Reduction in hybrid single muscle fiber proportions with resistance training in humans

The purpose of this investigation was to examine the effects of 12 wk of progressive resistance training (PRT) on single muscle fiber myosin heavy chain (MHC; I, I/IIa, I/IIa/IIx, IIa, IIa/IIx, IIx) isoform proportions in young individuals. Young, untrained men (YM; n = 6) and women (YW; n = 6) (age = 22 ± 1 and 25 ± 2 yr for YW and YM, respectively) received pre- and post-PRT muscle biopsies from the right vastus lateralis for single muscle fiber MHC distribution by electrophoretic analysis (192 ± 5 pre- and 183 ± 6 post-fibers/subject analyzed; 4,495 fibers total). Data are presented as percentages of the total fibers analyzed per subject. The PRT protocol elicited an increase in the pure MHC IIa (Δ = + 24 and + 27; YW and YM, respectively; P < 0.05) with no change in the pure MHC I distribution. The hybrid MHC distributions decreased I/IIa/IIx (Δ = −2; YM and YW; P < 0.05), IIa/IIx (Δ = −13 and −19 for YM and YW, respectively; P < 0.05), and total hybrid fiber proportion (I/IIa + I/IIa/IIx + IIa/IIx) decreased (Δ = −19 and −30 for YM and YW, respectively; P < 0.05) with the training, as did the MHC IIx distribution (Δ = −2; YW only; P < 0.05). Alterations in the predominance of MHC isoforms within hybrid fibers (decrease in MHC I-dominant I/IIa and nondominant MHC IIa/IIx, increase in MHC IIa-dominant IIa/IIx; P < 0.05) appeared to contribute to the increase in the MHC IIa proportion. Electrophoresis of muscle cross sections revealed an ∼7% increase ( P< 0.05) in MHC IIa proportion in both groups, whereas the MHC IIx decrease by 7.5 and 11.6% post-PRT in YW and YM, respectively. MHC I proportions increase in YM by 4.8% ( P < 0.05) post-PRT. These findings further support previous resistance training data in young adults with respect to the increase in the MHC IIa proportions but demonstrate that a majority of the change can be attributed to the decrease in single-fiber hybrid proportions.

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

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.1.143 ◽

2000 ◽

Vol 89 (1) ◽

pp. 143-152 ◽

Cited By ~ 174

Author(s):

Scott Trappe ◽

David Williamson ◽

Michael Godard ◽

David Porter ◽

Greg Rowden ◽

...

Keyword(s):

Resistance Training ◽

Muscle Fiber ◽

Contractile Function ◽

Vastus Lateralis ◽

Muscle Fibers ◽

Older Men ◽

Single Muscle ◽

Mhc I ◽

Before And After ◽

Mhc Iia

The purpose of this study was to examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (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 lateralis before and after PRT (pre- and post-PRT, respectively). For analysis, chemically skinned single muscle fibers were studied at 15°C for peak tension [the maximal isometric force (Po)], unloaded shortening velocity ( V o), and force-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 fibers were reported. Because of the minimal number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 20% (83 ± 1 to 100 ± 1 μm) and 13% (86 ± 1 to 97 ± 2 μm) in MHC I and IIa fibers, respectively ( P < 0.05). Po 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 75% (MHC I) and 45% (MHC IIa) after PRT ( P < 0.05). MHC I and IIa fiber power increased ( P < 0.05) from 7.7 ± 0.5 to 17.6 ± 0.9 μN · fiber lengths · s−1 and from 25.5 to 41.1 μN · fiber lengths · s−1, respectively. These data indicate that PRT in elderly men increases muscle cell size, strength, 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.

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Resistance training improves single muscle fiber contractile function in older women

AJP Cell Physiology ◽

10.1152/ajpcell.2001.281.2.c398 ◽

2001 ◽

Vol 281 (2) ◽

pp. C398-C406 ◽

Cited By ~ 116

Author(s):

Scott Trappe ◽

Michael Godard ◽

Philip Gallagher ◽

Chad Carroll ◽

Greg Rowden ◽

...

Keyword(s):

Resistance Training ◽

Single Cell ◽

Older Women ◽

Muscle Fiber ◽

Peak Power ◽

Older Men ◽

Single Muscle ◽

Mhc I ◽

Before And After ◽

Mhc Iia

The purpose of this study was to 1) examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older women ( n = 7; 74 ± 2 yr) and 2) to compare these results to our previously completed single cell PRT work with older men ( n = 7; 74 ± 2 yr) (Trappe S, Williamson D, Godard M, Porter D, Rowden G, and Costill D. J Applied Physiol 89:143–152, 2000). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsies were obtained from the vastus lateralis before and after the PRT. Chemically skinned single muscle fibers ( n = 313) were studied at 15°C for peak tension (Po), unloaded shortening velocity ( V o), and power. Due to the low number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 24% (90 ± 2 to 112 ± 6 μm; P < 0.05) in MHC I fibers with no change in MHC IIa fibers. Po increased ( P< 0.05) 33% in MHC I (0.76 ± 0.04 to 1.01 ± 0.09 mN) and 14% in MHC IIa (0.73 ± 0.04 to 0.83 ± 0.05 mN) fibers. Muscle fiber V o was unaltered in both fiber types with PRT. MHC I and IIa fiber power increased ( P< 0.05) 50% [11 ± 2 to 17 ± 2 μN · fiber length (FL) · s−1] and 25% (40 ± 8 to 51 ± 6 μN · FL · s−1), respectively. However, when peak power was normalized to cell size, no pre- to postimprovements were observed. These data indicate that PRT in elderly women increases muscle cell size, strength, and peak power in both slow and fast muscle fibers, which was similar to the older men. However, in contrast to the older men, no change in fiber V o or normalized power was observed in the older women. These data suggest that older men and women respond differently at the muscle cell level to the same resistance-training stimulus.

