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PubMedDate not supplied

A comparison of tibiofemoral joint forces and electromyographic activity during open and closed kinetic chain exercises.

We chose to investigate tibiofemoral joint kinetics (compressive force, anteroposterior shear force, and extension torque) and electromyographic activity of the quadriceps, hamstring, and gastrocnemius muscles during open kinetic chain knee extension and closed kinetic chain leg press and squat. Ten uninjured male subjects performed 4 isotonic repetitions with a 12 repetition maximal weight for each exercise. Tibiofemoral forces were calculated using electromyographic, kinematic, and kinetic data. During the squat, the maximal compressive force was 6139 +/- 1708 N, occurring at 91 degrees of knee flexion; whereas the maximal compressive force for the knee extension exercise was 4598 +/- 2546 N (at 90 degrees knee flexion). During the closed kinetic chain exercises, a posterior shear force (posterior cruciate ligament stress) occurred throughout the range of motion, with the peak occurring from 85 degrees to 105 degrees of knee flexion. An anterior shear force (anterior cruciate ligament stress) was noted during open kinetic chain knee extension from 40 degrees to full extension; a peak force of 248 +/- 259 N was noted at 14 degrees of knee flexion. Electromyographic data indicated greater hamstring and quadriceps muscle co-contraction during the squat compared with the other two exercises. During the leg press, the quadriceps muscle electromyographic activity was approximately 39% to 52% of maximal velocity isometric contraction; whereas hamstring muscle activity was minimal (12% maximal velocity isometric contraction). This study demonstrated significant differences in tibiofemoral forces and muscle activity between the two closed kinetic chain exercises, and between the open and closed kinetic chain exercises.

Adult↗

PubMed2003

Effect of antagonist muscle fatigue on knee extension torque.

The effect of hamstring fatigue on knee extension torque was examined at different knee angles for seven male subjects. Before and after a dynamic flexion fatigue protocol (180 degrees s(-1), until dynamic torque had declined by 50%), maximal voluntary contraction extension torque was measured at four knee flexion angles (90 degrees, 70 degrees, 50 degrees and 30 degrees ). Maximal torque generating capacity and voluntary activation of the quadriceps muscle were determined using electrical stimulation. Average rectified EMG of the biceps femoris was determined. Mean dynamic flexion torque declined by 48+/-11%. Extensor maximal voluntary contraction torque, maximal torque generating capacity, voluntary activation and average rectified EMG at the four knee angles were unaffected by the hamstring fatigue protocol. Only at 50 degrees knee angle was voluntary activation significantly lower (15.7%) after fatigue ( P<0.05). In addition, average rectified EMG before fatigue was not significantly influenced by knee angle. It was concluded that a fatigued hamstring muscle did not increase the maximal voluntary contraction extension torque and knee angle did not change coactivation. Three possible mechanisms may explain the results: a potential difference in recruited fibre populations in antagonist activity compared with the fibres which were fatigued in the protocol, a smaller loss in isometric torque generating capacity of the hamstring muscle than was expected from the dynamic measurements and/or a reduction in voluntary activation.

Adult↗

PubMed1988

Abnormalities in quadriceps-hamstring strength. Relationships in polymyositis and dermatomyositis.

Muscle strength determined as torque was measured in patients with dermatomyositis and polymyositis. Patients demonstrated weakness in both quadriceps and hamstring muscle groups. The ratio of quadriceps to hamstring torque (Q:H) was 1.93 +/- 0.38 in controls and 1.60 +/- 0.62 in patients. Patients with Q:H ratios that were below this mean were older, weaker, and were treated with greater doses of prednisone. Fifty-six percent of patients studied initially had low Q:H ratios, and 64% of all patients had low Q:H ratios at some time. The Q:H ratio in patients with steroid and thyroid myopathy, however, was not different than controls. It is hypothesized, therefore, that preferential involvement of the quadriceps group characterizes patients with inflammatory muscle disease.

Adult↗

PubMed1986

Effects of short-term electrical stimulation on the ultrastructure of rat skeletal muscles.

