Fiber Type Distribution Research Articles

Diaphragm muscle sarcopenia in Fischer 344 and Brown Norway rats.

What is the central question of this study? Several rat models are commonly used to study the physiology of ageing (e.g. Fischer 344 and Brown Norway rats are recommended by the USA National Institute of Ageing). Diaphragm muscle sarcopenia (ageing-related muscle weakness and atrophy) remains incompletely described in these rat models. What is the main finding and its importance? Diaphragm muscle sarcopenia is present in both the Fischer 344 and Brown Norway rat strains, but appears more pronounced in Fischer 344 rats. The risk for respiratory diseases increases in adults >65years of age, which may be attributable in part to ageing-related weakening and atrophy (i.e. sarcopenia) of the diaphragm muscle (DIAm). The mechanisms underlying DIAm sarcopenia remain unknown. Based on existing evidence, we hypothesized that sarcopenia is most evident in typeIIx and/or IIb DIAm fibres, i.e. more fatigable motor units. Currently, the USA National Institute on Aging supports Fischer 344 (F344) and Brown Norway (BN) rat strains for ageing-related research, yet DIAm sarcopenia has not been evaluated comprehensively in either strain. Thus, the present study examined DIAm sarcopenia in older adult F344 (24 months old, 50% survival) and BN rats (32months old, 50% survival), compared with young adult (6-month-old) F344 and BN rats. Measurements of contractility, contractile protein concentration, fibre type distribution and fibre cross-sectional area were obtained from midcostal DIAm strips. Maximal specific force was reduced by ∼24 and ∼13% in older F344 and BN rats, respectively. Additionally, although the cross-sectional area of typeI and IIa DIAm fibres was unchanged in both F344 and BN rats, the cross-sectional area of typeIIx and/or IIb DIAm fibres was reduced by ∼20 and ∼15% in F344 and BN rats, respectively. Thus, although there was ageing-related DIAm weakness and atrophy, selective to typeIIx and/or IIb DIAm fibres, in both F344 and BN rats, the sarcopenic phenotype was more pronounced in F344 rats.

Skeletal Muscle Phenotype and Performance of an Elite Mixed Martial Artist

PURPOSE: Mixed martial arts (MMA) requires a unique combination of muscular strength, power, and endurance. However, little is known regarding elite MMA athletes muscle characteristics at the cellular level. The purpose of this study was to determine the myocellular phenotype [fiber type, size, and myonuclear domain (MND) size] and whole muscle performance of an elite MMA fighter. METHODS: One male MMA athlete [Record: 8 wins, 2 losses; Ranked: top 10 in the Ultimate Fighting Championship (UFC) Light Heavyweight Division] volunteered to participate in this study [Age: 33 y, Height: 1.89 m, Mass: 102.1 kg (competes at 93.0 kg)]. The participant underwent a vastus lateralis muscle biopsy to analyze myocellular characteristics, which included myosin heavy chain (MHC) fiber type distribution (via SDS-PAGE), fiber size (cross-sectional area; CSA), and MND size (via immunofluorescent labeling and confocal microscopy). Whole muscle performance measures included hand grip dynamometry, peak isometric mid-thigh pulls, vertical jump (measured with no counter-movement), and 5 repeat Wingate Anaerobic Tests (WAnT). RESULTS: Muscle fiber type composition was 29% MHC I (pure slow-twitch fibers), 66% MHC IIa (pure fast-twitch fibers) and 5% hybrid fibers (containing multiple MHC types). Mean ± SE fiber CSA and MND size were 3,183 ± 225 m2 and 11,008 ± 1,331 m3, respectively. His grip strength was 78.4 kg, isometric mid-thigh pull peak force was 37.7 N/kg, and vertical jump was 57.2 cm. Additionally, the WAnT determined his peak power (PP): 1,075.89 W, relative PP: 10.45 W/kg, average power (AP): 838.87 W, fatigue index: 43.39%, and PP decrease over 5 rounds: 12.1%. CONCLUSIONS: This elite MMA athlete exhibited a homogeneous muscle fiber type (i.e. predominantly fast-twitch with few hybrids) with relatively small MND sizes compared to untrained men in the literature (using similar measures). These cellular characteristics may help partially explain the athletes elevated whole muscle strength, power, and endurance performance. This case study provides initial insight into the muscle physiology of high-level MMA fighters; future research should continue investigating the myocellular structure/function relationship among these unique athletes to further our knowledge regarding elite human muscle physiology.

