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Purpose: We tested the hypothesis that heat stress influences the closed-loop cardio-postural control by an increased blood pressure (BP) drop and postural sway. Methods: Fourteen healthy individuals (eight women) performed two orthostatic tests under thermal reference (TC; ~ 24 ºC) and HOT (~ 38 ºC) conditions. The center-of-pressure (COP) displacements and the electromyography (EMG) activity of the calf muscles (medial gastrocnemius and tibialis anterior) were recorded during the initial orthostasis (ORT onset) after the supine-to-stand challenge. At the same period, BP (beat-to-beat) was continuously monitored, and supine-to-stand variations (∆%) were calculated. Sublingual temperature (Tsl) was measured as a surrogate of internal temperature. Results: Tsl increased in HOT compared to TC (TC 36.5 ± 0.3 vs. HOT 36.7 ± 0.3 ºC; p < 0.01). COP distance was greater in HOT compared to TC condition (TC 596.6 ± 242.4 vs. HOT 680.2 ± 249.1 mm; p < 0.01). EMG activity of the gastrocnemius decreased in HOT compared to TC condition (TC 95.5 ± 19.8 vs. HOT 78.4 ± 22.8%mV; p = 0.02). EMG of tibialis did not change between TC and HOT (TC 83.5 ± 42.9 vs. HOT 66.1 ± 31.9% mV; p = 0.29). BP showed a greater fall in HOT compared to TC condition (∆%TC − 24.5 ± 13.2 vs. ∆%HOT − 33.2 ± 20.2%; p = 0.01). Conclusion: Heat stress causes a greater fall in blood pressure and a reduction in musculoskeletal pump activity during orthostatic onset. These effects could be potential mechanisms that underlie augmented postural instability under a heated environment. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effect of muscle force during active stretch on quantitative and qualitative indicators of exercise-induced muscle damage (EIMD) in the medial gastrocnemius (MG) muscle. Methods: Twelve recreationally active volunteers performed two trials of an eccentric heel drop exercise. Participants performed a single bout of low-load (body weight) and high-load (body weight + 30% body weight) exercises on separate legs. The total mechanical work output for each condition was matched between legs. Before, two hours and 48 h after each bout of eccentric exercise, electrically stimulated triceps surae twitch torque, muscle soreness, MG active fascicle length at maximum twitch torque and muscle passive stiffness were collected. Triceps surae electromyographic (EMG) activity, MG fascicle stretch and MG muscle–tendon unit (MTU) length were measured during the eccentric tasks. Results: The high-load condition increased triceps surae muscle activity by 6–9%, but reduced MG fascicle stretch (p < 0.001). MTU stretch was similar between conditions. The greater muscle force during stretch did not give rise to additional torque loss (5 vs 6%) or intensify muscle soreness. Conclusions: Adding 30% body weight during eccentric contractions has a modest impact on exercise-induced muscle damage in the medial gastrocnemius muscle. These results suggest that muscle load may not be an important determinant of stretch-induced muscle damage in the human MG muscle. The muscle investigated does exhibit large pennation angles and high series elastic compliance; architectural features that likely buffer muscle fibres against stretch and damage. [ABSTRACT FROM AUTHOR]

