Lateral Hamstrings Research Articles

A new field-test for assessing the medial and lateral hamstring strength at long-muscle length

This research investigates the influence of tibial rotations with knee flexion (KF) on the electromyographic (EMG) activities of hamstring muscles (HM) groups and the strength ratio between the medial and lateral rotation of the tibia. A cross-sectional design was employed to assess muscle activity, isometric strength and reliability. The research was conducted in a controlled laboratory environment. Thirty-six amateur male athletes were recruited as volunteers. The measures included peak muscle activity of the semitendinosus and biceps femoris long head, the knee flexors’ isometric strength ratio and reliability. The isometric strength ratios of medial (MR) to lateral (LR) tibial rotations were 0.94 ± 0.17 at 90°, and 0.93 ± 0.10 at both 60° and 30° of KF angulation. Tibial position significantly influenced knee flexion strength as well as HM activity, irrespective of KF angulation. Specifically, biceps femoris activity increased by 33.6% in LR compared to MR, while semitendinosus activity increased by 22.6% in MR compared to LR. The Knee-Rotation test (KR-test) can be a valuable tool for evaluating both HM groups (ICC > 0.87), and identifying the primary target for strengthening purposes during the injury prevention process. It provides insights for effective rehabilitation and training interventions.

Evaluation of Lateral and Medial Parts of the Hamstring Muscle Fatigue Symmetry in Professional Footballers Cleared to Play After ACL Reconstruction.

Objectives: Rupture of the anterior cruciate ligament (ACL) is a severe injury common in sports. It also has a high rate of re-injury. The aim of this work was to assess hamstring muscle fatigue in active football players after ACL reconstruction who were cleared to play and to determine symmetry between the lateral and medial hamstring muscles. Methods: In professional football players post ACL reconstruction (n = 25) and non-injured players (n = 26), the bioelectrical activity of the medial (biceps femoris-BF) and lateral (semimembranosus and semitendinosus-SEM) hamstring muscles was measured during 60 s of isometric contraction. The fatigue variables were calculated using the Continuous Wavelet Transform (CWT) tool. Results: The football players following ACL reconstruction demonstrated significant asymmetry in fatigue of the lateral and medial hamstring muscles, with greater fatigue in the SEM compared to the BF muscle. Moreover, in those after reconstruction, the changes are more pronounced, with higher muscle fatigue in both limbs (they have lower MDF than non-injured players) and more severe SEM muscle insufficiency (noted in both limbs but with greater intensity in the non-operated one). Conclusions: The higher SEM muscle fatigue observed in this study influenced the lateral-to-medial activation ratio within the hamstring muscle, which may be a probable cause of this muscle's insufficiency in laterally stabilizing the knee in the frontal and transverse plane. Furthermore, the hamstring muscles after reconstruction were more fatigued in both limbs, which may be another risk factor for ACL graft rupture. Therefore, increased fatigue in specific hamstring muscles may indicate the direction in which knee stabilization is compromised due to ACL overload. A muscle that becomes fatigued and inefficient more quickly also becomes ineffective in performing its function sooner, which can lead to increased overloading forces acting on the ACL graft.

Verification of the superiority of radiofrequency irradiation with static stretching over static stretching alone for hamstring tightness

IntroductionHealthy hamstring muscles are necessary for active living. Hamstring tightness is a widely reported problem among individuals from all levels of society. The effects of combining radiofrequency (RF) therapy with static stretching (SS) on hamstring tightness have not been investigated. Therefore, we aimed to verify the superiority of combining RF and SS over SS alone by comparing their immediate effects on hamstring flexibility. MethodsThis randomized controlled study included 33 participants with hamstring tightness. The participants were allocated to the RF (intervention; n = 17) or sham (n = 16) group. The RF group underwent SS simultaneously with RF therapy. The sham group underwent SS with sham RF (powered off). The range of motion (ROM) for knee extension and five muscle properties (tone, stiffness, elasticity, relaxation, and creep) of the lateral and medial hamstrings were measured before and after the intervention. ResultsThere was no significant difference in the ROM for knee extension (p = 0.295) between the RF and sham groups. The interaction between group and period (p > 0.05) was not significant for any of the muscle properties of the lateral and medial hamstrings besides lateral hamstring elasticity (p = 0.001). ConclusionRF therapy in conjunction with SS for hamstring tightness produced different changes in muscle properties compared with SS alone. However, these changes did not produce differences in the ROM for knee extension.

