Mechanisms of muscle fatigue in intense exercise

Fatigue-Related Changes in Running Technique and Mechanical Variables After a Maximal Incremental Test in Recreational Runners

Understanding the changes in running mechanics caused by fatigue is essential to assess its impact on athletic performance. Changes in running biomechanics after constant speed conditions are well documented, but the adaptive responses after a maximal incremental test are unknown. We compared the spatiotemporal, joint kinematics, elastic mechanism, and external work parameters before and after a maximal incremental treadmill test. Eighteen recreational runners performed 2-minute runs at 8 km·h-1 before and after a maximal incremental test on a treadmill. Kinematics, elastic parameters, and external work were determined using the OpenCap and OpenSim software. We did not find differences in spatiotemporal parameters and elastic parameters (mechanical work, ankle, and knee motion range) between premaximal and postmaximal test conditions. After the maximal test, the runners flexed their hips more at contact time (19.4°-20.6°, P = .013) and presented a larger range of pelvis rotation at the frontal plane (10.3°-11.4°, P = .002). The fatigue applied in the test directly affects pelvic movements; however, it does not change the lower limb motion or the spatiotemporal and mechanical work parameters in recreational runners. A larger frontal plane motion of the pelvis deserves attention due to biomechanical risk factors associated with injuries.

Head-neck cooling effects on central and peripheral fatigue, motor accuracy, and blood markers of stress in men with multiple sclerosis and healthy men: A randomized crossover study

BACKGROUND

The present study aimed to investigate whether head and neck cooling (at 18 °C next to the skin) and fatiguing submaximal exercise at a thermoneutral ambient temperature can induce peripheral and central responses in healthy men and those with multiple sclerosis (MS).

METHODS

A local head-neck cooling (at 18 °C next to the skin) intervention in men with a relapsing-remitting form of MS (n = 18; age 30.9 ± 8.1 years) and healthy men (n = 22; age 26.7 ± 5.9 years) was assessed. Men in both groups performed 100 intermittent isometric knee extensions with 5 s contractions and 20 s of rest. The primary variables were measured before exercise, after 50 and 100 repetitions, and 1 h after recovery. The central activation ratio, maximal voluntary contraction, electrically induced force, electromyography, contractile properties, blood markers, muscle temperature, and perception of effort were measured.

RESULTS

Compared with noncooled conditions, head and neck cooling increased the central capacity to activate exercising muscles but resulted in greater exercise-induced peripheral fatigue in men with MS (p < 0.05). Local cooling did not affect motor accuracy or the amplitude of electromyography signals; however, these factors were related to the intensity of the motor task (p > 0.05). The changes in central and peripheral fatigability induced by local cooling during submaximal exercise were more pronounced in men with MS than in healthy men (p < 0.05).

CONCLUSION

Head and neck cooling enhances central activation of muscles during exercise, leading to improved exercise performance compared with noncooled conditions in men with MS.

Polysaccharides from Artemisia argyi leaves: Environmentally friendly ultrasound-assisted extraction and antifatigue activities

Artemisia argyi leaf polysaccharide (AALPs) were prepared through ultrasound-assisted extraction (UAE), and their antifatigue activities were evaluated. Extraction was optimized using response surface methodology (RSM), which yielded the following optimal UAE conditions: ultrasonication power of 300 W, extraction temperature of 51 °C, liquid:solid ratio of 20 mL/g, and ultrasonication time of 47 mins. The above optimal conditions resulted in the maximum extraction rate of 10.49 %. Compared with hot water extraction (HWE), UAE supported higher yields and total sugar, uronic acid, and sulfate contents of AALPs. Meanwhile, AALP prepared through UAE (AALP-U) exhibited higher stability due to its smaller particle size and higher absolute value of zeta potential than AALP prepared through HWE (AALP-H). In addition, AALP-U demonstrated stronger antioxidant activity than AALP-H. In forced swimming tests on mice, AALP-U could significantly prolong swimming time with a dose-dependent effect, increase liver and muscle glycogen levels, and improve other biochemical indices, thus showing great potential for application in functional food.

Field assessment of active BSE: Trends over test days of subjective indicators and self-reported fatigue for railway construction workers

The research community has conducted several controlled "in -lab" assessments on the effectiveness of industrial exoskeletons, paving the way for their adoption. However, field testing, focusing on ergonomics and the user experience, could serve to enhance both end-users' awareness and address open doubts concerning true effectiveness of industrial exoskeletons. This study presents an analysis of qualitative data regarding the use of back-support exoskeletons during field trials in harsh civil engineering environments. This work evaluates the StreamEXO's (an active back-support exoskeleton) efficacy in reducing fatigue and the evolution of its perceived usefulness. This is achieved using qualitative data collection tools, during real scenarios testing over multiple-day trials. Collected data shows a positive correlation between self-reported fatigue, measured on a four verbal anchors-based Borg CR10 scale, and the use of the exoskeleton during physically demanding movements. Moreover, the evolution of scores throughout the testing sessions (90 minutes of exoskeleton use for three nonconsecutive days) suggests a trend due to the adaptation and learning curve of workers during the exoskeleton experience. The analysis of the open-ended answers highlights that the adaptation to physical interaction has a negative oscillation on day two to rise back during the third day, possibly correlated to a change in muscle pattern. The main critical factors affecting comfort during the exoskeleton experience are weight balance, body pressure, and thermal comfort, which can strongly affect device acceptance.

[Physiological assessment and management of post-COVID patients with normal cardiopulmonary imaging and functional tests]

OBJECTIVE

Contributing to elucidate the pathophysiology of dyspnoea and exertion intolerance in post-COVID syndrome patients with normal cardiopulmonary imaging and functional tests at rest, while determining their fitness and level of endurance in order to individualize working parameters for physical rehabilitation.

MATERIAL AND METHODS

After an anamnesis and clinical examination at rest, 27 subjects (50±11.9 years) (14 women) with post-COVID syndrome of more than 6 months of evolution performed a continuous maximal-incremental graded cardiopulmonary exercise test (CPET) with breath-by-breath gas-exchange monitoring and continuous ECG registration, on an electromagnetically braked cycle ergometer. The values obtained were compared with those of reference, gender or controls, using the Chi-square, t-Student or ANOVA test.

RESULTS

The clinical examination at rest and the CPET were clinically normal and without adverse events. Reasons for stopping exercise were leg discomfort. It is only worth noting a BMI=29.9±5.8kg/m2 and a basal lactate concentration of 2.1±0.7mmol/L. The physiological assessment of endurance showed the following results relative to predicted VO2máx: 1)peakVO2=80.5±18.6%; 2)VO2 at ventilatory threshold1 (VO2VT1): 46.0±12.9%; 3)VO2VT2: 57.2±16.4%; 4)working time in acidosis: 5.6±3,0minutes; and 5)maximum lactate concentration: 5.1±2.2mmol/L.

CONCLUSIONS

The CPET identified limited aerobic metabolism and early increase in glycolytic metabolism as causes of dyspnoea and exercise intolerance, determined fitness for physical rehabilitation, and individualized it based on the level of endurance.

The anti-fatigue and sleep-aiding effects vary significantly among different recipes containing Ganoderma lucidum extracts

Aims

This study aims to delve into the anti-fatigue and sleep-aiding effects of various formulations containing Ganoderma lucidum extracts.

Materials and methods

PGB [incorporating Ganoderma lucidum extract (GE), broken Ganoderma lucidum spore powder (GB) and Paecilomyces hepiali mycelium (PH)] and GBS [composed of GE, GB, and Ganoderma sinense powder (GS)] were chosen as representative recipes for this study. Mice were treated with these recipes or key components of Ganoderma lucidum for 14 consecutive days. Subsequently, a weight-bearing swimming experiment was conducted to assess the mice's exhaustion time and evaluate the anti-fatigue properties of the recipes. Sleep-aiding effects were analyzed by measuring the sleep latency and duration. Furthermore, levels of blood lactic acid, serum urea nitrogen, hepatic glycogen, muscle glycogen, and malondialdehyde (MDA) were measured in the livers and muscles.

