Head Of Muscle Research Articles

Differences in the recruitment properties of the corticospinal pathway between the biceps femoris and rectus femoris muscles

The neuromuscular activity in the hamstring and quadriceps muscles is vital for rapid force control during athletic movements. This study aimed to investigate the recruitment properties of the corticospinal pathway of the biceps femoris long head (BFlh) and rectus femoris (RF) muscles. Thirty-two male subjects were participated in this study. Corticospinal excitability was investigated for BFlh and RF during the isometric knee flexion and extension tasks, respectively, using transcranial magnetic stimulation. A sigmoidal relationship was observed between the stimulus intensity and amplitude of motor-evoked potentials and characterized by a plateau value, maximum slope, and threshold. Compared with RF, BFlh had a significantly lower plateau value (P < 0.001, d = 1.17), maximum slope (P < 0.001, r = 0.79), and threshold (P = 0.003, d = 0.62). The results showed that the recruitment properties of the corticospinal pathway significantly differ between BFlh and RF. These results reveal that when a sudden large force is required during athletic movements, the RF can produce force through a rapid increase in the recruitment of motor units. The BFlh, on the other hand, requires larger or more synchronized motor commands for enabling the proper motor unit behavior to exert large forces. These differences in the neurophysiological factors between the hamstrings and quadriceps can have a substantial effect on the balance of force generation during athletic activities.

The Human Neck is Part of the Musculoskeletal Core: Cervical Muscles Help Stabilize the Pelvis During Running and Jumping.

SynopsisDuring locomotion, cervical muscles must be active to stabilize the head as the body accelerates and decelerates. We hypothesized that cervical muscles are also part of the linked chain of axial muscles that provide core stabilization against torques applied to the hip joint by the extrinsic muscles of the legs. To test whether specific cervical muscles play a role in postural stabilization of the head and/or core stabilization of the pelvic girdle, we used surface electromyography to measure changes in muscle activity in response to force manipulations during constant speed running and maximum effort counter-movement jumps. We found that doubling the mass of the head during both running and maximum effort jumping had little or no effect on (1) acceleration of the body and (2) cervical muscle activity. Application of horizontal forward and rearward directed forces at the pelvis during running tripled mean fore and aft accelerations, thereby increasing both the pitching moments on the head and flexion and extension torques applied to the hip. These manipulations primarily resulted in increases in cervical muscle activity that is appropriate for core stabilization of the pelvis. Additionally, when subjects jumped maximally with an applied downward directed force that reduced acceleration and therefore need for cervical muscles to stabilize the head, cervical muscle activity did not decrease. These results suggest that during locomotion, rather than acting to stabilize the head against the effects of inertia, the superficial muscles of the neck monitored in this study help to stabilize the pelvis against torques imposed by the extrinsic muscles of the legs at the hip joint. We suggest that a division of labor may exist between deep cervical muscles that presumably provide postural stabilization of the head versus superficial cervical muscles that provide core stabilization against torques applied to the pelvic and pectoral girdles by the extrinsic appendicular muscles.

Role of Ras‐related C3 botulinum toxin substrate (Rac2) in northern snakehead ( Channa argus ) resistance to Aeromonas veronii infection

Ras-related C3 botulinum toxin substrate protein (Rac2) is an important member of the Ras family. Rac has a variety of biological functions and is closely connected with cytoskeleton formation, cell signal transduction, cell adhesion and cell apoptosis. In this study, to investigate the function of northern snakehead (Channa argus) Rac2, the full-length cDNA sequence of the Rac2 gene was obtained by RACE based on a differentially expressed Rac2 gene fragment from a SSH cDNA library of northern snakehead head kidney established in a previous study, and its physicochemical properties, protein structure and amino acid homology were analysed by bioinformatics methods. Real-time fluorescence quantitative PCR was used to analyse the expression and distribution of the Rac2 gene in different tissues of northern snakehead and the changes in its expression after infection with Aeromonas veronii. The results showed that the full-length cDNA sequence of the Rac2 gene was 1179 bp, and its ORF (579 bp) encoded 192 amino acids. Amino acid alignments showed that the Rac2 sequences of different species were highly homologous. Real-time fluorescence quantitative PCR analysis showed that the Rac2 gene was expressed in the head kidney, kidney, gill, heart, spleen, liver and muscle, but not in the midgut, of healthy northern snakehead. After infection with Aeromonas veronii, the expression level of Rac2 in different tissues of northern snakehead varied with the time after infection, but in most tissues, Rac2 was upregulated at 36 h after infection. These changes suggested that Rac2 might play an important role in the immune response of northern snakehead against pathogens. The results lay a foundation for further study of the molecular mechanism of northern snakehead immunity against pathogen infection and provide data to support future breeding of related disease-resistant varieties and disease control.

