Semitendinosus Research Articles

Biceps femoris muscle-tendon strain during an entire overground sprint acceleration: a biomechanical explanation for hamstring injuries in the acceleration phase

ABSTRACT The objectives of this study were to analyse the peak muscle-tendon (MT) strain of the hamstring during an entire acceleration sprint overground and examine their relationship with relative joint angles and segment orientation in the sagittal plane, which are the direct causes of MT strain. Kinematic data were recorded using a 3D inertial motion capture system in 21 male semi-professional soccer players during 40-metre overground sprint. Scaled musculoskeletal models were used to estimate peak MT strain in the hamstring over 16 steps. Biceps femoris long head (BFLH) exhibited the largest peaks in MT strain compared to semitendinosus (ST) and semimembranosus (SM) muscles across all the steps, with its overall strain decreased as the number of steps and maximum speed increased. Hip flexion angle was found to be a strong predictor (p < 0.001) of joint angles, being the orientation of the pelvis in the sagittal plane of the segment with the greatest influence (p < 0.001) on the peak MT strain of BFLH during sprinting. The current study provides a biomechanical explanation for the high proportion of hamstring injuries in the acceleration phase of sprinting.

129 Evaluating effects of myostatin loss-of-function mutation on piglets for potential causes of early mortality

Abstract Pigs with an engineered myostatin loss-of-function mutation in exon 3 (-1T) experience perinatal mortality of unknown cause. From 36 litters resulting from matings of sows and boars both heterozygous for the mutation, 240 total piglets were born but only 14% (5/35) of piglets with myostatin loss-of-function mutation survived or were viable beyond postnatal d 3. Thus, the objective was to evaluate the effects of this myostatin loss-of-function mutation on piglet organ and muscle development and blood parameters to determine potential causes of this excess mortality. Blood was collected for complete blood count and then piglets (n = 50) were euthanized at postnatal d 3. Piglets were dissected and longissimus muscle, semitendinosus muscle, heart, liver, lungs, kidneys, pancreas, spleen, stomach, small intestine, large intestine, testicles or female reproductive tract, and tongue were weighed. Front girth, back girth, and snout to rump were measured. Loin samples were used to genotype piglets into one of three groups: wild type (WT; unmutated myostatin, n = 13), heterozygous (HET, n = 21) and myostatin mutant (MKO, n = 10). Data were analyzed as a two-way ANOVA using the MIXED procedure of SAS to determine the effect of sex, genotype, and their interaction. Body weight (P = 0.67) and front girth (P = 0.13) were not different between genotypes, but back girth was reduced (P = 0.04) in MKO by 2.3 cm compared with WT and by 2.1 cm compared with HET piglets. MKO piglets had lighter (P ≤ 0.03) hearts, livers, kidneys, pancreases, spleens, stomachs, and small intestine compared with HET and WT piglets, on both an absolute basis and as a percentage of body weight. In general, compared with other other genotypes, MKO organs were 5 to 19% lighter. Surprisingly, muscle weights, both longissimus and semitendinosus muscles, were not different (P ≥ 0.15) between genotypes, either on an absolute basis or as a percentage of body weight. White blood cell count was not different; however, neutrophil count was increased in MKO compared with other genotypes. These data suggest that underdeveloped or undersized organs in MKO piglets may compromise their survivability. Additionally, increased neutrophil counts may be indicative of a stress response in MKO piglets.

Effect of sex and milk replacer with or without supplemental carnitine and arginine on growth characteristics, carcass, and meat quality of artificially reared low-birth weight pigs.