Key findings

The anti-fatigue abilities of the tested mice were significantly improved after treatment with PGB and their sleep quality improved as well with GBS treatment. PGB treatment for 14 days could significantly prolong the exhaustion time in weight-bearing swimming (from 10.1 ± 0.5 min to 15.2 ± 1.3 min). Meanwhile, glycogen levels in the livers and muscles were significantly increased, while the levels of serum lactic acid, serum urea nitrogen, and MDA in the livers and muscles were significantly decreased. In contrast, mice treated with GBS for 14 days experienced significant improvements in sleep quality, with shortened sleep latency (from 6.8 ± 0.7 min to 4.2 ± 0.4 min), extended sleep duration (from 88.3 ± 1.4 min to 152.5 ± 9.3 min), and decreased muscle MDA levels. These results indicated that Ganoderma lucidum extracts can be used for anti-fatigue and or aid in sleeping, depending on how they are prepared and administered.

Significance

This study provides experimental evidence and theoretical basis for the development of Ganoderma lucidum recipes that are specifically designed to help with anti-fatigue and sleep.

Metabolic and Perceptual Responses to Constant Heart Rate Exercise at Vigorous Intensities in Women

PURPOSE

This study quantified the metabolic demands (oxygen uptake (V̇O 2 )), power output adjustments, changes in the V̇O 2 /power output ratio, and perceptual responses (rating of perceived exertion (RPE)) during constant heart rate (HR) exercise performed within the vigorous intensity range (77%-95% HR peak ).

METHODS

Twelve women (mean ± SD age, 22 ± 4 yr) performed a graded exercise test to exhaustion to determine peak parameters, and three randomly ordered, constant HR trials to exhaustion or for 60 min at the lower (HR L = 77% HR peak ), middle (HR M = 86% HR peak ), and higher (HR H = 95% HR peak ) end of the vigorous intensity range. Time course of changes and patterns of responses were examined for V̇O 2 , power output, V̇O 2 /power output, and RPE for the composite and for each subject.

RESULTS

Across the HR L (time to exhaustion ( Tlim ) = 56.3 ± 9.9 min), HR M (51.8 ± 13.5 min), and HR H (27.2 ± 17.7 min) trials, V̇O 2 and power output decreased quadratically ( P < 0.05) relative to the initial value from 10% to 100% of Tlim , whereas the V̇O 2 /power output increased quadratically from 20% to 100% Tlim , and RPE increased linearly from 50% to 100% Tlim . The V̇O 2 and RPE, collapsed across time, for HR L (54.3% ± 3.3% V̇O 2peak , 11 ± 1.5 RPE) were lower than HR M (64.9% ± 4.5% V̇O 2peak , 14 ± 1.7 RPE), and both were lower than HR H (80.1% ± 4.1% V̇O 2peak , 17 ± 1.4 RPE). None of the 12 subjects at HR L , 6 at HR M , and 7 at HR H were within the vigorous V̇O 2 range.

CONCLUSIONS

The HR L was not sufficient to meet the desired metabolic intensity for vigorous exercise, whereas the middle to higher end of the range elicited a V̇O 2 within the prescribed range of only ~50%-60% of the subjects. This study indicated that exercise held constant at a percentage of HR peak cannot consistently be used to prescribe a desired metabolic stimulus.

Effects of Aerobic Exercise Therapy through Nordic Walking Program in Lactate Concentrations, Fatigue and Quality-of-Life in Patients with Long-COVID Syndrome: A Non-Randomized Parallel Controlled Trial

BACKGROUND

Long-COVID syndrome comprises a variety of signs and symptoms that develop during or after infection with COVID-19 which may affect the physical capabilities. However, there is a lack of studies investigating the effects of Long-COVID syndrome in sport capabilities after suffering from COVID-19 infection. The purpose of the study was to evaluate and compare lactate concentration and quality of life (QoL) in patients with Long-COVID with those who have not developed non-Long-COVID during Nordic walking exercise therapy.

METHODS

Twenty-nine patients (25.5 ± 7.1 years) took part in a non-randomized controlled trial, divided into two groups: a Long-COVID group (n = 16) and a non-Long-COVID control (n = 13). Patients were confirmed as having Long-COVID syndrome if they experienced fatigue or tiredness when performing daily activities and worsening of symptoms after vigorous physical or mental activity. All participants underwent a 12-week Nordic Walking program. Lactate concentration after exercise and distance covered during all sessions were measured. Pre- and Long-Nordic Walking program, the Modified Fatigue Impact Scale (MFIS), the Short Form 36 Health Survey (SF-36), and EURO QoL-5D (EQ-ED) were administered to assess fatigue and quality of life, respectively.

RESULTS

There was a lactate concentration effect between groups (F = 5.604; p = 0.024). However, there was no significant effect as a result of the session (F = 3.521; p = 0.121) with no interaction of group × session (F = 1.345; p = 0.414). The group main effect (F = 23.088; p < 0.001), time effect (F = 6.625; p = 0.026), and group × time (F = 4.632; p = 0.002) interaction on the SF-36 scale were noted. Also, there were a significant group main effect (F = 38.372; p < 0.001), time effect (F = 12.424; p = 0.005), and group × time interaction (F = 4.340; p = 0.014) on EQ-5D. However, there was only a significant group main effect (F = 26.235; p < 0.001) with no effect on time (F = 2.265; p = 0.160) and group × time (F = 1.584; p = 0.234) interaction on the MFIS scale.

CONCLUSIONS

The Long-COVID group showed higher lactate concentration compared with the control group during the 12 weeks of the Nordic Walking program. The Long-COVID group presented a decrease in fatigue with respect to the control group according to the MFIS scale, as well as improvement in quality of life after aerobic exercise therapy.

Responses to Exercise at the Critical Heart Rate vs. the Power Output Associated With the Critical Heart Rate

ABSTRACT

Succi, PJ, Dinyer-McNeely, TK, Voskuil, CC, Abel, MG, Clasey, JL, and Bergstrom, HC. Responses to exercise at the critical heart rate vs. the power output associated with the critical heart rate. J Strength Cond Res 37(12): 2362-2372, 2023-This study examined the physiological (volume of oxygen consumption [V̇ o2 ], heart rate [HR], power output [PO], respiration rate [RR], muscle oxygen saturation [%SmO 2 ]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP and MMG AMP] and mean power frequency [EMG MPF and MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise anchored at the critical heart rate (CHR) vs. the PO associated with CHR (PCHR). Nine subjects (mean ± SD ; age = 26 ± 3 years) performed a graded exercise test and 4 constant PO trials to exhaustion at 85-100% of peak PO (PP) to derive CHR and PCHR on a cycle ergometer. Responses were recorded during trials at CHR (173 ± 9 b·min -1 , time to exhaustion [T Lim ] = 45.5 ± 20.2 minutes) and PCHR (198 ± 58 W, T Lim = 21.0 ± 17.8 minutes) and normalized to their respective values at PP in 10% intervals. There were significant ( p ≤ 0.05) mode (CHR vs. PCHR) × time (10%-100% T Lim ) interactions for all variables ( p < 0.001-0.036) except MMG AMP ( p > 0.05). Post hoc analyses indicated differences across time for CHR V̇ o2 (%change = -22 ± 16%), PCHR V̇ o2 (19 ± 5%), CHR RR (24 ± 23%), PCHR RR (45 ± 14%), CHR PO (-33 ± 11%), PCHR HR (22 ± 5%), CHR RPE (22 ± 14%), PCHR RPE (39 ± 6%), CHR %SmO 2 (41 ± 33%), PCHR %SmO 2 (-18 ± 40%), CHR EMG AMP (-13 ± 15%), PCHR EMG AMP (13 ± 13%), CHR EMG MPF (9 ± 8%), CHR MMG MPF (7 ± 11%), and PCHR MMG MPF (-3 ± 14%). The critical heart rate was more sustainable than PCHR but required adjustments in PO which traversed intensity domains and caused dissociations of the responses previously observed in exercise anchored to PO. These dissociations indicated the demands to exercise varied with anchoring scheme and provides an important consideration for practitioners prescribing endurance exercise.

Loss of amyotrophic lateral sclerosis risk factor SCFD1 causes motor dysfunction in Drosophila

Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disease mostly resulting from a complex interplay between genetic, environmental and lifestyle factors. Common genetic variants in the Sec1 Family Domain Containing 1 (SCFD1) gene have been associated with increased ALS risk in the most extensive genome-wide association study (GWAS). SCFD1 was also identified as a top-most significant expression Quantitative Trait Locus (eQTL) for ALS. Whether loss of SCFD1 function directly contributes to motor system dysfunction remains unresolved. Here we show that moderate gene silencing of Slh, the Drosophila orthologue of SCFD1, is sufficient to cause climbing and flight defects in adult flies. A more severe knockdown induced a significant reduction in larval mobility and profound neuromuscular junction (NMJ) deficits prior to death before metamorphosis. RNA-seq revealed downregulation of genes encoding chaperones that mediate protein folding downstream of Slh ablation. Our findings support the notion that loss of SCFD1 function is a meaningful contributor to ALS and disease predisposition may result from erosion of the mechanisms protecting against misfolding and protein aggregation.

