Single Muscle Fiber Function Research Articles

Effects of Adjuvant Exercise and Nutrition Therapy on Muscle Fibre Biomechanics in Gastrointestinal Cancer Patients.

Patients with aggressive cancer, e.g., gastrointestinal cancer, are prone (≥50% chance) to developing cancer cachexia (CC). Little is known about the effects of CC on the biomechanical function of muscle. A promising prevention strategy was found in the form of a multi-modal therapy combining mild resistance exercise (e.g., whole-body electro-myostimulation, WB-EMS) and a protein-rich diet. In a previous study of ours, this was effective in counteracting the loss of muscle mass, yet a systematic and comprehensive assessment of active and passive single muscle fibre functions was so far absent. This pilot study investigated the biomechanical function of single muscle fibres (rectus abdominis) from the biopsies of conventionally treated (pre-)cachectic cancer ((pre-)CC) patients (m = 9), those receiving the multi-modal therapy comprising WB-EMS training and protein-rich nutrition (m = 3), and a control group (m = 5). Our findings not only align with previous findings showing the absolute force loss in CC that is accelerated by atrophy but also speak in favour of a different, potentially energy- and Ca2+-homeostasis-related effect that compromises muscle contraction (F ~0.9 mN vs. F ~0.6 mN in control patients). However, myofibrillar Ca2+ sensitivity and the quality of contraction were unaltered (pCa50: 5.6-5.8). Single fibres from the (pre-)CC patients receiving WB-EMS training and protein supplementation were significantly more compliant (p < 0.001 at ≥130% of resting length L0). Those fibres displayed a similar softness to the ones from the control patients (axial compliance ~15 m/N at ≥130% L0), while single fibres from the patients with (developing) cachexia were significantly stiffer (axial compliance ~7 m/N, p < 0.001 at ≥130% L0). Adjuvant multi-modal therapy (WB-EMS training and nutritional support) contributes to maintaining the axial compliance of single fibres and potentially improves the quality of life for patients at risk of developing CC.

Skeletal Muscle Function in the Oldest-Old: The Role of Intrinsic and Extrinsic Factors.

Although skeletal muscle function is diminished with advanced age, single muscle fiber function seems to be preserved. Therefore, this review examines the hypothesis that the skeletal muscle fiber, per se, is not the predominant factor responsible for the reduction in force-generating capacity in the oldest-old, but, rather, is attributable to a combination of factors external to the muscle fibers.

Improved single muscle fiber quality in the oldest-old.

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.

Single Muscle Fiber Characteristics of The Oldest-Old

PURPOSE: To examine single muscle fiber function in the oldest-old. METHODS: Vastus lateralis muscle biopsies were obtained from five healthy independently living individuals (3F/2M, 89 ± 1 y) enrolled in the Health, Aging and Body Composition (Health ABC) Study. Isolated myosin heavy chain (MHC) I and IIa muscle fibers were examined for cross-sectional area (CSA) and contractile properties prior to MHC isoform identification via SDS-PAGE. RESULTS: MHC I muscle fibers were 21% larger (P < 0.05) than MHC IIa. A summary of muscle fiber characteristics is provided below (values are means ± SE). CONCLUSION: This investigation was the first to examine single muscle fiber contractile properties of independently living individuals > 85 y. In line with previous aging research, MHC IIa fibers were smaller than MHC I, indicative of MHC IIa-specific atrophy. Normalized power (an indicator of muscle fiber quality incorporating size, strength and speed) of MHC I fibers from these individuals, when compared to previous research from our lab using identical procedures, was 28% higher than healthy 25 y olds and similar to younger octogenarians (∼82 y). MHC IIa normalized power was 63% greater than 25 y olds and 39% greater than younger octogenarians. These data support the idea that power output per unit size (i.e. muscle quality) of surviving muscle fibers improves with advancing age, a phenomenon more pronounced in MHC IIa fibers. Thus, a likely key contributor to the loss of muscle function with age is a quantitative loss of whole muscle specific force rather than a reduction in muscle quality of remaining muscle fibers.Table: No title available.

