Voluntary Isometric Contraction Research Articles

The Duration of Non-Local Muscle Fatigue Effects

Non-local muscle fatigue (NLMF) refers to a transient decline in the functioning of a non-exercised muscle following the fatigue of a different muscle group. Most studies examining NLMF conducted post-tests immediately after the fatiguing protocols, leaving the duration of these effects uncertain. The aim of this study was to investigate the duration of NLMF (1-, 3-, and 5-minutes). In this randomized crossover study, 17 recreationally trained participants (four females) were tested for the acute effects of unilateral knee extensor (KE) muscle fatigue on the contralateral homologous muscle strength, and activation. Each of the four sessions included testing at either 1-, 3-, or 5-minutes post-test, as well as a control condition for non-dominant KE peak force, instantaneous strength (force produced within the first 100-ms), and vastus lateralis and biceps femoris electromyography (EMG). The dominant KE fatigue intervention protocol involved two sets of 100-seconds maximal voluntary isometric contractions (MVIC) separated by 1-minute of rest. Non-dominant KE MVIC forces showed moderate and small magnitude reductions at 1-min (p < 0.0001, d = 0.72) and 3-min (p = 0.005, d = 0.30) post-test respectively. The KE MVIC instantaneous strength revealed large magnitude, significant reductions between 1-min (p = 0.021, d = 1.33), and 3-min (p = 0.041, d = 1.13) compared with the control. In addition, EMG data revealed large magnitude increases with the 1-minute versus control condition (p = 0.03, d = 1.10). In summary, impairments of the non-exercised leg were apparent up to 3-minutes post-exercise with no significant deficits at 5-minutes. Recovery duration plays a crucial role in the manifestation of NLMF.

Can the cross-education of strength attenuate the impact of detraining after a period of strength training? A quasi-randomized trial.

Unilateral strength training may attenuate the decline in muscle strength and size in homologous, contralateral muscles. This study aimed to determine whether the cross-education of strength could specifically attenuate the effects of detraining immediately after a short (prehabilitation-type) period of strength training. Twenty-six strength-trained participants were assigned to either four weeks of unilateral strength training of the stronger arm (UNI) or detraining (Detrain). Motor evoked potential (MEP) and cortical silent period (cSP) responses, muscle cross-sectional area (CSAFlexor; peripheral quantitative computed tomography) and maximal strength, rate of force development (RFD) and muscle activation (EMG) were examined in both elbow flexors before and after the intervention period. In UNI, one-repetition maximum (1-RM) strength improved in both the trained (∆ = 2.0 ± 0.9kg) and non-trained (∆ = 0.8 ± 0.9kg) arms despite cessation of training of the weaker arm, whereas 1-RM strength was unchanged in Detrain. Maximal voluntary isometric contraction, isokinetic peak torque, and RFD did not change in either group. No neural changes were detected in UNI, but cSP increased in Detrain (∆ = 0.010 ± 0.015s). CSAFlexor increased in the trained arm (∆ = 51 ± 43 mm2) but decreased in the non-trained arm (∆ = -53 ± 50 mm2) in UNI. CSAFlexor decreased in both arms in Detrain and at a similar rate to the non-trained arm in UNI. UNI attenuated the effects of detraining in the weaker arm as shown by the improvement in 1-RM strength. However, the cross-education of strength did not attenuate the decline in muscle size in the contralateral arm.

Sex differences in strength, functional capacity and mobility in patients with multiple sclerosis: An exploratory analysis

BackgroundPhysical exercise programs are commonly designed without consideration for sex differences. Nevertheless, disease progression exhibits sex-specific patterns, resulting in different functionality and strength performances. ObjectivesTo analyze sex differences in strength, functional capacity, and mobility, and to evaluate sex-dependent differences in leg strength in multiple sclerosis (MS) patients. MethodsA cross-sectional study was conducted with 35 participants (female: n = 19; Expanded Disability Status Scale (EDSS)= 3.0 ± 1.2, male: n = 16; EDSS= 3.3 ± 1.2). Body composition, maximal voluntary isometric contraction (MVIC), explosive strength (rate of force development, RFD), central activation ratio (CAR), functional capacity, and mobility were assessed. ResultsDifferences were observed between males and females (p = 0.001) in height, lean body mass and MVIC. No differences were observed in the other variables. Regarding the leg asymmetry, men showed higher values in the stronger leg for both MVIC (p < 0.001, d=large) and RFD, whereas women showed higher values only in RFD. Men with MS demonstrated a greater capacity to produce maximal strength than women with this disease. ConclusionsThe results found suggest that maximum strength differs between men and women in our sample of patients with multiple sclerosis. Furthermore, the weaker leg, regardless of sex, exhibits poorer results in explosive strength compared to the stronger leg. However, maximum strength only shows differences in men and not in women. Therefore, these findings should serve as a basis for rehabilitation professionals when planning training programs for this population.

