Individuals with chronic ankle instability show altered regional activation of the peroneus longus muscle during ankle eversion.

Individuals with chronic ankle instability (CAI) present muscular weakness and potential changes in the activation of the peroneus longus muscle, which likely explains the high recurrence of ankle sprains in this population. However, there is conflicting evidence regarding the role of the peroneus longus activity in CAI, possibly due to the limited spatial resolution of the surface electromyography (sEMG) methods (i.e., bipolar sEMG). Recent studies employing high-density sEMG (HD-sEMG) have shown that the peroneus longus presents differences in regional activation, however, it is unknown whether this regional activation is maintained under pathological conditions such as CAI. This study aimed to compare the myoelectric activity, using HD-sEMG, of each peroneus longus compartment (anterior and posterior) between individuals with and without CAI. Eighteen healthy individuals (No-CAI group) and 18 individuals with CAI were recruited. In both groups, the center of mass (COM) and the sEMG amplitude at each compartment were recorded during ankle eversion at different force levels. For the posterior compartment, the sEMG amplitude of CAI group was significantly lower than the No-CAI group (mean difference = 5.6% RMS; 95% CI = 3.4-7.6; p = 0.0001). In addition, it was observed a significant main effect for group (F1,32 = 9.608; p = 0.0040) with an anterior displacement of COM for the CAI group. These findings suggest that CAI alters the regional distribution of muscle activity of the peroneus longus during ankle eversion. In practice, altered regional activation may impact strengthening programs, prevention, and rehabilitation of CAI.

Electromyographic and kinematic parameters of the shoulder in wheelchair rugby players: case reports.

Wheelchair rugby was created as part of the rehabilitation for patients with spinal cord injury. The biomechanical analysis of wheelchair propulsion (WP) in these athletes seems to be a key element to understand the reasons behind musculoskeletal injuries. This case reports study aimed to describe the electromyographic activity and kinematic parameters of the shoulder during the propulsion phases on the wheelchair in two Paralympic rugby players (A1 and A2) with spinal cord injury. Myoelectric activity (three portions of the deltoid, biceps and triceps brachii) and kinematics of the shoulder were assessed during the push (PP) and recovery (RP) phases. These variables were calculated considering ten propulsion cycles by each athlete. The results showed a different muscle activation between players, A1 described a high average amplitude of the anterior deltoid (PP = 58.44 ± 16.35%MVC; RP = 43.16 ± 13.48%MVC) in both propulsion phases, while A2 generated high average activity of triceps brachii (29.28 ± 10.63%MVC) and middle deltoid (46.53 ± 14.48%MVC), during PP and RP, respectively. At the same time, the player with a C7-T1 spinal cord injury (A2) showed a higher range of motion in the three plans, considering both propulsion phases.

Regional changes in muscle activity do not underlie the repeated bout effect in the human gastrocnemius muscle.

The repeated bout effect (RBE) confers protection following exercise-induced muscle damage. Typical signs of this protective effect are significantly less muscle soreness and faster recovery of strength after the second bout. The aim of this study was to compare regional changes in medial gastrocnemius (MG) muscle activity and mechanical hyperalgesia after repeated bouts of eccentric exercise. Twelve healthy male participants performed two bouts of eccentric heel drop exercise (separated by 7 days) while wearing a vest equivalent to 20% of their body weight. High-density MG electromyographic amplitude maps and topographical pressure pain sensitivity maps were created before, two hours (2H), and two days (2D) after both exercise bouts. Statistical parametric mapping was used to identify RBE effects on muscle activity and mechanical hyperalgesia, using pixel-level statistics when comparing maps. The results revealed a RBE, as a lower strength loss (17% less; P < .01) and less soreness (50% less; P < .01) were found after the second bout. However, different muscle regions were activated 2H and 2D after the initial bout but not following the repeated bout. Further, no overall changes in EMG distribution or mechanical hyperalgesia were found between bouts. These results indicate that muscle activation is unevenly distributed during the initial bout, possibly to maintain muscle function during localized mechanical fatigue. However, this does not reflect a strategy to confer protection during the repeated bout by activating undamaged/non-fatigued muscle areas.

Temporal differences in the myoelectric activity of lower limb muscles during rearfoot and forefoot running: A statistical parametric mapping approach.