Effectiveness and safety of subthreshold vibration over suprathreshold vibration in treatment of muscle fatigue in elderly people

Muscle fatigue is common in many populations, particularly elderlies. Aging increases the incidence of muscle fatigue and delays its recovery. There is a huge debate about the current treatments for muscle fatigue, particularly in elderlies. Recently, it has been discovered that mechanoreceptors have an important role as a sensory system in sensing muscle fatigue which could enhance the body's response to muscle fatigue. The function of mechanoreceptors could be enhanced by applying either suprathreshold or subthreshold vibration. Although suprathreshold vibration improves muscle fatigue, it can cause desensitization of cutaneous receptors, discomfort, and paresthesia, which are barriers to clinical use. Subthreshold vibration has been approved as a safe and effective method of training for mechanoreceptors; however, its use and effectiveness in muscle fatigue have never been tested or explained. Possible physiological effects of subthreshold vibration in the treatment of muscle fatigue include: (1) Enhancing the function of mechanoreceptors themselves; (2) Increasing the firing rate and function of alpha motor neurons; (3) Increasing blood flow to fatigued muscles; (4) Decreasing the rate of muscle cell death in elderlies (sarcopenia); and (5) Driving motor commands and allow better performance of muscles to decrease fatigue incidence. In conclusion, the use of subthreshold vibration could be a safe and effective treatment for muscle fatigue in elderlies. It could enhance recovery from muscle fatigue. Finally, Subthreshold Vibration is safe and effective in treating muscle fatigue in comparison to suprathreshold vibration.

Curcumin (CUMINUP60®) mitigates exercise fatigue through regulating PI3K/Akt/AMPK/mTOR pathway in mice

Curcumin is a chemical constituent extracted from Curcuma longa L. Several clinical and preclinical studies have demonstrated that it can mitigate exercise fatigue, but the exact mechanism is still unknown. Therefore, we applied a mouse model of exercise fatigue to investigate the possible molecular mechanisms of curcumin's anti-fatigue effect. Depending on body mass, Kunming mice were randomly divided into control, caffeine (positive drug), and curcumin groups, and were given 28 days intragastric administration. Both the caffeine group and curcumin group showed significant improvement in exercise fatigue compared to the control group, as evidenced by the increase in time to exhaustion, as well as the higher quadriceps coefficient, muscle glycogen (MG) content, and increase in the expression of Akt, AMPK, PI3K, and mTOR proteins. While the curcumin group also significantly improved the exercise fatigue of the mice, demonstrating a lower AMP/ATP ratio and lactic acid (LA) content, and increased glycogen synthase (GS), and myonectin content compared to the caffeine group. Therefore, in the present study, we found that curcumin can exert a similar anti-fatigue effect to caffeine and may act by regulating energy metabolism through modulating the expression of the proteins in the PI3K/Akt/AMPK/mTOR pathway.

Effects and mechanism of gastrodin supplementation on exercise-induced fatigue in mice

Gastrodin reportedly exerts various pharmacological and health effects. However, the function of gastrodin in reducing exercise-induced fatigue remains elusive. Herein, we investigated the anti-fatigue effects of gastrodin on male mice and explored its possible mechanism of action. At 50 and 100 mg per kg per day, gastrodin significantly reduced fatigue in mice, confirmed using the forced swimming test, whereas no effect was noted at 20 mg per kg per day. Gastrodin preserved muscle and liver glycogen, increased superoxide dismutase activity, and decreased malondialdehyde, blood lactate, and blood urea nitrogen levels. Notably, gastrodin upregulated the mRNA expression levels of AMPK, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase 1. Gastrodin also regulated the composition of intestinal flora. These results confirmed that gastrodin activated AMPK and Nrf2/HO-1 pathways and regulated intestinal flora to improve performance in exhaustive exercise, suggesting that gastrodin is an effective functional food to alleviate exercise-induced fatigue.

The Impact of Fatigue on the Sense of Local and Global Rhythmic Movement

Efficient movement control and the mechanisms responsible for the sense of rhythm are still not fully understood. The purpose of this paper was to estimate the influence of fatigue on the sense of rhythm defined as specific order of movements and their rhythmic perception. It was examined in a holistic way, by analyzing both global and local aspects of the movement. Twenty adult participants (20.2 ± 0.4 years, ten females) took part in the experiment. The fatigue protocol was applied in four blocks, which consisted of 30-s consecutive jumping with 80% of maximal effort. Immediately after each fatigue block, the rhythm performance was evaluated in global and local tests. The global test was based on 45 continuous jumps and was divided into an assisted and an unassisted phase using the Optojump Next System. The local test was performed by bilateral tapping of lower limbs by means of the Vienna Test System. The hypothesis about the significant effect of fatigue on the sense of rhythm was falsified. In particular, we observed the lack of differences between global and local aspects of the movement. Moreover, female participants showed a better sense of rhythm than males. Regardless of the fatigue protocol, participants made larger errors with a lower movement frequency in local rhythmic tasks. The coefficient of variation showed that sex differences were only significant in the unassisted phase of the global rhythmic task. We suggest that movement variability metrics may provide additional information about the sense of rhythm, which should be explored more in future studies, not only dependent on fatigue.

Evaluation of Muscle Oxygen Dynamics in Children's Gait and Its Relationship with the Physiological Cost Index

The response of muscle oxygen saturation, which is an index for the energy metabolism of muscles during walking in children, and its relationship to the physiological cost index, which indicates walking efficiency, are unknown. This study aimed to evaluate muscle oxygen saturation in lower extremity muscles during walking in children, its changes with age, and the relationship between the physiological cost index. The oxygen saturation was measured by the amount of change during a two-minute walk, and the physiological cost index was calculated from the change in heart rate before and after exercise and walking speed. Results were compared for each muscle, and the correlation between the two was examined. Changes in muscle oxygen saturation were greater in the lower leg muscles, significantly greater in the tibialis anterior at six to seven years, and in the gastrocnemius medial head at eight to ten years. The physiological cost index was significantly correlated with changes in muscle oxygen saturation in the tibialis anterior (r = 0.44, p < 0.001). The lower leg muscles were metabolically active in children’s gait, and their response varied with age. Moreover, the muscle oxygenation dynamics of the tibialis anterior may influence walking efficiency.

Transcranial Direct Current Stimulation Enhances Exercise Performance: A Mini Review of the Underlying Mechanisms

Exercise performance (EP) is affected by a combination of factors including physical, physiological, and psychological factors. This includes factors such as peripheral, central, and mental fatigue, external peripheral factors such as pain and temperature, and psychological factors such as motivation and self-confidence. During the last century, numerous studies from different fields of research were carried out to improve EP by modifying these factors. During the last two decades, the focus of research has been mainly moved toward the brain as a dynamic ever-changing organ and the ways changes in this organ may lead to improvements in physical performance. Development of centrally-acting performance modifiers such as level of motivation or sleep deprivation and the emergence of novel non-invasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are the key motives behind this move. This article includes three sections. Section Introduction provides an overview of the mechanisms behind the reduction of EP. The main focus of the Effects of tDCS on EP section is to provide a brief description of the effects of tDCS on maximal and submaximal types of exercise and finally, the section Mechanisms Behind the Effects of tDCS on EP provides description of the mechanisms behind the effects of tDCS on EP.