The mechanistic bases of the power-time relationship: muscle metabolic responses and relationships to muscle fibre type.

The power-asymptote (critical power; CP) of the hyperbolic power-time relationship for high-intensity exercise defines a threshold between steady-state and non-steady-state exercise intensities and the curvature constant (W') indicates a fixed capacity for work >CP that is related to a loss of muscular efficiency. The present study reports novel evidence on the muscle metabolic underpinnings of CP and W' during whole-body exercise and their relationships to muscle fibre type. We show that the W' is not correlated with muscle fibre type distribution and that it represents an elevated energy contribution from both oxidative and glycolytic/glycogenolytic metabolism. We show that there is a positive correlation between CP and highly oxidative type I muscle fibres and that muscle metabolic steady-state is attainable <CP but not >CP. Our findings indicate a mechanistic link between the bioenergetic characteristics of muscle fibre types and the power-time relationship for high-intensity exercise. We hypothesized that: (1) the critical power (CP) will represent a boundary separating steady-state from non-steady-state muscle metabolic responses during whole-body exercise and (2) that the CP and the curvature constant (W') of the power-time relationship for high-intensity exercise will be correlated with type I and type IIx muscle fibre distributions, respectively. Four men and four women performed a 3min all-out cycling test for the estimation of CP and constant work rate (CWR) tests slightly >CP until exhaustion (Tlim ), slightly <CP for 24min and until the >CP Tlim isotime to test the first hypothesis. Eleven men performed 3min all-out tests and donated muscle biopsies to test the second hypothesis. Below CP, muscle [PCr] [42.6±7.1vs. 49.4±6.9mmol(kgd.w.)(-1) ], [La(-) ] [34.8±12.6vs. 35.5±13.2mmol(kgd.w.)(-1) ] and pH (7.11±0.08 vs. 7.10±0.11) remained stable between ∼12 and 24min (P>0.05 for all), whereas these variables changed with time >CP such that they were greater [[La(-) ] 95.6±14.1mmol(kgd.w.)(-1) ] and lower [[PCr] 24.2±3.9mmol(kgd.w.)(-1) ; pH 6.84±0.06] (P<0.05) at Tlim (740±186s) than during the <CP trial. The CP (234±53W) was correlated with muscle type I (r=0.67, P=0.025) and inversely correlated with muscle type IIx fibre proportion (r=-0.76, P=0.01). There was no relationship between W' (19.4±6.3kJ) and muscle fibre type. These data indicate a mechanistic link between the bioenergetic characteristics of different muscle fibre types and the power-duration relationship. The CP reflects the bioenergetic characteristics of highly oxidative type I muscle fibres, such that a muscle metabolic steady-state is attainable below and not above CP.

Resistance Training-induced Muscle Hypertrophy Is Not Determined By Repetition-load In Resistance-trained Men

We have previously shown that performing resistance exercise (RE) with high or low repetition-loads resulted in similar acute (protein turnover) and chronic (hypertrophy) adaptations. However, these studies were performed in RE-naïve trainees using unilateral leg exercises. Here we aimed to determine the effect of repetition-load on skeletal muscle hypertrophy and strength with a 12wk, whole-body RE intervention in RE-trained (RET) young men. We also evaluated the change and correlations of the post-RE rise in systemic hormone concentrations in relation to changes in skeletal muscle hypertrophy and strength. Forty-nine RET men (mean ± SEM, 23 ± 1 y, 86 ± 2 kg, 181 ± 1 cm) were randomly allocated into a high-repetition (lower load - 30-50% 1RM) group (HR: 20-25 repetitions/set, n=24) or a low-repetition (higher load - 70-90% 1RM) group (LR, 8-12 repetitions/set, n=25). Muscular strength increased for all exercises (p <0.01) and only the change in bench press was different between groups (HR; 9 ± 1, LR; 14 ±1 kg, p < 0.05). Lean body mass, type I and type II muscle fiber cross sectional area all increased following training (p < 0.01) with no significant differences between groups. There was no change in fibre type distribution pre- to post-intervention and no differences between groups. The acute post-RE rise in systemic hormones did not change as a result of training. The post-RE rise in total testosterone, insulin-like growth factor-1 and growth hormone had no correlation with any strength or hypertrophy outcome. These data show that in RET individuals repetition-load is a determinant of neither strength nor hypertrophic gains when RE is performed to volitional failure. In accordance with our previous findings we conclude that the post-RE rise in systemic hormones is not associated with or in any way predictive of changes in skeletal muscle hypertrophy or strength.