Forefoot (FF) and rearfoot (RF) running techniques can induce different lower-limb muscle activation patterns. However, few studies have evaluated temporal changes in the electromyographic activity (EMG) of lower limb muscles during running. The aim of this study was to compare temporal changes in EMG amplitude between RF and FF running techniques. Eleven recreational runners ran on a treadmill at a self-selected speed, once using a RF strike pattern and once using a FF strike pattern (randomized order). The EMG of five lower limb muscles [rectus femoris (RFe), biceps femoris (BF), tibialis anterior (TA), medial and lateral gastrocnemius (MG and LG)] was evaluated, using bipolar electrodes. EMG data from the RF and FF running techniques was then processed and compared with statistical parametric mapping (SPM), dividing the analysis of the running cycle into stance and swing phases. The MG and LG muscles showed higher activation during FF running at the beginning of the stance phase and at the end of the swing phase. During the end of the swing phase, the TA muscle's EMG amplitude was higher, when the RF running technique was used. A higher level of co-activation between the gastrocnemius and TA muscles was observed in both stance and swing phases using RF. The myoelectric behaviour of the RFe and BF muscles was similar during both running techniques. The current findings highlight that the two running techniques predominately reflect adjustments of the shank and not the thigh muscles, in both phases of the running cycle.HighlightsStatistical parametric mapping (SPM) can reveal temporal differences in muscle activity between running techniques.The medial and lateral gastrocnemius muscles were more active at specific time-instants of the initial stance and late swing phases during forefoot (FF) running compared to rearfoot (RF) running.Higher activation was observed for the tibialis anterior muscle at the end of the swing phase during RF runningContrary to the muscle activity differences observed in the leg muscles, the muscle activity of the thigh muscles was similar during RF and FF running.

Task-related differences in peroneus longus muscle fiber conduction velocity.

It has been identified that the peroneus longus presents a regional activity. Specifically, a greater activation of the anterior and posterior compartments has been observed during eversion, whereas a lower activation of the posterior compartment has been reported during plantarflexion. In addition to myoelectrical amplitude, motor unit recruitment can be inferred indirectly from muscle fiber conduction velocity (MFCV). However, there are few reports of MFCV of the regions that make up a muscle, and even less, MFCV of the peroneus longus compartments. This study aimed to analyze the MFCV of peroneus longus compartments during eversion and plantarflexion. Twenty-one healthy individuals were assessed. High-density surface electromyography was recorded from the peroneus longus during eversion and plantarflexion at 10%, 30%, 50%, and 70% of maximal voluntary isometric contraction. The posterior compartment presented a lower MFCV than the anterior compartment during plantarflexion, and both compartments did not show differences in MFCV during eversion; however, the posterior compartment showed an increase in MFCV during eversion compared to plantarflexion. Differences observed in the MFCV of the peroneus longus compartments could support a regional activation strategy and, to some extent, explain different motor unit recruitment strategies of the peroneus longus during ankle movements.

Acute Deltoid Injury in Ankle Fractures: A Biomechanical Analysis of Different Repair Constructs.

BACKGROUND: The importance of the deltoid ligament in the congruency and coupling of the tibiotalar joint is well known. The current trend is to repair it in cases of acute injuries in the context of ankle fractures; however, there is limited information on how it should be reconstructed. The objective of this study was to compare different deltoid ligament repair types in an ankle fracture cadaveric model. METHODS: Sixteen cadaveric foot-ankle-distal tibia specimens were used. All samples were prepared as a supination external rotation ankle fracture model. Axial load and cyclic axial rotations were applied on every specimen using a specifically designed frame. This test was performed without deltoid injury, with deltoid injury, and after repair. The reconstruction was performed in 4 different ways (anterior, posterior, middle, and combined). Medial clear space (MCS) was measured for each condition on simulated weightbearing (WB) and gravity stress (GS) radiographs. Reflective markers were used in tibia and talus, registering the kinematics through a motion analysis system to record the tibiotalar uncoupling. RESULTS: After deltoid damage, in all cases the MCS increased significantly on GS radiographs, but there was no increase in the MCS on WB radiographs. After repair, in all cases, the MCS was normalized. Kinematically, after deltoid damage, the tibiotalar uncoupling increased significantly. All isolated repairs achieved a similar tibiotalar uncoupling value as its baseline condition. The combined repair resulted in a significant decrease in tibiotalar uncoupling. CONCLUSION: Our results show that deltoid repair recovers the tibiotalar coupling mechanism in an ankle fracture model. Isolated deltoid repairs recovered baseline MCS and tibiotalar uncoupling values. Combined repairs may lead to overconstraint, which could lead to postoperative stiffness. Clinical studies are needed to prove these results and show clinically improved outcomes. CLINICAL RELEVANCE: This study helps in finding the optimum deltoid repair to use in an acute trauma setting.