The Effects of the Leg Position on the Nordic Hamstring Exercise Eccentric Force: A Randomized Cross-Over Study

Given the posterior chain configuration, it is anticipated that tibial positioning influences hamstring recruitment; medial hamstrings should be more activated during medial rotation, while lateral hamstrings should be more activated during lateral rotation. However, most studies showing this pattern have focused on concentric or isometric strength, leaving the influence on eccentric strength fairly unknown. Therefore, the aim of this study was to investigate the electromyographic response of the hamstring muscles during Nordic hamstring exercises in three leg positions: internal rotation, external rotation, and neutral. This study encompassed a randomized crossover study and used surface electromyography to analyze the activity of the biceps femoris and semitendinosus muscles during the Nordic hamstring exercise, in the three positions. Results indicated no statistically significant differences in muscle activation between positions or sides (p > 0.05), though small effect sizes were observed for the biceps femoris in different positions (η2 = 0.01–0.03). Furthermore, the internal rotation position generally elicited the highest muscle activations. Notably, biceps femoris muscles exhibited higher activations compared to semitendinosus muscles, with the greatest differences seen in the internal rotation position. This suggests that tibial rotation influences hamstring recruitment patterns; however, it was lower than expected.

The role of muscle function and pointe shoe characteristics in Arabesque movement among ballet dancers with non-specific low back pain

ABSTRACT This study aimed to investigate posterior chain muscle function and the influence of pointe shoes in ballet dancers with and without low back pain (LBP) in the Arabesque. Twenty-nine young professional ballet dancers (17 with LBP and 12 healthy controls) were recruited. Muscle strength and mechanical properties of the erector spinae and hamstrings were assessed. The displacement of centre of mass (COM) during Arabesque under different shoe conditions (R-class, Chacott, and own shoes) was measured with a motion capture system. The LBP group exhibited greater dynamic stiffness and decreased mechanical stress relaxation time in the lateral hamstring compared to the control group. During Arabesque, the LBP group demonstrated significantly greater anterior-posterior displacement of the COM and a larger percentage of time to achieve maximal trunk extension angle. The COM displacement in vertical and medial-lateral directions was smaller in the R-class than in their own shoes. LBP impacts muscle mechanical properties, particularly in the lateral hamstring. The compromised muscle function resulted in a longer time to spinal extension during Arabesque, signifying that reduced trunk control contributed to greater COM displacement. Hence, it is essential to emphasise that evaluating muscle properties and dynamic postural control is imperative for dancers experiencing LBP.

Effects of Ankle Position While Performing One- and Two-Leg Floor Bridging Exercises on Core and Lower Extremity Muscle Recruitment.