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Improved single muscle fiber quality in the oldest-old

Journal of Applied Physiology ◽

10.1152/japplphysiol.00479.2016 ◽

2016 ◽

Vol 121 (4) ◽

pp. 878-884 ◽

Cited By ~ 22

Author(s):

Greg J. Grosicki ◽

Robert A. Standley ◽

Kevin A. Murach ◽

Ulrika Raue ◽

Kiril Minchev ◽

...

Keyword(s):

Muscle Fiber ◽

Fiber Quality ◽

Oldest Old ◽

Muscle Fibers ◽

Muscle Quality ◽

Vastus Lateralis Muscle ◽

Single Muscle ◽

Mhc I ◽

Single Muscle Fiber ◽

Mhc Iia

We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 yr old) enrolled in The Health, Aging, and Body Composition Study (The Health ABC Study). Vastus lateralis muscle biopsies were obtained and single muscle fiber function was determined ( n = 105) prior to myosin heavy chain (MHC) isoform identification with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-sectional area of MHC I muscle fibers (5,576 ± 333 μm2; n = 58) was 21% larger ( P < 0.05) than MHC IIa fibers (4,518 ± 386 μm2; n = 47). Normalized power (an indicator of muscle fiber quality incorporating size, strength, and speed) of MHC I and IIa muscle fibers was 2.3 ± 0.1 and 17.4 ± 0.8 W/l, respectively. Compared with previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 yr olds and similar to younger octogenarians (∼80 yr old). Normalized power of MHC IIa fibers was 63% greater than 20 yr olds and 39% greater than younger octogenarians. These comparative data suggest that power output per unit size (i.e., muscle quality) of remaining muscle fibers improves with age, a phenomenon more pronounced in MHC IIa fibers. Age-related single muscle fiber quality improvements may be a compensatory mechanism to help offset decrements in whole muscle function.

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Single-muscle fiber contractile properties in lifelong aerobic exercising women

Journal of Applied Physiology ◽

10.1152/japplphysiol.00459.2019 ◽

2019 ◽

Vol 127 (6) ◽

pp. 1710-1719 ◽

Cited By ~ 6

Author(s):

Kevin J. Gries ◽

Kiril Minchev ◽

Ulrika Raue ◽

Gregory J. Grosicki ◽

Gwénaëlle Begue ◽

...

Keyword(s):

Aerobic Exercise ◽

Muscle Fiber ◽

Contractile Properties ◽

Single Muscle ◽

Mhc I ◽

Single Muscle Fiber ◽

Fiber Size ◽

Fast Twitch ◽

Mhc Iia ◽

Lifelong Exercise

The purpose of this study was to examine the effects of lifelong aerobic exercise on single-muscle fiber performance in trained women (LLE; n = 7, 72 ± 2 yr) by comparing them to old healthy nonexercisers (OH; n = 10, 75 ± 1 yr) and young exercisers (YE; n = 10, 25 ± 1 yr). On average, LLE had exercised ~5 days/wk for ~7 h/wk over the past 48 ± 2 yr. Each subject had a vastus lateralis muscle biopsy to examine myosin heavy chain (MHC) I and IIa single-muscle fiber size and function (strength, speed, power). MHC I fiber size was similar across all three cohorts (YE = 5,178 ± 157, LLE = 4,983 ± 184, OH = 4,902 ± 159 µm2). MHC IIa fiber size decreased ( P < 0.05) 36% with aging (YE = 4,719 ± 164 vs. OH = 3,031 ± 153 µm2), with LLE showing a similar 31% reduction (3,253 ± 189 µm2). LLE had 17% more powerful ( P < 0.05) MHC I fibers and offset the 18% decline in MHC IIa fiber power observed with aging ( P < 0.05). The LLE contractile power was driven by greater strength (+11%, P = 0.056) in MHC I fibers and elevated contractile speed (+12%, P < 0.05) in MHC IIa fibers. These data indicate that lifelong exercise did not benefit MHC I or IIa muscle fiber size. However, LLE had contractile function adaptations that enhanced MHC I fiber power and preserved MHC IIa fiber power through different contractile mechanisms (strength vs. speed). The single-muscle fiber contractile properties observed with lifelong aerobic exercise are unique and provide new insights into aging skeletal muscle plasticity in women at the myocellular level. NEW & NOTEWORTHY This is the first investigation to examine the effects of lifelong exercise on single-muscle fiber physiology in women. Nearly 50 yr of moderate to vigorous aerobic exercise training resulted in enhanced slow-twitch fiber power primarily by increasing force production, whereas fast-twitch fiber power was preserved primarily by increasing contractile speed. These unique muscle fiber power profiles helped offset the effects of fast-twitch fiber atrophy and highlight the benefits of lifelong aerobic exercise for myocellular health.

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