Changes in central and peripheral neuromuscular fatigue indices after concentric versus eccentric contractions of the knee extensors

Cell-free DNA kinetics in response to muscle-damaging exercise: A drop jump study

A significant increase in circulating cell-free DNA (cfDNA) occurs with physical exercise, which depends on the type of exertion and the duration. The aims of this study were as follows: (1) to investigate the time course of cfDNA and conventional markers of muscle damage from immediately after to 96 h after muscle-damaging exercise; and (2) to investigate the relationship between cfDNA and indicators of primary (low-frequency fatigue and maximal voluntary isometric contraction) and secondary (creatine kinase and delayed-onset muscle soreness) muscle damage in young healthy males. Fourteen participants (age, 22 ± 2 years; weight, 84.4 ± 11.2 kg; height, 184.0 ± 7.4 cm) performed 50 intermittent drop jumps at 20 s intervals. We measured cfDNA and creatine kinase concentrations, maximal voluntary isometric contraction torque, low-frequency fatigue and delayed-onset muscle soreness before and at several time points up to 96 h after exercise. Plasma cfDNA levels increased from immediately postexercise until 72 h postexercise (P < 0.01). Elevation of postexercise cfDNA was correlated with both more pronounced low-frequency fatigue (r = -0.52, P = 3.4 × 10-11) and delayed-onset muscle soreness (r = 0.32, P = 0.00019). Levels of cfDNA change in response to severe primary and secondary muscle damage after exercise. Levels of cfDNA exhibit a stronger correlation with variables related to primary muscle damage than to secondary muscle damage, suggesting that cfDNA is a more sensitive marker of acute loss of muscle function than of secondary inflammation or damaged muscle fibres.

Effects of muscular endurance and tendon extensibility on endurance of joint stiffness

In some sporting events (e.g., long-distance running), the ability to maintain joint stiffness is considered an essential physical ability. However, the determinants of joint stiffness endurance remain unclear. This study aimed to examine the effects of muscular endurance and tendon extensibility on joint stiffness endurance. Thirteen males performed the fatigue task (5 sets of 50 hopping). Ankle joint stiffness during drop jump was measured before and after fatigue task. The maximum number of repetitions at 30% of one repetition maximum for plantar flexion was measured as muscular endurance. Maximal elongation of the Achilles tendon was measured during ramp (with a low strain rate of tendon) and ballistic (with a high strain rate of tendon) contractions as tendon extensibility. Joint stiffness significantly decreased by 7.5% after the fatigue task (p = 0.033). The maximum number of repetitions at 30% of 1RM (79.6 ± 48.7 repetitions) was not significantly correlated with the relative change in joint stiffness (r = 0.283, p = 0.348). The maximal elongation of the Achilles tendon measured during ramp and ballistic contractions were not significantly associated with the relative change in joint stiffness (r = 0.326, p = 0.277 for ramp contraction; r = 0.438, p = 0.135 for ballistic contraction). These results suggest that muscular endurance and tendon extensibility were unrelated to joint stiffness endurance.

The Role of Contraction Mode in Determining Exercise Tolerance, Torque-Duration Relationship, and Neuromuscular Fatigue

PURPOSE

Critical torque (CT) and work done above it ( W ') are key predictors of exercise performance associated with neuromuscular fatigue. The aim of the present study was to understand the role of the metabolic cost of exercise in determining exercise tolerance, CT and W ', and the mechanisms of neuromuscular fatigue.

METHODS

Twelve subjects performed four knee extension time trials (6, 8, 10, and 12 min) using eccentric, isometric, or concentric contractions (3-s on/2-s off at 90°·s -1 or 30°·s -1 ) to modulate the metabolic cost of exercise. Exercise performance was quantified by total impulse and mean torque. Critical torque and W ' were determined using the linear relationship between total impulse and contraction time. Cardiometabolic, neuromuscular, and ventilatory responses were quantified. Neuromuscular function was evaluated by maximal voluntary contraction, resting potentiated single/doublet electrical stimulations, and superimposed single electrical stimulation to quantify neuromuscular, peripheral, and central fatigue, respectively.

RESULTS

Compared with isometric exercise, total impulse (+36% ± 21%; P < 0.001), CT (+27% ± 30%; P < 0.001), and W ' (+67% ± 99%; P < 0.001) were increased during eccentric exercise, whereas total impulse (-25% ± 7%; P < 0.001), critical torque (-26% ± 15%; P < 0.001), and W ' (-18% ± 19%; P < 0.001) were reduced in concentric exercise. Conversely, the metabolic response and the degree of peripheral fatigue were reduced during eccentric exercise, whereas they were increased during concentric exercise. Critical torque was negatively associated with oxygen consumption gain ( R2 = 0.636; P < 0.001), and W ' was negatively associated with rates of neuromuscular and peripheral fatigue indices ( R2 = 0.252-0.880; P < 0.001).

CONCLUSIONS

The contraction mode influenced both CT and W ', and consequently exercise tolerance, indicating that the metabolic cost of contraction played a key role.

Effects of Unilateral Eccentric versus Concentric Training of Nonimmobilized Arm during Immobilization

INTRODUCTION

The present study tested the hypothesis that eccentric training (ET) of nonimmobilized arm would attenuate negative effects of immobilization and provide greater protective effects against muscle damage induced by eccentric exercise after immobilization, when compared with concentric training (CT).

METHODS

Sedentary young men were placed to ET, CT, or control group ( n = 12 per group), and their nondominant arms were immobilized for 3 wk. During the immobilization period, the ET and CT groups performed five sets of six dumbbell curl eccentric-only and concentric-only contractions, respectively, at 20%-80% of maximal voluntary isometric contraction (MVCiso) strength over six sessions. MVCiso torque, root-mean square (RMS) of electromyographic activity during MVCiso, and bicep brachii muscle cross-sectional area (CSA) were measured before and after immobilization for both arms. All participants performed 30 eccentric contractions of the elbow flexors (30EC) by the immobilized arm after the cast was removed. Several indirect muscle damage markers were measured before, immediately after, and for 5 d after 30EC.

RESULTS

ET increased MVCiso (17% ± 7%), RMS (24% ± 8%), and CSA (9% ± 2%) greater ( P < 0.05) than CT (6% ± 4%, 9% ± 4%, 3% ± 2%) for the trained arm. The control group showed decreases in MVCiso (-17% ± 2%), RMS (-26% ± 6%), and CSA (-12% ± 3%) for the immobilized arm, but these changes were attenuated greater ( P < 0.05) by ET (3% ± 3%, -0.1% ± 2%, 0.1% ± 0.3%) than CT (-4% ± 2%, -4% ± 2%, -1.3% ± 0.4%). Changes in all muscle damage markers after 30EC were smaller ( P < 0.05) for the ET and CT than the control group, and ET than the CT group (e.g., peak plasma creatine kinase activity: ET, 860 ± 688 IU·L -1 ; CT, 2390 ± 1104 IU·L -1 ; control, 7819 ± 4011 IU·L -1 ).

CONCLUSIONS

These results showed that ET of the nonimmobilized arm was effective for eliminating the negative effects of immobilization and attenuating eccentric exercise-induced muscle damage after immobilization.

Acute adaptation of central and peripheral motor unit features to exercise-induced fatigue differs with concentric and eccentric loading

NEW FINDINGS

What is the central question of this study? Conflicting evidence exists on motor unit (MU) firing rate in response to exercise-induced fatigue, possibly due to the contraction modality used: Do MU properties adapt similarly following concentric and eccentric loading? What is the main finding and its importance? MU firing rate increased following eccentric loading only despite a decline in absolute force. Force steadiness deteriorated following both loading methods. Central and peripheral MU features are altered in a contraction type-dependant manner, which is an important consideration for training interventions.

