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Introduction: In individuals with patellofemoral pain (PFP), addressing increased knee valgus during weight-bearing activities typically involves strengthening weak hip muscles. However, recent literature highlights the role of altered descending central control in abnormal movements associated with PFP. While transcranial direct current stimulation (tDCS) has demonstrated the capacity to enhance neuroplasticity, its application targeting the corticomotor function of gluteal muscles in PFP remains unexplored. This study aimed to investigate the effects of combining bimodal tDCS with exercise on frontal plane kinematics in individuals with PFP. The hypothesis was that bimodal tDCS, specifically targeting the corticomotor function of the gluteal muscles, would augment the effectiveness of exercise interventions in improving frontal plane kinematics compared to sham stimulation. Methods: Ten participants with PFP participated in two sessions involving either bimodal tDCS or sham stimulation, concurrently with hip strengthening exercises. Weight-bearing tasks, including single leg squat, single leg landing, single leg hopping, forward step-down, and lateral step-down, were performed and recorded before and after each session. Pain visual analog scale (VAS) scores were also documented. A one-way ANOVA with repeated measures was employed to compare kinematics, while a Friedman test was used to compare VAS across the three conditions (pre-test, post-tDCS, and post-Sham). Results: We observed no significant differences in trunk lean angle, hip and knee frontal plane projection angles, or dynamic valgus index among the three conditions during the five weight-bearing tasks. VAS scores did not differ across the three conditions. Discussion and conclusion: A single session of tDCS did not demonstrate immediate efficacy in enhancing frontal plane kinematics or relieving pain in individuals with PFP. Considering observed positive outcomes in other neurological and orthopedic populations with multi-session tDCS applications, suggesting potential cumulative effects, further research is essential to explore the effects of multi-session tDCS on weight-bearing movement and underlying neurophysiology in individuals with PFP.

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BACKGROUND: Ankle sprains lead to an unexplained reduction of ankle eversion strength, and arthrogenic muscle inhibition (AMI) in peroneal muscles is considered one of the underlying causes. This study aimed to observe the presence of AMI in peroneal muscles among people with chronic ankle instability (CAI). METHODS: Sixty-three people with CAI and another sixty-three without CAI conducted maximal voluntary isometric contraction (MVIC) and superimposed burst (SIB) tests during ankle eversion, then fifteen people with CAI and fifteen without CAI were randomly invited to repeat the same tests to calculate the test-retest reliability. Electrical stimulation was applied to the peroneal muscles while the participants were performing MVIC, and the central activation ratio (CAR) was obtained by dividing MVIC torque by the sum of MVIC and SIB torques, representing the degree of AMI. RESULTS: The intra-class correlation coefficients were 0.77 (0.45-0.92) and 0.92 (0.79-0.97) for the affected and unaffected limbs among people with CAI, and 0.97 (0.91-0.99) and 0.93 (0.82-0.97) for the controlled affected and unaffected limbs among people without CAI; Significant group × limb interaction was detected in the peroneal CAR (p = 0.008). The CARs were lower among people with CAI in the affected and unaffected limbs, compared with those without CAI (affected limb = 82.54 ± 9.46%, controlled affected limb = 94.64 ± 6.37%, p < 0.001; unaffected limb = 89.21 ± 8.04%, controlled unaffected limb = 94.93 ± 6.01%, p = 0.016). The CARs in the affected limbs were lower than those in the unaffected limbs among people with CAI (p = 0.023). No differences between limbs were found for CAR in the people without CAI (p = 0.10). CONCLUSIONS: Bilateral AMI of peroneal muscles is observed among people with CAI. Their affected limbs have higher levels of AMI than the unaffected limbs.

