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Falls and frailty status are often associated with a decline in physical capacity and multifactorial assessment is highly recommended. Based on the functional and biomechanical parameters measured during clinical tests with an accelerometer integrated into smart eyeglasses, the purpose was to characterize a population of older adults through an unsupervised analysis into different physical performance groups. A total of 84 participants (25 men and 59 women) over the age of sixty-five (age: 74.17 ± 5.80 years; height: 165.70 ± 8.22 cm; body mass: 68.93 ± 13.55 kg) performed a 30 s Sit-to-Stand test, a six-minute walking test (6MWT), and a 3 m Timed Up and Go (TUG) test. The acceleration data measured from the eyeglasses were processed to obtain six parameters: the number of Sit-to-Stands, the maximal vertical acceleration values during Sit-to-Stand movements, step duration and length, and the duration of the TUG test. The total walking distance covered during the 6MWT was also retained. After supervised analyses comparison (i.e., ANOVAs), only one of the parameters (i.e., step length) differed between faller groups and no parameters differed between frail and pre-frail participants. In contrast, unsupervised analysis (i.e., clustering algorithm based on K-means) categorized the population into three distinct physical performance groups (i.e., low, intermediate, and high). All the measured parameters discriminated the low- and high-performance groups. Four of the measured parameters differentiated the three groups. In addition, the low-performance group had a higher proportion of frail participants. These results are promising for monitoring activities in older adults to prevent the decline of physical capacities. [ABSTRACT FROM AUTHOR]

The mechanisms underlying movement sense alterations following repeated eccentric contractions remain unclear. This study concomitantly investigated the effects of unilateral eccentric contractions on movement sense and on neuromuscular function at the knee before, immediately after (POST), 24 (POST24) and 48 (POST48) h after the exercise. Twelve participants performed sets of submaximal knee extensors (KE) eccentric contractions until a 20% decrease in maximal voluntary isometric contraction (MVIC) torque was reached. Threshold to detect passive movement (TTDPM) tasks were used to assess movement sense during both knee flexion (TTDPMFLEX) and extension (TTDPMEXT). KE fatigability was assessed using the interpolated twitch technique. TTDPM values expressed in seconds and the percentage of unsuccessful trials only increased at POST during TTDPMFLEX and TTDPMEXT. The 20%-MVIC decrease was associated with significant decreases in voluntary activation level (− 12.7%, p < 0.01) and potentiated doublet torque at 100 Hz (− 18.1%, p < 0.001). At POST24, despite persistent reductions of maximal voluntary and electrically evoked torques associated with increased perceived muscle soreness, TTDPM values and the percentage of unsuccessful trials returned to baseline values. Consequently, movement sense alterations were only observed in the presence of voluntary activation deficits, suggesting that some exercise-induced central alterations may affect the somatosensory function. [ABSTRACT FROM AUTHOR]

The article reports on research conducted to evaluate the effects four weeks of whole-body vibration training had on basketball players and the conventional training methods that were used with them. Researchers evaluated 18 competitive basketball players. They found that a whole-body vibration training program added to the conventional training of basketball players during the preseason and is an effective short-term stimulus to enhance knee extensor strength and squat jump performance.

The article presents sports medicine research that describes neuromuscular fatigue profile and maximal voluntary torque production in endurance-trained cyclists, triathletes, and power-trained athletes. There were three contraction modes to assess fatigue, isometric, concentric, and eccentric. Measures include maximal knee-extension torque, twitch contractile properties, activation level, and electromyographic activity of agonist and antagonist muscles. Results indicate the fatiguing exercise induced peripheral and central adaptations.

Objectives: Because the co-contraction of the gastrocnemius and hamstring muscles strains the anterior cruciate ligament, the role of the gastrocnemius muscle is of particular importance after semitendinosus and gracilis tendon autografts for anterior cruciate ligament reconstruction. This study aimed to examine the neuromuscular mechanisms underlying postsurgical torque deficits during knee flexion by using surface electromyography. Design: A total of 14 volunteer patients (eight men, six women; age, 32.5 ± 9.3 yrs; height, 1 72.7 ± 6 cm; weight, 69.6 ± 10.2 kg) were enrolled in the study; all had undergone anterior cruciate ligament reconstruction performed by the same surgeon. The neuromuscular mechanisms were assessed using isometric tests and surface electromyographic recordings at 19 mos postreconstruction. The torque deficits in the injured knee were compared with the uninjured knee, which served as control values. Results: Significant differences in torque production were observed between the two limbs at specific angular positions during the extension and flexion tests (P < 0.05). The difference in the root mean square myoelectrical activity between the limbs was computed at each tested position, revealing that the gastrocnemius muscle had greater activity at 75 degrees than at 45 degrees (P < 0.05). Conclusions: In deep flexion (>70 degrees), the gastrocnemius muscle may compensate for the weakened hamstrings and thereby strain the anterior cruciate ligament graft after anterior cruciate ligament semitendi- nosus and gracilis tendon reconstruction. [ABSTRACT FROM AUTHOR]