Biomechanical Cadaveric Evaluation of the Role of Medial Column Instability in Hallux Valgus Deformity.

BACKGROUND: Medial column instability is a frequent finding in patients with flatfeet and hallux valgus, within others. The etiology of hallux valgus is multifactorial, and medial ray axial rotation has been mentioned as having an individual role. Our objective was to design a novel cadaveric foot model where we could re-create through progressive medial column ligament damage some components of a hallux valgus deformity. METHODS: Ten fresh-frozen lower leg specimens were used, and fluorescent markers were attached in a multisegment foot model. Constant axial load and cyclic tibial rotation (to simulate foot pronation) were applied, including pull on the flexor hallucis longus tendon (FHL). We first damaged the intercuneiform (C1-C2) ligaments, second the naviculocuneiform (NC) ligaments, and third the first tarsometatarsal ligaments, leaving the plantar ligaments unharmed. Bony axial and coronal alignment was measured after each ligament damage. Statistical analysis was performed. RESULTS: A significant increase in pronation of multiple segments was observed after sectioning the NC ligaments. Damaging the tarsometatarsal ligament generated small supination and varus changes mainly in the medial ray. No significant change was observed in axial or frontal plane alignment after damaging the C1-C2 ligaments. The FHL pull exerted a small valgus change in segments of the first ray. DISCUSSION: In this biomechanical cadaveric model, the naviculocuneiform joint was the most important one responsible for pronation of the medial column. Bone pronation occurs along the whole medial column, not isolated to a certain joint. Flexor hallucis longus pull appears to play some role in frontal plane alignment, but not in bone rotation. This model will be of great help to further study medial column instability as one of the factors influencing medial column pronation and its relevance in pathologies like hallux valgus. CLINICAL RELEVANCE: This cadaveric model suggests a possible influence of medial column instability in first metatarsal pronation. With a thorough understanding of a condition's origin, better treatment strategies can be developed.

Location In Vivo of the Innervation Zone in the Human Medial Gastrocnemius Using Imposed Contractions: A Comparison of the Usefulness of the M-Wave and H-Reflex.

The anatomical territory where the neuromuscular junctions are grouped corresponds to the innervation zone (IZ). This can be located in-vivo using high-density electromyography and voluntary muscle contractions. However, in patients with motor impairment, the use of contractions imposed by electrical stimulation (ES) could be an alternative. The present study has two aims: Firstly, to describe the location of the IZ in-vivo of the medial gastrocnemius (MG) using imposed contractions by ES. Secondly, to compare the usefulness of M-waves and H-reflexes to localize the IZs. Twenty-four volunteers participated (age: 21.2 ± 1.5 years). ES was elicited in the tibial nerve to obtain M-waves and H-reflexes in the MG. The evaluators used these responses to localize the IZs relative to anatomical landmarks. M-wave and H-reflex IZ frequency identification were compared. The IZs of the MG were mostly located in the cephalocaudal direction, at 39.7% of the leg length and 34% of the knee's condylar width. The IZs were most frequently identified in the M-wave (83.33%, 22/24) compared to the H-reflex (8.33%, 2/24) (p > 0.001). Imposed contractions revealed that the IZ of the MG is located at 39.7% of the leg length. To locate the IZs of the MG muscle, the M-wave is more useful than the H-reflex.

Contribution of the peroneus longus neuromuscular compartments to eversion and plantarflexion of the ankle.