ABSTRACT

Force output of muscle is partly mediated by the adjustment of motor unit (MU) firing rate (FR). Disparities in MU features in response to fatigue may be influenced by contraction type, as concentric (CON) and eccentric (ECC) contractions demand variable amounts of neural input, which alters the response to fatigue. This study aimed to determine the effects of fatigue following CON and ECC loading on MU features of the vastus lateralis (VL). High-density surface (HD-sEMG) and intramuscular (iEMG) electromyography were used to record MU potentials (MUPs) from bilateral VLs of 12 young volunteers (six females) during sustained isometric contractions at 25% and 40% of the maximum voluntary contraction (MVC), before and after completing CON and ECC weighted stepping exercise. Multi-level mixed effects linear regression models were performed with significance assumed as P < 0.05. MVC decreased in both CON and ECC legs post-exercise (P < 0.0001), as did force steadiness at both 25% and 40% MVC (P < 0.004). MU FR increased in ECC at both contraction levels (P < 0.001) but did not change in CON. FR variability increased in both legs at 25% and 40% MVC following fatigue (P < 0.01). From iEMG measures at 25% MVC, MUP shape did not change (P > 0.1) but neuromuscular junction transmission instability increased in both legs (P < 0.04), and markers of fibre membrane excitability increased following CON only (P = 0.018). These data demonstrate that central and peripheral MU features are altered following exercise-induced fatigue and differ according to exercise modality. This is important when considering interventional strategies targeting MU function.

Less fatiguability in eccentric than concentric repetitive maximal muscle contractions

PURPOSE

Changes in elbow flexion torque and biceps brachii electromyogram (EMG) activity over 30 repetitive maximal voluntary concentric-only (CON-only), eccentric-only (ECC-only), and alternative concentric and eccentric (CON-ECC, 30 concentric + 30 eccentric) contractions were examined to compare their muscle fatigue profiles.

METHODS

Fifteen healthy young men performed CON-only, ECC-only and CON-ECC in their maximal effort between 10° and 100° elbow flexion on an isokinetic dynamometer at an angular velocity of 30°/s with a 3-s rest between contractions in a randomised order with ≥ 3 days between conditions. Changes in torque and EMG over the repeated contractions and maximal voluntary isometric contraction (MVC-ISO) torque with EMG before the first contraction and immediately after the last contraction were compared among conditions by two-way repeated measures analysis of variance.

RESULTS

The torque decreased (p < 0.01) from the first to 30th contraction in CON-only (- 49.5 ± 11.0%), ECC-only (- 32.2 ± 7.4%), and concentric (- 62.3 ± 8.7%) as well as eccentric phase (- 58.9 ± 9.3%) in CON-ECC (- 46.0 ± 12.3% overall). The magnitude of the decrease in the torque was greater (p < 0.01) for the CON-only than ECC-only, and the concentric than an eccentric phase in the CON-ECC. However, MVC-ISO torque decreased (p < 0.01) similarly after CON-only (- 42.9 ± 13.8%) and ECC-only (- 40.1 ± 9.2%), which was smaller (p < 0.01) than CON-ECC (- 56.8 ± 9.2%). EMG over contractions decreased (p < 0.01) for all conditions similarly from the first to the last contraction (- 28.5 ± 26.8%), and EMG in MVC-ISO also decreased similarly for all conditions (- 24.7 ± 35.8%).

CONCLUSION

These results suggest greater fatigue resistance in repetitive maximal eccentric than concentric contractions, but the fatigue assessed by MVC-ISO does not show it.

Isokinetic profiling of elite youth footballers: informing selection of a practicable and efficacious isokinetic screening test

Isokinetic dynamometry represents the clinical gold standard for strength assessment but testing lack consensus. Elite youth male football players (n = 28) completed 20 repetitions (analysed as four epochs) of eccentric knee flexor (eccKF) and concentric knee extensor (conKE) trials at 60, 180 and 270°∙s^-1, quantifying peak torque (PT) and functional range (FR). There was a significant (P < 0.001) main effect for fatigue and angular velocity in conKE PT; eccKF PT was not significant across epoch (P = 0.35) and velocity (P = 0.12) and a velocity x epoch interaction highlighted more repetitions were required to elicit fatigue as velocity increased. FR decreased with fatigue (P < 0.001) and velocity (P < 0.01) in conKE and eccKF, indicative of a narrowing of the strength curve. Clinical interpretation advocates an isokinetic test comprising at least 15 reps at a velocity ≥ 180°∙s^-1 and analysis beyond the peak of the strength curve (PT) to inform clinical reasoning and individualized exercise prescription.

Exercise induced muscle damage and repeated bout effect: an update for last 10 years and future perspectives

Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations. EIMD is the muscle damage occurring after one bout of unaccustomed exercise while RBE is the attenuation of the same muscle damage in subsequent second bout. RBE seems to have significant implications for exercise prescription. Despite existence of vast literature, there is lack of clarity on the effects of EIMD and RBE in a healthy population. The purpose of this study is to review the literature on EIMD and RBE in healthy participants published during the last 10 years. The search of major databases (including Scopus, Google Scholar and PubMed) was conducted using specific keywords ‘Exercise induced muscle damage’, ‘Repeated bout effect’, ‘Healthy participants’ ‘Pre-conditioning’, ‘Eccentric exercise’. Studies published from 2011 onwards which included EIMD and RBE assessment in healthy participants were included in this review. Database searching revealed a total of 38 studies on EIMD and RBE in healthy participants. Three major themes of papers were identified that focused on EIMD and RBE along with (1) age related differences, (2) sex-based differences, and (3) response in athletes. Findings of this comprehensive review suggests that both EIMD and RBE are age, and sex specific. Delayed onset muscle soreness played a major role in both EIMD and RBE in all the population types. Female participants are less susceptible to EIMD as compared to age-matched male counterparts. Moreover, both EIMD and RBE are more elicited in middle aged and younger adults as compared to children and older adults while the magnitude of RBE turns out to be minimal in trained individuals due to persisting adaptations.

Comparison between Eccentric-Only and Coupled Concentric-Eccentric Contractions for Neuromuscular Fatigue and Muscle Damage

PURPOSE

Eccentric contractions induce muscle damage, but less is known about the effects of preceding concentric contractions to eccentric contractions on muscle damage. We compared eccentric-only (ECC) and coupled concentric and eccentric contractions (CON-ECC) of the knee extensors for parameters of neuromuscular fatigue and muscle damage.

METHODS

Twenty participants (age, 19-36 yr) were randomly placed into an ECC or a CON-ECC group (n = 10 per group), without significant (P > 0.06) differences in baseline neuromuscular variables between groups. The ECC group performed six sets of eight ECC at 80% of ECC one-repetition maximum (1-RMecc), whereas the CON-ECC group performed six sets of eight alternating concentric (CON) and ECC (16 contractions per set) at 80% of CON 1-RM and 1-RMecc, respectively. Maximal voluntary isometric contraction force, rate of force development, resting twitch force, maximal M-wave (MMAX), voluntary activation, motor evoked potentials, corticospinal silent period, short interval intracortical inhibition, and muscle soreness were measured before, immediately after, and 1-3 d after exercise.