This study compared milk replacer either remaining unsupplemented (CON) or supplemented with 0.5g l-carnitine plus 16.7g l-arginine/kg (CarArg) and fed to 48 L-BtW artificially reared piglets (24 per group) from day 7 to 28 days of age. Eight farrowing series were needed to complete the study. On day 28, the lightest piglets were slaughtered, and the heaviest pigs were weaned. The heaviest pigs were weaned on day 28 and offered free access to a starter (weaning to 25kg body weight (BW)), grower (25-60kg BW), and finisher diet (60kg to 96kg BW on day 170 of age). After euthanization on day 28 and day 170, blood was sampled for assessment of serum metabolite and hormone concentrations, and the semitendinosus muscle (STM) was weighed, and later subjected to enzyme activity analysis and assessment of myofiber characteristics. In the 170-day old pigs carcass and meat quality traits were assessed. Growth data were analyzed as a two-way ANOVA, with dietary treatment and farrowing series as fixed effects, while remaining data were analyzed with dietary treatment, sex, their interaction, and farrowing series as main factors. Dietary treatments affected (P ≤ 0.049) muscle enzyme activity at both day 28, with greater CS and LDH activities and lower HAD:CS ratio in STM light portion, and lower LDH:CS ratio in STM dark portion, and 170 of age with lower HAD:CS ratio. In the starter period, CarArg pigs had greater average daily gain (P = 0.021) and average daily feed intake (P = 0.010). At slaughter, these pigs had lower (P = 0.013) glucose and greater (P = 0.022) urea serum concentrations. However, supplementing the milk replacer with carnitine and arginine had no long-term effects on growth performance, carcass composition, and meat quality of L-BtW pigs. In addition, muscle morphology and its myofiber-related properties remained unaffected by the supplementation.

Surgical treatment of patellar tendon rupture after total knee arthroplasty with a double-row repair method using the hamstring tendons: A novel technique with functional results.

Patellar tendon rupture (PTR) is extremely rare but serious complication after primary or revision total knee arthroplasty. Due to the serious failure rates of end-to-end repair techniques, various augmentation techniques have been described. In this study, the results of patients with PTR after reconstruction using our own technique with semitendinosus (ST) and gracilis tendons taken from the affected side were evaluated retrospectively. A total of 14 patients, whose diagnosis was made based on physical examination and clinical findings, and supported radiologically (ultrasonography), were included in the study. In these patients, reconstruction was performed using double-row repair technique with the ST and gracilis tendons. Active-passive knee joint range of motion, active knee extension loss, and the Caton-Deschamps index at preoperative and final follow-up visits were compared. Tegner-Lysholm knee score and Kujala score were used to evaluate functional results. In 14 patients (8 women and 6 men) with a mean age of 68.1 years, the median time between injury and surgery was 6.6 weeks. In all patients, the rupture was in the distal part of the patellar tendon. While the median preoperative Caton-Deschamps index was 1.8, the postoperative median value was found to be 1.25 after an average follow-up of 3.8 years (P = .014). The median preoperative knee extension loss decreased from 25° to 5° postoperatively. Tegner-Lysholm knee score and Kujala score of the patients at their last follow-up were significantly increased (P < .01). For PTR developing after total knee arthroplasty, the double-row reconstruction technique with ST and gracilis tendons is effective.

Performance, digestibility and meat quality from lambs fed diets with plantago lanceolata, Italian ryegrass or sainfoin herbages.