Compartmentalization of animal and human skeletal muscle by multiple motor nerve branches known as the neuromuscular compartment (NMC) has been observed primarily in muscles that participate in a plane of motion. In this context, the peroneus longus muscle contributes to eversion and plantarflexion of the ankle and the presence of NMCs has been reported. However, no research has reported the selective activation of the compartments of the peroneus longus during the performance of different ankle movements. The purpose of this research was to determine the contribution of peroneus longus NMCs, through multi-channel surface electromyography (sEMG), to eversion and plantarflexion movements. Multi-channel sEMG was recorded from the peroneus longus muscle by using an electrode grid during eversion and plantarflexion of the ankle at 10%, 30%, 50%, and 70% of maximal voluntary isometric contraction (MVIC). The root mean square and displacement of the center of mass position in the X (COMx) and Y (COMy) components were calculated. The primary finding was that eversion showed significantly higher sEMG amplitude than plantarflexion in the posterior compartment in low, moderate, and high percentages of MVIC. However, no significant difference in sEMG amplitude was observed in the anterior compartment between eversion and plantarflexion. In addition, a posterior displacement of the COMx in eversion compared to plantarflexion in all MVIC percentages, with greater topographic distancing of the COMx at higher levels of activation. In conclusion, the peroneus longus muscle presented NMCs; the anterior compartment contributed to both eversion and plantarflexion movements, whereas the posterior compartment mainly contributed to the eversion movement of the ankle in low, moderate, and high percentages of MVIC.

An Isolated Transosseous Flexible Suture Frame in the Treatment of Patellar Tendon Rupture Provides Adequate Mechanical Resistance.

INTRODUCTION: Acute patellar tendon ruptures are frequently observed in patients with metabolic comorbidities, and the benchmark treatment is surgical repair. It is desirable not to harm an already fragile biologic environment with sutures and hardware. We aimed to compare the mechanical requirements of an isolated, flexible, high-strength nonabsorbable transosseous suture frame with that of the Krackow suture technique. METHODS: A total of 12 cadaveric pieces were randomized into two groups: the isolated flexible frame group (n = 6) and the standard Krackow fixation group (n = 6). A traumatic rupture of the patellar tendon was performed, and a transosseous displacement sensor was installed on a validated biomechanical system. Gap formation was measured during 50 cycles of flexion and extension with traction on the quadriceps (250 N). Subsequently, specimens underwent progressive loading in a fixed flexion position until failure occurred. The data were analyzed using nonparametric statistical tools with a significance level of 5%. RESULTS: The isolated frame group had a smaller gap formation (1.7 mm) than the Krackow group (3.4 mm; P = 0.01). No significant difference existed in the median failure end points of the two groups (676 and 530 N, respectively; P = 0.11). DISCUSSION: Patellar tendon repair using an isolated, transosseous, flexible, suture frame outperformed using the traditional Krakow repair technique in gap formation. Further studies are needed to determine if this will result in better functional outcomes or fewer clinical failures. LEVEL OF EVIDENCE: Level IV, experimental case series.

Coordination of the rotational movement of the pelvis and the hip in men without low back pain, with control impairment of the lumbopelvic region in the sagittal plane.

Purpose To assess the presence of control impairment (CI) of the lumbopelvic region in the axial plane in men without low back pain (LBP) with CI in the sagittal plane. Methods : Twenty-four males, between 18 and 23 of age, BMI = normal, who did not report episodes of LBP in the 12 months prior to the study, were studied. Assessment of the sagittal control of the lumbopelvic region was performed during stand to sit. Nine participants demonstrated CI in sagittal plane and 15 did not. An active hip lateral rotation (HLR) test was performed, in which lumbopelvic rotation during HLR was assessed using a three-dimensional motion analysis system. Results : Patients with CI in sagittal plane had a greater percentage of their total lumbopelvic pelvic rotation at 60% of HLR range compared to those without CI (p < 0.05; d = 0.93). No significant differences in the total lumbopelvic and HLR range of motion were found between the groups. Conclusion : Men without LBP who experience CI of the lumbopelvic region in the sagittal plane also show CI in the axial plane. The control deficiencies were not related to the total range of lumbopelvic or HLR range of motion.

Proximal and Distal Failure Site Analysis in Percutaneous Achilles Tendon Rupture Repair.