Maximal strength measured via maximal voluntary contraction is known as a key factor in competitive sports performance as well as injury risk reduction and rehabilitation. Maximal strength and hypertrophy are commonly trained by performing resistance training programs. However, literature shows that long-term, long-lasting static stretching interventions can also produce significant improvements in maximal voluntary contraction. The aim of this study is to compare increases in maximal voluntary contraction, muscle thickness and flexibility after 6 weeks of stretch training and conventional hypertrophy training. Sixty-nine (69) active participants (f = 30, m = 39; age 27.4 ± 4.4 years, height 175.8 ± 2.1 cm, and weight 79.5 ± 5.9 kg) were divided into three groups: IG1 stretched the plantar flexors continuously for one hour per day, IG2 performed hypertrophy training for the plantar flexors (5 × 10–12 reps, three days per week), while CG did not undergo any intervention. Maximal voluntary contraction, muscle thickness, pennation angle and flexibility were the dependent variables. The results of a series of two-way ANOVAs show significant interaction effects (p < 0.05) for maximal voluntary contraction (ƞ2 = 0.143–0.32, p < 0.006), muscle thickness (ƞ2 = 0.11–0.14, p < 0.021), pennation angle (ƞ2 = 0.002–0.08, p = 0.077–0.625) and flexibility (ƞ2 = 0.089–0.21, p < 0.046) for both the stretch and hypertrophy training group without significant differences (p = 0.37–0.99, d = 0.03–0.4) between both intervention groups. Thus, it can be hypothesized that mechanical tension plays a crucial role in improving maximal voluntary contraction and muscle thickness irrespective whether long-lasting stretching or hypertrophy training is used. Results show that for the calf muscle, the use of long-lasting stretching interventions can be deemed an alternative to conventional resistance training if the aim is to increase maximal voluntary contraction, muscle thickness and flexibility. However, the practical application seems to be strongly limited as a weekly stretching duration of up to 7 h a week is opposed by 3 × 15 min of common resistance training. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the relationship between intramuscular adipose tissue (IntraMAT) and muscle stiffness (passive and mechanical) and lengthening in young individuals, hypothesizing that (1) passive muscle stiffness is negatively correlated with the IntraMAT content, and (2) the IntraMAT content is negatively correlated with mechanical changes in muscle stiffness and fascicle length during passive dorsiflexion. Methods: Twenty men and women (20.3 ± 1.3 years) participated in this study. Axial T1-weighted magnetic resonance imaging was performed at the thickest point of the medial gastrocnemius (MG) to measure the IntraMAT cross-sectional area (CSA) and muscle tissue CSA (units; cm2). The shear wave velocity (SWV) and fascicle length at the three ankle joint angles, namely 15° with plantarflexion (PF15), 0° with neutral position (NP), and 15° with dorsiflexion (DF15), were measured as parameters of muscle stiffness (unit; m/s) and lengthening (unit; cm) using ultrasound shear wave elastography and B-mode imaging. We further calculated the changes in SWV and fascicle length from PF15 to NP and from NP to DF15 as mechanical muscle stiffness and lengthening, respectively. Results: There was a relationship between IntraMAT CSA and absolute SWV at DF15 (r = − 0.47, P < 0.05). Further, a relationship was observed between IntraMAT CSA and change in SWV and fascicle length from NP to DF15 (r = − 0.47 and r = 0.59, P < 0.05); whereas no relationship was observed between changes in fascicle length and muscle SWV (r = − 0.23, P = 0.33). Conclusion: These results may indicate biomechanical and/or physiological associations between IntraMAT CSA and passive muscle stiffness. [ABSTRACT FROM AUTHOR]

To counteract the detrimental health effect of sitting all day long, it has been suggested to regularly break sitting time by standing. However, while the difference in energy expenditure, neuromuscular and/or cardiovascular demand of various postures from lying, sitting, and standing is well documented, little is known regarding the dynamic changes occurring during the sit-to-stand transition itself. The aim of the present study was then to describe the cardiometabolic and neuromuscular responses from sitting to standing and specifically during the time-course of this transition. Twelve healthy young participants were asked to perform standardized raises from sitting posture, while cardiometabolic (cardiorespiratory and hemodynamic variables) and neuromuscular (calf muscles' myoelectrical activity, spinal and supraspinal excitabilities) parameters were monitored. As a result, while there was a rapid adaptation for all the systems after rising, the neuromuscular system displayed the faster adaptation (~ 10 s), then hemodynamic (~ 10 to 20 s) and finally the metabolic variables (~ 30 to 40 s). Oxygen uptake, energy expenditure, ventilation, and heart rate were significantly higher and stroke volume significantly lower during standing period compared to sitting one. In calf muscles, spinal excitability (H-reflexes), was lowered by the sit-to-stand condition, while supraspinal drive (V-wave) was similar, indicating different cortico-spinal balance from sitting to standing. Although very heterogenous among participants in terms of magnitude, the present results showed a rapid adaptation for all the systems after rising and the health benefit, notably in terms of energy expenditure, appears rather modest, even if non negligeable. [ABSTRACT FROM AUTHOR]