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Background: We investigated the impact of 1) passive heating (PH) induced by single and intermittent/prolonged hot-water immersion (HWI) and 2) the duration of PH, on muscle contractile function under the unfatigued state, and during the development of muscle fatigue. Methods: Twelve young males volunteered for this study consisting of two phases: single phase (SP) followed by intermittent/prolonged phase (IPP), with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and HWI (44-45°C; water up to the waist level). SP-HWI included one continuous 45-min bath (from 15 to 60 min). IPP-HWI included an initial 45-min bath (from 15 to 60 min) followed by eight additional 15-min baths interspaced with 15-min breaks at room temperature between 75 and 300 min. Intramuscular (Tmu; measured in the vastus lateralis muscle) and rectal (Trec) temperatures were determined. Neuromuscular testing (performed in the knee extensors and flexors) was performed at baseline and 60 min later during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations of the knee extensors) was performed after the last neuromuscular testing of each trial. Results: HWI increased Tmu and Trec to 38°C-38.5°C (p < 0.05) during both SP and IPP. Under the unfatigued state, HWI did not affect electrically induced torques at 20 Hz (P20) and 100 Hz (P100). However, it induced a shift towards a faster contractile profile during both SP and IPP, as evidenced by a decreased P20/P100 ratio (p < 0.05) and an improved muscle relaxation (i.e., reduced half-relaxation time and increased rate of torque relaxation; p < 0.05). Despite a reduced voluntary activation (i.e., -2.63% ± 4.19% after SP-HWI and -5.73% ± 4.31% after IPP-HWI; condition effect: p < 0.001), HWI did not impair maximal isokinetic and isometric contraction torques. During the fatiguing protocol, fatigue index and the changes in muscle contractile properties were larger after HWI than CON conditions (p < 0.05). Finally, none of these parameters were significantly affected by the heating duration. Conclusion: PH induces changes in muscle contractile function which are not augmented by prolonged exposure when thermal stress is moderate.

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PURPOSE: To observe how knee proprioceptive acuity and quadriceps neuromuscular function change during and after repeated isokinetic knee-extension exercise in patients with anterior cruciate ligament reconstruction (ACLR) or meniscus surgery. METHODS: Patients with ACLR or meniscus surgery and matched controls (n = 19 in each group) performed knee-flexion replication at 15° and 75°, and quadriceps peak torque (PT), central activation ratio (CAR) and rate of torque development (RTD) at baseline and immediately after every five sets of isokinetic knee-extension exercise (times 1-5). RESULTS: Compared to the baseline, the ACLR and control groups displayed errors in knee-flexion replication at 75° only at time 5 (115.9-155.6%; p ≤ 0.04, d ≥ 0.97), whereas the meniscus surgery group exhibited errors at all time points (142.5-265.6%; p ≤ 0.0003, d ≥ 1.4). Significant percentage reductions in quadriceps CAR were observed between times 4 and 5 in the ACLR group (-5.8%; p = 0.0002, d = 0.96), but not in the meniscus surgery (-1.4%; n.s.) and control (0.1%; n.s.) groups. Significant percentage reductions in quadriceps RTD were observed between times 4 and 5 in the ACLR (-24.2%; p = 0.007, d = 0.99) and meniscus surgery (-23.0%; p = 0.01, d = 0.85) groups, but not in the control group (-0.2%; n.s.). CONCLUSION: Patients with ACLR or meniscus surgery displayed a greater loss in knee proprioceptive acuity and quadriceps neuromuscular function during and after exercise than healthy individuals. Evidence-based interventions to enhance exercise-induced fatigue resistance should be implemented following ACLR or meniscus surgery, aiming to prevent proprioceptive and neuromuscular changes within the knee joint and quadriceps. LEVEL OF EVIDENCE: III.

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CONTEXT: Exercise-induced fatigue reduces muscle force production and motoneuron pool excitability. However, it is unclear if patients with patellofemoral pain (PFP) experience further loss in quadriceps neuromuscular function due to fatigue during exercise and postexercise. OBJECTIVE: To observe how quadriceps maximal strength, activation, and force-generating capacity change during and after repetitive bouts of isokinetic knee-extension exercise in patients with PFP. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-two patients with PFP (visual analog scale mean pain severity = 4.2 of 10 cm, mean symptom duration = 38.6 months) and 19 healthy control individuals matched on age and body mass index. MAIN OUTCOME MEASURE(S): Quadriceps peak torque (PT), central activation ratio (CAR), and rate of torque development (RTD) were assessed at baseline and immediately after every 5 sets of knee-extension exercise (times 1-5). Participants continued knee-extension exercises until the baseline quadriceps PT dropped below 50% for 3 consecutive contractions. RESULTS: No group-by-time interaction was observed for quadriceps PT (F5,195 = 1.03, P = .40). However, group-by-time interactions were detected for quadriceps CAR (F5,195 = 2.63, P= .03) and RTD (F5,195 = 3.85, P = .002). Quadriceps CAR (-3.6%, P = .04, Cohen d = 0.53) and RTD (-18.9%, P = .0008, Cohen d = 1.02) decreased between baseline and time 1 in patients with PFP but not in their healthy counterparts (CAR -1.9%, P = .86; RTD -9.8%, P = .22). Quadriceps RTD also decreased between times 4 and 5 in patients with PFP (-24.9%, P = .002, Cohen d = 0.89) but not in the healthy group (-0.9%, P = .99). CONCLUSIONS: Patients with PFP appeared to experience an additional reduction in quadriceps activation, force-generating capacity, or both during the early and late stages of exercise compared with healthy individuals. Clinicians should be aware of such possible acute changes during exercise and postexercise and use fatigue-resistant rehabilitation programs for patients with PFP.