RESULTS

No significant (P ≥ 0.09) differences between ECC and CON-ECC were observed for changes in any variables after exercise. However, maximal voluntary isometric contraction force decreased immediately after exercise (ECC: -20.7% ± 12.8%, CON-ECC: -23.6% ± 23.3%) and was still reduced 3 d after exercise (ECC: -13.6% ± 13.4%, CON-ECC: -3.3% ± 21.2%). Rate of force development at 0-30 ms reduced immediately after exercise (ECC: -38.3% ± 33.9%, CON-ECC: -30.7% ± 38.3%). Voluntary activation, resting twitch force, and motor evoked potential/MMAX decreased and corticospinal silent period increased after exercise (all P ≤ 0.03), but short interval intracortical inhibition and MMAX did not change. Muscle soreness developed (P < 0.001) similarly for both groups (peak, 38.5 ± 29.5 mm).

CONCLUSIONS

CON-ECC did not exacerbate neuromuscular fatigue and muscle damage when compared with ECC, despite twice as many contractions performed. Thus, eccentric contractions (n = 48 in both groups) seemed to mainly mediate the neuromuscular responses observed.

Toward Soft Wearable Strain Sensors for Muscle Activity Monitoring

The force-generating capacity of skeletal muscle is an important metric in the evaluation and diagnosis of musculoskeletal health. Measuring changes in muscle force exertion is essential for tracking the progress of athletes during training, for evaluating patients’ recovery after muscle injury, and also for assisting the diagnosis of conditions such as muscular dystrophy, multiple sclerosis, or Parkinson’s disease. Traditional hardware for strength evaluation requires technical training for operation, generates discrete time points for muscle assessment, and is implemented in controlled settings. The ability to continuously monitor muscle force without restricting the range of motion or adapting the exercise protocol to suit specific hardware would allow for a richer dataset that can help unlock critical features of muscle health and strength evaluation. In this paper, we employ wearable, ultra-sensitive soft strain sensors for tracking changes in muscle deformation during contractions. We demonstrate the sensors’ sensitivity to isometric contractions, as well as the sensors’ capacity to track changes in peak torque over the course of an isokinetic fatiguing protocol for the knee extensors. The wearable soft system was able to efficiently estimate peak joint torque reduction caused by muscle fatigue (mean NRMSE = 0.15±0.03).

Resistance exercise with different workloads have distinct effects on cellular respiration of peripheral blood mononuclear cells

Little is known how acute exercise-induced inflammation and metabolic stress affect immune cell bioenergetics and the portion of its components. Therefore, we investigated acute effects of eccentric-only (E), concentric-only (C) and combined eccentric-concentric resistance exercise (E + C) bouts on cellular respiration of peripheral blood mononuclear cells (PBMCs). Twelve strength-trained young men performed bench press resistance exercises in randomized order. Venous blood samples were drawn at pre-, 5 min post- and 24 h post-exercise. Several PBMC respiration states were measured using high-resolution respirometry. Levels of leukocytes, interleukin 6 (IL-6), C-reactive protein (CRP), creatine kinase (CK), blood lactate and maximum voluntary isometric force were measured from the same time points. Effects of blood lactate and pH change on bioenergetics of PBMCs were investigated ex vivo. PBMC routine respiration (p = 0.017), free routine capacity (p = 0.025) and ET-capacity (p = 0.038) decreased immediately after E + C. E responded in opposite manner 5 min post-exercise compared to E + C (p = 0.013) and C (p = 0.032) in routine respiration, and to E + C in free routine activity (p = 0.013). E + C > C > E was observed for increased lactate levels and decreased isometric force that correlated with routine respiration (R = -0.369, p = 0.035; R = 0.352, p = 0.048). Lactate and pH change did not affect bioenergetics of PBMCs. Acute resistance exercise affected cellular respiration of PBMCs, with training volume and the amount of metabolic stress appear influential. Results suggest that acute inflammation response does not contribute to changes seen in cellular respiration, but the level of peripheral muscle fatigue and metabolic stress could be explaining factors.

Changes in biceps brachii muscle hardness assessed by a push-in meter and strain elastography after eccentric versus concentric contractions

Changes in biceps brachii muscle hardness assessed by a push-in meter (PM) and strain elastography (SE) were compared between eccentric (ECC) and concentric contractions (CON) of the elbow flexors to test the hypothesis that muscle hardness would increase greater after ECC. Ten men performed 5 sets of 10 ECC with their non-dominant arms and 5 sets of 10 CON with their dominant arms using a dumbbell corresponding to 50% of maximum voluntary isometric contraction (MVIC) force at 90º elbow flexion. Before and 1–4 days after the exercise, MVIC force, elbow joint angles, upper-arm circumference, and muscle soreness as muscle damage makers, and biceps brachii muscle hardness at maximally extended elbow joint by PM and SE were measured. Changes in these measures over time were compared between ECC and CON. All muscle damage markers showed greater changes after ECC than CON (p < 0.001). Muscle hardness assessed by PM and SE increased (p < 0.05) and peaked at 4 days post-ECC with 154.4 ± 90.0% (PM) and 156.2 ± 64.2% (SE) increases from the baseline, but did not change significantly after CON. The changes in muscle hardness post-ECC were correlated between PM and SE (r = 0.752, p < 0.001). A correlation (p < 0.001) between the normalized changes in resting elbow joint angle and changes in muscle hardness assessed by PM (r = − 0.772) or SE (r = − 0.745) was also found. These results supported the hypothesis and suggest that the increases in muscle hardness after ECC were associated with muscle damage (increased muscle stiffness), and PM and SE detected muscle hardness changes similarly.

Contralateral Effects of Eccentric Exercise and DOMS of the Plantar Flexors: Evidence of Central Involvement

Purpose: Peripheral and central factors play important roles in the reduction of motor performance following damaging eccentric exercise and delayed onset muscle soreness (DOMS). Following this regime, contralateral limbs could also be affected; however, the factors involved remain inconclusive. The purpose of this study was to distinguish the peripheral and central factors following eccentric contraction and DOMS of the plantar flexors in treated and contralateral homologous limbs. Methods: Ten males (BMI = 25.08 ± 1.69kgm^-2; age = 28.70 ± 4.24 years) were randomly assigned to experimental (DOM) or control (CON) groups. The DOM group performed a damaging eccentric exercise, while the CON group rested. Plasma creatine kinase (CK), pain rating scale (PRS), muscle stiffness, maximal voluntary contraction (MVC), and neural voluntary activation (VA) were measured before, after 10 min, and after 24, 48, and 72 hr on treated and contralateral limbs. Results: Following exercise, CK increased until after 48 hr, while PRS increased until after 72 hr compared to the CON group. Importantly, MVC was reduced at all time points, with the greatest reduction observed after 24 hr (-16%), while VA was affected until after 48 hr, with the greatest reduction at after 10 min (-7%). Interestingly, a "cross-over effect" was observed in contralateral limbs when PRS, MVC, and VA were negatively affected following the same pattern (time line) as treated limbs (-13% peak MVC reduction; -3.5% peak VA reduction). Conclusion: These findings suggest a substantial central contribution to the reduction in force immediately following eccentric exercise and to a lesser extent during the latter part of DOMS in both treated and contralateral limbs.

Muscle Shear Elastic Modulus Provides an Indication of the Protection Conferred by the Repeated Bout Effect

Background: The neuromuscular system is able to quickly adapt to exercise-induced muscle damage (EIMD), such that it is less affected by subsequent damaging exercise, a phenomenon known as the repeated bout effect (RBE). The objective was to determine whether the mechanical properties of the quadriceps, as evaluated by shear wave elastography (SWE), were less affected when a second bout of eccentric-biased exercise was performed 2 weeks later. It was hypothesized that the first bout would confer protection against extensive muscle damage through an adaptation of the muscle stiffness before the second bout (i.e., higher muscle stiffness).