Acute Responses to Traditional and Cluster-Set Squat Training With and Without Blood Flow Restriction.

Cornejo-Daza, PJ, Sánchez-Valdepeñas, J, Páez-Maldonado, J, Rodiles-Guerrero, L, Boullosa, D, León-Prados, JA, Wernbom, M, and Pareja-Blanco, F. Acute responses to traditional and cluster-set squat training with and without blood flow restriction. J Strength Cond Res XX(X): 000-000, 2024-To compare the acute responses to different set configurations (cluster [CLU] vs. traditional [TRA]) under distinct blood flow conditions (free vs. restricted) in full-squat (SQ). Twenty resistance-trained males performed 4 protocols that differed in the set configuration (TRA: continuous repetitions; vs. CLU: 30 seconds of rest every 2 repetitions) and in the blood flow condition (FF: free-flow; vs. blood flow restriction [BFR]: 50% of arterial occlusion pressure). The relative intensity (60% 1RM), volume (3 sets of 8 repetitions), and resting time (2 minutes) were equated. Mean propulsive force (MPF), velocity (MPV) and power (MPP), and electromyography (EMG) parameters were recorded during each repetition. Tensiomyography (TMG), blood lactate, countermovement jump (CMJ) height, maximal voluntary isometric contraction, in SQ, and movement velocity against the load that elicited a 1 m·s-1 velocity at baseline (V1-load) in SQ were assessed at pre- and post-exercise. The CLU protocols allowed a better maintenance of MPF, MPV, MPP, and EMG median frequency during the exercise compared to TRA (clu-time interaction, p < 0.05). The TRA protocols experienced greater impairments post-exercise in TMG- and EMG-derived variables (clu-time interaction, p < 0.05) and SQ and CMJ performance (clu-time interaction, p = 0.08 and p < 0.05, respectively), as well as higher blood lactate concentrations (clu-time interaction, p < 0.001) than CLU. Moreover, BFR displayed decreases in TMG variables (bfr-time interaction, p < 0.01), but BFR-CLU resulted in the greatest reduction in twitch contraction time (p < 0.001). Cluster sets reduced fatigue during and after the training session and BFR exacerbated impairments in muscle mechanical properties; however, the combination of both could improve contraction speed after exercise.

Pole Dancing-Specific Muscle Strength: Development and Reliability of a Novel Assessment Protocol.

Pole dancing is a physically demanding sport that combines dance and acrobatic movements on a vertical pole. Despite its highly growing popularity, there is currently limited research in the field. The aim of this study was to create and evaluate a strength assessment protocol for athletes in pole dancing, with a specific focus on functional positions on the pole. Thirty-two female pole dancing athletes participated in this study. Maximal voluntary isometric contractions (MVIC) were measured at three different sport-specific positions on the pole (shoulder abduction and adduction, and hip adduction), on two separate days (test and re-test) with a five to seven day interval between them. A hand-held dynamometer (Activ5- Activbody) stabilized on the pole was used for this study. The intra-session reliability was good to excellent for all sports-specific positions and for both sides of the body, across all different movements (ICC = 0.837-0.960, SEM = 5.02Kg-2.24Kg, and SDD = 27.46%-14.92%). Slightly better results were found regarding inter-session reliability (ICC = 0.927-0.970, SEM = 3.72Kg-1.97Kg, and SDD = 22.86%-15.19%). There was not a statistically significant difference between the MVICs between the left and right or dominant and non-dominant side in shoulder abduction (p = 0.105) and hip adduction (p = 0.282), in contrast to shoulder adduction (p = 0.00). The strength assessment protocol developed in the current study has proven to be a reliable and functional tool, with the potential for utilization in clinical practice as part of objective strength testing. Further studies are needed in order to expand the protocol to other muscle groups and positions and to generalize the results in all pole dancing populations such as male athletes.

Eccentric Exercise-Induced Muscle Damage Reduces Gross Efficiency.

The effect of eccentric exercise-induced muscle damage (EIMD) on cycling efficiency is unknown. The aim of the present study was to assess the effect of EIMD on gross and delta efficiency and the cardiopulmonary responses to cycle ergometry. Twenty-one recreational athletes performed cycling at 70%, 90% and 110% of the gas exchange threshold (GET) under control conditions (Control) and 24 h following an eccentric damaging protocol (Damage). Knee extensor isometric maximal voluntary contraction (MVC), potentiated twitch (Qtw,pot) and voluntary activation (VA) were assessed before Control and Damage. Gross and delta efficiency were assessed using indirect calorimetry, and cardiopulmonary responses were measured at each power output. Electromyography root-mean-square (EMGRMS) during cycling was also determined. MVC was 25 ± 18% lower for Damage than Control (p < 0.001). Gross efficiency was lower for Damage than Control (p < 0.001) by 0.55 ± 0.79%, 0.59 ± 0.73% and 0.60 ± 0.87% for 70%, 90% and 110% GET, respectively. Delta efficiency was unchanged between conditions (p = 0.513). Concurrently, cycling EMGRMS was higher for Damage than Control (p = 0.004). An intensity-dependent increase in breath frequency and V̇E/V̇CO2 was found, which were higher for Damage only at 110% GET (p ≤ 0.019). Thus, gross efficiency is reduced following EIMD. The concurrently higher EMGRMS suggests that increases in muscle activation in the presence of EIMD might have contributed to reduced gross efficiency. The lack of change in delta efficiency might relate to its poor reliability hindering the ability to detect change. The findings also show that EIMD-associated hyperventilation is dependent on exercise intensity, which might relate to increases in central command with EIMD.