Post Activation Potentiation in Upper and Lower Extremities

Post-Activation Potentiation (PAP) occurs when muscular performance during a fast, powerful movement increases due to a prior high force contraction. Previous researcher has found PAP in the lower extremity (LE) when a vertical jump is performed immediately after a set of heavy back squats. Yet, there has been limited observation of PAP in the upper extremity (UE). PURPOSE: To determine whether performing PAP exercises in the UE will be equally effective as in the LE. METHODS: 15 resistance trained men (age = 21.8±1.5 y, height = 1.81±0.1 m, body mass = 89.3±8.9 kg) had their one repetition maximum (1RM) back squat and bench press (153.7±27.9 kg and 117.9±19.9 kg, respectively) determined for proper load to activate PAP effects. On a subsequent day subjects performed fast, powerful movements pre- and post PAP enhancing resistance exercises (3 repetitions at 80% 1RM), which included vertical jump pre & post a back squat (LE) and bench press throw on smith-machine pre & post a bench press (UE). Force data of these performance exercises were collected using a force plate and peak force and center of mass velocity and power were measured pre- and post-PAP exercises for comparison. Significance was determined using a paired t-test. RESULTS: Peak force increased pre- to post-PAP exercises in both LE and UE, yet neither was significant (LE: 1863.3±212.2 N vs 1931.3±323.1 N, p=0.11; UE: 1829.5±292.3 N vs. 1841.5±253.9 N, p=0.73, respectively). There were no significant PAP improvements in performance in the LE or UE. CONCLUSION: Because majority of participants did not show PAP, there was no overall significance in the study. Some subjects exhibited positive PAP effects in both LE and UE, while others exhibited a decrease in performance. This corroborates several other studies that have noted PAP “responders” and “non-responders” potentially due to differences in training status or fiber type distribution patterns.

The effect of one-week intensive feed restriction and age on the carcass composition and meat quality of growing rabbits

The effect of one-week intensive feed restriction on the carcass characteristics, meat tenderness, cooking loss, and muscle fibre characteristics of growing rabbits was evaluated. Weaned rabbits (35 days) were divided into three groups: rabbits fed ad libitum (ADL), rabbits fed 50 g (R50), and rabbits fed 65 g (R65) of feed per animal per day in days 42-49 of age. Dressing out percentage was lower (-1.3% and -2.3% for R50 and R65, respectively) in restricted rabbits (P ≤ 0.001) but increased with age (P ≤ 0.001). Cooking loss signifi- cantly increased in restricted rabbits. A significant interaction between feeding regime and age was observed in the number of type αR muscle fibres, the highest number (P ≤ 0.05) was observed in the ADL rabbits (114.5) at 49 days, and the lowest was found in the R50 group at 70 days of age (25.0). Feed restriction increased the percentage of αW glycolytic fibres (P ≤ 0.01). A significant negative correlation was found between cooking loss and the cross sectional area of αW fibres (-0.486) and αR (-0.325). It could be concluded that one-week intensive feed restriction did not have a negative effect on meat tenderness and cooking loss, despite the fact that it affected muscle fibre type distribution.

Dietary Nitrate (NO3−)‐Induced Increases in Skeletal Muscle Contractile Function: High vs. Low Responders