After a unilateral muscle exercise, the performance of the non-exercised contralateral limb muscle can be also impaired. This crossover fatigue phenomenon is still debated in the literature and very few studies have investigated the influence of eccentric contractions. This study was designed to assess neuromuscular adaptations involved in the crossover fatigue of the non-exercised contralateral knee flexor muscles. Seventeen healthy young men performed a unilateral submaximal eccentric exercise of the right knee flexors until a 20% reduction in maximal voluntary isometric contraction torque was attained in the exercised limb. Before (PRE), immediately after exercise cessation (POST) and 24 hours later (POST24), neuromuscular function and perceived muscle soreness were measured in both the exercised limb and non-exercised limb. In addition, global perceived fatigue was assessed at each measurement time. At POST, significant reductions in maximal voluntary isometric contraction were observed in the exercised limb (-28.1%, p < 0.001) and in the non-exercised limb (-8.5%, p < 0.05), evidencing crossover fatigue. At POST, voluntary activation decreased in the exercised limb only (-6.0%, p < 0.001), while electrically evoked potentiated doublet torque was impaired in both the exercised limb and the non-exercised limb (-11.6%, p = 0.001). In addition, global perceived fatigue significantly increased at POST (p < 0.001). At POST24, all measured variables returned to PRE values, except for perceived muscle soreness scores exhibiting greater values than PRE (p < 0.05). A possible cumulative interaction between peripheral alterations and global perceived fatigue may account for the immediate crossover fatigue observed in the non-exercised limb. [ABSTRACT FROM AUTHOR]

Obesity affects nearly 660 million adults worldwide and is known for its many comorbidities. Although the phenomenon of obesity is not fully understood, science regularly reveals new determinants of this pathology. Among them, persistent organic pollutants (POPs) have been recently highlighted. Mainly lipophilic, POPs are normally stored in adipose tissue and can lead to adverse metabolic effects when released into the bloodstream. The main objective of this narrative review is to discuss the different pathways by which physical activity may counteract POPs' adverse effects. The research that we carried out seems to indicate that physical activity could positively influence several pathways negatively influenced by POPs, such as insulin resistance, inflammation, lipid accumulation, adipogenesis, and gut microbiota dysbiosis, that are associated with the development of obesity. This review also indicates how, through the controlled mobilization of POPs, physical activity could be a valuable approach to reduce the concentration of POPs in the bloodstream. These findings suggest that physical activity should be used to counteract the adverse effects of POPs. However, future studies should accurately assess its impact in specific situations such as bariatric surgery, where weight loss promotes POPs' blood release. [ABSTRACT FROM AUTHOR]

Context: Firefighters participating in mandatory physical exercise sessions are exposed to a high ankle sprains' injury risk. Although both physiological and psychological risk factors have been identified, few prospective studies considered the complex interaction of these factors in firefighters. Objective: To prospectively determine whether intrinsic physical risk factors and work-related environment predict ankle sprains occurring during on duty physical exercise in firefighters during an 8-month follow-up period. Design: Prospective. Setting: Fire Department and Rescue Service. Participants: Thirty-nine firefighters were selected based on convenience sampling. Intervention: Participants performed physical tests and completed questionnaires. Main outcome measures: Lower Quarter Y-Balance Test (YBT-LQ), Weight Bearing Lunge Test (WBLT), anthropometric measures, postural stability, chronic ankle instability scores (CAIT), previous injuries, and perceived psychosocial work environment (COPSOQ). Results.: During the follow-up, nine firefighters sustained an injury. YBT-LQ and WBLT per-formances, CAIT scores, history of previous ankle sprain and specific dimensions of the COPSOQ significantly differed between injured and uninjured firefighters. Lower limbs asym-metries of the YBT-LQ (i.e., anterior, posteromedial and posterolateral directions) and the WBLT were predictors of ankle sprains. Conclusions: These findings originally provide evidence that intrinsic factors mainly contrib-ute to ankle sprains, although psychosocial work environment assessment could also charac-terize firefighters at risk. [ABSTRACT FROM AUTHOR]

This study examined whether stereotype-inconsistent information interacts with implicit theories of ability to affect handgrip strength in older adults. Eighty-two retired older adults (13 men and 69 women) from 61 to 89 years old ( Mage = 75.8 years; SD = 6.9) performed maximum voluntary contractions (MVC) during a handgrip task in a design manipulating implicit theories of ability and stereotype-inconsistent information related to physical decline with aging. Participants were randomly assigned to one of three groups: incremental condition, entity condition, or control group. The results showed that in the incremental condition the stereotype-inconsistent information improved the peak MVC, the average MVC, the peak rate of force development (RFD), and RFD in the initial 50 ms of the MVC. This study therefore demonstrated that individuals with an incremental mindset who are exposed to stereotype-inconsistent information can boost their physical performance. These findings are discussed from the perspective of regulatory fit (i.e., when task framing is congruent with the individual's goal). [ABSTRACT FROM AUTHOR]

To test a novel instrumented knee brace intended for use as a rehabilitation system, based on inertial measurement units (IMU) to monitor home-based exercises, the device was compared to the gold standard of motion analysis. The purpose was to validate a new calibration method through functional tasks and assessed the value of adding magnetometers for motion analysis. Thirteen healthy young adults performed a 60-second gait test at a comfortable walking speed on a treadmill. Knee kinematics were captured simultaneously, using the instrumented knee brace and an optoelectronic camera system (OCS). The intraclass correlation coefficient (ICC) showed excellent reliability for the three axes of rotation with and without magnetometers, with values ranging between 0.900 and 0.972. Pearson's r coefficient showed good to excellent correlation for the three axes, with the root mean square error (RMSE) under 3° with the IMUs and slightly higher with the magnetometers. The instrumented knee brace obtained certain clinical parameters, as did the OCS. The instrumented knee brace seems to be a valid tool to assess ambulatory knee kinematics, with an RMSE of <3°, which is sufficient for clinical interpretations. Indeed, this portable system can obtain certain clinical parameters just as well as the gold standard of motion analysis. However, the addition of magnetometers showed no significant advantage in terms of enhancing accuracy. [ABSTRACT FROM AUTHOR]