BACKGROUND: Different techniques have been described for percutaneous Achilles tendon rupture repair, but no biomechanical evaluation has been performed separately for proximal and distal suturing techniques. The purpose of this study was to biomechanically analyze proximal versus distal percutaneous Achilles suture configurations during cyclic loading and load to failure. METHODS: A simulated, midsubstance rupture was created 6 cm proximal to the calcaneal insertion in fresh-frozen cadaveric Achilles tendons. Fifteen proximal specimens were divided into 3 groups: (A1) triple locking technique, (A2) Bunnell-type technique, and (A3) double Bunnell-type technique. Twelve distal specimens were divided into 2 groups: (B1) triple nonlocking technique and (B2) oblique technique. Repairs were subjected to cyclic testing and load to failure. Load to failure, cause of failure, and tendon elongation were evaluated. RESULTS: None of the proximal specimens and 7/12 of the distal ones failed in cyclic testing. The proximal fixation groups demonstrated significantly more strength than the distal groups (P = .001), achieving up to 710 N of failure load in Group A3. Groups B1and B2 failed on average at 380 N with no difference between them (P > .05). The majority of all repairs failed in the suture-tendon interface. Distal groups had more elongation during cyclic testing (13.7 mm) than proximal groups (9.4 mm) (P = .02). CONCLUSION: The distal fixation site in this Achilles tendon repair was significantly weaker than the proximal fixation site. A proximal modified suture configuration increased resistance to cyclic loading and load to failure significantly. CLINICAL RELEVANCE: A modification can be suggested to improve strength of the Achilles repair.

Comparison of total hip arthroplasty surgical approaches by Statistical Parametric Mapping.

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

Use of accelerometers for automatic regional chest movement recognition during tidal breathing in healthy subjects.

Recognition of breathing patterns helps clinicians to understand acute and chronic adaptations during exercise and pathological conditions. Wearable technologies combined with a proper data analysis provide a low cost option to monitor chest and abdominal wall movements. Here we set out to determine the feasibility of using accelerometry and machine learning to detect chest-abdominal wall movement patterns during tidal breathing. Furthermore, we determined the accelerometer positions included in the clusters, considering principal component domains. Eleven healthy participants (age: 21 ±â€¯0.2 y, BMI: 23.4 ±â€¯0.7 kg/m2, FEV1: 4.1 ±â€¯0.3 L, VO2: 4.6 ±â€¯0.2 mL/min kg) were included in this cross-sectional study. Spirometry and ergospirometry assessments were performed with participants seated with 13 accelerometers placed over the thorax. Data collection lasted 10  min. Following signal pre-processing, principal components and clustering analyses were performed. The Euclidean distances in respect to centroids were compared between the clusters (p < 0.05), identifying two clusters (p < 0.001). The first cluster included sensors located at the right and left second rib midline, body of sternum, left fourth rib midline, right and left second thoracic vertebra midline, and fifth thoracic vertebra. The second cluster included sensors at the fourth right rib midline, right and left seventh ribs, abdomen at linea alba, and right and left tenth thoracic vertebra midline. Costal-superior and costal-abdominal patterns were also recognized. We conclude that accelerometers placed on the chest and abdominal wall permit the identification of two clusters of movements regarding respiration biomechanics.

Biomechanical Cadaveric Evaluation of Partial Acute Peroneal Tendon Tears.

BACKGROUND: No clear guideline or solid evidence exists for peroneal tendon tears to determine when to repair, resect, or perform a tenodesis on the damaged tendon. The objective of this study was to analyze the mechanical behavior of cadaveric peroneal tendons artificially damaged and tested in a cyclic and failure mode. The hypothesis was that no failure would be observed in the cyclic phase. METHODS: Eight cadaveric long leg specimens were tested on a specially designed frame. A longitudinal full thickness tendon defect was created, 3 cm in length, behind the tip of the fibula, compromising 66% of the visible width of the peroneal tendons. Cyclic testing was initially performed between 50 and 200 N, followed by a load-to-failure test. Tendon elongation and load to rupture were measured. RESULTS: No tendon failed or lengthened during cyclic testing. The mean load to failure for peroneus brevis was 416 N (95% confidence interval, 351-481 N) and for the peroneus longus was 723 N (95% confidence interval, 578-868 N). All failures were at the level of the defect created. CONCLUSION: In a cadaveric model of peroneal tendon tears, 33% of remaining peroneal tendon could resist high tensile forces, above the physiologic threshold. CLINICAL RELEVANCE: Some peroneal tendon tears can be treated conservatively without risking spontaneous ruptures. When surgically treating a symptomatic peroneal tendon tear, increased efforts may be undertaken to repair tears previously considered irreparable.

Ankle perturbation generates bilateral alteration of knee muscle onset times after unilateral anterior cruciate ligament reconstruction.

