Exhaustive Treadmill Running Research Articles

Subject-specific sensitivity of several biomechanical features to fatigue during an exhaustive treadmill run

The aim of the present study was to examine the sensitivity of several movement features during running to exhaustion in a subject-specific setup adopting a cross-sectional design and a machine learning approach. Thirteen recreational runners, that systematically trained and competed, performed an exhaustive running protocol on an instrumented treadmill. Respiratory data were collected to establish the second ventilatory threshold (VT2) in order to obtain a reference point regarding the gradual accumulation of fatigue. A machine learning approach was adopted to analyze kinetic and kinematic data recorded for each participant, using a random forest classifier for the region pre and post the second ventilatory threshold. SHapley Additive exPlanations (SHAP) analysis was used to explain the models’ predictions and to provide insight about the most important variables. The classification accuracy value of the models adopted ranged from 0.853 to 0.962. The most important feature in six out of thirteen participants was the angular range in AP axis of upper trunk C7 (RTAPu) followed by maximum loading rate (RFDmaxD) and the angular range in the LT axis of the C7. SHAP dependence plots also showed an increased dispersion of predictions in stages around the second ventilatory threshold which is consistent with feature interactions. These results showed that each runner used the examined features differently to cope with the increase in fatigue and mitigate its effects in order to maintain a proper motor pattern.

Enhancing physiological recovery and subsequent exercise performance in the heat using a phase-change material cooling blanket

This study aimed to assess the effect of a phase-change material (PCM) cooling blanket for cooling between exercise bouts on recovery of physiological parameters and subsequent exercise performance in the heat. Eighteen male volunteers were recruited to participate in human trials involving two exhaustive treadmill running bouts (Bout1 for 3 km and Bout2 for 1.5 km) in a climate chamber (temperature = 33 °C; relative humidity = 40%). Participants were randomly subjected to one of two cooling conditions for a 10-min period between exercise bouts: CON: natural cooling; 10-min PCM: with a PCM cooling blanket for 10 min. Several physiological parameters including mean skin temperature (Tskin), oral temperature (Toral), core temperature (Tcore), heart rate (HR), mean arterial pressure (MAP), respiratory rate (RR), peripheral capillary oxygen saturation (SpO2), average running speed and rating of perceived exertion (RPE) scale score were analyzed. The results showed that compared to the CON group, participants in the 10-min PCM group had a significant lower Tskin, Tcore, HR and RR at post-cooling, as well as greater reductions in mean skin temperature (ΔTskin) and core temperature (ΔTcore) from post-Bout1 to post-cooling. Additionally, the 10-min PCM group exhibited significantly lower peak Tcore, peak HR and RPE scale score during Bout2, while the average running speed during Bout2 was significantly higher. The present study suggests that cooling with a PCM cooling blanket can enhance physiological recovery and subsequent exercise performance in the heat.

Elevated liver glycogenolysis mediates higher blood glucose during acute exercise in Barth syndrome.

Male TAFAZZIN shRNA transgenic (TG) and wild-type (WT) mice completed exhaustive treadmill running protocols to test exercise tolerance. Mice underwent 2H- and 13C-stable isotope infusions at rest and during a 30-minute treadmill running bout to quantify hepatic glucose production and associated nutrient fluxes under sedentary conditions and during acute exercise. Circulating and tissue (skeletal muscle and liver) samples were obtained during and following exercise to assess static metabolite levels. TG mice reached exhaustion sooner during exhaustive treadmill running protocols and exhibited higher plasma lactate concentrations after exhaustive exercise compared to WT mice. Arterial glucose levels were comparable between genotypes at rest, but higher in TG mice compared to WT mice during exercise. Consistent with the higher blood glucose, TG mice showed increased endogenous glucose production owing to elevated glycogenolysis compared to WT mice during exercise. Total gluconeogenesis, gluconeogenesis from glycerol, gluconeogenesis from phosphoenolpyruvate, pyruvate cycling, total cataplerosis, and anaplerotic fluxes were similar between TG and WT mice at rest and during exercise. However, lactate dehydrogenase flux and TCA cycle fluxes trended higher in TG mice during exercise. Liver glycogen content in TG was higher in TG vs. controls. Our data in the Tafazzin knockdown mouse suggest that elevated anaerobic metabolism during rest and exercise previously reported in humans with BTHS are supported by the finding of higher hepatic glycogenolysis.

