Effects of a 15-d race on plasma steroid levels and leg muscle fitness in runners.

Abstract

Effects of increased training distance on resting plasma testosterone and adrenal steroid levels, serum markers of protein catabolism and muscle fiber damage, and field tests of leg muscle fitness were studied in 19 male marathon runners. Data were collected 1-2 d before and 1 d after a 400-km road race over 15 d. The runners maintained their usual training speeds even though the race distance was twice their regular mileage. Testosterone levels decreased 31% (P less than 0.01), from 23.5 +/- 1.7 to 16.2 +/- 1.0 nmol.l-1. The ratio of cortisol to testosterone increased 83% (P less than 0.01). Blood urea nitrogen (BUN) concentration increased from 16.7 +/- 0.7 to 21.8 +/- 1.0 mg.dl-1 (P less than 0.05) and serum total protein decreased from 7.09 +/- 0.10 to 6.88 +/- 0.08 g.dl-1 (P less than 0.05). Serum creatine kinase (CK) activity increased 380%, from 152 +/- 11 to 731 +/- 74 U.l-1 (P less than 0.001) and was associated with persistent leg muscle soreness. There were no significant changes in body weight, estimated lean body weight, hematocrit, or plasma cortisol, aldosterone, progesterone, androstenedione, and DHEA sulfate levels. Test scores for leg power (vertical jump), strength (dead lift), flexibility (sit-and-reach), and speed (timed stands) did not change significantly. The decrease in plasma testosterone did not correlate with the changes in either BUN, total protein, or CK. The results indicate that existent leg muscle fitness was unaltered despite the suppression of circulating testosterone and the development of early protein catabolism and muscular damage.