Fluctuations in External Peak Demands Across Quarters During Basketball Games

The purpose of this study was to compare external peak demands (PDs) across quarters (Q) in basketball. Thirteen elite, junior, male basketball players were monitored using electronic performance tracking systems. There were studied intervals for different time windows to determine the external PD for distance (m); player load; distance covered in four different zones; accelerations; and decelerations. A mixed linear model was run to identify differences among quarters, and the auto-correlation function was carried out to determine fluctuations across the whole game. The results showed significant differences between Q1 vs. Q2 for distance, player load, and standing–walking distance; between Q1 vs. Q3 for distance, player load, and HSR; between Q1 vs. Q4 for distance, player load, standing–walking, and HSR; and between Q3 vs. Q4 for distance and player load. These findings suggest that external PD for running-based demands (distance, player load, and high-speed running) decrease across basketball games with the most notable declines occurring between the first and fourth quarters. Nevertheless, it is important to note that non-significant differences were found between quarters for several external PD variables (jogging, running, acceleration, and deceleration) across different time windows. Findings from the present study reinforce the importance of considering specific PD variables for different functions due to the specific insight each provides.

Effects of a thorstensson fatiguing protocol on isometric and isokinetic performance

OBJECTIVE: Having participants perform 50 maximal isokinetic contractions, as introduced by Thorstensson and Karlsson (1976), is to this day one of the most commonly used fatigue protocols. Purpose: To determine to what extent a Thorstensson fatiguing protocol affects isokinetic and isometric performance characteristics. METHODS: Twenty-five college-aged men performed an isokinetic fatigue protocol consisting of 50 maximal elbow flexions at a moderate speed (180∘⋅s-1). Pre- and post-tests were used to calculate fatigue indices (FI%) for the following variables: isometric and isokinetic peak torque (PT), isometric rate of torque development (RTD), and maximum acceleration (ACCmax). RESULTS: Each of the four dependent variables significantly decreased with fatigue (each demonstrated p< 0.001), but not of the same magnitude. Isometric PT FI (-18.7%) was significantly less than isokinetic PT FI (-45.1%, p⩽ 0.001) and ACCmax FI (-26.3%) was significantly less than isometric RTD FI (-54.9%, p⩽ 0.001). There was a significant positive relationship between isometric and isokinetic PT FI% (r= 0.60, p< 0.002) as well as between isometric PT FI% and RTD FI% (r= 0.40, p< 0.046). There was no significant relationship observed between RTD FI% and ACCmax FI% nor between isokinetic PT FI% and ACCmax FI%. CONCLUSIONS: This investigation observed different patterns of response in maximal strength between isometric and isokinetic assessments following a isokinetic fatigue protocol. Additionally, the ability to rapidly generate strength and velocity had significantly different responses to fatigue between isometric and dynamic assessments. Due to these different responses, we recommend that assessments of fatigue at least include the same testing modality as the modality of the fatigue protocol.

Acute effects of different rest intervals between agonist-antagonist paired-sets in the neuromuscular system performance of young adults

INTRODUCTION

The agonist-antagonist paired-sets (APS) is a resistance training that involves alternating between exercises for agonist/antagonist muscles of a joint, with little or no rest between then. There is evidence that APS is more strenuous than traditional methods, but evidence on the optimal RI between agonist-antagonist actions is unknown.

OBJECTIVE

The aim of this study was to compare different rest intervals between agonist-antagonist actions during APS in young adults.

METHOD

Fifty healthy men (mean age 23.2 ± 2.8 years; 1.76 ± 0.1m height, 78.03 ± 8.1 kg) were included and performed three different agonist-antagonist paired-sets protocols separated by 72h, consisting of 4 sets of 10 repetitions. The protocols differed in terms of the rest interval between the knee flexion and extension movements: 0s (no rest); 60s and 120s. The rest intervals between exercise sets were standardized at 60s. Total work, peak torque, neuromuscular efficiency, surface EMG amplitude (sEMG, root mean square) and fatigue index obtained by processing of sEMG signal, were compared between rest intervals and exercise sets within each protocol.

RESULTS

There were no significant differences between rest intervals for total work, peak torque and neuromuscular efficiency (P > 0.05), but significant differences were found for sEMG and fatigue (P < 0.01), in which the protocol with 60s interval resulted in greater fatigue.

CONCLUSION

We showed that peak torque, total work and neuromuscular efficiency were not different between RI. The 60s RI showed a lower sEMG and a greater muscle fatigue. Although there were no significant differences, the NME was higher in the 60s interval.

Analysis of Pacing Strategies in AMRAP, EMOM, and FOR TIME Training Models during "Cross" Modalities

Empirically, it is widely discussed in “Cross” modalities that the pacing strategy developed by an athlete or trainee has a significant impact on the endurance performance in a WOD in the AMRAP, EMOM, or FOR TIME model. We can observe at least six pacing strategies adopted during the cyclical modalities in the endurance performance in the scientific literature. However, besides these modalities, exercises of acyclical modalities of weightlifting and gymnastics are performed in the “Cross” modalities. These exercises may not allow the same pacing strategies adopted during cyclic modalities’ movements due to their motor characteristics and different intensity and level of effort imposed to perform the motor gesture. In addition to the intensity and level of effort that are generally unknown to the coach and athlete of the “Cross” modalities, another factor that can influence the adoption of a pacing strategy during a WOD in the AMRAP, EMOM, or FOR TIME model is the task endpoint knowledge, which varies according to the training model used. Thus, our objective was to evaluate situations in which these factors can influence the pacing strategies adopted in a self-regulated task with cyclic and acyclic modalities movements during an endurance workout in the AMRAP, EMOM, and FOR TIME model. Given the scarcity of studies in the scientific literature and the increasing discussion of this topic within the “Cross” modalities, this manuscript can help scientists and coaches better orient their research problems or training programs and analyze and interpret new findings more accurately.

Higher Playing Times Accumulated Across Entire Games and Prior to Intense Passages Reduce the Peak Demands Reached by Elite, Junior, Male Basketball Players

The aim of this study was to analyze the effects of different factors on the external peak demands (PD) encountered by elite, junior, male basketball players in games, including the (1) total playing time during games and (2) playing time accumulated directly prior to each PD episode. Workload variables included the PD for total distance, distance covered in different intensity zones, accelerations >2 m·s-2 (ACC), decelerations <-2 m·s-2 (DEC), and PlayerLoad. PD were calculated across different sample durations for each variable. Linear mixed models were used to identify differences in PD between groups based on playing times. PD for total distance (5-min window), high-speed running (>18 km·h-1) distance (2-min window), and ACC (30-s, 45-s, 1-min, 2-min, and 5-min windows) were significantly (p < .05) higher for players who completed lower total playing times (16.6 ± 2.4 min) than players who completed higher total playing times (25.0 ± 3.4 min). The PD for total distance (30-s, 45-s, 1-min, and 2-min windows), high-speed running distance (30-s and 5-min windows), and PlayerLoad (1-min and 2-min windows) were significantly (p < .05) higher for players who accumulated lower playing times before each PD episode than players who accumulated higher playing times before each PD episode. Players who undertake less playing time overall and prior to each PD episode can reach higher peak external loads aggregated across varied time windows. These findings can inform tactical coaching decisions during games for high external loads to be accomplished during important passages of play.

How recreational marathon runners hit the wall: A large-scale data analysis of late-race pacing collapse in the marathon

INTRODUCTION

In the marathon, how runners pace and fuel their race can have a major impact on race outcome. The phenomenon known as hitting the wall (HTW) refers to the iconic hazard of the marathon distance, in which runners experience a significant slowing of pace late in the race, typically after the 20-mile mark, and usually because of a depletion of the body's energy stores.

AIM

This work investigates the occurrence of significant late-race slowing among recreational marathoners, as a proxy for runners hitting the wall, to better understand the likelihood and nature of such slowdowns, and their effect on race performance.

METHODS

Using pacing data from more than 4 million race records, we develop a pacing-based definition of hitting the wall, by identifying runners who experience a sustained period of slowing during the latter stages of the marathon. We calculate the cost of these slowdowns relative to estimates of the recent personal-best times of runners and compare slowdowns according to runner sex, age, and ability.

RESULTS

We find male runners more likely to slow significantly (hit the wall) than female runners; 28% of male runners hit the wall compared with 17% of female runners, χ2(1, N = 1, 928, 813) = 27, 693.35, p < 0.01, OR = 1.43. Such slowdowns are more frequent in the 3 years immediately before and after a recent personal-best (PB) time; for example, 36% of all runners hit the wall in the 3 years before a recent PB compared with just 23% in earlier years, χ2(1, N = 509, 444) = 8, 120.74, p < 0.01, OR = 1.31. When runners hit the wall, males slow more than females: a relative slowdown of 0.40 vs. 0.37 is noted, for male and female runners, when comparing their pace when they hit the wall to their earlier race (5km-20km) pace, with t(475, 199) = 60.19, p < 0.01, d = 0.15. And male runners slow over longer distances than female runners: 10.7km vs. 9.6km, respectively, t(475, 199) = 68.44, p < 0.01, d = 0.17. Although, notably the effect size of these differences is small. We also find the finish-time costs of hitting the wall (lost minutes) to increase with ability; r2(7) = 0.91, p < 0.01 r2(7) = 0.81, p < 0.01 for male and female runners, respectively.