We have recently reported that acute ingestion of dietary NO3−, an important source of nitric oxide (NO) via the enterosalivary pathway, increases the maximal speed and power of skeletal muscle in healthy individuals, in athletes, and in patients with systolic heart failure. This ergogenic effect is hypothesized to be the result of NO‐mediated stimulation of soluble guanyl cyclase and hence production of cyclic GMP. However, consistent with studies of the effects of dietary NO3− on blood pressure or aerobic exercise performance, not all of the subjects we studied previously demonstrated comparable improvements in muscle speed and/or power. In the present investigation we sought to identify factors contributing to this interindividual variability. Eighteen healthy subjects (12 men and 6 women) ranging in age from 22 to 79 (mean 48±20) y were studied used a randomized, double‐blind, placebo‐controlled, crossover design. On one occasion, subjects were tested 2 h after ingesting a concentrated beetroot juice (BRJ) supplement containing 11.2 mmol NO3−. On another, they were tested 2 h after ingesting BRJ depleted of NO3− (placebo). Breath NO was measured periodically as an indicator of NO bioavailability, and muscle contractility was assessed using isokinetic dynamometry. For all subjects combined, dietary NO3− increased (P&lt;0.05) peak knee extensor torque, and hence power, at 6.28 rad/s (~½maximal velocity; Vmax) from 6.38±2.16 to 6.53±2.33 W/kg, or by 2.4%. Individual changes, however, ranged from −21.5 to +26.8%, with 14 of 18 subjects being positive “responders”. This interindividual variability was not significantly correlated with age (i.e., r=−0.19; P=0.45), with in vivo indicators of muscle fiber type distribution, i.e., baseline Vmax (i.e., r=0.10; P=0.68) or fatigability (i.e., r=−0.14; P=0.58), or with the increase in breath NO in either absolute (i.e., r=−0.21; P=0.41) or relative (i.e., r=−0.18; P=0.46) terms. In contrast, significant positive correlations were observed between the magnitude of the dietary nitrate NO3− ‐induced increase in power and female sex (i.e., r=0.53; P=0.02) and dose of NO3−/kg of body mass (i.e., r=0.47; P=0.05). However, the latter correlation appears to have simply been the result of the women being lighter on average, as there was no correlation between the relative improvement in muscle power and dose of NO3−/kg of body mass when the men (i.e., r=0.14; P=0.66) or women (i.e., r=0.26; P=0.62) were analyzed separately. We conclude that the magnitude of the dietary NO3− ‐induced increase in muscle power is independent of age, baseline muscle function, or increase in whole‐body NO bioavailability, but that women generally benefit more than men. The effect of NO3− dose on muscle speed and power, on the other hand, awaits further study.Support or Funding InformationResearch reported in this publication was supported by the Barnes‐Jewish Hospital Foundation, the Washington University Mentors in Medicine and C‐STAR programs, and Washington University Institute of Clinical and Translational Sciences grant UL1 TR000448 from the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not necessarily represent the official view of the NIH.

Diaphragm abnormalities in heart failure and aging: mechanisms and integration of cardiovascular and respiratory pathophysiology.

Inspiratory function is essential for alveolar ventilation and expulsive behaviors that promote airway clearance (e.g., coughing and sneezing). Current evidence demonstrates that inspiratory dysfunction occurs during healthy aging and is accentuated by chronic heart failure (CHF). This inspiratory dysfunction contributes to key aspects of CHF and aging cardiovascular and pulmonary pathophysiology including: (1) impaired airway clearance and predisposition to pneumonia; (2) inability to sustain ventilation during physical activity; (3) shallow breathing pattern that limits alveolar ventilation and gas exchange; and (4) sympathetic activation that causes cardiac arrhythmias and tissue vasoconstriction. The diaphragm is the primary inspiratory muscle; hence, its neuromuscular integrity is a main determinant of the adequacy of inspiratory function. Mechanistic work within animal and cellular models has revealed specific factors that may be responsible for diaphragm neuromuscular abnormalities in CHF and aging. These include phrenic nerve and neuromuscular junction alterations as well as intrinsic myocyte abnormalities, such as changes in the quantity and quality of contractile proteins, accelerated fiber atrophy, and shifts in fiber type distribution. CHF, aging, or CHF in the presence of aging disturbs the dynamics of circulating factors (e.g., cytokines and angiotensin II) and cell signaling involving sphingolipids, reactive oxygen species, and proteolytic pathways, thus leading to the previously listed abnormalities. Exercise-based rehabilitation combined with pharmacological therapies targeting the pathways reviewed herein hold promise to treat diaphragm abnormalities and inspiratory muscle dysfunction in CHF and aging.

