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PubMed1997

The action of the rectus femoris muscle following distal tendon transfer: does it generate knee flexion moment?

Rectus femoris transfer surgery involves detaching the rectus femoris from the patella and reattaching it posterior to the knee. While this procedure is thought to convert the rectus femoris from a knee extensor to a knee flexor, the moments generated by this muscle after transfer have never been measured. We used intramuscular electrodes to stimulate the rectus femoris in four subjects, two after transfer to the semitendinosus and two after transfer to the iliotibial band, while measuring the resultant knee moment. Electromyographic activity was monitored in the quadriceps, hamstrings, and gastrocnemius muscles to verify that the rectus femoris was the only muscle activated by the stimulus. We found that the rectus femoris generated a knee extension moment in all of the subjects tested. This finding suggests that transfer surgery does not convert the rectus femoris to a knee flexor, and that a mechanism exists which may transmit the force generated by the rectus femoris anterior to the knee joint center after distal tendon transfer.

Adolescent↗

PubMed2000

Muscle force production and functional performance in spastic cerebral palsy: relationship of cocontraction.

OBJECTIVE: To determine cocontraction's relation to strength and motor function in children with spastic cerebral palsy (CP). DESIGN: Prospective evaluation with a convenience sample of 10 subjects. SETTING: Pediatric rehabilitation center at a tertiary care hospital. PATIENTS: Ten ambulatory children with spastic CP, mean age 5 to 14yrs. MAIN OUTCOME MEASURES: A single comprehensive assessment of hamstring and quadriceps muscle strength; gait analysis while monitoring electromyographic (EMG) activity in those muscles; administration of the Gross Motor Function Measure (GMFM); heart-rate monitoring during quiet rest versus gait to compute an energy expenditure index (EEI). Cocontraction ratios and magnitudes were determined for the gait and strength testing trials using the EMG data. RESULTS: Cocontraction ratios during strength tests correlated directly with those during free gait. Cocontraction magnitude and total EMG magnitude had an inverse relationship to EEI; children with more muscle activity in the agonist and antagonist tended to be more energy efficient. Knee extensor muscle strength correlated positively with the GMFM and gait velocity. Neither cocontraction ratio nor magnitude during gait was related to strength. CONCLUSIONS: Children with CP used a similar muscle activation strategy across two different motor tasks. Strength and cocontraction were uniquely related to different aspects of motor function. Further research is needed to quantify more precisely cocontraction and force to EMG relations in this population.

Adolescent↗

PubMed2002

Intra- and extra-articular anterior cruciate ligament reconstruction utilizing autogeneous semitendinosus and gracilis tendons: 5-year clinical results.

This prospective study examined 50 patients who underwent ACL surgery using hamstring tendons with a modification including intra- and extra-articular reconstruction. All patients were athletes competing at a high level in various sports. Full return to sports was allowed at 4 months. IKDC score and KT-2000 were used for assessing clinical outcome at a mean of 6.4 years (5-7 years) Resumption of sport, Tegner activity score, and isokinetic test were also used. The IKDC score showed 92% of normal or nearly normal knees. Of the 50 patients 48 regained full extension, and only two had extension deficit between 0 degrees and 3 degrees. KT evaluation was less than 3 mm in 38 cases (76%), 3-5 mm in 9 (18%), and more than 5 mm in 3 (6%). In 90% of cases the patient resumed sport at the same level. The mean Tegner activity score was 8.1 (5-10). The isokinetic test showed no deficit for hamstring and quadriceps muscles. Removal of staples was necessary in eight cases (16%) due to femoral lateral bursitis. Acute reconstruction had significantly better clinical assessment of abnormal laxity and KT value. Men had significantly better results then women. This technique demonstrated a high reliability, low morbidity, low functional deficit and fast recovery using hamstring grafts.

Acute Disease↗

PubMed2004

Genetic variation in the human vitamin D receptor is associated with muscle strength, fat mass and body weight in Swedish women.

