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Purpose: Power output at the moderate-to-heavy-intensity transition decreases during prolonged exercise, and resilience to this has been termed 'durability'. The purpose of this study was to assess the relationship between durability and the effect of prolonged exercise on severe-intensity performance, and explore intramuscular correlates of durability. Methods: On separate days, 13 well-trained cyclists and triathletes (V̇O2peak, 57.3 ± 4.8 mL kg−1 min−1; training volume, 12 ± 2.1 h week−1) undertook an incremental test and 5-min time trial (TT) to determine power output at the first ventilatory threshold (VT1) and severe-intensity performance, with and without 150-min of prior moderate-intensity cycling. A single resting vastus lateralis microbiopsy was obtained. Results: Prolonged exercise reduced power output at VT1 (211 ± 40 vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rs = 0.719, P = 0.007). Durability of VT1 was not related to vastus lateralis carnosine content, citrate synthase activity, or complex I activity (P > 0.05). Conclusion: These data provide the first direct support that durability of the moderate-to-heavy-intensity transition is an important performance parameter, as more durable athletes exhibited smaller reductions in 5-min TT performance following prolonged exercise. We did not find relationships between durability and vastus lateralis carnosine content, citrate synthase activity, or complex I activity. [ABSTRACT FROM AUTHOR]

Background: Lower activation of higher threshold (type-II) motor units (MUs) has been suggested in children compared with adults. We examined child–adult differences in discrete MU activation of the flexor carpi radialis (FCR). Methods: Fifteen boys (10.2 ± 1.4 years), and 17 men (25.0 ± 2.7 years) completed 2 laboratory sessions. Following a habituation session, maximal voluntary isometric wrist flexion torque (MVIC) was determined before completing trapezoidal isometric contractions at 70%MVIC. Surface electromyography was captured by Delsys Trigno Galileo sensors and decomposed into individual MU action potential trains. Recruitment threshold (RT), and MU firing rates (MUFR) were calculated. Results: MVIC was significantly greater in men (10.19 ± 1.92 Nm) than in boys (4.33 ± 1.47 Nm) (p < 0.05), but not statistically different after accounting for differences in body size. Mean MUFR was not different between boys (17.41 ± 7.83 pps) and men (17.47 ± 7.64 pps). However, the MUFR–RT slope was significantly (p < 0.05) steeper (more negative) in boys, reflecting a progressively greater decrease in MUFR with increasing RT. Additionally, boys recruited more of their MUs early in the ramped contraction. Conclusion: Compared with men, boys tended to recruit their MUs earlier and at a lower percentage of MVIC. This difference in MU recruitment may explain the greater decrease in MUFR with increasing RT in boys compared with men. Overall, these findings suggest an age-related difference in the neural strategy used to develop moderate–high torque in wrist flexors, where boys recruit more of their MUs earlier in the force gradation process, possibly resulting in a narrower recruitment range. [ABSTRACT FROM AUTHOR]

Purpose: Autonomic control of orofacial areas is an integral part of the stress response, controlling functions such as pupil dilatation, salivation, and skin blood flow. However, the specific control of blood flow in head muscles during stress is unknown. This study aims to investigate the hemodynamic response of temporalis and masseter muscles in response to five different stressors. Methods: Sixteen healthy individuals were subjected to a randomized series of stressors, including cold pressor test, mental arithmetic test, apnea, isometric handgrip, and post-handgrip muscle ischemia, while in the sitting posture. Finger-pulse photoplethysmography was used to measure arterial blood pressure, heart rate, and cardiac output. Near-infrared spectroscopy was used to measure changes in tissue oxygenation and hemoglobin indices from the temporalis and masseter muscles. Results: All stressors effectively and significantly increased arterial blood pressure. Tissue oxygenation index significantly increased in both investigated head muscles during mental arithmetic test (temporalis: 4.22 ± 3.52%; masseter: 3.43 ± 3.63%) and isometric handgrip (temporalis: 3.45 ± 3.09%; masseter: 3.26 ± 3.07%), suggesting increased muscle blood flow. Neither the masseter nor the temporalis muscles evidenced a vasoconstrictive response to any of the stressors tested. Conclusion: In the different conditions, temporalis and masseter muscles exhibited similar hemodynamic patterns of response, which do not include the marked vasoconstriction generally observed in limb muscles. The peculiar sympathetic control of head muscles is possibly related to the involvement of these muscles in aggressive/defensive reactions and/or to their unfavorable position with regard to hydrostatic blood levels. [ABSTRACT FROM AUTHOR]

There is increasing appreciation of the role of rate of torque development (RTD) in physical function of older adults (OAs). This study compared various RTD strategies and electromyography (EMG) in the knee extensors and focused on discriminating groups with potential limitations in voluntary activation (VA) and associations of different RTD indices with functional tests that may be affected by VA in OAs. Neuromuscular function was assessed in 20 younger adults (YAs, 22.0 ± 1.7 years) and 50 OAs (74.4 ± 7.0 years). Isometric ballistic and peak torque during maximal voluntary contractions (pkTMVC), doublet stimulation and surface EMG were assessed and used to calculate VA during pkTMVC and RTD and rate of EMG rise during ballistic contractions. Select mobility tests (e.g., gait speed, 5× chair rise) were also assessed in the OAs. Voluntary RTD and RTD normalized to pkTMVC, doublet torque, and peak doublet RTD were compared. Rate of EMG rise and voluntary RTD normalized to pkTMVC did not differ between OAs and YAs, nor were they associated with functional test scores. Voluntary RTD indices normalized to stimulated torque parameters were significantly associated with VA (r = 0.319–0.459), and both indices were significantly lower in OAs vs YAs (all p < 0.020). These RTD indices showed significant association with the majority of mobility tests, but there was no clear advantage among them. Thus, voluntary RTD normalized to pkTMVC was ill-suited for use in OAs, while results suggests that voluntary RTD normalized to stimulated torque parameters may be useful for identifying central mechanisms of RTD impairment in OAs. Clinical trial registration number NCT02505529; date of registration 07/22/2015. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to determine whether the modulation of primary afferent depolarization (PAD) and homosynaptic post-activation depression (HPAD) are involved in the lower efficacy of Ia-afferent-α-motoneuron transmission commonly observed during lengthening compared to isometric and shortening conditions. Methods: 15 healthy young individuals participated in two experimental sessions dedicated to measurement in passive and active muscle states, respectively. In each session, PAD, HPAD and the efficacy of Ia-afferent-α-motoneuron transmission were evaluated during lengthening, shortening and isometric conditions. PAD was evaluated with D1 inhibition technique. Posterior tibial nerve stimulation was used to study HPAD and the efficacy of the Ia-afferent-α-motoneuron transmission through the recording of the soleus Hoffmann reflex (H reflex). Results: PAD was increased in lengthening than shortening (11.2%) and isometric (12.3%) conditions regardless of muscle state (P < 0.001). HPAD was increased in lengthening than shortening (5.1%) and isometric (4.2%) conditions in the passive muscle state (P < 0.05), while no difference was observed in the active muscle state. H reflex was lower in lengthening than shortening (− 13.2%) and isometric (− 9.4%) conditions in both muscle states (P < 0.001). Conclusion: These results highlight the specific regulation of PAD and HPAD during lengthening conditions. However, the differences observed during passive lengthening compared to shortening and isometric conditions seem to result from an increase in Ia-afferent discharge, while the variations highlighted during active lengthening might come from polysynaptic descending pathways involving supraspinal centres that could regulate PAD mechanism. [ABSTRACT FROM AUTHOR]