Given there are no known studies which have examined multiple lower extremity muscles between different ankle positions during bridging activities, the objective was to assess how employing two different ankle positions (PF versus DF) while performing five common bridging exercises (three bipedal and two unipedal) used in rehabilitation and athletic performance affect core and select lower extremity muscle EMG recruitment. Twenty healthy subjects performed a 5 s isometric hold during five two- and one-leg bridge exercises: (1) on right leg with left knee to chest (1LB-LFlex); (2) on right leg with left knee extended (1LB-LExt); (3) standard two-leg bridge (2LB); (4) two-leg bridge with resistance band around knees (2LB-ABD); and (5) two-leg bridge with ball between knees (2LB-ADD). Surface electromyographic (EMG) data were collected using a Noraxon Telemyo Direct Transmission System from fourteen muscles: (1) three superficial quadriceps (VM, VL, and RF); (2) three hip abductors (TFL, GMED, and GMAX); (3) medial hamstrings (ST) and lateral hamstrings (BF); (4) hip adductors (ADD); (5) erector spinae (ES); (6) latissimus dorsi (LATS); (7) upper rectus abdominis (RA); and (8) external oblique (EO) and internal oblique (IO). EMG data were normalized by maximum voluntary isometric contractions (MVICs). A paired t-test (p < 0.01) was used to assess differences in normalized mean EMG activities between DF and PF for each exercise. EMG activities were significantly greater in DF than PF for the (a) VM, VL, and RF during 1LB-LFlex; (b) ADD during 1LB-LFlex, 1LB-LExt; (c) EO during 1LB-LFlex; and (d) IO during 1LB-LFex. In contrast, EMG activities were significantly greater in PF than DF for ST and BF during all five bridge exercises. Bridging with PF (feet flat) was most effective in recruiting the hamstrings, while bridging with DF (feet up) was most effective in recruiting the quadriceps, hip adductors, and internal and external obliques.

Quadriceps and Hamstrings Activation Peaks Earlier as Athletes Repeatedly Hop, but There are Differences Depending on ACL Reconstruction Technique.

After Anterior Cruciate Ligament Reconstruction (ACLR) athletes face the challenge of regaining their previous competitive level while avoiding re-injury and early knee joint cartilage degeneration. Quadriceps and hamstrings strength reductions and neuromuscular alterations potentially related to risk of re-injury are present after ACLR and relate to deficits in muscle activation. Cross-sectional laboratory study. To examine quadriceps and hamstrings muscle activation during repeated hops in healthy pivoting-sport athletes and those who had undergone ACLR (bone-tendon-bone and semitendinosus graft) who had met functional criteria allowing return to training. Surface electromyography (SEMG) was recorded from vastus medialis and lateralis and medial and lateral hamstrings bilaterally during 30 seconds' repeated hopping in male athletes on average eight months after ACLR surgery (5-12 months). All patients underwent hamstring (HS) (n=24) or bone-tendon-bone (BTB) reconstruction (n=20) and were compared to healthy controls (n=31). The SEMG signals were normalized to those obtained during maximal voluntary isometric contraction. A significant time shift in peak muscle activation (earlier) was seen for: vastus medialis and vastus lateralis activation in the control group, in the BTB group's healthy (but not injured) leg and both legs of the HS group. A significant time shift in peak muscle activation was seen for lateral hamstrings (earlier) in all but the BTB group's injured leg and the medial hamstrings in the control group only. Lower peak activation levels of the vastus lateralis (p\<0.001) and vastus medialis (p\<0.001) were observed in the injured compared to healthy legs and lower peak lateral hamstrings activity (p\<0.009) in the injured leg compared to control leg. Decline in medial hamstring peak activation (p\<0.022) was observed between 1st and 3rd phase of the hop cycle in all groups. Repeated hop testing revealed quadriceps and hamstring activation differences within ACLR athletes, and compared to healthy controls, that would be missed with single hop tests. 3.

Gait analysis of a patient after femoral nerve and malignant soft tissue tumor resections: a case report

BackgroundMalignant femoral soft tissue tumors are occasionally resected together with the femoral nerves, but this can cause loss of knee extensor muscle activity. To the best of our knowledge, no previous reports have detailed the gait analysis of such cases in combination with electromyography. Herein, we report the gait analysis of a patient who underwent left groin synovial sarcoma and left femoral nerve resection 12 years ago.Case presentationWe analyzed the gait of a 38-year-old man who was able to walk unaided after the resection of a synovial sarcoma in the left groin together with the ipsilateral femoral nerve. The muscle activities of the affected medial (MH) and lateral hamstrings (LH), and lateral heads of the gastrocnemius (GL) were increased during 50–75% of the stance phase. The hip flexion angle of the affected limb was smaller, and the ankle plantar flexion angle of the affected limb was larger than that of the non-affected limb. This means that in the affected limb, the hip and ankle angles were adjusted to prevent knee collapse, and the MH, LH, and GL muscles contributed in the mid- and late-stance phases. Moreover, we found that the hamstring and gastrocnemius of the affected limb worked together to keep the ipsilateral knee extended in the mid-stance phase and slightly flexed in the late-stance phase.ConclusionsPatients capable of walking after femoral nerve resection may control their hamstrings and gastrocnemius muscles collaboratively to prevent ipsilateral knee collapse in the mid- and late-stance phases.

