Rotator cuff tears (RCT) are common. Prior work studied effects of RCT severity, load, and task on functional performance, but no work has examined the combined effect of factors or age- and sex-based effects, which was the objective of this study. Models representing young/older adult males/females with varying RCT severity were used. Seven external loads were applied to the hand during 3 functional tasks. Multiple 2-way ANOVAs and exploratory mixed effects model were used to determine muscle force differences between RCT severity, external load, sex, age, and task. Root mean squared error (RMSE) was used to quantify hand deviation. The deltoid, pectoralis major, infraspinatus, and teres minor muscles increased force for interactions of RCT severity, external load, age, sex, and task and the following main effects: RCT severity (all p < 0.0043), external load (all p < 0.0001), female sex (all p < 0.0001), age (all p < 0.0214), and multi-planar tasks (all p < 0.0001). Larger force contributions occurred for female/older adults with increased RCT severity/external load. Greatest hand deviation occurred for massive tear severity, 66.7 N load for all model permutations (all RMSE > 0.0077 m), with greater deviation for multi-planar vs planar tasks. Study outcomes aid in development of sex, age, and RCT severity specific rehabilitation that incorporates multi-planar movement.

This study examined the angle-based variations in the dynamic control ratio (DCRab), defined as the peak concentric moment of the quadriceps (Qcon) divided by its hamstring counterpart (Hecc) when calculated calculated at 1° intervals, during isokinetic fatiguing conditions. Sixteen men performed 30 maximal concentric knee extensions and eccentric flexions of the right and left knees at speeds of 120°/s and 180°/s. Data were analyzed using ratio values extracted from three repetition segments (4-6, 14-16, and 27-29) and presented graphically. All DCRab curves followed asymmetric second-order patterns, with the values near end-RoM (full extension: 5-7°) significantly higher than at RoM onset (95° of flexion), reflecting increased hamstring moment output. Fatigue reduced the Q and H moment at the equilibrium point [DCRe(M); Hecc = Qcon] and shifted the angle at which the DCRe occurred [DCRe(∠)] rightward, indicating altered muscle balance. DCRe(M) correlated with DCRe(∠): r = 0.84-0.90, while the DCRe(∠) correlated with angle of peak moment (r = 0.63-0.88), especially at 180°/s. Notably, the DCRe(∠) occurred at 20-30° of knee extension and correlated with the angle of peak moment of Hecc at 180°/s, indicating enhanced joint protection. No significant inter-limb differences were found in either Qcon or Hecc strength (p = 0.520). The use of the DCRab and its derivatives, the DCRe(M) and DCRe(∠) indicates that fatigue may affect Q-H balance. Thus, these parameters may aid in assessing the risk of knee injury and design of rehabilitation protocols.

Electromyographic (EMG) recordings of the tensor fascia latae (TFL) muscle are commonly used to assess muscle activation, yet electrode type and amplitude normalisation method can influence data interpretation. This study compared surface and fine-wire EMG recordings of the TFL during dynamic step-up and step-down tasks, and examined the effect of three amplitude normalisation methods on the TFL EMG patterns: maximum voluntary isometric contraction (MVIC), peak of the mean from average across task trials, and peak of the individual trial peaks. Eight physically active participants (5 females, 3 males) performed five trials of each task with EMG recorded from the dominant leg. Two participants were excluded due to artefact contamination or absent fine-wire signals. Surface EMG demonstrated higher early activation during the step-up task compared to fine-wire EMG (p = 0.013); a difference likely attributable to crosstalk from adjacent muscles. Normalisation methods also altered the timing (time of onset) of ensemble waveforms and between-participant variability, with MVIC introducing greater variability but preserving physiological meaning, while task-based methods reduced variability but removed amplitude information. These findings highlight the contradictory results and limitations of both surface and fine-wire EMG when applied in isolation to the TFL. Rather than endorsing one technique as superior, this study provides a tutorial regarding how methodological choices can shape interpretation and potentially lead to misleading conclusions. Future studies incorporating intra-subject variability testing and high-density surface EMG are needed to optimise electrode placement and improve methodological reliability when studying small, anatomically complex muscles such as the TFL.

