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To compare biceps femoris long head (BFlh) muscle tendon unit and fascicle function during Nordic hamstring exercise (NHE) variations with different hip range of motion.Cross-sectional.Twelve healthy volunteers (age: 24 ± 4 years; mass: 77 ± 6 kg; height: 177 ± 4 cm) performed two NHE variations: NHE with hips in neutral (fixed) position (conventional NHE); and NHE with hip flexion/extension. BFlh fascicle length behaviour was assessed using a dual transducer ultrasound configuration. BFlh and semitendinosus muscle electromyography, lower limb kinematics and knee flexion moment were also recorded. A biomechanical model was used to estimate BFlh muscle-tendon unit (MTU) length. Statistical Parametric Mapping was used to assess timing differences in outcome variables across the movement.In both variations, during much of the exercise (~30-80% of movement phase), BFlh fascicles undergo little length change (isometric) while the MTU lengthens. Fascicles stretched considerably just in the last ~20% of the exercise, and changes in fascicle length (2 cm stretch) were smaller in comparison to changes in MTU length (4 cm stretch). Hip flexion resulted in the muscle tendon unit and fascicles operating at longer lengths until approximately 80% of the movement phase.The decoupling between fascicle and MTU length seen during the NHE variations suggests that stretch of the elastic tissue of the MTU has an important role in absorbing energy during Nordic hamstring exercises. This may be important when considering adaptations to BFlh muscle and connective tissues that might occur from NHE training.

Purpose To investigate the effect of muscle force during active stretch on quantitative and qualitative indicators of exercise-induced muscle damage (EIMD) in the medial gastrocnemius (MG) muscle. Methods Twelve recreationally active volunteers performed two trials of an eccentric heel drop exercise. Participants performed a single bout of low-load (body weight) and high-load (body weight + 30% body weight) exercises on separate legs. The total mechanical work output for each condition was matched between legs. Before, two hours and 48 h after each bout of eccentric exercise, electrically stimulated triceps surae twitch torque, muscle soreness, MG active fascicle length at maximum twitch torque and muscle passive stiffness were collected. Triceps surae electromyographic (EMG) activity, MG fascicle stretch and MG muscle–tendon unit (MTU) length were measured during the eccentric tasks. Results The high-load condition increased triceps surae muscle activity by 6–9%, but reduced MG fascicle stretch (p Conclusions Adding 30% body weight during eccentric contractions has a modest impact on exercise-induced muscle damage in the medial gastrocnemius muscle. These results suggest that muscle load may not be an important determinant of stretch-induced muscle damage in the human MG muscle. The muscle investigated does exhibit large pennation angles and high series elastic compliance; architectural features that likely buffer muscle fibres against stretch and damage.

The integration of electromyography (EMG) and ultrasound imaging has provided important information about the mechanisms of muscle activation and contraction. Unfortunately, EMG does not allow an accurate assessment of the interplay between the neural drive received by muscles, changes in fascicle length (FL) and the force/torque produced. We aimed to assess the relationship between modulations in tibialis anterior (TA) motor unit (MU) firing rate, FL and dorsiflexion torque (DT) using ultrasound-transparent high-density EMG electrodes. EMG and ultrasound images were recorded simultaneously from TA, using a 32-electrode silicon matrix, while performing isometric dorsiflexion, at diverse ankle joint positions (0° and 30° plantar flexion) and torques (20% and 40% of maximum). EMG signals were decomposed into individual MUs and changes in FL were assessed with a fascicle-tracking algorithm. MU firings were converted into a cumulative spike train (CST) that was cross-correlated with DT (CST-DT) and FL (CST-FL). High cross-correlations were found for CST-FL, 0.60 (range: 0.31-0.85) and CST-DT 0.71 (range: 0.31-0.88). Cross-correlation lags revealed that the delay between CST-FL (~75ms) was significantly smaller than CST-DT (~150ms, pNEW AND NOTEWORTHYBy employing ultrasound-transparent high-density surface EMG electrodes, we show that modulations in tibialis anterior motor unit discharge rate were closely related to both changes in its fascicle length and resultant torque. These relationships allowed quantifying delays between neural drive and muscle shortening as well as muscle shortening and torque during submaximal isometric contractions, providing an accurate estimation of the time required to generate muscle force and subsequent production of torque via the tendon.