Purpose: To compare muscle growth adaptations between traditional high-load training and low-load training with blood flow restriction (BFR) in the calf muscles over 6 weeks. Methods: 27 trained individuals performed calf exercise in both legs for 6 weeks. Each leg was randomly assigned to one of the two conditions: (1) Traditional (70% of 1RM) training (TRAD); and (2) Low-load (30% of 1RM) training with BFR. In addition, subjects performed standing calf raises with or without BFR. Measures were taken pre- and post-intervention. Results: For the posterior muscle site, there was no condition (BFR vs. TRAD) × time (pre vs. post) interaction (p = 0.15). In addition, there was no main effect for condition (p = 0.83) or time (p = 0.20). For the lateral muscle site, there was no condition × time interaction (p = 0.47). In addition, there was no main effect for condition (p = 0.10) or time (p = 0.57). For the medial muscle site, there was no condition × time interaction (p = 0.60). In addition, there was no main effect for condition (p = 0.44) or time (p = 0.72). For RPE, there was no condition × time interaction. However, there was a main effect for condition (p < 0.05) with BFR having higher RPE. For discomfort, there was no condition × time interaction. However, there was a main effect for condition (p < 0.001) with the BFR condition displaying higher discomfort. Conclusion: No muscle growth was detected in the calf musculature. BFR was not more effective at eliciting muscle hypertrophy compared to traditional training. However, it was accompanied with higher exertion and discomfort. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the present study was to determine whether there are sex differences in fatigue-induced changes in quiet standing and dynamic balance and establish whether changes in muscle torque and resting stiffness may explain the potential sex differences in balance responses. Methods: Sixteen recreationally active men (age; 24.8 ± 5.0 years, height; 178.2 ± 5.6 cm, mass; 77.8 ± 13.2 kg) and 10 women (age; 21.0 ± 1.6 years, height; 167 ± 5.3 cm, mass; 61.3 ± 8.9 kg) were assessed for postural sway, Y balance test performance, isokinetic and isometric knee extensor torque and resting stiffness of the vastus lateralis (VL), gastrocnemius lateralis (GL) and Achilles tendon (AT) before and immediately after fatiguing exercise. The fatigue protocol consisted of five sets of 20-drop jumps. Results: The fatiguing exercise elicited similar magnitude (effects size; ES) reductions in muscle torque (men; ES = 0.45–0.80, women; ES = 0.46–0.52), dynamic balance (men; ES = 0.45–0.74, women; ES = 0.47–0.79) and resting VL stiffness (men; ES = 0.46, women; ES = 0.36) in men and women (all p < 0.05). For quiet standing balance, fatigue induced an increase in postural sway metrics (ES = 0.64–1.28) and reduction in resting GL stiffness (ES = 0.40) in men (both p < 0.001) but not women (p > 0.05). Conclusion: Fatiguing exercise, when producing a similar level of force reduction, induces similar magnitude reductions in dynamic postural control and resting VL stiffness in men and women. Distinct deteriorations in quiet standing balance in men but not women were accompanied by modifications in calf muscle stiffness following exercise-induced muscle fatigue. [ABSTRACT FROM AUTHOR]

Purpose: Although it is known that peripheral arterial disease (PAD) is associated with chronic myopathies, the acute muscular responses to exercise in this population are less clear. This study used diffusion tensor imaging (DTI) to compare acute exercise-related muscle damage between PAD patients and healthy controls. Methods: Eight PAD patients and seven healthy controls performed graded plantar flexion in the bore of a 3T MRI scanner. Exercise began at 2 kg and increased by 2 kg every 2 min until failure, or completion of 10 min of exercise. DTI images were acquired from the lower leg pre- and post-exercise, and were analyzed for mean diffusivity, fractional anisotropy (FA), and eigenvalues 1–3 (λ1–3) of the medial gastrocnemius (MG) and tibialis anterior (TA). Results: Results indicated a significant leg by time interaction for mean diffusivity, explained by a significantly greater increase in diffusivity of the MG in the most affected legs of PAD patients (11.1 × 10–4 ± 0.5 × 10–4 mm2/s vs. 12.7 × 10–4 ± 1.2 × 10–4 mm2/s at pre and post, respectively, P = 0.02) compared to healthy control subjects (10.8 × 10–4 ± 0.3 × 10–4 mm2/s vs. 11.2 × 10–4 ± 0.5 × 10–4 mm2/s at pre and post, respectively, P = 1.0). No significant differences were observed for the TA, or λ1–3 (all P ≥ 0.06). Moreover, no reciprocal changes were observed for FA in either group (all P ≥ 0.29). Conclusion: These data suggest that calf muscle diffusivity increases more in PAD patients compared to controls after exercise. These findings are consistent with the notion that acute exercise results in increased muscle damage in PAD. [ABSTRACT FROM AUTHOR]