Effects of Running Speeds and Exhaustion on Iliotibial Band Strain during Running.

Iliotibial band syndrome (ITBS) is one of the most prevalent overuse injuries in runners. The strain rate in the iliotibial band (ITB) has been theorized to be the primary causative factor in the development of ITBS. Running speed and exhaustion might lead to an alteration in the biomechanics that influence the strain rate in the iliotibial band. To identify how exhaustion states and running speeds affect the ITB strain and strain rate. A total of 26 healthy runners (including 16 males and 10 females) ran at a normal preferred speed and a fast speed. Then, participants performed a 30 min exhaustive treadmill run at a self-selected speed. Afterward, participants were required to run at similar speeds to those of the pre-exhaustion state. Both the exhaustion and running speeds were revealed to have significant influences on the ITB strain rate. After exhaustion, an increase of approximately 3% in the ITB strain rate was observed for both the normal speed (p = 0.001) and the fast speed (p = 0.008). Additionally, a rapid increase in the running speed could lead to an increase in the ITB strain rate for both the pre- (9.71%, p = 0.000) and post-exhaustion (9.87%, p = 0.000) states. It should be noted that an exhaustion state could lead to an increase in the ITB strain rate. In addition, a rapid increase in running speed might cause a higher ITB strain rate, which is proposed to be the primary cause of ITBS. The risk of injury should also be considered due to the rapid increase in the training load involved. Running at a normal speed in a non-exhaustive state might be beneficial for the prevention and treatment of ITBS.

A single dose of exercise stimulates skeletal muscle mitochondrial plasticity in myotonic dystrophy type 1.

Myotonic dystrophy type 1 (DM1) is the second most common muscular dystrophy after Duchenne and is the most prevalent muscular dystrophy in adults. DM1 patients that participate in aerobic exercise training experience several physiological benefits concomitant with improved muscle mitochondrial function without alterations in typical DM1-specific disease mechanisms, which suggests that correcting organelle health is key to ameliorate the DM1 pathology. However, our understanding of the molecular mechanisms of mitochondrial turnover and dynamics in DM1 skeletal muscle is lacking. Skeletal muscle tissue was sampled from healthy and DM1 mice under sedentary conditions and at several recovery time points following an exhaustive treadmill run. We demonstrate that DM1 patients exhibit an imbalance in the transcriptional apparatus for mitochondrial turnover and dynamics in skeletal muscle. Additionally, DM1 mice displayed elevated expression of autophagy and mitophagy regulators. A single dose of exercise successfully enhanced canonical exercise molecular pathways and skeletal muscle mitochondrial biogenesis despite failing to alter the cellular pathology in DM1 mice. However, treadmill running stimulated coordinated organelle fusion and fission signaling, as well as improved alternative splicing of Optic atrophy 1. Exercise also evoked autophagy and mitophagy pathways in DM1 skeletal muscle resulting in the normalized expression of autophagy- and lysosome-related machinery responsible for the clearance of dysfunctional organelles. Collectively, our data indicate that mitochondrial dynamics and turnover processes in DM1 skeletal muscle are initiated with a single dose of exercise, which may underlie the adaptive benefits previously documented in DM1 mice and patients.

