Successive time courses of strength development and steroid hormone responses to heavy-resistance training.

Subjects (5 males, 5 females) performed heavy-resistance exercise at a constant stimulus 3 days/wk for 8 wk. Work rates were then increased to higher but constant levels for an additional 8 wk. Half times of the first training period were 14 and 10 days for the bench press and parallel squat, respectively. The second time course resulted in only one-third of the overall magnitude of strength increases for both exercises as the first, and the kinetics were slower in the parallel squat but similar in the bench press (half time 13 days). Skeletal muscle fiber area was significantly increased (19%) in fast-twitch fibers by the end of the second training period. Postexercise elevations in serum cortisol and prolactin were seen only in the male subjects. Because the males trained at considerably higher work loads than the females, these results imply that absolute amounts of resistance may be an essential requirement for inducing certain hormonal responses. Serum cortisol levels in males after exercise were blunted by the 5th wk of the first time course. For serum testosterone, neither resting nor higher post-exercise concentrations were different at any point of the training periods for either sex. We conclude that the strength time course results are not inconsistent with current thought on factors contributing to strength accumulation. The absence of a specific serum androgenic response with strength development may be related to the fact that the constant exercise stimulus is not conducive to establishing clear-cut hormone-strength relationships.