Purpose: It is suggested that the early phase (< 50 ms) of force development during a muscle contraction is associated with intrinsic contractile properties, while the late phase (> 50 ms) is associated with maximal force. There are no direct investigations of single muscle fibre rate of force development (RFD) as related to joint-level RFD Methods: Sixteen healthy, young (n = 8; 26.4 ± 1.5 yrs) and old (n = 8; 70.1 ± 2.8 yrs) males performed maximal voluntary isometric contractions (MVC) and electrically evoked twitches of the knee extensors to assess RFD. Then, percutaneous muscle biopsies were taken from the vastus lateralis and chemically permeabilized, to assess single fibre function. Results: At the joint level, older males were ~ 30% weaker and had ~ 43% and ~ 40% lower voluntary RFD values at 0–100 and 0–200 ms, respectively, than the younger ones (p ≤ 0.05). MVC torque was related to every voluntary RFD epoch in the young (p ≤ 0.001), but only the 0–200 ms epoch in the old (p ≤ 0.005). Twitch RFD was ~ 32% lower in the old compared to young (p < 0.05). There was a strong positive relationship between twitch RFD and voluntary RFD during the earliest time epochs in the young (≤ 100 ms; p ≤ 0.01). While single fibre RFD was unrelated to joint-level RFD in the young, older adults trended (p = 0.052–0.055) towards significant relationships between joint-level RTD and Type I single fibre RFD at the 0–30 ms (r2 = 0.48) and 0–50 ms (r2 = 0.49) time epochs. Conclusion: Electrically evoked twitches are good predictors of early voluntary RFD in young, but not older adults. Only the older adults showed a potential relationship between single fibre (Type I) and joint-level rate of force development. [ABSTRACT FROM AUTHOR]

Aim: The acute myocellular responses of caffeine supplementation during resistance exercise (RE) have not been investigated. β2-Adrenergic receptors (β2AR) may be a target of the stimulatory effects of caffeine and stimulate bioenergetic pathways including protein kinase A (PKA), and mitogen-activated protein kinases (MAPK). Purpose: Elucidate the effects of pre-workout supplementation on signaling responses to an acute RE bout. Methods: In a randomized, counter-balanced, double-blind, placebo-controlled, within-subject crossover study, ten resistance-trained males (mean ± SD; age = 22 ± 2.4 years, height = 175 ± 7 cm, body mass = 84.1 ± 11.8 kg) consumed a caffeine containing multi-ingredient pre-workout supplement (SUPP) or color and flavor matched placebo (PL) 60 min prior to an acute RE bout of barbell back squats. Pre- and post-exercise muscle biopsies were analyzed for the phosphorylation (p-) of β2AR, PKA, and MAPK (ERK, JNK, p38). Epinephrine was determined prior to supplementation (baseline; BL), after supplementation but prior to RE (PRE), and immediately after RE (POST). Results: Epinephrine increased at PRE in SUPP (mean ± SE: 323 ± 34 vs 457 ± 68 pmol/l; p = 0.028), and was greatest at POST in the SUPP condition compared to PL (5140 ± 852 vs 2862 ± 498 pmol/l; p = 0.006). p-β2AR and p-MAPK increased post-exercise (p < 0.05) with no differences between conditions (p > 0.05). Pearson correlations indicated there was a relationship between epinephrine and p-β2AR in PL (r = − 0.810; p = 0.008), and p-β2AR and ERK in SUPP (r = 0.941; p < 0.001). Conclusion: Consumption of a caffeine containing pre-workout supplement improves performance, possibly through increases in pre-exercise catecholamines. However, the acute myocellular signaling responses were largely similar post-exercise. [ABSTRACT FROM AUTHOR]

Purpose: Mitochondrial dynamics are regulated by the differing molecular pathways variously governing biogenesis, fission, fusion, and mitophagy. Adaptations in mitochondrial morphology are central in driving the improvements in mitochondrial bioenergetics following exercise training. However, there is a limited understanding of mitochondrial dynamics in response to inactivity. Methods: Skeletal muscle biopsies were obtained from middle-aged males (n = 24, 49.4 ± 3.2 years) who underwent sequential 14-day interventions of unilateral leg immobilisation, ambulatory recovery, and resistance training. We quantified vastus lateralis gene and protein expression of key proteins involved in mitochondrial biogenesis, fusion, fission, and turnover in at baseline and following each intervention. Results: PGC1α mRNA decreased 40% following the immobilisation period, and was accompanied by a 56% reduction in MTFP1 mRNA, a factor involved in mitochondrial fission. Subtle mRNA decreases were also observed in TFAM (17%), DRP1 (15%), with contrasting increases in BNIP3L and PRKN following immobilisation. These changes in gene expression were not accompanied by changes in respective protein expression. Instead, we observed subtle decreases in NRF1 and MFN1 protein expression. Ambulatory recovery restored mRNA and protein expression to pre-intervention levels of all altered components, except for BNIP3L. Resistance training restored BNIP3L mRNA to pre-intervention levels, and further increased mRNA expression of OPA-1, MFN2, MTFP1, and PINK1 past baseline levels. Conclusion: In healthy middle-aged males, 2 weeks of immobilisation did not induce dramatic differences in markers of mitochondria fission and autophagy. Restoration of ambulatory physical activity following the immobilisation period restored altered gene expression patterns to pre-intervention levels, with little evidence of further adaptation to resistance exercise training. [ABSTRACT FROM AUTHOR]

Glycogen is a branched, glucose polymer and the storage form of glucose in cells. Glycogen has traditionally been viewed as a key substrate for muscle ATP production during conditions of high energy demand and considered to be limiting for work capacity and force generation under defined conditions. Glycogenolysis is catalyzed by phosphorylase, while glycogenesis is catalyzed by glycogen synthase. For many years, it was believed that a primer was required for de novo glycogen synthesis and the protein considered responsible for this process was ultimately discovered and named glycogenin. However, the subsequent observation of glycogen storage in the absence of functional glycogenin raises questions about the true role of the protein. In resting muscle, phosphorylase is generally considered to be present in two forms: non-phosphorylated and inactive (phosphorylase b) and phosphorylated and constitutively active (phosphorylase a). Initially, it was believed that activation of phosphorylase during intense muscle contraction was primarily accounted for by phosphorylation of phosphorylase b (activated by increases in AMP) to a, and that glycogen synthesis during recovery from exercise occurred solely through mechanisms controlled by glucose transport and glycogen synthase. However, it now appears that these views require modifications. Moreover, the traditional roles of glycogen in muscle function have been extended in recent years and in some instances, the original concepts have undergone revision. Thus, despite the extensive amount of knowledge accrued during the past 100 years, several critical questions remain regarding the regulation of glycogen metabolism and its role in living muscle. [ABSTRACT FROM AUTHOR]