Determining voluntary activation in synergistic muscles: a novel mechanomyographic approach

PurposeDrawing on correlations between the mechanomyographic (MMG) and the force signal, we devised a novel approach based on MMG signal analysis to detect voluntary activation (VA) of the synergistic superficial heads of the quadriceps muscle. We hypothesized that, after a fatiguing exercise, the changes in the evoked MMG signal of each quadriceps head would correlate with the changes in the level of VA in the whole quadriceps.MethodsTwenty-five men underwent a unilateral single-leg quadriceps exercise to failure. Before and after exercise, VA was assessed by interpolated-twitch-technique via nerve stimulation during and after maximum voluntary contraction (MVC). The force and MMG signal were recorded from vastus lateralis, vastus medialis, and rectus femoris. The MMG peak-to-peak was calculated and the voluntary activation index (VAMMG), defined as the superimposed/potentiated MMG peak-to-peak ratio, was determined from the MMG signal for each head.ResultsVAMMG presented a very high intraclass correlation coefficient (0.981–0.998) and sensitivity (MDC95%: 0.42–6.97%). MVC and VA were decreased after exercise in both the exercising [MVC:−17(5)%, ES −0.92; VA: −7(3)%, ES −1.90] and the contralateral limb [MVC: −9(4)%, ES −0.48; VA: −4(1)%, ES −1.51]. VAMMG was decreased in both the exercising [~ −9(6)%, ES −1.77] and contralateral limb [~ −3(2)%, ES −0.57], with a greater decrease in VAMMG noted only in the vastus medialis of the exercising limb. Moderate-to-very high correlations were found between VAMMG and VA (R-range: 0.503–0.886) before and after exercise.ConclusionVAMMG may be implemented to assess VA and provide further information when multiple synergistic muscle heads are involved in fatiguing exercises.

Common fibular nerve palsy due to fabella compression: An illustrative case report

BackgroundThe fabella is a sesamoid bone situated in the tendon of the lateral head of the gastrocnemius muscle behind the lateral femoral condyle. Common fibular nerve injury may occur anywhere on its course and the most common etiology remains compression at the level of the head of the fibula. Compression by a fabella is a very unusual cause of common fibular nerve palsy and only few case reports are described in the literature. We present here an illustrative case. Case DescriptionA 50-year-old female patient presented with a left drop-foot evolving for two weeks without pain or sensory deficit.Clinical examination revealed a paresis of the left foot dorsiflexors muscles (3/5).A compressive neuropathy of the common fibular nerve at the level of the fibula head was demonstrated by nerve conduction studies. Ultrasound of the left knee revealed nerve compression by a fabella. Early decompressive surgery was performed and the fabella was excised. We noticed an almost complete recovery probably due to early treatment (4+/5 two months after surgery). ConclusionsCommon fibular nerve palsy related to fabella compression is very uncommon. Good clinical outcome has been described at 1–2 years with an early work-up and a prompt surgical decompression.