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After spinal cord injury (SCI), motoneuron death occurs at and around the level of injury which induces changes in function and organization throughout the nervous system, including cortical changes. Muscle affected by SCI may consist of both innervated (accessible to voluntary drive) and denervated (inaccessible to voluntary drive) muscle fibers. Voluntary activation measured with transcranial magnetic stimulation (VATMS) can quantify voluntary cortical/subcortical drive to muscle but is limited by technical challenges including suboptimal stimulation of target muscle relative to its antagonist. The motor evoked potential (MEP) in the biceps compared to the triceps (i.e., MEP ratio) may be a key parameter in the measurement of biceps VATMS after SCI. We used paired pulse TMS, which can inhibit or facilitate MEPs, to determine whether the MEP ratio affects VATMS in individuals with tetraplegia. Ten individuals with tetraplegia following cervical SCI and ten non-impaired individuals completed single pulse and paired pulse VATMS protocols. Paired pulse stimulation was delivered at 1.5, 10, and 30 ms inter-stimulus intervals (ISI). In both the SCI and non-impaired groups, the main effect of the stimulation pulse (paired pulse compared to single pulse) on VATMS was not significant in the linear mixed-effects models. In both groups for the stimulation parameters we tested, the MEP ratio was not modulated across all effort levels and did not affect VATMS. Linearity of the voluntary moment and superimposed twitch moment relation was lower in SCI participants compared to non-impaired. Poor linearity in the SCI group limits interpretation of VATMS. Future work is needed to address methodological issues that limit clinical application of VATMS.

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BACKGROUND: Assessment of voluntary activation is useful in the study of neuromuscular impairments, particularly after spinal cord injury (SCI). Measurement of voluntary activation with transcranial magnetic stimulation (VATMS) is limited by technical challenges, including the difficulty in preferential stimulation of cortical neurons projecting to the target muscle and minimal stimulation of antagonists. Thus, the motor evoked potential (MEP) response to TMS in the target muscle compared to its antagonist may be an important parameter in the assessment of VATMS. OBJECTIVE: The purpose of this study was to evaluate the effect of isometric elbow flexion angle on two metrics in individuals with tetraplegia following SCI: 1) the ratio of biceps/triceps MEP amplitude across a range of voluntary efforts, and 2) VATMS. METHODS: Ten individuals with tetraplegia and ten nonimpaired individuals were recruited to participate in three sessions wherein VATMS was assessed at 45°, 90°, and 120° of isometric elbow flexion. RESULTS: In SCI participants, the biceps/triceps MEP ratio was not modulated by elbow angle. In nonimpaired participants, the biceps/triceps MEP ratio was greater in the more flexed elbow angle (120° flexion) compared to 90° during contractions of 50% and 75% MVC, but VATMS was not different. VATMS assessed in the more extended elbow angle (45° flexion) was lower relative to 90° elbow flexion; this effect was dependent on the biceps/triceps MEP ratio. In both groups, VATMS was sensitive to the linearity of the voluntary moment and superimposed twitch relationship, regardless of elbow angle. Linearity was lower in SCI relative to nonimpaired participants. CONCLUSIONS: Increasing the MEP ratio via elbow angle did not enable estimation of VATMS in SCI participants. VATMS may not be a viable approach to assess neuromuscular function in individuals with tetraplegia.

