Whole-muscle and single-fibre contractile properties and myosin heavy chain isoforms in humans

Single muscle fibre contractile characteristics with lifelong endurance exercise

KEY POINTS

A hallmark trait of ageing skeletal muscle health is a reduction in size and function, which is most pronounced in the fast muscle fibres. We studied older men (74 ± 4 years) with a history of lifelong (>50 years) endurance exercise to examine potential benefits for slow and fast muscle fibre size and contractile function. Lifelong endurance exercisers had slow muscle fibres that were larger, stronger, faster and more powerful than young exercisers (25 ± 1 years) and age-matched non-exercisers (75 ± 2 years). Limited benefits with lifelong endurance exercise were noted in the fast muscle fibres. These findings suggest that additional exercise modalities (e.g. resistance exercise) or other therapeutic interventions are needed to target fast muscle fibres with age.

ABSTRACT

We investigated single muscle fibre size and contractile function among three groups of men: lifelong exercisers (LLE) (n = 21, 74 ± 4 years), old healthy non-exercisers (OH) (n = 10, 75 ± 2 years) and young exercisers (YE) (n = 10, 25 ± 1 years). On average, LLE had exercised ∼5 days week^-1 for ∼7 h week^-1 over the past 53 ± 6 years. LLE were subdivided based on lifelong exercise intensity into performance (LLE-P) (n = 14) and fitness (LLE-F) (n = 7). Muscle biopsies (vastus lateralis) were examined for myosin heavy chain (MHC) slow (MHC I) and fast (MHC IIa) fibre size and function (strength, speed, power). LLE MHC I size (7624 ± 2765 μm² ) was 25-40% larger (P < 0.001) than YE (6106 ± 1710 μm² ) and OH (5476 ± 2467 μm² ). LLE MHC I fibres were ∼20% stronger, ∼10% faster and ∼30% more powerful than YE and OH (P < 0.05). By contrast, LLE MHC IIa size (6466 ± 2659 μm² ) was similar to OH (6237 ± 2525 μm² ; P = 0.854), with both groups ∼20% smaller (P < 0.001) than YE (7860 ± 1930 μm² ). MHC IIa contractile function was variable across groups, with a hierarchical pattern (OH > LLE > YE; P < 0.05) in normalized power among OH (16.7 ± 6.4 W L^-1 ), LLE (13.9 ± 4.5 W L^-1 ) and YE (12.4 ± 3.5 W L^-1 ). The LLE-P and LLE-F had similar single fibre profiles with MHC I power driven by speed (LLE-P) or force (LLE-F), suggesting exercise intensity impacted slow muscle fibre mechanics. These data suggest that lifelong endurance exercise benefited slow muscle fibre size and function. Comparable fast fibre characteristics between LLE and OH, regardless of training intensity, suggest other exercise modes (e.g. resistance training) or myotherapeutics may be necessary to preserve fast muscle fibre size and performance with age.

The Influence of Growth, Maturation and Resistance Training on Muscle-Tendon and Neuromuscular Adaptations: A Narrative Review

The purpose of this article is to provide an overview of the growth, maturation and resistance training-related changes in muscle-tendon and neuromuscular mechanisms in youth, and the subsequent effect on performance. Sprinting, jumping, kicking, and throwing are common movements in sport that have been shown to develop naturally with age, with improvements in performance being attributed to growth and maturity-related changes in neuromuscular mechanisms. These changes include moderate to very large increases in muscle physiological cross-sectional area (CSA), muscle volume and thickness, tendon CSA and stiffness, fascicle length, muscle activation, pre-activation, stretch reflex control accompanied by large reductions in electro-mechanical delay and co-contraction. Furthermore, a limited number of training studies examining neuromuscular changes following four to 20 weeks of resistance training have reported trivial to moderate differences in tendon stiffness, muscle CSA, muscle thickness, and motor unit activation accompanied by reductions in electromechanical delay (EMD) in pre-pubertal children. However, the interaction of maturity- and training-related neuromuscular adaptions remains unclear. An understanding of how different neuromuscular mechanisms adapt in response to growth, maturation and training is important in order to optimise training responsiveness in youth populations. Additionally, the impact that these muscle-tendon and neuromuscular changes have on force producing capabilities underpinning performance is unclear.

Weak Association Between Vastus Lateralis Muscle Fiber Composition and Fascicle Length in Young Untrained Females

The aim of the study was to investigate the relationships between vastus lateralis muscle fiber length and fiber type composition in individuals with minimal exposure to systematic resistance/power training. In sixty female physical education students (age: 21.03 ± 2.1 years, body weight: 59.8 ± 9.7 kg, body height: 166.2 ± 6.5 cm), with no experience in systematic training, lean body mass, VL muscle architecture and fiber composition type, countermovement jumping (CMJ) performance, and isometric leg press rate of force development were evaluated. Data were analyzed for all participants, as well as two equally numbered groups assigned according to their maximum countermovement jumping power (High-Power or Low-Power group). Significant but low correlations were found between type II muscle fiber percentage and fascicle length (N = 60, p < 0.05). Significant correlations were found between type IIa and IIx muscle fiber percentage cross-sectional area (%CSA) and fascicle length (N = 60; r = 0.321, and r = 0.378; respectively, p < 0.05). These correlations were higher for the High-Power group (r = 0.499, and r = 0.522; respectively, p < 0.05), and lower, and nonsignificant, for the Low-Power group. The best predictor of strength/power performance was the lean body mass of the lower extremities (r = 0.389-0.645, p < 0.05). These results suggest that in females with minimal exposure to systematic training, fascicle length may be weakly linked with type II fiber areas, only in females with high-power profiles.

Estimates of persistent inward currents increase with the level of voluntary drive in low-threshold motor units of plantar flexor muscles

This study tested whether estimates of persistent inward currents (PICs) in the human plantar flexors would increase with the level of voluntary drive. High-density surface electromyograms were collected from soleus and gastrocnemius medialis of 21 participants (29.2 ± 2.6 yr) during ramp-shaped isometric contractions to 10%, 20%, and 30% (torque rise and decline of 2%/s and 30-s duration) of each participant's maximal torque. Motor units identified in all the contraction intensities were included in the paired-motor unit analysis to calculate delta frequency (ΔF) and estimate the PICs. ΔF is the difference in discharge rate of the control unit at the time of recruitment and derecruitment of the test unit. Increases in PICs were observed from 10% to 20% [Δ = 0.6 pulse per second (pps); P < 0.001] and from 20% to 30% (Δ = 0.5 pps; P < 0.001) in soleus and from 10% to 20% (Δ = 1.2 pps; P < 0.001) but not from 20% to 30% (Δ = 0.09 pps; P = 0.724) in gastrocnemius medialis. Maximal discharge rate increased for soleus and gastrocnemius medialis from 10% to 20% [Δ = 1.75 pps (P < 0.001) and Δ = 2.43 pps (P < 0.001), respectively] and from 20% to 30% [Δ = 0.80 pps (P < 0.017) and Δ = 0.92 pps (P = 0.002), respectively]. The repeated-measures correlation identified associations between ΔF and increases in maximal discharge rate for soleus (r = 0.64; P < 0.001) and gastrocnemius medialis (r = 0.77; P < 0.001). An increase in voluntary drive tends to increase PIC strength, which has key implications for the control of force but also for comparisons between muscles or studies when relative force levels might be different. Increases in voluntary descending drive amplify PICs in humans and provide an important spinal mechanism for motor unit discharging, and thus force output modulation.NEW & NOTEWORTHY Animal experiments and computational models have shown that motor neurons can amplify the synaptic input they receive via persistent inward currents. Here we show in humans that this amplification varies proportionally to the magnitude of the voluntary drive to the muscle.