PurposeWe aimed to identify a blood flow restriction (BFR) endurance exercise protocol that would both maximize cardiopulmonary and metabolic strain, and minimize the perception of effort.MethodsTwelve healthy males (23 ± 2 years, 75 ± 7 kg) performed five different exercise protocols in randomized order: HI, high-intensity exercise starting at 105% of the incremental peak power (P peak); I-BFR30, intermittent BFR at 30% P peak; C-BFR30, continuous BFR at 30% P peak; CON30, control exercise without BFR at 30% P peak; I-BFR0, intermittent BFR during unloaded exercise. Cardiopulmonary, gastrocnemius oxygenation (StO2), capillary lactate ([La]), and perceived exertion (RPE) were measured.ResultsV̇O2, ventilation (V̇ E), heart rate (HR), [La] and RPE were greater in HI than all other protocols. However, muscle StO2 was not different between HI (set1-57.8 ± 5.8; set2-58.1 ± 7.2%) and I-BRF30 (set1-59.4 ± 4.1; set2-60.5 ± 6.6%, p

Purpose: Whole-body fat oxidation during exercise can be measured non-invasively during athlete profiling. Gaps in understanding exist in the relationships between fat oxidation during incremental fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during prolonged fed-state exercise. Methods: Seventeen endurance-trained males underwent a (i) fasted, incremental cycling test to assess peak whole-body fat oxidation (PFO), (ii) resting vastus lateralis microbiopsy, and (iii) 30-min maximal-effort cycling time-trial preceded by 2-h of fed-state moderate-intensity cycling to assess endurance performance and fed-state metabolism on separate occasions within one week. Results: PFO (0.58 ± 0.28 g.min−1) was associated with vastus lateralis citrate synthase activity (69.2 ± 26.0 μmol.min−1.g−1 muscle protein, r = 0.84, 95% CI 0.58, 0.95, P < 0.001), CD36 abundance (16.8 ± 12.6 μg.g−1 muscle protein, rs = 0.68, 95% CI 0.31, 1.10, P = 0.01), pre-loaded 30-min time-trial performance (251 ± 51 W, r = 0.76, 95% CI 0.40, 0.91, P = 0.001; 3.2 ± 0.6 W.kg−1, r = 0.62, 95% CI 0.16, 0.86, P = 0.01), and fat oxidation during prolonged fed-state cycling (r = 0.83, 95% CI 0.57, 0.94, P < 0.001). Addition of PFO to a traditional model of endurance (peak oxygen uptake, power at 4 mmol.L−1 blood lactate concentration, and gross efficiency) explained an additional ~ 2.6% of variation in 30-min time-trial performance (adjusted R2 = 0.903 vs. 0.877). Conclusion: These associations suggest non-invasive measures of whole-body fat oxidation during exercise may be useful in the physiological profiling of endurance athletes. [ABSTRACT FROM AUTHOR]

Purpose: Neuromuscular electrical stimulation (NMES) is often delivered at frequencies that recruit motor units (MUs) at unphysiologically high rates, leading to contraction fatigability. Rotating NMES pulses between multiple electrodes recruits subpopulations of MUs from each site, reducing MU firing rates and fatigability. This study was designed to determine whether rotating pulses between an increasing number of stimulation channels (cathodes) reduces contraction fatigability and increases the ability to generate torque during NMES. A secondary outcome was perceived discomfort. Methods: Fifteen neurologically intact volunteers completed four sessions. NMES was delivered over the quadriceps through 1 (NMES1), 2 (NMES2), 4 (NMES4) or 8 (NMES8) channels. Fatigability was assessed over 100 contractions (1-s on/1-s off) at an initial contraction amplitude that was 20% of a maximal voluntary contraction. Torque–frequency relationships were characterized over six frequencies from 20 to 120 Hz. Results: NMES4 and NMES8 resulted in less decline in peak torque (42 and 41%) over the 100 contractions than NMES1 and NMES2 (53 and 50% decline). Increasing frequency from 20 to 120 Hz increased torque by 7, 13, 21 and 24% MVC, for NMES1, NMES2, NMES4 and NMES8, respectively. Perceived discomfort was highest during NMES8. Conclusion: NMES4 and NMES8 reduced contraction fatigability and generated larger contractions across a range of frequencies than NMES1 and NMES2. NMES8 produced the most discomfort, likely due to small electrodes and high current density. During NMES, more is not better and rotating pulses between four channels may be optimal to reduce contraction fatigability and produce larger contractions with minimal discomfort compared to conventional NMES configurations. [ABSTRACT FROM AUTHOR]

Purpose: Aerobic exercise capacity is reduced in patients with chronic kidney disease, partly due to alterations at the muscular and microvascular level. This study evaluated oxygen uptake (VO2) kinetics as indicator of muscular oxidative metabolism in a population of Kidney Transplant Recipients (KTRs).Methods: Two groups of KTRs enrolled 3 (n = 21) and 12 months (n = 14) after transplantation and a control group of healthy young adults (n = 16) underwent cardiopulmonary exercise testing on cycle-ergometer. The protocol consisted in two subsequent constant, moderate-load exercise phases with a final incremental test until exhaustion.Results: The time constant of VO2 kinetics was slower in KTRs at 3 and 12 months after transplantation compared to controls (50.4 ± 13.1 s and 43.8 ± 11.6 s vs 28.9 ± 8.4 s, respectively; P < 0.01). Peak VO2 was lower in KTRs evaluated 3 months after transplantation compared to patients evaluated after 1 year (21.3 ± 4.3 and 26.4 ± 8.0 mL/kg/min; P = 0.04). Blood haemoglobin (Hb) concentration was higher in KTRs evaluated at 12 months (12.8 ± 1.7 vs 14.6 ± 1.7 g/dL; P < 0.01). Among KTRs, τ showed a moderate negative correlation with Peak VO2 (ρ = - 0.52) and Oxygen uptake efficiency slope (OUES) (r = - 0.57) while no significant correlation with Hb and peak heart rate.Conclusions: KTRs show slower VO2 kinetics compared to healthy controls. Hb and peak VO2 seem to improve during the first year after transplantation. VO2 kinetics were significantly associated with indices of cardiorespiratory fitness, but less with central determinants of aerobic capacity, thus suggesting a potential usefulness of adding this index of muscular oxidative metabolism to functional evaluation in KTRs. [ABSTRACT FROM AUTHOR]

Previous studies have reported associations of polymorphisms in the IGF1 gene with phenotypes of body composition (BC). The purpose of this study was to identify phenotypes of BC and physical function that were associated with the IGF1 promoter polymorphism (rs35767, −C1245T). Subjects from the Health, Aging, and Body Composition Study, white males and females (n = 925/836) and black males and females (533/705) aged 70–79 years were genotyped for the polymorphism. Phenotypes of muscle size and function, bone mineral density, and BC were analyzed for associations with this polymorphism. To validate and compare these findings, a cohort of young (mean age = 24.6, SD = 5.9) white men and women (n = 173/296) with similar phenotypic measurements were genotyped. An association with BC was identified in elderly females when significant covariates (physical activity, age, smoking status, body mass index) were included. White women with C/C genotype had 3% more trunk fat and 2% more total fat than those with C/T (P