Caffeine Attenuates Exacerbated Central Fatigue during Moderate Intensity Cycling Exercise in Women with Fibromyalgia.

To compare the development of fatigability during a moderate intensity cycling exercise between women with fibromyalgia (FM) and control women (CON) after acute ingestion of caffeine and placebo. Ten FM and 10 CON women performed a 30-minute moderate intensity cycling exercise one hour after the ingestion of a capsule containing either caffeine or a placebo. Fatigability and its central and peripheral determinants were determined via changes from pre- to post-15 and post-30 minutes of exercise in maximal voluntary isometric contractions (MVIC), voluntary activation (VA), and quadriceps potentiated twitch torque (Qtw-pot), respectively. Heart rate, muscle oxygen saturation, perceptive responses, mood state, localized and widespread pain, and sleepiness were also monitored during and after exercise. There was a time vs. group interaction for MVIC and VA (p < 0.001) but not for Qtw-pot (p = 0.363), indicating a greater rate of fatigability development, mainly caused by central mechanisms, in the FM than in the CON group. There was also a main effect of condition for VA (p = 0.011), indicating that caffeine attenuates central mechanisms of fatigability in both groups. Caffeine ingestion also increased muscle oxygenation, perceived vigor, and energy, and decreased leg muscle pain, sleepiness, and perceived fatigue in both groups. However, caffeine improved perceived pleasure/displeasure and exercise adherence likelihood only in the FM group. Compared to CON, women with FM present a greater rate of fatigability during exercise, mainly of central origin. Caffeine seems to be a promising bioactive to counteract the central mechanisms of fatigability and improve the exercise experience among FM women.

Intramuscular fat infiltration influences mechanical properties during muscle contraction in older women.

Although evidence suggests that intramuscular fat infiltration may influence muscle strength, the precise mechanisms remain unclear. This study aimed to determine whether intramuscular fat infiltration affects muscle mechanical properties during contraction, and whether these mechanical properties mediate the relationship between intramuscular fat infiltration and muscle strength. Seventy-nine healthy older women aged 75.1±6.8 years were included in this study. The echo intensity (EI) of the vastus lateralis (VL) was measured as an intramuscular fat infiltration index using B-mode ultrasonography. Maximum voluntary isometric contraction strength (MVIC) was assessed using a dynamometer. The VL shear elastic modulus (G), a mechanical property index, was measured using ultrasound shear wave elastography under various muscle contraction conditions, at rest and at 15, 30, and 45% MVIC (G0, G15, G30, and G45). To evaluate the degree of increase in the shear elastic modulus with increasing muscle contraction intensity, the slope of the regression line (Gslope) between muscle contraction and shear elastic modulus was calculated for each participant. The results showed that EI was significantly associated with G30 and G45 but not with G0 or G15. The EI can significantly explain the inter-individual differences in Gslope. Mediation analysis revealed that the effect of EI on MVIC through Gslope was significant (indirect effect = -0.31, 95% confidence interval [-0.57, -0.12]). These findings suggest that a greater EI is associated with a lower G during muscle contraction. Furthermore, our results show that the relationship between EI and MVIC is mediated by Gslope.

30-sit-to-stand power is a better tool than isometric knee extensor strength to detect motor impairment in people with haemophilic arthropathy.

Regular assessment of motor impairments is crucial in people with haemophilic arthropathy (PwHA). This study aimed to determine if there are differences in 30-secondssit-to-stand (30-STS) power and maximal voluntary isometric contraction (MVIC) of the knee extensors between PwHA and healthy control group (CG). The secondary aims were to investigate the correlation between 30-STS power and MVIC of knee extensors with clinical characteristics and to assess their effectiveness in identifying motor impairment in PwHA. A cross-sectional study was conducted by collecting data from PwHA (n=17) and a sedentary CG (n=15). MVIC (torque) and 30-STS power were normalised to body mass. Correlation analysis and simple linear regression adjusted for age were used to assess the association between tests and clinical variables. Using z-scores derived from the mean and standard deviation of the CG, we compared the MVIC and the 30-STS power in PwHA. PwHA showed lower MVIC and 30-STS power compared to CG (p<.001; large effect size d>.8). Lower 30-STS power was associated with greater joint impairment and greater fear of movement, whereas MVIC showed no association with clinical variables. 30-STS power showed a lower z-score compared to MVIC (p<.001). In addition, 30-STS power detected 47% of PwHA with motor impairment compared to 0% for MVIC (p=.002). Our results suggest that 30-STS power may be more effective than knee extensors MVIC in detecting motor impairment in PwHA. Consequently, lower limb skeletal muscle power, rather than maximum knee extensor strength, appears to be more affected in PwHA.