Tissue-Engineered Skeletal Muscle Models to Study Muscle Function, Plasticity, and Disease

Skeletal muscle possesses remarkable plasticity that permits functional adaptations to a wide range of signals such as motor input, exercise, and disease. Small animal models have been pivotal in elucidating the molecular mechanisms regulating skeletal muscle adaptation and plasticity. However, these small animal models fail to accurately model human muscle disease resulting in poor clinical success of therapies. Here, we review the potential of in vitro three-dimensional tissue-engineered skeletal muscle models to study muscle function, plasticity, and disease. First, we discuss the generation and function of in vitro skeletal muscle models. We then discuss the genetic, neural, and hormonal factors regulating skeletal muscle fiber-type in vivo and the ability of current in vitro models to study muscle fiber-type regulation. We also evaluate the potential of these systems to be utilized in a patient-specific manner to accurately model and gain novel insights into diseases such as Duchenne muscular dystrophy (DMD) and volumetric muscle loss. We conclude with a discussion on future developments required for tissue-engineered skeletal muscle models to become more mature, biomimetic, and widely utilized for studying muscle physiology, disease, and clinical use.

Effects of Complex Training on Sprint, Jump, and Change of Direction Ability of Soccer Players: A Systematic Review and Meta-Analysis

The aim of this meta-analysis was to evaluate the effects of complex training (CT) on sprint, jump, and change of direction (COD) ability among soccer players. After an electronic search, 10 peer-reviewed articles were considered in the meta-analysis. The athletes included in this meta-analysis were amateur to professional level male soccer players (age range, 14–23 years). These studies incorporated CT in soccer players who were compared to a control group. Significant moderate to large improvements were observed in the CT group [sprint: standard mean difference (SMD) = 0.92–1.91; jump: SMD = 0.96–1.58; COD: SMD = 0.97–1.49] when compared to control groups. Subgroup analysis were also conducted based on age, duration, and competitive level. The beneficial effects of CT were greater in players <18 vs. ≥18 years (linear sprinting; SMD = 2.01 vs. −0.13), after ≥8 vs. <8 weeks (jumping and COD; SMD = 1.55–2.01 vs. 0.31–0.64, respectively) and among professional vs. amateur players (linear sprinting and with COD; SMD = 1.53–1.58 vs. 0.08–0.63, respectively). In conclusion, regular soccer training programs may be supplemented with CT to improve sprint, jump, and COD performance. A longer duration of CT (≥8 weeks) seems to be optimal in improving the physical abilities of soccer players. Professional players and <18 years players may benefit more from CT program.

Current perspectives on obesity and skeletal muscle contractile function in older adults

Obesity has become one of the most pressing public health issues of the 21st century and currently affects a substantial proportion of the older adult population. Although the cardiometabolic complications are well documented, research from the past 20 years has drawn attention to the detrimental effects of obesity on physical performance in older adults. Obesity-related declines in physical performance are due, in part, to compromised muscle strength and power. Recent evidence suggests there are a number of mechanisms potentially underlying reduced whole muscle function, including alterations in myofilament protein function and cellular contractile properties, and these may be related to morphological adaptations, such as shifts in fiber type composition and increased intramyocellular lipid content within skeletal muscle. To date, even less research has focused on how exercise and weight loss interventions for obese older adults affect these mechanisms. In light of this work, we provide an update on the current knowledge related to obesity and skeletal muscle contractile function and highlight a number of questions to address potential etiologic mechanisms as well as intervention strategies, which may help advance our understanding of how physical performance can be improved among obese older adults.

Effect of environmental temperature change on the neuromechanical function of the quadriceps muscle

AbstractThis study compared neuromechanical characteristics of voluntary (maximum voluntary contraction (MVC) peak torque, rate of torque development (RTD), voluntary activation (VA)) and electrically stimulated contractions (peak torque, RTD) when performed under the same temperature conditions. Twelve physically active males performed two isometric MVCs of the quadriceps muscle group in an isokinetic dynamometer. The MVCs were performed after lower limb submersion for 20 min in hot (40°C) or cold (10°C) water. A control MVC was performed in ambient room temperature (17 ± 0.7°C). Electrical twitches were delivered at rest pre-MVC (Unpotentiated), during the plateau phase of the MVC (Superimposed) and post-MVC (Potentiated). Peak torque for MVC, Unpotentiated and Potentiated was recorded. RTD was calculated for the MVC (at 50, 100, 150, 200 ms and peak torque time points), Unpotentiated and Potentiated twitches, while VA (using the central activation ratio method) was calculated. There was no significant change between conditions in MVC peak torque, MVC RTD, VA and (averaged) twitch peak torque (p > 0.05). Twitch RTD for the hot condition (1025.0 ± 163.0 N·m·s^-1) was significantly higher (p = 0.003) than control (872.3 ± 142.9 N·m·s^-1). In conclusion, environmental temperature changes, in the range examined, do not affect the ability to generate maximum torque or any of the RTD parameters in maximum voluntary isometric contractions. In contrast, increased heat results in higher RTD in electrically stimulated contractions, most likely induced by reduced contraction time. This has practical implications for the use of electromyostimulation for injury prevention.

Association of Compartmental Leg Lean Mass Measured by Dual X-Ray Absorptiometry With Force Production

Raymond-Pope, CJ, Dengel, DR, Fitzgerald, JS, and Bosch, TA. Association of compartmental leg lean mass measured by dual X-ray absorptiometry with force production. J Strength Cond Res 34(6): 1690-1699, 2020-We recently reported a novel method for measuring upper leg anterior/posterior compartmental composition. The purpose of this study was to determine the association of this method with measures of muscle-specific and explosive strength and to compare this method with traditional dual energy X-ray absorptiometry (DXA) measurements of total and upper leg masses. We hypothesize this method will be related to muscle-specific strength measured by isokinetic dynamometry and explosive strength measured by jump mechanography. Nineteen NCAA Division I college athletes (10 women; age = 20.4 ± 1.4 years; height = 1.8 ± 0.1 m; body mass = 73.8 ± 17.0 kg) underwent 3 DXA scans (1 total body, 2 lateral) and knee extension/flexion strength assessment using isokinetic dynamometry at 3 velocities (60, 120, and 180°·s). A subset of 10 participants also completed a squat jump on a force platform on a different day. Pearson correlations compared 3 separate lean soft-tissue mass (LSTM) regions of interest (total leg, upper leg, and compartmental leg) with (a) isokinetic peak torque and (b) squat jump height, peak force, and peak and average rate of force development. Compartmental leg LSTM demonstrated similar correlations (r = 0.437-0.835) with peak torque in comparison with total leg (r = 0.463-0.803) and upper leg (r = 0.449-0.795) LSTM. Summed right and left total leg (r = 0.830-0.940), total upper leg (r = 0.824-0.953), and anterior (r = 0.582-0.798) and posterior (r = 0.750-0.951) compartmental leg LSTM demonstrated moderate-to-strong correlations with all squat jump variables, particularly jump height (p < 0.05). The lateral segmentation DXA scanning method demonstrated feasibility in assessing compartmental leg LSTM in relation with isokinetic and squat jump measurements-important outcomes when examining an athlete's response to training and rehabilitation.

Passive muscle stretching reduces estimates of persistent inward current strength in soleus motor units

Prolonged (≥60 s) passive muscle stretching acutely reduces maximal force production at least partly through a suppression of efferent neural drive. The origin of this neural suppression has not been determined; however, some evidence suggests that reductions in the amplitude of persistent inward currents (PICs) in the motoneurons may be important. The aim of the present study was to determine whether acute passive (static) muscle stretching affects PIC strength in gastrocnemius medialis (GM) and soleus (SOL) motor units. We calculated the difference in instantaneous discharge rates at recruitment and de-recruitment (ΔF) for pairs of motor units in GM and SOL during triangular isometric plantar flexor contractions (20% maximum) both before and immediately after a 5 min control period and immediately after five 1 min passive plantar flexor stretches. After stretching, there was a significant reduction in SOL ΔF (-25.6%; 95% confidence interval, CI=-45.1% to -9.1%, P=0.002) but not GM ΔF These data suggest passive muscle stretching can reduce the intrinsic excitability, via PICs, of SOL motor units. These findings (1) suggest that PIC strength might be reduced after passive stretching, (2) are consistent with previously established post-stretch decreases in SOL but not GM EMG amplitude during contraction, and (3) indicate that reductions in PIC strength could underpin the stretch-induced force loss.

