MUSCLE-FIBER HYPERTROPHY - HYPERPLASIA, AND CAPILLARY DENSITY IN COLLEGE MEN AFTER RESISTANCE TRAINING

Twelve male subjects with recreational resistance training backgrounds completed 12 wk of intensified resistance training (3 sessions/wk; 8 exercises/session; 3 sets/exercise; 10 repetitions maximum/set). All m ajor muscle groups mere trained, with four exercises emphasizing the f orearm flexors. After training, strength (1-repetition maximum preache r curl) increased by 25% (P < 0.05). Magnetic resonance imaging scans revealed an increase in the biceps brachii muscle cross-sectional area (CSA) (hem 11.8 +/- 2.7 to 13.3 +/- 2.6 cm(2): n = 8; P < 0.05), Musc le biopsies of the biceps brachii revealed increases CP < 0.05) in fib er areas for type I (fi om 4,196 +/- 859 to 4,617 +/- 1,116 mu m(2); n = 11) and II fibers (from 6,378 +/- 1,552 to 7,474 +/- 2,017 mu m(2); n = 11). Fiber number estimated fram the above measurements did not c hange after training (293.2 +/- 61.5 x 10(3) pretraining; 297.5 +/- 69 .5 x 10(3) posttraining; n = 8). However, the magnitude of muscle fibe r hypertrophy may influence this response because those subjects with less relative muscle fiber hypertrophy, but Similar increases in muscl e CSA, showed evidence of an increase in fiber number. Capillaries per fiber increased significantly (P < 0.05) for both type I (from 4.9 +/ - 0.6 to 5.5 +/- 0.7; n = 10) and II fibers (from 5.1 +/- 0.8 to 6.2 /- 0.7: n = 10). No changes occurred in capillaries per fiber area or muscle area. In conclusion, resistance training resulted in hypertroph y of the total muscle CSA and fiber areas with no change in estimated fiber number, whereas capillary changes were proportional to muscle fi ber growth.