Transcutaneous spinal cord stimulation (tSCS) is used to induce neural plasticity and enhance motor function recovery following a stroke. Examining real-time changes under tSCS regulation would provide comprehensive insights into the mechanisms underlying motor functional recovery and neural plasticity. However, the real-time changes in the rate of torque development and neural excitability during tSCS remain unclear. This study explored the real-time changes in the rate of torque development and corticospinal excitability during tSCS. Twenty healthy individuals participated in two separate experiments, each with a tSCS condition and control condition. Under the tSCS condition, tSCS was applied to the Th11-Th12 spinous processes at an intensity twice the sensory threshold of the trunk muscles. The peak rate of torque development in the explosive lower limb extension movement in Experiment 1 and motor-evoked potential (MEP) amplitudes in Experiment 2 were assessed before the intervention and with (tSCS condition) or without tSCS (control).The peak rate of torque development and MEP amplitudes increased during tSCS compared to before tSCS (P = 0.038 and 0.047, respectively). However, the control condition had no significant effect. These findings demonstrate that tSCS enhances the rate of torque development and increases corticospinal excitability in healthy individuals, offering valuable fundamental insights into tSCS mechanisms and potential neurorehabilitation applications.

Advanced aging is accompanied by marked declines in motor performance in males and females including reductions in strength, speed and power of limb muscles that begin as early as midlife (∼>40 years) and accelerate from ∼65 years of age. Low muscle power and strength is exacerbated by increased fatigability with aging of limb muscles during dynamic contraction tasks and larger performance variability (between and within older adults), especially in older females. Starting in midlife, females exhibit earlier and larger age-related reductions in muscle strength and power and athletic performance than males of the same age and this is paralleled by increased prevalence of poor health, frailty, and loss of independence. This review presents evidence of key neural and muscular mechanisms affecting the motor unit, the age-related reductions in motor performance and the increased variability in healthy old and very old males and females. Muscular atrophy, particularly of fast-twitch (Type II) fibers, contractile slowing, degradation of neuromuscular junctions, and impairments in motor unit activation collectively underpin sarcopenia and impaired motor and functional performance among older adults. This review also briefly highlights approaches to understanding the protective effects of physical activity and high-resistance training on the age-related changes in muscle and neural function, even in the oldest adults. Such interventions delay functional declines and emphasize the adaptability of the aging neuromuscular system. Opportunities abound for future research to focus on understanding the specific mechanisms driving neural and muscular degeneration and optimizing exercise strategies to improve neuromuscular health of old males and females.

This study aimed to describe muscle coactivation during knee joint-position sense (KJPS) assessments in healthy individuals, before and after muscle fatigue, and to analyse the implications for the magnitude of errors and directional bias.

Functional electrical stimulation (FES) has been documented to provide invaluable, therapeutic effect. The success of FES applications relies on the positioning of stimulation electrodes closely to the muscle motor points. During joint movement, however, motor points may shift as the muscle length changes. Using an objective procedure to define motor points, we assessed how much and how relevantly knee extensors' motor point location changes with joint angle.

Understanding the neuromuscular demands of explosive tasks is essential for enhancing performance and reducing injury risk. This study analyzed inter-limb activation of the medial and lateral gastrocnemius during take-off and landing phases of bilateral and unilateral countermovement jumps (CMJ) and horizontal jumps (HJ), examining its relationship with inter-limb asymmetry and performance. Twenty-six physically active participants performed CMJ and HJ tasks while bilateral surface electromyography was recorded from both gastrocnemius heads. Jump performance was evaluated using flight time (CMJ) and distance (HJ), and asymmetry indices were computed between dominant and non-dominant limbs. Results showed significantly greater muscle activity during take-off than landing across all conditions (p < 0.05). During CMJ landings, the medial gastrocnemius was more active than the lateral, with no activation differences found between unilateral and bilateral jumps. A moderate positive correlation was observed between CMJ performance and bilateral take-off asymmetry (r = 0.43, p = 0.02). Conversely, greater activation in the non-dominant gastrocnemius was negatively associated with performance in both CMJ and HJ (r = -0.39 to -0.48, p < 0.05). In conclusion, gastrocnemius muscles display phase-specific activation patterns. Moderate asymmetry during take-off may benefit performance, while excessive activation in the non-dominant limb may reflect compensatory strategies detrimental to jump efficiency.

Exercise is a first-line treatment for rotator cuff (RC) tendinopathy, but responses are variable. Defining mechanisms underlying patient improvement is necessary. This study investigated the relationship between neuromuscular factors-specifically peak force, rate of force development (RFD), and muscle activation onset-and patient-reported disability outcomes during an 8-week resistance exercise program.