External Resistance Is Imperative for Training-Induced Efferent Neural Drive Enhancement in Older Adults

Strength training performed with heavy loads and maximal intended velocity is documented to enhance efferent neural drive to maximally contracting musculature in older adults. However, it remains unclear whether the neural plasticity following training result from motor skill learning or if external resistance is a prerequisite. To investigate this, we assessed electrically evoked potentials (H-reflex and V-waves normalized to maximal M-wave) and voluntary activation (VA) in 36 older adults (73 ± 4 years) randomized to 3 weeks of plantar flexion strength training, with (maximal strength training [MST]) or without (unloaded ballistic training [UBT]) heavy external loading (90% of one repetition maximum), or a control group. Both training groups aimed to execute the concentric phase of movement as fast and forcefully as possible. The MST group improved maximal voluntary contraction (MVC) and rate of force development (RFD) by 18% ± 13% (p = .001; Hedges g = 0.66) and 35% ± 17% (p &lt; .001; g = 0.94), respectively, and this was different (MVC: p = .013; RFD: p = .001) from the UBT group which exhibited a 7% ± 8% (p = .033; g = 0.32) increase in MVC and a tendency to increase RFD (p = .119; g = 0.22). Concomitant improvements in efferent neural drive (Vmax/Msup ratio: 0.14 ± 0.08 to 0.24 ± 0.20; p = .010) and a tendency towards increased VA (79% ± 9% to 84% ± 5%; p = .098), were only apparent after MST. No changes were observed in Hmax/Mmax ratio for the groups. In conclusion, external loading during exercise training appears to be a prerequisite for efferent neural drive enhancement in older adults. Thus, strength training with heavy loads should be recommended to counteract the typically observed age-related decline in motoneuron firing frequency and recruitment.

Early and late rapid torque characteristics and select physiological correlates in middle-aged and older males

Purpose

The purpose of this study was to compare early and late rapid torque parameters of the plantar flexors (PFs) in middle-aged (MM) and older (OM) males, and determine the effect of normalization to peak torque (PT) and muscle cross-sectional area (CSA).

Methods

Twenty-nine healthy, MM (n = 14; 45 ± 2 yrs) and OM (n = 15; 65 ± 3 yrs) performed rapid, maximal isometric contractions of the PFs. PT, as well as rate of torque development and impulse during the early (0–50 ms; RTD_0-50, IMP_0-50) and late (100–200 ms; RTD_100-200, IMP_100-200) contraction phases were calculated. Torque at 50 (TQ₅₀), 100 (TQ₁₀₀), and 200 (TQ₂₀₀) ms was also obtained. CSA and echo-intensity (EI) of the gastrocnemii were acquired via ultrasonography. Torque variables were normalized to PT and CSA. Rate of EMG rise (RER) for the medial gastrocnemius was calculated at 30, 50 and 75 ms.

Results

TQ₁₀₀ (MM = 69.71 ± 16.85 vs. OM = 55.99 ± 18.54 Nm; p = 0.046), TQ₂₀₀ (MM = 114.76 ± 26.79 vs. OM = 91.56 ± 28.10 Nm; p = 0.031), and IMP_100-200 (MM = 4.79 ± 1.11 vs. OM = 3.83 ± 1.17 Nm·s; p = 0.032) were lower in OM. PT, TQ₅₀, RTD_0-50, IMP_0-50, RTD_100-200, RER, CSA, and EI were similar between groups (p > 0.05). No differences were found for normalized torque variables (p > 0.05). EI was moderately associated with normalized torque parameters only (r = -0.38 –-0.45). RER, at 75 ms, was moderately correlated with early, absolute torque measures and rapid torque variables made relative to PT and CSA (r = 0.41 –-0.64).

Conclusion

Late rapid torque parameters of the PFs were preferentially impaired in OM compared to MM, and PT as well as CSA appeared to mediate this result.

Fiber Type Composition and Rate of Force Development in Endurance- and Resistance-Trained Individuals

Methenitis, S, Spengos, K, Zaras, N, Stasinaki, A-N, Papadimas, G, Karampatsos, G, Arnaoutis, G, and Terzis, G. Fiber type composition and rate of force development in endurance- and resistance-trained individuals. J Strength Cond Res 33(9): 2388-2397, 2019-The purpose of the study was to investigate the relationship between muscle fiber composition and the rate of force development (RFD) in well-trained individuals with different training background. Thirty-eight young men with different training background participated: 9 endurance runners, 10 power-trained individuals, 9 strength-trained individuals, and 10 sedentary individuals. They performed maximal isometric leg press for the measurement of RFD. Body composition (dual x-ray absorptiometry) and vastus lateralis fiber type composition were also evaluated. When all participants were examined as a group, moderate correlations were found between the percent of type II muscle fibers and RFD between 100 and 600 milliseconds (r = 0.321-0.497; p ≤ 0.05). The correlation coefficients were higher for the cross-sectional area (CSA) and the %CSA of type II and IIx muscle fibers (r = 0.599-0.847; p < 0.001). For the power group, RFD up to 250 milliseconds highly correlated with % type IIx muscle fibers and type IIx fiber CSA (r = 0.670-0.826; p ≤ 0.05), as well as with %CSA of type IIx fibers (r = 0.714-0.975; p ≤ 0.05). Significant correlations were found between the relative RFD (·kg lower extremities lean mass) and CSA-%CSA of type II and IIx fibers for the power group (r = 0.676-0.903; p ≤ 0.05). No significant correlations were found between muscle morphology and RFD for the other groups. In conclusion, the present data suggest that there is a strong link between the type IIx muscle fibers and early RFD and relative RFD in power-trained participants. Type II fibers seem to be moderately linked with RFD in non-power-trained individuals.

Effects of Rest Position on Morphology of the Vastus Lateralis and Its Relationship with Lower-Body Strength and Power

Ultrasonography of the lower body typically encompasses supine rest due to fluid shifts affecting tissue size and composition. However, vastus lateralis (VL) examination is completed in the lateral recumbent position, and this positional change may influence morphology and its ability to predict function. This study aimed to examine the effect of position on VL morphology and its relationship with lower-body performance. Cross-sectional area (CSA), muscle thickness (MT), pennation angle (PA), echo intensity (UnCorEI), subcutaneous adipose tissue thickness (SFT), and echo intensity corrected for SFT (CorEI) were assessed in 31 resistance-trained males (23.0 ± 2.1 yrs; 1.79 ± 0.08 m; 87.4 ± 11.7 kg) immediately after transitioning from standing to supine (IP), after 15 min of standing (ST), and after 15 min of rest in three recumbent positions: supine (SUP), dominant lateral recumbent (DLR), non-dominant lateral recumbent (NDLR). Participants also completed unilateral vertical jumps, isometric/isokinetic tests, and a one-repetition maximum leg press. CSA, MT, PA, and SFT were greater in ST compared to NDLR, DLR, and SUP (p < 0.05). CSA, UnCorEI, and CorEI were different between recumbent positions; however no differences were observed for MT, PA, and SFT. Different magnitudes of relationships were observed between muscle morphological characteristics measured after rest in different positions and performance variables. Muscle morphology in IP generally appears to be the best predictor of performance for most variables, although utilizing the NDLR and DLR positions may provide comparable results, whereas morphology measured in ST and SUP provide weaker relationships with physical performance. IP also requires less time and fewer requirements on the technician and subject, thus researchers should consider this positioning for VL examination.