Supraspinal, spinal, and motor unit adjustments to fatiguing isometric contractions of the knee extensors at low and high submaximal intensities in males.

Contraction intensity is a key factor determining the development of muscle fatigue and it has been shown to induce distinct changes along the motor pathway. The role of cortical and spinal inputs that regulate motor unit (MU) behaviour during fatiguing contractions is poorly understood. We studied the cortical, spinal, and neuromuscular response to sustained fatiguing isometric tasks performed at 20 and 70% of the maximum isometric voluntary contraction (MVC), together with MUs behaviour of knee extensors in healthy active males. Neuromuscular function was assessed before and after performing both tasks. Cortical and spinal responses during exercise were measured via stimulation of the motor cortex and spinal cord. High density electromyography was used to record individual MUs from the vastus lateralis (VL). Exercise at 70% MVC induced greater decline in MVC (p = 0.023), and potentiated twitch force compared to 20%MVC (p < .001), with no difference in voluntary activation (p = 0.514). Throughout exercise, corticospinal responses were greater during the 20%MVC task (p < 0.001), and spinal responses increased over time in both tasks (p ≤ 0.042). MU discharge rate increased similarly following both tasks (p ≤ 0.043) while recruitment and de-recruitment thresholds were unaffected (p ≥ 0.295). These results suggest that increased excitability of cortical and spinal inputs might be responsible for the increase in MU discharge rate. The increase in evoked responses together with the higher MUs discharge rate might be required to compensate for peripheral adjustments to sustain fatiguing contractions at different intensities.

Targeted activation of Nrf2 prevents losses in leg muscle mass and strength during 2 weeks of immobilization in young adults

Introduction: Leg immobilization results in substantial losses in muscle mass and strength. Strategies aimed at minimizing these losses have proven largely ineffective. Elevated oxidative stress has been identified as a potential mechanism contributing to these losses. Therefore, we tested the hypothesis that PB125, an activator of Nrf2 (the master regulator of the endogenous antioxidant system), and MitoQ, a mitochondrial-targeted antioxidant, would decrease the deleterious effects of limb immobilization on muscle mass and strength. Methods: A double-blind, placebo-controlled trial was performed in a cohort of twenty young healthy adults (6M/14F, Age: 28±7 y; Height: 169±7 cm; Mass: 70±14 kg). Participants were randomized into either placebo (n=7), PB125 (n=6), or MitoQ (n=7). Supplementation and measures of physical activity using an accelerometer began 2 weeks prior to single leg immobilization and continued through 2 weeks of immobilization. Knee extensor muscle strength was tested before and after immobilization using isometric maximal voluntary contractions (MVC) and isokinetic contractions (120 and 60 degrees/s). Muscle mass was determined by MRI, and thigh lean muscle volume from image slices between the patellar tendon and gluteal muscle were assessed. Results: Physical activity, measured by steps per day, decreased by 55-65% during limb immobilization for all groups (p &lt;0.05). Isometric muscle strength was significantly decreased following placebo (145±40 to 119±27 kg; p &lt;0.05) and MitoQ (148±36 to 118±36 kg; p &lt;0.05), but not PB125 (140±55 to 144±71 kg, p=0.7). Similarly, isokinetic muscle strength measured at 120 and 60 degrees/s was significantly decreased in placebo and MitoQ but preserved with PB125. Lean muscle volume in the immobilized limb significantly decreased by ~4% in placebo (p&lt;0.05) and MitoQ (p&lt;0.05) but was preserved with PB125 (p =0.55). Conclusions: Targeted activation of Nrf2 with PB125 preserved muscle mass and strength following 2 weeks of leg immobilization. In contrast, both placebo and MitoQ had no impact on immobilization-induced losses in muscle mass and strength. These findings provide novel evidence that targeting Nrf2 offsets the detrimental skeletal muscle effects of limb immobilization in young, healthy individuals. NIH-R01HL142603 and VA Merit-I01CX001999. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Resistance exercise following short term muscle disuse leads to enhanced mitochondrial activity and dynamics