Quantifying demands on the hamstrings during high-speed running: A systematic review and meta-analysis.

Hamstring strain injury (HSI) remains a performance, economic, and player availability burden in sport. High-speed running (HSR) is cited as a common mechanism for HSI. While evidence exists regarding the high physical demands on the hamstring muscles in HSR, meta-analytical synthesis of related activation and kinetic variables is lacking. A systematic search of Medline, Embase, Scopus, CINAHL, SportDiscus, and Cochrane library databases was conducted in accordance with the PRISMA 2020 guidelines. Studies reporting hamstring activation (electromyographic [EMG]) or hamstring muscle/related joint kinetics were included where healthy adult participants ran at or beyond 60% of maximum speed (activation studies) or 4 m per second (m/s) (kinetic studies). A total of 96 studies met the inclusion criteria. Run intensities were categorized as "slow," "moderate," or "fast" in both activation and kinetic based studies with appropriate relative, and raw measures, respectively. Meta-analysis revealed pooled mean lateral hamstring muscle activation levels of 108.1% (95% CI: 84.4%-131.7%) of maximal voluntary isometric contraction (MVIC) during "fast" running. Meta-analysis found swing phase peak knee flexion internal moment and power at 2.2 Newton meters/kilogram (Nm/kg) (95% CI: 1.9-2.5) and 40.3 Watts/kilogram (W/kg) (95% CI: 31.4-49.2), respectively. Hip extension peak moment and power was estimated as 4.8 Nm/kg (95% CI: 3.9-5.7) and 33.1 W/kg (95% CI: 17.4-48.9), respectively. As run intensity/speed increases, so do the activation and kinetic demands on the hamstrings. The presented data will enable clinicians to incorporate more objective measures into the design of injury prevention and return-to-play decision-making strategies.

Effect of 8-Weeks PNF Stretching on Muscle Strength and Neuromuscular Activity of the Hamstring Muscles

Background: Hamstring injuries are common in sports that involve rapid, forceful lengthening of the hamstring muscles, such as sprinting, jumping, and kicking. This type of injury is more likely to occur in team sports such as football and handball. Objectives: The purpose of this study was to investigate chronic effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle strength and neuromuscular activity of the hamstring muscle. Methods: Six male team sports players (age: 24.38 ± 1.94 years; height: 180.73 ± 6.05 cm; body-mass: 80.23 ± 10.42 kg) were recruited for this study. Participants completed a 2-month rehabilitation program that included three sessions per week of contract-relax (CR) PNF stretching. Neuromuscular activity and strength were evaluated by electromyography (EMG) and force sensor before and after 8 weeks of CR-PNF stretching. Results: The neuromuscular activity of the medial and lateral hamstring muscles was significantly different between pre-and post-training for the apex and area of muscle (P &lt; 0.01). Similarly, there was a large difference between pre- and post-training for hamstring muscle strength (medial and lateral) in the contract and relax positions (P &lt; 0.001). Conclusions: Eight weeks of contract-relax proprioceptive neuromuscular facilitation (PNF) stretching is effective in increasing neuromuscular activity and muscle strength in the hamstring muscles.

Is peak hamstrings muscle-tendon length criterion a sufficient indicator to recommend against surgical lengthening of hamstrings?