Reactive Strength Index and Knee Extension Strength Characteristics Are Predictive of Single-Leg Hop Performance After Anterior Cruciate Ligament Reconstruction

Birchmeier, T, Lisee, C, Geers, B, and Kuenze, C. Reactive strength index and knee extension strength characteristics are predictive of single-leg hop performance after anterior cruciate ligament reconstruction. J Strength Cond Res 33(5): 1201-1207, 2019-Single-leg hop distance is incorporated into return to sport criteria after anterior cruciate ligament reconstruction (ACLR) because of its relationship with knee extension strength; however, it may be related to other strength and plyometric characteristics. The purpose of this study was to assess the association between isometric knee extension strength and plyometric characteristics, including amortization and reactive strength index (RSI), measured during a single-leg drop vertical jump and single-leg hop performance in individuals with unilateral ACLR. Participants attended 2 testing sessions. During the first session, a biomechanical analysis using a 3D motion capture system was performed to measure RSI and amortization during a single-leg drop vertical jump for maximal height. Participants completed a single hop and a triple hop for maximal distance. During the second session, isometric knee extension strength was measured during a maximal voluntary isometric contraction. Strength characteristics included peak torque, rate of torque development (RTD), RTD 0-100 ms (RTD 100), and RTD 100-200 ms (RTD 200). Fifty-two individuals (17 men/35 women) participated. Multivariable regression models revealed jump height, peak torque, and RTD 200 explained 60.9% of the variance in normalized single-leg hop distance (p < 0.001). Reactive strength index, peak torque, RTD 200, and RTD 100 significantly explained 61.8% of the variance in normalized triple hop distance (p < 0.001). Single hop distance may indicate improved knee extension strength, whereas triple hop distance may indicate improvement in reactive strength. Training to improve RSI may improve triple hop performance and clinical outcomes in this population.

Phase-Specific Changes in Rate of Force Development and Muscle Morphology Throughout a Block Periodized Training Cycle in Weightlifters

The purpose of this study was to investigate the kinetic and morphological adaptations that occur during distinct phases of a block periodized training cycle in weightlifters. Athlete monitoring data from nine experienced collegiate weightlifters was used. Isometric mid-thigh pull (IMTP) and ultrasonography (US) results were compared to examine the effects of three specific phases of a training cycle leading up to a competition. During the high volume strength-endurance phase (SE) small depressions in rate of force development (RFD) but statistically significant (p ≤ 0.05) increases in vastus lateralis cross-sectional area (CSA), and body mass (BM) were observed. The lower volume higher intensity strength-power phase (SP) caused RFD to rebound above pre-training cycle values despite statistically significant reductions in CSA. Small to moderate increases only in the earlier RFD time bands (<150 ms) occurred during the peak/taper phase (PT) while CSA and BM were maintained. Changes in IMTP RFD and CSA from US reflected the expected adaptations of block periodized training phases. Changes in early (<100 ms) and late (≥150 ms) RFD time bands may not occur proportionally throughout different training phases. Small increases in RFD and CSA can be expected in well-trained weightlifters throughout a single block periodized training cycle.

A fast, reliable and sample-sparing method to identify fibre types of single muscle fibres

Many skeletal muscle proteins are present in a cell-specific or fibre-type dependent manner. Stimuli such as exercise, aging, and disease have been reported to result in fibre-specific responses in protein abundances. Thus, fibre-type-specific determination of the content of specific proteins provides enhanced mechanistic understanding of muscle physiology and biochemistry compared with typically performed whole-muscle homogenate analyses. This analysis, however, is laborious and typically not performed. We present a novel dot blotting method for easy and rapid determination of skeletal muscle fibre type based on myosin heavy chain (MHC) isoform presence. Requiring only small amounts of starting muscle tissue (i.e., 2–10 mg wet weight), muscle fibre type is determined in one-tenth of a 1–3-mm fibre segment, with the remainder of each segment pooled with fibre segments of the same type (I or II) for subsequent protein quantification by western blotting. This method, which we validated using standard western blotting, is much simpler and cheaper than previous methods and is adaptable for laboratories routinely performing biochemical analyses. Use of dot blotting for fibre typing will facilitate investigations of fibre-specific responses to diverse stimuli, which will advance our understanding of skeletal muscle physiology and biochemistry.

Rate of Force Development and Muscle Architecture after Fast and Slow Velocity Eccentric Training

The aim of the study was to investigate the rate of force development (RFD) and muscle architecture early adaptations in response to training with fast- or slow-velocity eccentric squats. Eighteen young novice participants followed six weeks (two sessions/week) of either fast-velocity (Fast) or slow-velocity (Slow) squat eccentric-only training. Fast eccentric training consisted of nine sets of nine eccentric-only repetitions at 70% of 1-RM with <1 s duration for each repetition. Slow eccentric training consisted of five sets of six eccentric-only repetitions at 90% of 1-RM with ~4 sec duration for each repetition. Before and after training, squat 1-RM, countermovement jump (CMJ), isometric leg press RFD, and vastus lateralis muscle architecture were evaluated. Squat 1-RM increased by 14.5 ± 7.0% (Fast, p < 0.01) and by 5.4 ± 5.1% (Slow, p < 0.05). RFD and fascicle length increased significantly in the Fast group by 10–19% and 10.0 ± 6.2%, p < 0.01, respectively. Muscle thickness increased only in the Slow group (6.0 ± 6.8%, p < 0.05). Significant correlations were found between the training induced changes in fascicle length and RFD. These results suggest that fast eccentric resistance training may be more appropriate for increases in rapid force production compared to slow eccentric resistance training, and this may be partly due to increases in muscle fascicle length induced by fast eccentric training.

Muscle Fiber and Performance Changes after Fast Eccentric Complex Training

INTRODUCTION

The purpose of this study was to examine the effects of a short-term fast eccentric and ballistic complex training program on muscle power, rate of force development (RFD), muscle fiber composition, and cross-sectional area (CSA).

METHODS

Sixteen male physical education students were randomly assigned to either a training group (TG, n = 8) or a control group (n = 8). The TG followed a 6-wk low volume training program, including fast eccentric squat training with an individually optimized load of 74% ± 7% of maximal half-squat strength (1RM) twice per week and a ballistic training session with loaded (30% 1RM) and unloaded jump squats, once per week, all combined with unloaded plyometric jumps.

RESULTS

Half squat 1RM was increased in the TG from 1.87 ± 0.28 to 2.14 ± 0.31 kg per kilogram body mass (14.4% ± 9.3%, P = 0.01). The percentage of types I, IIA, and IIX fibers were similar in the two groups at pretesting and did not change after the intervention period (P = 0.53-0.89). Muscle fiber CSA increased in all fiber types by 8.3% to 11.6% (P = 0.02 to 0.001) in TG only. Countermovement jump height and peak power measured at five different external loads (0%-65% of 1RM) only increased in the TG by approximately 20% to 36% (P < 0.01) and approximately 16% to 22% (P < 0.01), respectively. Peak ground reaction force during jump squats remained unchanged in both groups, whereas RFD increased in the TG only (40%-107%, P = 0.001).

CONCLUSIONS

A combination of low-volume fast eccentric and ballistic jump squat training with plyometric jumps in a strength-power potentiation complex format, induced substantial increases in peak leg muscle power, RFD, and maximal strength, accompanied by gains in CSA of all muscle fiber types, without a reduction in fast twitch fiber composition.

Myogenesis in Drosophila melanogaster: Dissection of Distinct Muscle Types for Molecular Analysis

Drosophila is a useful model organism for studying the molecular signatures that define specific muscle types during myogenesis. It possesses significant genetic conservation with humans for muscle disease causing genes and a lack of redundancy that simplifies functional analysis. Traditional molecular methods can be utilized to understand muscle developmental processes such as Western blots, in situ hybridizations, RT-PCR and RNAseq, to name a few. However, one challenge for these molecular methods is the ability to dissect different muscle types. In this protocol we describe some useful techniques for extracting muscles from the pupal and adult stages of development using flight and jump muscles as an example.

