Acute effect of static stretching and pilates stretching on the concentric muscle strength of the knee extensors and flexors.

INTRODUCTION: The effects of stretching exercises on muscle strength have been widely researched in the literature, however, there are no studies investigating the effects of Pilates stretching. OBJECTIVE: To compare the effects of static stretching and Pilates stretching on the concentric muscle strength of the knee extensors and flexors. METHOD: 102 trained young adults were randomized into three groups: static stretching (n = 33); Pilates stretching (n = 34); control (n = 35). Isokinetic evaluation of the knee extensor and flexor muscles was performed at 60°/s and 180°/s, pre and post acute intervention with stretching. Interventions in the static stretching and Pilates stretching groups occurred in 3 sets x 30 s for each body region considered (a-knee extensor muscles; b-knee flexor muscles). The control group did not perform any intervention. RESULTS: No difference (p > 0.05) was observed between the groups after the intervention. There was only a significant intragroup improvement for the control group on the isokinetic muscle strength of the knee flexors at 180°/s, with a moderate effect size, considering the entire sample (p = 0.040; d = 0.42) and when considering only male gender (p = 0.010; d = 0.60). CONCLUSION: Static stretching or Pilates stretching performed as a warm-up did not impair or enhance the concentric muscle strength performance of the knee extensors and flexors. In this way, both forms of stretching can be considered as preparatory exercises before muscle strength training.

Effects of static exercises on hip muscle fatigue and knee wobble assessed by surface electromyography and inertial measurement unit data.

Hip muscle weakness can be a precursor to or a result of lower limb injuries. Assessment of hip muscle strength and muscle motor fatigue in the clinic is important for diagnosing and treating hip-related impairments. Muscle motor fatigue can be assessed with surface electromyography (sEMG), however sEMG requires specialized equipment and training. Inertial measurement units (IMUs) are wearable devices used to measure human motion, yet it remains unclear if they can be used as a low-cost alternative method to measure hip muscle fatigue. The goals of this work were to (1) identify which of five pre-selected exercises most consistently and effectively elicited muscle fatigue in the gluteus maximus, gluteus medius, and rectus femoris muscles and (2) determine the relationship between muscle fatigue using sEMG sensors and knee wobble using an IMU device. This work suggests that a wall sit and single leg knee raise activity fatigue the gluteus medius, gluteus maximus, and rectus femoris muscles most reliably (p < 0.05) and that the gluteus medius and gluteus maximus muscles were fatigued to a greater extent than the rectus femoris (p = 0.031 and p = 0.0023, respectively). Additionally, while acceleration data from a single IMU placed on the knee suggested that more knee wobble may be an indicator of muscle fatigue, this single IMU is not capable of reliably assessing fatigue level. These results suggest the wall sit activity could be used as simple, static exercise to elicit hip muscle fatigue in the clinic, and that assessment of knee wobble in addition to other IMU measures could potentially be used to infer muscle fatigue under controlled conditions. Future work examining the relationship between IMU data, muscle fatigue, and multi-limb dynamics should be explored to develop an accessible, low-cost, fast and standardized method to measure fatiguability of the hip muscles in the clinic.

Effects of far-infrared radiation lamp therapy on recovery from a simulated soccer-match in elite female soccer players.

We investigated the effects of far-infrared radiation (FIR) lamp therapy on changes in muscle damage and performance parameters following six sets of 15-min Loughborough intermittent shuttle test (LIST), a simulated soccer match. Twenty-four elite female soccer players (20-24 y) were assigned into FIR or sham treatment group (n = 12/group). The participants received a 60-min FIR or sham treatment (30 min per muscle) over knee extensors (KE) and flexors (KF) at 2, 25, 49, 73, and 97 h post-LIST. Maximal voluntary isometric contraction (MVC) torque and muscle soreness of the KE and KF, plasma creatine kinase (CK) activity as muscle damage markers, and several performance parameters including countermovement jump (CMJ) and Yo-Yo intermittent recovery test level 1 (YYIR1) were measured before and 1, 24, 48, 72, 96, and 120 h post-LIST. Changes in the measures were compared between groups by a mixed-design two-way ANOVA. The running distance covered during LIST and changes in the measures at 1-h post-LIST (before the treatment) were similar (p = 0.118-0.371) between groups. Changes in muscle damage markers at 24-120 h post-LIST were smaller (p < 0.05, η2 = 0.208-0.467) for the FIR (e.g., MVC-KE torque decrease at 48-h post-LIST: -1 ± 2%, peak KE soreness: 16 ± 10 mm, peak CK: 172 ± 42 IU/L) than sham group (-11 ± 9%, 33 ± 7 mm, 466 ± 220 IU/L, respectively). Performance parameters recovered faster (p < 0.05, η2 = 0.142-0.308) to baseline for the FIR (e.g., decreases at 48-h post-LIST; CMJ: 0 ± 1%, YYIR1: 0 ± 1%) than sham group (-6 ± 2%, -9 ± 6%, respectively). These results suggest that the FIR lamp therapy was effective for enhancing recovery from a soccer match.