Isometric fascicle behaviour of the biceps femoris long head muscle during Nordic hamstring exercise variations

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

Fatty Gastrocnemius Muscle: A Case Report

BackgroundThe gastrocnemius muscle is a superficial two‐headed muscle located in the posterior compartment of the leg, consisting of two heads: medial head and lateral head. The gastrocnemius muscle plays a significant role in our daily activities because its function is plantar flexing the foot at the ankle joint and flexing the leg at the knee joint. We report a very rare case of fatty gastrocnemius.MethodsThe abnormal gastrocnemius muscles were encountered during the dissection of the lower limbs of a 63‐year‐old female cadaver. For histological examination, muscular samples were sectioned from the top, middle, and bottom of two heads of both legs. A total of six muscular slides, nerve slides, artery slides were all stained with Hematoxylin and Eosin (H&amp;E) stains. Slides were analyzed using light microscopy.ResultFor anatomy analysis, the medial heads of both gastrocnemius muscles of the lower limbs are completely infiltrated by adipose tissue. But the lateral heads of gastrocnemius muscles on both sides are almost healthy. Only the bottom of the lateral head of gastrocnemius muscles shows adipose tissue, but the middle and topdo not. Additionally, the medial heads connect to the tibial nerve and arteries normally. No abnormal adipose tissue was observed in other muscles throughout the body. For histological analysis, the entire medial heads and the bottom lateral heads are replaced by adipose cells, but the middle and top of the lateral heads are healthy muscle cells. No abnormalities or pathologies were observed in the nerves or arteries.ConclusionBoth medial heads of the gastrocnemius muscle appear to have become adipose tissue. While no underlying cause was identified it appears the pathology was spreading to the medial head.

Accessory Head(s) of the Palmaris Longus Muscle in an 86 Year‐Old White Female Cadaver and an 81 Year‐Old White Male Cadaver

It is known that the palmaris longus muscle is one of the most variable muscles in the human body. The palmaris longus muscle has a high morphological diversity and variations are frequently reported in the literature. Recognizing anatomical variation in the palmaris longus muscle and tendon is important for clinical associations such as neurovascular entrapment and compression, as well as tendon graft and transfer for reconstruction. While neglecting to identify palmaris longus variations rarely leads to an increase in mortality, it is essential to identify for clinical relevance. During anatomical dissection of fifty cadavers in the 2020 undergraduate first‐year anatomy course at the Uniformed Services University of Health Sciences (USUHS), we found two separate cases of accessory heads of the palmaris longus muscle. The first case involved a preserved 86‐year‐old White Female who had one unilateral accessory head of the left palmaris longus muscle. The second case involved a preserved 81‐year‐old White Male who had a unilateral pair of accessory heads of the right palmaris longus muscle.

Design of a control framework for lower limb exoskeleton rehabilitation robot based on predictive assessment

BackgroundPatients suffering from lower limb dyskinesia, especially in early stages of rehabilitation, have weak residual muscle strength in affected limb and require passive training by the lower limb rehabilitation robot. Anatomy indicates that the biceps femoris short head muscle has a strong influence on knee motion at the swing phase of walking. We sought to explore how it would influence on gait cycle in optimization framework. However, the training trajectory of conventional rehabilitation robots performing passive training usually follows gait planning based on general human gait data, which cannot simultaneously ensure both effective rehabilitation of affected limbs with varying severity pathological gait and comfort of the wearer within a safe motion trajectory. MethodsTo elucidate the effects of weakness and contracture, we systematically introduced isolated defects into the musculoskeletal model and generated walking simulations to predict the gait adaptation due to these defects. An impedance control model of the rehabilitation robot is developed. Knee joint parameters optimized by predictive forward dynamics simulation are adopted as the expected values for the robot controller to achieve customized adjustment of the robot motion trajectory. FindingsSevere muscle contracture leads to severe knee flexion; severe muscle weakness induces a significant posterior tilt of the upper trunk, which hinders walking speed. InterpretationOur simulation results attempt to reveal pathological gait features, which may help to reproduce the simulation of pathological gait. Furthermore, the robot simulation results show that the robot system achieves a speedy tracking by setting a larger stiffness value. The model also allows the implementation of different levels of damping or elasticity effects.Trial registration: The method proposed in this paper is an initial basic study that did not reach clinical trials and therefore retains retrospectively registered.

Triceps and cutaneous radial nerve branches investigated via an axillary anterior arm approach: new findings in a fresh-cadaver anatomical study.