Purpose: Despite the widespread occurrence of muscle cramps, their underlying neurophysiological mechanisms remain unknown. To better understand the etiology of muscle cramps, this study investigated acute effects of muscle cramping induced by maximal voluntary isometric contractions (MVIC) and neuromuscular electrical stimulation (NMES) on the amplitude of Hoffmann reflexes (H-reflex) and compound muscle action potentials (M-wave). Methods: Healthy men (n = 14) and women (n = 3) participated in two identical sessions separated by 7 days. Calf muscle cramping was induced by performing MVIC of the plantar flexors in a prone position followed by 2.5-s NMES over the plantar flexors with increasing frequency and intensity. H-reflexes and M-waves evoked by tibial nerve stimulation in gastrocnemius medialis (GM) and soleus were recorded at baseline, and after MVIC-induced cramps and the NMES protocol. Results: Six participants cramped after MVIC, and H-reflex amplitude decreased in GM and soleus in Session 1 (− 33 ± 32%, − 34 ± 33%, p = 0.031) with a similar trend in Session 2 (5 cramped, p = 0.063), whereas the maximum M-wave was unchanged. After NMES, 11 (Session 1) and 9 (Session 2) participants cramped. H-reflex and M-wave recruitment curves shifted to the left in both sessions and muscles after NMES independent of cramping (p ≤ 0.001). Conclusion: Changes in H-reflexes after a muscle cramp induced by MVIC and NMES were inconsistent. While MVIC-induced muscle cramps reduced H-reflex amplitude, muscle stretch to end cramping was a potential contributing factor. By contrast, NMES may potentiate H-reflexes and obscure cramp-related changes. Thus, the challenge for future studies is to separate the neural consequences of cramping from methodology-based effects. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to explore how compression stockings affect the energetics and biomechanics during walking.Methods: Sixteen male adults participated in this study. Participants completed walking trials on the treadmill and force plates, wearing compression stockings (CS) or nothing as a control condition (CON). The data obtained included metabolic rate, muscle activation, step frequency and step length as well as their variability, joint kinematics and joint kinetics.Results: The effect of compression stockings on metabolic rate was trivial (CS: 3.81 ± 0.44 W kg-1, CON: 3.83 ± 0.46 W kg-1, p = 0.84, d = 0.05). Activation of calf muscles, step frequency and step length as well as their variability, joint range of motion and joint powers did not show a significant difference between conditions (p = 0.09-0.90, d = 0.01-0.34). The peak knee extension moment during the early stance phase had a tendency to increase (CS: 0.57 ± 0.27 N m kg-1, CON: 0.51 ± 0.28 N m kg-1, p = 0.05, d = 0.19) while the peak knee flexion moment during the late swing phase had a tendency to decrease (CS: 0.16 ± 0.10 N m kg-1, CON: 0.19 ± 0.12 N m kg-1, p = 0.10, d = 0.21). The peak ankle dorsiflexion moment during the early stance phase significantly increased (CS: 0.11 ± 0.06 N m kg-1, CON: 0.08 ± 0.05 N m kg-1, p = 0.02, d = 0.58) while the peak ankle plantar flexion moment during the late swing phase significantly decreased (CS: 1.41 ± 0.12 N m kg-1, CON: 1.47 ± 0.14 N m kg-1, p = 0.02, d = 0.45).Conclusions: Compression stockings have a limited effect on improving energetics of walking, but they may play a role in improving biomechanics by altering the relative contribution of knee and ankle moments to propulsion. [ABSTRACT FROM AUTHOR]

Purpose: The recovery of muscle oxygen consumption (m[Formula: see text]O2) after exercise provides a measure of skeletal muscle mitochondrial capacity, as more and better-functioning mitochondria will be able to restore m[Formula: see text]O2 faster to the pre-exercise state. The aim was to measure muscle mitochondrial capacity using near-infrared spectroscopy (NIRS) within a healthy, normally active population and relate this to parameters of aerobic fitness, investigating the applicability and relevance of using NIRS to assess muscle mitochondrial capacity non-invasively.Methods: Mitochondrial capacity was analysed in the gastrocnemius and flexor digitorum superficialis (FDS) muscles of eight relatively high-aerobic fitness ([Formula: see text]O2peak ≥ 57 mL/kg/min) and eight relatively low-aerobic fitness male subjects ([Formula: see text]O2peak ≤ 47 mL/kg/min). Recovery of whole body [Formula: see text]O2, i.e. excess post-exercise oxygen consumption (EPOC) was analysed after a cycling protocol.Results: Mitochondrial capacity, as analysed using NIRS, was significantly higher in high-fitness individuals compared to low-fitness individuals in the gastrocnemius, but not in the FDS (p = 0.0036 and p = 0.20, respectively). Mitochondrial capacity in the gastrocnemius was significantly correlated with [Formula: see text]O2peak (R2 = 0.57, p = 0.0019). Whole body [Formula: see text]O2 recovery was significantly faster in the high-fitness individuals (p = 0.0048), and correlated significantly with mitochondrial capacity in the gastrocnemius (R2 = 0.34, p = 0.028).Conclusion: NIRS measurements can be used to assess differences in mitochondrial muscle oxygen consumption within a relatively normal, healthy population. Furthermore, mitochondrial capacity correlated with parameters of aerobic fitness ([Formula: see text]O2peak and EPOC), emphasising the physiological relevance of the NIRS measurements. [ABSTRACT FROM AUTHOR]