Purpose: This review provides an overview of the current knowledge of the nutritional strategies to treat the signs and symptoms related to EIMD. These strategies have been organized into the following sections based upon the quality and quantity of the scientific support available: (1) interventions with a good level of evidence; (2) interventions with some evidence and require more research; and (3) potential nutritional interventions with little to-no-evidence to support efficacy. Method: Pubmed, EMBASE, Scopus and Web of Science were used. The search terms 'EIMD' and 'exercise-induced muscle damage' were individually concatenated with 'supplementation', 'athletes', 'recovery', 'adaptation', 'nutritional strategies', hormesis'. Result: Supplementation with tart cherries, beetroot, pomegranate, creatine monohydrate and vitamin D appear to provide a prophylactic effect in reducing EIMD. β-hydroxy β-methylbutyrate, and the ingestion of protein, BCAA and milk could represent promising strategies to manage EIMD. Other nutritional interventions were identified but offered limited effect in the treatment of EIMD; however, inconsistencies in the dose and frequency of interventions might account for the lack of consensus regarding their efficacy. Conclusion: There are clearly varying levels of evidence and practitioners should be mindful to refer to this evidence-base when prescribing to clients and athletes. One concern is the potential for these interventions to interfere with the exercise-recovery-adaptation continuum. Whilst there is no evidence that these interventions will blunt adaptation, it seems pragmatic to use a periodised approach to administering these strategies until data are in place to provide and evidence base on any interference effect on adaptation. [ABSTRACT FROM AUTHOR]

Purpose: Decline in skeletal muscle mitochondrial oxidative capacity (MOC) is associated with reduced aerobic capacity and increased risk of cardiovascular and metabolic disease. Measuring skeletal muscle MOC may be an alternative method to assess aerobic capacity, especially for individuals unable to perform a whole-body maximum oxygen uptake protocol. In this study, linear regression analysis in two leg muscles was performed to determine whether MOC values could be used to predict whole-body peak oxygen uptake.Methods: MOC was measured with near infrared spectroscopy (NIRS) in the medial gastrocnemius (MG) and vastus lateralis (VL) muscles of 26 participants (age, 27.1 ± 5.8 years old). Whole-body peak oxygen uptake (VO2 peak) was determined by indirect calorimetry during a continuous ramp protocol on a cycle ergometer.Results: VO2 peak values were significantly correlated with the muscle recovery rate constant (k) of the MG (kMG, r = 0.59; p < 0.01) and VL (kVL, r = 0.63; p < 0.01) muscles. Summing recovery rate constants of both muscles together (kMG + kVL) improved the strength of the correlation with VO2 peak (r = 0.78; p < 0.0001) and could explain a majority of the variance (R2 = 0.61) between the two measurements.Conclusion: Data suggest that NIRS can provide reliable MOC measurements on two leg muscles that correlate well with whole-body peak oxygen uptake. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated whether muscle cooling and its associated effects on skeletal muscle oxidative responses, blood gases, and hormonal concentrations influenced energy metabolism during cycling. Methods: Twelve healthy participants (Males: seven; Females: five) performed two steady-state exercise sessions at 70% of ventilatory threshold on a cycle ergometer. Participants completed one session with pre-exercise leg cooling until muscle temperature (Tm) decreased by 6 °C (LCO), and a separate session without cooling (CON). They exercised until Tm returned to baseline and for an additional 30 min. Cardiovascular, respiratory, metabolic, hemodynamic variables, and skeletal muscle tissue oxidative responses were assessed continuously. Venous blood samples were collected to assess blood gases, and hormones. Results: Heart rate, stroke volume, and cardiac output all increased across time but were not different between conditions. V̇O2 was greater in LCO when muscle temperature was restored until the end of exercise (p < 0.05). Cycling in the LCO condition induced lower oxygen availability, tissue oxygenation, blood pH, sO2%, and pO2 (p < 0.05). Insulin concentrations were also higher in LCO vs. CON (p < 0.05). Importantly, stoichiometric equations from respiratory gases indicated no differences in fat and CHO oxidation between conditions. Conclusion: The present study demonstrated that despite muscle cooling and the associated oxidative and biochemical changes, energy metabolism remained unaltered during cycling. Whether lower local and systemic oxygen availability is counteracted via a cold-induced activation of lipid metabolism pathways needs to be further investigated. [ABSTRACT FROM AUTHOR]

Purpose: Excess production of reactive oxygen species (ROS) from the mitochondria can promote mitochondrial dysfunction and has been implicated in the development of a range of chronic diseases. As such there is interest in whether mitochondrial-targeted antioxidant supplementation can attenuate mitochondrial-associated oxidative stress. We investigated the effect of MitoQ and CoQ10 supplementation on oxidative stress and skeletal muscle mitochondrial ROS levels and function in healthy middle-aged men.Methods: Skeletal muscle and blood samples were collected from twenty men (50 ± 1 y) before and following six weeks of daily supplementation with MitoQ (20 mg) or CoQ10 (200 mg). High-resolution respirometry was used to determine mitochondrial respiration and H2O2 levels, markers of mitochondrial mass and antioxidant defences were measured in muscle samples and oxidative stress markers in urine and blood samples.Results: Both MitoQ and CoQ10 supplementation suppressed mitochondrial net H2O2 levels during leak respiration, while MitoQ also elevated muscle catalase expression. However, neither supplement altered urine F2-isoprostanes nor plasma TBARS levels. Neither MitoQ nor CoQ10 supplementation had a significant impact on mitochondrial respiration or mitochondrial density markers (citrate synthase, mtDNA/nDNA, PPARGC1A, OXPHOS expression).Conclusion: Our results suggest that neither MitoQ and CoQ10 supplements impact mitochondrial function, but both can mildly suppress mitochondrial ROS levels in healthy middle-aged men, with some indication that MitoQ may be more effective than CoQ10. [ABSTRACT FROM AUTHOR]

Purpose: Electro-induced (EI) muscle actions are largely used in healthy subjects to improve motor performance, in frail/older subjects to limit sarcopenia and mobility loss, and in pathological subjects to restore functional abilities after injury and/or surgical operation. Their effects on motor output (e.g., muscle strength and power, and motor performance) are relatively well known, but their effects on postural balance are not. However, postural balance turns out to be a determining factor for motor skills in terms of motor performance and prevention of falls (especially in older/frail and pathological subjects). Hence, this review addresses the acute and chronic effects of EI muscle actions on postural balance, comparing them to the effects of voluntary (VOL) muscle actions.Method: Narrative review.Result: In acute, fatigue-generating application, EI muscle actions impair postural balance but less than VOL muscle actions. In chronic application, EI muscle actions induce beneficial effects on postural balance in pathological and aged (or frail) subjects. However, they have no or very little impact on healthy and young subjects. In aged (and probably pathological) subjects, EI muscle actions alone or superimposed onto voluntary contractions (EI + VOL) are less efficient than VOL muscle actions in improving postural balance.Conclusion: In practice, as part of populations too frail/fragile or unable (sarcopenic or pathological persons) to regularly undertake VOL motor tasks required to efficiently struggle against the loss of mobility and the risk of fall, the EI muscle actions turn out to be particularly relevant to implement. [ABSTRACT FROM AUTHOR]