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

Effect of M-wave Amplitude on Inter-evaluator Concordance and Number of Detected Innervation Zones in the Medial Gastrocnemius Using Multichannel Electromyography / Efecto de la Amplitud de la Onda M sobre la Concordancia entre Evaluadores y el Número de Zonas de Inervación Detectadas en el Gastrocnemio Medial Mediante Electromiografía Multicanal

SUMMARY: The Innervation Zones (IZ) correspond to clusters of neuromuscular junctions. The traditional method of locating IZs through voluntary muscle contractions may not be feasible in individuals with motor disorders. Imposed contractions by electrostimulation are an alternative. However, there is limited evidence regarding the factors that affect inter-evaluator concordance and the number of localized IZs when using imposed contraction. The main objective of this research was to determine the effect of the amplitude of compound motor action potentials (CMAPs) containing the M-wave on inter-evaluator agreement. As a secondary objective, was investigate the effect on the number of detected IZs. Twenty-four healthy volunteers (age: 21.2 ± 1.5years, weight: 67.4 ± 13.2kg, height: 1.68 ± 0.80m) participated in the study. Electrostimulation was applied to the tibial nerve to induce contraction of the medial gastrocnemius. The IZ were identified based on the M-wave recorded through multichannel electromyography. A receiver operating characteristic (ROC) analysis was conducted to assess sensitivity and specificity in detecting the IZs. Inter-rater agreement was evaluated using a two-way mixed effects test to determine the intraclass correlation coefficients (ICC). A p-value less than 0.05 was considered statistically significant. The ROC analysis revealed that for both evaluators, a specificity of 95% was achieved with an amplitude ≥30 %. The area under the ROC curve was 0.980 [0.964, 0.996], indicating a strong influence of CMAP amplitude on detection of IZs. The highest level of agreement (ICC = 0.788 [0.713, 0.844]) among the evaluators was observed with CMAP amplitudes equal to or greater than 80 % of the maximum M-wave. The findings of this study demonstrate that both the number and the inter-evaluator concordance for detecting IZs using imposed contractions are strongly influenced by the amplitude of the M-wave. Higher M-wave amplitudes were associated with improved concordance and increased IZ detection, making it crucial to standardize amplitude settings for reliable outcomes.

Las Zonas de Inervación (IZ) corresponden a grupos de uniones neuromusculares. El método tradicional para localizar IZs mediante contracciones musculares voluntarias puede no ser factible en personas con trastornos motores. Las contracciones impuestas mediante electro estimulación son una alternativa. Sin embargo, existe poca evidencia sobre los factores que afectan la concordancia entre evaluadores y el número de IZs localizadas al usar este tipo de contracciones. El objetivo de esta investigación fue determinar el efecto de la amplitud de los potenciales de acción motores compuestos (PAMCs) que contienen la onda M sobre la concordancia entre evaluadores. Como objetivo secundario, se investigó el efecto sobre el número de IZs detectadas. Veinticuatro voluntarios sanos (edad: 21.2 ± 1.5 años, peso: 67.4 ± 13.2 kg, altura: 1.68 ± 0.80 m) participaron en el estudio. Se aplicó electroestimulación al nervio tibial para inducir la contracción del gastrocnemio medial. Las IZs se identificaron según la onda M registrada mediante electromiografía multicanal. Se realizó un análisis de curva de las característica del receptor (ROC) para evaluar la sensibilidad y especificidad en la detección de las IZs. La concordancia entre evaluadores se evaluó utilizando una prueba de efectos mixtos de dos vías para determinar los coeficientes de correlación intraclase (ICC). Se consideró un valor de p menor que 0.05 como estadísticamente significativo. El análisis ROC reveló que para ambos evaluadores se logró una especificidad del 95% con una amplitud ≥30 %. El área bajo la curva ROC fue de 0.980 [0.964, 0.996], lo que indica una fuerte influencia de la amplitud del CMAP en la detección de las IZs. El nivel más alto de concordancia (ICC = 0.788 [0.713, 0.844]) entre los evaluadores se observó con amplitudes de CMAP iguales o mayores al 80 % de la onda M máxima. Los hallazgos de este estudio demuestran que tanto el número como la concordancia entre evaluadores para detectar IZs mediante contracciones impuestas están fuertemente influenciados por la amplitud de la onda M. Las amplitudes más altas de la onda M se asociaron con una concordancia mejorada y un aumento en la detección de IZs, lo que hace crucial estandarizar los ajustes de amplitud para obtener resultados confiables.