Methods: Sixteen males performed two identical bouts of downhill walking separated by 2 weeks (45 min at 4.5 km.h−1; gradient: 25%; load: 30% of the body mass). Rectus femoris (RF) and vastus lateralis (VL) resting shear elastic modulus (µ) and EIMD symptoms were measured before and up to 7 days following the exercise bouts. Changes in neuromuscular function was evaluated by maximal voluntary contraction torque, voluntary activation level, evoked mechanical response to single and double (10 and 100 Hz doublets) electrical stimulation. An index of protection (IP) was calculated for EIMD symptoms to assess magnitude the RBE.

Results: EIMD symptoms were less affected after the second than the first exercise bout. RF and VL-µ increased (p &lt; 0.001) only after the first exercise. RF µ was elevated up to 2 weeks after the end of the first exercise (p &lt; 0.001) whereas VL µ was only increased up to 24 h. The increase in µ observed 2 weeks after the end of the first exercise was correlated with the IP; i.e., attenuation of alterations in muscle µ, 10 Hz-doublet amplitude and rate of torque development after the second exercise bout (p &lt; 0.05).

Conclusion: We showed that muscle µ assessed by SWE was sensitive to the RBE, with a differential effect between VL and RF. The persistent increase in µ was associated with the attenuation of neuromuscular impairments observed after the second bout, suggesting that the increased muscle stiffness could be a “protective” adaptation making muscles more resistant to the mechanical strain associated to eccentric contractions.

The Effects of High-Intensity Functional Training on Cognition in Older Adults with Cognitive Impairment: A Systematic Review

(1) Background: High-Intensity Functional Training (HIFT) is a new exercise modality that emphasizes multi-joint functional movements adaptable to any fitness level and promotes greater muscle recruitment. Previous studies have evaluated the positive effects of HIFT on mental and cognitive health but have not evaluated it in older people. This study aims to conduct a systematic review of randomized controlled trials assessing the effects of HIFT on general cognition in older adults with cognitive impairment. (2) Methods: Following the PRISMA 2020 guideline, articles that did a high-intensity functional physical exercise intervention on cognitive performance in older adults with mild to moderate cognitive impairment (MMSE > 10) or dementia, aged 55 years or older, published between 2011 and 2021 in five different electronic databases: PubMed, Web of Science, Scopus, CINAHL, and Cochrane plus were included. (3) Results: 7 articles were included, all having general cognition as their primary outcome. All assessed general cognition using the Mini-Mental State Examination, the ADAS-Cog, or both. All studies had at least one HIFT experimental group with a frequency of 2 sessions per week and a variable duration between protocols of 12, 13, 16, and 26 weeks. Two articles showed that a progressive HIFT program improves general cognition, four articles showed no significant changes within or between groups and one article concluded that a HIFT intervention does not slow cognitive decline. (4) Conclusions: Evidence exists of the benefits of HIFT on general cognition in older adults with cognitive impairment, assessed using the MMSE, the ADAS-cog, or both. Two articles that showed improvement in cognitive function used progressive HIFT with 80% RM at 6, 12, and 1 weeks; however, in the other articles, due to the heterogeneity of intervention protocols, measurement time points, and control group activities, mixed results were evidenced

Panax ginseng Supplementation Increases Muscle Recruitment, Attenuates Perceived Effort, and Accelerates Muscle Force Recovery After an Eccentric-Based Exercise in Athletes

ABSTRACT

Cristina-Souza, G, Santos-Mariano, AC, Lima-Silva, AE, Costa, PL, Domingos, PR, Silva, SF, Abreu, WC, De-Oliveira, FR, and Osiecki, R. Panax Ginseng supplementation increases muscle recruitment, attenuates perceived effort, and accelerates muscle force recovery after an eccentric-based exercise in athletes. J Strength Cond Res 36(4): 991-997, 2022-The effect of Panax ginseng during and after an eccentric-based exercise is underexplored. In this study, we investigated the effect of Panax ginseng on muscle force and muscle excitation during an eccentric-based exercise and on subsequent muscle damage and delayed-onset muscle soreness (DOMS). Using a randomized, double-blind, crossover design, 10 male track and field athletes consumed Panax ginseng or placebo for 8 days. At the fifth day, they performed 4 sets until concentric failure of a half-squat exercise, with eccentric action increased by using an eccentric-inductor device attached to their knees. The rating of perceived exertion (RPE) and vastus lateralis electromyographic (EMG) activity was measured during the half-squat. Plasma lactate dehydrogenase (LDH) and creatine kinase (CK) concentrations, DOMS, and maximal isometric voluntary contractions (MIVCs) with EMG recording were measured at 24, 48, and 72 hours after the half-squat. Panax ginseng attenuated RPE and increased EMG during the sets. The MIVC remained reduced 48 hours after exercise in the placebo but returned to baseline 24 hours after exercise in the Panax ginseng, with values at 24 and 48 hours after exercise significantly higher in the Panax ginseng than in the placebo. The EMG during MIVC was higher in the Panax ginseng than in the placebo over the time points. No significant effect of Panax ginseng on LDH, CK, and DOMS was observed. These findings suggest that Panax ginseng increases muscle excitation and attenuates perceived effort during an eccentric-based exercise as well as accelerates the recovery of muscle force in well-trained athletes.

Effect of fatigue strength exercise on anterior thigh skin temperature rewarming after cold stress test

Although dynamic thermography skin temperature assessment has been used in medical field, scientific evidence in sports is scarce. The aim of the study was to assess changes in anterior thigh skin temperature in response to a cold stress test after a strength exercise fatiguing protocol. Ten physically active adults performed a familiarization session and two strength exercise sessions, one with dominant and the other with non-dominant lower limb. Participants performed bouts of 10 concentric and eccentric contractions of leg extensions in an isokinetic device until reaching around 30% of force loss. Infrared thermographic images were taken at baseline conditions and after the fatigue level from both thighs after being cooled using a cryotherapy system. ROIs included vastus medialis, rectus femoris, adductor and vastus lateralis. Skin temperature rewarming was assessed during 180s after the cooling process obtaining the coefficients of the following equation: ΔSkin temperature = β₀ + β_{1 *} ln(T), being β₀ and β₁ the constant and slope coefficients, respectively, T the time elapsed following the cold stress in seconds, and ΔSkin temperature the difference between the skin temperature at T respect and the pre-cooling moment. Lower β₀ and higher β₁ were found for vastus lateralis and rectus femoris in the intervention lower limb compared with baseline conditions (p < 0.05 and ES > 0.6). Adductor only showed differences in β₀ (p = 0.01 and ES = 0.92). The regressions models obtained showed that β₀ and β₁ had a direct relationship with age and muscle mass, but an inverse relationship with the number of series performed until 30% of fatigue (R² = 0.8). In conclusion, fatigue strength exercise results in a lower skin temperature and a faster thermal increase after a cold stress test.