Scan-Free and Fully Automatic Tracking of Native Knee Anatomy from Dynamic Stereo-Radiography with Statistical Shape and Intensity Models.

Kinematic tracking of native anatomy from stereo-radiography provides a quantitative basis for evaluating human movement. Conventional tracking procedures require significant manual effort and call for acquisition and annotation of subject-specific volumetric medical images. The current work introduces a framework for fully automatic tracking of native knee anatomy from dynamic stereo-radiography which forgoes reliance on volumetric scans. The method consists of three computational steps. First, captured radiographs are annotated with segmentation maps and anatomic landmarks using a convolutional neural network. Next, a non-convex polynomial optimization problem formulated from annotated landmarks is solved to acquire preliminary anatomy and pose estimates. Finally, a global optimization routine is performed for concurrent refinement of anatomy and pose. An objective function is maximized which quantifies similarities between masked radiographs and digitally reconstructed radiographs produced from statistical shape and intensity models. The proposed framework was evaluated against manually tracked trials comprising dynamic activities, and additional frames capturing a static knee phantom. Experiments revealed anatomic surface errors routinely below 1.0 mm in both evaluation cohorts. Median absolute errors of individual bone pose estimates were below 1.0 ∘ or mm for 15 out of 18 degrees of freedom in both evaluation cohorts. Results indicate that accurate pose estimation of native anatomy from stereo-radiography may be performed with significantly reduced manual effort, and without reliance on volumetric scans.

Home-based resistance training performed at either fast or slow speeds improves power output in older adults.

PURPOSE: We investigated the effect of an unsupervised, body mass- home-based resistance training program in older adults performed at either a fast or slow contractile speed on changes to muscle-power, -volume, -architecture, and fatigue resistance of the knee extensors. METHODS: Thirty-two male older adults (age 65-88 years) were separated into 1) fast-speed exercise (Fast-group), 2) slow-speed exercise (Slow-group), and 3) no exercise (Control-group) groups. Participants in the exercise groups performed 30-45 repetitions of knee-extension and sit-to-stand exercises 3 times a week for 8 weeks with different exercise speed between the groups. Before and after the intervention period, the following variables were measured: Isotonic power, isometric strength, twitch contractile properties, muscle-activity, -architecture, and -quality, neuromuscular fatigue resistance of the knee extensors, and thigh muscle volume. RESULTS: Peak power was increased in both the Fast-group (+24 %, P < 0.01, d = 0.65) and Slow-group (+12 %, P < 0.05, d = 0.33) but not in the Control-group. Training increased pennation angle of the vastus lateralis in both the Fast-group (+8 %, P < 0.01, d = 0.42) and Slow-group (+8 %, P < 0.01, d = 0.42), while only the Fast-group showed increase in pennation angle of the rectus femoris (+12 %, P < 0.01, d = 0.64) and thigh muscle volume (+16 %, P < 0.01, d = 0.52). There was no time × group interaction effect for the other neuromuscular measures. CONCLUSIONS: Unsupervised, body mass- and home-based resistance training performed at either fast or slow speeds can improve muscle power in older adults, while fast-speed exercise may be preferable over slow-speed owing to the relatively greater improvement of muscle-power, -volume, -architecture, and better time efficiency.

Distal hamstrings tendons mechanical properties at rest and contraction using free-hand 3-D ultrasonography.