Purpose: Exposure to hypoxia has been suggested to activate multiple adaptive pathways so that muscles are better able to maintain cellular energy homeostasis. However, there is limited research regarding the tissue specificity of this response. The aim of this study was to investigate the influence of tissue specificity on mitochondrial adaptations of rat skeletal and heart muscles after 4 weeks of normobaric hypoxia (FiO2: 0.10).Methods: Twenty male Wistar rats were randomly assigned to either normobaric hypoxia or normoxia. Mitochondrial respiration was determined in permeabilised muscle fibres from left and right ventricles, soleus and extensorum digitorum longus (EDL). Citrate synthase activity and the relative abundance of proteins associated with mitochondrial biogenesis were also analysed.Results: After hypoxia exposure, only the soleus and left ventricle (both predominantly oxidative) presented a greater maximal mass-specific respiration (+48 and +25%, p < 0.05) and mitochondrial-specific respiration (+75 and +28%, p < 0.05). Citrate synthase activity was higher in the EDL (0.63 ± 0.08 vs 0.41 ± 0.10 µmol min- 1 µg- 1) and lower in the soleus (0.65 ± 0.17 vs 0.87 ± 0.20 µmol min- 1 µg- 1) in hypoxia with respect to normoxia. There was a lower relative protein abundance of PGC-1α (-25%, p < 0.05) in the right ventricle and a higher relative protein abundance of PGC-1β (+43%, p < 0.05) in the left ventricle of rats exposed to hypoxia, with few differences for protein abundance in the other muscles.Conclusion: Our results show a muscle-specific response to 4 weeks of normobaric hypoxia. Depending on fibre type, and the presence of ventricular hypertrophy, muscles respond differently to the same degree of environmental hypoxia. [ABSTRACT FROM AUTHOR]

Purpose: Age-related exercising leg blood flow (LBF) responses during dynamic knee-extension exercise and forearm blood flow responses during handgrip exercise are preserved in normally active men but attenuated in activity-matched women. We explored whether these age- and sex-specific effects are also apparent during isometric calf plantar-flexion incremental exercise.Methods: Normally active young men (YM, n = 15, 24 ± 2 years), young women (YW, n = 8, 22 ± 1 years), older men (OM, n = 13, 70 ± 7 years) and older women (OW, n = 10, 64 ± 7 years) were tested. LBF was measured between contractions using venous occlusion plethysmography.Results: Peak force obtained was higher (P < 0.05) in men compared with women and in young compared with older individuals. However, peak LBF (YM; 971 ± 328 ml min-1, OM; 985 ± 504 ml min-1, YW; 844 ± 366 ml min-1, OW; 960 ± 244 ml min-1) and peak leg vascular conductance [LVC = LBF/(MAP + hydrostatic pressure)] responses (YM; 6.0 ± 1.8 ml min-1 mmHg-1, OM; 5.5 ± 2.8 ml min-1 mmHg-1, YW; 5.3 ± 2.1 ml min-1 mmHg-1, OW; 5.5 ± 1.6 ml min-1 mmHg-1) were similar among the four groups. Furthermore, the hyperaemic (YM; 8.8 ± 3.7 ml min-1 %Fpeak-1 OM; 8.3 ± 5.4 ml min-1 %Fpeak-1, YW; 8.2 ± 3.5 ml min-1 %Fpeak-1, OW; 9.6 ± 2.2 ml min-1 %Fpeak-1) and vasodilatory responses (YM; 0.053 ± 0.020 ml min-1 mmHg-1 %Fpeak-1, OM; 0.048 ± 0.028 ml min-1 mmHg-1 %Fpeak-1, YW; 0.051 ± 0.019 ml min-1 mmHg-1 %Fpeak-1, OW; 0.055 ± 0.014 ml min-1 mmHg-1 %Fpeak-1) were not different among the four groups. These results were accompanied by similar resting LBF responses among groups and were not affected when data were normalised to estimated leg muscle mass.Conclusions: Our results demonstrate that exercising LBF responses during isometric incremental calf muscle exercise are preserved in older men and women, suggesting that the previously observed age-related attenuations in leg and forearm hyperaemia among women may be muscle-group specific. [ABSTRACT FROM AUTHOR]

