Effect of resistance training on single muscle fiber contractile function in older men

The purpose of this study was to examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance trainin g (PRT) in older men (n = 7; age = 74 +/-: 2 yr and weight = 75 +/- 5 kg). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsy samples were obtained from the vastus late-ralis before and after PRT (pre- and post-PRT, respectively). For analysis, chemically skinn ed single muscle fibers were studied at 15 degrees C for peak tension [the maximal isometric force (P-o)], unloaded shortening velocity (V-o), and for ce-velocity parameters. In this study, a total of 199 (89 pre- and 110 post -PRT) myosin heavy chain (MHC) I and 99 (55 pre- and 44 post-PRT) MHC IIa f ibers were reported. Because of the minimal number of hybrid fibers identif ied post-PRT, direct comparisons were limited to MHC I and IIa fibers. Musc le fiber diameter increased 20% (83 +/- 1 to 100 +/- 1 mu m) and 13% (86 +/ - 1 to 97 +/- 2 mu m) in MHC I and IIa fibers, respectively (P < 0.05). P-o was higher (P < 0.05) in MHC I(0.58 +/- 0.02 to 0.90 +/- 0.02 mN) and IIa (0.68 +/- 0.02 to 0.85 +/- 0.03 mN) fibers. Muscle fiber V-o was elevated 7 5% (MHC I) and 45% (MHC IIa) after PRT (P < 0.05). MHC I and IIa fiber powe r increased (P < 0.05) from 7.7 +/- 0.5 to 17.6 +/- 0.9 mu N . fiber length s . s(-1) and from 25.5 to 41.1 mu N . fiber lengths . s(-1) respectively. These data indicate that PRT in elderly men increases muscle cell size, str ength, contractile velocity, and power in both slow- and fast-twitch muscle fibers. However, it appears that these changes are more pronounced in the MHC I muscle fibers.