Effects of sex and joint action on voluntary activation

The current study tested the hypothesis that voluntary activation during maximal voluntary contraction (MVC) conditionally depends on sex and joint action. Twenty-eight healthy adults (14 of each sex) performed knee extensor MVC and plantar flexor MVC at extended and flexed knee positions. Voluntary activation during MVC was assessed using a twitch interpolation technique. The voluntary activation during plantar flexor MVC at the extended knee position was significantly lower (P = 0.020, 95% confidence interval 1.4 to 14.6, Cohen’s d for between-subject design = 0.94) in women (88.3% ± 10.0%) than in men (96.2% ± 6.6%). In contrast, no significant sex differences were shown in the voluntary activation during knee extensor MVC (93.7% ± 5.9% (women) vs. 95.0%  ± 3.9% (men)) and during plantar flexor MVC at the flexed knee position (90.4% ± 12.2% (women) vs. 96.8% ± 5.6% (men)). The voluntary activation during knee extensor MVC was significantly higher (P = 0.001, 95% confidence interval 2.1 to 8.8, Cohen’s d for within-subject design = 0.69) than that during plantar flexor MVC at the extended knee position in women, whereas the corresponding difference was not observed in men. The results revealed that the existence of sex difference in the voluntary activation during MVC depends on joint action and joint angle.

Maximal strength training: the impact of eccentric overload

The search for the most potent strength training intervention is continuous. Maximal strength training (MST) yields large improvements in force-generating capacity (FGC), largely attributed to efferent neural drive enhancement. However, it remains elusive whether eccentric overload, before the concentric phase, may augment training-induced neuromuscular adaptations. A total of 53 23 ± 3 (SD)-yr-old untrained males were randomized to either a nontraining control group (CG) or one of two training groups performing leg press strength training with linear progression, three times per week for 8 wk. The first training group carried out MST with four sets of four repetitions at ~90% one-repetition maximum (1RM) in both action phases. The second group performed MST with an augmented eccentric load of 150% 1RM (eMST). Measurements were taken of 1RM and rate of force development (RFD), countermovement jump (CMJ) performance, and evoked potentials recordings [V-wave (V) and H-reflex (H) normalized to M-wave (M) in musculus soleus]. 1RM increased from 133 ± 16 to 157 ± 23 kg and 123 ± 18 to 149 ± 22 kg and CMJ by 2.3 ± 3.6 and 2.2 ± 3.7cm for MST and eMST, respectively (all P < 0.05). Early, late, and maximal RFD increased in both groups [634-1,501 N/s (MST); 644-2,111 N/s (eMST); P < 0.05]. These functional improvements were accompanied by increased V/M-ratio (MST: 0.34 ± 0.11 to 0.42 ± 14; eMST: .36 ± 0.14 to 0.43 ± 13; P < 0.05). Resting H/M-ratio remained unchanged. Training-induced improvements did not differ. All increases, except for CMJ, were different from the CG. MST is an enterprise for large gains in FGC and functional performance. Eccentric overload did not induce additional improvements, suggesting firing frequency and motor unit recruitment during MST may be maximal. NEW & NOTEWORTHY This is the first study to apply evoked potential recordings to investigate effects on efferent neural drive following high-intensity strength training with and without eccentric overload in a functionally relevant lower extremity exercise. We document that eccentric overload does not augment improvements in efferent neural drive or muscle force-generating capacity, suggesting that high-intensity concentric loads may maximally tax firing frequency and motor unit recruitment.

Trained females exhibit less fatigability than trained males after a heavy knee extensor resistance exercise session

PURPOSE

We examined differences between trained males and females in measures of muscular fatigability and central motor output after a resistance exercise session.

METHODS

Sixteen trained males (n = 8) and females (n = 8) participated in the study. Knee extensor maximal torque and rate of torque development were measured before and after the exercise session, and the twitch interpolation technique was used during the maximal efforts to derive measures of voluntary activation and muscle contractility by supramaximal stimulation of the femoral nerve using 10 and 100 Hz doublets. Surface electromyograms were recorded during all maximal efforts to examine maximal and rate of quadriceps muscle activation.

RESULTS

After exercise, maximal torque was reduced for both sexes by 26.3 ± 12.5% (p < 0.001). Absolute and relative vRTD was reduced only for males after exercise (p < 0.05). The early (0-50 ms) rate of muscle activation rise was similarly reduced for both sexes between 2.6 and 16.4% s^-1 (p < 0.01), but males experienced an average decrease of 82.5 ± 72.1% s^-1 for the maximal rate of muscle activation compared to no change for females (p = 0.02). Males had greater reductions (p < 0.05) for maximal twitch amplitudes and rate of twitch development (- 51.1 ± 21.5% and - 49.9 ± 22.8%, respectively) compared to females (- 35.8 ± 13.7% and - 31.5 ± 14.0%, respectively).

CONCLUSIONS

These findings suggest that trained females are resistant to reductions in rapid torque development, despite similar reductions in maximal torque, after resistance exercise, with this result explained by better-maintained muscle contractility and maximal rate of muscle activation compared to males.

Acute reduction of lower-body contractile function following a microbiopsy of m. vastus lateralis

Twenty-three resistance trained men 18-35 years (23 [3] years, 1.8 [0.1] m, 81 [10] kg body mass, 2.3 [1.1] years resistance training experience; mean [SD]) performed repeated maximal voluntary isometric squats (ISQ) and countermovement jumps (CMJ) pre- and +30 minutes post a unilateral microbiopsy of m. vastus lateralis. ISQ and CMJ were simultaneously measured by two force plates sampling ipsilateral (biopsied) and contralateral (non-biopsied) limb force. Bilateral limb force (ipsilateral + contralateral) and imbalance (ipsilateral/bilateral) data are reported as % change from pre-biopsy (mean [95% CI]). A post-biopsy reduction in bilateral ISQ peak force (-17 [-23, -11] %; P < 0.001), ISQ rate of force development (RFD; -28 [-41, -15] %, P = 0.002) and CMJ peak take-off force (-7 [-13, -1]%, P = 0.019) occurred. Imbalance was observed for ISQ peak force (3.2 [2.1, 4.3] %, P < 0.001), RFD (2.8 [1.6, 4.0] %, P < 0.001) and CMJ landing (3.3 [1.0, 5.6] %, P = 0.009), resultant of a force transfer from the ipsilateral (biopsied) to the contralateral (non-biopsied) limb. These data suggest that in young, resistance trained men a modulatory influence on maximal voluntary static and dynamic lower-body contractile function is evoked acutely (+30 minutes) following a microbiopsy of m. vastus lateralis.

Quadriceps Rate of Torque Development and Disability in Persons With Tibiofemoral Osteoarthritis

Background Declines in the ability to rapidly generate quadriceps muscle torque may underlie disability in individuals with tibiofemoral osteoarthritis. Objective To determine whether quadriceps rate of torque development (RTD) predicts self-reported disability and physical performance outcomes in individuals with tibiofemoral osteoarthritis. Methods This controlled laboratory, cross-sectional study assessed quadriceps strength and RTD in 76 individuals (55% female; mean ± SD age, 61.83 ± 7.11 years) with symptomatic and radiographic tibiofemoral osteoarthritis. Early (0-50 milliseconds), late (100-200 milliseconds), and overall peak RTDs were quantified in the symptomatic (involved) and contralateral limbs and used to calculate bilateral average values. Disability was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function subscale and 3 physical performance tests, including the (1) 20-m fast-paced walk, (2) 30-second chair stand, and (3) timed stair climb. Separate univariate regression models were used to determine the unique associations among measures of quadriceps RTD, WOMAC function score, and physical performance outcomes after accounting for quadriceps strength (change in R²). Results Greater involved-side late RTD and greater bilateral average early RTD were associated with faster walking (change in R² = 0.05, P = .013 and change in R² = 0.05, P = .043, respectively). Greater bilateral average late RTD was associated with faster walking (change in R² = 0.20, P<.001) and faster stair climb (change in R² = 0.11, P = .001). No quadriceps RTD variable was significantly associated with WOMAC function score (change in R² range, <0.01-0.017). Conclusion Involved-limb quadriceps RTD was weakly associated with physical performance outcomes, but not self-reported disability, in individuals with tibiofemoral osteoarthritis. Bilateral average quadriceps RTD was moderately associated with walking speed. Level of Evidence Prognosis, level 2b. J Orthop Sports Phys Ther 2018;48(9):694-703. Epub 22 May 2018. doi:10.2519/jospt.2018.7898.