Tendon properties impact human locomotion, influencing sports performance, and injury prevention. Hamstrings play a crucial role in sprinting, particularly the biceps femoris long head (BFlh), which is prone to frequent injuries. It remains uncertain if BFlh exhibits distinct mechanical properties compared to other hamstring muscles. This study utilized free-hand three-dimensional ultrasound to assess morphological and mechanical properties of distal hamstrings tendons in 15 men. Scans were taken in prone position, with hip and knee extended, at rest and during 20%, 40%, 60%, and 80% of maximal voluntary isometric contraction of the knee flexors. Tendon length, volume, cross-sectional area (CSA), and anteroposterior (AP) and mediolateral (ML) widths were quantified at three locations. Longitudinal and transverse deformations, stiffness, strain, and stress were estimated. The ST had the greatest tendon strain and the lowest stiffness as well as the highest CSA and AP and ML width strain compared to other tendons. Biceps femoris short head (BFsh) exhibited the least strain, AP and ML deformation. Further, BFlh displayed the highest stiffness and stress, and BFsh had the lowest stress. Additionally, deformation varied by region, with the proximal site showing generally the lowest CSA strain. Distal tendon mechanical properties differed among the hamstring muscles during isometric knee flexions. In contrast to other bi-articular hamstrings, the BFlh high stiffness and stress may result in greater energy absorption by its muscle fascicles, rather than the distal tendon, during late swing in sprinting. This could partly account for the increased incidence of hamstring injuries in this muscle.

Increasing cadence with a metronome and running barefoot changes the sagittal kinematics of the lower limbs and trunk.

The purpose was to compare two non-laboratory based running retraining programs on lower limb and trunk kinematics in recreational runners. Seventy recreational runners (30 ± 7.3 years old, 40% female) were randomised to a barefoot running group (BAR), a group wearing a digital metronome with their basal cadence increased by 10% (CAD), and a control group (CON). BAR and CAD groups included intervals from 15 to 40 min over 10 weeks and 3 days/week. 3D sagittal kinematics of the ankle, knee, hip, pelvis, and trunk were measured before and after the retraining program, at comfortable and high speeds. A 3 × 2 mixed ANOVA revealed that BAR and CAD groups increased knee and hip flexion at footstrike, increased peak hip flexion during stance and flight phase, decreased peak hip extension during flight phase, and increased anterior pelvic tilt at both speeds after retraining. In addition, BAR increased ankle plantar flexion at footstrike and increased anterior trunk tilt. Both retraining programs demonstrated significant moderate to large effect size changes in parameters that could reduce the mechanical risks of injury associated with excessive knee stress, which is of interest to coaches, runners and those prescribing rehabilitation and injury prevention programs.

A Method to Track 3D Knee Kinematics by Multi-Channel 3D-Tracked A-Mode Ultrasound.

This paper introduces a method for measuring 3D tibiofemoral kinematics using a multi-channel A-mode ultrasound system under dynamic conditions. The proposed system consists of a multi-channel A-mode ultrasound system integrated with a conventional motion capture system (i.e., optical tracking system). This approach allows for the non-invasive and non-radiative quantification of the tibiofemoral joint's six degrees of freedom (DOF). We demonstrated the feasibility and accuracy of this method in the cadaveric experiment. The knee joint's motions were mimicked by manually manipulating the leg through multiple motion cycles from flexion to extension. To measure it, six custom ultrasound holders, equipped with a total of 30 A-mode ultrasound transducers and 18 optical markers, were mounted on various anatomical regions of the lower extremity of the specimen. During experiments, 3D-tracked intra-cortical bone pins were inserted into the femur and tibia to measure the ground truth of tibiofemoral kinematics. The results were compared with the tibiofemoral kinematics derived from the proposed ultrasound system. The results showed an average rotational error of 1.51 ± 1.13° and a translational error of 3.14 ± 1.72 mm for the ultrasound-derived kinematics, compared to the ground truth. In conclusion, this multi-channel A-mode ultrasound system demonstrated a great potential of effectively measuring tibiofemoral kinematics during dynamic motions. Its improved accuracy, nature of non-invasiveness, and lack of radiation exposure make this method a promising alternative to incorporate into gait analysis and prosthetic kinematic measurements later.