Introduction: Short-term muscle unloading (~7-10 days) can be usually experienced following injury or hospitalisation, leading to muscle disuse atrophy, muscle weakness and changes in motor control. In such contexts, exercise countermeasures can be employed to overcome these neuromuscular impairments. Surprisingly, the effects of exercise countermeasures following the exposure to muscle unloading has been scarcely investigated. Hence, this study aimed to investigate the functional and molecular adaptations to a 21-day resistance training (RT) program following short term muscle disuse. We hypothesised that a period of resistance exercise following short-term unloading would speed up the recovery on muscle mass and function mostly by an effcient counteraction of the molecular regulators of muscle disuse atrophy consistent with the exercise modality employed. Methods: A 10-day unilateral lower limb suspension (ULLS) model was applied to eleven healthy young males (22.09 ± 2.91 y), followed by a 21-day RT program for the knee extensors performed at 70% of the 1RM (3 times/wk, 9 sessions in total). Data acquisition was performed before the ULLS period, after 10 days of unloading and after 21 days of resistance exercise. Quadriceps femoris isometric maximum voluntary contraction (MVC) was evaluated by dynamometry and quadriceps CSA was assessed by ultrasonography. Succinate dehydrogenase (SDH, a key component of the citric acid cycle and of the respiratory electron transfer chain) staining was performed on frozen cryosections obtained from VL biopsies, whereas western blot analyses were carried out for several mitochondrial-related proteins and transcriptomics data were obtained by RNA-seq. Results: Following ULLS, QF MVC and CSA decreased (-29.3%, p&lt;0.001, and -4.5%, p&lt;0.05, respectively). After the 21-d of RT, MVC was fully brought back (+42% compared to post-ULLS) whereas QF CSA showed a very marked hypertrophy (+18.6%, p&lt;0.001, compared to post-ULLS). SDH immunoreactivity was not affected by unloading but revealed a significant increase after exercise compared to post ULLS values (~+20%, p&lt;0.001). In addition, mitochondrial dynamics were highly influenced by resistance exercise, as mitochondrial pro-fusion (MFN1, MFN2, OPA1) and fission (DRP1, pDRP1616) proteins were markedly increased in response to RT compared to post-ULLS values (p&lt;0.05). Further, PGC-1a levels showed a trend to decrease after ULLS but even a stronger trend to increase after resistance exercise compared to post-ULLS (p=0.056). Transcriptomics analyses showed that the most differentially expressed genes were identified in the pathways related to oxidative phosphorylation, in which the top regulated genes after resistance training were mitochondrial related genes (CKMT2, UQCRH, ACSS1, MDH1, COX7A2, CYCS, SLC16A1), presenting a marked reduction after ULLS and being significantly enhanced after RT. When compared to baseline, the genes which showed a positive “rebound effect” after resistance exercise were mostly related to mitochondrial function (MT-ATP6, MT-CO2, MT-ND3). Noteworthy, among these latter genes, the top upregulated one was APLNR, coding for apelin receptor protein, a positive regulator of inter-myofibrillar mitochondrial content in sarcopenia and ageing. Conclusions: Resistance exercise was effective in recovering muscle mass and function after 10 days of disuse, but it enhanced mitochondrial activity, biogenesis, and dynamics far beyond the expected effects for such exercise modality. In fact, mitochondrial-related genes expression was the most affected by exercise. This suggests that mitochondrial dynamics could play an essential role in the recovery of neuromuscular alterations induced by short term disuse. We put forward the hypothesis that the prior level of physical activity and a prior exposure to short-term muscle disuse could be driving the nature of adaptations to subsequent resistance training. Funding: The present work was funded by the Italian Space Agency (ASI), MARS-PRE, Project, n. DC-VUM-2017-006. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Relationships between nitric oxide biomarkers and physiological outcomes following dietary nitrate supplementation

Dietary nitrate (NO3−) supplementation can increase nitric oxide (NO) bioavailability, reduce blood pressure (BP) and improve muscle contractile function in humans. Plasma nitrite concentration (plasma [NO2−]) is the most oft-used biomarker of NO bioavailability. However, it is unclear which of several NO biomarkers (NO3−, NO2−, S-nitrosothiols (RSNOs)) in plasma, whole blood (WB), red blood cells (RBC) and skeletal muscle correlate with the physiological effects of acute and chronic dietary NO3− supplementation. Using a randomized, double-blind, crossover design, 12 participants (9 males) consumed NO3−-rich beetroot juice (BR) (∼12.8 mmol NO3−) and NO3−-depleted placebo beetroot juice (PL) acutely and then chronically (for two weeks). Biological samples were collected, resting BP was assessed, and 10 maximal voluntary isometric contractions of the knee extensors were performed at 2.5–3.5 h following supplement ingestion on day 1 and day 14. Diastolic BP was significantly lower in BR (−2 ± 3 mmHg, P = 0.03) compared to PL following acute supplementation, while the absolute rate of torque development (RTD) was significantly greater in BR at 0–30 ms (39 ± 57 N m s−1, P = 0.03) and 0–50 ms (79 ± 99 N m s−1, P = 0.02) compared to PL following two weeks supplementation. Greater WB [RSNOs] rather than plasma [NO2−] was correlated with lower diastolic BP (r = −0.68, P = 0.02) in BR compared to PL following acute supplementation, while greater skeletal muscle [NO3−] was correlated with greater RTD at 0–30 ms (r = 0.64, P=0.03) in BR compared to PL following chronic supplementation. We conclude that [RSNOs] in blood, and [NO3−] in skeletal muscle, are relevant biomarkers of NO bioavailability which are related to the reduction of BP and the enhanced muscle contractile function following dietary NO3− ingestion in humans.