Skeletal muscle fiber size and fiber type distribution in human cancer: Effects of weight loss and relationship to physical function

Cancer patients frequently experience weight loss, with negative consequences for functionality and prognosis. The extent to which muscle atrophy contributes to weight loss, however, is not clear, as few studies have directly measured muscle fiber morphology in cancer patients. Whole body and regional tissue composition were measured, along with the cross-sectional area (CSA) and fiber type of mechanically-isolated, single muscle fibers, in 19 cancer patients (8 with a history of weight loss, 11 weight-stable) and 15 non-diseased controls. Whole body fat mass was reduced in cancer patients with a history of weight loss, but no differences in whole body or leg fat-free mass were apparent. In contrast, reductions (∼20%) in single muscle fiber CSA were found in both slow-twitch, myosin heavy chain (MHC) I and fast-twitch, MHC IIA fibers in both weight-stable patients and those with a history of weight loss. Fiber type distribution showed a shift towards a fast-twitch phenotype compared to controls, which may preserve muscle function in cancer patients despite atrophy, as positive relationships were found between the fractions of hybrid MHC IIAX and I/IIA fibers and 6-min walk performance. Our results suggest that, although not apparent from whole body or regional measurements, cancer is associated with reduced skeletal muscle fiber size independent of weight loss history and a shift towards fast-twitch fibers, phenotypes that resemble adaptations to muscle disuse.

Comparison of M.Semitendinosus Morphometry and Structure in Gilts and Barrows at Market Age

Abstract The aim of this paper was to investigate the differences in morphometric characteristics and histological structure of m. semitendinosus, between gilts and barrows of German Landrace breed at the end of the fattening period. Morphometric characteristics (weight, length, diameter and cross sectional area) of m. semitendinosus were not significantly different, while gender as a factor influenced the histological properties of this muscle. A very high statistical difference (p&lt;0.01) in the total number of muscle fibers in m. semitendinosus was determined, with gilts having a higher total fiber number. The cross sectional area of fast twitch oxidative (FTO) fibers was significantly higher (p&lt;0.05) in barrows. Gender did not affect the distribution of different fiber types: in both gender, the most present fiber types (48-52 %) were fast twitch glycolitic (FTG), FTO fibers represented 27-30 % of the total fiber number, while slow twitch oxidative fibers (STO) were the least represented (≈ 20 %).

ID 113 – Neurophysiology and biopsy of paraspinal muscles in idiopathic scoliosis

Objective The pathogenesis of idiopathic scoliosis (IS) remains poorly understood. Local changes in deep paraspinal muscles and/or dysfunction of spinal inhibitory circuits are not fully elucidated. We compared the morphological and functional changes of paraspinal muscles on both sides of the scoliosis curve. Methods Before corrective surgery we performed EMG and muscle biopsy of paraspinal muscles at convexity and concavity of scoliotic curve in 10 subjects with IS (8 women, 11–29years). Cutaneous silent period (CSP) induced by noxious digit II stimulation in thenar muscles was recorded in IS patients and in healthy volunteers. Results Right curve convexity had 8 subjects. All of them presented changes in muscle fiber distribution with numerical predominance of type I on the curve convexity. Seven subjects have increased MUP amplitude on this side (range 10–62%). CSP did not significantly differ between concavity and convexity but shortening of CSP duration was observed in more pronounced scoliotic curve. Conclusion Our findings demonstrate a significant asymmetry in fiber type distribution corresponding with an altered function in paraspinal muscles with predominance on convexity of scoliotic curve. Spinal inhibitory reflex is preserved; however, it could be modulated in more progressive IS. Supported by Grants PRVOUK P34, IGA-NT 13693.

Improving human skeletal muscle myosin heavy chain fiber typing efficiency.

Single muscle fiber sodium dodecyl sulfate polyacrylamide gel-electrophoresis (SDS-PAGE) is a sensitive technique for determining skeletal muscle myosin heavy chain (MHC) composition of human biopsy samples. However, the number of fibers suitable to represent fiber type distribution via this method is undefined. Muscle biopsies were obtained from the vastus lateralis (VL) of nine resistance-trained males (25±1year, height=179±5cm, mass=82±8kg). Single fiber MHC composition was determined via SDS-PAGE. VL fiber type distribution [percent MHC I, I/IIa, IIa, IIa/IIx, and total "hybrids" (i.e. I/IIa+IIa/IIx)] was evaluated according to number of fibers analyzed per person (25 vs. 125). VL fiber type distribution did not differ according to number of fibers analyzed (P>0.05). VL biopsy fiber type distribution of nine subjects is represented by analyzing 25 fibers per person. These data may help minimize cost, personnel-time, and materials associated with this technique, thereby improving fiber typing efficiency in humans.