Purpose: This study examined eccentric-induced fatigue effects on knee flexor (KF) neuromuscular function and on knee position sense. This design was repeated across two experimental sessions performed 1 week apart to investigate potential repeated bout effects. Methods: Sixteen participants performed two submaximal bouts of KF unilateral eccentric contractions until reaching a 20% decrease in maximal voluntary isometric contraction force. Knee position sense was evaluated with position-matching tasks in seated and prone positions at 40° and 70° of knee flexion so that KF were either antagonistic or agonistic during the positioning movement. The twitch interpolation technique was used to assess KF neuromuscular fatigue. Perceived muscle soreness was also assessed. Measurements were performed before, immediately (POST) and 24 h after (POST24) each eccentric bout. Results: No repeated bout effect on neuromuscular function and proprioceptive parameters was observed. At POST, central and peripheral factors contributed to the force decrement as shown by significant decreases in voluntary activation level (− 3.8 ± 4.8%, p < 0.01) and potentiated doublet torque at 100 Hz (− 10 ± 15.8%, p < 0.01). At this time point, position-matching errors significantly increased by 1.7 ± 1.9° in seated position at 40° (p < 0.01). At POST24, in presence of muscle soreness (p < 0.05), although KF neuromuscular function had recovered, position-matching errors increased by 0.6 ± 2.6° in prone position at 40° (p < 0.01). Conclusion: These results provide evidence that eccentric-induced position sense alterations may arise from central and/or peripheral mechanisms depending on the testing position. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to determine whether 7 weeks of standardized (same number and duration of repetitions, sets and rest strictly identical) electromyostimulation training of the elbow flexor muscles would induce strength gains equivalent to those of voluntary isometric training in isometric, eccentric and concentric contractions. Twenty-five males were randomly assigned to an electromyostimulated group (EMS, n =9), a voluntary isometric group (VOL, n =8), or a control group (CON, n =8). Maximal voluntary isometric, eccentric and concentric strength, electromyographic (EMG) activity of the biceps and triceps brachii muscles, elbow flexor muscle activation (twitch interpolation technique) and contractile properties were assessed before and after the training period. The main findings were that the isometric torque gains of EMS were greater than those of VOL after the training period (P <0.01) and that the eccentric and concentric torque gains were equivalent. In both groups, we observed that the mechanical twitch (Pt) was increased (P <0.05) and that torque improvements were not mediated by neural adaptations. Considering the respective intensities of the training programs (i.e., submaximal contractions for EMS versus maximal for VOL), it can be concluded that electromyostimulation training would be more efficient than voluntary isometric training to improve both isometric and dynamic strength. [Copyright &y& Elsevier]

This study investigated the etiology of neuromuscular fatigue induced by a 5-m shuttle run test (5MSRT) in soccer players. Nineteen adult male amateur soccer players (age: 20.0 ± 2.9 years) participated in the present study. Before and after the 5MSRT, they were instructed to complete a maximal voluntary isometric contraction (MVIC) of the knee extensors (KE) during and after which two electrical stimulations were applied at the femoral nerve. Voluntary activation level (VAL), surface electromyography recordings (sEMG), electrophysiological (Mmax) and potentiated resting twitch (Ptw) responses of the KE were compared between pre- and post-5MSRT. Rating of perception exertion (RPE) was also assessed before, during the test immediately following each sprint repetition and after the test. The distance covered during each sprint significantly decreased as the number of trials performed increased (p<.05). The RPE reported following each sprint significantly increased throughout the test. In addition, MVIC (-9%), sEMG (-23%), VAL (-15%), Ptw (-26%) and Mmax (~22%) of the KE were lowered from pre-to-post 5MSRT (.001 < p < .01). The 5MSRT induced a decrease of repeated-sprint running performance and MVIC of the KE. These decrements were accompanied by lowered VAL, sEMG, Ptw and Mmax values of the KE reflecting the involvement of both the central and peripheral origins in the 5MSRT-induced fatigue. Given the important muscle stress induced by 5MSRT, this strenuous test must be applied with caution, after an inevitable familiarization phase, and not during the competition period to avoid the risk of serious injury. [ABSTRACT FROM AUTHOR]