Transient impairments in single muscle fibre contractile function after prolonged cycling in elite endurance athletes

Prolonged muscle activity impairs whole-muscle performance and function. However, little is known about the effects of prolonged muscle activity on the contractile function of human single muscle fibres. The purpose of this study was to investigate the effects of prolonged exercise and subsequent recovery on the contractile function of single muscle fibres obtained from elite athletes. Nine male triathletes (26±1years, 68±1mL O2 min(-1) kg(-1) , training volume 16±1hweek(-1) ) performed 4h of cycling exercise (at 73% of HRmax ) followed by 24h of recovery. Biopsies from vastus lateralis were obtained before and following 4h exercise and following 24h recovery. Measurements comprised maximal Ca(2+) -activated specific force and Ca(2+) sensitivity of slow type I and fast type II single muscle fibres, as well as cycling peak power output. Following cycling exercise, specific force was reduced to a similar extent in slow and fast fibres (-15 and -18%, respectively), while Ca(2+) sensitivity decreased in fast fibres only. Single fibre-specific force was fully restored in both fibre types after 24h recovery. Cycling peak power output was reduced by 4-9% following cycling exercise and fully restored following recovery. This is the first study to demonstrate that prolonged cycling exercise transiently impairs specific force in type I and II fibres and decreases Ca(2+) sensitivity in type II fibres only, specifically in elite endurance athletes. Further, the changes in single fibre-specific force induced by exercise and recovery coincided temporally with changes in cycling peak power output.

Resistance training of long duration modulates force and unloaded shortening velocity of single muscle fibres of young women

The aim of the present study was to clarify the impact of long term (1 year) resistance training (RT) on structure and function of single muscle fibres of vastus lateralis in young female subjects. Five young women (age: 25.4 ± 6.2 year) performed exercise sessions at 60% of single subject own repetition maximum (1 RM) 1 h twice a week. Maximum voluntary force was determined pre- and post-RT and was found to significantly increase post-RT ensuring a successful impact of RT on muscle performance in vivo. Needle muscle biopsy samples were obtained both pre- and post-RT and the following determinations were performed: myosin heavy chain isoform (MHC) distribution of the whole muscle samples by SDS–PAGE; cross sectional area (CSA), specific force (Po/CSA) and maximum shortening velocity ( Vo) of a large population ( n = 358) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS–PAGE. The results suggest that the long duration of RT can determine a significant increase in specific force (Po/CSA) and unloaded shortening velocity ( Vo) of single muscle fibres in female subjects, whereas no muscle fibre hypertrophy and no shift in MHC isoform content was observed.

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

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 (approximately 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.

Single muscle fiber function with concurrent exercise or nutrition countermeasures during 60 days of bed rest in women

There is limited information on skeletal muscle properties in women with unloading and countermeasure programs to protect the unloading-induced atrophy. The current investigation tested the hypothesis that a concurrent aerobic and resistance exercise training program would preserve size and contractile function of slow- and fast-twitch muscle fibers. A secondary objective was to test the hypothesis that a leucine-enriched high-protein diet would partially attenuate single fiber characteristics. Vastus lateralis muscle biopsies were obtained before and on day 59 of bed rest from a control (BR; n = 8), nutrition (BRN; n = 8), or exercise (BRE; n = 8) group. Single muscle fibers were studied for diameter, peak force (P(o)), contractile velocity, and power. Those in the BR group had a decrease (P < 0.05) in myosin heavy chain (MHC) I diameter (-14%), P(o) (-35%), and power (-42%) and MHC IIa diameter (-16%) and P(o) (-31%; P = 0.06) and an increase (P < 0.05) in MHC hybrid fibers. Changes in size and function of MHC I (-19 to -44%) and IIa (-21% to -30%) fibers and MHC distribution in BRN individuals were similar to results in the BR group. In BRE conditions, MHC I and IIa size and contractile function were preserved during bed rest. These data show that the concurrent exercise program preserved the myocellular profile of the vastus lateralis muscle during 60-day bed rest. To combat muscle atrophy and function with long-term unloading, the exercise prescription program used in this study should be considered as a viable training program for the upper leg muscles, whereas the nutritional intervention used cannot be recommended as a countermeasure for skeletal muscle.