CONCLUSIONS

While the findings from this study are consistent with qualitative results from earlier single-race or smaller-scale studies, the new insights into the risk and nature of slowdowns, based on the runner sex, age, and ability, have the potential to help runners and coaches to better understand and calibrate the risk/reward trade-offs that exist as they plan for future races.

Delayed Impairment of Postural, Physical, and Muscular Functions Following Downhill Compared to Level Walking in Older People

Transient symptoms of muscle damage emanating from unaccustomed eccentric exercise can adversely affect muscle function and potentially increase the risk of falling for several days. Therefore, the aims of the present study were to investigate the shorter- and longer-lasting temporal characteristics of muscle fatigue and damage induced by level (i.e., concentrically biased contractions) or downhill (i.e., eccentrically biased contractions) walking on postural, physical, and muscular functions in older people. Nineteen participants were matched in pairs for sex, age and self-selected walking speed and allocated to a level (n = 10, age = 72.3 ± 2.9 years) or downhill (n = 9, age = 72.1 ± 2.2 years) walking group. Postural sway, muscle torque and power, physical function (5× and 60 s sit-to-stand; STS), and mobility (Timed-Up-and-Go; TUG) were evaluated at baseline (pre-exercise), 1 min, 15 min, 30 min, 24 h, and 48 h after 30 min of level (0% gradient) or downhill (−10% gradient) walking on a treadmill. Following downhill walking, postural sway (+66 to 256%), TUG (+29%), 60 s STS (+29%), five times STS (−25%) and concentric power (−33%) did not change at 1–30 min post exercise, but were significantly different (p < 0.05) at 24 and48 h post-exercise when compared to baseline (p < 0.05). Muscle torque decreased immediately after downhill walking and remained impaired at 48 h post-exercise (−27 to −38%). Immediately following level walking there was an increase in postural sway (+52 to +98%), slower TUG performance (+29%), fewer STS cycles in 60 s (−23%), slower time to reach five STS cycles (+20%) and impaired muscle torque (−23%) and power (−19%) which returned to baseline 30-min after exercise cessation (p > 0.05). These findings have established for the first time distinct impairment profiles between concentric and eccentric exercise. Muscle damage emanating from eccentrically biased exercise can lead to muscle weakness, postural instability and impaired physical function persisting for several days, possibly endangering older adult’s safety during activities of daily living by increasing the risk of falls.

The patterns of exercise-induced β-endorphin expression in the central nervous system of rats

Exercise at different intensities is able to induce different physical and psychological statuses of the subjects. The β-endorphin (β-EP) in central nervous system is thought to play an important role in physical exercise. However, its expression patterns and physiological effects in the central nuclei under different exercise states are not well understood. Five-week old male Sprague-Dawley rats were randomly divided into two groups of 21 each: Control and Exercise. Control rats were sedentary while Exercise rats were arranged to run on a treadmill (5-week adapting or moderate exercise and 2-week high-intensity exercise). Seven rats were taken from each group at day33, day42 and day49 for examination of blood biochemical parameters (lactate, Lac; blood urea nitrogen, BUN; glucose) and for detection of nuclei β-EP level with immunohistochemistry. The results showed that Lac and BUN levels were significant increased after the high intensity exercise. The five-week exercise caused a significantly increased β-EP in caudate putamen (CPu), amygdala, paraventricular thalamic nucleus (PVT), ventromedial hypothalamus nucleus (VMH) and gigantocellular reticular nucleus (Gi). The high intensity exercise induced an elevated β-EP in CPu and nucleus of the solitary tract (Sol), but a decreased β-EP in globus pallidus (GP). Compared with Control, exercise rats showed an elevated β-EP in CPu, PVT, VMH, accumbens nucleus, Gi and Sol, and a decreased β-EP in GP at day49. The β-EP levels in acurate nucleus, periadueductal gray and parabrachial nucleus were not changed at day33, 42 and 49. In conclusion, β-EP levels in different nuclei changed under the moderate and high intensity exercises, which may contribute to modifying exercise-produced psychological and physiological effects.

Reciprocity Between Skeletal Muscle AMPK Deletion and Insulin Action in Diet-Induced Obese Mice

Insulin resistance due to overnutrition places a burden on energy-producing pathways in skeletal muscle (SkM). Nevertheless, energy state is not compromised. The hypothesis that the energy sensor AMPK is necessary to offset the metabolic burden of overnutrition was tested using chow-fed and high-fat (HF)-fed SkM-specific AMPKα1α2 knockout (mdKO) mice and AMPKα1α2lox/lox littermates (wild-type [WT]). Lean mdKO and WT mice were phenotypically similar. HF-fed mice were equally obese and maintained lean mass regardless of genotype. Results did not support the hypothesis that AMPK is protective during overnutrition. Paradoxically, mdKO mice were more insulin sensitive. Insulin-stimulated SkM glucose uptake was approximately twofold greater in mdKO mice in vivo. Furthermore, insulin signaling, SkM GLUT4 translocation, hexokinase activity, and glycolysis were increased. AMPK and insulin signaling intersect at mammalian target of rapamycin (mTOR), a critical node for cell proliferation and survival. Basal mTOR activation was reduced by 50% in HF-fed mdKO mice, but was normalized by insulin stimulation. Mitochondrial function was impaired in mdKO mice, but energy charge was preserved by AMP deamination. Results show a surprising reciprocity between SkM AMPK signaling and insulin action that manifests with diet-induced obesity, as insulin action is preserved to protect fundamental energetic processes in the muscle.

Postactivation potentiation effect of two lower body resistance exercises on repeated jump performance measures

This study examined the postactivation potentiation effects of combining squat and deadlift exercises on subsequent repeated jump performance. Fifteen, resistance-trained youth wrestlers were randomly allocated to either undertake back squats (BSq), deadlift (DL) or BSq and DL as supersets (BSq+DL), with a repeated jump protocol performed 8-minutes post-exercise in each session. Thereafter, a control condition (CON) was completed involving a general warm-up, followed by the repeated jump protocols. Power outputs, flight time, contact time and reactive strength index were recorded from each repeated jump protocol. Measures were compared between the BSq, DL and BSq+DL sessions and between sessions that generated the best power output (BEST) with CON via inferential statistics and effect size (ES) calculations. The BSq condition exhibited significantly greater power output compared to the CON condition (p<0.05, ES = 1.07), although no differences were identified for the other conditioning activities. Furthermore, power output, flight time and reactive strength index were significantly greater for the BEST compared to the CON condition (p<0.05, ES = 0.97–1.47). Results indicated that BSq was the optimal conditioning activity to increase power output during a repeated jump protocol. However, greater improvement during the BEST condition suggests that the type of conditioning activity should also be considered on an individual-basis.

Can Proprioceptive Training Enhance Fatigability and Decrease Progression Rate of Sarcopenia in Seniors? A Novel Approach

Sarcopenia is a common condition in older adults, which causes the frequent occurrence of muscle fatigue. Muscle fatigue commonly develops among seniors. Muscle fatigue is a type of physical fatigue that occurs due to either motor or sensory dysfunctions. Current interventions developed to decrease the occurrence of muscle fatigue, which include either increasing rest periods or subdividing large tasks into small ones. The effectiveness of these interventions is highly contradicted. Recently, researchers discovered that mechanoreceptors are the main receptors of muscle fatigue, however, no clinical study investigated the effect of performing proprioceptive training to enhance the mechanoreceptors and decrease the occurrence of muscle fatigue. Performing proprioceptive training could improve muscle fatigue by improving its sensory part. The function of mechanoreceptors might consequently enhance fatigue and decrease the progression rate of sarcopenia. Thus, this review was conducted to suggest a novel approach of treatment to enhance fatigue and decrease Sarcopenia in seniors. This might be accomplished through increasing the firing rate of α- motor neurons, increasing the amount of Ca²⁺ ions in the neuromuscular junction, slowing the progression rate of Sarcopenia, and correcting movement deviations, which commonly occur with muscle fatigue in seniors. In conclusion, proprioceptive training could play an effective role in decreasing the progression rate of sarcopenia and enhancing the fatigability among seniors.