Plantago species, which is known to adapt to different climatic conditions, drought, temperature and different soil types. The aim of this study was to compare the effects of P. lanceolata herbage on fattening performance, rumen variables, digestibility, meat quality, meat nutrients and meat textural variables in lambs with the values of Italian ryegrass and sainfoin herbages. The lambs were fed total mix ration (TMR) with concentrated feed (about 30%) plus forage (about 70%) (P. lanceolata, PLA, Italian ryegrass (Lolium multiflorum); IRY or sainfoin (Onobrychis viciifolia) herbages, SAI). Twenty-four male lambs (Akkaraman breed) were assigned to three treatments with 8 lambs in each group. Fattening performance parameters, digestibility and carcass variables were determined. Meat quality and shelf life variables (oxidation, fatty acid profile and textural variables) was detected in the loin (Musculus longissimus), shoulder (M. deltoideus) and leg (M. semitendinosus) muscle samples, which were rested for 24 h +4°C and stored at -20°C for one week, one month, three months and six months. The dry matter (DM) intake, body weight gain, feed efficiency and carcass yield values of lambs, the DM and organic matter (OM) digestions (DMD and OMD) of TMRs, and the pH value, ammonia-nitrogen and short chain fatty acid (SCFA) concentrations of rumen fluid in lambs consuming PLA were similar to those of IRY and SAI (p > 0.05). PLA increased water holding capacity (WHC) and decreased cooking loss of meat compared to feeding with those of IRY and SAI (p < 0.05). The peroxide value (PV) and malondialdehyde (MDA) concentration increased with the stocking time in the meats (p < 0.05). Therefore, PV and MDA concentrations of shoulder, leg and loin meats up to 6th months for PLA were lower than those of IRY and SAI (p < 0.05). The linoleic acid concentration of loin and shoulder meats in PLA were higher than those of IRY and SAI (p < 0.05). The average oleic acid and ∑ω6 fatty acids concentration of meat in PLA was lower than those in IRY and SAI (p < 0.05). Atherogenic index and thrombogenic index values and palmitic acid levels of meat in PLA were similar to those in IRY, but lower than those in SAI (p < 0.05). Springiness, cohesiveness, resilience, hardness and chewiness values of the textural analysis parameters in meat of PLA were lower than those of IRY and SAI. As a result, effect of P. lanceolata on the fattening performance and rumen fermentation of lambs were similar with those of Italian ryegrass (Gramineae family) and sainfoin (Leguminosae family) forages and, it had a positive effect on meat quality (water holding capacity, cooking loss) and meat shelf life criteria (MDA, PV, fatty acid profile and textural variables). For functional lamb meat production, P. lanceolata can be included in the diet of lamb fattening.

Derivation and long-term maintenance of porcine skeletal muscle progenitor cells

Culture of muscle cells from livestock species has typically involved laborious enzyme-based approaches that yield heterogeneous populations with limited proliferative and myogenic differentiation capacity, thus limiting their use in physiologically-meaningful studies. This study reports the use of a simple explant culture technique to derive progenitor cell populations from porcine muscle that could be maintained and differentiated long-term in culture. Fragments of semitendinosus muscle from 4 to 8 week-old piglets (n = 4) were seeded on matrigel coated culture dishes to stimulate migration of muscle-derived progenitor cells (MDPCs). Cell outgrowths appeared within a few days and were serially passaged and characterised using RT-qPCR, immunostaining and flow cytometry. MDPCs had an initial mean doubling time of 1.4 days which increased to 2.5 days by passage 14. MDPC populations displayed steady levels of the lineage-specific markers, PAX7 and MYOD, up until at least passage 2 (positive immunostaining in about 40% cells for each gene), after which the expression of myogenic markers decreased gradually. Remarkably, MDPCs were able to readily generate myotubes in culture up until passage 8. Moreover, a decrease in myogenic capacity during serial passaging was concomitant with a gradual increase in the expression of the pre-adipocyte markers, CD105 and PDGFRA, and an increase in the ability of MDPCs to differentiate into adipocytes. In conclusion, explant culture provided a simple and efficient method to harvest enriched myogenic progenitors from pig skeletal muscle which could be maintained long-term and differentiated in vitro, thus providing a suitable system for studies on porcine muscle biology and applications in the expanding field of cultured meat.

Effects of foam rolling on hamstrings stiffness in damaged and non-damaged muscle states.

Introduction: The aim of this study was to examine the effects of foam rolling (FR) on hamstring muscles stiffness in both non-damaged and exercise-induced muscle damage (EIMD) states, using shear wave ultrasound elastography to measure changes in shear modulus. Methods: Fourteen healthy adults (25.5 ± 4.7 years) participated in a within-participant repeated measures design, with a 2-minute FR intervention applied on one leg and contralateral leg serving as a control. The damaging protocol encompassed maximal eccentric knee extensions performed on an isokinetic dynamometer and the Nordic hamstring exercise, consisting of 3 sets of 10 and 6 repetitions, respectively. Measurement were taken at baseline and then 1h, 24h and 48h after the damaging protocol. Results: The results indicated no significant time × leg interaction for shear modulus in biceps femoris, semimembranosus, and semitendinosus muscles in both non-damaged and damaged states. Notably, there was a significant increase in biceps femoris (p = 0.001; η2 = 0.36) and semitendinosus (p < 0.001; η2 = 0.44) shear modulus after EIMD, but no significant differences were found between the FR and control leg, which was also the case for muscle soreness, range of motion, and passive resistive torque (p = 0.239-0.999 for interactions). Discussion: The absence of significant changes post-FR intervention suggests a limited role of short-duration FR in altering muscle stiffness during recovery from EIMD. These findings contribute to the understanding of FR's role in muscle recovery. Although this was not directly investigated, our results suggest a predominance of central mechanisms rather than direct mechanical modifications in muscle properties. This research highlights the necessity for additional investigations to explore how FR interventions influence muscles in different states and to elucidate the mechanisms underlying these influences.