Muscle Damage Indicated by Maximal Voluntary Contraction Strength Changes From Immediately to 1 Day After Eccentric Exercise of the Knee Extensors

The present study examined if the magnitude of changes in indirect muscle damage markers could be predicted by maximal voluntary isometric contraction (MVIC) torque changes from immediately to 1 day after eccentric exercise. Twenty-eight young men performed 100 maximal isokinetic (60°/s) eccentric contractions of the knee extensors. MVIC torque, potentiated doublet torque, voluntary activation (VA) during MVIC, shear modulus of rectus femoris (RF), vastus medialis and lateralis, and muscle soreness of these muscles were measured before, immediately after, and 1–3 days post-exercise. Based on the recovery rate of the MVIC torque from immediately to 1-day post-exercise, the participants were placed to a recovery group that showed an increase in the MVIC torque (11.3–79.9%, n = 15) or a no-recovery group that showed no recovery (−71.9 to 0%, n = 13). No significant difference in MVIC torque decrease immediately post-exercise was found between the recovery (−33 ± 12%) and no-recovery (−32 ± 9%) groups. At 1–3 days, changes in MVIC torque (−40 to −26% vs. −22 to −12%), potentiated doublet torque (−37 to −22% vs. −20 to −9%), and proximal RF shear modulus (29–34% vs. 8–15%) were greater (p < 0.05) for the no-recovery than recovery group. No significant group differences were found for muscle soreness. The recovery rate of MVIC torque was correlated (p < 0.05) with the change in MVIC torque from baseline to 2 (r = 0.624) or 3 days post-exercise (r = 0.526), or peak change in potentiated doublet torque at 1–3 days post-exercise from baseline (r = 0.691), but not correlated with the changes in other dependent variables. These results suggest that the recovery rate of MVIC torque predicts changes in neuromuscular function but not muscle soreness and stiffness following eccentric exercise of the knee extensors.

Skeletal muscle and cerebral oxygenation levels during and after submaximal concentric and eccentric isokinetic exercise

The aim was to investigate the potential differences in muscle (vastus lateralis) and cerebral (prefrontal cortex) oxygenation levels as well as in the number of repetitions and total work output between isokinetic eccentric and concentric exercise at a moderate relative intensity until exhaustion. Ten recreationally active young men underwent two isokinetic exercise sessions either concentric or eccentric, one on each randomly selected leg. The protocols were performed at 60°/s and an intensity corresponding to 60% of the maximal voluntary contraction (MVC) of each contraction type. Concentric torque was significantly lower compared to eccentric torque in both peak values and at values corresponding to 60% of MVC [230 ± 18 Nm vs. 276 ± 19 Nm (P = .014) and 137 ± 12 Nm vs. 168 ± 11 Nm, respectively (P = .010)]. The participants performed 40% more contractions during eccentric compared to concentric exercise [122 ± 15 vs. 78 ± 7, respectively]. No differences were found in the levels of oxyhaemoglobin, deoxyhemoglobin, total haemoglobin and tissue saturation index when eccentric and eccentric exercise regimes were compared (all P > .05). Our results demonstrate that eccentric exercise of moderate intensity leads to greater resistance to fatigue and more work output compared to concentric exercise, despite the comparable muscle and cerebral oxygenation levels.

Neuromuscular responses to isometric, concentric and eccentric contractions of the knee extensors at the same torque-time integral

PURPOSE

The present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters.

METHOD

Healthy men (18-24 years) were placed to either isometric (ISO), concentric (CONC), or eccentric (ECC) group (n = 11/group) that performed corresponding contractions of the knee extensors to exert the same amount of torque-time integral (24,427 ± 291 Nm·s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10 Hz and 100 Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1 h, 1 day and 2 days after each exercise, and were compared among the groups.

RESULTS

MVC torque decreased immediately after ISO (- 17.0 ± 8.3%), CONC (- 21.7 ± 11.5%) and ECC (- 26.2 ± 15.6%) similarly (p = 0.35), but the decrease sustained longer (p < 0.05) for ECC (2 days post-exercise: - 12.9 ± 14.8%) and ISO (- 5.5 ± 7.9%) than CONC (+ 5.0 ± 11.0%). Muscle soreness developed after ECC (25.1 ± 19.8 mm) and ISO (17.5 ± 21.0 mm) similarly (p = 0.15). Voluntary activation decreased immediately (- 3.7 ± 6.6%) and 1 h post-exercise (- 4.7 ± 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (- 30.1 ± 15.6%) and 1 h post-exercise (- 35.0 ± 12.8%) for ECC than others, and the decrease in 10/100 Hz ratio was also greater immediately (- 30.5 ± 12.6%) and 1 h after ECC (- 23.8 ± 10.3%) than others.

CONCLUSION

ISO, CONC and ECC with the same torque-time integral produced similar neuromuscular fatigue at immediately post-exercise, but the force loss was longer-lasting after ISO and ECC than CONC, and the changes in peripheral fatigue parameters were the greatest after ECC, suggesting greater muscle damage.

Recovery From Eccentric Squat Exercise in Resistance-Trained Young and Master Athletes With Similar Maximum Strength: Combining Cold Water Immersion and Compression

The aim of this study was to investigate whether recovery from eccentric squat exercise varies depending on age and to assess whether the use of a mixed-method recovery (MMR) consisting of cold water immersion and compression tights benefits recovery. Sixteen healthy and resistance-trained young (age, 22.1±2.1years; N=8) and master male athletes (age, 52.4±3.5years; N=8), who had a similar half squat 1-repetition maximum relative to body weight, completed two identical squat exercise training sessions, separated by a 2-week washout period. Training sessions were followed by either MMR or passive recovery (PR). Internal training loads [heart rate and blood lactate concentration (BLa)] were recorded during and after squat sessions. Furthermore, maximal voluntary isometric contraction (MVIC) force, countermovement jump (CMJ) height, resting twitch force of the knee extensors, serum concentration of creatine kinase (CK), muscle soreness (MS), and perceived physical performance capability (PPC) were determined before and after training as well as after 24, 48, and 72h of recovery. A three-way mixed ANOVA revealed a significant time effect of the squat protocol on markers of fatigue and recovery (p<0.05; decreased MVIC, CMJ, twitch force, and PPC; increased CK and MS). Age-related differences were found for BLa, MS, and PPC (higher post-exercise fatigue in younger athletes). A significant two-way interaction between recovery strategy and time of measurement was found for MS and PPC (p<0.05; faster recovery after MMR). In three participants (two young and one master athlete), the individual results revealed a consistently positive response to MMR. In conclusion, master athletes neither reach higher fatigue levels nor recover more slowly than the younger athletes. Furthermore, the results indicate that MMR after resistance exercise does not contribute to a faster recovery of physical performance, neuromuscular function, or muscle damage, but promotes recovery of perceptual measures regardless of age.

Concentric versus eccentric cycling at equal power output or effort perception: Neuromuscular alterations and muscle pain

This study aimed to compare neuromuscular alterations and perceptions of effort and muscle pain induced by concentric and eccentric cycling performed at the same power output or effort perception. Fifteen participants completed three 30-min sessions: one in concentric at 60% peak power output (CON) and two in eccentric, at the same power output (ECC_POWER ) or same perceived effort (ECC_EFFORT ). Muscle pain, perception of effort, oxygen uptake as well as rectus femoris and vastus lateralis electromyographic activities were collected when pedaling. The knee extensors maximal voluntary contraction (MVC) torque, the torque evoked by double stimulations at 100 Hz and 10 Hz (Dt100; Dt10), and the voluntary activation level (VAL) were evaluated before and after exercise. Power output was higher in ECC_EFFORT than CON (89.1 ± 23.3% peak power). Muscle pain and effort perception were greater in CON than ECC_POWER (p < 0.03) while muscle pain was similar in CON and ECC_EFFORT (p > 0.43). MVC torque, Dt100, and VAL dropped in all conditions (p < 0.04). MVC torque (p < 0.001) and the Dt10/ Dt100 ratio declined further in ECC_EFFORT (p < 0.001). Eccentric cycling perceived as difficult as concentric cycling caused similar muscle pain but more MVC torque decrease. A given power output induced lower perceptions of pain and effort in eccentric than in concentric yet similar MVC torque decline. While neural impairments were similar in all conditions, eccentric cycling seemed to alter excitation-contraction coupling. Clinicians should thus be cautious when setting eccentric cycling intensity based on effort perception.