Purpose: The present study was performed to determine the impact of hypoxia on working muscle oxygenation during incremental running, and to compare tissue oxygenation between the thigh and calf muscles.Methods: Nine distance runners and triathletes performed incremental running tests to exhaustion under normoxic and hypoxic conditions (fraction of inspired oxygen = 0.15). Peak pulmonary oxygen uptake ([Formula: see text]) and tissue oxygen saturation (StO2) were measured simultaneously in both the vastus lateralis and medial gastrocnemius.Results: Hypoxia significantly decreased peak running speed and [Formula: see text] (p < 0.01). During incremental running, StO2 in the vastus lateralis decreased almost linearly, and the rate of decrease from warm-up (180 m min-1) to [Formula: see text] was significantly greater than in the medial gastrocnemius under both normoxic and hypoxic conditions (p < 0.01). StO2 in both muscles was significantly decreased under hypoxic compared with normoxic conditions at all running speeds (p < 0.01). The rate at which StO2 was decreased by hypoxia was greater in the vastus lateralis as the running speed increased, whereas it changed little in the medial gastrocnemius.Conclusions: These results suggest that the thigh is more deoxygenated than the calf under hypoxic conditions, and that the effects of hypoxia on tissue oxygenation differ between these two muscles during incremental running. [ABSTRACT FROM AUTHOR]

Purpose: 23Na MRI demonstrated increased tissue sodium concentrations in a number of pathologies. Acute atrophy results in muscle fibre volume shrinking that may result in a relative increase of extracellular volume and might affect sodium concentration. Thus, we hypothesized that local unloading of the calf muscles would lead to a decrease in muscle volume and an increase in muscle tissue sodium concentration.Method: One lower leg of 12 healthy male subjects was submitted to a 60 day long period of unloading using the Hephaistos orthosis, while the other leg served as control. 23Na MRI and 2D PD-weighted Dixon turbo spin echo were obtained from the control and orthosis leg using a 3T scanner. For quantification, a sodium reference phantom was used with 10, 20, 30, and 40 mmol/L NaCl solution.Result: Tissue sodium concentration (TSC) increased as an effect of unloading in the orthosis leg. Relative increases were 17.4 ± 16.8% (P = 0.005) in gastrocnemius medialis muscle, 11.1 ± 12.5 (P = 0.037) in gastrocnemius lateralis muscle, 16.2 ± 4.7% (P < 0.001) in soleus muscle, 10.0 ± 10.5% (P = 0.009) in the ventral muscle group, and 10.7 ± 10.0% (P = 0.003) in the central muscle group, respectively. TSC in the control leg did not significantly change. In the orthosis leg, muscle volume decreased as follows: medial gastrocnemius muscle: -5.4 ± 8.3% (P = 0.043) and soleus muscle: -7.8 ± 15.0% (P = 0.043).Conclusion: Unloading atrophy is associated with an increase in muscle sodium concentration. 23Na MRI is capable of detecting these rather small changes. [ABSTRACT FROM AUTHOR]