Functional capacity improves in-line with neuromuscular performance after 12 weeks of non-linear periodization strength training in the elderly

BACKGROUND

While it is accepted that resistance training can improve functional capacity in older individuals, the neuromuscular source of this improvement has yet to be identified.

AIM

This study investigated the link between improved neuromuscular performance and functional capacity after a 12-week resistance training period in untrained healthy older individuals.

METHODS

Fifteen older men and women (60-71 years) adhered to a 4-week control period, followed by 12 weeks of non-linear resistance training for the lower limbs. Maximum dynamic leg press strength (1-RM), maximum isometric knee extension torque and rate of torque development (RTD) were evaluated at - 4, 0, 4, 8, and 12 weeks, and muscle activity was assessed at 0, 4, 8, and 12 weeks. Functional capacity tests (chair rise, stair ascent and descent, and timed up and go) were performed at - 4, 0, and 12 weeks.

RESULTS

No changes occurred during the control period, but the group increased their 1-RM strength (from 142 ± 53 to 198 ± 43 kg, p = 0.001), which was accompanied by an increase in vastus lateralis activation (p = 0.008) during the intervention. Increase was observed at all RTD time intervals at week 8 (p < 0.05). Significant improvements in all the functional capacity tests were observed at week 12 (p < 0.05).

DISCUSSION

Despite the expected increase in strength, RTD, muscle activity, and functional capacity, there was no significant relationship between the changes in neuromuscular performance and functional capacity. While resistance training elicits various positive improvements in healthy older individuals, actual strength gain did not influence the gain in functional capacity.

CONCLUSION

The present study highlights the exact cause that improved the functional capabilities during resistance training are currently unknown.

Diagnostic work-up in steroid myopathy

INTRODUCTION

Steroid myopathy is a well-known sign of endogenous Cushing's syndrome as well as a side effect of glucocorticoid administration. The clinical finding of muscle weakness and the clinical inspection of the muscle size are the most commonly used diagnostic tools, sometimes in combination with needle electromyography, but there are no means to detect the myopathy before the appearance of clinical or electrodiagnostic signs. Until now, no guidelines have been produced for a disease-specific evaluation of muscle impairment in patients with Cushing's syndrome.

REVIEW

We reviewed the measurement properties and limitations of the following tools that are currently adopted in clinical research and routine care for diagnosis and monitoring of steroid myopathy: muscle strength assessment; needle biopsy; intramuscular and surface electromyography; laboratory assays; muscle mass assessments (through bioelectrical impedance analysis, dual-energy X-ray absorptiometry, and computed tomography).

CONCLUSIONS

We suggest that the management of steroid myopathy patients in clinical research and practice would benefit from a multidisciplinary approach based on the combined assessment of muscle mass, strength, and performance. However, further studies are required to establish an operational definition of steroid myopathy and to identify population-specific criteria for diagnosis of the myopathic process.

Properties of the vastus lateralis muscle in relation to age and physiological function in master cyclists aged 55-79 years

In this study, results are reported from the analyses of vastus lateralis muscle biopsy samples obtained from a subset (n = 90) of 125 previously phenotyped, highly active male and female cyclists aged 55–79 years in regard to age. We then subsequently attempted to uncover associations between the findings in muscle and in vivo physiological functions. Muscle fibre type and composition (ATPase histochemistry), size (morphometry), capillary density (immunohistochemistry) and mitochondrial protein content (Western blot) in relation to age were determined in the biopsy specimens. Aside from an age‐related change in capillary density in males (r = −.299; p = .02), no other parameter measured in the muscle samples showed an association with age. However, in males type I fibres and capillarity (p < .05) were significantly associated with training volume, maximal oxygen uptake, oxygen uptake kinetics and ventilatory threshold. In females, the only association observed was between capillarity and training volume (p < .05). In males, both type II fibre proportion and area (p < .05) were associated with peak power during sprint cycling and with maximal rate of torque development during a maximal voluntary isometric contraction. Mitochondrial protein content was not associated with any cardiorespiratory parameter in either males or females (p > .05). We conclude in this highly active cohort, selected to mitigate most of the effects of inactivity, that there is little evidence of age‐related changes in the properties of VL muscle across the age range studied. By contrast, some of these muscle characteristics were correlated with in vivo physiological indices.

Study on the transcriptional regulatory mechanism of the MyoD1 gene in Guanling bovine

The MyoD1 gene plays a key role in regulating the myoblast differentiation process in the early stage of skeletal muscle development. To understand the functional elements of the promoter region and transcriptional regulation of the bovine MyoD1 gene, we cloned eight fragments from the sequence region of the MyoD1 gene promoter and inserted them into eukaryotic expression vectors for cotransfection with the mouse myoblast cell line C2C12 and Madin-Darby bovine kidney (MDBK) line. A variety of transcription factor binding sites in the longest 5'-flanking fragment from Guanling cattle MyoD1-P1 were predicted by using the online software TFSEARCH and ALGGEN PROMO as well as validated by the promoter-binding TF profiling assay II and yeast one-hybrid (Y1H) assay, including MyoD, VDR, MEF1, MEF2, SF1, and Myf6. Myf6 strongly activated the MyoD1 promoter, while MyoD1 was also capable of efficiently activating the expression of its own promoter. The transcription factors MEF2A, SF1, and VDR were further confirmed to be capable of binding to MyoD1 by Y1H system experiments. The effects of the Guanling cattle MyoD1 gene on the mRNA expression of the MEF2A, SF1, and VDR genes were determined by using a lentivirus-mediated overexpression technique, confirming that overexpression of the MyoD1 gene upregulated the mRNA expression of MEF2A as well as downregulated the expression of SF1 and VDR in the process of muscle myogenesis. Our study revealed the effects of transcription factors including MEF2A, SF1 and VDR on regulatory aspects of MyoD1, providing abundant information for transcriptional regulation of MyoD1 in muscle differentiation.

Muscle and Tendon Contributions to Reduced Rate of Torque Development in Healthy Older Males

Background

The ability to rapidly generate and transfer muscle force is essential for effective corrective movements in order to prevent a fall. The aim of this study was to establish the muscle and tendon contributions to differences in rate of torque development (RTD) between younger (YM) and older males (OM).

Method

Twenty-eight young males (23.9 years ± 1.1) and 22 old males (68.5 years ± 0.5) were recruited for assessment of Quadriceps Anatomical CSA (ACSA), maximal voluntary contraction (MVC), rate of torque development (RTD), and tendon biomechanical properties. Activation capacity (AC), maximal muscle twitch df/dt) and time to peak EMG amplitude (TTPE) were also assessed.

Results

Absolute RTD (aRTD) was lower in OM (577.5 ± 34.6 Nm/s vs 881.7 ± 45.6 Nm/s, p < .0001). RTD remained lower in OM following normalization (nRTD) for muscle ACSA (9.93 ± 0.7 Nm/s/cm2 vs 11.9 ± 0.6 Nm/s/cm2, p < .05). Maximal muscle twitch df/dt (1,086 Nm∙s-1 vs 2,209 Nm∙s-1, p < .0001), TTPE (109.2 ± 8.6ms vs 154.6 ± 16.6 ms, p < .05), and AC (75.8 ± 1.5% vs 80.1 ± 0.9%, p < .01) were all affected in OM. Tendon stiffness was found to be lower in OM (1,222 ± 78.4 N/mm vs 1,771 ± 154.1 N/mm, p < .004). nRTD was significantly correlated with tendon stiffness (R2 = .15).