The effect of fatigue on the ankle and knee kinematics and kinetics in moderately and highly trained healthy non-rearfoot runners

ABSTRACT The aim of this study was to compare selected ankle and knee kinematic and kinetic parameters before and after a prolonged exhaustive treadmill run between two groups of non-rearfoot footstrike pattern (NRFP) runners with different training volumes. Twenty-eight habitual NRFP runners were assigned to two groups based on their weekly training volume (Highly-trained (HT)/Moderately-trained (MT)). Participants underwent the VO2max test, and the exhaustive treadmill ran with biomechanical analysis at the beginning and the end. The two-way RMANOVA was used to assess differences between the groups and the phase of the run. A paired t-test was used for post-hoc analysis in case of significant interaction effect. Kinetic results showed significant group effect for ankle plantarflexion moment and hip external rotation moment (end-phase: both greater in MT group). Kinematic results showed significant group×phase interaction for ankle dorsiflexion angle (end-phase: greater in MT group) at initial contact (IC), peak knee flexion angle (end-phase: greater in MT group), and peak ankle eversion angle during the stance phase (end-phase: greater in HT group). Additionally, a group effect was found for knee flexion angle at IC (end-phase: greater in HT group). This study suggests that HT healthy NRFP runners may have less potential for increased biomechanical risk of AT overload during an exhaustive run.

Heart Electrical Activity during Ventricular Repolarization in Rats after Acute Exhaustive Treadmill Running

Heart Electrical Activity during Ventricular Repolarization in Rats after Acute Exhaustive Treadmill Running

고강도 탈진 달리기 후 정적 휴식이 동적 균형에 미치는 영향

This study examined the effect of a 5-min cooling down following a high-intense treadmill running on dynamic balance in college students. Eighteen college students (9 males and 9 females) underwent two sessions of an intense and exhaustive treadmill running with and without a passive cooling down followed by Y-balance tests. Analysis of variance with repeated measures showed a significant gender by treatment by time interaction(FSUB(1,2,16)/SUB = 97.309, p .001). Males had a significantly higher 10-min post-exercise recovery Y-balance test with a 5-min cool-down compared to without a 5-min cool-down. Females had significantly higher scores in the 5-min, 10-min, and 30-min post-exercise recovery Y-balance tests with a 5-min cool-down compared to without a 5-min cool-down. The current findings of the study suggest that cooling down plays a critical role in recovering post-exercise dynamic balance, especially in females.

Exhaustive Exercise Increases Spontaneous but Not fMLP-Induced Production of Reactive Oxygen Species by Circulating Phagocytes in Amateur Sportsmen.

Simple SummaryStrenuous exercise can alter various functions of circulating phagocytes. We tested whether exhaustive exercise could influence spontaneous and fMLP-induced oxidant production (measured with luminol enhanced whole blood chemiluminescence (LBCL) normalized per phagocyte count) by blood phagocytes in amateur sportsmen. Exhaustive exercise transiently enhanced (no more than one hour from the end of bout) spontaneous oxidants generation by circulating phagocytes, while response to fMLP was decreased up to 24 h post exercise. It is suggested that a short lived increase in spontaneous oxidants production can switch on various mechanisms leading to an increase in antioxidant activity in regularly training subjects.Strenuous exercise alters the oxidative response of blood phagocytes to various agonists. However, little is known about spontaneous post exercise oxidant production by these cells. In this cross-over trial, we tested whether an exhaustive treadmill run at a speed corresponding to 70% of VO2max affects spontaneous and fMLP-provoked oxidant production by phagocytes in 18 amateur sportsmen. Blood was collected before, just after, and 1, 3, 5 and 24 h post exercise for determination of absolute and normalized per phagocyte count spontaneous (a-rLBCL, rLBCL) and fMLP-induced luminol-enhanced whole blood chemiluminescence (a-fMLP-LBCL, fMLP-LBCL). a-rLBCL and rLBCL increased by 2.5- and 1.5-times just after exercise (p < 0.05) and then returned to baseline or decreased by about 2-times at the remaining time-points, respectively. a-fMLP-LBCL increased 1.7- and 1.6-times just after and at 3 h post-exercise (p < 0.05), respectively, while fMLP-LBCL was suppressed by 1.5- to 2.3-times at 1, 3, 5 and 24 h post-exercise. No correlations were found between elevated post-exercise a-rLBCL, a-fMLP-LBCL and run distance to exhaustion. No changes of oxidants production were observed in the control arm (1 h resting instead of exercise). Exhaustive exercise decreased the blood phagocyte-specific oxidative response to fMLP while increasing transiently spontaneous oxidant generation, which could be a factor inducing secondary rise in antioxidant enzymes activity.