Lysine Distinctively Manipulates Myogenic Regulatory Factors and Wnt/Ca2+ Pathway in Slow and Fast Muscles, and Their Satellite Cells of Postnatal Piglets.

Muscle regeneration, representing an essential homeostatic process, relies mainly on the myogenic progress of resident satellite cells, and it is modulated by multiple physical and nutritional factors. Here, we investigated how myogenic differentiation-related factors and pathways respond to the first limiting amino acid lysine (Lys) in the fast and slow muscles, and their satellite cells (SCs), of swine. Thirty 28-day-old weaned piglets with similar body weights were subjected to three diet regimens: control group (d 0-28: 1.31% Lys, n = 12), Lys-deficient group (d 0-28: 0.83% Lys, n = 12), and Lys rescue group (d 0-14: 0.83% Lys; d 15-28: 1.31% Lys, n = 6). Pigs on d 15 and 29 were selectively slaughtered for muscular parameters evaluation. Satellite cells isolated from fast (semimembranosus) and slow (semitendinosus) muscles were also selected to investigate differentiation ability variations. We found Lys deficiency significantly hindered muscle development in both fast and slow muscles via the distinct manipulation of myogenic regulatory factors and the Wnt/Ca2+ pathway. In the SC model, Lys deficiency suppressed the Wnt/Ca2+ pathways and myosin heavy chain, myogenin, and myogenic regulatory factor 4 in slow muscle SCs but stimulated them in fast muscle SCs. When sufficient Lys was attained, the fast muscle-derived SCs Wnt/Ca2+ pathway (protein kinase C, calcineurin, calcium/calmodulin-dependent protein kinase II, and nuclear factor of activated T cells 1) was repressed, while the Wnt/Ca2+ pathway of its counterpart was stimulated to further the myogenic differentiation. Lys potentially manipulates the differentiation of porcine slow and fast muscle myofibers via the Wnt/Ca2+ pathway in opposite trends.

Novel technique of predicting the dimensions of 5-stranded hamstring grafts for anterior cruciate ligament reconstruction: A descriptive study

BackgroundPrediction of hamstring tendon autografts is essential when planning a ligament reconstruction surgery. This is especially important in cases of multiple ligament reconstruction surgeries. This study was designed to predict the dimensions of 5-stranded hamstring grafts from anthropometric parameters in patients undergoing anterior cruciate ligament (ACL) reconstruction surgery. Methods172 patients undergoing ACL reconstruction with hamstring autografts were included in the study. Preoperative parameters included age, gender, height, weight, body mass index (BMI), thigh length, thigh circumference, and tibia length; intraoperative parameters included semitendinosus (ST) and gracilis (G) length and diameter, final 5-stranded graft length and diameter. Pre-operative data was correlated with intra-operative data using tests of significance. ResultsHeight, tibia and thigh length were greater in males (p < 0.05) whereas BMI was greater in females (p < 0.05). G and ST length alongwith 5-stranded graft length and diameter were significantly greater in males (p < 0.05). The graft dimensions could be correlated with the pre-operative anthropometric parameters using specific equations. This was applicable to the lengths and diameters of ST, G and 5-stranded grafts. We also noted that an increase in age was associated with a reduction in graft dimensions except for the diameter of G graft in females and length of 5-stranded grafts in males. Conclusion5-stranded hamstring graft dimensions can be reliably predicted using anthropometric parameters and this eases surgical planning.