Purpose: Resistance exercise induces muscle growth and is an important treatment for age-related losses in muscle mass and strength. Myokines are hypothesized as a signal conveying physiological information to skeletal muscle, possibly to "fine-tune" other regulatory pathways. While myokines are released from skeletal muscle following contraction, their role in increasing muscle mass and strength in response to resistance exercise or training is not established. Recent research identified both local and systemic release of myokines after an acute bout of resistance exercise. However, it is not known whether myokines with putative anabolic function are mechanistically involved in producing muscle hypertrophy after resistance exercise. Further, nitric oxide (NO), an important mediator of muscle stem cell activation, upregulates the expression of certain myokine genes in skeletal muscle.Method: In the systemic context of complex hypertrophic signaling, this review: (1) summarizes literature on several well-recognized, representative myokines with anabolic potential; (2) explores the potential mechanistic role of myokines in skeletal muscle hypertrophy; and (3) identifies future research required to advance our understanding of myokine anabolism specifically in skeletal muscle.Result: This review establishes a link between myokines and NO production, and emphasizes the importance of considering systemic release of potential anabolic myokines during resistance exercise as complementary to other signals that promote hypertrophy.Conclusion: Investigating adaptations to resistance exercise in aging opens a novel avenue of interdisciplinary research into myokines and NO metabolites during resistance exercise, with the longer-term goal to improve muscle health in daily living, aging, and rehabilitation. [ABSTRACT FROM AUTHOR]

Background: The electromyographic threshold (EMGTh) has been suggested to indicate the onset of accelerated higher-threshold (type-II) MU recruitment. Previous research has demonstrated that boys' EMGTh occurs at higher relative exercise intensities than men's in both cycling- and isometric-based testing. Girls‒women EMGTh differences were demonstrated only in cycling, but findings were clouded by low EMGTh-detection rates in women (68%) and particularly in girls (45%) PURPOSE: To examine the EMGTh, in girls and women, using the same males-employed isometric-based test protocol, and compare the females' findings with those previously obtained in the males.Methods: Seventeen girls and 17 women had their EMGTh determined as well as their one-repetition-maximum isometric knee-extension strength (1RM). Vastus-lateralis sEMG root mean square was recorded and the EMGTh was defined as the exercise intensity (%1RM) at the bi-segmental point of the least sum of squares.Results: EMGTh was detected in 88.2% of girls and 94.1% of women and occurred at higher relative intensities in the girls than in women (56.0 ± 11.1 vs. 47.7 ± 8.0% 1RM). The girls' 1RM (normalized to lean body mass) was only 69.1% that of the women.Conclusions: Girls' EMGTh values are higher compared with women's, possibly reflecting lower ability to activate higher-threshold (type-II) motor units. The females' EMGTh and detection-rate values were similar to the corresponding values previously observed in males. The females' age-related difference in the recruitment of higher-threshold motor units, as reflected by the EMGTh, appears to be on par with the males. [ABSTRACT FROM AUTHOR]

The NMR visibility of the signals from erythrocyte hemoglobin (Hb) presents an opportunity to assess the vascular PO2 (partial pressure of oxygen) in vivo to gather insight into the regulation of O2 transport, especially in contracting muscle tissue. Some concerns, however, have arisen about the validity of using the Val E11 signal as an indicator of PO2, since its intensity depends on tertiary structural changes, in contrast to the quaternary structure changes associated with relaxed (R) and tense (T) transition during O2 binding. We have examined the Val E11 and Tyr C7 signal intensity as a function of Hb saturation by developing an oximetry system, which permits the comparative analysis of the NMR and spectrophotometric measurements. The spectrophotometric assay defines the Hb saturation level at a given PO2 and yields standard oxygen-binding curves. Under defined PO2 and Hb saturation values, the NMR measurements have determined that the Val E11 signal, as well as the Tyr C7 signal, tracks closely Hb saturation and can therefore serve as a vascular oxygen biomarker.

Background: Children have been hypothesized to utilize higher-threshold (type-II) motor units (MUs) to a lesser extent than adults. Two recent studies, using a cycling-based EMG-threshold (EMGTh) protocol, supported the hypothesis, showing children's EMGTh intensities to be higher than adults'. Conclusions, however, were hampered by children's low EMGTh detection rates. Insufficiently high contractile forces at exhaustion were postulated as the reason for non-detection, predominantly in children. An intermittent isometric contraction test (IICT) protocol facilitates higher contractile forces prior to exhaustion and was shown effective in EMGTh testing of adults.Purpose: Determine whether an IICT protocol would enhance EMGTh detection in children, and consequently increase the magnitude of the previously observed child-adult EMGTh differences.Methods: 18 boys and 21 men completed one-repetition-maximum (1RM) isometric knee-extension test. The IICT protocol followed, commencing at 25%1RM and comprising five isometric contractions per load, incremented by ~ 3%1RM to exhaustion. Vastus lateralis surface EMG was recorded and EMGTh, expressed as %1RM, was defined as the onset of the EMG-response's steeper segment.Results: EMGTh was detected in 88.9% of boys and 95.2% of men, and occurred at higher relative intensities in boys (56.4 ± 9.2%1RM) than in men (46.0 ± 6.8%1RM). This 10.4% difference was 57% greater than the corresponding, previously reported cycling-based age-related difference.Conclusions: With the boys' detection rate nearly on par with the men's, the IICT protocol appears to overcome much of the intensity limitation of cycling-based protocols and provide a more sensitive EMGTh detection tool, thus extending the previously observed boys‒men difference. This difference adds supports to the notion of children's more limited type-II MU recruitment capacity. [ABSTRACT FROM AUTHOR]

The plasticity of skeletal muscle, whether an increase in size, change in metabolism, or alteration in structural properties, is in a continuous state of flux largely dependent upon physical activity. Much of the past research has expounded upon these ever-changing aspects of the muscle fiber following exercise. Specifically, endocrine and paracrine signaling have been heavily investigated lending to much of the past literature comprised of such endocrinological dynamics following muscle activity. Mechanotransduction, the ability of a cell to convert a mechanical stimulus into an intracellular biochemical response, has garnered much less attention. Recent work, however, has demonstrated the physical continuity of the muscle fiber, specifically demonstrating a continuous physical link between the extracellular matrix (ECM), cytoskeleton, and nuclear matrix as a means to rapidly regulate gene expression following a mechanical stimulus. Similarly, research has shown mechanical stimuli to directly influence cytoplasmic signaling whether through oxidative adaptations, increased muscle size, or enhanced muscle integrity. Regrettably, minimal research has investigated the role that exercise may play within the mechanotransducing signaling cascades. This proposed line of study may prove paramount as muscle-related diseases greatly impact one's ability to lead an independent lifestyle along with contributing a substantial burden upon the economy. Thus, this review explores both biophysical and biochemical mechanotransduction, and how these signaling pathways may be influenced following exercise. [ABSTRACT FROM AUTHOR]