Spectral components in electromyograms from four regions of the human masseter, in natural dentate and edentulous subjects with removable prostheses and implants.

OBJECTIVE: To compare the frequency or spectral components between different regions of the superficial masseter in young natural dentate and total edentulous older adults rehabilitated with removable prostheses and fixed-implant support. A secondary objective was to compare these components between the three groups. DESIGN: 21 young natural dentate and 28 edentulous (14 with removable prostheses and 14 with fixed-implant support) were assessed. High-density surface electromyography (sEMG) was recorded in four portions of the superficial masseter during submaximal isometric bites. Spectral components were obtained through a spectral analysis of the sEMG signals. An analysis of mixed models was used to compare the spectral components. RESULTS: In all groups, the spectral components of the anterior portion were lower than in the posterior region (p < 0.05). Both edentulous groups showed lower spectral components and median frequency slope than the natural dentate group (p < 0.05). The removable prostheses group showed the greatest differences with natural dentate group. CONCLUSIONS: There were significant differences in the spectral components recorded in the different regions of the superficial masseter. The lower spectral components and fatigability of older adults rehabilitated with prostheses could be a cause of a greater loss of type II fibers, especially in the removable prostheses group.

Changes in the ankle muscles co-activation pattern after 5 years following total ankle joint replacement.

BACKGROUND: The Hintegra® arthroplasty provides inversion-eversion stability, permits axial rotation, ankle flexion-extension, and improvements of the gait patterns are expected up to 12 months of rehabilitation. However, sensorimotor impairments are observed in ankle flexors/extensors muscles after rehabilitation, with potential negative effects on locomotion. Here we determined the timing and amplitude of co-activation of the tibialis anterior and medial gastrocnemius muscles during gait by assessing non-operated and operated legs of patients with total ankle replacement, 5 years after surgery. METHODS: Twenty-nine patients (age: 58 [5.5] years, height: 156.4 [6.5] cm, body mass: 72.9 [6.5] kg, 10 men, and 19 women) that underwent Hintegra® ankle arthroplasty were included. Inclusion criteria included 5 years prosthesis survivorship. The onset and offset of muscle activation (timing), as well as the amplitude of activation, were determined during barefoot walking at self-selected speed by surface electromyography. The timing, percentage, and index of co-activation between the tibialis anterior and medial gastrocnemius were quantified and compared between non-operated and operated legs. FINDINGS: The operated leg showed higher co-activation index and temporal overlapping between tibialis anterior and medial gastrocnemius during gait (p < 0.001). INTERPRETATION: The neuromuscular changes developed during the process of degeneration do not appear to be restored 5 years following arthroplasty. The insertion of an ankle implant may restore anatomy and alignment but neuromuscular adaptations to degeneration are not corrected by 5 years following joint replacement.

Influence of fatigue and velocity on the latency and recruitment order of scapular muscles.

OBJECTIVES: To determine the influence of velocity and fatigue on scapular muscle activation latency and recruitment order during a voluntary arm raise task, in healthy individuals. DESIGN: Cross-sectional study. SETTING: University laboratory. PARTICIPANTS: Twenty three male adults per group (high-velocity and low-velocity). MAIN OUTCOME MEASURES: Onset latency of scapular muscles [Anterior deltoid (AD), lower trapezius (LT), middle trapezius (MT), upper trapezius (UT), and serratus anterior (SA)] was assessed by surface electromyography. The participants were assigned to one of two groups: low-velocity or high-velocity. Both groups performed a voluntary arm raise task in the scapular plane under two conditions: no-fatigue and fatigue. RESULTS: The UT showed early activation (p < 0.01) in the fatigue condition when performing the arm raise task at a high velocity. At a low velocity and with no muscular fatigue, the recruitment order was MT, LT, SA, AD, and UT. However, the recruitment order changed in the high-velocity with muscular fatigue condition, since the recruitment order was UT, AD, SA, LT, and MT. CONCLUSIONS: The simultaneous presence of fatigue and high-velocity in an arm raise task is associated with a decrease in the UT activation latency and a modification of the recruitment order of scapular muscles.