Purpose: Our study aimed to compare the immediate and prolonged effects of submaximal eccentric (ECC) and concentric (CON) fatiguing protocols on the etiology of hamstrings’ motor performance fatigue.On separate days, 16 males performed sets of 5 unilateral ECC or CON hamstrings' contractions at 80% of their 1 Repetition Maximum (1 RM) until a 20% decrement in maximal voluntary isometric contraction (MVC) torque was reached. Electrical stimulations were delivered during and after MVCs at several time points: before, throughout, immediately after (POST) and 24 h (POST 24) after the exercise. Potentiated twitch torques (T100 and T10, respectively) were recorded in response to high and low frequency paired electrical stimulations, and hamstrings’ voluntary activation (VA) level was determined using the interpolated twitch technique. For statistical analysis, all indices of hamstrings’ motor performance fatigue were expressed as a percentage of their respective baseline value.At POST, T100 (ECC: -13.3%; CON: −9.7%; p < 0.001), T10 (ECC: −5.1%; CON: −11.8%; p < 0.05) and hamstrings' VA level (ECC: −3.0%; CON: −2.4%; p < 0.001) were significantly reduced from baseline, without statistical differences between fatigue conditions. At POST24, all indices of hamstrings’ motor performance fatigue returned to their baseline values.These results suggest that the contribution of muscular and neural mechanisms in hamstrings’ motor performance fatigue may not depend on contraction type. This may have implications for practitioners, as ECC and CON strengthening could be similarly effective to improve hamstrings’ fatigue resistance.Methods: Our study aimed to compare the immediate and prolonged effects of submaximal eccentric (ECC) and concentric (CON) fatiguing protocols on the etiology of hamstrings’ motor performance fatigue.On separate days, 16 males performed sets of 5 unilateral ECC or CON hamstrings' contractions at 80% of their 1 Repetition Maximum (1 RM) until a 20% decrement in maximal voluntary isometric contraction (MVC) torque was reached. Electrical stimulations were delivered during and after MVCs at several time points: before, throughout, immediately after (POST) and 24 h (POST 24) after the exercise. Potentiated twitch torques (T100 and T10, respectively) were recorded in response to high and low frequency paired electrical stimulations, and hamstrings’ voluntary activation (VA) level was determined using the interpolated twitch technique. For statistical analysis, all indices of hamstrings’ motor performance fatigue were expressed as a percentage of their respective baseline value.At POST, T100 (ECC: -13.3%; CON: −9.7%; p < 0.001), T10 (ECC: −5.1%; CON: −11.8%; p < 0.05) and hamstrings' VA level (ECC: −3.0%; CON: −2.4%; p < 0.001) were significantly reduced from baseline, without statistical differences between fatigue conditions. At POST24, all indices of hamstrings’ motor performance fatigue returned to their baseline values.These results suggest that the contribution of muscular and neural mechanisms in hamstrings’ motor performance fatigue may not depend on contraction type. This may have implications for practitioners, as ECC and CON strengthening could be similarly effective to improve hamstrings’ fatigue resistance.Results: Our study aimed to compare the immediate and prolonged effects of submaximal eccentric (ECC) and concentric (CON) fatiguing protocols on the etiology of hamstrings’ motor performance fatigue.On separate days, 16 males performed sets of 5 unilateral ECC or CON hamstrings' contractions at 80% of their 1 Repetition Maximum (1 RM) until a 20% decrement in maximal voluntary isometric contraction (MVC) torque was reached. Electrical stimulations were delivered during and after MVCs at several time points: before, throughout, immediately after (POST) and 24 h (POST 24) after the exercise. Potentiated twitch torques (T100 and T10, respectively) were recorded in response to high and low frequency paired electrical stimulations, and hamstrings’ voluntary activation (VA) level was determined using the interpolated twitch technique. For statistical analysis, all indices of hamstrings’ motor performance fatigue were expressed as a percentage of their respective baseline value.At POST, T100 (ECC: -13.3%; CON: −9.7%; p < 0.001), T10 (ECC: −5.1%; CON: −11.8%; p < 0.05) and hamstrings' VA level (ECC: −3.0%; CON: −2.4%; p < 0.001) were significantly reduced from baseline, without statistical differences between fatigue conditions. At POST24, all indices of hamstrings’ motor performance fatigue returned to their baseline values.These results suggest that the contribution of muscular and neural mechanisms in hamstrings’ motor performance fatigue may not depend on contraction type. This may have implications for practitioners, as ECC and CON strengthening could be similarly effective to improve hamstrings’ fatigue resistance.Conclusion: Our study aimed to compare the immediate and prolonged effects of submaximal eccentric (ECC) and concentric (CON) fatiguing protocols on the etiology of hamstrings’ motor performance fatigue.On separate days, 16 males performed sets of 5 unilateral ECC or CON hamstrings' contractions at 80% of their 1 Repetition Maximum (1 RM) until a 20% decrement in maximal voluntary isometric contraction (MVC) torque was reached. Electrical stimulations were delivered during and after MVCs at several time points: before, throughout, immediately after (POST) and 24 h (POST 24) after the exercise. Potentiated twitch torques (T100 and T10, respectively) were recorded in response to high and low frequency paired electrical stimulations, and hamstrings’ voluntary activation (VA) level was determined using the interpolated twitch technique. For statistical analysis, all indices of hamstrings’ motor performance fatigue were expressed as a percentage of their respective baseline value.At POST, T100 (ECC: -13.3%; CON: −9.7%; p < 0.001), T10 (ECC: −5.1%; CON: −11.8%; p < 0.05) and hamstrings' VA level (ECC: −3.0%; CON: −2.4%; p < 0.001) were significantly reduced from baseline, without statistical differences between fatigue conditions. At POST24, all indices of hamstrings’ motor performance fatigue returned to their baseline values.These results suggest that the contribution of muscular and neural mechanisms in hamstrings’ motor performance fatigue may not depend on contraction type. This may have implications for practitioners, as ECC and CON strengthening could be similarly effective to improve hamstrings’ fatigue resistance. [ABSTRACT FROM AUTHOR]