Ischemic Conditioning Reduces Neuromuscular Fatigability During Dynamic Exercise Post Stroke

INTRODUCTION: In addition to baseline muscle weakness, stroke survivors often demonstrate increased neuromuscular fatigability (an acute exercise-induced reduction in power, hereafter referred to as fatigability), which limits endurance during functional tasks. Ischemic conditioning (IC) is a non-invasive and easy-to-administer intervention that can reduce fatigability in stroke survivors during a sustained isometric contraction of their paretic knee extensors. However, IC’s effects on fatigability during dynamic contractions are unknown, despite the greater relevance to everyday activities. Additionally, fatigability is known to be task specific. Thus, the purpose of this study was to quantify the effects of IC on fatigability (percent reduction in power) during dynamic contractions of the paretic knee extensors in stroke survivors. We hypothesized that fatigability would be less after a single session of IC versus IC-sham treatment in stroke survivors. Methods: Eight stroke survivors (66 ± 6 years of age, 6 male) performed 60 maximal voluntary concentric contractions (1 every 4 seconds) with their paretic knee extensors against a resistance of 30% of their maximal voluntary isometric contraction torque through a 60-degree range of motion after receiving a single session of IC and IC-sham treatment on two separate days. IC consisted of 5 sets of 5-minute upper thigh blood flow occlusion at 225 mmHg (25 mmHg for IC-sham) with 5 minutes of no occlusion between each set. The order of the 2 sessions was randomized. All participants visited the laboratory on a different day for functional measurements (Fugl-Meyer Assessment, 10-meter walk test, and 6-minute walk test). Reduction in power was calculated as the difference between the highest average power output from 5 consecutive contractions within the first 15 contractions and the average power output from the last 5 contractions. A paired t-test was used to compare if fatigability during dynamic exercise would differ between the 2 sessions after IC and IC-sham treatment. Pearson correlation was performed to determine the relationship between the difference in fatigability (after IC versus IC-sham treatment) and functional measurements. Results: After a single session of IC treatment, stroke survivors were less fatigable compared to IC-sham treatment (21.9 ± 19.2% power reduction vs. 29.4 ± 19.0%, p = 0.016). Improvement in fatigability after IC versus IC-sham treatment was positively correlated with Fugl-Meyer Assessment lower extremity motor score ( r = 0.82, p = 0.013). CONCLUSION: These preliminary results indicate that IC could serve as a potential intervention to reduce fatigability during dynamic exercise in stroke survivors, especially those who are mildly affected by stroke. Funding Source: American Heart Association Predoctoral Fellowship (903373, ZZ) and Eunice Kennedy Shriver National Institute of Child Health and Human Development R01 Grant (HD099340, AH &amp; MD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Repeated bout effect and muscle damage at variable eccentric exercise intensities in active young men: a longitudinal repeated measures investigation

Abstract Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations and at various intensities. Despite the existence of vast literature, there is lack of comparison of low versus submaximal versus maximal intensity required for preconditioning. The aim of the study was to compare the muscle damage and RBE at various intensities of eccentric exercise in active young men. Thirty-six healthy, physically active men were recruited and randomly assigned to three different groups low-high (L-H, n = 12), submaximal-high (M-H, n = 12) and maximal-high (H-H, n = 12). All participants performed 2 exercise bouts separated by 14 days. L-H, M-H and H-H groups performed low (10% of 1RM), moderate (50% of 1RM) and high (90% of 1RM) intensity eccentric exercise for knee extensors, respectively, in the 1st bout followed by high (100% of 1RM) intensity in the second bout. Muscle soreness (SOR), thigh circumference (CIR), maximal voluntary isometric contraction (MVIC), range of motion (ROM) and blood lactate (Bl Lac) were measured before, immediately, at 24 h, at 48 h and at 72 h after exercise. A significant effect of time appeared for MVIC (), CIR (), ROM () and Bl Lac (). The bout × time interaction, as well as bout × time × group interaction was also found significant indicating changes in muscle strength and ROM. Circumference changed significantly with a significant bout × group interaction effect . SOR () was significant between the bouts. Therefore, exhibiting attenuation of muscle damage markers after the second bout. Findings of the present study showed that muscle damage was evident at all three intensities. Moreover, it was greater after moderate and high intensity as compared to low intensity eccentric exercise. RBE was elicited after three intensities indicating their role in preconditioning the muscles of active men.