The purpose of this study was to determine the effects of short-term, 2,500-Hz carrier-wave frequency electrical stimulation on the ultrastructure of fast-twitch rat skeletal muscles. Thirteen Sprague-Dawley male rats were divided into three groups: daily treatment (Group 1), every-other-day treatment (Group 2), and control (Group 3). The medial quadriceps femoris and hamstring (semitendinosus and semimembranosus) muscles of the right thigh were treated with short-term electrical stimulation. After treatment, the animals were sacrificed, and their treated and sham quadriceps femoris and hamstring muscles were removed, fixed by immersion, and processed for electron microscopy. Morphometric measurements were made on electron micrographs using a Videoplan computer system, and the results were analyzed statistically. The results revealed that mitochondria, triads, and glycogen content of the fast-twitch muscles changed to resemble those of slow-twitch muscles. In view of these results, clinicians should consider the possibility that similar changes also might occur in human subjects under clinical conditions.

Animals↗

PubMed2006

Hamstring antagonist moment estimation using clinically applicable models: Muscle dependency and synergy effects.

The purpose of this study was to examine whether prediction of antagonist moment (M(flx)) of the hamstrings using clinically applicable models depends on the muscles examined. Nine healthy males performed maximal isometric knee extension and flexion contractions at 0 degrees , 45 degrees and 90 degrees angles. Calibration knee flexion efforts were also performed at different levels of intensity. The resulting electromyographic (EMG) - moment curves were fitted using polynomial equations which were then used to estimate M(flx) from the antagonist EMG. Analysis of variance designs showed that the M(flx) predicted using the biceps femoris EMG was not significantly different compared with those predicted using the semitendinosus EMG data (p>0.05). Further, prediction of M(flx) using the EMG of both muscles or a combination of EMGs and architectural properties reduced estimation error but did not provide significantly different predicted values compared with the simpler single-muscle EMG - moment models (p<0.05). It appears that M(flx) prediction using the present EMG - moment model is not muscle specific. Prediction using models which combine EMG data and anatomic parameters of the hamstring muscle components yielded more accurate estimates and therefore their use to examine co-contraction levels is recommended.

Achilles Tendon↗

PubMed2026

Intervention components, training dose, and adherence in exercise-based prevention of hamstring strain injury in football: a systematic review and meta-analysis.

OBJECTIVE: To quantify associations between exercise-based prevention programmes and hamstring strain injury (HSI) risk in football participants, and whether training dose and adherence modify effects. METHODS: Six databases were searched to 1 October 2025. Randomised and cluster-randomised trials comparing HSI prevention programmes with usual practice or warm-up in football participants were included. Random-effects meta-analysis pooled risk ratios (RRs); subgroup analyses and meta-regression assessed effect modification. RESULTS: Fifteen trials (n = 7,465) were analysed. Programmes reduced HSI risk (RR = 0.51, 95% CI 0.36-0.71), with I²=57% and a prediction interval crossing the null (0.18-1.40). Based on a control event rate of 7.8%, absolute risk reduction was 3.8% (38 fewer HSIs per 1000 participants; 95% CI 23-50 fewer). Effects were stronger for shorter interventions (1-6 months; RR = 0.43) than longer interventions (7-10 months; RR = 0.77; P for interaction=0.04), and for elite/semi-professional players (RR = 0.38) than amateur players (RR = 0.77; P for interaction = 0.02). Training frequency and weekly volume did not modify effects, whereas adherence did. High adherence (≥75%) was associated with lower HSI risk (RR = 0.36, 95% CI 0.28-0.48), whereas low adherence (<75%) showed no clear benefit (RR = 0.92, 95% CI 0.68-1.23; P for interaction <0.00001). Each 10% increase in adherence corresponded to an RR multiplier of 0.83 (approximately 17% lower RR). Certainty of evidence was low. CONCLUSION: Exercise-based programmes reduce HSI risk in football when implementation supports sustained adherence. Effects may be stronger in shorter interventions and elite populations, but evidence remains insufficient to differentiate programme types or components.

Humans↗

PubMedDate not supplied

Biomechanics of walking, running, and sprinting.

