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The purpose of this investigation was to determine the effects of a 12-week progressive resistance-training program (PRT) on single muscle fiber calcium sensitivity in six older women (73 +/- 2 years). Muscle biopsy samples of the vastus lateralis were obtained pre- and post-PRT. Chemically skinned single muscle fibers ( n=274) were dissected and studied. The experimental sequence for each fiber was the determination of peak maximal isometric tension ( P(o)) at pCa 4.5 (pCa=-log[Ca(2+)]), and then subsequent submaximal activations of the fiber at nine Ca(2+) concentrations (pCa 6.8 to 4.7). Myosin heavy chain (MHC) I fiber (slow-twitch) diameter increased 16% ( P<0.05) with no change in MHC IIa fibers (fast-twitch) pre- to post-PRT, respectively. P(o) in MHC I fibers increased 34% ( P<0.05) as a result of the training with no change in MHC IIa fibers. The mean MHC I Ca(2+) activation threshold (minimal amount of Ca(2+) necessary to induce tension) increased from 6.83 +/- 0.02 to 6.91 +/- 0.01 ( P<0.05), as did the mean half-maximal activation (pCa(50)), 5.51 +/- 0.02 to 5.71 +/- 0.03 ( P<0.05) with PRT. The slope of the Hill plot above ( n(1)) the pCa(50) for MHC I did not change significantly with the PRT. However, the slope of the Hill plot below ( n(2)) the pCa(50) for MHC I demonstrated an increase ( P<0.05) with training. There were no differences with MHC IIa fibers with PRT for any of the variables measured. In conclusion, the results of this investigation indicate that myofibril Ca(2+) sensitivity and activation properties are altered in MHC I, but not MHC IIa fibers with PRT in older women. The alterations in the MHC I Ca(2+) properties appear to have an effect on the mechanisms involved with skeletal muscle adaptability in older women following PRT.

The purpose of this investigation was to determine the effects of a 12-week progressive resistance-training program (PRT) on single muscle fiber calcium sensitivity in six older women (73±2 years). Muscle biopsy samples of the vastus lateralis were obtained pre- and post-PRT. Chemically skinned single muscle fibers (n=274) were dissected and studied. The experimental sequence for each fiber was the determination of peak maximal isometric tension (Po) at pCa 4.5 (pCa=–log[Ca2+]), and then subsequent submaximal activations of the fiber at nine Ca2+ concentrations (pCa 6.8 to 4.7). Myosin heavy chain (MHC) I fiber (slow-twitch) diameter increased 16% (P<0.05) with no change in MHC IIa fibers (fast-twitch) pre- to post-PRT, respectively. Po in MHC I fibers increased 34% (P<0.05) as a result of the training with no change in MHC IIa fibers. The mean MHC I Ca2+ activation threshold (minimal amount of Ca2+ necessary to induce tension) increased from 6.83±0.02 to 6.91±0.01 (P<0.05), as did the mean half-maximal activation (pCa50), 5.51±0.02 to 5.71±0.03 (P<0.05) with PRT. The slope of the Hill plot above (n1) the pCa50 for MHC I did not change significantly with the PRT. However, the slope of the Hill plot below (n2) the pCa50 for MHC I demonstrated an increase (P<0.05) with training. There were no differences with MHC IIa fibers with PRT for any of the variables measured. In conclusion, the results of this investigation indicate that myofibril Ca2+ sensitivity and activation properties are altered in MHC I, but not MHC IIa fibers with PRT in older women. The alterations in the MHC I Ca2+ properties appear to have an effect on the mechanisms involved with skeletal muscle adaptability in older women following PRT. [ABSTRACT FROM AUTHOR]