Exercise Prior to Lower Extremity Peripheral Artery Disease Improves Endurance Capacity and Hindlimb Blood Flow by Inhibiting Muscle Inflammation.

Lower extremity peripheral artery disease (PAD) is associated with functional decline. Physical exercise has been proven to be an effective therapeutic strategy for PAD; however the effect of exercise initiated before PAD remains unknown. Here, we investigated the preventive effects of exercise on endurance capacity, hindlimb perfusion, and on polarization profile of circulating monocytes and limb muscle macrophages. ApoE−/− mice were subjected to 5-week running wheel exercise or remained sedentary before induction of hindlimb ischemia. The two groups were thereafter kept sedentary. Exercised mice prior to PAD showed higher exhaustive treadmill running distance and time than sedentary mice. Preventive exercise also increased perfusion, arteriole density, and muscle regeneration in the ischemic hindlimb. Moreover, preventive exercise prevented ischemia-induced increased gene expression of pro-inflammatory M1 macrophages markers and cytokines in the ischemic muscle, while no changes were observed for anti-inflammatory M2 macrophage markers. Flow cytometry analysis showed that the proportion of circulating pro-inflammatory monocyte subtype decreased whereas that of anti-inflammatory monocytes increased with preventive exercise. Overall, we show that exercise initiated before PAD improves endurance performance and hindlimb perfusion in mice probably via inhibition of M1 macrophage polarization and inflammation in the ischemic muscle. Our study provides experimental evidence for a role of regular exercise in primary prevention of PAD.

Sensitivity of movement features to fatigue during an exhaustive treadmill run

ABSTRACT The objective of the present study was to examine the sensitivity of several movement variables during running to exhaustion adopting a cross-sectional design. Thirteen recreational runners, that systematically trained and competed, performed an exhaustive running protocol on an instrumented treadmill. Respiratory data were collected to establish the ventilatory threshold in order to obtain a reference point regarding the gradual accumulation of fatigue. A machine learning approach was adopted to analyse a set of 29,650 data points (individual steps) of kinetic and kinematic data, using a random forest classifier for the region pre and post the ventilatory threshold. The overall accuracy of the model was 0.914 (95% CI: 0.907–0.919). The four most important variables, and more sensitive in predictive ability, as it was concluded from the variable importance procedure and the partial dependence (PD), were the angular range in AP axis of upper trunk C7, the maximum loading rate, the angular range in LT axis of the C7 and the maximum value of the ground reaction force. Two-dimensional PD revealed considerable interactions for certain areas of the joint distributions between kinetic and kinematic data. These results provide a direction towards understanding the interconnections of kinetics and kinematics of the torso to maintain the coordinated running pattern under fatigue conditions. Highlights Trunk frontal plane kinematics is the most sensitive parameter to fatigue. Practitioners should consider this finding during endurance training. Kinetics exhibit a stable linear increase in mean values but a non-linear increase in variance during an exhaustive incremental treadmill run. This may affect training at a submaximal fatigued state. Specific areas in the joint distributions of kinetics and kinematics during treadmill running exhibit increased sensitivity in predicting fatigue state.

Therapeutic Approaches for Volumetric Muscle Loss Injury: A Systematic Review and Meta-Analysis.