Purpose: This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions.Methods: Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response.Results: At HT, FT, and ET, reductions in maximal voluntary force (MVC; -11, -20 and -27%, respectively, P ≤ 0.01), potentiated twitch force (-15, -23 and -23%, respectively, P < 0.05), voluntary activation (FT, -15 and ET, -18%, P ≤ 0.01), and voluntary activation measured with TMS (-11, -15 and -17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6-11%; ICC2,1 0.83-0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5-18%; ICC2,1 0.63-0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3-6%; ICC2,1 0.90-0.98).Conclusion: Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this double-blind, randomized, placebo-controlled clinical trial was to investigate the effects of the natural combination medicine Traumeel (Tr14) consisting of 14 diluted biological and mineral components on the inflammatory immune response and recovery up to 72 h after repetitive bouts of bicycle tests.Methods: Antigen-stimulated IL-1ra and IL-6 were defined as primary outcome measures. Moreover, various immunological and serum muscle damage markers were investigated. The evaluation was performed using the score of the area under the curve with respect to increase (AUCi) for 24 and 72 h after the second exercise test (EX2).Results: The Tr14 group indicated a lower decrease of lymphocytes by tendency (p = 0.06) and a lower activation of lymphocyte activation markers (CD62L absolute: p = 0.04; CD69: p = 0.01 and CD69 absolute: p = 0.05) in the period 24 h after EX2. In addition, the Tr14 group indicated a higher expression of antigen-stimulated CCL3 (p = 0.01), CCL4 (p = 0.07) and serum CCL2 (p = 0.05) in the period 24 h after EX2. There was a tendentially lower decrease of monocytes (p = 0.09) and a lower expression of antigen-stimulated MMP-3 (p = 0.01) in the Tr14 group in the period 72 h after EX2. However, antigen-stimulated IL-1ra and IL-6 showed no group differences.Conclusion: In line with the previous results, it was shown that Tr14 attenuates the adaptive immune response partially. Furthermore, the results indicate that Tr14 is able to stimulate the innate immune system via an increased production of pro-inflammatory chemokines. It is speculated that the higher expression of chemokines might play a role in the regeneration and recovery after exercise. [ABSTRACT FROM AUTHOR]

The article focuses on research into the impact of resistance exercise overtraining in changes in resting mitogen-activated protein kinases (MAPK). It examined changes in resting and total phosphorylation status of extracellular signal-regulated kinase 1/2, p38-MAPK, and c-Jun NH2-terminal kinase after a period of resistance exercise overtraining. It commented on differential expression of total and the ratio of phosphorylated/total MAPK following overtraining.

Purpose: Muscle fatigue has been identified as a risk factor for spontaneous muscle injuries in sport. However, few studies have investigated the accumulated effects of muscle fatigue on human muscle contractile properties. This study aimed to determine whether repeated bouts of exercise inducing acute fatigue leads to longer-term fatigue-related changes in muscle contractile properties.Methods: Maximum voluntary contraction (MVC), electromyographic (EMG) and mechanomyographic (MMG) measures were recorded in the biceps brachii of 11 participants for 13 days, before and after a maximally fatiguing exercise protocol. The exercise protocol involved participants repetitively lifting a weight (concentric contractions only) equal to 40 % MVC, until failure.Results: A significant (p < 0.05) acute pre- to post-exercise decline of biceps brachii MVC and median power frequency (MPF) was observed each day, whilst no difference existed between pre-exercise MVC or MPF values on subsequent days (days 2-13). However, decreases in number of lift repetitions and in pre-exercise MMG values of muscle belly displacement, contraction velocity and half-relaxation velocity were observed through to day 13.Conclusions: Whilst MVC and MPF measures resolved by the following day's test session, MMG measures indicated an ongoing decrement in muscle performance through days 2-13 consistent with the decline in lift repetitions observed. These results suggest that MMG may be more sensitive in detecting accumulated muscle fatigue than the 'gold standard' measures of MVC/MPF. Considering that muscle fatigue leads to injury, the on-going monitoring of MMG derived contractile properties of muscles in athletes may aid in the prediction of fatigued-induced muscle injury. [ABSTRACT FROM AUTHOR]

Purpose: Many studies have focused on maximum torque exerted by ankle joint muscles during plantar flexion. While strength parameters are typically measured with isokinetic or isolated ankle dynamometers, these devices often present substantial limitations for the measurement of torque because they account for force in only 1 dimension (1D), and the device often constrains the body in a position that augments torque through counter movements. The purposes of this study were to determine the contribution of body position to ankle plantar-flexion torque and to assess the use of 1D and 3D torque sensors.Methods: A custom designed 'Booted, Open-Unit, Three dimension, Transportable, Ergometer' (B.O.T.T.E.) was used to quantify plantar flexion in two conditions: (1) when the participant was restrained within the unit (locked-unit) and (2) when the participant's position was independent of the ankle dynamometer (open-unit). Ten young males performed maximal voluntary isometric plantar-flexion contractions using the B.O.T.T.E. in open and locked-unit mechanical configurations.Results: The B.O.T.T.E. was reliable with ICC higher than 0.90, and CV lower than 7 %. The plantar-flexion maximal resultant torque was significantly higher in the locked-unit compared with open-unit configuration (P < 0.001; +61 to +157 %) due to the addition of forces from the body being constrained within the testing device. A 1D compared with 3D torque sensor significantly underestimated the proper capacity of plantar-flexion torque production (P < 0.001; -37 to -60 %).Conclusions: Assessment of plantar-flexion torque should be performed with an open-unit dynamometer mounted with a 3D sensor that is exclusive of accessory muscles but inclusive of all ankle joint movements. [ABSTRACT FROM AUTHOR]

Purpose: We quantified the acute and chronic effects of whole body vibration on athletic performance or its proxy measures in competitive and/or elite athletes. Methods: Systematic literature review and meta-analysis. Results: Whole body vibration combined with exercise had an overall 0.3 % acute effect on maximal voluntary leg force (−6.4 %, effect size = −0.43, 1 study), leg power (4.7 %, weighted mean effect size = 0.30, 6 studies), flexibility (4.6 %, effect size = −0.12 to 0.22, 2 studies), and athletic performance (−1.9 %, weighted mean effect size = 0.26, 6 studies) in 191 (103 male, 88 female) athletes representing eight sports (overall effect size = 0.28). Whole body vibration combined with exercise had an overall 10.2 % chronic effect on maximal voluntary leg force (14.6 %, weighted mean effect size = 0.44, 5 studies), leg power (10.7 %, weighted mean effect size = 0.42, 9 studies), flexibility (16.5 %, effect size = 0.57 to 0.61, 2 studies), and athletic performance (−1.2 %, weighted mean effect size = 0.45, 5 studies) in 437 (169 male, 268 female) athletes (overall effect size = 0.44). Conclusions: Whole body vibration has small and inconsistent acute and chronic effects on athletic performance in competitive and/or elite athletes. These findings lead to the hypothesis that neuromuscular adaptive processes following whole body vibration are not specific enough to enhance athletic performance. Thus, other types of exercise programs (e.g., resistance training) are recommended if the goal is to improve athletic performance. [ABSTRACT FROM AUTHOR]

This article reviews the concept of maximal oxygen consumption ( $$\dot{V}\hbox{O}_{2\text{max} }$$ ) from the perspective of multifactorial models of $$\dot{V}\hbox{O}_{2\text{max} }$$ limitation. First, I discuss procedural aspects of $$\dot{V}\hbox{O}_{2\text{max} }$$ measurement: the implications of ramp protocols are analysed within the theoretical work of Morton. Then I analyse the descriptive physiology of $$\dot{V}\hbox{O}_{2\text{max} }$$ , evidencing the path that led to the view of monofactorial cardiovascular or muscular $$\dot{V}\hbox{O}_{2\text{max} }$$ limitation. Multifactorial models, generated by the theoretical work of di Prampero and Wagner around the oxygen conductance equation, represented a radical change of perspective. These models are presented in detail and criticized with respect to the ensuing experimental work. A synthesis between them is proposed, demonstrating how much these models coincide and converge on the same conclusions. Finally, I discuss the cases of hypoxia and bed rest, the former as an example of the pervasive effects of the shape of the oxygen equilibrium curve, the latter as a neat example of adaptive changes concerning the entire respiratory system. The conclusion is that the concept of cardiovascular $$\dot{V}\hbox{O}_{2\text{max} }$$ limitation is reinforced by multifactorial models, since cardiovascular oxygen transport provides most of the $$\dot{V}\hbox{O}_{2\text{max} }$$ limitation, at least in normoxia. However, the same models show that the role of peripheral resistances is significant and cannot be neglected. The role of peripheral factors is greater the smaller is the active muscle mass. In hypoxia, the intervention of lung resistances as limiting factors restricts the role played by cardiovascular and peripheral factors. [ABSTRACT FROM AUTHOR]