A biomechanical study of 13 runners which consisted of 2 male sprinters, 5 experienced joggers, and 6 elite long-distance runners were studied. We obtained hip, knee, and ankle joints motions in the sagittal plane and electromyographic data from specific muscle groups. As the speed of gait increased, the length of stance phase progressively decreased from 62% for walking to 31% for running and to 22% for sprinting. The sagittal plane motion increased as the speed of gait increased. Generally speaking, the body lowers its center of gravity with the increased speed by increasing flexion of the hips and knees and magnifying dorsiflexion at the ankle joint. Electromyographic activity about the knee demonstrated increased activity in the quadricep muscle group and hamstring group with increased speed. Muscle function about the ankle joint demonstrated that the posterior calf musculature which normally functions during the midstance phase in walking became a late swing phase muscle and was active through the first 80% of stance phase, as compared to 15% in walking. Beside the changes in the electromyographic activity of the muscles, the anterior compartment muscles of the calf undergo a concentric contracture at the time of initial floor contact during running and sprinting but undergo an eccentric contraction during walking.

Ankle Joint↗

PubMed1994

Pelvic stabilization during resistance training: its effect on the development of lumbar extension strength.

The purpose of this study was to evaluate and compare resistance exercise training with and without pelvic stabilization on the development of isolated lumbar extension strength. Isometric torque of the isolated lumbar extensor muscles was measured at seven positions through a 72 degree range-of-motion on 47 men and 30 women before and after 12 weeks of variable resistance lumbar extension training. Subjects were assigned to either a group that trained with pelvic stabilization (P-STAB, n = 21), a group that trained without pelvic stabilization (NO-STAB, n = 41), or a control group that did not train (n = 15). Subjects trained once a week with 8 to 12 repetitions to volitional exhaustion. The P-STAB and NO-STAB groups showed significant (p < or = 0.05) and similar increases in the weight load used for training (P-STAB = 24.1 +/- 9.4kg; NO-STAB = 19.4 +/- 11.0kg) during the 12-week training period. In contrast, posttraining isometric torque values describing isolated lumbar extension strength improved only for the P-STAB group (23.5%, p < or = 0.05) and not for the NO-STAB group (-1.2%, p > 0.05) relative to controls. These data indicate that pelvic stabilization is required to effectively train the lumbar extensor muscles. The increased training load for the NO-STAB group is probably the result of exercising the muscles involved in pelvic rotation (hamstring and buttock muscles).

Adult↗

PubMed1981

Isokinetic thigh muscle strength after ligament reconstruction in the knee joint: results from a 5-10 year follow-up after reconstructions of the anterior cruciate ligament in the knee joint.

We evaluated the thigh muscle strength using an isokinetic dynamometer in 80 patients 5 to 10 years following anterior cruciate ligament reconstruction. Patients with good results also had good muscle function, both of their flexor and their extensor muscles. Patients with poor results demonstrated reduced muscle strength in both their hamstrings and their quadriceps. Patients with fair functional results demonstrated reduced strength of their extensor muscles compared to their normal leg. However, strength in their operated leg's flexor muscles was unchanged compared to their normal leg. This may be due to the fact that strong hamstring muscles can compensate for some instability of the anterior cruciate ligament.

Adolescent↗

PubMed2001

Arthroscopically assisted reconstruction of the anterior cruciate ligament. A follow-up report.

BACKGROUND: The purpose of this study was to further delineate the outcome of arthroscopically assisted anterior cruciate ligament reconstruction in 125 patients who had previously been followed for two to five years. One of the original 125 patients was excluded from the present study because of insufficient follow-up, and an additional group of 101 patients was added. All 225 patients in the present study were followed for a minimum of six years. METHODS: Patients were randomly assigned to reconstruction with a double-stranded semitendinosus-gracilis graft with use of a two-incision technique (group I), reconstruction with a patellar ligament graft with use of a two-incision technique (group II), or reconstruction with a patellar ligament graft with use of a single-incision endoscopic technique (group III). The groups were compared with regard to the rate of graft failure, the amount of instability, knee strength, radiographic signs of degenerative changes, and functional outcome. RESULTS: There was no significant difference among the three groups with regard to the rate of graft failure, the amount of knee instability, or the functional outcome. A normal or nearly normal functional outcome was recorded for 208 (92%) of the 225 patients. There were significant differences among the groups with regard to quadriceps muscle-strength deficits: group I had fewer patients with deficits than group III, and groups I and III both had fewer patients with deficits than group II (p = 0.04). There also were significant differences among the groups with regard to hamstring muscle-strength deficits: group III had fewer patients with deficits than group II, and group II had fewer patients with deficits than group I (p < 0.01). Twelve knees (16%) in group I, six knees (8%) in group II, and eight knees (11%) in group III showed radiographic evidence of progressive degenerative changes, but the differences among the three groups were not significant. CONCLUSION: Although 11.6% of the 225 knees had radiographic evidence of degenerative arthritis at a minimum of six years after arthroscopically assisted reconstruction of the anterior cruciate ligament, the choice of graft and the technique of reconstruction did not seem to affect the rate of development of these changes.