Hyperventilation-Aided Recovery for Extra Repetitions on Bench Press and Leg Press

Sakamoto, A, Naito, H, and Chow, CM. Hyperventilation-aided recovery for extra repetitions on bench press and leg press. J Strength Cond Res 34(5): 1274-1284, 2020-Hyperventilation (HV)-induced alkalosis, an ergogenic strategy, improved repeated pedaling sprint performance through enhanced H removal. However, it did not confer beneficial effects on other forms of exercises. This study investigated the benefits of HV-aided recovery on lifting repetitions and joint velocity during resistance training involving multiple joints and both concentric and eccentric contractions. Eleven power-trained men (mean ± SD age: 22.5 ± 4.3 years, training experience: 8.3 ± 3.6 years) performed 6 sets each of bench press and leg press at 80% 1 repetition maximum. Each set was continued until failure, with a 5-minute recovery between sets. In protocol A, HV was implemented for 30 seconds before the first, third, and fifth sets of each exercise (HV-aided recovery), whereas spontaneous breathing continued throughout the recovery before the second, fourth, and sixth sets (control recovery). In protocol B, the order of the HV and control recoveries was reversed. For both protocols, reductions in repetitions (range: -4.7% to -22.5%) and velocity (range: -23.1% to -37.7%) were consistently observed after control recovery (p < 0.05), whereas HV-aided recovery resulted in increased repetitions (range: +21.3% to +55.7%) and velocity (range: +6.3% to +15.3%) (p < 0.05) or no reductions in these measures from the previous set. The total repetitions performed across 6 sets (protocols A and B combined) were greater after the HV-aided than control recovery (p ≤ 0.001) in bench press (44 ± 10 vs. 36 ± 10 reps, increased by 27.1 ± 24.1%) and leg press (64 ± 9 vs. 50 ± 15 reps, increased by 35.2 ± 29.5%). Hyperventilation-aided recovery may boost the effectiveness of resistance training through increased training volume and lifting velocity.

Low-load resistance training to task failure with and without blood flow restriction: muscular functional and structural adaptations

The application of blood flow restriction (BFR) during resistance exercise is increasingly recognized for its ability to improve rehabilitation and for its effectiveness in increasing muscle hypertrophy and strength among healthy populations. However, direct comparison of the skeletal muscle adaptations to low-load resistance exercise (LL-RE) and low-load BFR resistance exercise (LL-BFR) performed to task failure is lacking. Using a within-subject design, we examined whole muscle group and skeletal muscle adaptations to 6 wk of LL-RE and LL-BFR training to repetition failure. Muscle strength and size outcomes were similar for both types of training, despite ~33% lower total exercise volume (load × repetition) with LL-BFR than LL-RE (28,544 ± 1,771 vs. 18,949 ± 1,541 kg, P = 0.004). After training, only LL-BFR improved the average power output throughout the midportion of a voluntary muscle endurance task. Specifically, LL-BFR training sustained an 18% greater power output from baseline and resulted in a greater change from baseline than LL-RE (19 ± 3 vs. 3 ± 4 W, P = 0.008). This improvement occurred despite histological analysis revealing similar increases in capillary content of type I muscle fibers following LL-RE and LL-BFR training, which was primarily driven by increased capillary contacts (4.53 ± 0.23 before training vs. 5.33 ± 0.27 and 5.17 ± 0.25 after LL-RE and LL-BFR, respectively, both P < 0.05). Moreover, maximally supported mitochondrial respiratory capacity increased only in the LL-RE leg by 30% from baseline (P = 0.006). Overall, low-load resistance training increased indexes of muscle oxidative capacity and strength, which were not further augmented with the application of BFR. However, performance on a muscle endurance test was improved following BFR training.

Can Proprioceptive Training Reduce Muscle Fatigue in Patients With Motor Neuron Diseases? A New Direction of Treatment

Muscle fatigue is a serious problem in patients with motor neuron diseases (MNDs). It commonly disturbs both daily life activity and rehabilitation tolerance. A particular concern should be taken when MNDs occur in older ages. Older patients with MNDs usually have a worse clinical presentation and a lower survival rate. This could increase the occurrence of muscle fatigue. Muscle fatigue occurs due to a dysfunction in either motor or sensory systems. Current exercise interventions performed to decrease the occurrence of muscle fatigue focused only on treating motor causes of muscle fatigue. It has been demonstrated that these interventions have a high debate in their effectiveness on decreasing the occurrence of muscle fatigue. Also, these exercise interventions ignored training the affected sensory part of muscle fatigue, however, the important role of the sensory system in driving the motor system. Thus, this review aimed to develop a novel exercise intervention by using proprioceptive training as an intervention to decrease the occurrence of muscle fatigue in patients with MNDs particularly, older ones. The physiological effects of proprioceptive training to decrease the occurrence of muscle fatigue could include two effects. The first effect includes the ability of the proprioceptive training to increase the sensitivity of muscle spindles as an attempt to normalize the firing rate of α-motoneurons, which their abnormalities have major roles in the occurrence of muscle fatigue. The second effect includes its ability to correct the abnormal movement-compensations, which develop due to the biomechanical constraints imposed on patients with MNDs.

A Narrative Review of Cancer-Related Fatigue (CRF) and Its Possible Pathogenesis

Many cancer patients suffer from severe fatigue when treated with chemotherapy or radiotherapy; however, the etiology and pathogenesis of this kind of fatigue remains unknown. Fatigue is associated with cancer itself, as well as adjuvant therapies and can persist for a long time. Cancer patients present a high degree of fatigue, which dramatically affects the quality of their everyday life. There are various clinical research studies and reviews that aimed to explore the mechanisms of cancer-related fatigue (CRF). However, there are certain limitations in these studies: For example, some studies have only blood biochemical texts without histopathological examination, and there has been insufficient systemic evaluation of the dynamic changes in relevant indexes. Thus, we present this narrative review to summarize previous studies on CRF and explore promising research directions. Plenty of evidence suggests a possible association between CRF and physiological dysfunction, including skeletal muscular and mitochondrial dysfunction, peripheral immune activation and inflammation dysfunction, as well as central nervous system (CNS) disorder. Mitochondrial DNA (mtDNA), mitochondrial structure, oxidative pressure, and some active factors such as ATP play significant roles that lead to the induction of CRF. Meanwhile, several pro-inflammatory and anti-inflammatory cytokines in the peripheral system, even in the CNS, significantly contribute to the occurrence of CRF. Moreover, CNS function disorders, such as neuropeptide, neurotransmitter, and hypothalamic-pituitary-adrenal (HPA) axis dysfunction, tend to amplify the sense of fatigue in cancer patients through various signaling pathways. There have been few accurate animal models established to further explore the molecular mechanisms of CRF due to different types of cancer, adjuvant therapy schedules, living environments, and physical status. It is imperative to develop appropriate animal models that can mimic human CRF and to explore additional mechanisms using histopathological and biochemical methods. Therefore, the main purpose of this review is to analyze the possible pathogenesis of CRF and recommend future research that will clarify CRF pathogenesis and facilitate the formulation of new treatment options.

The relation between central variables, electromyography signals and peripheral microcirculation during intensive treadmill exercise

BACKGROUND

Aerobic exercise under muscle fatigue can lead to muscular damage and injuries. Finding the correlations between central and peripheral microcirculation variables, as well as with electromyography signals of leg muscles during aerobic exercise, may contribute to early muscle fatigue identification. The goal of this study was to characterize the peripheral compensation following intensive exercise for assessment of muscle performance based on non-invasive techniques.

METHODS

The experimental protocol included two days of measurements. Electrocardiography tests and anthropometric measurements of the volunteers (N = 14) were carried out. The maximal aerobic ability (first day), as well as electromyography and cutaneous hemodynamic variables (second day) were measured during treadmill run. A score-based Bayesian network machine-learning algorithm was used to predict ventilation values based on cutaneous hemodynamic measurements.

FINDINGS

Transcutaneous oxygen tension can be used to identify anaerobic threshold for both trained and untrained subjects during treadmill running, while electromyography can be used to identify anaerobic threshold only of trained subjects. Predicted values of ventilation, based on the transcutaneous oxygen tension, showed high correlation with actual values. Prediction accuracy was better among trained subjects, compared to the untrained ones.