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BACKGROUND: A randomized controlled trial was conducted to analyze the effects of 10 weeks of strength training (ST) on voluntary activation, muscle activity, muscle contractile properties, and spasticity in people with MS. METHODS: 30 participants were randomized to either an experimental [EG] (n = 18) or a control [CG] (n = 12) group. The EG carried out 10-weeks of ST, where the concentric phase was performed at maximum voluntary velocity. Muscle activity of the vastus lateralis (surface electromyography (sEMG) during the first 200 ms of contraction), maximal neural drive (peak sEMG), voluntary activation (central activation ratio), and muscle contractile function (via electrical stimulation) of the knee extensor muscles, as well as spasticity, were measured pre- and post-intervention. RESULTS: The EG showed a significant improvement with differences between groups in muscle activity in EMG0-200 (p = 0.031; ES = -0.8) and maximal neural drive (p = 0.038; ES = -0.8), as well as improvement in the ST group with a trend towards significance in EMG0-100 (p = 0.068; ES = -0.6). CAR increased after intervention in ST group (p = 0.010; ES=-0.4). Spasticity also improved in the ST group, with differences between group after intervention, in first swing excursion (right leg: p = 0.006; ES = -1.4, left leg: p = 0.031; ES = -1.2), number of oscillations (right leg: p = 0.001; ES = -0.4, left leg: p = 0.031; ES = -0.4) and duration of oscillations (left leg: p = 0.002; ES = -0.6). Contractile properties remain unchanged in both ST group and CG. CONCLUSIONS: 10 weeks of ST improves muscle activity during the first 200 ms of contraction, maximal neural conduction, and spasticity in people with MS. However, ST does not produce adaptations in muscle contractile properties in this population.

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BACKGROUND: Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction (ACLR). Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio (CAR) derived from the burst superimposition technique, as well as by using different types of electrical stimulators and pulse train conditions. However, it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR. This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature. METHODS: Quadriceps strength and voluntary activation were examined in 18 ACLR participants (12 quadriceps/patellar tendon graft, 6 hamstring tendon graft; time since ACLR: 1.06 ± 0.82 years, mean ±  SD) at 90° of knee flexion using 2 stimulators (Digitimer and Grass) and pulse train conditions (3-pulse and 10-pulse). Voluntary activation was quantified by calculating both CAR and percent activation. RESULTS: Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation (p < 0.001). Voluntary activation estimates were not affected by pulse train conditions when using percent activation; however, 3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR (p = 0.003). Voluntary activation did not differ between stimulators (p > 0.05); however, the Digitimer evoked greater torque at rest than the Grass (p < 0.001). CONCLUSION: These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.

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CONTEXT: Lesser hip muscle strength is commonly observed in females with patellofemoral pain (PFP) compared with females without PFP and is associated with poor subjective function and single-leg squat (SLS) biomechanics. Hip muscle weakness is theorized to be related to PFP, suggesting centrally mediated muscle inhibition may influence the observed weakness. The central activation ratio (CAR) is a common metric used to quantify muscle inhibition via burst superimposition. However, gluteal inhibition has yet to be evaluated using this approach in females with PFP. The study objectives are to (1) describe gluteal activation in the context of subjective function, hip strength, and squatting biomechanics and (2) examine the relationship of gluteal activation with subjective function and squatting biomechanics in females with PFP. DESIGN: Cross-sectional. METHODS: Seven females with PFP (age = 22.8 [3.6] y; mass = 69.4 [18.0] kg; height = 1.67 [0.05] m, duration of pain = 6-96 mo) completed this study. Subjective function was assessed with the Anterior Knee Pain Scale, while fear-avoidance beliefs were assessed with the Fear-Avoidance Belief Questionnaire physical activity and work subscales. Biomechanical function was assessed with peak hip and knee angles and moments in the sagittal and frontal planes during SLS. Gluteus medius (GMed) and gluteus maximus (GMax) activation were assessed with the CAR. Descriptive statistics were calculated, and relationships between variables were assessed with Spearman rho correlations. RESULTS: The CAR of GMed and GMax was 90.5% (8.1%) and 84.0% (6.3%), respectively. Lesser GMed CAR was strongly associated with greater hip adduction during SLS (ρ = -.775, P = .02) and greater fear-avoidance beliefs-physical activity subscale (ρ = -.764, P = .018). CONCLUSION: We found a wide range in GMed and GMax activation across females with PFP. Lesser GMed activation was associated with greater hip adduction during SLS and fear of physical activity, suggesting that gluteal inhibition should be assessed in patients with PFP.