People living with HIV (PLHIV) are not physically active enough. As nonexercisers are perceived as less healthy, less active and less strong, it is likely that PLHIV would be subject to a nonexerciser stereotype threat. We looked to elucidate the effect of the emerging nonexerciser stereotype on handgrip strength performance among less active PLHIV. We also sought to observe the modulating role of self-efficacy in the relationship between stereotype activation and performance. Eighteen PLHIV were recruited to participate in two experimental sessions in which both a stereotypical context and self-efficacy were manipulated. Participants performed a handgrip task comprising a 15-s fatiguing maximal voluntary isometric contraction (MVC) exercise preceded (Pre) and followed (Post) by 5-s MVCs. In each session, (i.e. high and low self-efficacy), four experimental conditions (i.e. Control 1; Control 2; Stereotypical; Self-Efficacy) were performed. A significant performance decrease of the 15-s fatiguing MVC exercise was systematically observed when the nonexerciser stereotype was induced (0.01 < p < 0.001). In addition, this performance re-increased after a high self-efficacy manipulation (p < 0.001). Pre- and post- 5-s MVCs were also significantly depressed after the stereotypical condition (0.01 < p < 0.001) and improved following high self-efficacy manipulation (p < 0.001). Our results revealed a detrimental stereotype threat effect on performance during a handgrip task when the nonexerciser stereotype was activated. A high self-efficacy feedback increased performances significantly whereas no significant difference was observed between the stereotypical and low self-efficacy conditions. These results indicate that self-efficacy can modulate the deteriorating effect of a negative exercise stereotype on task performance in less active PLHIV. Highlights Handgrip strength was decreased and performance fatigability increased when a negative exercise stereotype was induced. Performance fatigability and handgrip strength were restored after positive performance feedback was given. Positive task performance feedback could temper the detrimental effects of a negative stereotypical context among less active people living with HIV. [ABSTRACT FROM AUTHOR]

We investigated the cross-over effect of muscle fatigue and its time course on the non-exercising contralateral limb (NEL) after unilateral fatiguing contractions of the ipsilateral exercising limb (EL). For this purpose, 15 males performed two bouts of 100-second maximal isometric knee extensions with the exercising limb, and neuromuscular function of both the EL and NEL was assessed before (PRE), after a first fatiguing exercise (MID) and after a second fatiguing exercise (POST). Maximal voluntary isometric torque production declined in the EL after the first bout of exercise (−9.6%; p<0.001) while in the NEL, the decrease occurred after the second bout of exercise (−10.6%; p<0.001). At MID, torque decline of the EL was strictly associated to an alteration of the mechanical twitch properties evoked by neurostimulation of the femoral nerve (i.e., peak twitch torque, maximal rate of twitch development). According to these markers, we suggest that peripheral fatigue occurred. At POST, after the second bout of exercise, the voluntary activation level of the knee extensor muscles was altered from PRE (−9.1%; p<0.001), indicating an overall central failure in both the EL and NEL. These findings indicate that two bouts of unilateral fatiguing exercise were needed to induce a cross-over effect of muscle fatigue on the non-exercising contralateral limb. Differential adjustments of the motor pathway (peripheral fatigue vs. central fatigue) might contribute to the respective torque decline in the EL and the NEL. Given that our unilateral fatiguing exercise induced immediate maximal torque reduction in the EL and postponed the loss of torque production in the NEL, it is also concluded that the time course of muscle fatigue differed between limbs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Aims and objectives: To get a deeper understanding of correlates of perceived HIV‐related fatigue by exploring its associations with sociodemographic characteristics and physical activity level of HIV‐infected people. Background: Previous studies on HIV‐related fatigue have mainly focused on physiological and psychological characteristics, but few have considered its associations with sociodemographic variables. In addition, while physical activity has been found to reduce acute fatigue among HIV‐infected people, its links with chronic HIV‐related fatigue remain to be explored. Design: The study employed an observational and cross‐sectional survey design. The manuscript was organised according to STROBE guidelines. Method: A total of 560 people living with HIV in France completed a measure of perceived physical fatigue using the Fatigue Intensity Scale. The predictors targeted sociodemographic characteristics and two measures of individuals' reported level of physical activity. Data were analysed by a stepwise multiple regression model. Results: The results showed that lower age, higher physical activity level and socio‐economic status were significantly associated with reduced perceived physical fatigue, explaining 25% of the variance. Conclusions: The results highlighted the importance of considering sociodemographic and lifestyle characteristics to better characterise HIV‐related fatigue, in particular in an era where HIV as a chronic illness challenges questions of quality of life throughout increasingly longer lifespans. Relevance to clinical practice: The results of this study have implications for HIV care professionals in terms of improving strategies for managing chronic fatigue or promoting physical activity according to more specific profiles of HIV‐infected people. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to investigate the effects on motor function, muscle strength, and endurance of short-term neuromuscular electrical stimulation training of the tibialis anterior muscles in patients with facioscapulohumeral muscular dystrophy type 1 (FSHD1 ) in comparison with healthy controls. Design: This prospective study included 10 patients with FSHD1 and 10 healthy participants. Maximal voluntary isometric contraction of ankle dorsiflexion and a 2-min sustained dorsiflexion maximal voluntary contraction with surface electromyography recordings of the tibialis anterior and the soleus muscles were measured and motor function clinical tests were performed before and after the training period. Results: No significant short term training effect was found in any of the investigated variables for either group, although a tendency towards an increase was noted for the manual muscle testing of the FSHD1. Patients with FSHD1 showed lower maximal voluntary contraction force and lower maximal tibialis anterior surface electromyography amplitude than healthy participants. During the 2-min sustained maximal voluntary contraction, the percentage of force loss was lower for the FSHD1 patients, suggesting that they were experiencing a lower amount of muscle fatigue compared to the healthy participant group. Conclusion: The present neuromuscular electrical stimulation protocol was not strenuous enough and/or the parameters of stimulation were not adequate to improve dorsiflexion strength, muscle endurance, and motor function in FSHD1 patients and healthy participants. [ABSTRACT FROM AUTHOR]