Resistance Training to Failure vs. Not to Failure: Acute and Delayed Markers of Mechanical, Neuromuscular, and Biochemical Fatigue

ABSTRACT

González-Hernández, JM, García-Ramos, A, Colomer-Poveda, D, Tvarijonaviciute, A, Cerón, J, Jiménez-Reyes, P, and Márquez, G. Resistance training to failure vs. not to failure: acute and delayed markers of mechanical, neuromuscular, and biochemical fatigue. J Strength Cond Res 35(4): 886-893, 2021-This study aimed to compare acute and delayed markers of mechanical, neuromuscular, and biochemical fatigue between resistance training sessions leading to or not to failure. Twelve resistance-trained men completed 2 sessions that consisted of 6 sets of the full-squat exercise performed against the 10 repetitions maximum load. In a randomized order, in one session the sets were performed to failure and in the other session the sets were not performed to failure (5 repetitions per set). Mechanical fatigue was quantified through the recording of the mean velocity during all repetitions. The neuromuscular function of the knee extensors was assessed through a maximal voluntary contraction and the twitch interpolation technique before training, immediately after each set, and 1, 24, and 48 hours post-training. Serum creatine kinase (CK) and aspartate aminotransferase (AST) were measured before training and 1, 24, and 48 hours post-training to infer muscle damage. Alpha was set at a level of 0.05. A higher velocity loss between sets was observed during the failure protocol (-21.7%) compared with the nonfailure protocol (-3.5%). The markers of peripheral fatigue were generally higher and long lasting for the failure protocol. However, the central fatigue assessed by the voluntary activation was comparable for both protocols and remained depressed up to 48 hours post-training. The concentrations of CK and AST were higher after the failure protocol revealing higher muscle damage compared with the nonfailure protocol. These results support the nonfailure protocol to reduce peripheral fatigue and muscle damage, whereas the central fatigue does not seem to be affected by the set configuration.

The effect of custom-fitted compression garments worn overnight for recovery from judo training in elite athletes

This study investigated the effects of custom-fitted compression garments (CG) worn during recovery over a multi-day training camp in elite judo players (judoka). A single blind, placebo-controlled study was carried out in 11 elite judoka, using a two-way crossover design. Two three-day training camps were completed in CG and placebo conditions in a random order. Changes in performance and physiological markers were compared between conditions. Judoka were assessed before training for (maximal) isometric knee extension and grip strength, countermovement jump performance and bench-press velocity, alongside soreness, limb circumferences, plasma creatine kinase activity (CK) and perceived bruising. Measurements were repeated after 12, 36 and 43 h of training, whereupon judoka rated the effectiveness of each intervention. Knee extension and bench-press performance demonstrated significant familiarization (p < 0.001), and were excluded from subsequent analysis. Jump performance was unaffected by training (p > 0.05). Grip strength declined throughout training (p < 0.001), with peak decrements of -9.7% indicating mild muscle damage. Increases in bruising, CK and soreness demonstrated highly variable, if significant (p < 0.001) responses. Although CG were perceived as significantly more effective than placebo for recovery (p = 0.046), no effects were observed for any other outcome (p > 0.05). Compression conferred no statistically significant impact upon recovery markers in elite judoka throughout training. Muscle damage responses were inconsistent in this population. Individual athletes would be advised to monitor habitually-used performance measures while using CG to ascertain whether perceptual benefits translate into enhanced recovery. HighlightsCompression garments were perceived as more effective for recovery than placebo by elite judoka.However, no measures of performance or muscle damage were enhanced by CG.Randori was associated with inconsistent muscle damage responses in elite judoka, while lower-body performance was not impaired.Individual athletes would be advised to monitor habitually-used performance measures while using CG to ascertain whether perceptual benefits translate into enhanced recovery.

Downhill running impairs peripheral but not central neuromuscular indices in elbow flexor muscles

The purpose of this study was to examine the effects of a 1-h downhill running exercise on the elbow flexor muscles’ neuromuscular functions. Seventeen adults (Control [CON]: n = 9; Experimental [EXP]: n = 8) completed this study. The CON rested for 30 min while the EXP performed the downhill running. Before, 10 min, 24 h, and 48 h after the interventions, dependent variables (knee extensor muscle soreness, elbow flexion and knee extension isometric strength, elbow flexion resting twitch and voluntary activation [VA], and the biceps surface electromyography [EMG] amplitude) were measured. Knee extensor muscle soreness was significantly greater in the EXP than the CON group following the intervention throughout the entire 48 h. This was accompanied by the greater decline in the knee extension strength in the EXP than the CON (mean ± SD: -6.9 ± 3.4% vs. 1.0 ± 3.2%, p = 0.044). The elbow flexion strength, VA, and EMG amplitude were not affected by the exercise. However, the decline of the elbow flexion resting twitch was greater in the EXP than the CON (−19.6 ± 6.3% vs. 8.7 ± 5.9%, p = 0.003). Therefore, the downhill running impaired the remote elbow flexor muscles at a peripheral level.

Eccentric Resistance Training in Youth: A Survey of Perceptions and Current Practices by Strength and Conditioning Coaches

BACKGROUND

Eccentric resistance training (ERT) in youth is advocated for aiding performance and injury risk. However, research investigating the applied practices of ERT in youth is in its infancy. In this study, we surveyed the perceptions and practices of practitioners utilizing ERT in youth to provide an understanding of its current application in practice.

METHODS

Sixty-four strength and conditioning coaches completed an online survey reporting their current use of ERT in youth using both open and closed questions.

RESULTS

Coaches deemed the inclusion of ERT important in youth with its inclusion based upon factors such as maturation status, training age and strength levels. Coaches also displayed an awareness of the physiological responses to eccentric exercise in youth compared to adults. ERT was primarily used for injury prevention, with the majority of coaches using body-weight and tempo exercises. Furthermore, utilizing eccentric hamstrings exercises was reported as highly important. The frequency of ERT tended to increase in older age groups and coaches mainly prescribed self-selected rest intervals. Finally, the need for further research into the training guidelines of ERT in youth was highlighted, in which coaches require more information on how maturation influences training adaptations and the fatigue-recovery responses.

CONCLUSION

Coaches emphasized the importance of including ERT for both performance and injury prevention factors in youth although further research is required to generate practical guidelines for coaches in order to support its inclusion within practice.

Altered Position Sense after Submaximal Eccentric Exercise-inducing Central Fatigue

PURPOSE

The purpose of this study was to concomitantly investigate the acute and delayed effects of a submaximal eccentric-induced muscle fatigue on the position sense and the neuromuscular function of the right knee extensor muscles.

METHODS

Thirteen young and physically active participants performed a unilateral isokinetic eccentric exercise of their right lower limb until a decrease in maximal voluntary isometric contraction (MVIC) of 20% was reached. Neuromuscular (i.e., MVIC, voluntary activation (VA) level, and evoked contractile properties [DB100 and DB10]) and psychophysical evaluations (i.e., bilateral position-matching task, perceived muscle soreness, and perceived fatigue) were performed at four time points: before (PRE), immediately after (POST), 24 (POST24), and 48 (POST48) the exercise.