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Voluntary activation (VA) is measured by applying supramaximal electrical stimulation to a muscle during a maximal voluntary contraction (MVC). The amplitude of the evoked muscle twitch is used to determine any VA deficit, and indicates incomplete central neural drive to the motor units. People with stroke experience VA deficits and greater levels of central fatigue, which is the decrease in VA that occurs following exercise. This study investigated the between-session reliability of VA and central fatigue of the tibialis anterior muscle (TA) in people with chronic stroke (n = 12), using the interpolated twitch technique (ITT), adjusted-ITT, and central activation ratio (CAR) methods. On two separate sessions, supramaximal electrical stimulation was applied to the TA when it was at rest and maximally activated, at the start and end of a 30-s isometric dorsiflexor MVC. The most reliable measures of VA were obtained using the CAR calculation on transformed data, which produced an ICC of 0.92, and a lower bound confidence interval in the good range (95% CI 0.77 to 0.98). Reliability was lower for the CAR calculation on non-transformed data (ICC 0.82, 95% CI 0.63 to 0.91) and the ITT and adjusted-ITT calculations on transformed data (ICCs 0.82, 95% CIs 0.51 to 0.94), which had lower bound confidence intervals in the moderate range. The two ITT calculations on non-transformed data demonstrated the poorest reliability (ICCs 0.62, 95% CI 0.25 to 0.74). Central fatigue measures demonstrated very poor reliability. Thus, the reliability for VA in people with chronic stroke ranged from good to poor, depending on the calculation method and statistical analysis method, whereas the reliability for central fatigue was very poor.

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Lingual weakness frequently occurs after stroke and is associated with deficits in speaking and swallowing. Chronic weakness after stroke has been attributed to both impaired central activation of target muscles and reduced force-generating capacity within muscles. How these factors contribute to lingual weakness is not known. We hypothesized that lingual weakness due to middle cerebral artery occlusion (MCAO) would manifest as reduced muscle force capacity and reduced muscle activation. Rats were randomized into MCAO or sham surgery groups. Maximum volitional tongue forces were quantified 8 wk after surgery. Hypoglossal nerve stimulation was used to assess maximum stimulated force, muscle twitch properties, and force-frequency response. The central activation ratio was determined by maximum volitional/maximum stimulated force. Genioglossus muscle fiber type properties and neuromuscular junction innervation were assessed. Maximum volitional force and the central activation ratio were significantly reduced with MCAO. Maximum stimulated force was not significantly different. No significant differences were found for muscle twitch properties, unilateral contractile properties, muscle fiber type percentages, or fiber size. However, the twitch/tetanus ratio was significantly increased in the MCAO group relative to sham. A small but significant increase in denervated neuromuscular junctions (NMJs) and fiber-type grouping occurred in the contralesional genioglossus. Results suggest that the primary cause of chronic lingual weakness after stroke is impaired muscle activation rather than a deficit of force-generating capacity in lingual muscles. Increased fiber type grouping and denervated NMJs in the contralesional genioglossus suggest that partial reinnervation of muscle fibers may have preserved force-generating capacity, but not optimal activation patterns.NEW & NOTEWORTHY Despite significant reductions in maximum volitional forces, the intrinsic force-generating capacity of the protrusive lingual muscles was not reduced with unilateral cerebral ischemia. Small yet significant increases in denervated NMJs and fiber-type grouping of the contralesional genioglossus suggest that the muscle underwent denervation and reinnervation. Together these results suggest that spontaneous neuromuscular plasticity was sufficient to prevent atrophy, yet central activation deficits remain and contribute to chronic lingual weakness after stroke.