Conclusion

These observations provide evidence that in absolute terms, a lower RTD in the elderly adults is caused by slower muscle contraction speeds, slower TTPE, reduced ACSA, reduced MVC, and a decrease in tendon stiffness. Once the RTD is normalized to quadriceps ACSA, only MVC and tendon stiffness remain influential. This strongly reinforces the importance of both muscle and tendon characteristics when considering RTD.

Critical determinants of combined sprint and endurance performance: an integrative analysis from muscle fiber to the human body

Optimizing physical performance is a major goal in current physiology. However, basic understanding of combining high sprint and endurance performance is currently lacking. This study identifies critical determinants of combined sprint and endurance performance using multiple regression analyses of physiologic determinants at different biologic levels. Cyclists, including 6 international sprint, 8 team pursuit, and 14 road cyclists, completed a Wingate test and 15-km time trial to obtain sprint and endurance performance results, respectively. Performance was normalized to lean body mass^2/3 to eliminate the influence of body size. Performance determinants were obtained from whole-body oxygen consumption, blood sampling, knee-extensor maximal force, muscle oxygenation, whole-muscle morphology, and muscle fiber histochemistry of musculus vastus lateralis. Normalized sprint performance was explained by percentage of fast-type fibers and muscle volume ( R² = 0.65; P < 0.001) and normalized endurance performance by performance oxygen consumption ( V̇o₂), mean corpuscular hemoglobin concentration, and muscle oxygenation ( R² = 0.92; P < 0.001). Combined sprint and endurance performance was explained by gross efficiency, performance V̇o₂, and likely by muscle volume and fascicle length ( P = 0.056; P = 0.059). High performance V̇o₂ related to a high oxidative capacity, high capillarization × myoglobin, and small physiologic cross-sectional area ( R² = 0.67; P < 0.001). Results suggest that fascicle length and capillarization are important targets for training to optimize sprint and endurance performance simultaneously.-Van der Zwaard, S., van der Laarse, W. J., Weide, G., Bloemers, F. W., Hofmijster, M. J., Levels, K., Noordhof, D. A., de Koning, J. J., de Ruiter, C. J., Jaspers, R. T. Critical determinants of combined sprint and endurance performance: an integrative analysis from muscle fiber to the human body.

The influence of sodium bicarbonate on maximal force and rates of force development in the triceps surae and brachii during fatiguing exercise

NEW FINDINGS

What is the central question of this study? Does metabolic alkalosis in humans, induced by sodium bicarbonate, affect rates of skeletal muscle fatigue differentially in muscle groups composed predominately of slow- and fast-twitch fibres? What is the main finding and its importance? Sodium bicarbonate exhibited no effect on the fatigue profile observed between triceps surae and brachii muscle groups during and after 2 min of tetanic stimulation. For the first time in exercising humans, we have profiled the effect of sodium bicarbonate on the voluntary and involuntary contractile characteristics of muscle groups representative of predominately slow- and fast-twitch fibres. The effect of metabolic alkalosis on fibre-specific maximal force production and rates of force development (RFD) has been investigated previously in animal models, with evidence suggesting an improved capacity to develop force rapidly in fast- compared with slow-twitch muscle. We have attempted to model in vivo the fatigue profile of voluntary and involuntary maximal force and RFD in the triceps surae and brachii after sodium bicarbonate (NaHCO₃ ) ingestion. In a double-blind, three-way repeated-measures design, participants (n = 10) ingested either 0.3 g kg^-1 NaHCO₃ (ALK) or equivalent calcium carbonate (PLA) prior to 2 min of continuous (1 Hz) supramaximal stimulation (300 ms at 40 Hz) of the triceps surae or brachii, with maximal voluntary efforts (maximal voluntary torque) coupled with direct muscle stimulation also measured at baseline, 1 and 2 min. Metabolic alkalosis was achieved in both ALK trials but was not different between muscle groups. Regardless of the conditions, involuntary torque declined nearly 60% in the triceps brachii (P < 0.001) and ∼30% in the triceps surae (P < 0.001). In all trials, there was a significant decline in normalized involuntary RFD (P < 0.05). Maximal voluntary torque declined nearly 28% but was not different between conditions (P < 0.01), and although declining nearly 21% in voluntary RFD (P < 0.05) there was no difference between PLA and ALK in either muscle group (P = 0.93). Sodium bicarbonate exhibited no effect on the fatigue observed between representative fibre-type muscle groups on maximal voluntary and involuntary torque or rates of torque development during and after 2 min of tetanic stimulation.

Age-related reduction in single muscle fiber calcium sensitivity is associated with decreased muscle power in men and women

Age-related declines in human skeletal muscle performance may be caused, in part, by decreased responsivity of muscle fibers to calcium (Ca²⁺). This study examined the contractile properties of single vastus lateralis muscle fibers with various myosin heavy chain (MHC) isoforms (I, I/IIA, IIA and IIAX) across a range of Ca²⁺ concentrations in 11 young (24.1±1.1years) and 10 older (68.8±0.8years) men and women. The normalized pCa-force curve shifted rightward with age, leading to decreased activation threshold (pCa₁₀) and/or Ca²⁺ sensitivity (pCa₅₀) for all MHC isoforms examined. In older adults, the slope of the pCa-force curve was unchanged in MHC I-containing fibers (I, I/IIA), but was steeper in MHC II-containing fibers (IIA, IIAX), indicating greater cooperativity compared to young adults. At sub-maximal [Ca²⁺], specific force was reduced in MHC I-containing fibers, but was minimally decreased in MHC IIA fibers as older adults produced greater specific forces at high [Ca²⁺] in these fibers. Lessor pCa₅₀ in MHC I fibers independently predicted reduced isokinetic knee extensor power across a range of contractile velocities, suggesting that the Ca²⁺ response of slow-twitch fibers contributes to whole muscle dysfunction. Our findings show that aging attenuates Ca²⁺ responsiveness across fiber types and that these cellular alterations may lead to age-related reductions in whole muscle power output.

Comparison of the Relationship between Lying and Standing Ultrasonography Measures of Muscle Morphology with Isometric and Dynamic Force Production Capabilities

The purpose of the current study was (1) to examine the differences between standing and lying measures of vastus lateralis (VL), muscle thickness (MT), pennation angle (PA), and cross-sectional area (CSA) using ultrasonography; and (2) to explore the relationships between lying and standing measures with isometric and dynamic assessments of force production-specifically peak force, rate of force development (RFD), impulse, and one-repetition maximum back squat. Fourteen resistance-trained subjects (age = 26.8 ± 4.0 years, height = 181.4 ± 6.0 cm, body mass = 89.8 ± 10.7 kg, back squat to body mass ratio = 1.84 ± 0.34) agreed to participate. Lying and standing ultrasonography images of the right VL were collected following 48 hours of rest. Isometric squat assessments followed ultrasonography, and were performed on force platforms with data used to determine isometric peak force (IPF), as well as RFD and impulse at various time points. Forty-eight hours later, one-repetition maximum back squats were performed by each subject. Paired-samples t-tests revealed statistically significant differences between standing and lying measurements of MT (p < 0.001), PA (p < 0.001), and CSA (p ≤ 0.05), with standing values larger in all cases. Further, standing measures were correlated more strongly and abundantly to isometric and dynamic performance. These results suggest that if practitioners intend to gain insight into strength-power potential based on ultrasonography measurements, performing the measurement collection with the athlete in a standing posture may be preferred.