INTERPRETATION

Transcutaneous oxygen tension could be used for prediction of maximal oxygen consumption during intense exercise and thus may provide improved assessment of premature fatigue during exercise.

The Effect of Exercise on the Skin Content of the Reduced Form of NAD and Its Response to Transient Ischemia and Reperfusion in Highly Trained Athletes

Reduced nicotinamide adenine dinucleotide (NADH) is synthesized in the cellular nucleus, cytoplasm and mitochondria but oxidized into NAD+ almost exclusively in mitochondria. Activation of human skin by the 340 nm ultraviolet light triggers natural fluorescence at the light length of 460 nm, which intensity is proportional to the skin NADH content. This phenomenon is used by the Flow Mediated Skin Fluorescence (FMSF) which measures changes in the skin NADH content during transient ischemia and reperfusion. We examined the effects of exercise to exhaustion on the skin changes of NADH in response to 200 s forearm ischemia and reperfusion in 121 highly trained athletes (94 men and 27 women, long-distance running, triathlon, taekwondo, rowing, futsal, sprint running, fencing, and tennis). We found that exercise until exhaustion changes the skin content of NADH, modifies NADH turnover at rest, during ischemia and reperfusion in the most superficial living skin cells. Compared to the pre-exercise, there were significant increases in: mean fluorescence recorded during rest as the baseline value (B mean) (p < 0.001), the maximal fluorescence that increased above the baseline during controlled forearm ischemia (FImax) (p < 0.001, only in men), the minimal fluorescence after decreasing below the baseline during reperfusion (FRmin) (p < 0.001 men; p < 0.01 women) and the difference between B mean and FRmin (R min) (p < 0.01), and reductions in the difference between FImax and B mean (I max) (p < 0.001) and I max/IRampl ratio (CImax) (p < 0.001) after the incremental exercise test. There was no statistical difference between pre- and post-exercise the maximal range of the fluorescence change during ischemia and reperfusion (IRampl). In conclusion, exercise to exhaustion modifies the skin NADH content at rest, during ischemia and reperfusion as well as the magnitude of changes in the NADH caused by ischemia and reperfusion. Our findings suggest that metabolic changes in the skin NADH accompanying exercise extend beyond muscles and affect other cells and organs.

SPRINTING. . . Dietary Approaches to Optimize Training Adaptation and Performance

Although sprint athletes are assumed to primarily be interested in promoting muscle hypertrophy, it is the ability to generate explosive muscle power, optimization of power-to-weight ratio, and enhancement of anaerobic energy generation that are key outcomes of sprint training. This reflects the physique of track sprinters, being characterized as ecto-mesomorphs. Although there is little contemporary data on sprinters dietary habits, given their moderate energy requirements relative to body mass, a carbohydrate intake within the range of 3-6 g·kg^-1·day^-1 appears reasonable, while ensuring carbohydrate availability is optimized around training. Similarly, although protein needs may be twice general population recommendations, sprint athletes should consume meals containing ∼0.4 g/kg high biological value protein (i.e., easily digested, rich in essential amino acids) every 3-5 hr. Despite the short duration of competitions and relative long-recovery periods between races, nutrition still plays an important role in sprint performance. As energy expenditure moderates during competition, so too should intake of energy and macronutrients to prevent unwanted weight gain. Further adjustments in macronutrient intake may be warranted among athletes contemplating optimization of power-to-weight ratio through reductions in body fat prior to the competitive season. Other novel acute methods of weight loss have also been proposed to enhance power-to-weight ratio, but their implementation should only be considered under professional guidance. Given the metabolic demands of sprinting, a few supplements may be of benefit to athletes in training and/or competition. Their use in competition should be preceded with trialing in training to confirm tolerance and perceived ergogenic potential.

The impact of exercise on mitochondrial dynamics and the role of Drp1 in exercise performance and training adaptations in skeletal muscle

OBJECTIVE

Mitochondria are organelles primarily responsible for energy production, and recent evidence indicates that alterations in size, shape, location, and quantity occur in response to fluctuations in energy supply and demand. We tested the impact of acute and chronic exercise on mitochondrial dynamics signaling and determined the impact of the mitochondrial fission regulator Dynamin related protein (Drp)1 on exercise performance and muscle adaptations to training.

METHODS

Wildtype and muscle-specific Drp1 heterozygote (mDrp1+/-) mice, as well as dysglycemic (DG) and healthy normoglycemic men (control) performed acute and chronic exercise. The Hybrid Mouse Diversity Panel, including 100 murine strains of recombinant inbred mice, was used to identify muscle Dnm1L (encodes Drp1)-gene relationships.

RESULTS

Endurance exercise impacted all aspects of the mitochondrial life cycle, i.e. fission-fusion, biogenesis, and mitophagy. Dnm1L gene expression and Drp1Ser616 phosphorylation were markedly increased by acute exercise and declined to baseline during post-exercise recovery. Dnm1L expression was strongly associated with transcripts known to regulate mitochondrial metabolism and adaptations to exercise. Exercise increased the expression of DNM1L in skeletal muscle of healthy control and DG subjects, despite a 15% ↓(P = 0.01) in muscle DNM1L expression in DG at baseline. To interrogate the role of Dnm1L further, we exercise trained male mDrp1+/- mice and found that Drp1 deficiency reduced muscle endurance and running performance, and altered muscle adaptations in response to exercise training.

CONCLUSION

Our findings highlight the importance of mitochondrial dynamics, specifically Drp1 signaling, in the regulation of exercise performance and adaptations to endurance exercise training.

The Influence of Sport-Field Properties on Muscle-Recruitment Patterns and Metabolic Response

PURPOSE

To investigate different sport-field properties' influence on muscle-recruitment patterns and metabolic response during a series of running and agility drills.

METHODS

Eleven male athletes were fitted with a standard multipurpose training shoe. The test protocol consisting of 4 high-intensity trials with 60-s rests between trials performed on 2 fields with different properties. Time-dependent field properties were measured using the American Standards for Testing and Materials protocol (F-1936). A 30-m pretest and posttest sprint determined fatigue and player performance. Electromyography (EMG) recorded muscle activity for vastus medialis, biceps femoris, gastrocnemius medial head, and tibialis anterior, and metabolic activity analyzed maximal oxygen consumption, heart rate, respiratory exchange ratio, metabolic equivalent, and energy expenditure.

RESULTS

A difference was calculated for muscle activity across trials (P = .01) for both surfaces. Muscle activity was <13% on the field with less energy return (P = .01). Metabolic components (maximal oxygen consumption, heart rate, respiratory exchange ratio, metabolic equivalent, and energy expenditure) were significantly different across trials (P = .01) but not significantly different between fields. The participants completed the agility course (5.2%) faster on the field with greater energy return, while caloric expenditure was similar between fields.

CONCLUSIONS

The findings indicate that field mechanical properties influence muscle-activation patterns. The field demonstrating the greatest magnitude of energy return produces the lowest sprint and agility course times; however, performing on a field exhibiting unfamiliar mechanical properties could cause the athlete to produce atypical movement patterns that might contribute to overuse of the neuromuscular system.

Metabolic homeostasis: oxidative phosphorylation and the metabolic requirements of higher plants and animals

A model of oxidative phosphorylation and its regulation is presented, which is consistent with the experimental data on metabolism in higher plants and animals. The variables that provide real-time control of metabolic status are: intramitochondrial [NAD+]/[NADH], energy state ([ATP]/[ADP][Pi]), and local oxygen concentration ([O2]). ATP consumption and respiratory chain enzyme content are tissue specific (liver vs. heart muscle), and the latter is modulated by chronic alterations in ATP consumption (i.e., endurance training etc.). ATP consumption affects the energy state, which increases or decreases as necessary to match synthesis with consumption. [NAD+]/[NADH], local [O2], and respiratory chain content determine the energy state at which match of synthesis and utilization is achieved. Tissues vary widely in their ranges of ATP consumption. Expressed as the turnover of cytochrome c, the rates may change little (7 to 12/s) (liver) or a lot (1 to >300/s) (flight muscle of birds, bats, and insects). Ancillary metabolic pathways, including creatine or arginine kinase, glycerol phosphate shuttle, fatty acid, and citric acid cycle dehydrogenases, are responsible for meeting tissue-specific differences in maximal rate and range in ATP utilization without displacing metabolic homeostasis. Intramitochondrial [NAD+]/[NADH], [ATP], and [Pi] are adjusted to keep [ADP] and [AMP] similar for all tissues despite large differences in ranges in ATP utilization. This is essential because [ADP] and [AMP], particularly the latter, have major roles in regulating the activity of many enzymes and signaling pathways (AMP deaminase, AMP dependent protein kinases, etc.) common to all higher plants and animals.