Exploring Human-Exoskeleton Interaction Dynamics: An In-Depth Analysis of Knee Flexion-Extension Performance across Varied Robot Assistance-Resistance Configurations.

Knee rehabilitation therapy after trauma or neuromotor diseases is fundamental to restore the joint functions as best as possible, exoskeleton robots being an important resource in this context, since they optimize therapy by applying tailored forces to assist or resist movements, contributing to improved patient outcomes and treatment efficiency. One of the points that must be taken into account when using robots in rehabilitation is their interaction with the patient, which must be safe for both and guarantee the effectiveness of the treatment. Therefore, the objective of this study was to assess the interaction between humans and an exoskeleton during the execution of knee flexion-extension movements under various configurations of robot assistance and resistance. The evaluation encompassed considerations of myoelectric activity, muscle recruitment, robot torque, and performed movement. To achieve this, an experimental protocol was implemented, involving an individual wearing the exoskeleton and executing knee flexion-extension motions while seated, with the robot configured in five distinct modes: passive (P), assistance on flexion (FA), assistance on extension (EA), assistance on flexion and extension (CA), and resistance on flexion and extension (CR). Results revealed distinctive patterns of movement and muscle recruitment for each mode, highlighting the complex interplay between human and robot; for example, the largest RMS tracking errors were for the EA mode (13.72 degrees) while the smallest for the CR mode (4.47 degrees), a non-obvious result; in addition, myoelectric activity was demonstrated to be greater for the completely assisted mode than without the robot (the maximum activation levels for the vastus medialis and vastus lateralis muscles were more than double those when the user had assistance from the robot). Tracking errors, muscle activations, and torque values varied across modes, emphasizing the need for careful consideration in configuring exoskeleton assistance and resistance to ensure effective and safe rehabilitation. Understanding these human-robot interactions is essential for developing precise rehabilitation programs, optimizing treatment effectiveness, and enhancing patient safety.

Isokinetic Knee Muscle Strength Parameters and Anthropometric Indices in Athletes with and without Hyperextended Knees.

Background and Objectives: Hypermobility has been linked to decreased knee performance, including isokinetic and isometric knee strength. This study aimed to determine whether athletes with and without knee hyperextension have different hamstring-to-quadriceps strength (H/Q) ratios and to investigate the associations between knee hyperextension indices and H/Q ratios and anthropometric characteristics. Materials and Methods: The sample consisted of 47 healthy male athletes without knee injuries aged 23.48 ± 3.54 years. The variables included the degree of knee hypermobility, isokinetic parameters of the leg musculature, and anthropometric indices. Differences between athletes with and without hyperextension were calculated using an independent sample t-test, effect sizes, and discriminant analysis, while associations between the variables were checked by Pearson's correlation coefficient and multiple regression analysis. Results: Athletes with hyperextended knees had shorter legs (t value = -2.23, p = 0.03, moderate ES) and shins (t = -2.64, p = 0.01, moderate ES) and a lower H/Q ratio at an angular velocity of 60°/s (t = -2.11, p = 0.04, moderate ES) than those in the nonhyperextended group did; these differences were supported by discriminant analysis (Wilks' L = 0.60, p = 0.01). An increase in the H/Q ratio at an angular velocity of 60°/s was associated with the degree of knee hypermobility (R = -0.29, p = 0.04). Conclusions: This research showed that athletes with knee hypermobility have weaker hamstring strength and thus a lower H/Q strength ratio at lower angular velocities. These findings suggest that targeted strength training programs for leg (i.e., hamstrings) muscles should help individuals with knee hypermobility.

Individuals With Chronic Ankle Instability Show Abnormalities in Maximal and Submaximal Isometric Strength of the Knee Extensor and Flexor Muscles.