Effects of Aging and Fatigue on Human Skeletal Muscle Cellular Contractile Function

Aging is associated with a reduction in skeletal muscle mass and function, known as sarcopenia. While reductions in contractile force are typically explained by loss in muscle cellular cross sectional area (CSA) loss of contractile power during high velocity contractions exceed reductions in force and cannot be solely explained by loss of muscle size and are observed at the single fiber within the same myosin heavy chain isoform (MHC). These phenomenon may be explained by myosin binding protein C (MyBP-C), which is known to modulate contractile force and velocity in a phosphorylation-dependent manner in both cardiac and skeletal muscle. Few studies have investigated the inherent contractile performance of single fibers between old and young adults, and none have explored the effects of altered MyBP-C phosphorylation on single fiber function. Therefore, the PURPOSE of this study was to investigate the effects of age and fatigue-induced MyBP-C phosphorylation on single fiber contractile performance. We HYPOTHESIZED that isometric tension will be enhanced in older adults but velocity and power will be reduced, and fatigue will enhance velocity and power in single fibers. To test this hypothesis, we recruited 4 young (18-35) and 3 older (65-80) adult males to perform a single bout of unilateral knee extensions at 30% maximal voluntary isometric contraction (MVIC) until task failure. Immediately following, a bilateral biopsy of the vastus lateralis (VL) muscle was performed on the fatigued and non-fatigued control limbs. Tissue was either flash frozen for western blot or prepared for mechanical analysis of single fiber tension (Tmax), velocity (Vmax), and power (Pmax) under optimal intracellular metabolic conditions. Our analyses were limited to MHC IIA due to differences in fiber type distribution between the groups. Our RESULTS showed that neither age nor fatigue had an effect on contractile performance in MHC IIA fibers. However, independent analysis of fatigue within age groups suggest trends towards an increase in velocity (p=0.055) in young (MHC IIA) and reduction in tension (p=0.085) in old (MHC I) adult fibers. We CONCLUDE that fatigue may modulate contractile function in the single fiber in an age- and fiber-type dependent manner. Future studies will be aimed at collecting multiple fiber types and investigating the role of biological sex. Wu Tsai Human Performance Alliance. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Effects of Anchoring a Fatiguing Forearm Flexion Task to a High vs. Low Rating of Perceived Exertion on Torque and Neuromuscular Responses.

Ortega, DG, Housh, TJ, Smith, RW, Arnett, JE, Neltner, TJ, Schmidt, RJ, and Johnson, GO. The effects of anchoring a fatiguing forearm flexion task to a high versus low rating of perceived exertion on torque and neuromuscular responses. J Strength Cond Res 38(5): e219-e225, 2024-This study examined the torque and neuromuscular responses following sustained, isometric, forearm flexion tasks anchored to 2 ratings of perceived exertion (RPE). Nine men (mean ± SD: age = 21.0 ± 2.4 years; height = 179.5 ± 5.1 cm; body mass = 79.6 ± 11.4 kg) completed maximal voluntary isometric contractions (MVIC) before and after sustained, isometric, forearm flexion tasks to failure anchored to RPE = 2 and RPE = 8. The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) signal were recorded from the biceps brachii. Normalized torque was divided by normalized EMG AMP to calculate neuromuscular efficiency (NME). A dependent t-test was used to assess the mean difference for time to task failure (TTF). Repeated-measures analysis of variances was used to compare mean differences for MVIC and normalized neuromuscular parameters. There was no significant difference in TTF between RPE = 2 and RPE = 8 (p = 0.713). The MVIC decreased from pretest to posttest at RPE = 2 (p = 0.009) and RPE = 8 (p = 0.003), and posttest MVIC at RPE = 8 was less than that at RPE = 2 (p < 0.001). In addition, NME decreased from pretest to posttest (p = 0.008). There was no change in normalized EMG AMP or EMG MPF (p > 0.05). The current findings indicated that torque responses were intensity specific, but TTF and neuromuscular responses were not. Furthermore, normalized EMG AMP and EMG MPF remained unchanged but NME decreased, likely due to peripheral fatigue and excitation-contraction coupling failure. Thus, this study provides information regarding the neuromuscular responses and mechanisms of fatigue associated with tasks anchored to RPE, which adds to the foundational understanding of the relationship between resistance exercise and the perception of fatigue.