Controversy remains about whether exercise-induced muscle damage (EIMD) and the subsequent repeated bout effect (RBE) are caused by the stretching of an activated muscle, or the production of high force at long, but constant, muscle lengths. The aim of this study was to determine the influence of muscle fascicle stretch elicited during different muscle contraction types on the magnitude of EIMD and the RBE. Fourteen participants performed an initial bout of lower limb exercise of the triceps surae. One leg performed sustained static contractions at a constant long muscle length (ISO), whereas the contralateral leg performed a bout of eccentric heel drop exercise (ECC). Time under tension was matched between the ECC and ISO conditions. Seven days later, both legs performed ECC. Plantar flexor twitch torque, medial gastrocnemius (MG) fascicle length and muscle soreness were assessed before, 2 h and 2 days after each exercise bout. MG fascicle length and triceps surae surface electromyography were examined across the bouts of exercise. We found that both ECC and ISO conditions elicited EIMD and a RBE. ISO caused less damage 2 h after the initial bout (14% less drop in twitch torque, P = 0.03) and less protection from soreness 2 days after the repeated bout (56% higher soreness, P = 0.01). No differences were found when comparing neuromechanical properties across exercise bouts. For MG, the action of stretching an active muscle seems to be more important for causing damage than a sustained contraction at a long length.

The repeated bout effect (RBE) confers protection following exercise-induced muscle damage. Typical signs of this protective effect are significantly less muscle soreness and faster recovery of strength after the second bout. The aim of this study was to compare regional changes in medial gastrocnemius (MG) muscle activity and mechanical hyperalgesia after repeated bouts of eccentric exercise. Twelve healthy male participants performed two bouts of eccentric heel drop exercise (separated by 7 days) while wearing a vest equivalent to 20% of their body weight. High-density MG electromyographic amplitude maps and topographical pressure pain sensitivity maps were created before, two hours (2H), and two days (2D) after both exercise bouts. Statistical parametric mapping was used to identify RBE effects on muscle activity and mechanical hyperalgesia, using pixel-level statistics when comparing maps. The results revealed a RBE, as a lower strength loss (17% less; P

Controversy remains about whether exercise-induced muscle damage (EIMD) and the subsequent repeated bout effect (RBE) are caused by the stretching of an activated muscle, or the production of high force at long, but constant, muscle lengths. The aim of this study was to determine the influence of muscle fascicle stretch elicited during different muscle contraction types on the magnitude of EIMD and the RBE.Fourteen participants performed an initial bout of lower limb exercise of the triceps surae. One leg performed sustained static contractions at a constant long muscle length (ISO), whereas the contralateral leg performed a bout of eccentric heel drop exercise (ECC). Time under tension was matched between the ECC and ISO conditions. Seven days later, both legs performed ECC. Plantar flexor twitch torque, medial gastrocnemius (MG) fascicle length and muscle soreness were assessed before, 2 h and 2 days after each exercise bout. MG fascicle length and triceps surae surface electromyography were examined across the bouts of exercise.We found that both ECC and ISO conditions elicited EIMD and a RBE. ISO caused less damage 2 h after the initial bout (14% less drop in twitch torque, P = 0.03) and less protection from soreness 2 days after the repeated bout (56% higher soreness, P = 0.01). No differences were found when comparing neuromechanical properties across exercise bouts.For MG, the action of stretching an active muscle seems to be more important for causing damage than a sustained contraction at a long length.