Our goal was to understand the impact of regenerative therapies on the functional capacity of skeletal muscle following volumetric muscle loss (VML) injury. An extensive database search (e.g., PubMed, Cochrane Library, and ClinicalTrials.gov) was conducted up through January 2019 to evaluate the following: "In humans or animals with VML injury, is treatment better than no treatment at recovering functional capacity?" Study eligibility criteria required studies to have both an untreated and at least one treated VML injury group. From 2312 study reports, 44 studies met the inclusion criteria. Quantitative functional capacity data (absolute and/or normalized strength) or proportional measures (histological analysis quantifying viable muscle tissue, mitochondrial function, and/or exhaustive treadmill running) were extracted for use. While both human and animal studies were included in the searches, only animal studies met the eligibility criteria. Using a random-effects model, Hedges' g was used as the effect size (ES) and calculated such that a positive ES indicated treatment efficacy. The overall ES was 0.75 (95% confidence interval: 0.53-0.96; p < 0.0000001), indicating that the treatments, on average, resulted in a significant improvement in functional capacity. From network meta-analyses, it was determined that an acellular biomaterial combined with stem and/or progenitor cells had the greatest treatment effectiveness. The findings indicate that various treatments in animal models of VML improve the functional capacity of muscle compared to leaving the injury untreated; however, the ∼16% beneficial effect is small. Our results suggest that current regenerative therapy paradigms require further maturation to achieve clinically meaningful improvements in the functional capacity of the muscle. Impact Statement Our most salient findings are that (1) various treatment approaches used in animal models of volumetric muscle loss (VML) injury improve functional capacity compared to leaving the injury untreated and (2) an acellular biomaterial in combination with cellular components was the most effective treatment to improve functional capacity following VML injury to date. The nature of our findings has substantial implications for regenerative medicine, biomedical engineering, and rehabilitative techniques currently being evaluated and developed for VML injury repair, and are pivotal to the progression of the regenerative medicine effort aimed at restoring maximal function to traumatized and disabled limbs.

Sparassis crispa Intake Improves the Reduced Lipopolysaccharide-Induced TNF-α Production That Occurs upon Exhaustive Exercise in Mice.

Our previous study showed that lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α production is inhibited by acute exhaustive exercise in mice, leading to transient immunodepression after exercise. Sparassis crispa (SC), an edible mushroom, has immunopotentiative properties. This study aimed to clarify the effects of SC intake on reduced LPS-induced TNF-α production upon exhaustive exercise in mice. Male C3H/HeN mice were randomly divided into three groups: normal chow intake + resting sedentary, normal chow intake + acute exhaustive treadmill running exercise, and SC intake (chow containing 5% SC powder for 8 weeks) + the exhaustive exercise groups. Each group was injected with LPS immediately after the exhaustive exercise or rest. Plasma and tissue TNF-α levels were significantly decreased by exhaustive exercise. However, this reduction of the TNF-α level was partially attenuated in the plasma and small intestine by SC intake. Although levels of TLR4 and MyD88 protein expression were significantly decreased in tissues by exhaustive exercise, the reduction of TLR4 and MyD88 levels in the small intestine was partially attenuated by SC intake. These results suggest that SC intake attenuates exhaustive exercise-induced reduction of TNF-α production via the retention of TLR4 and MyD88 expression in the small intestine.

Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism.

The human gut microbiome is linked to many states of human health and disease.1 The metabolic repertoire of the gut microbiome is vast, but the health implications of these bacterial pathways are poorly understood. In this study, we identify a link between members of the genus Veillonella and exercise performance. We observed an increase Veillonella relative abundance in marathon runners post-marathon and isolated a strain of Veillonella atypica from stool samples. Inoculation of this strain into mice significantly increased exhaustive treadmill runtime. Veillonella utilize lactate as their sole carbon source, which prompted us to perform shotgun metagenomic analysis in a cohort of elite athletes, finding that every gene in a major pathway metabolizing lactate to propionate is at higher relative abundance post-exercise. Using 13C3-labeled lactate in mice we demonstrate that serum lactate crosses the epithelial barrier into the lumen of the gut. We also show that intrarectal instillation of propionate is sufficient to reproduce the increased treadmill runtime performance observed with V. atypica gavage. Taken together, these studies reveal that V. atypica improves runtime via its metabolic conversion of exercise-induced lactate into propionate, thereby identifying a natural, microbiome-encoded enzymatic process that enhances athletic performance.