Force Production and Electromyographic Activity during Different Flywheel Deadlift Exercises.

This study aimed to characterize and compare force production and muscle activity during four flywheel deadlift exercises (bilateral [Bi] vs. unilateral [Uni]) with different loading conditions (vertical [Ver] vs. horizontal [Hor]). Twenty-three team-sport athletes underwent assessments for exercise kinetics (hand-grip force), along with surface electromyography (sEMG) of the proximal (BFProx) and medial biceps femoris (BFMed), semitendinosus (ST), and gluteus medius (GM). Mean and peak force were highest (p < 0.001) in Bi + Ver compared with Bi + Hor, Uni + Ver, and Uni + Hor. Although no significant differences were observed between Bi + Hor and Uni + Ver, both variants showed higher (p < 0.001) average force and peak eccentric force when compared with Uni + Hor. The presence of eccentric overload was only observed in the vertically loaded variants. Bi + Ver and Uni + Ver showed higher (p < 0.05) sEMG levels in BFProx and BFMed compared with the Uni + Hor variant. In addition, Uni + Ver registered the largest GM and ST sEMG values. In conclusion, the vertical variants of the flywheel deadlift exercise led to higher muscle force production and sEMG compared with their horizontal counterparts. Both Bi + Ver and Uni + Ver may be effective in promoting an increase in hamstring muscles activity and muscle force at long muscle length, while the Uni + Ver variant may be more effective in promoting GM and ST involvement.

The Effect of Hip Flexor Tightness on Muscle Activity during the Front Squat

The purpose of this study was to compare peak and mean surface electromyography (sEMG) in the rectus femoris (RF), gluteus maximus (GM), biceps femoris (BF), semitendinosus (ST) muscles, and GM:BF muscle co-activation ratio during front squat between resistance trained females with and without hip flexor tightness. Peak and mean sEMG was recorded during three repetitions of 75% of one-repetition maximum (1RM) front squat of resistance trained females who either had hip flexor tightness (n = 9) or did not have hip flexor tightness (n = 7). Observed mean sEMG of the GM and BF was used to calculate GM:BF muscle co-activation. The result of the independent samples t-test indicated a statistically significant difference in peak RF (p = .013), peak (p = .001) and mean (p = .045) BF, and GM:BF muscle co-activation (p = .042) between those with and without hip flexor tightness during the ascending phase of a 75% 1RM front squat. The results indicate the RF and BF to be more active in resistance trained females with hip flexor tightness than those without hip flexor tightness during the front squat, potentially lowering GM activation relative to the BF. Fitness professionals should consider providing a hip flexor stretching interventions to prevent over activation of the BF when selecting the front squat as a resistance training exercise.

Changes in hamstring contractile properties during the competitive season in young football players.

The study aimed to examine alterations and imbalances in hamstring muscle contractile properties among young football players throughout their competitive season, and to understand how these changes might contribute to the risk of muscle injuries. Hamstring injuries are particularly common in football, yet the underlying causes and effective prevention methods remain unclear. The research involved 74 young footballers who were assessed before the season (pre-test) and after 12 weeks of training (post-test). To evaluate changes in hamstring muscle contractile properties, specifically the left and right biceps femoris (BF) and semitendinosus (ST), tensiomyography (TMG) parameters were utilized. In comparison to the BF muscle, significant differences in time delay (Td) between the left and right sides in the post-test (p = 0.0193), and maximal displacement (Dm) between the left and right sides at the pre-test (p = 0.0395). However, significant differences in Dm were observed only in the left ST muscle between the pre- and post-tests (p = 0.0081). Regarding lateral symmetry, BF registered measurements of 79.7 ± 13.43 (pre-test) and 77.4 ± 14.82 (post-test), whereas ST showed measurements of 87.0 ± 9.79 (pre-test) and 87.5 ± 9.60 (post-test). These assessments provided TMG reference data for hamstring muscles in young footballers, both before the season and after 12 weeks of in-season training. The observed changes in the contractile properties and decrease in lateral symmetry of the BF in both tests suggest an increased risk of injury.