Purpose: Resent research has suggested that loaded multi-joint movements could reveal a linear force-velocity ( F- V) relationship. The aim of the present study was to evaluate the F- V relationship both across different types of vertical jumps and across different F and V variables. Methods: Ten healthy subjects performed maximum various vertical jumps that were either loaded or unloaded by constant external forces of up to 30 % of their body weight. Both the maximum and averaged F and V data were recorded. Results: The observed F- V relationships proved to be strong (median correlation coefficients ranged 0.78-0.93) and quasi-linear. Their F- and V-intercepts and the calculated maximum power ( P) were highly reliable (0.85 < ICC < 0.98), while their concurrent validity with respect to their directly measured values was on average moderate-to-large. The obtained F- V relationships also revealed that (1) the assessment of maximum F and P could be somewhat more reliable and valid than the assessment of maximum V, (2) natural countermovement jumps should be employed rather than the jumps performed from a fixed squat position, while (3) both maximum and averaged F and V variables could be used despite revealing markedly different regression parameters. Conclusions: The data generally reveal a reliable, valid, strong and quasi-linear F- V relationship across variety of vertical jumps and the recorded F and V variables. Therefore, we conclude that the loaded vertical jumps could be developed into a routine method for testing the force, velocity, and power generating capacity of leg extensors. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to investigate whether subsensory electrical noise stimulation applied over the tibialis anterior (TA) muscles may reduce postural oscillations during quiet stance and to compare such reductions with those obtained by applying the noise stimulation over the triceps surae (TS) muscles. The rationale relies on the use of noise stimulation to enhance the sensitivity of sensory receptors, thereby improving the performance of the postural control system. As recent evidence suggested that the TA muscle might be a better source of proprioceptive information during quiet stance than the TS muscles, the main hypothesis of the present study was that subsensory noise stimulation applied to the TA muscles should be more efficient for postural stabilization than a similar stimulation to the TS. Methods: Participants had their postural steadiness assessed while subsensory electrical noise was applied bilaterally to their TA or TS muscles and also while the stimulation was applied bilaterally to both TA and TS muscles. No stimulation was delivered in the control condition. Results: Time-domain and frequency-domain parameters based on center of mass and center of pressure signals were significantly reduced when noise stimulation was applied to the anterior and/or to the posterior leg muscles. No consistent differences in postural sway parameters were observed among the stimulation conditions. Conclusions: This is the first investigation showing that subsensory stimulation applied over the TA muscles alone is effective in attenuating postural sway, with TS stimulation being equally effective. These findings may have useful applications for the development of medical/rehabilitation devices designed to improve postural steadiness in people with balance impairments. [ABSTRACT FROM AUTHOR]

Purpose: The present study evaluated the effects of creatine monohydrate (CrM) consumption post-exercise on body composition and muscle strength in middle to older males following a 12-week resistance training program. Methods: In a double-blind, randomized trial, 20 males aged between 55 and 70 years were randomly assigned to consume either CrM-carbohydrate (CHO) [20 g days CrM + 5 g days CHO × 7 days, then 0.1 g kg CrM + 5 g CHO on training days (average dosage of ~8.8 g)] or placebo CHO (20 g days CHO × 7 days, then 5 g CHO on training days) while participating in a high intensity resistance training program [3 sets × 10 repetitions at 75 % of 1 repetition maximum (1RM)], 3 days weeks for 12 weeks. Following the initial 7-day 'loading' phase, participants were instructed to ingest their supplement within 60 min post-exercise. Body composition and muscle strength measurements, blood collection and vastus lateralis muscle biopsy were completed at 0, 4, 8 and 12 weeks of the supplement and resistance training program. Results: A significant time effect was observed for 1RM bench press ( p = 0.016), leg press ( p = 0.012), body mass ( p = 0.03), fat-free mass ( p = 0.005) and total myofibrillar protein ( p = 0.005). A trend for larger muscle fiber cross-sectional area in the type II fibers compared to type I fibers was observed following the 12-week resistance training ( p = 0.08). No supplement interaction effects were observed. Conclusion: Post-exercise ingestion of creatine monohydrate does not provide greater enhancement of body composition and muscle strength compared to resistance training alone in middle to older males. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the selective effects of different types of external loads applied in vertical jump training on both the performance and muscle power output of the squat (SJ) and countermovement jump (CMJ). Methods: Physically active males practiced maximum unconstrained vertical jumps over an 8-week period with no load, with either a negative or positive load exerted by a nearly constant external force that altered their body weight, and with a loaded vest that increased both the body weight and inertia. The magnitude of all applied loads corresponded to 30 % of body weight. Results: A similar training-associated increase in jump height was observed in all experimental groups in both CMJ (7.4-11.8 %) and SJ (6.4-14.1 %). The relative increase in power output was comparable to the increase in jump height in SJ (7.4-11.5 %), while the power increase in CMJ was relatively small and load-specific (0.5-9.5 %). The observed differences could originate from the changes in the CMJ pattern, reflected through the depth of the counter movement that particularly increased after the training with negative load (42 %) and no load (21 %). The same participants also revealed increased CMJ duration, reduced ground reaction forces, as well as reduced maximum and average power output when compared with other training groups. Conclusion: Jump training with the applied loads could lead to a comparable improvement in jumping performance. However, the observed load-specific adaptations of CMJ pattern could decouple the training-associated increase in jump height from the increase in muscle power output. [ABSTRACT FROM AUTHOR]

This study investigated the changes in muscular activity and tissue oxygenation while lifting and lowering a load of 20, 40, 60 or 80 % of one repetition maximum (1RM) with elbow flexor muscles until failure. The surface electromyogram (EMG) was recorded in biceps brachii (BB), brachioradialis (BRD) and triceps brachii (TB). For BB, a tissue oxygenation index (TOI) and a normalized total hemoglobin index (nTHI) were recorded by near-infrared spectroscopy. The number of repetitions decreased with the increase in load ( P < 0.001), and the four loading conditions induced a decrease in MVC force immediately after failure ( P < 0.001). The average of rectified EMG amplitude (aEMG) of elbow flexors increased for all loads during muscle shortening (SHO) and lengthening (LEN) phases of the movement ( P < 0.05), except for the 80 % load during LEN phase. At failure, the aEMG was greater during the SHO than the LEN phase ( P < 0.05), except for the 20 % load. TOI decreased for all loads and phases ( P < 0.05) but less ( P < 0.01) for the 20 % than 60 and 80 % loads ( P < 0.01), and for LEN compared with SHO phase. At failure, TOI was negatively associated with aEMG during the SHO ( r = 0.99) and LEN ( r = 0.82) phases, while TOI and aEMG were positively associated with load magnitude ( r > 0.90) in both movement phases. This study emphasizes the influence of load magnitude and movement phase (SHO and LEN) on neuromuscular and oxydative adjustments during movements that involve lifting and lowering a load until failure. [ABSTRACT FROM AUTHOR]

