentrations (9, 29). Indeed, in the explosive exercise, women seemed to be unable to exhaust themselves as men did (22). During heavy resistance exercise, the acute neuromuscular changes were greater than those caused by explosive exercise in men and especially in women (22). Since the hormonal responses appear to be related to the intensity of the exercise protocol, it is of interest to examine if the hormonal responses of an exercise protocol with low (40% of 10RM) loads but performed as explosively as possible are similar to those of moderate (70%) and high (100%) intensity exercises.
If the hormonal responses are related to the amount of muscle mass activated and to the metabolic changes, it is expected that the greatest responses will be observed after the 100% intensity exercise. In explosive situations, the muscles are also activated maximally but with a shorter duration of each repetition, accompanied by a lower metabolic response. It is not clear whether this type of stimulus is large enough to cause considerable hormonal changes. The purpose of this study was to examine acute hormonal responses in men and women to 3 heavy resistance but clearly different exercise protocols: (a) submaximal, (b) maximal heavy resistance, and (c) maximal explosive resistance exercises.