Muscle Quality is More Impaired in Sarcopenic Patients With Chronic Obstructive Pulmonary Disease

BackgroundQuadriceps muscle fiber atrophy and a loss of oxidative type I muscle fibers and mitochondrial content often occur in chronic obstructive pulmonary disease (COPD), which adversely affects exercise performance. Sarcopenia is an age-related syndrome characterized by wasting and weakness of muscle mass. We recently showed in a large cohort of patients that COPD-related sarcopenia, in particular in male patients, was not only associated with impaired quadriceps muscle strength but also with decreased exercise performance endurance, which could imply involvement of altered muscle fiber type composition. Hence, we hypothesized that both the fiber atrophy and loss of oxidative muscle fibers are more pronounced in sarcopenic compared with nonsarcopenic patients with COPD. ObjectiveThe objective of this study was to investigate quadriceps muscle fiber-type characteristics in relation to presence of sarcopenia in patients with COPD and in healthy age-matched controls. DesignFor this retrospective cross-sectional study, body composition (assessed by dual-energy x-ray absorptiometry) and quadriceps muscle biopsy (fiber type distribution and sizes) data were collected from 45 patients with COPDs (aged 42–77 years) and 52 healthy controls (aged 50–77 years). Sarcopenia was based on assessment of appendicular skeletal muscle mass index. ResultsSarcopenia was found in 5.8% of healthy controls and in 31.1% of patients with COPD (P < .01). The proportion of oxidative type I fibers and size of type IIx muscle fibers were decreased in patients with COPD, and the sarcopenic subgroup showed a further decreased proportion as well as a lower size of type I fibers. ConclusionsType I muscle fiber proportion is lower in sarcopenic compared with nonsarcopenic patients with COPD. Longitudinal studies may elucidate if the loss of muscle oxidative phenotype drives or accelerates the process of muscle wasting.

Mitochondrial impairment induced by postnatal ActRIIB blockade does not alter function and energy status in exercising mouse glycolytic muscle in vivo

Because it leads to a rapid and massive muscle hypertrophy, postnatal blockade of the activin type IIB receptor (ActRIIB) is a promising therapeutic strategy for counteracting muscle wasting. However, the functional consequences remain very poorly documented in vivo. Here, we have investigated the impact of 8-wk ActRIIB blockade with soluble receptor (sActRIIB-Fc) on gastrocnemius muscle anatomy, energy metabolism, and force-generating capacity in wild-type mice, using totally noninvasive magnetic resonance imaging (MRI) and dynamic(31)P-MRS. Compared with vehicle (PBS) control, sActRIIB-Fc treatment resulted in a dramatic increase in body weight (+29%) and muscle volume (+58%) calculated from hindlimb MR imaging, but did not alter fiber type distribution determined via myosin heavy chain isoform analysis. In resting muscle, sActRIIB-Fc treatment induced acidosis and PCr depletion, thereby suggesting reduced tissue oxygenation. During an in vivo fatiguing exercise (6-min repeated maximal isometric contraction electrically induced at 1.7 Hz), maximal and total absolute forces were larger in sActRIIB-Fc treated animals (+26 and +12%, respectively), whereas specific force and fatigue resistance were lower (-30 and -37%, respectively). Treatment with sActRIIB-Fc further decreased the maximal rate of oxidative ATP synthesis (-42%) and the oxidative capacity (-34%), but did not alter the bioenergetics status in contracting muscle. Our findings demonstrate in vivo that sActRIIB-Fc treatment increases absolute force-generating capacity and reduces mitochondrial function in glycolytic gastrocnemius muscle, but this reduction does not compromise energy status during sustained activity. Overall, these data support the clinical interest of postnatal ActRIIB blockade.

Effects of Two Different Weight Training Programs on Swimming Performance and Muscle Enzyme Activities and Fiber Type.