The Effect of Restricted Hip Extension on Muscle Activity During Functional Movements

Background: Hip flexor tightness is a common problem affecting both active and sedentary individuals and can lead to the development of movement deficiencies potentially resulting in altered muscle activity around the hip joint. The overhead squat, inline lunge, and single leg step-up are common functional movements used to asses for movement deficiencies. The purpose of the study was to compare surface electromyography (sEMG) in the rectus femoris (RF), gluteus maximus (GM), biceps femoris (RF), and semitendinosus (ST) muscles and GM:BF co-activation ratio during the over-head squat, in-line lunge, and step-up between healthy females with and without hip flexor tightness. Methods: Participants were screened for hip flexor tightness using the modified Thomas Test and classified into a tight hip flexor and non-tight hip flexor group. Muscle activity data was collected using sEMG on the RF, GM, BF, and ST muscles during three functional movements: The over-head squat, in-line lunge, and step-up. Results: There were no statically significant differences in muscles between those with hip flexor tightness and healthy controls during the three tested movements. However, those with hip flexor tightness displayed greater hamstring utilization during all movements (Hedges g = 0.37 - 0.73). Conclusions: Those who have hip flexor tightness appear to adopt a more hamstring-based movement strategy to complete functional movements. More research is warranted to determine the extent to which hip flexor tightness affects functional movement patterns and muscle activity surrounding the hip joint.

Hamstring Strain Ultrasound Case Series: Dominant Semitendinosus Injuries in National Collegiate Athletic Association Division I Athletes.

Authors of previous studies of patients with acute hamstring strains have reported injury to the biceps femoris and semitendinosus (ST) in 50% to 100% and 0% to 30%, respectively. This retrospective case series of hamstring injuries in National Collegiate Athletic Association Division I collegiate athletes exhibited an injury pattern on ultrasound imaging that differed from what would be expected based on prior literature. We examined ultrasound images of 38 athletes with acute hamstring strains for injury location (proximal muscle, proximal myotendinous junction, midportion of muscle, distal muscle) and affected muscles (biceps femoris, ST, or semimembranosus). Twenty-six athletes (68.4%) injured the ST, and 9 athletes (23.7%) injured the biceps femoris long head. Most athletes (23, 60.5%) injured the proximal portion of the muscle or myotendinous junction. Though this study had many limitations, we demonstrated more frequent involvement of the ST and less frequent involvement of the biceps femoris than reported in the literature.

Myosin heavy chain isoform expression and meat quality characteristics of different muscles in yak (Bos grunniens)

Myosin heavy chain (MHC) isoforms and meat quality characteristics of different muscles were investigated to explore their potential relationships in yaks. Results showed that semitendinosus (ST), longissimus thoracis (LT), and infraspinatus (IS) have a greater ratio of MHC IIb (47.84%), MHC IIa (73.27%), and MHC I (24.26%), respectively, than the other two muscles. Compared with LT or ST, IS exhibited more intense color, greater water-holding capacity, and initial tenderness with higher intermuscular fat (IMF) and collagen (of lower cross-linking level), presenting overall better quality. Variations in MHC isoforms accounted for the muscle-specific meat quality. Specifically, MHC I was positively associated with redness, myoglobin, IMF, collagen, pH, and thermal stability and negatively associated with myofibril fragmentation index, fiber thickness, collagen cross-linking, and drip loss. These results provide insights into the relationships between MHC isoforms and meat quality in yaks and the MHC I isoform has an extensive influence on meat quality.

Muscle Morphology Does Not Solely Determine Knee Flexion Weakness After Anterior Cruciate Ligament Reconstruction with a Semitendinosus Tendon Graft: A Combined Experimental and Computational Modeling Study.