Purpose: To examine the effects of low-load knee extensor training to fatigue with and without blood flow restriction (BFR) on calf vascular conductance, calf venous compliance, and peripheral arterial stiffness in middle-aged individuals. Methods: Eleven men (55 ± 8 years) and five post-menopausal women (57 ± 5 years) completed 6 weeks of unilateral knee extensor training with one limb exercising with BFR (BFR limb) and the contralateral limb exercising without BFR (free flow, FF limb). Before and after the training, femoral pulse wave velocity (PWV), calf blood flow (normalized as conductance), and calf venous compliance were measured in each limb. Results: PWV increased following training in both limbs (main effect of time, p = 0.036; BFR limb 8.9 ± 0.8 vs. 9.5 ± 0.9 m/s, FF limb 9.0 ± 1.2 vs. 9.0 ± 1.1; Pre vs. Post). Calf blood flow increased ( p = 0.026) in the FF limb (25.0 ± 7.0 vs. 31.8 ± 12.0 flow/mmHg; Pre vs. Post) but did not change ( p = 0.831) in the BFR limb (29.1 ± 11.3 vs. 28.7 ± 11.5 flow/mmHg; Pre vs. Post). Calf venous compliance did not change in either limb following training. Conclusions: These results suggest low-load BFR resistance training to fatigue elicits small increases in peripheral arterial stiffness without eliciting concomitant changes in venous compliance. In addition, unlike low-load knee extensor training without BFR, training with BFR did not enhance calf blood flow. [ABSTRACT FROM AUTHOR]

Mechanical loading of human tendon stimulates collagen synthesis, but the relationship between acute loading responses and training status of the tendon is not clear. We tested the effect of prolonged load deprivation on the acute loading-induced collagen turnover in human tendons, by applying the same absolute load to a relative untrained Achilles tendon (2 -week immobilization period prior to acute loading) and a habitually loaded contra -lateral Achilles tendon, respectively, within the same individuals. Eight untrained, healthy males had one lower limb totally immobilized for 2 weeks, whereas the contra -lateral leg was used habitually. Following the procedure both Achilles tendons and calf muscles were loaded with the same absolute load during a 1 -h treadmill run. Tissue collagen turnover was measured by microdialysis performed post -immobilization but pre -exercise around both Achilles tendons and compared to values obtained by 72 -h post -exercise. Power Doppler was used to monitor alterations in intratendinous blood flow velocity of the Achilles tendon and MRI used to quantitate changes in tendon cross -section area. Acute loading resulted in an increased collagen synthesis 72 h after the run in both Achilles tendons ( p < 0.05) with no significant difference. No signs of acute tendon overloading were demonstrated by Power Doppler, and tendon cross -section area did not change as a result of immobilization and reloading. The present study indicates that 2 weeks of tendon load deprivation is not sufficient to affect the normal adaptive response to loading determined as increased collagen synthesis of peritendinous Achilles tendon tissue in humans. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the mechanisms of cell death (apoptosis vs. necrosis) during muscle atrophy induced by 1 week of hindlimb suspension. Biochemical and morphological parameters were examined in murine soleus and gastrocnemius muscles. A total of 70 male Charles River CD1 mice were randomly assigned to seven groups (n = 10/group): Cont (loading control conditions) and 6HS, 12HS, 24HS, 48HS, 72HS and 1wkHS with respect to the period of hindlimb suspension (HS). Compared to the Cont, skeletal muscle atrophy was confirmed by a significant decrease of 44 and of 17% in fiber cross-sectional areas in the gastrocnemius and soleus, respectively. A significant increase in caspase-3 activity was noticed in 6HS (196%, P < 0.05) and in 12HS (201%, P < 0.05), as well as the amount of cytosolic mono- and oligonucleosomes at 12HS (142%, P < 0.05) and 24HS (203%, P < 0.05) in the gastrocnemius and soleus, respectively. The profile of necrotic markers showed a peak of myeloperoxidase activity at 24HS (170%, P < 0.05) and at 72HS (114%, P < 0.05) in the gastrocnemius and soleus, respectively. The analysis of N-acetylglucosaminidase activity evidenced more increment in the soleus at 72HS (60%, P < 0.05). The analysis of the basal values of these parameters suggested that apoptosis prevailed in the slow-twitch muscle analyzed, whereas lysosomic activity seemed to be more pronounced in the gastrocnemius. The morphological data supported the biochemical results pointing towards a shift from apoptosis to necrosis, which seems to corroborate the aponecrosis theory. [ABSTRACT FROM AUTHOR]