Anterior Cruciate Ligament↗

PubMed1989

Cerebrovascular accidents.

CVA comprises a large number of clinical entities, depending on the site of infarction in the brain. Accurate evaluation of deficits in the patient's sensory and/or motor systems and the patient's intellectual status are paramount in establishing realistic rehabilitation goals. With respect to the motor system, two types of voluntary movement may occur. These include synergistic or pattern movement and selective movement. Spasticity in the affected lower extremity may result in a variety of lower-extremity deformities and contractures. Those most commonly encountered include hip flexion and adduction contracture, inadequate knee flexion and knee flexion contracture, and ankle equinus, varus, and equinovarus. Correct evaluation of deformities may be aided by the use of poly-EMG analysis and evaluation after nerve block or motor point blocks. In hemiplegic gait dysfunction, the basic requirements for functional ambulation include (1) ability to maintain standing balance; (2) voluntary hip flexion; (3) leg stability; and (4) ability to follow instructions and adequate motivation. Often a hemiplegic patient can be trained to ambulate if an adequate extensor synergy pattern develops, since mass extension can provide stability of the leg for weight bearing. Medical rehabilitative management of the CVA patient includes early mobilization, restorative exercises (including neuromuscular facilitation techniques), measures to prevent or correct contractures, the use of AFOs, and occasionally functional electrical stimulation. Orthopedic management of deformities in CVA is indicated where conservative measures fail. Surgical procedures seek to alter the forces causing shortening of the muscles and tendons. Hence, the most commonly performed surgical procedures include (1) tendon lengthening or release; (2) soft-tissue release; and (3) tendon transfer. Surgery for hip contractures is not common; however, occasional release of hip flexors is indicated when hip flexion contracture impedes ambulation or prone lying. Inadequate knee flexion, caused by dysphasic quadriceps contraction, can be corrected by release of the vastus medialis and rectus femoris muscles. Distal hamstring tendon release with or without knee joint capsule release is the surgical procedure of choice for severe knee flexion contractures. Surgical correction of an equinus deformity is by TAL, with or without neurectomy of tibial nerve branches to the gastrocsoleus muscles. Severe ankle varus may require a SPLATT procedure. Surgery for equinovarus includes the combined surgery for both equinus and varus (that is, TAL and SPLATT procedures). Toe curling is corrected by toe flexor releases.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebrovascular Disorders↗

PubMed2005

Surgical repair of complete proximal hamstring tendon ruptures in water skiers and bull riders: a report of four cases and review of the literature.

OBJECTIVE: Hamstring strains are one of the most common muscle strains in athletes; however, complete rupture of the proximal hamstring origin is rare and results from significant trauma. The objective of this paper is to present our experience of management of complete ruptures where surgical repair resulted in good results in both acute and delayed cases. METHODS: Two water skiers and two bull riders sustained complete rupture of the proximal origin of the hamstring muscles. All underwent repair of the hamstring origin and sciatic nerve neurolysis. A post operative hamstring rehabilitation programme was instituted. Regular follow up was performed at 2, 3, 6, 9, and 12 months. RESULTS: At a minimum final follow up of 12 months all patients had regained functional knee flexion strength with no pain and a near normal range of knee flexion. All four individuals were able to return to their previous line of work and three were able to return to their pre-injury level of sport. CONCLUSION: Complete rupture of the hamstring origin is a potentially devastating sports injury that has implications affecting the individual's activities of daily living as well as potential as a sportsperson. Surgical repair restores the distorted anatomy, allows early functional rehabilitation, and avoids the potential debilitating neurological problem of gluteal sciatica.