BackgroundExcessive knee flexion during stance in children with cerebral palsy is often treated by surgical hamstrings lengthening. Pre-operative hamstrings muscle-tendon length can be estimated from kinematics and often used for decision making to rule out surgical lengthening if peak hamstrings muscle-tendon length is ‘Not Short’. Research questionIf peak hamstrings muscle-tendon length is within two standard deviations of typical, is that a sufficient indicator to rule out surgical hamstrings lengthening? MethodsThree motion analysis centers retrospectively identified children with cerebral palsy, age 6–17 years, who had consecutive gait analyses with knee flexion at initial contact > 20° and popliteal angle > 35° at initial study. Three groups were considered: Medial Hamstrings Lengthening (MHL), Medial and Lateral Hamstrings Lengthening (MLHL), no surgical intervention (Control). Peak hamstrings muscle-tendon length at initial gait study was computed and categorized as ‘Short’ or ‘Not Short’. Two outcomes variables were considered: change in peak knee extension (PKE) and change in pelvic tilt. Univariate comparisons of all variables were assessed along with a multivariate stepwise regression analysis to identify pre-operative characteristics that may predict post-operative improvement. Results440 individuals met inclusion criteria. Percentage of individuals with improved PKE by grouping were- MHL-‘Short’: 60%, MHL-‘Not Short’: 65%, MLHL-‘Short’: 74%, MLHL-‘Not Short’: 74%, Control ‘Short’: 20%, Control ‘Not Short’: 19%. Percentage of individuals with worsened pelvic tilt were- MHL-‘Short’: 25%, MHL-‘Not Short’: 11%, MLHL-‘Short’: 42%, MLHL-‘Not Short’: 21% with significantly more individuals in MHL-‘Short’ subgroup compared to MHL-‘Not Short’. Multivariate analysis suggested that pre-operative pelvic tilt and weak hip extensor strength have the largest effect on predicting post-operative increase in APT. Peak muscle-tendon length was not a significant predictor of post-operative knee kinematics or increase in APT. SignificanceThis study suggests that hamstrings muscle-tendon length criteria by itself is not a sufficient indicator to recommend against hamstrings lengthening.

Hamstring activation deficits in different jumping directions in athletes with a history of hamstring strain injuries: a cross-sectional laboratory study

ABSTRACT This study aimed to investigate the hamstring onset time and recruitment level during jumping tasks in athletes with chronic hamstring strain injuries. Thirteen hamstring injured athletes and thirteen matched healthy athletes were recruited. Activation onset time and muscle recruitment (median frequency of the EMG) of the lateral hamstring (LH) and medial hamstring (MH) was measured during double leg jumps in vertical and horizontal directions on the force platforms. The peak vertical ground reaction force and loading rate were obtained for all jumps. The injured group showed a delayed onset time (p = 0.029) and a lower recruitment of the LH during the landing (p = 0.018) than the control group. Activation deficits in the injured group led to a higher landing force and loading rate. Additionally, the LH and MH were lesser recruited in the vertical direction than the horizontal directions in the landing. In conclusion, athletes with hamstring injuries show hamstring activation deficits of the injured leg during jumping leading to degrading jump-landing performance. Also, jumping in different directions play a role to modify the recruitment of the hamstrings in the injured athletes. Therefore, movement plane is suggested to be considered in clinical rehabilitation for the hamstring injury.

Effect of Schatzker type VI tibial plateau fractures combined with a proximal fibular and/or posterolateral joint facet fracture on early postoperative functional recovery