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CONTEXT: Patellofemoral pain (PFP) is often categorized by researchers and clinicians using subjective self-reported PFP characteristics; however, this practice might mask important differences in movement biomechanics between PFP patients. OBJECTIVE: To determine whether biomechanical differences exist during a high-demand multiplanar movement task for PFP patients with similar self-reported PFP characteristics but different quadriceps activation levels. DESIGN: Cross-sectional design. SETTING: Biomechanics laboratory. PARTICIPANTS: A total of 15 quadriceps deficient and 15 quadriceps functional (QF) PFP patients with similar self-reported PFP characteristics. INTERVENTION: In total, 5 trials of a high-demand multiplanar land, cut, and jump movement task were performed. MAIN OUTCOME MEASURES: Biomechanics were compared at each percentile of the ground contact phase of the movement task (α = .05) between the quadriceps deficient and QF groups. Biomechanical variables included (1) whole-body center of mass, trunk, hip, knee, and ankle kinematics; (2) hip, knee, and ankle kinetics; and (3) ground reaction forces. RESULTS: The QF patients exhibited increased ground reaction force, joint torque, and movement, relative to the quadriceps deficient patients. The QF patients exhibited: (1) up to 90, 60, and 35 N more vertical, posterior, and medial ground reaction force at various times of the ground contact phase; (2) up to 4° more knee flexion during ground contact and up to 4° more plantarflexion and hip extension during the latter parts of ground contact; and (3) up to 26, 21, and 48 N·m more plantarflexion, knee extension, and hip extension torque, respectively, at various times of ground contact. CONCLUSIONS: PFP patients with similar self-reported PFP characteristics exhibit different movement biomechanics, and these differences depend upon quadriceps activation levels. These differences are important because movement biomechanics affect injury risk and athletic performance. In addition, these biomechanical differences indicate that different therapeutic interventions may be needed for PFP patients with similar self-reported PFP characteristics.

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OBJECTIVES: To investigate the effects of acute branched-chain amino acid (BCAA) supplementation on cycling performance and neuromuscular fatigue during a prolonged, self-paced cycling time-trial. DESIGN: Randomised double-blind counterbalanced crossover. METHODS: Eighteen recreationally active men (mean±SD; age: 24.7±4.8 years old; body-weight, BW: 67.1±6.1kg; height: 171.7±4.9cm) performed a cycling time-trial on an electromagnetically-braked cycle ergometer. Participants were instructed to complete the individualised total work in the shortest time possible, while ingesting either BCAAs (pre-exercise: 0.084gkg-1 BW; during exercise: 0.056gkg-1h-1) or a non-caloric placebo solution. Rating of perceived exertion, power, cadence and heart rate were recorded throughout, while maximal voluntary contraction, muscle voluntary activation level and electrically evoked torque using single and doublet stimulations were assessed at baseline, immediately post-exercise and 20-min post-exercise. RESULTS: Supplementation with BCAA reduced (287.9±549.7s; p=0.04) time-to-completion and ratings of perceived exertion (p≤0.01), while concomitantly increasing heart rate (p=0.02). There were no between-group differences (BCAA vs placebo) in any of the neuromuscular parameters, but significant decreases (All p≤0.01) in maximal voluntary contraction, muscle voluntary activation level and electrically evoked torque (single and doublet stimulations) were recorded immediately following the trial, and these did not recover to pre-exercise values by the 20min recovery time-point. CONCLUSIONS: Compared to a non-caloric placebo, acute BCAA supplementation significantly improved performance in cycling time-trial among recreationally active individuals without any notable changes in either central or peripheral factors. This improved performance with acute BCAA supplementation was associated with a reduced rating of perceived exertion.

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The objective of this study was to investigate the immediate effects of electroacupuncture and manual acupuncture on hip flexion range of motion (ROM), knee joint (flexion replication at 15° and 45°) and quadriceps (strength and activation) function. Forty-five neurologically healthy adults participated in this randomized controlled laboratory study. Straight leg raise test, modified Thomas test, and hip abductors strength test were performed to determine acupoints. Afterwards, one of three 15-min treatments (control-no treatment, electroacupuncture, or manual acupuncture) was randomly applied using determined acupoints. Measurements (hip flexion ROM, and knee joint and quadriceps function) were recorded at baseline, and at 0, 20, and 40 min post treatment. Both electroacupuncture (4.0°, ES = 0.41) and manual acupuncture (5.4°, ES = 0.95) treatment immediately increased hip flexion ROM, and the increased values persisted for 40-min (p = 0.01). Knee flexion replication (at 15°: p = 0.17; 45°: p = 0.19) and quadriceps activation (p = 0.71) did not change at any of the time points. Post-treatment, both electroacupuncture and manual acupuncture decreased quadriceps strength at 0-min (electroacupuncture: 9.2%, p < 0.0001, ES = 0.60) and 40-min (electroacupuncture: 7.3%, p = 0.005, ES = 0.55; manual acupuncture: 8.7%, p = 0.01, ES = 0.54). A single session of either electroacupuncture or manual acupuncture treatment (selected acupoints based on physical examination) may immediately improve joint flexibility but reduce muscle strength.