Background The most common surgical approaches in use for total hip arthroplasty are the lateral and posterior. When comparing these approaches in terms of gait biomechanics, studies usually rely on pre-defined discrete variables related to the events of gait cycle. However, this analysis may miss differences in other parts of the movement pattern that are not explored. We applied Statistical Parametric Mapping to compare hip kinematics between patients who underwent arthroplasty using either a lateral or posterior approach, contrasting these results with discrete variable analysis. Methods Twenty-two participants (11 lateral, 11 posterior; age between 50 and 80 years) underwent gait analysis before, 3 weeks and 12 weeks after hip arthroplasty. One-dimensional (e.g. time-varying) trajectories and zero-dimensional (e.g. peak extension) discrete variables were used to assess differences between groups in each plane of hip movement (sagittal, frontal, and transverse). Findings One-dimensional and zero-dimensional analyses found no significant differences between groups. Statistical Parametric Mapping revealed that both groups presented significant changes over time in hip adduction at 11–43% of the gait cycle. Zero-dimensional analysis seems to overstate sagittal plane changes over time since no such changes were found by Statistical Parametric Mapping. Interpretation Our results agreed with previous studies suggesting that surgical approach do not affect hip kinematics at the early post-operative stage after arthroplasty. However, Statistical Parametric Mapping revealed changes in frontal plane kinematics over time that were underestimated by the zero-dimensional variables. These findings suggest hip adduction impairment up to 12 weeks after arthroplasty.

Changes in muscle fascicle mechanics have been postulated to underpin the repeated bout effect (RBE) observed following exercise-induced muscle damage (EIMD). However, in the medial gastrocnemius (MG), mixed evidence exists on whether fascicle stretch amplitude influences the level of EIMD, thus questioning whether changes in fascicle mechanics underpin the RBE. An alternative hypothesis is that neural adaptations contribute to the RBE in this muscle. The aim of this study was to investigate the neuromechanical adaptations during and after repeated bouts of a highly controlled muscle lengthening exercise that aimed to maximize EIMD in MG. In all, 20 subjects performed two bouts of 500 active lengthening contractions (70% of maximal activation) of the triceps surae, separated by 7 days. Ultrasound constructed fascicle length-torque (L-T) curves of MG, surface electromyography (EMG), maximum torque production, and muscle soreness were assessed before, 2 hours and 2 days after each exercise bout. The drop in maximum torque (4%) and the increase in muscle soreness (24%) following the repeated bout were significantly less than following the initial bout (8% and 59%, respectively), indicating a RBE. However, neither shift in the L-T curve nor changes in EMG parameters were present. Furthermore, muscle properties during the exercise were not related to the EIMD or RBE. Our results show that there are no global changes in gastrocnemius mechanical behavior or neural activation that could explain the observed RBE in this muscle. We suggest that adaptations in the non-contractile elements of the muscle are likely to explain the RBE in the triceps surae.

PurposeEccentric exercise is widely used to increase muscle fascicle lengths and thus decrease the risk of muscle strain injuries. However, the mechanisms behind this protection are still unknown. The aim of this study was to determine whether Biceps femoris long head (BFlh) fascicle length increases in response to three weeks of eccentric exercise training are the result of addition of in-series sarcomeres within muscle fibres.MethodsTen recreationally active participants (age: 27 ± 3 years, mass: 70 ± 14 kg, height: 174 ± 9 cm) completed three weeks of Nordic hamstring exercise (NHE) training. We collected in vivo sarcomere and muscle fascicle images of the BFlh in two regions (central and distal), utilising microendoscopy and 3D ultrasonography. These images allowed us to estimate sarcomere length, sarcomere number and fascicle lengths before and after the training intervention.ResultsEccentric knee flexion strength increased after the training (15%, P < 0.001, ηp2= 0.75). Further, we found a significant increase in fascicle (21%, P < 0.001, ηp2 = 0.81) and sarcomere (17%, P < 0.001, ηp2 = 0.9) lengths in the distal but not in the central portion of the muscle. The estimated number of in series sarcomeres did not change in either region.ConclusionFascicle length adaptations appear to be heterogeneous in the BFlf in response to three weeks of NHE training. An increase in sarcomere length, rather than the addition of sarcomeres in series, appears to be underlying this adaptation. The mechanism driving regional increases in fascicle and sarcomere length remain unknown, but we speculate it may be driven by regional changes in the passive tension of muscle or connective tissue adaptations.