The Effect of Acute Sleep Restriction on Running Mechanics during an Exhaustive Run

PURPOSE: Inadequate sleep is a known risk factor for injury, but the mechanisms by which sleep restriction increases injury risk remain unknown. The purpose of this study was to determine if running mechanics during an exhaustive run, including average peak impact accelerations between the tibia and the forehead, would be altered following one night of sleep restriction. METHODS: Two male and seven female subjects (21 ±3yrs, 55 ±10kg) completed an exhaustive treadmill run following either 8 hours (well-rested, WR) or 3 hours of sleep (sleep-restricted, SR) in a randomized crossover design, separated by at least one week. The exhaustive treadmill run was performed at an intensity equal to the subject’s ventilatory threshold until volitional fatigue. Wireless inertial measurement units (IMUs) were placed on the right tibia and forehead. Average right tibia peak impact accelerations (RtPk), average head peak impact accelerations (HdPk), and shock attenuation (ratio of RtPk to HdPk) were measured for 3 minutes during the first 2-5 minutes and final 3 minutes. Paired t-tests were used to compare each dependent variable (shock attenuation, RtPk, HdPk) between conditions (WR vs SR). RESULTS: Time to exhaustion during the exhaustive treadmill test was not significantly different between the WR and SR conditions respectively (38.5 ±15.3 minutes, 40.0 ±14.7 minutes, p = 0.69). There were no significant differences in shock attenuation between conditions during the first 2-5 minutes (WR: 58.96 ±7.09, SR: 57.72 ±7.33, p = 0.55) and final 3 minutes (WR: 58.00 ±8.73, SR: 57.53 ±7.58, p = 0.84). No significant differences were found between conditions for RtPk (WR: 5.19 ±0.73g, SR: 5.07 ±0.92g, p = 0.49, WR: 5.38 ±0.87g, SR: 5.29 ±0.96g, p = 0.64) and HdPk (WR: 2.12 ±0.44g, SR: 2.11 ±0.37g, p = 0.79, WR: 2.22 ±0.45g, SR: 2.20 ± 0.36g, p = 0.76) during the first 2-5 minutes and final 3 minutes respectively. CONCLUSION: Running mechanics were not altered following one night of sleep restriction. These data suggest that one night of inadequate sleep is not sufficient to alter running mechanics, however more research is needed to understand the possible effects of chronic sleep restriction and its potential influence on injury risk during running.

Altered multi-muscle coordination patterns in habitual forefoot runners during a prolonged, exhaustive run

Introduction: In response to fatigue during an exhaustive treadmill run, forefoot runner’s muscles must adapt to maintain their pace. From a neuromuscular control perspective, certain muscles may not be able to sustain the force to meet the run’s demands; thus, there may be alternative muscle coordination in the lower extremity that allows for continued running for an extended period of time. The aim of this study was to quantify the change in muscle coordination during a prolonged run in forefoot runners.Methods: Thirteen forefoot runners performed exhaustive treadmill runs (mean duration: 15.4 ± 2.2 min). The muscle coordination of seven lower extremity muscles was quantified using a high-resolution time–frequency analysis together with a pattern recognition algorithm.Results: The mean EMG intensity for the lateral and medial gastrocnemius muscles decreased with the run (p = 0.02; 0.06). The weight factors of the second principal pattern decrease by 128.01% by the end of run (p = 0.05, Cohen’s d = 0.42) representing a relatively greater biceps femoris activation in midstance but smaller midstance rectus femoris, vastus medialis, triceps surae, and tibialis anterior activation.Discussion: These results suggest that forefoot runners cannot sustain plantar flexor activation throughout an exhaustive run and change their muscle coordination strategy as a compensation. Understanding the underlying compensation mechanisms humans use to cope with fatigue will help to inform training modalities to enhance these late stage muscle activation strategies for athletes with the goal of improving performance and reducing injury.