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Persistent quadriceps strength deficits in individuals with anterior cruciate ligament reconstruction (ACLr) have been attributed to arthrogenic muscle inhibition (AMI). The purpose of the present study was to investigate the effect of vibration-induced hamstrings fatigue on AMI in patients with ACLr. Eight participants with unilateral ACLr (post-surgery time: M = 46.5, SD = 23.5 months; age: M = 21.4, SD = 1.4 years) and eight individuals with no previous history of knee injury (age: M = 22.5, SD = 2.5 years) were recruited. A fatigue protocol, consisting of 10 min of prolonged local hamstrings vibration, was applied to both the ACLr and control groups. The central activation ratio (CAR) of the quadriceps was measured with a superimposed burst of electrical stimulation, and hamstrings/quadriceps coactivation was assessed using electromyography (EMG) during isometric knee extension exercises, both before and after prolonged local vibration. For the ACLr group, the hamstrings strength, measured by a load cell on a purpose-built chair, was significantly (P = 0.016) reduced about 14.5%, indicating fatigue was actually induced in the hamstrings. At baseline, the ACLr group showed a trend (P = 0.051) toward a lower quadriceps CAR (M = 93.2%, SD = 6.2% versus M = 98.1%, SD = 1.1%) and significantly (P = 0.001) higher hamstrings/quadriceps coactivation (M = 15.1%, SD = 6.2% versus M = 7.5%, SD = 4.0%) during knee extension compared to the control group. The fatigue protocol significantly (P = 0.001) increased quadriceps CAR (from M = 93.2%, SD = 6.2% to M = 97.9%, SD = 2.8%) and significantly (P = 0.006) decreased hamstrings/quadriceps coactivation during knee extension (from M = 15.1%, SD = 6.2% to M = 9.5%, SD = 4.5%) in the ACLr group. In conclusion, vibration-induced hamstrings fatigue can alleviate AMI of the quadriceps in patients with ACLr. This finding has clinical implications in the management of recovery for ACLr patients with quadriceps strength deficits and dysfunction.

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The effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON; 18 °C), hot (HOT; 35 °C), and HOT with head and neck cooling (HOTcooling). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOTcooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C; P < 0.05). Head and neck thermal sensation was similar in HOTcooling (4.2 ± 1.4) and CON (4.4 ± 0.9; P > 0.05) but lower than HOT (5.9 ± 1.5; P < 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P < 0.05). MVF and CAR were also lower in HOTcooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P > 0.05). Furthermore, they were greater in HOTcooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.

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CONTEXT: While arthrogenous muscle inhibition associated with knee injuries is evident, the relative magnitude of functional deficiency related to each individual knee pathology is unclear. OBJECTIVE: To compare the knee joint and quadriceps dysfunction among patients with anterior knee pain (AKP) without surgical history and those with surgical history (anterior cruciate ligament reconstruction [ACLR]; meniscus surgery) without current AKP, with matched healthy controls. DESIGN: Cross-sectional study. SETTING: Laboratory. PARTICIPANTS: A total of 66 patients with knee pathologies and 30 controls. MAIN OUTCOME MEASURES: Pain perception and lower-extremity functional outcomes were assessed. Knee joint function was measured by replication tests. Quadriceps function was measured by strength, voluntary activation, and torque-generating capacity. RESULTS: Patients with AKP reported greater pain perception compared with the other knee conditions (4.3 vs 0.1 of 10 in Numeric Pain Rating Scale, P < .0001). Compared with the controls: (1) patients with AKP showed a greater error on knee-flexion replications at 75° (2.9° vs 5.4°, P = .002), (2) patients with AKP and ACLR showed less quadriceps strength (AKP: 3.3 vs 2.6 N·m/kg, P = .002; ACLR: 3.3 vs 2.7 N·m/kg, P = .02) and voluntary activation (AKP: 0.982 vs 0.928, P < .0001; ACLR: 0.982 vs 0.946, P = .003), and (3) all knee pathologies reported lower scores on functional outcomes (79 vs 65 of 80 points in Lower-Extremity Functional Scale, P < .0001) and showed less quadriceps torque-generating capacity (10.7 vs 7.8 N·m/s/kg, P < .0001). Among the knee pathologies, patients with AKP showed less quadriceps voluntary activation compared with the patients with meniscus surgery (0.928 vs 0.964, P = .03). CONCLUSION: As patients with AKP had an additional impairment in knee joint flexion replications and reported a less score in functional outcomes, knee pain may produce a greater impact on functional deficiency.