Activities of Daily Living↗

PubMed1998

Comparison of injuries in elite senior and junior Australian football.

Three thousand and thirty one AFL and 1034 injuries in the VSFL U/18 competition were recorded by club doctors over the 1992, 1993 and 1994 seasons. Hamstring strains had the highest incidence (86.4 per 10,000 player hours) and prevalence (30.2 hours missed per 1000 hours) of any injury in the AFL, but were significantly less common in the U/18 competition. Other injuries which were common in both competitions were ankle sprains, thigh haematomas, concussion, groin strains and head lacerations. Injury prevalence was higher overall in the AFL, with lower limb muscle strains (hamstring, calf, quadriceps) being significantly more prevalent than in the U/18 competition. Injuries which were significantly more prevalent in the U/18 competition included stress fractures and concussion. Subsequent to this study, coaches and medical staff in the U/18 competition were made aware of the high risk of stress fractures in young footballers with heavy training loads. The AFL injury survey is ongoing and in the process of being computerised; risk factors for specific injuries with high rates are being studied further.

Adolescent↗

PubMed2005

Hamstring injuries of the hip.

Hamstring injuries can be classified with regard to the site of involvement. Traumatic disorders at the proximal bone-tendon origin are best defined as avulsion injuries, such as ischial tuberosity fractures and hamstring tendon tears. Musculotendinous lesions include muscle strains and muscle contusions. Most hamstring injuries occur after in-direct trauma from excessive stretching or forceful contraction, leading to avulsion injuries or muscle strains and tears. Insufficient warm-up, lack of flexibility, inadequate muscle strength and endurance, or abnormal contraction and running may predispose to such injuries. In the event of blunt direct trauma, a muscle contusion, intramuscular hematoma, myositis ossificans, or compartment syndrome may develop.

Athletic Injuries↗

PubMed1999

Muscular strength, body composition and health responses to the use of testosterone enanthate: a double blind study.

To determine the effect the steroid, testosterone enanthate (TE) had on upper body strength, body composition and health. Twenty one male weight training subjects were randomly assigned in a double blind method to either a 3.5 mg(-1) x kg(-1) TE (n=11) or placebo (n=10) weight training group. The subjects were monitored during a 12 week administration phase and a subsequent 12 week follow up phase. Subjects were tested on a number of strength and size measurements, whilst having their health monitored. The results from the study revealed that the testosterone/weight training group improved significantly (p<0.05) more than the placebo/weight training group during and immediately after the administration phase on a 1 repetition maximum bench press. With regards to body composition, body weight, arm girth and rectus femoris circumference all increased significantly greater in the TE group compared to the placebo. Furthermore, the abdomen skinfold showed significant decreases in the TE group compared to the placebo group at post testing, follow up mid testing and the follow up post testing occasions. With the exception of the abdomen skinfold no within or between group differences were evident following a cycling off period of 12 weeks. Changes to baseline health indicators were reported in some subjects following testosterone usage. This included an average elevation in systolic blood pressure in all TE subjects by 10 mm Hg, a mild increase in hereditary frontal alopecia, increased muscle tightness (hamstrings and pectorals), a mild increase in libido over the first two weeks with a subsequent fall to normal, mild acne, subjective changes to personality including an increase in aggression, irritability and positive mood responses. Consequently, moderate doses of TE combined with weight training can result in short term significant changes in upper body strength and body composition, with corresponding changes to baseline health in some individuals.

Adult↗

PubMed1992

Coordination of the leg muscles in backlift and leglift.

Net joint moments are often used to quantify the loading of structures (e.g. the intervertebral disc at L5S1) during lifting. This quantification method is also used to evaluate the loading of the knee, for instance, to determine the effect of backlifting as opposed to leglifting. However, the true loading of the joint as derived from net joint moments can be obscured by a possible co-contraction of antagonists. To unravel the mechanisms that determine the net joint moments in the knee, the leglift was compared to the backlift. Although a completely different net knee moment curve was found when comparing the two lifting techniques, it appeared to be closely related to the ground reaction force vector and its orientation with respect to the joint centre of rotation (R > 0.995). This close relation was established by co-contraction of both flexors and extensors of the knee. Furthermore, a close relation appeared to exist between the joint moment difference between hip and knee and the activity difference between rectus femoris muscle and hamstring (R = 0.72 and 0.83 in leglift and backlift, respectively). The knee-ankle joint moment difference and the activity of the gastrocnemius showed a close relation as well (R = -0.89 and 0.96 in leglift and backlift, respectively). These relations can be interpreted as a mechanism to distribute net moments across joints. It is concluded that during lifting tasks the intermuscular coordination is aimed at coupling of joint moments, such that the ground reaction force points in a direction that provides balance during the movement. The use of net joint moments as direct indicators for joint loading (e.g. knee) seems, therefore, questionable.