The distal semitendinosus tendon is commonly harvested for anterior cruciate ligament reconstruction, inducing substantial morbidity at the knee. The aim of this study was to probe how morphological changes of the semitendinosus muscle after harvest of its distal tendon for anterior cruciate ligament reconstruction affects knee flexion strength and whether the knee flexor synergists can compensate for the knee flexion weakness. Ten participants 8-18months after anterior cruciate ligament reconstruction with an ipsilateral distal semitendinosus tendon autograft performed isometric knee flexion strength testing (15°, 45°, 60°, and 90°; 0° = knee extension) positioned prone on an isokinetic dynamometer. Morphological parameters extracted from magnetic resonance images were used to inform a musculoskeletal model. Knee flexion moments estimated by the model were then compared with those measured experimentally at each knee angle position. A statistically significant between-leg difference in experimentally-measured maximal isometric strength was found at 60° and 90°, but not 15° or 45°, of knee flexion. The musculoskeletal model matched the between-leg differences observed in experimental knee flexion moments at 15° and 45° but did not well estimate between-leg differences with a more flexed knee, particularly at 90°. Further, the knee flexor synergists could not physiologically compensate for weakness in deep knee flexion. These results suggest additional factors other than knee flexor muscle morphology play a role in knee flexion weakness following anterior cruciate ligament reconstruction with a distal semitendinosus tendon graft and thus more work at neural and microscopic levels is required for informing treatment and rehabilitation in this demographic.

Effect of hindlimb unloading on hamstring muscle activity in rats.

The changes in knee axial rotation plays an important role in traumatic and non-traumatic knee disorders. It is known that support afferentation can affect the axial rotator muscles. The condition of innervation of the ST and BFp has changed in non terrestrial and terrestrial vertebrates in evolution, thus we hypothesized this situation might be replayed by hindlimb unloading (HU). In the present study the EMG activity of two hamstring muscles, m. semitendinosus (ST) and m. biceps femoris posterior (BFp), which are antagonists in axial rotation of the tibia, was examined before and after 7 days of HU. During locomotion and swimming the ST flexor-burst activity was increased in the stance to swing transition and in the retraction-protraction transition, respectively, while those of BFp remained unchanged. Both ST and BFp non-burst extensor activity increased during stepping and decreased during swimming. Our results show that: 1) The flexor-burst activity of ST and BFp depends differently on the load-dependent sensory input in the step cycle. 2) Shift of the activity gradient towards ST in the stance to swing transition could produce excessive internal tibia torque, which can be used as an experimental model of non-traumatic musculoskeletal disorders. 3) The mechanisms of activity of ST and BFp may be based on reciprocal activity of homologous muscles in primary tetrapodomorph and depend on the increased role of supraspinal control.

Moment arm and torque generating capacity of semitendinosus following tendon harvesting for anterior cruciate ligament reconstruction: A simulation study.

Altered semitendinosus (ST) morphology and distal tendon insertion following anterior cruciate ligament reconstruction (ACLR) may reduce knee flexion torque generating capacity of the hamstrings via impaired ST force generation and/or moment arm. This study used a computational musculoskeletal model to simulate mechanical consequences of tendon harvest for ACLR on ST function by modeling changes in ST muscle tendon insertion point, moment arm, and torque generating capacity across a physiological range of motion. Simulated ST function was then compared between ACLR and uninjured contralateral limbs. Magnetic resonance imaging from 18 individuals with unilateral history of ACLR involving a hamstring autograft was used to analyse bilateral hamstring muscle (ST, semimembranosus, bicep femoris long head and short head) morphology and distal ST tendon insertion. The ACLR cohort was sub-grouped into those with and without ST regeneration. For each participant with ST regeneration (n = 7), a personalized musculoskeletal model was created including postoperative remodeling of ST using OpenSim 4.1. Knee flexion and internal rotation moment arms and torque generating capacities of hamstrings were evaluated. Bilateral differences were calculated with an asymmetry index (%) ([unaffected limb-affected limb]/[unaffected limb + affected limb]*100%). Smaller moment arms or knee torques within injured compared to uninjured contralateral limbs were considered a deficit. Compared to uninjured contralateral limbs, ACLR limbs with tendon regeneration (n = 7) had minor reductions in knee flexion (5.80% [95% confidence interval (CI) = 3.97-7.62]) and internal rotation (4.92% [95% CI = 2.77-7.07]) moment arms. Decoupled from muscle morphology, altered ST moment arms in ACLR limbs with tendon regeneration resulted in negligible deficits in knee flexion (1.20% [95% CI = 0.34-2.06]) and internal rotation (0.24% [95% CI = 0.22-0.26]) torque generating capacity compared to uninjured contralateral limbs. Coupled with muscle morphology, ACLR limbs with tendon regeneration had substantial deficits in knee flexion (19.32% [95% CI = 18.35-20.28]) and internal rotation (15.49% [95% CI = 14.56-16.41]) torques compared to uninjured contralateral limbs. Personalized musculoskeletal models with measures of ST distal insertion and muscle morphology provided unique insights into post-ACLR ST and hamstring function. Deficits in knee flexor and internal rotation moment arms and torque generating capacities were evident in those with ACLR even when tendon regeneration occurred. Future studies may wish to implement this framework in personalized musculoskeletal models following ACLR to better understand individual muscle function for injury prevention and treatment evaluation.