The authors sought to describe the anatomy of the radial nerve and its branches when exposed through an axillary anterior arm approach. Bilateral upper limbs of 10 fresh cadavers were dissected after dyed latex was injected into the axillary artery. Via the anterior arm approach, all triceps muscle heads could be dissected and individualized. The radial nerve overlaid the latissimus dorsi tendon, bounded by the axillar artery on its superior surface, then passed around the humerus, together with the lower lateral arm and posterior antebrachial cutaneous nerve, between the lateral and medial heads of the triceps. No triceps motor branch accompanied the radial nerve's trajectory. Over the latissimus dorsi tendon, an antero-inferior bundle, containing all radial nerve branches to the triceps, was consistently observed. In the majority of the dissections, a single branch to the long head and dual innervations for the lateral and medial heads were observed. The triceps long and proximal lateral head branches entered the triceps muscle close to the latissimus dorsi tendon. The second branch to the lateral head stemmed from the triceps lower head motor branch. The triceps medial head was innervated by the upper medial head motor branch, which followed the ulnar nerve to enter the medial head on its anterior surface. The distal branch to the triceps medial head also originated near the distal border of the latissimus dorsi tendon. After a short trajectory, a branch went out that penetrated the medial head on its posterior surface. The triceps lower medial head motor branch ended in the anconeus muscle, after traveling inside the triceps medial head. The lower lateral arm and posterior antebrachial cutaneous nerve followed the radial nerve within the torsion canal. The lower lateral brachial cutaneous nerve innervated the skin over the biceps, while the posterior antebrachial cutaneous nerve innervated the skin over the lateral epicondyle and posterior surface of the forearm. The average numbers of myelinated fibers were 926 in the long and 439 in the upper lateral head and 658 in the upper and 1137 in the lower medial head motor branches. The new understanding of radial nerve anatomy delineated in this study should aid surgeons during reconstructive surgery to treat upper-limb paralysis.

Effect of high intensity laser in the treatment of myofascial trigger points in symptomatic knee osteoarthritis: A randomized single-blinded controlled trial

Background: Osteoarthritis (OA) is one of the most prevalent causes of musculoskeletal pain and disability among the middle age and elderly population. It significantly affects the overall quality of life of the affected individuals. Objectives: To find out the impact of high intensity laser therapy (HILT) on myofascial trigger points (MTrPs) in symptomatic knee OA. Methods: This is a single-blinded pre–post randomized experimental trial. A total of 40 patients, both male and female, falling within the age group of 35-55 years, BMI 25–29.9 Kg/Cm2, diagnosed with bilateral knee osteoarthritis (grade 2), were recruited as participants of the study. All the participants were clinically evaluated for the signs and symptoms of myofascial pain, tenderness over the vastus medialis muscle and the medial head of the gastrocnemius muscle. The participants were randomly allocated into two groups with n=20 in each group. The participants of the experimental group received high-power laser therapy and underwent exercises on the MTrPS of the vastus medialis and the medial head of the gastrocnemius muscle. The participants of the control group received placebo laser "sham laser" and underwent exercises for the vastus medialis and the medial head of the gastrocnemius muscle. A blood cortisol level test, pressure algometer, digital electronic goniometer, and the KOOS-PS questionnaire were used to measure the pain level, pain threshold, knee ROM, and knee function. Outcome assessment was done at Day 0 and post intervention at the end of 4 weeks. Results: The MANOVA test revealed that both groups improved significantly in all parameters at week 4, with the HILT group improving more than the sham group in blood cortisol levels, pressure algometer measures, knee passive ROM, and KOOS scores (P &lt; .05). Conclusion: HILT is an efficient approach in the treatment of MTrPs in knee OA.