Influence of exercise and nutrition countermeasures during 60 d of bedrest in women: Soleus single muscle fiber function

Twenty-one women underwent 60 d bedrest (BR, n=7) to examine the effect of a concurrent aerobic (27 sessions) and resistance (19 sessions) exercise (BRE, n=6) or a leucine enriched high protein nutrition (BRN, n=8) countermeasure. Muscle biopsies were obtained before and day 59 of bedrest. Single muscle fibers were studied for diameter (Dia), peak force (Po), normalized peak force (Po/CSA), contractile velocity (Vo) and MHC composition. Only MHC I fibers were included due to low prevalance of other MHC isoforms. Single muscle fiber Dia decreased (P<0.05) 15% in BR (91±3 vs. 77±4 μm), and 14% in BRN (94±3 vs. 81±3 μm). Po decreased (P<0.05) 36% in BR (0.52± 0.04 vs. 0.33±0.03 mN) and 21% in BRN (0.60±0.06 vs. 0.44±0.03 mN). No changes in Po/CSA or Vo were observed in BR, BRN or BRE. For the BRE group, three individuals increased Dia (+5%) and Po (+18%) and three individuals had a decline in Dia (−22%) and Po (−48%). As a result, a non-significant decline in Dia (−10%) and Po (−18%) were observed for the entire BRE group. These data show that individual responses in the BRE group were apparent for the soleus MHC I fibers. A homogeneous decline in the BRN group and the similarity to the BR group indicates that the nutritional countermeasure did not provide a benefit for the MHC I soleus muscle fibers. Sponsors: NASA, ESA, CNES

Influence of exercise and nutrition countermeasures during 60 d of bedrest in women: Vastus lateralis single muscle fiber function

Twenty-four women underwent 60 d of bedrest (BR, n=8) to examine the effect of a concurrent aerobic (27 sessions) and resistance (19 sessions) exercise (BRE, n=8) or a leucine enriched high protein nutrition (BRN, n=8) countermeasure. Muscle biopsies were obtained before and day 59 of bedrest. Slow (MHC I) and fast (MHC IIa) muscle fibers were studied for diameter (Dia), peak force (Po), normalized peak force (Po/CSA), contractile velocity (Vo), and MHC composition. BR had a decrease (P<0.05) in MHC I Dia (−13%), Po (−36%), and Po/CSA (−17%). A similar trend was observed in BR MHC IIa fibers for Dia (−15%; P=0.09) and Po (−25%; P=0.14). BRN had a decrease (P<0.05) in MHC I Dia (−18%) and Po (−38%) and MHC IIa Dia (−26%). BRN had a trend for a decrease in MHC IIa Po (−41%; P=0.10). BR and BRN MHC I and IIa Vo was unchanged. BRE MHC I and IIa fiber Dia, Po, Po/CSA, and Vo were unchanged with bedrest. These data show that the MHC I fibers were more affected than the MHC IIa fibers with bedrest. The concurrent exercise-training program preserved MHC I and IIa diameter and contractile function during bedrest. The nutrition countermeasure did not provide any benefit for myofiber diameter or peak tension. Sponsors: NASA, ESA, CNES

Effect of Marathon Run Training On Single Muscle Fiber Function

Effect of Marathon Run Training On Single Muscle Fiber Function

Effect of Marathon Run Training On Single Muscle Fiber Function

Effect of Marathon Run Training On Single Muscle Fiber Function