BACKGROUND: It has been shown that chronic ankle instability (CAI) leads to abnormalities in neuromuscular control of more proximal joints than the ankle. Although strength of the hip and the ankle muscles has been largely investigated providing concordant results, limited evidence with contrasting results has been reported regarding knee extensor and flexor muscles. PURPOSE: To investigate maximal and submaximal isometric muscle strength in individuals with CAI. STUDY DESIGN: Controlled laboratory study. METHODS: Fifteen participants with unilateral CAI and 15 healthy matched controls were recruited. To quantify maximal strength, peak forces were recorded during a maximal isometric voluntary contraction of knee extensor and flexor muscles at 30° and 90° of knee flexion and normalized by the body weight of each participant. At both angles, submaximal isometric contractions at 20%, 50%, and 80% of the maximal voluntary isometric contraction were performed to analyze strength steadiness, in terms of coefficient of variation, and strength accuracy, in terms of absolute error. During all the assessments, knee extensor and flexor muscle activation was recorded by means of surface electromyography. RESULTS: Knee flexor maximal isometric strength was significantly lower in the injured limb of individuals with CAI in comparison with healthy controls at both 30° (0.15 ± 0.05 vs 0.20 ± 0.05; P < .05) and 90° (0.14 ± 0.04 vs 0.18 ± 0.05; P < .05). Knee extensor and flexor steadiness was significantly lower (higher coefficient of variation) in both the injured and the noninjured limbs of individuals with CAI in comparison with healthy individuals at 90° and at 30° for knee flexor steadiness of the injured limb. Knee extensor and flexor accuracy was lower (higher absolute error) in both the injured and noninjured limbs of individuals with CAI in comparison with healthy individuals, mainly at 30°, while at 90° it was lower only in the injured limb. No differences between the 2 groups were found for maximal isometric strength of knee extensor muscles, as well as for muscle activations. CONCLUSION: Individuals with CAI show abnormalities in maximal and submaximal isometric strength of knee flexor muscles, and submaximal strength of the knee extensor muscles. Further studies should deeply investigate mechanisms leading to these abnormalities. CLINICAL RELEVANCE: Rehabilitation interventions should consider abnormalities of neuromuscular control affecting joints more proximal than the ankle in individuals with CAI. REGISTRATION: NCT05273177 (ClinicalTrials.gov identifier).

Assessing the reliability of biomechanical variables during a horizontal deceleration task in healthy adults.

Horizontal deceleration technique is an underpinning factor to musculoskeletal injury risk and performance in multidirectional sport. This study primarily assessed within- and between-session reliability of biomechanical and performance-based aspects of a horizontal deceleration technique and secondarily investigated the effects of limb dominance on reliability. Fifteen participants completed four horizontal decelerations on each leg during test and retest sessions. A three-dimensional motion analysis system was used to collect kinetic and kinematic data. Completion time, ground contact time, rate of horizontal deceleration, minimum centre of mass height, peak eccentric force, impulse ratio, touchdown distance, sagittal plane foot and knee angles at initial contact, maximum sagittal plane thorax angle, and maximum knee flexion moment were assessed. Coefficients of variation (COV) and intraclass correlation coefficients (ICC) were used to assess within- and between-session reliability, respectively. Seven variables showed "great" within-session reliability bilaterally (COV ≤9.13%). ICC scores were 'excellent' (≥0.91; n = 4), or 'good' (0.76-0.89; n = 7), bilaterally. Limb dominance affected five variables; three were more reliable for the dominant leg. This horizontal deceleration task was reliable for most variables, with little effect of limb dominance on reliability. This deceleration task may be reliably used to assess and track changes in deceleration technique in healthy adults.

The effect of marathon running on the lower extremity kinematics and muscle activities during walking and running tasks.

Patellofemoral pain syndrome (PFPS) is a common injury among runners, and it is thought that abnormal lower extremity biomechanics contribute to its development. However, the relationship between biomechanical changes after a marathon and PFPS injury remains limited. This study aims to investigate whether differences in knee and hip kinematics and lower extremity muscle activities exist in recreational runners before and after a marathon. Additionally, it aims to explore the relationship between these biomechanical changes and the development of PFPS injury. 12 recreational runners participated in the study. Kinematics and muscle activities of the lower extremity were recorded during walking (5 km/h) and running (10 km/h) tasks within 24 hours before and within 5 hours after a marathon. After the marathon, there was a significant decrease in peak knee flexion (walking: p = 0.006; running: p = 0.006) and an increase in peak hip internal rotation (walking: p = 0.026; running: p = 0.015) during the stance phase of both walking and running compared to before the marathon. The study demonstrates a decrease in knee flexion and an increase in hip internal rotation during the stance phase of gait tasks after completing a marathon, which may increase the risk of developing PFPS injury.