Background: The main objective of the current study was to develop and validate a French exercise stereotype scale for people living with HIV (PLHIV) in order to gain visibility to the possible barriers and facilitators for exercise in PLHIV and thus enhance their quality of life. Methods: A series of four complementary studies was carried out with a total sample of 524 participants to: (a) develop a preliminary version of the HIV Exercise Stereotype Scale (HIVESS) (Stage 1), (b) confirm the factorial structure of the instrument (Stage 2), (c) evaluate the stability of the instrument (Stage 3), and (d) examine the construct and divergent validity of the scale (Stage 4). Results: Results provided support for a 14-item scale with three sub-scales reporting stereotypes related to exercise benefits, exercise risks and lack of capacity for exercise with Cronbach's alphas of .77, .69 and .76 respectively. Results showed good factorial structure, strong reliability and indicators of convergent validity relating to self-efficacy, exercise and quality of life. Conclusion: The HIVESS presented satisfactory psychometric properties, constitutes a reliable and valid instrument to measure exercise stereotypes among PLHIV and has applications for future research and clinical practice. [ABSTRACT FROM AUTHOR]

Intrinsic motivation (IM) is often viewed as a spontaneous tendency for action. Recent behavioral and neuroimaging evidence indicate that IM, in comparison to extrinsic motivation (EM), solicits the motor system. Accordingly, we tested whether IM leads to greater excitability of the motor cortex than EM. To test this hypothesis, we used two different tasks to induce the motivational orientation using either words representing each motivational orientation or pictures previously linked to each motivational orientation through associative learning. Single-pulse transcranial magnetic stimulation over the motor cortex was applied when viewing the stimuli. Electromyographic activity was recorded on the contracted first dorsal interosseous muscle. Two indexes of corticospinal excitability (the amplitude of motor-evoked potential and the length of cortical silent period) were obtained through unbiased automatic detection and analyzed using a mixed model that provided both statistical power and a high level of control over all important individual, task, and stimuli characteristics. Across the two tasks and the two indices of corticospinal excitability, the exposure to IM-related stimuli did not lead to a greater corticospinal excitability than EM-related stimuli or than stimuli with no motivational valence ( ps > .20). While these results tend to dismiss the advantage of IM at activating the motor cortex, we suggest alternative hypotheses to explain this lack of effect, which deserves further research. [ABSTRACT FROM AUTHOR]

Although firefighting is known to engender a high rate of injury, few studies have examined the contribution of physical exercise, burnout and coping strategies to firefighting-related injuries. Data were collected from a population-based sample of 220 male firefighters. In a descriptive study, the nature and site of the injuries and the relationships among firefighter injuries, physical exercise, burnout and coping strategies were examined. Sprains were the most prevalent type of injury (98%), followed by tendinitis (40%) and muscle tears (30%). More than two thirds of these injuries were located at the ankle. Weekly hours of physical exercise, cognitive weariness at work, social support seeking, problem-focused coping and emotional exhaustion were significantly related to these injuries. The findings suggest that physical exercise and cognitive weariness can be considered as risk factors for French firefighter injuries, whereas problem-focused coping can be seen as a protective factor. More research is needed to explain the relationship between social support seeking and injury. [ABSTRACT FROM AUTHOR]

The objective was to investigate the influence of surface electromyography (sEMG) processing methods on the quantification of muscle activity during whole-body vibration (WBV) exercises. sEMG activity was recorded while the participants performed squats on the platform with and without WBV. The spikes observed in the sEMG spectrum at the vibration frequency and its harmonics were deleted using state-of-the-art methods, i.e. (1) a band-stop filter, (2) a band-pass filter, and (3) spectral linear interpolation. The same filtering methods were applied on the sEMG during the no-vibration trial. The linear interpolation method showed the highest intraclass correlation coefficients (no vibration: 0.999, WBV: 0.757-0.979) with the comparison measure (unfiltered sEMG during the no-vibration trial), followed by the band-stop filter (no vibration: 0.929-0.975, WBV: 0.661-0.938). While both methods introduced a systematic bias (P < 0.001), the error increased with increasing mean values to a higher degree for the band-stop filter. After adjusting the sEMG(RMS) during WBV for the bias, the performance of the interpolation method and the band-stop filter was comparable. The band-pass filter was in poor agreement with the other methods (ICC: 0.207-0.697), unless the sEMG(RMS) was corrected for the bias (ICC ⩾ 0.931, %LOA ⩽ 32.3). In conclusion, spectral linear interpolation or a band-stop filter centered at the vibration frequency and its multiple harmonics should be applied to delete the artifacts in the sEMG signals during WBV. With the use of a band-stop filter it is recommended to correct the sEMG(RMS) for the bias as this procedure improved its performance. [ABSTRACT FROM AUTHOR]