Greater intramuscular metabolic perturbations contribute to faster muscle fatigue development in males than females during intermittent isometric exercise

INTRODUCTION: Previous studies reported faster performance fatigability in males than females during isometric exercise, ultimately prolonging time to task failure in the latter at the same relative intensity. Several authors suggested anatomical and physiological factors as primary determinants, but it remains unknown whether exercise-related accumulation of metabolites within skeletal muscle differentially affects fatigue development in female and males. PURPOSE: This study aimed to investigate intramuscular metabolic perturbations during fatiguing intermittent isometric knee-extensor exercise in males and females. Herein, we tested the hypothesis that greater metabolic perturbation during intermittent isometric exercise results in greater fatigue development in males compared to females. Methods: Fifteen males (M)(26±2y) and fifteen eumenorrheic females (F)(24±3y) visited the laboratory twice. During visit 1, isometric knee-extensors critical torque (CT) was estimated by a 5-min all-out test. In visit 2, participants performed intermittent isometric knee-extensor exercises to task failure at 110% of CT. To determine knee-extensors magnitude and etiology of fatigue maximal voluntary isometric contraction (MVIC), voluntary activation (VA) and potentiated twitches (St) amplitudes were evaluated before (PRE), at 9min (MID), and at task failure (POST). At the same time points, intramuscular pH and concentrations of ATP, PCr, Cr and La were determined in vastus lateralis muscle biopsies. Results: Time to task failure was shorter in M than F (1017±498 vs 1511±506s; P&lt;.01). At PRE, MVIC torque was higher in M than F (259±70 vs 152±24Nm; P&lt;.001). Relative decline in MVIC torque from PRE to MID was greater in M than F (-43±9 vs -34±8% from PRE; P&lt;.05) but reached similar decline at POST (-55±7 vs -53±6% from PRE). VA decreased throughout the test similarly in both sexes (P&lt;.001). St loss from PRE was higher in M than F (-45±13 vs -37±15%; P&lt;.05) at MID whereas no sex differences were observed at POST. Muscle pH decreased at a similar rate in M and F during the test (P&lt;.03). Muscle [ATP] did not change from PRE to MID or POST. Muscle [Cr] increased at a similar rate in M and F during the test (P&lt;.01). Muscle [PCr] was lower in M than F at any time point (P&lt;.03). At MID, [La] increased to a greater extent in M than F (P&lt;.01) with no between-sex differences at POST. CONCLUSION: Males showed greater fatigue development than females associated with greater metabolic perturbation during intermittent isometric exercise performed at same relative intensity. Higher PCr depletion and higher La accumulation suggest females were less fatigable than males due to higher glycolytic rate and less intramuscular inorganic phosphate concentration. The present work was funded by a Travelling Fellowship grant JEBTF2210859 to MC from The Company Of Biologists Limited. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Neuromuscular Control during the Bench Press Exercise Performed with Free Weights and Pneumatic Loading

The main objective of the research was to determine neuromuscular control for different external loads, from 75% to 100% 1 RM (One Rep Max), during the flat bench press (BP) exercise performed with free weights and pneumatic loading. Despite extensive research on the internal structure of the BP exercise, few studies have examined the differences between muscular activity during the flat bench press movement between Free Weights and Pneumatic Loading. For this purpose, 10 male, trained subjects performed the BP exercise under two conditions with three different external loads (70%, 85%, and 100% 1RM), alternately with free weights and pneumatic loading. Pneumatic loading was performed on the Keiser Power Rack, where the pneumatic load was transferred as the resistance of the cables attached to the ground. EMG activity was recorded during the lifts for the following muscles: PM (Pectoralis Major), AD (Anterior Deltoid), Tblat, and TBlong (Triceps Brachii). The EMG signals were sampled at a rate of 1000 Hz. Signals were band-pass filtered with a cutoff frequency of 8 Hz and 450 Hz, after which the root-mean-square (RMS) was calculated. After completion of all the tests in a single day, 2–3 s evaluations of Maximal Voluntary Isometric Contraction (MVIC) of the prime movers in the bench press movement (AD, PM, and TBlong) were performed according to SENIAM procedures. The results of the present study indicate that pneumatic loading provides a significantly different muscle activation pattern compared to a standard bar during a heavy-loaded BP exercise. The pneumatic load was superior in activating the AD and TB muscles compared to the standard bar during the BP exercise.

A dataset for fatigue estimation during shoulder internal and external rotation movements using wearables

Wearable sensors have recently been extensively used in sports science, physical rehabilitation, and industry providing feedback on physical fatigue. Information obtained from wearable sensors can be analyzed by predictive analytics methods, such as machine learning algorithms, to determine fatigue during shoulder joint movements, which have complex biomechanics. The presented dataset aims to provide data collected via wearable sensors during a fatigue protocol involving dynamic shoulder internal rotation (IR) and external rotation (ER) movements. Thirty-four healthy subjects performed shoulder IR and ER movements with different percentages of maximal voluntary isometric contraction (MVIC) force until they reached the maximal exertion. The dataset includes demographic information, anthropometric measurements, MVIC force measurements, and digital data captured via surface electromyography, inertial measurement unit, and photoplethysmography, as well as self-reported assessments using the Borg rating scale of perceived exertion and the Karolinska sleepiness scale. This comprehensive dataset provides valuable insights into physical fatigue assessment, allowing the development of fatigue detection/prediction algorithms and the study of human biomechanical characteristics during shoulder movements within a fatigue protocol.