Muscle synergy-informed neuromusculoskeletal modelling to estimate knee contact forces in children with cerebral palsy.

Cerebral palsy (CP) includes a group of neurological conditions caused by damage to the developing brain, resulting in maladaptive alterations of muscle coordination and movement. Estimates of joint moments and contact forces during locomotion are important to establish the trajectory of disease progression and plan appropriate surgical interventions in children with CP. Joint moments and contact forces can be estimated using electromyogram (EMG)-informed neuromusculoskeletal models, but a reduced number of EMG sensors would facilitate translation of these computational methods to clinics. This study developed and evaluated a muscle synergy-informed neuromusculoskeletal modelling approach using EMG recordings from three to four muscles to estimate joint moments and knee contact forces of children with CP and typically developing (TD) children during walking. Using only three to four experimental EMG sensors attached to a single leg and leveraging an EMG database of walking data of TD children, the synergy-informed approach estimated total knee contact forces comparable to those estimated by EMG-assisted approaches that used 13 EMG sensors (children with CP, n = 3, R2 = 0.95 ± 0.01, RMSE = 0.40 ± 0.14 BW; TD controls, n = 3, R2 = 0.93 ± 0.07, RMSE = 0.19 ± 0.05 BW). The proposed synergy-informed neuromusculoskeletal modelling approach could enable rapid evaluation of joint biomechanics in children with unimpaired and impaired motor control within a clinical environment.

Post-Activation-Performance Enhancement: Possible Contributing Factors.

This study aimed to narrow down the possible mechanisms of Post-Activation Performance Enhancement (PAPE), especially if they are exclusively found in the muscle. It was therefore investigated whether (1) the PAPE effect is influenced by neural factors and (2) if Post-Activation-Potentiation (PAP) influences PAPE. Thirteen strength-trained participants (26.5 ± 3.2 years) took part in at least one of three interventions (PAP, PAPE-Electrical (PAPEE), and PAPE-Voluntary (PAPEV)). Conditioning contractions (CC) and testing involved isometric knee extensions performed on an isokinetic device at an 80° knee flexion angle. The CC was either performed voluntarily (PAP, PAPEV) or was evoked through electrical stimulation (PAPEE). Testing was performed at baseline and after two seconds, four minutes, eight minutes, and twelve minutes of the CC. Maximum voluntary isometric contractions (MVIC) for the PAPE trials and supramaximal twitches for the PAP trial were used for testing. Parameters of interest were peak torque and rate of torque development (RTD), and electromyography (EMG) amplitude of the quadriceps (only PAPE). Repeated measures ANOVA and simple contrast comparisons were used for statistical analysis. Peak torque (p < 0.001, η2p = 0.715) and RTD (p = 0. 005, η2p = 0.570) increased significantly during the PAP protocol immediately two seconds after the CC and decreased to near baseline values for the following time points (p > 0.05). Peak torque, RTD, and peak EMG showed no significant differences during PAPEE and PAPEV trials (p > 0.05). Due to the lack of a visible PAPE effect, the question of whether neural mechanisms influence PAPE cannot be answered. Due to the time course of the PAP analysis, it is questionable if these mechanisms play a role in PAPE. The assumption that the PAP mechanism influences PAPE cannot be confirmed for the same reason.

Immediate crossover fatigue after unilateral submaximal eccentric contractions of the knee flexors involves peripheral alterations and increased global perceived fatigue.

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.

Musculoskeletal model degrees of Freedom: Frontal plane constraints are hindering our understanding of human movement.