The infrapatellar fat pad (IFP) plays a role in the mechano-pathology of patients with knee osteoarthritis (OA), and its morphological changes during walking may serve as an indicator for detecting the condition. However, the effects of knee muscle activation on IFP morphology during walking in patients with knee OA remain unclear. This study investigated the relationship between muscle activation and morphological changes in the IFP during walking in patients with knee OA. Twenty-two patients with knee OA were enrolled in this cross-sectional study. IFP thickness and kinematic and kinetic data were measured during walking using ultrasound imaging and a three-dimensional motion analysis system. The activities of the quadriceps and hamstring muscles were recorded simultaneously, and muscle co-contraction indices were calculated. No correlation was found between quadriceps activation and IFP parameters. By contrast, a significant negative correlation was observed between morphological changes in the IFP and lateral muscle co-contraction during the stance phase. These results suggest that co-contraction of knee muscles involves poor IFP dynamics during walking, potentially playing a role in the development of mechano-pathological changes in patients with knee OA.

The study aimed at investigating voluntary activation of ankle dorsiflexors in patients with hip osteoarthritis before and after total hip arthroplasty (THA). Twenty-six subjects with unilateral end-stage hip osteoarthritis were assessed for voluntary activation level (VAL) of ankle dorsiflexors of operative and non-operative sides using twitch interpolation technique. Maximal isometric force (MVIC), intrinsic electrically-evoked force (EF) and rate of force development (RFD) at 50 ms, 100 ms and 200 ms during voluntary contractions were also collected. Patients were assessed on the preoperative and third postoperative days and data were compared to 26 age-matched healthy subjects. Patients revealed lower VAL (before surgery: MD 7.7 %, CI 0.4, 14.9; after surgery: MD 12.4 %; CI 5.5, 19.2), MVIC, EF and RFD than healthy subjects on the operative side. On the nonoperative side, patients revealed lower postoperative VAL than healthy subjects (MD 9.0 %, CI 2.4, 15.6) as well as lower evoked force and RFD before and after surgery. Bilateral activation failure of ankle dorsiflexors was found in patients undergoing THA. Such impairments were accompanied by deficits in maximal, evoked and explosive force. These findings confirmed impairments in neuromuscular function of muscles that do not surround the affected joint and may depend on supraspinal pathophysiological mechanisms and learned non-use.

The ability to prevent a fall after a walking perturbation is dependent upon the initial, modifiable conditions related to stability. Individuals may proactively modify their gait to maintain stability by increasing co-contraction about the ankle, increasing the resistance to a perturbing force. The purpose of this study was to investigate whether such proactive ankle co-contraction occurs when walking under the threat of large perturbations. Participants walked on a computer-controlled treadmill under nine randomly ordered task conditions with combinations of three walking speeds and three perturbation conditions. Bilateral EMG of the tibialis anterior and medial gastrocnemius were recorded. Co-contraction indices (CCI) of these muscles during stance prior to a perturbation were calculated. The effects of walking perturbation condition and speed on CCI were assessed using a 3x3 repeated-measures ANOVA. There were no significant interactions of perturbation and speed. There was a significant main effect of perturbation condition, with higher CCI in anterior and posterior perturbations compared to no perturbation. These results suggest that co-contraction occurs in a manner that may increase resistance to perturbations. Future studies will determine the extent to which populations with a high risk of falling are able to proactively modify their gait in anticipation of a perturbation.

Gait training with impeding horizontal force around the center of mass (COM) improves gait speed due to enhancements on activities in gastrocnemius (GC) muscles; however, the underlying neural mechanisms of these changes remain unclear. This study aimed to examine the influence of impeding horizontal force around the COM during gait on oscillatory neural drives to lower leg muscles using coherence analysis of paired surface electromyography, which in the alpha and beta bands reflect subcortical and cortical origins, respectively. Twenty healthy young adults participated in three gait conditions: normal gait without additional horizontal force, and gait with aiding and impeding horizontal forces, which were applied with a load of 5 % of body weight at the second sacral spine level via a waist belt. Medialis and lateralis GC intermuscular coherence in the alpha band (7.5-15 Hz) was significantly higher under the impeding force condition compared to the aiding force and normal gait conditions, whereas beta-band (15-35 Hz) coherence was significantly higher in the impeding force condition only compared to the aiding force condition. Impeding horizontal force around the COM during gait enhances oscillatory neural drives, predominantly from subcortical origins to GC muscles, with additional cortical contributions.