PurposeThe objective of this study was to investigate the effect of proximal fibular and/or posterolateral joint facet (PJF) fractures on early functional recovery after Schatzker type VI tibial plateau fractures (TPFs).MethodsSeventy-nine patients with Schatzker type VI TPFs sustained from November 2016 to February 2021 were divided into three groups according to the integrity of the proximal fibula and PJF (groups A, B, and C). Details including demographics, duration of surgery, and complications were recorded. The Western Ontario and McMaster Universities Osteoarthritis index (WOMAC) score, Hospital for Special Surgery (HSS) score, lateral knee pain and lateral hamstring tightness were ascertained at the final follow-up. The HSS and WOMAC scores have high reliability in evaluating knee function and osteoarthritis.ResultsThere was a significant difference in the HSS score between groups A and C (P < 0.001) and between groups B and C (P = 0.036). The hospital stay was significantly different between groups A and C (P = 0.038) and between groups B and C (P = 0.013). There was a significant difference in lateral knee pain and lateral hamstring tightness between groups A and C (P < 0.001) and between groups B and C (P < 0.001).ConclusionOur study demonstrates that proximal fibular and PJF fractures do not increase the time from injury to surgery, the incidence of complications, or the duration of surgery for Schatzker type VI TPFs. However, fractures of the proximal fibula significantly increase the hospital stay, reduce knee function, and cause lateral knee pain and lateral hamstring tightness. Combined proximal fibular fracture is more decisive than PJF involvement for prognosis.

Hamstring Muscle Stiffness Affects Lower Extremity Muscle Recruitment and Landing Forces during Double-Legs Vertical Jump

ABSTRACT It is unclear how hamstring stiffness influences lower limb muscle activation during jump-landing mechanics. The study aimed to investigate the role of the hamstring stiffness on lower limb muscle recruitment during jumping manoeuvres. Thirty male athletes were recruited and allocated into high- and low-stiffness groups. Hamstring stiffness was determined as the average stiffness of bilateral hamstrings using a MyotonPRO. Surface electromyography of the bilateral gluteus maximus, quadriceps, and hamstring muscles was assessed during the takeoff, at ground contact, and at landing, while ground reaction force (GRF) was measured during the squat jump, countermovement jump, and drop vertical jump. The results showed that athletes with greater hamstring stiffness exhibited a higher median frequency of the lateral hamstrings in both limbs and the vastus medialis in the dominant limb than the low-stiffness group during takeoff, adjustment, and landing phases for all vertical jumps. The high stiffness group landed with lower vertical GRF in the drop vertical jump. In conclusion, athletes with high hamstring stiffness showed greater motor unit recruitment during takeoff and landing phases. This recruitment did not influence takeoff performance but aid with absorbing landing force. Therefore, the contribution of the lower limb muscle stiffness should be considered in sports activities.

Model-based estimation of muscle and ACL forces during turning maneuvers in alpine skiing

In alpine skiing, estimation of the muscle forces and joint loads such as the forces in the ACL of the knee are essential to quantify the loading pattern of the skier during turning maneuvers. Since direct measurement of these forces is generally not feasible, non-invasive methods based on musculoskeletal modeling should be considered. In alpine skiing, however, muscle forces and ACL forces have not been analyzed during turning maneuvers due to the lack of three dimensional musculoskeletal models. In the present study, a three dimensional musculoskeletal skier model was successfully applied to track experimental data of a professional skier. During the turning maneuver, the primary activated muscles groups of the outside leg, bearing the highest loads, were the gluteus maximus, vastus lateralis as well as the medial and lateral hamstrings. The main function of these muscles was to generate the required hip extension and knee extension moments. The gluteus maximus was also the main contributor to the hip abduction moment when the hip was highly flexed. Furthermore, the lateral hamstrings and gluteus maximus contributed to the hip external rotation moment in addition to the quadratus femoris. Peak ACL forces reached 211 N on the outside leg with the main contribution in the frontal plane due to an external knee abduction moment. Sagittal plane contributions were low due to consistently high knee flexion (> 60^{circ }), substantial co-activation of the hamstrings and the ground reaction force pushing the anteriorly inclined tibia backwards with respect to the femur. In conclusion, the present musculoskeletal simulation model provides a detailed insight into the loading of a skier during turning maneuvers that might be used to analyze appropriate training loads or injury risk factors such as the speed or turn radius of the skier, changes of the equipment or neuromuscular control parameters.