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CONTEXT:: Quadriceps function is a significant contributor to knee joint health that is influenced by central and peripheral factors, especially after anterior cruciate ligament reconstruction (ACLR). OBJECTIVE:: To assess differences of unilateral quadriceps isometric strength and activation between the involved limb and contralateral limb of individuals with ACLR and healthy controls. DATA SOURCES:: Web of Science, SportDISCUS, PubMed, CINAHL, and the Cochrane Database were all used during the search. STUDY SELECTION:: A total of 2024 studies were reviewed. Twenty-eight studies including individuals with a unilateral history of ACLR, isometric knee extension strength normalized to body mass, and quadriceps activation measured by central activation ratios (CARs) through a superimposed burst technique were identified for meta-analysis. The methodological quality of relevant articles was assessed using a modified Downs and Black scale. Results of methodological quality assessment ranged from low to high quality (low, n = 10; moderate, n = 8; high, n = 10). STUDY DESIGN:: Meta-analysis. LEVEL OF EVIDENCE:: Level 2. DATA EXTRACTION:: Means, standard deviations, and sample sizes were extracted from articles, and magnitude of between-limb and between-group differences were evaluated using a random-effects model meta-analysis approach to calculate combined pooled effect sizes (ESs) and 95% CIs. ESs were classified as weak ( d < 0.19), small ( d = 0.20-0.49), moderate ( d = 0.50-0.79), or large ( d > 0.80). RESULTS:: The involved limb of individuals with ACLR displayed lower knee extension strength compared with the contralateral limb (ES, -0.78; lower bound [LB], -0.99; upper bound [UB], -0.58) and healthy controls (ES, -0.76; LB, -0.98; UB, -0.53). The involved limb displayed a lower CAR compared with healthy controls (ES, -0.84; LB, -1.18; UB, -0.50) but not compared with the contralateral limb (ES, -0.15; LB, -0.37; UB, 0.07). The ACLR contralateral limb displayed a lower CAR (ES, -0.73; LB, -1.39; UB, -0.07) compared with healthy control limbs but similar knee extension strength (ES, -0.24; LB, -0.68; UB, -0.19). CONCLUSION:: Individuals with ACLR have bilateral CAR deficits and involved limb strength deficits that persist years after surgery. Deficits in quadriceps function may have meaningful implications for patient-reported and objective outcomes, risk of reinjury, and long-term joint health after ACLR.

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OBJECTIVE: Fibromyalgia (FM) is characterized by widespread muscle pain and central neural deregulation. Previous studies showed increased muscle fiber conduction velocity (CV) in non-painful muscles of FM patients. This study investigates the relationship between central activation and the CV in FM. METHODS: Twenty-two females with primary FM and 21 controls underwent surface electromyography of the non-painful biceps brachii. Mean CVs were calculated from the motor unit potential velocities (CV-MUPs), and the CV-MUPs' statistical distributions were presented as histograms. The amount of muscle activity (average rectified voltage, ARV) was measured. RESULTS: The CV was higher in the FM-group than in the controls (P = 0.021), with CV-MUPs generally shifted to higher values, indicative of increased muscle membrane propagation speeds. The largest increase in the CV of the FM-group occurred when adopting and maintaining a limb position at only 5% of maximum strength (P < 0.001); the CV did not, as normal, increase with greater force. However, the ARV in both groups similarly increased with force. CONCLUSIONS: In fibromyalgia patients, the muscle membrane propagation speed increases independently of the force load or amount of muscle activity produced. When adopting a limb position, the patients show an augmented muscle membrane reaction, suggesting deregulation from higher neural centers. SIGNIFICANCE: These findings contribute to understanding fibromyalgia.

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