RESULTS

The acute 20% MVIC reduction (P < 0.001) was associated with both central (i.e., -13% VA decrease, P < 0.01) and peripheral (i.e., -18% and -42% reduction of DB100 and DB10, respectively, P < 0.001) fatigue. In the following days (POST24 and POST48), VA levels had recovered despite the presence of a persisting peripheral fatigue and delayed-onset muscle soreness. Knee position sense, as revealed by position errors, was significantly altered only at POST (P < 0.05) with participants overestimating the length of their knee extensor. Position errors and VA deficits were significantly correlated at POST (r = -0.60, P = 0.03). Position errors returned to nonsignificant control values in the following days.

CONCLUSION

The acute central fatigue induced by the eccentric exercise contributes to the position sense disturbances. Central fatigue might lead to alterations in the sensory structures responsible for the integration and the processing of position-related sensory inputs.

Moving forward with backward pedaling: a review on eccentric cycling

PURPOSE

There is a profound gap in the understanding of the eccentric cycling intensity continuum, which prevents accurate exercise prescription based on desired physiological responses. This may underestimate the applicability of eccentric cycling for different training purposes. Thus, we aimed to summarize recent research findings and screen for possible new approaches in the prescription and investigation of eccentric cycling.

METHOD

A search for the most relevant and state-of-the-art literature on eccentric cycling was conducted on the PubMed database. Literature from reference lists was also included when relevant.

RESULTS

Transversal studies present comparisons between physiological responses to eccentric and concentric cycling, performed at the same absolute power output or metabolic load. Longitudinal studies evaluate responses to eccentric cycling training by comparing them with concentric cycling and resistance training outcomes. Only one study investigated maximal eccentric cycling capacity and there are no investigations on physiological thresholds and/or exercise intensity domains during eccentric cycling. No study investigated different protocols of eccentric cycling training and the chronic effects of different load configurations.

CONCLUSION

Describing physiological responses to eccentric cycling based on its maximal exercise capacity may be a better way to understand it. The available evidence indicates that clinical populations may benefit from improvements in aerobic power/capacity, exercise tolerance, strength and muscle mass, while healthy and trained individuals may require different eccentric cycling training approaches to benefit from similar improvements. There is limited evidence regarding the mechanisms of acute physiological and chronic adaptive responses to eccentric cycling.

Contralateral Effects by Unilateral Eccentric versus Concentric Resistance Training

PURPOSE

Unilateral resistance training increases muscle strength of the contralateral homologous muscle by the cross-education effect. Muscle damage induced by second eccentric exercise bout is attenuated, even when it is performed by the contralateral limb. The present study compared the effects of unilateral eccentric training (ET) and concentric training (CT) of the elbow flexors (EF) on maximal voluntary isometric contraction (MVC) strength and muscle damage of the contralateral untrained EF.

METHODS

Young men were placed into ET, CT, ipsilateral repeated bout (IL-RB), and contralateral repeated bout (CL-RB) groups (n = 12 per group). The ET and CT groups performed unilateral EF training consisting of five sets of six eccentric and concentric contractions, respectively, once a week for 5 wk by increasing the intensity from 10% to 100% of MVC, followed by 30 maximal eccentric contractions (30MaxEC) of the opposite EF 1 wk later. The IL-RB group performed two bouts of 30MaxEC separated by 2 wk using the nondominant arm, and CL-RB group performed two bouts of 30MaxEC with a different arm for each bout in 1-wk apart.

RESULTS

The MVC increased (P < 0.05) greater for the trained (19% ± 8%) and untrained (11% ± 5%) arms in ET when compared with those in CT (10% ± 6%, 5% ± 2%). The magnitude of changes in muscle damage markers was reduced by 71% ± 19% after the second than the first bout for IL-RB group, and by 48% ± 21% for CL-RB group. Eccentric training and CT attenuated the magnitude by 58% ± 25% and 13% ± 13%, respectively, and the protective effect of ET was greater (P < 0.05) than CL-RB, but smaller (P < 0.05) than IL-RB.

CONCLUSIONS

These results showed that cross-education effect was stronger for ET than CT, and progressive ET produced greater contralateral muscle damage protective effect than a single eccentric exercise bout.

An examination of acute cross-over effects following unilateral low intensity concentric and eccentric exercise

We compared the effects of low intensity concentric (CON) and eccentric (ECC) exercise on the force and neural responses of the dominant (exercised) elbow flexors (EFs), and studied if these conditions could induce cross-over effects to the contralateral (non-exercised) EFs. Fifteen subjects (8 males) completed all conditions (CON and ECC: 6 sets of low intensity exercise to failure; control: rest) in separate visits with a randomized order. Maximal isometric force and electromyography (EMG) of the dominant and contralateral EFs were assessed at pre, immediate-, 24-, and 48-h-post. Two-factor (condition and time) linear mixed-model analyses were performed to examine the force and EMG responses. Immediately post CON, contralateral EFs force was significantly (p = 0.026) higher (12.41%) than control, but no cross-over effects regarding the neural responses were observed. Immediately post ECC, dominant EFs force was significantly lower in ECC, compared to CON (p = 0.003) and control (p < 0.001). This force remained depressed at 24- and 48-h post ECC, when compared to CON (p < 0.001) and control (p < 0.001). Our data suggests that submaximal unilateral exercises are not likely to impair contralateral muscle strength performance. Instead, concentric exercises may acutely improve muscle strength for the contralateral limb. However, this effect is not explained by changes in muscle excitation.

Corticospinal excitability is altered similarly following concentric and eccentric maximal contractions

PURPOSE

To examine corticospinal excitability and neuromuscular function following the completion of eccentric (ECC) or concentric (CON) maximal exercises of same mechanical work.

METHODS

Ten males (29.9 ± 11.8 years) performed maximal isokinetic knee extensor contractions in four experimental sessions. The two first sessions (one in ECC and one in CON) ended with a dynamic peak torque loss of 20%. The work completed in each contraction type was then achieved in the other contraction type. Neuromuscular function- maximal voluntary isometric contraction (MVIC), voluntary activation level (VAL), potentiated doublet (Dt), M-wave- and corticospinal excitability- motor evoked potential (MEP) amplitude and silent period (SP)-were assessed in the vastus lateralis (VL) and rectus femoris (RF) muscles at 20% MVIC before and immediately after exercise.

RESULTS

To lose 20% of dynamic peak torque subjects performed 1.8 times more work in ECC than CON (P = 0.03), inducing a non-different decline in MVIC (P = 0.15). VAL dropped after the ECC sessions only (- 8.5 ± 6.7%; all P < 0.027). Only, the CON session featuring the greatest work affected Dt amplitude (- 9.4 ± 23.8%; P = 0.047). In both muscles, MEP amplitude decreased (all P < 0.001) and MEP SP stayed constant (all P > 0.45), irrespective of contraction type (all P > 0.15).

CONCLUSION

Same-work maximal ECC and CON exercises induced similar fatigue level but from different origins (preferentially central for ECC vs peripheral for CON). Yet, net corticospinal excitability did not depend on contraction type.

Maturation-related changes in the development and etiology of neuromuscular fatigue

PURPOSE

The aim of the present study was to investigate the role of maturation on the etiology of neuromuscular fatigue induced by repeated maximal voluntary isometric contractions (MVIC).

