Morphological and Functional Characteristics of Skeletal Muscle Fibers From Hormone-replaced and Nonreplaced Postmenopausal Women

Abstract

We tested the hypothesis that cross-bridge mechanisms of contraction differed in early postmenopausal women who did or did not receive hormone replacement therapy (HRT). Vastus lateralis biopsies were obtained from 17 postmenopausal women (49-57 years old), 8 of whom were on HRT for the previous 24 +/- 5 months and 9 of whom were never on HRT. Electrophoresis and enzyme histochemistry revealed that fiber myosin heavy chain (MHC) isoform distribution, the cross-sectional area (CSA) of slow and fast fibers, and the relative CSA occupied by each, were similar for HRT and non-HRT groups. Single permeabilized fibers containing type IIa MHC had greater Ca(2+)-activated peak specific force, unloaded shortening velocity, and peak power than fibers containing type I MHC, but in all cases the values for HRT and non-HRT groups were similar. In this cross-sectional study, we found no evidence that Ca(2+)-activated fiber function, MHC isoform distribution, or relative CSA occupied by slow and fast fibers differed between HRT and non-HRT groups.

Regulation of Physiological and Metabolic Function of Muscle by Female Sex Steroids

“…Permeabilized fibers do not have intact nerve or membranes so excitation-coupling mechanisms are bypassed and contractile responses directly reflect contractile protein function. In support of the hypothesis that hormones affect contractile proteins, permeabilized fibers from rat soleus muscles generated 20% lower specific force 10–14 weeks following ovariectomy compared with fibers from control rats (71). In contrast, permeabilized fibers from women who were and were not on hormone therapy showed no difference in specific force (72).…”

Discrepancies between Skinned Single Muscle Fibres and Whole Thigh Muscle Function Characteristics in Young and Elderly Human Subjects

“…The intrinsic contributor of peak strength loss is derived from neuromuscular function, which is dependent on excitation-contraction coupling and alterations in cross-bridge mechanisms [16, 25–31]. There are different CSA values in each group, and type I in particular has a remarkable pattern compared with the other types (the CSA is greater in men than in women).…”

“…SDS-PAGE was run at a constant voltage of 90 V for 30 min and 140 V for 5.5 h [22]. A protein homogenate mixture of human muscle MHC I, IIa, and IIx was used as the MHC standard, and the order of migration of each human MHC in the gel is shown according to a previously described method [25] (Figure 2). Gels loaded with single muscle fibres were subjected to silver staining to identify the MHC isoforms of each single muscle fibre, and densitometry was performed by using an analytical software (Bio-1D Light; Vilber Laurat, Marne-la-Vallée, France).…”

Whole‐Body‐Vibration Training Increases Knee‐Extension Strength and Speed of Movement in Older Women

“…Reduction in muscle mass with a preferential loss of type II fibers 10 has been associated with an age‐related decrease in physical activity resulting in reduced loading of the musculoskeletal system 11 . Moreover, some studies have reported that decreases in serum sex hormones are involved in a reduction of muscle mass, 12,13 whereas other studies have not supported these findings 14 . Fortunately, it has been proven that resistance and explosive strength training programs can alleviate deterioration of the muscular system with aging 3,15–18 .…”