МСКТ-семиотика мышц при хроническом остеомиелите бедра и голени

Introduction It is known that the function and structure of the muscles of the thigh and lower leg are closely related to the function of the lower limb, which is impaired to one degree or another in all patients with chronic osteomyelitis. However, the nature of structural changes in the muscles, which, in turn, affect the condition of the bones, has not been well studied. Purpose of the work To study the features of changes in the muscles of the thigh and lower leg in patients with chronic osteomyelitis according to MSCT data. Material and methods The study is retrospective conducted at a single centre of Evidence level IV. Multislice computed tomography (MSCT) was used in 112 patients with chronic osteomyelitis of long bones of the lower extremities to study the radiological morphology of the muscles of the thigh and lower leg, including density, muscle belly area, and anatomical features. Twenty patients had chronic osteomyelitis in the area of transosseous elements (pins). The mean age of the patients was 48.5 ± 9.8 years. Males prevailed among the patients (87.5 %). The cause of osteomyelitis in 107 cases was trauma or surgery, five patients had consequences of hematogenous osteomyelitis. Results The results of the study showed that the muscles of the thigh and lower leg in patients with chronic osteomyelitis have pronounced dystrophic changes. In 89.4 % of patients, they were manifested by an increase in the density of the anterior tibial muscle, long extensor of the toes (84.7 %), peroneal muscles (78.5 %) and a decrease in the density of the head of the gastrocnemius muscle (91.3 %). In 10.6 % of the patients, there was a decrease in the density of the anterior tibial muscle, the long extensor of the fingers. In all patients with chronic osteomyelitis of the femur, the density of the muscles of the anterior and posterior groups was reduced, except for the musculus vastus intermedius of the thigh that was characterized by fibrotic changes with an increase in density. Conclusion The data obtained indicate that radiological morphological changes in muscles occur in all patients with chronic osteomyelitis of the femur and lower leg. The most pronounced alterations in the architectonics were in the anterior tibial and gastrocnemius muscles, and the intermediate broad muscle of the thigh.

Morphological association between muscle attachments and ossification sites in the late cartilaginous skull of tuatara embryos.

During development, the embryonic cartilaginous skull in most vertebrates is partially replaced by bones with endochondral and perichondral ossifications. Muscle attachments are thought to influence the patterns of ossification and, hence, the differentiation of the skull. To investigate the association between muscle attachments and early ossifications of reptilian embryos, we conducted digital 3D reconstructions of the cranium, the head, and the neck musculature from a histological section series of a late term embryonic tuatara, Sphenodon punctatus, with a total body length of 52 mm. As the sole living rhynchocephalian species, it is an important outgroup in comparative studies of squamate evolution. We found that head and neck muscles are largely associated with early ossification of the basal plate and the palatoquadrate, and with three other ossifications in an older specimen with a total body length of 72 mm. These results suggest that tensile forces resulting from embryonic muscle contraction are largely, but not exclusively, correlated with the area of endochondral ossification in the chondrocranium and palatoquadrate in tuatara. Beyond little-known genetic factors, the complexity of chondrocranial architecture, the progress of its development, and the effect of multiple muscle transmitting forces in the chondrocranium must be considered to provide a more comprehensive discussion of the mechanical properties of the embryonic skull.

Accumulation of some heavy metals in Tenualosa ilisha (Hamilton, 1822) collected from Shatt Al-Arab River

In the present study, the concentrations of various heavy metals including copper, nickel, lead, cadmium, iron and manganese were investigated in several organs (muscles of head, muscles of trunks, muscles of tails, liver, gills, gonads and intestine) of Tenualosa ilisha (Hamilton, 1822) which was collected from Shatt Al-Arab river during the period between February 2013 and September 2013. Heavy metal concentrations were measured by using Flame Atomic Absorption Spectrophotometer. The results of the heavy metals during study period showed that the highest concentration was 41.910 µg/g (dry weight) for iron between February and March, whereas the least concentration was 0.036 µg/g (dry weight) for lead between June and July. Also, they showed that the highest concentration was 27.470 µg/g (dry weight) for iron in liver, whereas the least concentration was 0.003 µg/g (dry weight) for lead in muscles of tails.