Existing models of muscle deconditioning such as bed rest are expensive and time-consuming. We propose a new model utilizing a weighted suit to manipulate muscle strength, power, or endurance relative to body weight. The aims of the study were to determine as to which muscle measures best predict functional task performance and to determine muscle performance thresholds below which task performance is impaired. Twenty subjects performed seven occupational astronaut tasks (supine and upright seat egress and walk, rise from fall, hatch opening, ladder climb, object carry, and construction board activity), while wearing a suit weighted with 0-120 % of body weight. Models of the relationship between muscle function/body weight and task completion time were developed using fractional polynomial regression and verified with pre- and post-flight astronaut performance data. Spline regression was used to identify muscle function thresholds for each task. Upright seat egress and walk was the most difficult task according to the spline regression analysis thresholds. Thresholds normalized to body weight were 17.8 N/kg for leg press isometric force, 17.6 W/kg for leg press power, 78.8 J/kg for leg press work, 5.9 N/kg isometric knee extension and 1.9 Nm/kg isokinetic knee extension torque. Leg press maximal isometric force/body weight was the most reliable measure for modeling performance of ambulatory tasks. Laboratory-based manipulation of relative strength has promise as an analog for spaceflight-induced loss of muscle function. Muscle performance values normalized to body weight can be used to predict occupational task performance and to establish relevant strength thresholds. [ABSTRACT FROM AUTHOR]

The aim of this work is to show how changes in surface electromyographic activity (sEMG) during a repetitive, non-constant force contraction can be detected and interpreted on the basis of the amplitude distribution provided by high-density sEMG techniques. Twelve healthy male subjects performed isometric shoulder elevations, repeating five times a force ramp profile up to 25 % of the maximal voluntary contraction (MVC). A 64-electrode matrix was used to detect sEMG from the trapezius muscle. The sEMG amplitude distribution was obtained for the force levels in the range 5-25 % MVC with steps of 5 % MVC. The effect of force level, subject, electrode position and ramp repetition on the sEMG amplitude distribution was tested. The sEMG amplitude was significantly smaller in the columns of the electrode grid over the tendons (repeated measures ANOVA, p < 0.01). The barycentre of the distribution of sEMG amplitude was subject-specific (Kruskal-Wallis test, p < 0.01), and shifted caudally with the increase of force levels and cranially with the repetition of the motor task (both p < 0.01, repeated measures ANOVA). The results are discussed in terms of motor unit recruitment in different muscle sub-portions. It is concluded that the sEMG amplitude distribution obtained by multichannel techniques provides useful information in the study of muscle activity, and that changes in the spatial distribution of the recruited motor units during a force varying isometric contraction might partially explain the variability observed in the activation pattern of the upper trapezius muscle. [ABSTRACT FROM AUTHOR]

Muscle strength and mass decline in sedentary individuals with aging. The present study investigated the effects of both age and 21 weeks of progressive hypertrophic resistance training (RT) on skeletal muscle size and strength, and on myostatin and myogenin mRNA expression in 21 previously untrained young men (26.0 ± 4.3 years) and 18 older men (61.2 ± 4.1 years) and age-matched controls. Vastus lateralis muscle biopsies were taken before and after RT. Type I and type II muscle fiber cross-sectional areas increased more in young men than in older men after RT ( P < 0.05). Concentric leg extension increased ( P < 0.05) more after 10.5 weeks in young men compared to older men, but after 21 weeks no statistical differences existed. The daily energy and protein intake were greater ( P < 0.001) in young subjects. Both myostatin and myogenin mRNA expression increased in older when compared with young men after RT ( P < 0.05). In conclusion, after RT, muscle fiber size increased less in older compared to young men. This was associated with lower protein and energy intake and increases in myostatin gene expression in older when compared to young men. [ABSTRACT FROM AUTHOR]

This study investigated the hypothesis that the duration of aerobic-based cycle exercise would affect the adaptations in substrate and metabolic regulation that occur in vastus lateralis in response to a short-term (10 day) training program. Healthy active but untrained males ( n = 7) with a peak aerobic power ( $$ \dot{V}{\text{O}}_{{ 2 {\text{ peak}}}} $$) of 44.4 ± 1.4 ml kg min participated in two different training programs with order randomly assigned (separated by ≥2 weeks). The training programs included exercising at a single intensity designated as light (L) corresponding to 60 % $$ \dot{V}{\text{O}}_{{ 2 {\text{ peak}}}} $$, for either 30 or 60 min. In response to a standardized task (60 % $$ \dot{V}{\text{O}}_{{ 2 {\text{ peak}}}} $$), administered prior to and following each training program, L attenuated the decrease ( P < 0.05) in phosphocreatine and the increase ( P < 0.05) in free adenosine diphosphate and free adenosine monophosphate but not lactate. These effects were not altered by daily training duration. In the case of muscle glycogen, training for 60 versus 30 min exaggerated the increase ( P < 0.05) that occurred, an effect that extended to both rest and exercise concentrations. No changes were observed in $$ \dot{V}{\text{O}}_{{ 2 {\text{ peak}}}} $$ measured during progressive exercise to fatigue or in $$ \dot{V}{\text{O}}_{ 2} $$ and RER during submaximal exercise with either training duration. These findings indicate that reductions in metabolic strain, as indicated by a more protected phosphorylation potential, and higher glycogen reserves, can be induced with a training stimulus of light intensity applied for as little as 30 min over 10 days. Our results also indicate that doubling the duration of daily exercise at L although inducing increased muscle glycogen reserves did not result in a greater metabolic adaptation. [ABSTRACT FROM AUTHOR]

The objective of the present repeat-measures study was to determine whether plasma serum levels of testosterone, cortisol, osteocalcin or type I collagen C-telopeptide (CT) are acutely affected following an electro-myostimulation (EMS) bout, and their relation to bone mineral density and muscle mass. Ten men with recent (8 weeks) thoracic spinal cord injury (SCI) (ASIA A) and 10 age-matched able-bodied (AB) men performed one EMS bout on the quadriceps femoris muscle. Blood samples were drawn at basal condition, immediately after EMS, and 15 min, 30 min, 24 h and 48 h post-EMS. Muscle cross-sectional area was measured by magnetic resonance imaging. Bone mineral density (BMD) was determined by dual-energy X-ray absorptiometry. In the SCI group, a significant decrease in testosterone, cortisol and CT together with a significant increase in testosterone/cortisol ratio and osteocalcin/CT ratio was observed after EMS. For the AB subjects, only testosterone and CT decreased significantly following EMS. Muscle size was only related to testosterone/cortisol ratio in the SCI sample ( R = 0.659, p < 0.05), whereas BMD did not show any relation to any biomarker. Acute EMS in recent spinal cord injured men seems to induce positive effects on bone turnover biomarkers, and anabolic and catabolic hormones. [ABSTRACT FROM AUTHOR]