Acute fatigue-induced alterations in hamstring muscle properties after repeated Nordic hamstring exercises.

This study aimed to investigate the impact of the Nordic hamstring exercises (NHE) on acute fatigue-induced alterations in the mechanical and morphological properties of hamstring muscles. The second aim was to define the blood flow and perfusion after NHE in recreational active volunteers. Twenty-two individuals volunteered to participate in the study. This study investigated fatigue outcomes: rate of perceived exertion (RPE) scale and average force generated during NHE; mechanical properties (stiffness); morphological properties (thickness, pennation angle, and fascicle length), and vascularity index (VI) of the semitendinosus (ST) and biceps femoris long head (BFLH) at baseline, immediately post-exercise and 1-h post-exercise. The NHE fatigue procedure consisted of six bouts of five repetitions. The results showed an increase in thickness and pennation angle of BFLH and ST immediately post-exercise and a decrease in thickness and pennation angle of BFLH and ST 1-h post-exercise. While the fascicle length of BFLH and ST decreased immediately post-exercise and increased 1-h post-exercise. The VI for two muscles increased immediately post-exercise and after 1-h post-exercise. Moreover, we found a relationship between RPE and average force, that is, as RPE increased during NHE, average force decreased. In conclusion, eccentric NHE exercises significantly and acutely affect BFLH and ST. The NHE fatigue protocol significantly affected the mechanical and morphological properties of BFLH and ST muscles, changing their thickness, fascicle length, pennation angle, and VI.

Lower limb electromyographic characteristics and implications of taekwondo roundhouse kick "hit" and "miss" actions.

To compare the muscular characteristics of "hit" and "miss" actions in roundhouse kicks among taekwondo athletes, and explore the similarities, differences, and implications for training, motion tests were conducted on ten taekwondo athletes using Noraxon32 and VICON. The results showed no significant differences (p > 0.05) in integrated electromyography (EMG) during the initiation and kicking phases between "miss" and "hit" actions. However, during the retraction phase, significant differences (p < 0.05) were observed in the left rectus femoris, left peroneus longus, right biceps femoris, right semitendinosus, and right tibialis anterior muscles. The tibialis anterior muscle of the swinging leg was activated first in the "hit" action, while the biceps femoris was activated first in the "miss" action. The supporting-side rectus femoris was activated first in the "hit" action, whereas it was the biceps femoris in the "miss" action. In both techniques, the gluteus maximus was the last muscle to be activated. The "miss" action had a longer cycle, and the duration of muscle work was longer than in the "hit" action. During the retraction phase of the front leg roundhouse kick, the muscles worked more than during the kicking phase, with the erector spinae and tibialis anterior being the core force-producing muscles in both techniques, characterized by high EMG values and long activation times. In the "miss" action, the thigh muscles drove the calf muscles, while the "hit" action exhibited the opposite pattern. "Hit" actions had a faster cycle compared to "miss," with greater force generation in "miss." The hip flexors and knee extensors of the kicking leg were the core force-producing muscles during the kicking process, determining the effectiveness and completion of the action.