The Effect of Workload on Exercise Volume during Exhaustive Anaerobic Treadmill Running

Anaerobic capacity has implications in health and sport performance. Sprint interval training improves anaerobic capacity, aerobic factors as well as performance. Optimal durations for taxing anaerobic capacity have been shown to be 60 seconds, and have been elicited using Anaerobic Speed Test (AST). In order to maintain this optimal duration for multiple sets, a decreasing workloads method must be used as fatigue increases following each set. These workloading methods must be compared to determine which protocol allows for the maximum exercise volume to be achieved. PURPOSE: The purpose of this study was to compare the effects of three different workload protocols on exercise volume completed during multiple sets of exhaustive anaerobic running on a treadmill. METHODS: Twelve male subjects (mean ± SD; age = 22.7 ± 4 yr, height:172.9 ± 6.9 cm, weight:75.9 ± 10.3 kg, VO2 max: 57.3 ± 6 ml/kg/min) completed three sessions of high intensity running on a graded treadmill with three different protocols using parameters adopted from the AST (20% grade, 8 mph to exhaustion). Four sets were completed during each protocol. Protocols included: 1) constant sets (CS): no descending workload in all four sets, 2) descending speed (DS): the speed is decreased by 10% for each subsequent set, 3) descending grade (DG): the grade is decreased by 10% for each subsequent set. RESULTS: Total exercise volume achieved during the four sets of the DS protocol was significantly higher than both the CS (p<0.01) and DG (p<0.01) protocols. Time to exhaustion achieved during the 2nd, 3rd and 4th sets of the DS protocol were significantly higher than the 2nd, 3rd and 4th sets of the CS protocol, all under p<0.01. Cadence during the 3rd set of the DS protocol was significantly lower than the 3rd set of the CS protocol (p<0.01). Additionally, cadence during the 4th set of the DS protocol was significantly higher than the 4th sets of the CS and DG protocols (p<0.01). CONCLUSIONS: The longer times per set and greater volume achieved during the DS protocol, in comparison to the DG and CS protocols, suggests the potential for a greater training effect. Differences in cadence values among the protocols could help explain differences in performance implicating muscle fiber type recruitment and fatigue.

Enhanced maximal exercise capacity, vasodilation to electrical muscle contraction, and hind limb vascular density in ASIC1a null mice.

Acid‐sensing ion channel (ASIC) proteins form extracellular proton‐gated, cation‐selective channels in neurons and vascular smooth muscle cells and are proposed to act as extracellular proton sensors. However, their importance to vascular responses under conditions associated with extracellular acidosis, such as strenuous exercise, is unclear. Therefore, the purpose of this study was to determine if one ASIC protein, ASIC1a, contributes to extracellular proton‐gated vascular responses and exercise tolerance. To determine if ASIC1a contributes to exercise tolerance, we determined peak oxygen (O2) uptake in conscious ASIC1a−/− mice during exhaustive treadmill running. Loss of ASIC1a was associated with a greater peak running speed (60 ± 2 vs. 53 ± 3 m·min−1, P = 0.049) and peak oxygen (O2) uptake during exhaustive treadmill running (9563 ± 120 vs. 8836 ± 276 mL·kg−1·h−1, n = 6–7, P = 0.0082). There were no differences in absolute or relative lean body mass, as determined by EchoMRI. To determine if ASIC1a contributes to vascular responses during muscle contraction, we measured femoral vascular conductance (FVC) during a stepwise electrical stimulation (0.5–5.0 Hz at 3 V for 60 sec) of the left major hind limb muscles. FVC increased to a greater extent in ASIC1a−/− versus ASIC1a+/+ mice (0.44 ± 0.03 vs. 0.30 ± 0.04 mL·min−1·100 g hind limb mass−1 · mmHg−1, n = 5 each, P = 0.0009). Vasodilation following local application of external protons in the spinotrapezius muscle increased the duration, but not the magnitude, of the vasodilatory response in ASIC1a−/− mice. Finally, we examined hind limb vascular density using micro‐CT and found increased density of 0–80 μm vessels (P < 0.05). Our findings suggest an increased vascular density and an enhanced vasodilatory response to local protons, to a lesser degree, may contribute to the enhanced vascular conductance and increased peak exercise capacity in ASIC1a−/− mice.