Induced acceleration analyses have expanded our understanding on the contributions of muscle forces to center of mass and segmental kinematics during a myriad of tasks. While these techniques have identified a subset of major muscle that contribute to locomotion, most analyses have included models with only one frontal plane degree of freedom (dof) actuated by the hip joint. The purpose of this study was to define the impact of including knee and subtalar joint frontal plane dof on model superposition accuracy and muscle specific contributions to mediolateral accelerations. Induced acceleration analyses were performed using OpenSim with the Lai model on a freely available dataset of one subject running at 4 m/s. Analyses were performed on four models (standard, with subtalar joint, with frontal plane knee, and combined frontal plane knee with subtalar) with the kinematic constraint and perturbation analyses. Root mean square error and correlations were computed against experimental kinematics. Adding frontal plane dofs improved mediolateral acceleration correlations on average by > 0.25 while only minimally impacting errors. The constraints method performed better than the perturbation method for mediolateral accelerations. Including frontal plane knee dof resulted in muscle and method specific responses. All muscles presented with a complete flip of polarity for constraint method, imparted by allowing the medial/lateral muscles to contribute according to their anatomical function. Only the gluteus medius flipped for the perturbation method. This study provides significant support for the inclusion of frontal plane knee and subtalar dof and the need for reevaluation of muscle contributions via induced acceleration.

Cadence Modulation during Eccentric Cycling Affects Perception of Effort But Not Neuromuscular Alterations.

INTRODUCTION: A recent study showed that cadence modulation during short eccentric cycling exercise affects oxygen consumption (V̇O 2 ), muscular activity (EMG), and perception of effort (PE). This study examined the effect of cadence on V̇O 2 , EMG, and PE during prolonged eccentric cycling and exercise-induced neuromuscular alterations. METHODS: Twenty-two participants completed three sessions 2-3 wk apart: 1) determination of the maximal concentric peak power output, familiarization with eccentric cycling at two cadences (30 and 60 rpm at 60% peak power output), and neuromuscular testing procedure; 2) and 3) 30 min of eccentric cycling exercise at a cadence of 30 or 60 rpm. PE, cardiorespiratory parameters, and vastus lateralis and rectus femoris EMG were collected during exercise. The knee extensors' maximal voluntary contraction torque, the torque evoked by double stimulations at 100 Hz (Dt100) and 10 Hz (Dt10), and the voluntary activation level were evaluated before and after exercise. RESULTS: V̇O 2 , EMG, and PE were greater at 30 than 60 rpm (all P < 0.05). Maximal voluntary contraction torque, evoked torque, and Dt10/Dt100 ratio decreased (all P < 0.01) without cadence effect (all P > 0.28). Voluntary activation level remained constant after both eccentric cycling exercises ( P = 0.87). CONCLUSIONS: When performed at the same power output, eccentric cycling exercise at 30 rpm elicited a greater PE, EMG, and cardiorespiratory demands than pedaling at 60 rpm. Exercise-induced fatigability was similar in both eccentric cycling conditions without neural impairments, suggesting that eccentric cycling seemed to alter more specifically muscular function, such as the excitation-contraction coupling process. In a rehabilitation context, eccentric cycling at 60 rpm seems more appropriate because it will induce lower PE for similar strength loss compared with 30 rpm.

Association of cartilage metabolism biomarkers and 25(OH)D levels with muscle biomechanical functions in professional rowers and canoeists.

The purpose of the study was to assess the association of cartilage metabolism biomarkers and vitamin D metabolite levels with muscle biomechanical functions in professional rowers and canoeists. The serum levels of aggrecan, cartilage oligomeric matrix protein (COMP), and 25-hydroxyvitamin D (25(OH)D) were determined in elite male sweep-oar rowers (n = 24) and canoeists (n = 15). This was followed by a biomechanical study consisting in isometric measurement of peak torque (PT) of muscles involved in the rowing cycle in the athletes. There were found significant correlations of COMP with the ratio of trunk PT flexor to extensor (p < 0.05) and 25(OH)D with trunk PT-left rotators (p < 0.05), knee joints PT-left and right flexor (p ≤ 0.01), ratio of knee joint PT-right flexor to knee joint PT-right extensor (p < 0.05) in rowers and aggreccan with elbow joint PT of the right flexor (p ≤ 0.01) and extensor (p = 0.05) in canoeists. The correlations of COMP and aggrecan levels with PT of the muscle groups studied in rowers and canoeists indicate the importance of stabilizing the muscular system in cartilage metabolism. The relationship between 25(OH)D status and biomechanical parameters confirm that vitamin D plays an important role in maintaining skeletal muscle health.

Strength Training Is Beneficial for Knee Health.

According to this study.