Lienhard, K, Vienneau, J, Nigg, S, Meste, O, Colson, SS, and Nigg, BM. Relationship between lower limb muscle activity and platform acceleration during whole-body vibration exercise. J Strength Cond Res 29(10): 2844-2853, 2015—The purpose of this study was to identify the influence of different magnitudes and directions of the vibration platform acceleration on surface electromyography (sEMG) during whole-body vibration (WBV) exercises. Therefore, a WBV platform was used that delivers vertical vibrations by a side-alternating mode, horizontal vibrations by a circular mode, and vibrations in all 3 planes by a dual mode. Surface electromyography signals of selected lower limb muscles were measured in 30 individuals while they performed a static squat on a vibration platform. The WBV trials included 2 side-alternating trials (Side-L: 6 Hz, 2.5 mm; Side-H: 16 Hz, 4 mm), 2 circular trials (Circ-L: 14 Hz, 0.8 mm; Circ-H: 43 Hz, 0.8 mm), and 4 dual-mode trials that were the combinations of the single-mode trials (Side-L/Circ-L, Side-L/Circ-H, Side-H/Circ-L, Side-H/Circ-H). Furthermore, control trials without vibration were assessed, and 3-dimensional platform acceleration was quantified during the vibration. Significant increases in the root mean square of the sEMG (sEMGRMS) compared with the control trial were found in most muscles for Side-L/Circ-H (+17 to +63%, p # 0.05), Side-H/Circ-L (+7 to +227%, p # 0.05), and Side-H/Circ-H (+21 to +207%, p , 0.01) and in the lower leg muscles for Side-H (+35 to +138%, p # 0.05). Furthermore, only the vertical platform acceleration showed a linear relationship (r = 0.970, p , 0.001) with the averaged sEMGRMS of the lower limb muscles. Significant increases in sEMGRMS were found with a vertical acceleration threshold of 18 m s-2 and higher. The present results emphasize that WBV exercises should be performed on a platform that induces vertical accelerations of 18 m s -2 and higher. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether the excessive spikes observed in the surface electromyography (sEMG) spectrum recorded during whole-body vibration (WBV) exercises contain motion artifacts and/or reflex activity. The occurrence of motion artifacts was tested by electrical recordings of the patella. The involvement of reflex activity was investigated by analyzing the magnitude of the isolated spikes during changes in voluntary background muscle activity. Eighteen physically active volunteers performed static squats while the sEMG was measured of five lower limb muscles during vertical WBV using no load and an additional load of 33 kg. In order to record motion artifacts during WBV, a pair of electrodes was positioned on the patella with several layers of tape between skin and electrodes. Spectral analysis of the patella signal revealed recordings of motion artifacts as high peaks at the vibration frequency (fundamental) and marginal peaks at the multiple harmonics were observed. For the sEMG recordings, the root mean square of the spikes increased with increasing additional loads (p < 0.05), and was significantly correlated to the sEMG signal without the spikes of the respective muscle (r range: 0.54--0.92, p < 0.05). This finding indicates that reflex activity might be contained in the isolated spikes, as identical behavior has been found for stretch reflex responses evoked during direct vibration. In conclusion, the spikes visible in the sEMG spectrum during WBV exercises contain motion artifacts and possibly reflex activity. [ABSTRACT FROM AUTHOR]

This study aimed at investigating concurrent changes in cognitive control and cerebral oxygenation (Cox) during steady intense exercise to volitional exhaustion. Fifteen participants were monitored using prefrontal near-infrared spectroscopy and electromyography of the thumb muscles during the completion of an Eriksen flanker task completed either at rest (control condition) or while cycling at a strenuous intensity until exhaustion (exercise condition). Two time windows were matched between the conditions to distinguish a potential exercise-induced evolutive cognitive effect: an initial period and a terminal period. In the initial period, Cox remained unaltered and, contrary to theoretical predictions, exercise did not induce any deficit in selective response inhibition. Rather, the drop-off of the delta curve as reaction time lengthened suggested enhanced efficiency of cognitive processes in the first part of the exercise bout. Shortly before exhaustion, Cox values were severely reduced – though not characteristic of a hypofrontality state – while no sign of deficit in selective response inhibition was observed. Despite this, individual’s susceptibility to making fast impulsive errors increased and less efficient online correction of incorrect activation was observed near exhaustion. A negative correlation between Cox values and error rate was observed and is discussed in terms of cerebral resources redistribution. [ABSTRACT FROM AUTHOR]

Purpose: To describe the most effective parameters maximizing muscle activity during whole-body vibration (WBV) exercises on a vertically vibrating (VV) platform. Methods: The influence of (1) WBV vs. no vibration, (2) vibration frequency (25, 30, 35, 40 Hz), (3) platform peak-to-peak displacement (1.2, 2 mm), and (4) additional loading (no load, 17, 33 kg) on surface electromyographic (sEMG) activity of five lower limb muscles was investigated in eighteen participants. Results: (1) Comparing WBV to no vibration, sEMG of the calf muscles was significantly higher with an additional load of 33 kg independently of the displacement and the frequency ( P < 0.05). During WBV, (2) muscle activity at 40 Hz WBV was significantly higher than at 25 Hz for the gastrocnemius lateralis (GL) for all loads, and for the vastii medialis and lateralis using the 33 kg load ( P < 0.05); (3) sEMG of all lower limb muscles was significantly increased with the 2 mm compared to the 1.2 mm peak-to-peak displacement ( P < 0.05); (4) an effect of additional load was found in the GL, with significantly higher neuromuscular activation for the 33 kg load than no load ( P < 0.05). Conclusions: On a VV platform, we recommend the use of a high platform displacement in combination with a high vibration frequency to provoke the highest muscle activity enhancement. Without maxing out the acceleration stimuli, calf muscles' sEMG can be enhanced with an additional load of 33 kg which corresponded to 50 % of the body mass. [ABSTRACT FROM AUTHOR]