The effects of 2 different weight training programs incorporating bench press (BP) and pullover (PO) exercises on swimming performance, power, enzyme activity, and fiber type distribution were studied on 16 men (age = 23 ± 4 years). A 30-second group (n = 6) performed up to 20 repetitions of BP and PO in 30 seconds. The 2-minute group (n = 6) performed a maximum of 80 repetitions of BP and PO in 2 minutes. As participants reached the prescribed 20 or 80 repetitions, the weight was increased 4.5 kg. A third group (n = 4) served as nontraining controls. Exercise groups trained 3 times per week for 6 weeks. Maximal effort swims of 50 and 200 yd were performed before and after training. Training resulted in increases in work on both exercises in both groups pre- to post-training (BP 30 seconds, 722 ± 236-895 ± 250 kg; PO 30 seconds, 586 ± 252-1,090 ± 677 kg; and BP 2 minutes, 1,530 ± 414-1,940 ± 296; PO 2 minutes, 1,212 ± 406-2,348 ± 194, p ≤ 0.05). Swim performances of the 30-second group improved for both the 50-yd (32.0 ± 6.9 seconds, 30.0 ± 5.9 seconds, p ≤ 0.05) and 200-yd swims 200.0 ± 54 seconds, 182 ± 45.1 seconds (p ≤ 0.05), whereas 2-minute training improved only the 200-yd swim (198.3 ± 32.3 seconds, 186.2 ± 32.2 seconds). No changes in swim performance were observed for the control group. Triceps muscle succinate dehydrogenase activities increased (pre 3.48 ± 1.1 μmol · g(-1) wet weight per minute, post 6.25 ± 1.5 μmoles · g(-1) wet weight per minute, p ≤ 0.05) in only the 30-second training group, whereas phosphofructokinase activities and fiber type distribution did not change in either training group. This study has demonstrated that a 30-second 20-repetition weight training program, specific to the swimming musculature without concurrent swim training, improves swimming performances at both 50- and 200-yd distances.

Hierro y ejercicio en la insuficiencia cardiaca: ¿cómo evaluar los cambios relevantes?

Quadriceps muscle fiber atrophy and a loss of oxidative type I muscle fibers and mitochondrial content often occur in chronic obstructive pulmonary disease (COPD), which adversely affects exercise performance. Sarcopenia is an age-related syndrome characterized by wasting and weakness of muscle mass. We recently showed in a large cohort of patients that COPD-related sarcopenia, in particular in male patients, was not only associated with impaired quadriceps muscle strength but also with decreased exercise performance endurance, which could imply involvement of altered muscle fiber type composition. Hence, we hypothesized that both the fiber atrophy and loss of oxidative muscle fibers are more pronounced in sarcopenic compared with nonsarcopenic patients with COPD.The objective of this study was to investigate quadriceps muscle fiber-type characteristics in relation to presence of sarcopenia in patients with COPD and in healthy age-matched controls.For this retrospective cross-sectional study, body composition (assessed by dual-energy x-ray absorptiometry) and quadriceps muscle biopsy (fiber type distribution and sizes) data were collected from 45 patients with COPDs (aged 42–77 years) and 52 healthy controls (aged 50–77 years). Sarcopenia was based on assessment of appendicular skeletal muscle mass index.Sarcopenia was found in 5.8% of healthy controls and in 31.1% of patients with COPD (P < .01). The proportion of oxidative type I fibers and size of type IIx muscle fibers were decreased in patients with COPD, and the sarcopenic subgroup showed a further decreased proportion as well as a lower size of type I fibers.Type I muscle fiber proportion is lower in sarcopenic compared with nonsarcopenic patients with COPD. Longitudinal studies may elucidate if the loss of muscle oxidative phenotype drives or accelerates the process of muscle wasting.

Social variables exert selective pressures in the evolution and form of primate mimetic musculature.