Adult↗

PubMed1984

Responses of cardiac vagus and sympathetic nerves to excitation of somatic and visceral nerves.

Somato-vagal and somato-sympathetic reflex responses were studied by recording simultaneously the activity of cardiac vagal and sympathetic efferents following excitation of various somatic (and 1 visceral) nerves in chloralose-anesthetized dogs. Stimulation of pure cutaneous (infraorbital, superficial radial, sural nerves), muscle (gastrocnemius, hamstring nerves) and mixed nerves (sciatic, brachial, intercostal, spinal) with short trains of pulses inhibited the activity of cardiac vagus nerve and excited that of cardiac sympathetic nerve after a latency of approximately 40-60 ms, depending on the nerve stimulated. These responses were followed by the opposite response, i.e. excitation of vagus and long-lasting inhibition ('silent period') of sympathetic nerve activity. These biphasic reflex responses recorded from both autonomic nerves had similar latencies so that a clear reciprocal relationship was observed. In addition to the above reflex responses which were observed in most instances, two peaks of excitation of short duration were recorded from the vagus nerve, in some instances, and an 'early (spinal) reflex' in sympathetic nerve was also observed. Both excitatory and inhibitory responses described above in either nerve were readily evoked by excitation of Group II (A beta), but not Group I (A alpha), afferent fibers and increased in magnitude when Group III (A delta) afferents were also excited. Group IV (C) afferent contributed insignificantly to the somato-vagal reflex. The vagus nerve discharge evoked by sinus nerve stimulation was inhibited during reflex inhibition produced by somatic nerve stimulation. The latency of such inhibition was less than 20 ms and lasted for 100 ms after sural nerve stimulation. We conclude that, as in case of the baroreceptor reflex and autonomic component of the 'defense reaction', the somato-vagal and somato-sympathetic reflex responses are reciprocal in nature.

Animals↗

PubMed2003

The effects of ACL injury on lower extremity activation during closed kinetic chain exercise.

AIM: Injury to the anterior cruciate ligament (ACL) has been suggested to alter the neuromuscular mechanism in the lower extremity. However, conclusive evidence regarding this occurrence has yet to be established during closed kinetic chain exercise. The purpose of this study was to assess differences in muscle activation during slideboard exercise between non-injured, ACL deficient, and ACL reconstructed individuals. METHODS EXPERIMENTAL DESIGN: comparative study. SETTING: research laboratory. PARTICIPANTS: subjects for this study included 10 healthy, non-injured (NI) individuals, 7 uni-lateral ACL deficient (ACLD) individuals, and 6 uni-lateral ACL reconstructed (ACLR) individuals. INTERVENTIONS: EMG activity was measured from the vastus medialis (VM), vastus lateralis (VL), medial hamstring (MH), lateral hamstring (LH), tibialis anterior (TA), and medial gastrocnemius (MG) muscles during slideboard performance. MEASURES: EMG for each muscle during each of 6 phases of 1 average slideboard cycle was expressed as a percentage of EMG during a maximal voluntary contraction. RESULTS: The results demonstrated that during slideboard phase I the VM, VL, and TA muscles generated the greatest amount of activity as compared to the other muscles. Vastus medialis muscle activation was found to be significantly higher than the other muscles in the involved/dominant limb, as compared to the non-involved/non-dominant limb during slideboard phase II. During slideboard phases III-VI, tibialis anterior muscle activation was found to be consistently higher than the other muscles, while hamstring muscle activity was consistently the lowest. CONCLUSION: It is concluded that adaptive changes following ACL injury during a dynamic, closed kinetic chain activity such as the slideboard exercise, may be a restoration of a bi-lateral balance in muscle activation.

Adult↗