스쿼트 운동 시 기능적 다리 길이 차이가 넙다리 근육 활성도에 미치는 영향

Leg-length discrepancy can cause not just issues in daily life, but functional problems such as abnormal walking, decreased balance, and musculoskeletal concerns. Squat exercises are highly stable and can exert a large for strength because the same strength is applied to both lower extremities. However, for a subject with leg-length discrepancy, balanced strength is not applied to the lower extremities; this can cause structural malalignment and unbalanced muscle activation. It is necessary to determine the influence of functional leg-length discrepancy on thigh muscle activation during squat exercises. Subjects with no leg-length discrepancy performed squats under two conditions—no leg-length discrepancy and simulated leg-length discrepancy with the left foot on a 3-cm-thick plate. We measured muscle activation of the vastus lateralis, vastus medialis, and medial and lateral hamstring by electromyography. The activations of the vastus lateralis and vastus medialis were significantly greater without leg-length discrepancy than with it (p<.05). Medial and lateral hamstring activation exhibited no significant difference. No muscles showed significant difference between the right and left legs in terms of activation under any condition. Therefore, leg-length discrepancy led to inefficiency in squat exercises and this factor should be removed prior to exercise.

Comparison of muscle activity of hamstrings as knee flexors and hip extensors and effect of tibial and hip rotation on the contribution of hamstrings

BackgroundLimited studies have compared the muscle activity of the medial and lateral hamstrings as knee flexors with tibial internal and external rotation and hip extensors with hip internal and external rotation. In particular, hamstring activity during hip extension with hip rotation has rarely been investigated. ObjectiveThis study aimed to compare the muscle activity of the medial and lateral hamstrings as knee flexors and hip extensors and to compare the activity of these muscles according to tibial rotation during isometric knee flexion and hip rotation during isometric hip extension. MethodsA total of 23 healthy adults participated in the study. The electromyographic (EMG) activity of the hamstrings was measured during maximal isometric knee flexion and maximal isometric hip extension. In addition, tibial rotation was applied actively during maximal isometric knee flexion, whereas hip rotation was applied actively during maximal isometric hip extension. ResultsEMG activity during maximal isometric knee flexion with tibial internal and external rotation was significantly higher than that during maximal isometric hip extension with hip internal and external rotation, respectively. For EMG activity according to tibial and hip rotation, there was no significant difference between tibial internal and external rotation during maximal isometric knee flexion, whereas there was a significant difference between hip internal and external rotation during maximal isometric hip extension. ConclusionHamstring activity was higher for knee flexors than for hip extensors. However, hip rotation during maximal isometric hip extension is an effective intervention for selective muscle activation of the medial and lateral hamstrings.

The Evaluation of Asymmetry in Isokinetic and Electromyographic Activity (sEMG) of the Knee Flexor and Extensor Muscles in Football Players after ACL Rupture Reconstruction and in the Athletes following Mild Lower-Limb Injuries.

This study was aimed at evaluating knee stabilizer (quadriceps and hamstring) muscle strength and the medio-lateral symmetry of hamstring fatigue in football players after ACL reconstruction and with mild lower extremity injuries. The study comprised 65 professional football players who were divided into three groups: Group 1 (n = 24; 22.7 ± 3.6 years; 175 ± 4 cm; 77.3 ± 7.6 kg) after ACL reconstruction, Group 2 (n = 21; 20.5 ± 3.7 years; 177 ± 6 cm; 74.3 ± 9.1 kg) with mild lower-limb injuries (grade 1 muscle strains) and Group 3 (n = 20; 23.1 ± 2.8 years; 178 ± 6 cm; 75.8 ± 8.8 kg) without injuries in the past 3 years. The concentric isokinetic test (10 knee flexions and extensions at 60, 180 and 300°/s with a 30 s interval for rest) was performed on both limbs. Fatigue symmetry between the medial and lateral hamstrings was measured with sEMG during 60 s of isometric contractions. In comparison to the other groups, the injured leg demonstrated significantly lower values of peak torque for the quadriceps (G1-G2 = 48%, 38%, 14%; G1-G3 = 49%, 25%, 14%) and hamstring muscles (G1-G2 = 36%, 35%, 18%; G1-G3 = 64%, 28%, 17%) as well as lower values of hamstring muscle work (G1-G2 = 262 J, 157 J; G1-G3 = 219 J, 179 J) and power (G1-G2 = 34 W; 11 W; G1-G3 = 29 W, 12 W). No significant differences were noted in strength between Groups 2 and 3. The significantly higher fatigue of the BF compared to the SEM muscle was seen in Group 1 for the involved (mean difference = 0.12) and uninvolved limbs (mean difference = -0.10), but in Group 2, a non-significant trend towards asymmetry was also noted. No asymmetry in hamstring muscle fatigue was determined in Group 3. The results of our study allow us to indicate that active football players who previously met the RTS criteria, had deficits in lower-limb muscle performance 2-3 years after reconstruction, which could lead to ACL re-injury. This observation is potentially of importance because these deficits may not be subjectively reported by such athletes and also may not be visible in regular orthopedic and physiotherapeutic assessment.