P128. POPLITEAL ARTERY ENTRAPMENT SYNDROME: CURRENT CONCEPTS, SURGICAL STRATEGIES, AND LESSONS LEARNED

PURPOSE: Popliteal Artery Entrapment Syndrome (PAES) occurs in younger patients, predominantly female athletes and results in complete popliteal artery occlusion with plantarflexion. It remains an underdiagnosed cause of exercise-induced pain. Our group has been treating this condition for over a decade and we will review our experience, outcomes, complications, and strategies that we have developed to achieve satisfactory outcomes. METHODS: A retrospective chart review is conducted to identify all patients that underwent surgical management for PAES at Boston Children’s Hospital and Beth Israel Deaconess Medical Center since 2010. Patient demographics, patient reported outcome measures, diagnostic workup and intraoperative details, complications and final outcomes are analyzed. RESULTS: A total of 40 consecutive patients underwent surgical decompression for PAES. A vast majority of patients presented with delayed diagnosis and had undergone prior surgery for presumed Exertional Compartment Syndrome. Dynamic ultrasound has been found to be the most reliable diagnostic modality. Intraoperative ultrasound and nerve stimulation have allowed us to delineate key maneuvers that are critical to successful decompression. The most common complication is superficial wound separation. Tibial nerve compression at the soleal sling remains an important differential diagnosis in this patient population. CONCLUSION: The diagnosis of PAES remains challenging due to its rarity and our lack of understanding of its pathophysiology. The management of these patients requires a collaborative multidisciplinary approach. Surgical management includes a thorough dissection of the popliteal fossa with excision of the deep head of the gastrocnemius muscle and plantaris, if present.

Assessment of the effects of foamrolling on the pain threshold in professional basketball players

Background. Auto-massage with the use of special rollers is now a popular form of biological regeneration in sport. The aim of the study was to assess the impact of the proposed scheme (me­thodology) of myofascial auto-release on changes in the pain threshold within selected muscle trigger points in professional basketball players. Material and methods. The research was carried out on 20 basketball players of the 2nd Men's Ba­sketball League. The average age of the respondents was 23.35 ± 4.3 years. The study included 4 training units in one week. Pain sensation threshold was measured using the Pain Test FPX Algometer (Wagner). Measurements were taken on the first and last day of the tests according to the scheme: before and after training, and after rolling. The pain threshold was examined on the following trigger points of the muscles: descending and ascending part of trapezius muscle, levator scapula, rectus femoris muscle, tensor fascia lataeand the medial head of the gastrocnemius muscle. The subjects rolled the areas of ​​the above-mentioned muscles 4 days after training (each time for a total of 10 minutes), according to a standardized schedule. Results and conclusions. Based on the obtained results, it was found that the proposed self-massage regimen performed immediately after basketball training had a significant effect on changes in the pain threshold in some muscle areas. Significant differences were observed on the first day of the study in the descending part of the trapezius muscle and the levator scapulae on the left side (p &lt;0.05). After the entire 4-day rolling session, significant differences were found in the pain threshold on the levator scapulae muscle on both sides of the spine (p = 0.03). An important trend was noted regarding the majority of the examined muscle points, after the self-massage by rolling, the pain threshold increased (muscle pain sensitivity decreased). According to the subjective opinion, the majority of basketball players (90%) consider rolling to be an effective method of post-workout regeneration and see the need for systematic use of this form of auto-massage. According to the vast majority of competitors, the presented method of rolling resulted in an improvement in post-workout regeneration (85%) and a reduction in muscle stiffness (60%). Tissue rolling after exercise seems to be an important complementary approah to biological regeneration in sport.

ASSOCIATIONS BETWEEN QUADRICEPS PASSIVE STIFFNESS AND PATELLOFEMORAL JOINT ALIGNMENTS IN SENIOR ADULTS

Purpose: Patellar malalignments would increase patellofemoral joint (PFJ) stress causing pain and structural changes, which are associated with PFJ osteoarthritis. The individual muscle heads of quadriceps have force vectors pulling the patella to the different directions of translation and rotation. The active contraction of the quadriceps muscle has been known to be crucial for normal patellar tracking. In addition to active tension, increased muscle passive stiffness, characterized by altered elasticity, may also affect patellar positions.

Muscle forces and fascicle behavior during three hamstring exercises.