It is known that the relevance of a peripheral stenosis for muscle function increases with exercise. Our intention was to investigate the impact of a moderate cuff stenosis (CS) at 120 mmHg of the superficial femoral artery on high-energy phosphate (HEP) metabolism during isotonic, incremental calf exercise. Serial phosphorus 31 magnetic resonance spectroscopy (31P MRS) and velocity-encoded phase-contrast MR imaging (VEPC MRI) were carried out in each leg of ten healthy male volunteers. Each leg underwent four increments of calf exercise (2, 3, 4 and 5 W) followed by recovery during separate exercise sessions with and without a CS at 120 mmHg. The serial 31P MRS measurements had a time resolution of 10 s. VEPC MRI was performed at the end of each increment during separate sessions. During all increments, we detected significant differences ( P < 0.05) in the phosphocreatine (PCr) time constants and the amount of PCr hydrolysis between the sessions without and with CS. Regarding the time courses of the PCr, inorganic phosphate (Pi) and pH level, we observed significant differences ( P < 0.002) during exercise and recovery. During both conditions, the end-increment PCr levels as well as blood flow correlated significantly with the mechanical power. The PCr time constants during exercise significantly correlated with the intramuscular pH, but not with blood flow or mechanical power. However, the PCr recovery time constants correlated significantly with blood flow and end-exercise pH. Our study shows that reduction of blood flow due to a peripheral stenosis results in a prolongation of PCr time constants, decreased PCr and pH level as well as increased Pi level during exercise. We believe that 31P MRS during incremental exercise might provide additional information for assessing the relevance of a peripheral stenosis and its impact on muscle function. [ABSTRACT FROM AUTHOR]

Ageing is associated with an increased susceptibility to muscle damage but little is known on how this affects muscle recovery after exercise. Hence, this study is aiming at investigating the effects of a heavy-resistance training session of neuromuscular recovery of the calf muscles of a group of elderly men aged >65. Maximal isometric and isokinetic torque, muscle voluntary activation (VA) capacity, surface electromyographic activity (EMG), peak-to-peak amplitude of action potentials associated with twitch responses of plantar flexors were evaluated before and 5 min (post1), 24 h (post2) and 48 h (post3) after 10 sets of 10 repetitions of a calf raise exercise performed at an intensity of 70% of the individual, one repetition maximum. Blood samples were taken before and 1, 48, 96 and 144 h after the training session and assayed for serum creatine kinase (CK), lactate dehydrogenase (LDH) and myoglobin (Mb). Peak torque during eccentric and concentric (120 degrees s-1) contractions and twitch parameters were significantly reduced at post1, and recovered completely at post2. No significant changes were found in integrated EMG, M-wave amplitudes and VA throughout the entire test period. CK and LDH concentrations reached peak values 48 h after the exercise session and returned to the pre-exercise values 96 h after the training session. Serum Mb level increased by 73.2% 1 h after exercise and recovered at 48 h. The reduction in peak torque following a strength training session in an elderly population could be explained mainly by fatigue of peripheral origin. After 24 h the elders recovered completely their capacities of strength production, despite muscle damage being still evident 48 h after the strength training session. [ABSTRACT FROM AUTHOR]

The purpose of this study was to use a model of aging to examine the relationships between passive properties of the calf muscles and plantarflexion concentric isokinetic torque characteristics. Eighty-one active women 20–84 years of age were tested using a Kin-Com isokinetic dynamometer interfaced with electromyography (EMG). The passive properties were tested by stretching the muscles from relaxed plantarflexion to a maximal dorsiflexion (DF) angle at a rate of 5°·s–1 (0.087 rad·s–1) with minimal raw EMG activity (<0.05 mV). The maximal concentric torque was tested from maximal passive DF into plantarflexion at four randomly ordered velocities of 30, 60, 120, and 180°·s–1. Pearson correlation coefficients (Bonferroni adjusted) indicated a hierarchical order of high to moderate positive correlations between four passive properties and the peak and mean concentric torque for all test velocities. Correlation coefficients for the four passive properties ranged from 0.50 to 0.78 (P<0.001), and the coefficients of determination (r2) from higher to lower were: (1) maximal DF passive resistive torque (r2: 0.50–0.62), (2) length extensibility (r2: 0.40–0.49), (3) maximal muscle length (r2: 0.28–0.41), and (4) passive elastic stiffness in the last half of the full-stretch range of motion (r2: 0.25–0.31). The maximal DF passive resistive torque and the length extensibility accounted for 50–62% and 40–49% of the variability in the concentric torque, respectively. The results indicate that the concentrically stronger calf muscles of active women were positively correlated with passively stronger, longer, and stiffer calf muscles, which are characteristics of the calf muscles of younger women. Further studies are needed to examine whether therapeutic interventions, such as stretching and strengthening, can promote adaptations in the calf muscles of older women to attain these more youthful characteristics. [ABSTRACT FROM AUTHOR]