Alterations in single muscle fiber calcium sensitivity with resistance training in older women.
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.
Human Performance Laboratory, Ball State, University, Muncie, IN 47306, USA.
M P
MP
Godard
P M
PM
Gallagher
U
U
Raue
S W
SW
Trappe
D000222:Adaptation, Physiological / Q000502:physiology*; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*
D002118:Calcium