Mammals use their faces in social interactions more so than any other vertebrates. Primates are an extreme among most mammals in their complex, direct, lifelong social interactions and their frequent use of facial displays is a means of proximate visual communication with conspecifics. The available repertoire of facial displays is primarily controlled by mimetic musculature, the muscles that move the face. The form of these muscles is, in turn, limited by and influenced by phylogenetic inertia but here we use examples, both morphological and physiological, to illustrate the influence that social variables may exert on the evolution and form of mimetic musculature among primates. Ecomorphology is concerned with the adaptive responses of morphology to various ecological variables such as diet, foliage density, predation pressures, and time of day activity. We present evidence that social variables also exert selective pressures on morphology, specifically using mimetic muscles among primates as an example. Social variables include group size, dominance 'style', and mating systems. We present two case studies to illustrate the potential influence of social behavior on adaptive morphology of mimetic musculature in primates: (1) gross morphology of the mimetic muscles around the external ear in closely related species of macaque (Macaca mulatta and Macaca nigra) characterized by varying dominance styles and (2) comparative physiology of the orbicularis oris muscle among select ape species. This muscle is used in both facial displays/expressions and in vocalizations/human speech. We present qualitative observations of myosin fiber-type distribution in this muscle of siamang (Symphalangus syndactylus), chimpanzee (Pan troglodytes), and human to demonstrate the potential influence of visual and auditory communication on muscle physiology. In sum, ecomorphologists should be aware of social selective pressures as well as ecological ones, and that observed morphology might reflect a compromise between the demands of the physical and the social environments.

Histochemick� vlastnosti svalov�ch vl�ken u jehnat plemene texel

The trial was performed on 12 Texel lambs (6 males and 6 females) in selected flock. The lambs were slaughtered at the age of 180 days and samples of musculus longissimus lumborum et thoracis (MLLT) and musculus quadriceps femoris (QFM) were collected. The histochemical traits of fiber cross sectional area, diameter and perimeter were monitored. Subsequently the fiber type distribution was calculated and evaluated. The dataset was evaluated using SAS. Significantly higher pH value (+0.88; P < 0.01) was marked in females, while significantly higher L* attribute was observed in males. No differences between males and females were detected in histochemical evaluation. On the other hand significant differences (P < 0.05 to 0.01) were observed in fiber type distribution and cross sectional area parameters of MLLT and QMF muscles. In praxis the results are usable for meat scientists, sheep breeders or the meat industry.

Muscle fibre types in the reduced forelimb and enlarged hindlimb of the quokka (Setonix brachyurus, Macropodidae)

The quokka (Setonyx brachyurus) is restricted to two offshore islands and small isolates on the mainland of south-western Australia. It displays a tendency to saltatorial locomotion and moves at speed by bipedal hopping, although it also uses its forelimbs at low speed. Its bipedal adaptation involves enlarged hind limbs, with elongated feet. The fibre type distribution of the elbow and knee extensors, and the ankle plantar flexors, in comparison with two eutherians, the quadrupedal rhesus monkey, as a locomotor generalist, and the jerboa, a small eutherian hopping species morphologically similar to the quokka, were studied. The quokka’s forelimb showed the same characteristics as that of the jerboa, lacking the fatigue-resistant Type I fibres that are used to sustain posture. As in the jerboa, the gastrocnemius lateralis was the muscle head with the highest proportion of fast twitch fibres. Muscular fibre pattern is not identical in the quokka and the jerboa hindlimb, but it appears that both species have similar anatomical adaptations to saltatorial locomotion. Differences in muscle fibre proportions could be due to several factors including, resting posture, body size and the propensity for elastic energy storage, the burrowing behaviour of the jerboa, but also to phylogenetic constraints where the adaptation to hop on the hindlimbs is a shared behaviour of the Macropodoidea (jerboas are the only Dipodidae to have elongated hindlimbs).

Skeletal muscle ultrastructure and function in statin-tolerant individuals.

Statins have well-known benefits on cardiovascular mortality, though up to 15% of patients experience side effects. With guidelines from the American Heart Association, American College of Cardiology, and American Diabetes Association expected to double the number of statin users, the overall incidence of myalgia and myopathy will increase. We evaluated skeletal muscle structure and contractile function at the molecular, cellular, and whole tissue levels in 12 statin tolerant and 12 control subjects. Myosin isoform expression, fiber type distributions, single fiber maximal Ca(2+) -activated tension, and whole muscle contractile force were similar between groups. No differences were observed in myosin-actin cross-bridge kinetics in myosin heavy chain I or IIA fibers. We found no evidence for statin-induced changes in muscle morphology at the molecular, cellular, or whole tissue levels. Collectively, our data show that chronic statin therapy in healthy asymptomatic individuals does not promote deleterious myofilament structural or functional adaptations.