Knowledge about muscular forces and fascicle behavior during hamstring exercises can optimize exercise prescription, but information on these outcomes across different exercises is lacking. We aimed to characterize and compare lower‐limb muscle forces and biceps femoris long head muscle fascicle behavior between three hamstring exercises: the Nordic hamstring curl (NHC), single‐leg Roman chair (RCH), and single‐leg deadlift (DL). Ten male participants performed the exercises while full‐body kinematics, ground reaction forces, surface muscle activation, and biceps femoris long head fascicle behavior were measured. Mean fascicle length was highest in the DL, followed by the RCH and NHC. Fascicle lengthening was higher in the NHC compared with the RCH and DL, with no difference between the RCH and DL. Biceps femoris short and long head, semitendinosus, and semimembranosus peak forces were generally higher in the NHC compared with the RCH and DL, while mean forces during the eccentric phase were generally not different between the NHC and RCH. Peak forces in the NHC coincided with low biceps femoris long head and semimembranosus muscle activation. The NHC generally has the highest peak hamstring muscle forces and results in more fascicle lengthening when compared to the DL and RCH. The NHC may therefore be most effective to promote increases in fascicle length. While the NHC may be effective to promote biceps femoris short head and semitendinosus strength adaptations, the RCH and DL may be more effective to promote strength increases in the biceps femoris long head and semimembranosus.

The Effect of Axial Compression and Distraction on Cervical Facet Cartilage Apposition During Shear and Bending Motions

During cervical spine trauma, complex intervertebral motions can cause a reduction in facet joint cartilage apposition area (CAA), leading to cervical facet dislocation (CFD). Intervertebral compression and distraction likely alter the magnitude and location of CAA, and may influence the risk of facet fracture. The aim of this study was to investigate facet joint CAA resulting from intervertebral distraction (2.5 mm) or compression (50, 300 N) superimposed on shear and bending motions. Intervertebral and facet joint kinematics were applied to multi rigid-body kinematic models of twelve C6/C7 motion segments (70 ± 13 year, nine male) with specimen-specific cartilage profiles. CAA was qualitatively and quantitatively compared between distraction and compression conditions for each motion; linear mixed-effects models (α = 0.05) were applied. Distraction significantly decreased CAA throughout all motions, compared to the compressed conditions (p < 0.001), and shifted the apposition region towards the facet tip. These observations were consistent bilaterally for both asymmetric and symmetric motions. The results indicate that axial neck loads, which are altered by muscle activation and head loading, influences facet apposition. Investigating CAA in longer cervical spine segments subjected to quasistatic or dynamic loading may provide insight into dislocation and fracture mechanisms.

Difference of Hamstring Activity Between Bilateral and Unilateral Nordic Hamstring Exercises With a Sloped Platform.

This study aimed to examine the differences in electromyographic (EMG) activity of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles, break-point angle (BPA), and the angle at peak BFlh EMG activity between bilateral and unilateral Nordic hamstring exercise (NHE) on a sloped platform. This study was designed as a case-control study. Fourteen men participated in the study. The participants initially performed maximum voluntary isometric contraction (MVIC) on the prone leg curl to normalize the peak hamstring EMG amplitude as the %MVIC. Then, participants were randomized to perform the following 3 variations of NHE: bilateral (N40) or unilateral (N40U) NHE with a platform angle of 40°, and unilateral NHE with a platform angle of 50° (N50U). The EMG activities of the BFlh and ST and the knee flexion angle during the NHE variations were recorded to calculate the EMG activity of the BFlh and ST in terms of the %MVIC, the angle at peak BFlh EMG, and BPA. The BFlh %MVIC was significantly higher in N40U (P < .05) and N50U (P < .05) than in N40. A significant difference in BFlh %MVIC and ST %MVIC was observed between N40U (P < .05) and N50U (P < .05). The mean values of BPA and the angle at peak BFlh EMG were <30° for all NHE variations. In the late swing phase of high-speed running, BFlh showed higher EMG activity; thus, unilateral NHE may be a specific hamstring exercise for hamstring injury prevention.