METHODS

Nine prepubertal boys (9.9 ± 1.3 years), eight male adolescents (13.6 ± 1.3 years) and eleven men (23.4 ± 3.0 years) performed a series of repeated isometric MVICs of the knee extensors until the MVIC torque reached 60% of its initial value. Magnetic stimulations were delivered to the femoral nerve every five MVICs to follow the course of voluntary activation level (VA) and the potentiated twitch torque (Qtw_pot).

RESULTS

Task failure was reached after 52.9 ± 12.7, 42.6 ± 12.5, and 26.6 ± 6.3 repetitions in boys, adolescents and men, respectively. VA remained unchanged in men whereas it decreased significantly and similarly in boys and adolescents (p < 0.001). In contrast, Qtw_pot remained unchanged in boys and decreased significantly less in adolescents than adults (p < 0.05).

CONCLUSIONS

Children and adolescents experience less peripheral and more central fatigue than adults. However, adolescents experience more peripheral fatigue than children for a comparable amount of central fatigue. This finding supports the idea that the tolerance of the central nervous system to peripheral fatigue could increase during maturation.

The Effect of Phase Change Material on Recovery of Neuromuscular Function Following Competitive Soccer Match-Play

Aim: Cryotherapy is commonly implemented following soccer match-play in an attempt to accelerate the natural time-course of recovery, but the effect of this intervention on neuromuscular function is unknown. The aim of the present study was to examine the effect of donning lower-body garments fitted with cooled phase change material (PCM) on recovery of neuromuscular function following competitive soccer match-play.

Methods: Using a randomized, crossover design, 11 male semi-professional soccer players wore PCM cooled to 15°C (PCM_cold) or left at ambient temperature (PCM_amb; sham control) for 3 h following soccer match-play. Pre-, and 24, 48, and 72 h post-match, participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation (TMS) during isometric knee-extension and at rest were measured to assess central nervous system (CNS) (voluntary activation, VA) and muscle contractile (quadriceps potentiated twitch force, Q_tw,pot) function. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump [countermovement jump (CMJ) height and reactive strength index (RSI)] performance. A belief questionnaire was completed pre- and post-intervention to determine the perceived effectiveness of each garment.

Results: Competitive soccer match-play elicited persistent decrements in MVC, VA measured with femoral nerve stimulation, Q_tw,pot, as well as reactive strength, fatigue and muscle soreness (P < 0.05). Both MVC and VA were higher at 48 h post-match after wearing PCM_cold compared with PCM_amb (P < 0.05). However, there was no effect of PCM on the magnitude or time-course of recovery for any other neuromuscular, physical function, or perceptual indices studied (P > 0.05). The belief questionnaire revealed that players perceived that both PCM_cold and PCM_amb were moderately effective in improving recovery, with no difference between the two interventions (P = 0.56).

Conclusion: Although wearing cooled PCM garments improved MVC and VA 48 h following match-play, the lack of effect on measures of physical function or perceptual responses to match-play suggest that PCM offers a limited benefit to the recovery process. The lack of effect could have been due to the relatively small magnitude of change in most of the outcome measures studied.

The relationship between stiffness and pain following unaccustomed eccentric exercise: the effects of gentle stretch and repeated bout

PURPOSE

To determine how muscle stiffness and pain which develop after eccentric exercise are affected by gentle stretching and repeated exercise.

METHODS

Twenty-one healthy female participants undertook eccentric exercise of the elbow flexors and changes in resting elbow flexion angle (REFA; a measure of muscle stiffness), pain on stretch scale, pain elicited by pressure (PPT pain, a measure of mechanoreceptor hypersensitivity), and upper arm girth were followed for 7 days after exercise. The effects of gentle passive stretching on pain and muscle stiffness were investigated 2 and 4 days after exercise. Eleven participants also repeated the exercise with the same arm 6 weeks after the first bout.

RESULTS

There was a significant relationship between the pain on stretch scale and increased REFA (day 4; R² = 0.65, p < 0.001), whereas there was no relationship between REFA and PPT pain. REFA was reduced by passive stretching and pain on stretch scale was also reduced from 3.0 (1.4, 5.1) to 0.75 (0.0, 2.0) [median (IQR), p = 0.01]. PPT pain was unaffected by the passive stretching, as was muscle swelling. Following the repeated bout, increases in REFA were much reduced, as was pain on stretch scale (p = 0.02). However, PPT pain was not significantly different between the two bouts of exercise.

CONCLUSIONS

The results indicate that reductions in pain on stretch scale, either by gentle passive stretching or as the result of repeated exercise, are primarily due to reductions in muscle stiffness which develops after eccentric exercise, whereas mechanoreceptor hypersensitivity is relatively unaffected.

Smart System for Prediction of Accurate Surface Electromyography Signals Using an Artificial Neural Network

Bioelectric signals are used to measure electrical potential, but there are different types of signals. The electromyography (EMG) is a type of bioelectric signal used to monitor and recode the electrical activity of the muscles. The current work aims to model and reproduce surface EMG (SEMG) signals using an artificial neural network. Such research can aid studies into life enhancement for those suffering from damage or disease affecting their nervous system. The SEMG signal is collected from the surface above the bicep muscle through dynamic (concentric and eccentric) contraction with various loads. In this paper, we use time domain features to analyze the relationship between the amplitude of SEMG signals and the load. We extract some features (e.g., mean absolute value, root mean square, variance and standard deviation) from the collected SEMG signals to estimate the bicep’ muscle force for the various loads. Further, we use the R-squared value to depict the correlation between the SEMG amplitude and the muscle loads by linear fitting. The best performance the ANN model with 60 hidden neurons for three loads used (3 kg, 5 kg and 7 kg) has given a mean square error of 1.145, 1.3659 and 1.4238, respectively. The R-squared observed are 0.9993, 0.99999 and 0.99999 for predicting (reproduction step) of smooth SEMG signals.

Local high-frequency vibration therapy following eccentric exercises reduces muscle soreness perception and posture alterations in elite athletes

PURPOSE

Exercise-induced muscle damage produces painful sensations (delayed onset of muscle soreness, DOMS). DOMS causes compensatory postural adaptations, which in turn affect athletes' walking and running gait biomechanics. It is still debated whether the postural changes are due to impaired proprioception or pain perception. To disambiguate between these two contrasting hypotheses, we designed a study that tested post-exercise postural adjustments in two groups of athletes: a group who was administered a vibration therapy (VT), to attenuate pain perception, and a control group.

METHODS

Thirty professional futsal players were tested on five different occasions: baseline, eccentric exercises (EE) session day, 24, 48 and 72 h after EE. Vibration therapy (120 Hz) was applied on legs muscles for 15 min in the experimental group, while no vibration was applied in the control group. The measurements included: isokinetic evaluation, stabilometric test, perceived soreness evaluation and serum levels of creatine kinase, and lactate dehydrogenase.

RESULTS

48 h after EE, the control group showed changes in biomechanical parameters (antero-rotations of pelvis, p < 0.05). A substantial alteration in the hip kinematics was found, associated to a reduced contractile force (p < 0.01) and soreness perception. On the contrary, the VT group did not show any change in posture and pain perception. High-intensity VT decreases EE effects on muscle strength and DOMS.

CONCLUSIONS

DOMS significantly changes athletes' posture; but postural changes disappear following a VT therapy that decreases pain perception. It is concluded that soreness perception is the main cause of postural changes and that its effects can be counteracted using VT therapy.