Background The aim of this study was to compare muscle activation onset times of knee muscles between the involved and uninvolved knee of patients with unilateral anterior cruciate ligament reconstruction (ACLR), and the uninjured knees of healthy subjects after a controlled perturbation at the ankle level. Methods Fifty male amateur soccer players, 25 with unilateral ACLR using semitendinosus-gracilis graft (age = 28.36 ± 7.87 years; time after surgery = 9 ± 3 months) and 25 uninjured control subjects (age = 24.16 ± 2.67 years) participated in the study. Two destabilizing platforms (one for each limb) generated a controlled perturbation at the ankle of each participant (30°of inversion, 10°plantarflexion simultaneously) in a weight bearing condition. The muscle activation onset times of semitendinosus (ST) and vastus medialis (VM) was detected through an electromyographic (EMG) analysis to assess the neuromuscular function of knee muscles. Results Subjects with ACLR had significant delays in EMG onset in the involved (VM = 99.9 ± 30 ms; ST = 101.7 ± 28 ms) and uninvolved knee (VM = 100.4 ± 26 ms; ST = 104.7 ± 28 ms) when compared with the healthy subjects (VM = 69.1 ± 9 ms; ST = 74.6 ± 9 ms). However, no difference was found between involved and uninvolved knee of the ACLR group. Discussion The results show a bilateral alteration of knee muscles in EMG onset after a unilateral ACLR, responses that can be elicited with an ankle perturbation. This suggests an alteration in the central processing of proprioceptive information and/or central nervous system re-organization that may affect neuromuscular control of knee muscles in the involved and uninvolved lower limbs.

Indexación: Scopus. The sensorimotor system helps to maintain functional joint stability during movement. After anterior cruciate ligament (ACL) injury and reconstruction, several sensorimotor deficits may arise, including altered proprioception and changes in neuromuscular control. It is still unknown whether the type of autograft used in the reconstruction may influence knee sensorimotor impairments. The aim of this study was to comparatively assess the effects of the hamstring tendon (HT) and bone-patellar tendon-bone (BPTB) ACL reconstruction techniques on knee sensorimotor control 6–12 months post-operation. A total of 83 male subjects participated in this study: 27 healthy participants, 30 BPTB-operated patients and 26 HT-operated patients. Active joint position sense in 3 ranges of motion (90–60, 60–30, and 30–0 of knee flexion), isometric steadiness, and onset of muscle activation were used to compare sensorimotor system function between groups. Both operated groups had a small (< 5) but significant joint position sense error in the 30–0 range when compared to the healthy group. No significant differences were found between the operated and the control groups for isometric steadiness or onset of muscle activation. The results of this study suggest that operated patients present knee proprioceptive deficits independently of surgical technique. Nevertheless, the clinical implications of this impairment are still unknown. It seems that selected surgical approach for ACL reconstruction do not affect functioning of the sensorimotor system to a large degree. © 2018 San Martín-Mohr et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0205658