NEW & NOTEWORTHY Oxidative phosphorylation has an intrinsic program that sets and stabilizes cellular energy state ([ATP]/[ADP][Pi]), and thereby metabolic homeostasis. A computational model consistent with regulation of oxidative phosphorylation in higher plants and animals is presented. Focus is on metabolism ancillary to oxidative phosphorylation by which it was integrated into preexisting metabolic regulation and adapted by evolution to develop cells and tissues with differing rates of ATP utilization: i.e., liver versus brain versus muscle.

Age-Related Differences in Functional Hamstring/Quadriceps Ratio Following Soccer Exercise in Female Youth Players: An Injury Risk Factor

PURPOSE

Fatigue negatively alters dynamic knee control, and the functional hamstring/quadriceps ratio (H/Q_FUNC) plays an important role in stabilizing the joint. The aim of this study was to investigate the influence of soccer-specific exercise on H/Q_FUNC in under (U) 13-, U15-, and U17-year-old female soccer players.

METHODS

A total of 36 female players performed concentric and eccentric actions of the hamstrings at 60°, 120°, and 180°/s before and after an age group-specific field-based soccer protocol. H/Q_FUNC was determined in the first 30° of knee flexion.

RESULTS

Significant angle × velocity (P = .001) and time × angle (P = .033) interaction effects were found indicating a lower H/Q_FUNC with increased movement velocity at 0°-10° as opposed to greater knee flexion angles. Fatigue-related effects were only evident near full knee extension. Probabilistic inferences indicated that changes in H/Q_FUNC were generally unclear in U13s, likely detrimental in U15s, and very likely beneficial in U17s.

CONCLUSIONS

Altered muscular control following soccer-specific exercise is age dependent with players' 1-year post-peak height velocity at greatest risk of injury. Injury prevention and screening need to be age and maturation appropriate, should consider the effects of fatigue, and include movements near full extension.

Following a Long-Distance Classical Race the Whole-Body Kinematics of Double Poling by Elite Cross-Country Skiers Are Altered

Introduction: Although short-term (approximately 10-min) fatiguing DP has been reported not to alter the joint kinematics or displacement of the centre of mass (COM) of high-level skiers, we hypothesize that prolonged DP does change these kinematics, since muscular strength is impaired following endurance events lasting longer than 2 h.

Methods: During the 58-km Marcialonga race in 2017, the fastest 15 male skiers were videofilmed (100 fps, FHD resolution in the sagittal plane) on two 20-m sections (inclines: 0.7 ± 0.1°) 48 km apart (i.e., 7 and 55 km from the start), approximating 50- km Olympic races. The cameras were positioned perpendicular to and about 40 m from the middle of each section and spatial dimensions adjusted for each individual track skied. Pole and joint kinematics, as well as displacement of the COM during two DP cycles were assessed.

Results: The 10 skiers who fulfilled our inclusion criteria finished the race in 2 h 09 min 19 s ± 28 s. Displacements of the joints and COM were comparable to previous observations on skiers roller skiing on a flat treadmill at similar speeds in the laboratory. 55 km after the start, cycle velocity and length were lower (P < 0.001 and P = 0.002, respectively) and the angular range of elbow joint flexion during the initial part of the poling phase reduced, while shoulder angle was greater during the first 35% of the DP cycle (all P < 0.05). Moreover, the ankle angle was increased and forward displacement of the COM reduced during the first 80% of the cycle.

Conclusion: Prolonged DP reduced the forward displacement of the COM and altered arm kinematics during the early poling phase. The inefficient utilization of COM observed after 2 h of competition together with potential impairment of the stretch-shortening of arm extensor muscles probably attenuated generation of poling force. To minimize these effects of fatigue, elite skiers should focus on maintaining optimal elbow and ankle kinematics and an effective forward lean during the propulsive phase of DP.

Equine endurance race pacing strategy differs between finishers and non-finishers in 120 km single-day races

Race pace strategy has been extensively studied in human sports, such as running, cycling and swimming. In contrast, pacing strategy appears to have been virtually ignored in equestrian sport despite the potential for contributing to performance optimisation. The aim of the present study was to analyse data available in the public domain for electronically-timed FEI 120 km (single day) CEI** endurance races that took place in Europe and the Middle East in 2016 and 2017. Competition records for 389 horses in 24 races, each consisting of 4 phases (loops/laps), were evaluated; 56% (n=219) of horses successfully completed the races analysed, with the remaining 44% (n=170) not finishing. The majority of horses that did not finish were withdrawn for gait related reasons (n=125; 74%). Across the duration of the races, horses that successfully finished recorded 7% slower average speeds (P=0.0001) compared to those that did not finish. Loop (lap) speed decreased sequentially throughout races from loop 1 > loop 2 > loop 3 for both the horses that completed and those that failed to complete, but the rate of decrease was greater in horses that did not complete. Horses withdrawn at the first veterinary check for ‘gait’ recorded a 36% faster average speed than those withdrawn at the finish (P=0.0001). Horses withdrawn for ‘metabolic’ reasons at the finish recorded a significant increase in loop speed from loop 3 to the final loop (P=0.02), with their speed increasing by an average of 7% on the final loop. Horses that failed to finish races completed loop 1 at a faster speed than those horses that finished and subsequently had a greater reduction in speed across the remaining loops. In contrast, horses that finished successfully had a slower loop 1 speed and completed subsequent loops at a higher percentage of their loop 1 speed. Consideration of race pace strategy in equine endurance racing may be a tool to reduce gait and metabolic eliminations and increase the chance of completion.

A Taxonomy of Fatigue Concepts and Their Relation to Hearing Loss

Fatigue is common in individuals with a variety of chronic health conditions and can have significant negative effects on quality of life. Although limited in scope, recent work suggests persons with hearing loss may be at increased risk for fatigue, in part due to effortful listening that is exacerbated by their hearing impairment. However, the mechanisms responsible for hearing loss-related fatigue, and the efficacy of audiologic interventions for reducing fatigue, remain unclear. To improve our understanding of hearing loss-related fatigue, as a field it is important to develop a common conceptual understanding of this construct. In this article, the broader fatigue literature is reviewed to identify and describe core constructs, consequences, and methods for assessing fatigue and related constructs. Finally, the current knowledge linking hearing loss and fatigue is described and may be summarized as follows: Hearing impairment may increase the risk of subjective fatigue and vigor deficits; adults with hearing loss require more time to recover from fatigue after work and have more work absences; sustained, effortful, listening can be fatiguing; optimal methods for eliciting and measuring fatigue in persons with hearing loss remain unclear and may vary with listening condition; and amplification may minimize decrements in cognitive processing speed during sustained effortful listening. Future research is needed to develop reliable measurement methods to quantify hearing loss-related fatigue, explore factors responsible for modulating fatigue in people with hearing loss, and identify and evaluate potential interventions for reducing hearing loss-related fatigue.

The changes in classical and nonlinear parameters after a maximal bout to elicit fatigue in competitive swimming

The aim was to assess the effect of fatigue on linear and nonlinear parameters in swimming. Twenty-four fitness-oriented swimmers performed a maximal bout of 100 m at front-crawl to elicit fatigue. Before (pre-) and immediately after (post-test) the bout, participants swam an all-out 25 m to derive the speed fluctuation (dv), approximate entropy (ApEn) and fractal dimension (FD) from the speed-time series collected by a speedo-meter. Swim speed was 10.85% slower in the post-test than in the pre-test (p < .001, η² = 0.72). There was an effect of the fatigue on the dv with a moderate effect size. The dv increased shifting the 95CI band from 0.116-0.134 to 0.140-0.161. The ApEn showed non-significant variations between the pre- and post-test having the 95CI of pre- and post-test overlapped (pre: 0.659-0.700; post: 0.641-0.682). The FD showed as well a significant variation (the 95CI moved from 1.954-1.965 to 1.933-1.951). It can be concluded that in swimming there are changes in classical and nonlinear parameters under fatigue.