Maximal Oxygen Uptake Is Achieved in Hypoxia but Not Normoxia during an Exhaustive Severe Intensity Run.

Highly aerobically trained individuals are unable to achieve maximal oxygen uptake () during exhaustive running lasting ~2 min, instead plateaus below after ~1 min. Hypoxia offers the opportunity to study the () response to an exhaustive run relative to a hypoxia induced reduction in . The aim of this study was to explore whether there is a difference in the percentage of achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic 67.0 ± 5.2 ml.kg−1.min−1) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (FiO2 0.13). The data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR was less than normoxic (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic was achieved (102 ± 8% ramp, P = 0.490). The phase II time constant was greater in hypoxia (12.7 ± 2.8 s) relative to normoxia (10.4 ± 2.6 s) (P = 0.029). The results demonstrate that highly aerobically trained individuals cannot achieve during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower in hypoxia despite a slightly slower response.

Influence of Post-Exercise Carbohydrate-Protein Ingestion on Muscle Glycogen Metabolism in Recovery and Subsequent Running Exercise.

We examined whether carbohydrate-protein ingestion influences muscle glycogen metabolism during short-term recovery from exhaustive treadmill running and subsequent exercise. Six endurance-trained individuals underwent two trials in a randomized double-blind design, each involving an initial run-to-exhaustion at 70% VO2max (Run-1) followed by 4-h recovery (REC) and subsequent run-to-exhaustion at 70% VO2max (Run-2). Carbohydrate-protein (CHO-P; 0.8 g carbohydrate·kg body mass [BM-1]·h-1 plus 0.4 g protein·kg BM-1·h-1) or isocaloric carbohydrate (CHO; 1.2 g carbohydrate·kg BM-1·h-1) beverages were ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run-1, postrecovery and fatigue in Run-2. Time-to-exhaustion in Run-1 was similar with CHO and CHO-P (81 ± 17 and 84 ± 19 min, respectively). Muscle glycogen concentrations were similar between treatments after Run-1 (99 ± 3 mmol·kg dry mass [dm-1]). During REC, muscle glycogen concentrations increased to 252 ± 45 mmol·kg dm-1 in CHO and 266 ± 30 mmol·kg dm-1 in CHO-P (p = .44). Muscle glycogen degradation during Run-2 was similar between trials (3.3 ± 1.4 versus 3.5 ± 1.9 mmol·kg dm-1·min-1 in CHO and CHO-P, respectively) and no differences were observed at the respective points of exhaustion (93 ± 21 versus 100 ± 11 mmol·kg dm-1; CHO and CHO-P, respectively). Similarly, time-to-exhaustion was not different between treatments in Run-2 (51 ± 13 and 49 ± 15 min in CHO and CHO-P, respectively). Carbohydrate-protein ingestion equally accelerates muscle glycogen resynthesis during short-term recovery from exhaustive running as when 1.2 g carbohydrate·kg BM-1·h-1 are ingested. The addition of protein did not alter muscle glycogen utilization or time to fatigue during repeated exhaustive running.