Reduction in single muscle fiber rate of force development with aging is not attenuated in world class older masters athletes

Normal adult aging is associated with impaired muscle contractile function; however, to what extent cross-bridge kinetics are altered in aging muscle is not clear. We used a slacken restretch maneuver on single muscle fiber segments biopsied from the vastus lateralis of young adults (∼23 yr), older nonathlete (NA) adults (∼80 yr), and age-matched world class masters athletes (MA; ∼80 yr) to assess the rate of force redevelopment ( ktr) and cross-bridge kinetics. A post hoc analysis was performed, and only the mechanical properties of “slow type” fibers based on unloaded shortening velocity ( Vo) measurements are reported. The MA and NA were ∼54 and 43% weaker, respectively, for specific force compared with young. Similarly, when force was normalized to cross-sectional area determined via the fiber shape angularity data, both old groups did not differ, and the MA and NA were ∼43 and 48% weaker, respectively, compared with young ( P < 0.05). Vo for both MA and NA old groups was 62 and 46% slower, respectively, compared with young. Both MA and NA adults had approximately two times slower values for ktr compared with young. The slower Vo in both old groups relative to young, coupled with a similarly reduced ktr, suggests impaired cross-bridge kinetics are responsible for impaired single fiber contractile properties with aging. These results challenge the widely accepted resilience of slow type fibers to cellular aging.

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

Journal of Applied Physiology ◽

10.1152/jappl.2001.91.5.1955 ◽

2001 ◽

Vol 91 (5) ◽

pp. 1955-1961 ◽

Cited By ~ 97

Author(s):

D. L. Williamson ◽

P. M. Gallagher ◽

C. C. Carroll ◽

U. Raue ◽

S. W. Trappe

Keyword(s):

Resistance Training ◽

Muscle Fiber ◽

Vastus Lateralis ◽

Electrophoretic Analysis ◽

Training Data ◽

Single Muscle ◽

Hybrid Fibers ◽

Mhc I ◽

Single Muscle Fiber ◽

Mhc Iia

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

The Aging Male ◽

10.1080/13685530008500350 ◽

2000 ◽

Vol 3 (4) ◽

pp. 217-218

Keyword(s):

Resistance Training ◽

Muscle Fiber ◽

Contractile Function ◽

Older Men ◽

Single Muscle ◽

Single Muscle Fiber

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Preserved single muscle fiber specific force in facioscapulohumeral muscular dystrophy

Neurology ◽

10.1212/wnl.0000000000008977 ◽

2020 ◽

Vol 94 (11) ◽

pp. e1157-e1170 ◽

Cited By ~ 2

Author(s):

Saskia Lassche ◽

Nicol C. Voermans ◽

Robbert van der Pijl ◽

Marloes van den Berg ◽

Arend Heerschap ◽

...

Keyword(s):

Muscle Fiber ◽

Vastus Lateralis ◽

Muscle Fibers ◽

Fatty Infiltration ◽

Facioscapulohumeral Muscular Dystrophy ◽

Single Muscle ◽

Healthy Controls ◽

Specific Force ◽

Single Muscle Fiber ◽

Muscle Biopsies

ObjectiveTo investigate single muscle fiber contractile performance in muscle biopsies from patients with facioscapulohumeral muscular dystrophy (FSHD), one of the most common hereditary muscle disorders.MethodsWe collected 50 muscle biopsies (26 vastus lateralis, 24 tibialis anterior) from 14 patients with genetically confirmed FSHD and 12 healthy controls. Single muscle fibers (n = 547) were isolated for contractile measurements. Titin content and titin phosphorylation were examined in vastus lateralis muscle biopsies.ResultsSingle muscle fiber specific force was intact at saturating and physiologic calcium concentrations in all FSHD biopsies, with (FSHDFAT) and without (FSHDNORMAL) fatty infiltration, compared to healthy controls. Myofilament calcium sensitivity of force is increased in single muscle fibers obtained from FSHD muscle biopsies with increased fatty infiltration, but not in FSHD muscle biopsies without fatty infiltration (pCa50: 5.77–5.80 in healthy controls, 5.74–5.83 in FSHDNORMAL, and 5.86–5.90 in FSHDFAT single muscle fibers). Cross-bridge cycling kinetics at saturating calcium concentrations and myofilament cooperativity did not differ from healthy controls. Development of single muscle fiber passive tension was changed in all FSHD vastus lateralis and in FSHDFAT tibialis anterior, resulting in increased fiber stiffness. Titin content was increased in FSHD vastus lateralis biopsies; however, titin phosphorylation did not differ from healthy controls.ConclusionMuscle weakness in patients with FSHD is not caused by reduced specific force of individual muscle fibers, even in severely affected tissue with marked fatty infiltration of muscle tissue.

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Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00761.2007 ◽

2008 ◽

Vol 294 (3) ◽

pp. R939-R947 ◽

Cited By ~ 45

Author(s):

Scott Trappe ◽

Andrew Creer ◽

Kiril Minchev ◽

Dustin Slivka ◽

Emily Louis ◽

...

Keyword(s):

Muscle Fiber ◽

Soleus Muscle ◽

Contractile Function ◽

Exercise Program ◽

Bed Rest ◽

Single Fiber ◽

Single Muscle ◽

Mhc I ◽

Single Muscle Fiber ◽

Concurrent Exercise

The soleus muscle has been consistently shown to atrophy more than other leg muscles during unloading and is difficult to protect using various exercise countermeasure paradigms. However, the efficacy of aerobic exercise, a known stimulus for oxidative adaptations, has not been tested in combination with resistance exercise (RE), a known hypertrophic stimulus. We hypothesized that a concurrent exercise program (AE + RE) would preserve soleus fiber myosin heavy chain (MHC) I size and function during 60 days of bed rest. A secondary objective was to test the hypothesis that a leucine-enriched high protein diet would partially protect soleus single fiber characteristics. Soleus muscle biopsies were obtained before and after bed rest from a control (BR; n = 7), nutrition (BRN; n = 8), and exercise (BRE; n = 6) group. Single muscle fiber diameter (Dia), peak force (Po), contractile velocity, and power were studied. BR decreased ( P < 0.05) MHC I Dia (−14%), Po (−38%), and power (−39%) with no change in contractile velocity. Changes in MHC I size (−13%) and contractile function (∼30%) from BRN were similar to BR. BRE decreased ( P < 0.05) MHC I Dia (−13%) and Po (−23%), while contractile velocity increased ( P < 0.05) 26% and maintained power. These soleus muscle data show 1) the AE + RE exercise program maintained MHC I power but not size and strength, and 2) the nutrition countermeasure did not benefit single fiber size and contractile function. The divergent response in size and functional MHC I soleus properties with the concurrent exercise program was a unique finding further highlighting the challenges of protecting the unloaded soleus.

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