Introduction: balance posture is noticeable in the variations occurring on the plantar center of pressure (COP) due to internal or external disorders. The objective of this study was to determine the limit of head anteposition in an antero-posterior direction to which a subject may be exposed to without significant modifications to plantar center of pressure and postural balance, conducting a pre-experimental study. Methods: a convenience sample of 30 healthy male subjects with aligned posture aged 20 to 25 years (22.6 ± 1.88) was selected. The following subjects were excluded: individuals taking drugs that affect posture and balance, who practiced intense physical activity 24 hours prior to the study or who suffered any disease of spine and lower extremities. The study complied with the Declaration of Helsinki and an informed consent was signed. To determine COP in orthostatic position, a force plate (Kistler model 9286BA) was used. Subjects were requested to take a bipedal position on the plate. A plumb line was placed over the tragus, in between subject and observer, recording oscillations for 30 seconds. The experiment was repeated by gradually inducing a head anteposition until reaching 5 centimeters. The Wilcoxon test was used to prove the null hypothesis. Results: the average displacement from the plantar center of pressure in orthostatic position per root mean square on the x-axis was 0,25170 and on the y-axis was 0,34987. With 1 cm of induced head antepopsition, the plantar center of pressure varied significantly to 0,23031 on the x-axis and 0,36576 on the y-axis. Conclusion: the minimum anterior displacement of skull significantly modifying the plantar center of pressure and postural balance is 1 cm. RESUMEN. Introducción: el balance postural se evidencia en las variaciones que pueda sufrir el centro de presión plantar (COP) debido a disturbios internos o externos. El objetivo del presente trabajo consistió en determinar el límite de anteposición de cráneo, en un sentido antero-posterior, a que puede estar sometido un sujeto sin que se modifique significativamente el centro de presión plantar y el balance postural, para lo cual se realizó un estudio preexperimental. Métodos: se obtuvo una muestra por conveniencia conformada por 30 hombres sanos, posturalmente alineados, entre 20 y 25 años de edad (22,6±1,88). Se excluyeron los sujetos consumidores de medicamentos que afectan la postura y el balance, que practicaron actividad física intensa las 24 horas previas al estudio o que sufrían patologías de columna y miembros inferiores. Se siguió la declaración de Helsinki y se firmó un consentimiento informado. Para determinar el COP en posición ortostática se utilizó una plataforma de fuerza Kistler® modelo 9286BA. Se les solicitó a los sujetos adoptar una posición bípeda sobre la plataforma. Se ubicó una plomada por sobre el tragus, entre el sujeto y el observador, y se grabó la oscilación durante 30 segundos. El experimento se repitió al inducir progresivamente una anteposición de cráneo hasta alcanzar los 5 centímetros. Para contrastar la hipótesis nula se utilizó el test de Wilcoxon. Resultados: el promedio del desplazamiento del centro de presión plantar en posición ortostática, según la raíz media cuadrática en el eje x, fue de 0,25170 y en el eje y fue de 0,34987. Con 1 cm de anteposición de cabeza inducida, el centro de presión plantar varió significativamente a 0,23031 en el eje x y a 0,36576 en el eje y. Conclusión: el mínimo desplazamiento anterior de cráneo desde el cual se modifica significativamente el centro de presión plantar y el balance postural corresponde a 1 cm.

This study examined the contributions of individual muscles to changes in energetic cost of transport (COT) over seven walking speeds, and compared results between healthy young and elderly subjects. Twenty six participants (13 young aged 18–30; 13 old aged 70–80) were recruited. COT (O2/kg body mass/km) was calculated by standardizing the mean oxygen consumption recorded during steady state walking. Electromyography signals from 10 leg muscles were used to calculate the cumulative activity required to traverse a unit of distance (CMAPD) for each muscle at each speed. In the old group CMAPD was correlated with COT, presented higher and more variable values, and showed greater increases around optimal speed for all studied muscles. Soleus CMAPD was independent of speed in the young group, but this was not evident with aging. Greater energy cost of walking in older individuals seems to be attributable to increased energy cost of all lower limb muscles.

INTRODUCCIÓN: con el fin de establecer la relación entre el lado y sentido de la inclinación del plano oclusal en niños con asimetría postural de la unidad supraescapular, se hizo un estudio observacional en 34 sujetos de nueve y diez años de edad. MÉTODOS: la asimetría postural y la inclinación del plano oclusal utilizando una platina de fox fueron medidas a través de un análisis fotográfico estandarizado por el software Kinovea 0.7.10 versión 2. RESULTADOS: 18 sujetos de la muestra presentaron ángulo cervical medio occipital-cintura escapular menor (ACMOCEM) a la izquierda con un ángulo mínimo de 87,4°; 4 de ellos mostraron plano oclusal elevado (POE) en el mismo lado, con respecto al plano bipupilar; 11 de ellos lo mostraron elevado a la derecha y 3 de ellos no presentaron inclinación del plano oclusal. 16 sujetos de la muestra presentaron un ACMOCEM a la derecha con ángulo mínimo de 87,13°; 5 de ellos mostraron POE al mismo lado, 7 lo mostraron elevado a la izquierda y 4 no presentaron inclinación del plano oclusal. Los estadígrafos utilizados fueron media y desviación estándar. CONCLUSIONES: se concluyó que en niños sanos con asimetría postural existe tendencia a mostrar un plano oclusal más bajo del lado de la inclinación de cabeza supuestamente debido a factores de crecimiento dentoalveolar.