Chronic β2 -adrenoceptor agonist treatment alters muscle proteome and functional adaptations induced by high intensity training in young men

KEY POINTS

While several studies have investigated the effects of exercise training in human skeletal muscle and the chronic effect of β₂ -agonist treatment in rodent muscle, their effects on muscle proteome signature with related functional measures in humans are still incompletely understood. Herein we show that daily β₂ -agonist treatment attenuates training-induced enhancements in exercise performance and maximal oxygen consumption, and alters muscle proteome signature and phenotype in trained young men. Daily β₂ -agonist treatment abolished several of the training-induced enhancements in muscle oxidative capacity and caused a repression of muscle metabolic pathways; furthermore, β₂ -agonist treatment induced a slow-to-fast twitch muscle phenotype transition. The present study indicates that chronic β₂ -agonist treatment confounds the positive effect of high intensity training on exercise performance and oxidative capacity, which is of interest for the large proportion of persons using inhaled β₂ -agonists on a daily basis, including athletes.

ABSTRACT

Although the effects of training have been studied for decades, data on muscle proteome signature remodelling induced by high intensity training in relation to functional changes in humans remains incomplete. Likewise, β₂ -agonists are frequently used to counteract exercise-induced bronchoconstriction, but the effects β₂ -agonist treatment on muscle remodelling and adaptations to training are unknown. In a placebo-controlled parallel study, we randomly assigned 21 trained men to 4 weeks of high intensity training with (HIT+β₂ A) or without (HIT) daily inhalation of β₂ -agonist (terbutaline, 4 mg dose^-1 ). Of 486 proteins identified by mass-spectrometry proteomics of muscle biopsies sampled before and after the intervention, 32 and 85 were changing (false discovery rate (FDR) ≤5%) with the intervention in HIT and HIT+β₂ A, respectively. Proteome signature changes were different in HIT and HIT+β₂ A (P = 0.005), wherein β₂ -agonist caused a repression of 25 proteins in HIT+β₂ A compared to HIT, and an upregulation of 7 proteins compared to HIT. β₂ -Agonist repressed or even downregulated training-induced enrichment of pathways related to oxidative phosphorylation and glycogen metabolism, but upregulated pathways related to histone trimethylation and the nucleosome. Muscle contractile phenotype changed differently in HIT and HIT+β₂ A (P ≤ 0.001), with a fast-to-slow twitch transition in HIT and a slow-to-fast twitch transition in HIT+β₂ A. β₂ -Agonist attenuated training-induced enhancements in maximal oxygen consumption (P ≤ 0.01) and exercise performance (6.1 vs. 11.6%, P ≤ 0.05) in HIT+β₂ A compared to HIT. These findings indicate that daily β₂ -agonist treatment attenuates the beneficial effects of high intensity training on exercise performance and oxidative capacity, and causes remodelling of muscle proteome signature towards a fast-twitch phenotype.

Influence of platinum harmonized textile on neuromuscular, systemic and subjective recovery

The clothing manufacturer Venex Life-Science tracks the strategy to enhance recovery process through implementing platinum harmonized technology (PHT) into their Venex^® Regeneration Wear. The proposed mechanisms of the regeneration wear are an increase of parasympathetic activity and an increase of the temperature due far-infrared radiation. The purpose of this study was to investigate potential effects of Venex regeneration wear on the recovery of neuromuscular, systemic and subjective parameters following exercise. In a randomized, single-blinded cross-over design, 13 strength-trained male participants performed two exercise sessions in one day. After the first exercise session and for 3 nights following the exercise day participants wore the Venex regeneration wear or a placebo product. Measures of isometric maximum voluntary contraction (MVC), voluntary activation (VA) and potentiated twitch torque (PTT) of the knee extensors, as well as maximum jump height during the Counter-Movement and Drop Jump, creatinkinase (CK) and subjective parameters (perceived pain, recovery condition and sleep quality) were obtained before and after each exercise session and 24, 48, and 72 hours after the first exercise session. MVC, PTT, CK and jump parameters changed over time during the exercise day as well as on the following days, however, there were no significant differences between treatments. Subjective parameters showed strong effect sizes (i. e. Cohen’s d > 0.6) in favor for Venex but no significant differences between treatments. Based on these findings, it is concluded that wearing a platinum harmonized textile following exercise did not improve neuromuscular and systemic recovery in a trained male population to a statistical noticeable extent. However, the findings for the subjective parameters suggest some potential for enhanced recovery that requires further research.

Modifying motor unit territory placement in the Fuglevand model

The Fuglevand model is often used to address challenging questions in neurophysiology; however, there are elements of the neuromuscular system unaccounted for in the model. For instance, in some muscles, slow and fast motor units (MUs) tend to reside deep and superficially in the muscle, respectively, necessarily altering the development of surface electromyogram (EMG) power during activation. Thus, the objective of this study was to replace the randomized MU territory (MUT) placement algorithm in the Fuglevand model with an optimized method capable of reflecting these observations. To accomplish this, a weighting term was added to a previously developed optimization algorithm to encourage regionalized MUT placement. The weighting term consequently produced significantly different muscle fibre type content in the deep and superficial portions of the muscle. The relation between simulated EMG and muscle force was found to be significantly affected by regionalization. These changes were specifically a function of EMG power, as force was unaffected by regionalization. These findings suggest that parameterizing MUT regionalization will allow the model to produce a larger variety of EMG-force relations, as is observed physiologically, and could potentially simulate the loss of specific MU types as observed in ageing and clinical populations.

Pelvic-Floor Properties in Women Reporting Urinary Incontinence After Surgery and Radiotherapy for Endometrial Cancer

BACKGROUND

Endometrial cancer is the fourth most prevalent cancer in Canadian women. Radiotherapy (RT) is frequently recommended as an adjuvant treatment. There is a high prevalence (>80%) of urinary incontinence (UI) after RT. It is plausible that UI is associated, at least in part, with alterations of the pelvic-floor muscles (PFM).

OBJECTIVE

The aim of this exploratory study was to compare the PFM functional properties of women reporting UI after hysterectomy and RT for endometrial cancer with those of women with a history of hysterectomy but without UI.

DESIGN

A descriptive cross-sectional study was conducted. Eleven women were recruited for the affected group, and 18 were recruited for the comparison group.

METHODS

Urogenital and bowel functions were assessed using International Consultation on Incontinence Questionnaires, and PFM properties were evaluated using a Montreal dynamometer. Nonparametric tests were used for comparison of personal characteristics, functional status, and muscle properties. A correspondence analysis detailed the association between UI severity and PFM properties.

RESULTS

Maximal opening of dynamometer branches, maximal vaginal length, PFM maximum force and rate of force development in a strength test, and number of rapid contractions during a speed test were reduced in the affected group. No significant difference was found for the endurance test. The severity of UI was found to correspond to the rate of force development and the number of rapid contractions in a speed test, endurance, age, and vaginal length.

LIMITATIONS

The results are limited to the population studied. The small sample size limited the strength of the conclusions.

CONCLUSIONS

Some evidence of alterations in PFM properties were found in women with UI after hysterectomy and RT for endometrial cancer. These alterations appeared to be associated with UI, suggesting a possible role for rehabilitation.

The effects of electromyostimulation application timing on denervated skeletal muscle atrophy

INTRODUCTION

In this study we evaluated the effect of electromyostimulation (EMS) on myosin heavy chain (MHC) isoform expression in denervated rat muscles to determine the optimal timing for EMS application.

METHODS

EMS was initiated on post-injury day 1 for the group with denervation receiving immediate EMS (DIEMS) and on post-injury day 15 for the group with denervation receiving delayed EMS (DDEMS) in rat denervated muscles. Muscle wet weight and muscle fiber cross-sectional area (FCSA) were measured. MHC isoforms were analyzed in both protein homogenates and single muscle fibers.

RESULTS

The expression levels of IIx and IIb isoforms of MHC were significantly lower and higher, respectively, in the gastrocnemius muscles of the DIEMS group, but not the DDEMS group. The DIEMS group also showed larger FCSA and a lower proportion of hybrid single fibers compared with the DDEMS group.

DISCUSSION

These results indicate that immediate EMS is more effective than delayed EMS for aiding recovery of denervation-induced MHC changes. Muscle Nerve 56: E154-E161, 2017.