Clinical evaluation of dysphagia requires modeling different phases of swallowing. This process is expensive, invasive, subjective, and typically based on Videofluoroscopic Swallowing Study (VFSS) studies. This work evaluates the use of surface electromyography (sEMG) signals for detecting bolus passage through the mandible line (ManL) and upper esophageal sphincter (UES) in patients with oropharyngeal dysphagia. The paper introduces a novel method where GRU networks are fed with spectrograms resulting from processing sEMG signals. Using VFSS as the gold standard, our results yielded F1 scores up to 96% for binary, and 80% for tri-class classifications, outperforming state-of-the-art methods. The detection was more accurate with larger volumes and thinner consistencies. These results indicate that sEMG is a promising biosignal especially because of its non-invasiveness nature, making it an ideal complement to VFSS for dysphagia diagnosis and monitoring.

In surface electromyography, optimal electrode placement is critical. Various techniques are available for placing the electrodes appropriately, yet these are rarely assessed for accuracy, especially for electrode placement away from neighboring muscles considering the large variation in individual muscle morphology. This study evaluated triceps surae electrode placement using SENIAM recommendations and expert palpation, relative to anatomical muscle boundaries.

Ankle proprioception is essential for dynamic stability, but fatigue may impair force sense and neuromuscular control, increasing injury risk. Their relationship remains unclear.

Commercial electromyographic recording systems usually include two different methods for jitter measurement, based on peaks or threshold-crossing. There is reported evidence that the measurements obtained with both methods from discharges recorded with concentric needle electrodes offer comparable results, but this evidence is scarce. This study aimed to replicate such studies and extract conclusions related to the use of the two methods.

Walking involves multitasking, and many individuals with stroke exhibit dual-task interference, gait instability, and altered lower limb muscle activity even during single-task walking. This study investigated dual-task interference in individuals with stroke and its relationship to single-task walking characteristics. A total of 30 participants completed single-task and dual-task walking. Correct response rate (CRR), dual-task effect, and percentage change in walking speed were assessed using inertial sensors and surface electromyography. The root mean square (RMS) of trunk acceleration and the sample entropy of lower limb acceleration signals were computed. Higher CRR during walking (p = 0.048) and faster walking speed under single-task conditions (p < 0.001) were observed. Mean dual-task effect was - 32.2 %. RMS, sample entropy, and co-contraction index were elevated during dual-task walking (all p < 0.001). Changes in walking speed were associated with co-contraction index (ρ =  - 0.380, p = 0.039), RMS (ρ =  - 0.764, p < 0.001), and sample entropy (ρ =  - 0.734, p < 0.001). Regression analysis indicated that single-task walking speed, RMS, and sample entropy predicted instability during dual-task walking (R = 0.545). These results suggest that compromised postural control during single-task walking increases susceptibility to cognitive interference, emphasizing the importance of targeted gait stability training.

To compare the whole-body muscles glucose metabolism during walking among patients with knee osteoarthritis (KOA) with and without knee extensor weakness using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

The biceps femoris long head (BF) exhibits complex morphology, with fascicle orientation and aponeurotic curvature varying along its length. In vivo assessment of fascicle length (FL), pennation angle (PA), and muscle thickness (MT) is commonly performed with B-mode ultrasound (US), yet probe placement may confound interpretation of morphological variation. This study examined the effects of probe trajectory on BF architecture by synchronizing conventional B-mode US with two-dimensional kinematic tracking. Nineteen males were scanned in a side-lying position with the hip and knee flexed at 20°. B-mode US scans were performed along three paths: Central (center of the mediolateral width), 10 mm medial, and 10 mm lateral relative to Central. A high-speed camera tracked probe movement, synchronized with the US video. Measurements included FL, PA, and intermediate (IT) and full muscle thickness (MT) at four points along the muscle. Probe path significantly influenced FL and PA but not MT or IT. Medial and lateral scans produced longer fascicles and smaller PAs compared to the central path (p < 0.05). Differences in FL and PA exceeded 10 %, corresponding to ∼7-10 mm in FL and 2-3° in PA. These magnitudes equal or surpass values often attributed to training adaptations or injury-related remodeling. Probe trajectory can bias BF architectural estimates by amounts that rival physiologically meaningful changes, highlighting the need for standardized scanning protocols.

The objective was to examine the intra- and inter-rater reliability of three instruments for measuring ankle dorsiflexion (ADF) range of motion (ROM) and degree of asymmetry in the Weight-Bearing Lunge Test (WBLT). Additionally, the study evaluated the agreement between these tools in both asymptomatic and symptomatic populations.