Purpose: This study was designed to investigate whether the intensity modulation of a neuromuscular electrical stimulation (NMES) protocol delivered over the nerve trunk of the plantar flexors would lead to differential peripheral and central contributions of muscle fatigue. Methods: Three fatiguing isometric protocols of the plantar flexors matched for the same amount of isometric torque-time integral (TTI) were randomly performed including a volitional protocol at 20 % of the maximal voluntary contraction (MVC) and two NMES protocols (one at constant intensity, CST; the other at intensity level progressively adjusted to maintain 20 % of MVC, PROG). Results: No time x protocol interaction was found for any of the variables. The MVC decreased similarly (≈12 %, p < 0.001) after all protocols, so did the potentiated twitch responses ( p = 0.001). Although voluntary activation of the plantar flexors did not change, maximal H-reflex to M-wave ratio of the soleus (SOL) and the gastrocnemius medialis (GM) muscles showed an overall increase (SOL: p = 0.037, GM: p = 0.041), while it remained stable for the gastrocnemius lateralis muscle ( p = 0.221). A main time effect was observed only for the SOL maximal V-wave to the superimposed M-wave ratio ( p = 0.024) and to the superimposed H-reflex ( p = 0.008). While similar central and peripheral adaptations were observed after the three fatiguing protocols, the individual contribution of the three different triceps surae muscles was different. Conclusion: Whether the current intensity was increased or not, the adaptations after a NMES protocol yield to similar muscle fatigue adaptations as voluntary contractions likely through similar pathways matching a similar TTI. [ABSTRACT FROM AUTHOR]

The study aims to determine the validity and reproducibility of step duration and step length parameters measured during walking in healthy participants using an accelerometer embedded in smart eyeglasses. Twenty young volunteers participated in two identical sessions comprising a 30 s gait assessment performed at three different treadmill speeds under two conditions (i.e., with and without a cervical collar). Spatiotemporal parameters (i.e., step duration and step length normalized by the lower limb length) were obtained with both the accelerometer embedded in smart eyeglasses and an optoelectronic system. The relative intra- and inter-session reliability of step duration and step length computed from the vertical acceleration data were excellent for all experimental conditions. An excellent absolute reliability was observed for the eyeglasses for all conditions and concurrent validity between systems was observed. An accelerometer incorporated in smart eyeglasses is accurate to measure step duration and step length during gait. [ABSTRACT FROM AUTHOR]

Abstract: This study compared the effects of 6-week whole-body vibration (WBV) training programs with different frequency and peak-to-peak displacement settings on knee extensor muscle strength and power. The underlying mechanisms of the expected gains were also investigated. Thirty-two physically active male subjects were randomly assigned to a high-frequency/high peak-to-peak displacement group (HH; n =12), a low-frequency/low peak-to-peak displacement group (LL; n =10) or a sham training group (SHAM; n =10). Maximal voluntary isometric, concentric and eccentric torque of the knee extensors, maximal voluntary isometric torque of the knee flexors, jump performance, voluntary muscle activation, and contractile properties of the knee extensors were assessed before and after the training period. Significant improvement in knee extensor eccentric voluntary torque (P <0.01), knee flexor isometric voluntary torque (P <0.05), and jump performance (P <0.05) was observed only for HH group. Regardless of the group, knee extensor muscle contractile properties (P <0.05) were enhanced. No modification was observed for voluntary muscle activation or electrical activity of agonist and antagonist muscles. We concluded that high-frequency/high peak-to-peak displacement was the most effective vibration setting to enhance knee extensor muscle strength and jump performance during a 6-week WBV training program and that these improvements were not mediated by central neural adaptations. [ABSTRACT FROM AUTHOR]

Wearable sensors have recently been used to evaluate biomechanical parameters of everyday movements, but few have been located at the head level. This study investigated the relative and absolute reliability (intra- and inter-session) and concurrent validity of an inertial measurement unit (IMU) embedded in smart eyeglasses during sit-to-stand (STS) movements for the measurement of maximal acceleration of the head. Reliability and concurrent validity were investigated in nineteen young and healthy participants by comparing the acceleration values of the glasses' IMU to an optoelectronic system. Sit-to-stand movements were performed in laboratory conditions using standardized tests. Participants wore the smart glasses and completed two testing sessions with STS movements performed at two speeds (slow and comfortable) under two different conditions (with and without a cervical collar). Both the vertical and anteroposterior acceleration values were collected and analyzed. The use of the cervical collar did not significantly influence the results obtained. The relative reliability intra- and inter-session was good to excellent (i.e., intraclass correlation coefficients were between 0.78 and 0.91) and excellent absolute reliability (i.e., standard error of the measurement lower than 10% of the average test or retest value) was observed for the glasses, especially for the vertical axis. Whatever the testing sessions in all conditions, significant correlations (p < 0.001) were found for the acceleration values recorded either in the vertical axis and in the anteroposterior axis between the glasses and the optoelectronic system. Concurrent validity between the glasses and the optoelectronic system was observed. Our observations indicate that the IMU embedded in smart glasses is accurate to measure vertical acceleration during STS movements. Further studies should investigate the use of these smart glasses to assess the STS movement in unstandardized settings (i.e., clinical and/or home) and to report vertical acceleration values in an elderly population of fallers and non-fallers. [ABSTRACT FROM AUTHOR]