Comparison of gluteus medius and hamstring activation during seven plyometric exercises on three training surfaces

IntroductionPlyometric exercise is known as one of the key components of neuromuscular training programs. It is also possible to obtain higher muscular activity by exercising on tatami and mats. The purpose of the study was to evaluate the activity of hamstring and gluteus medius in 7 typical plyometric exercises on 3 different surfaces and identify the best exercises and surfaces that would further increase hamstring and gluteus medius activity.MethodsThe study involved 20 male athletes. The participants performed 7 plyometric exercises on 3 surfaces: ground, tatami, and mat. The electromyographic activity of muscles was recorded with a ME6000 device in 2 phases: feedforward and feedback. To analyse the data, 2-way ANOVA with repeated measures and a Bonferroni post-hoc test were used.ResultsGluteus medius was most active in the feedforward phase in single-leg frontal plane hop (SLFPH), and in the feedback phase in SLFPH and single-leg sagittal plane hop (SLSPH) (&lt;i&gt;p&lt;/i&gt; = 0.001). The medial hamstring and lateral hamstring showed the highest values of activity in the feedforward phase in SLSPH, SLFPH, and double-leg sagittal plane hop (DLSPH) (&lt;i&gt;p&lt;/i&gt; = 0.001). There was no significant difference between the surfaces (&lt;i&gt;p&lt;/i&gt; &gt; 0.05).ConclusionsSLSPH, DLSPH, and SLFPH improve the recruitment and the strength of gluteus medius and hamstrings and should be given considerable attention in training programs. Exercise on the ground, tatami, and mattress is allowed and in terms of the purpose of the research, there is no difference between them.

Effect of 8-Weeks PNF Stretching on Muscle Strength and Neuromuscular Activity of the Hamstring Muscles

Background: Hamstring injuries are common in sports that involve rapid, forceful lengthening of the hamstring muscles, such as sprinting, jumping, and kicking. This type of injury is more likely to occur in team sports such as football and handball. Objectives: The purpose of this study was to investigate chronic effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle strength and neuromuscular activity of the hamstring muscle. Methods: Six male team sports players (age: 24.38 ± 1.94 years; height: 180.73 ± 6.05 cm; body-mass: 80.23 ± 10.42 kg) were recruited for this study. Participants completed a 2-month rehabilitation program that included three sessions per week of contract-relax (CR) PNF stretching. Neuromuscular activity and strength were evaluated by electromyography (EMG) and force sensor before and after 8 weeks of CR-PNF stretching. Results: The neuromuscular activity of the medial and lateral hamstring muscles was significantly different between pre-and post-training for the apex and area of muscle (P &lt; 0.01). Similarly, there was a large difference between pre- and post-training for hamstring muscle strength (medial and lateral) in the contract and relax positions (P &lt; 0.001). Conclusions: Eight weeks of contract-relax proprioceptive neuromuscular facilitation (PNF) stretching is effective in increasing neuromuscular activity and muscle strength in the hamstring muscles.