Morphometry and oxidative capacity of slow-twitch (type I) and fast-twitch (type IIa and IIb) muscle fibers obtained from vastus lateralis needle biopsies were compared between younger (21-30 yr) and older (51-62 yr) normal fit (maximal O2 uptake = 47.0 vs. 32.3 ml.kg-1.min-1) and endurance-trained (66.3 vs. 52.7 ml.kg-1.min-1) men (n = 6/group). The older groups had smaller type IIa (31%) and IIb (40%) fiber areas and fewer capillaries surrounding these fibers than did younger groups. The reduced type II fiber areas and capillary contacts associated with aging were also observed in the older trained men. However, the capillary supply per unit type II fiber area was not affected by age but was enhanced by training. Additionally, on the basis of quantitative histochemical analysis, succinate dehydrogenase activities of type IIa fibers in the older trained men [4.07 +/- 0.68 (SD) mmol.min-1.l-1] were similar to those observed in younger trained men (4.00 +/- 0.48 mmol.min-1.l-1) and twofold higher than in older normal fit men (2.01 +/- 0.65 mmol.min-1.l-1; age x fitness interaction, P < 0.05). Type I muscle fibers were unaffected by age but were larger and had more capillary contacts and higher succinate dehydrogenase activities in the trained groups. The findings of this study suggest that aging results in a decrease in type II fiber size and oxidative capacity in healthy men and that this latter effect can be prevented by endurance training. Conclusions regarding the effects of age and training status on muscle capillarization depend largely on how these data are expressed.
The hypothalamic-pituitary-testicular (H-P-T) axis was evaluated in groups of endurance-trained (TRG) and untrained (UNT) males. Each group was subjected to: 1) a 4-h resting hormonal profile [testosterone (T), free-testosterone (FT), estradiol (E2), luteinizing hormone (LH), prolactin (PRL), and cortisol (C)], 2) a dopamine antagonist (DA; 10 micrograms.kg-1 body weight) challenge to the pituitary-testes, and 3) a gonadotropin-releasing hormone (GnRH; 120 micrograms.kg-1 body weight) challenge to the pituitary-testes. Compared to UNT, the TRG resting T (4.8 +/- 0.7 vs 7.1 +/- 1.2 ng.ml-1, p = 0.05) and PRL (3.3 +/- 1.4 vs 7.0 +/- 2.3 ng.ml-1, p = 0.09) were lower while LH was elevated (15.0 +/- 1.8 vs 11.8 +/- 1.5 mIU.ml-1, p = 0.06). The DA challenge produced a greater integrated PRL response in the TRG (2962.7 +/- 265.1 ng +/- ml-1.min) than in the UNT (1735.3 +/- 282.0 ng.ml-1.min; p = 0.01). No significant changes were observed in T following the DA-induced PRL rise. The TRG had a blunted LH response (817.2 +/- 111.6 mIU.ml-1.min) following the GnRH injection as compared to the UNT (1493.7 +/- 213.4 mIU.ml-1.min; P less than 0.02). T levels were significantly (p less than 0.03) increased in both groups by the LH rise after the GnRH challenge (TRG = 9.9 +/- 5.0%; UNT = 8.6 +/- 9.9%, respectively), but no significant between group differences were observed. Results suggest endurance training produces an enhanced PRL and attenuated LH release by the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)
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