OBJECTIVE: Bone mineral density (BMD) is under strong genetic control and a number of candidate genes have been associated with BMD. Both muscle strength and body weight are considered to be important predictors of BMD but far less is known about the genes affecting muscle strength and fat mass. The purpose of this study was to investigate the poly adenosine (A) repeat and the BsmI SNP in the vitamin D receptor (VDR) in relation to muscle strength and body composition in healthy women. DESIGN: A population-based study of 175 healthy women aged 20-39 years was used. METHODS: The polymorphic regions in the VDR gene (the poly A repeat and the BsmI SNP) were amplified by PCR. Body mass measurements (fat mass, lean mass, body weight and body mass index) and muscle strength (quadriceps, hamstring and grip strength) were evaluated. RESULTS: Individuals with shorter poly A repeat, ss and/or absence of the linked BsmI restriction site (BB) have higher hamstring strength (ss vs LL, P=0.02), body weight (ss vs LL, P=0.049) and fat mass (ss vs LL, P=0.04) compared with women with a longer poly A repeat (LL) and/or the presence of the linked BsmI restriction site (bb). CONCLUSIONS: Genetic variation in the VDR is correlated with muscle strength, fat mass and body weight in premenopausal women. Further functional studies on the poly A microsatellite are needed to elucidate whether this is the functionally relevant locus or if the polymorphism is in linkage disequilibrium with a functional variant in a closely situated gene further downstream of the VDR 3'UTR.

Absorptiometry, Photon↗

PubMed2001

Neuromuscular Response Characteristics in Men and Women After Knee Perturbation in a Single-Leg, Weight-Bearing Stance.

OBJECTIVE: We examined whether muscle response times and activation patterns in the lower extremity differed between men and women in response to a rotational knee perturbation while standing in a single-leg, weight-bearing stance. DESIGN AND SETTING: We used a lower extremity perturbation device to produce a sudden, forward, and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Subjects completed 10 trials of both internal and external rotation perturbation; the first 5 acceptable trials were averaged and used for data analysis. Two separate, repeated-measures analyses of variance were used to compare myoelectric response times and activation patterns between men and women for both internal and external rotation perturbation. SUBJECTS: Thirty-two female (19 lacrosse, 13 soccer) and 32 male (lacrosse) healthy intercollegiate athletes participated in the study. MEASUREMENTS: We used surface electromyography to record long latency reflex times of the medial and lateral quadriceps, hamstring, and gastrocnemius muscles. RESULTS: Women responded faster than men, primarily due to a shorter latency in quadriceps activation. However, men and women exhibited no difference in muscle-recruitment order. CONCLUSIONS: Although men and women demonstrated similar muscle-recruitment patterns to an imposed lower extremity perturbation, women tended to activate their quadriceps earlier than men. Whether this earlier quadriceps activation diminishes the ability of the hamstrings to adequately stabilize the knee joint or subjects the anterior cruciate ligament to greater risk of injury is still unknown and requires further study. Furthermore, although surface electromyography and measurement of myoelectric response times are useful in evaluating the timing, activation order, and coactivity patterns of the knee musculature, future studies should evaluate sex differences across the complete response continuum, including measures of intrinsic muscle stiffness, electromechanical delay, and time to force production.

Journal Article↗

PubMedDate not supplied

Therapeutic electrical stimulation for spasticity: quantitative gait analysis.

Improvement in motor function following electrical stimulation is related to strengthening of the stimulated spastic muscle and inhibition of the antagonist. A 26-year-old man with familial spastic paraparesis presented with gait dysfunction and bilateral lower limb spastic muscle tone. Clinically, muscle strength and sensation were normal. He was considered appropriate for a trial of therapeutic electrical stimulation following failed trials of physical therapy and baclofen. No other treatment was used concurrent with the electrical stimulation. Before treatment, quantitative gait analysis revealed 63% of normal velocity and a crouched gait pattern, associated with excessive electromyographic activity in the hamstrings and gastrocnemius muscles. Based on these findings, bilateral stimulation of the quadriceps and anterior compartment musculature was performed two to three times per week for three months. Repeat gait analysis was conducted three weeks after the cessation of stimulation treatment. A 27% increase in velocity was noted associated with an increase in both cadence and right step length. Right hip and bilateral knee stance motion returned to normal (rather than "crouched"). No change in the timing of dynamic electromyographic activity was seen. These findings suggest a role for the use of electrical stimulation for rehabilitation of spasticity. The specific mechanism of this improvement remains uncertain.

Adult↗

PubMed2006

Influence of vibration on delayed onset of muscle soreness following eccentric exercise.

UNLABELLED: Delayed onset muscle soreness (DOMS), which may occur after eccentric exercise, may cause some reduction in ability in sport activities. For this reason, several studies have been designed on preventing and controlling DOMS. As vibration training (VT) may improve muscle performance, we designed this study to investigate the effect of VT on controlling and preventing DOMS after eccentric exercise. METHODS: Fifty healthy non-athletic volunteers were assigned randomly into two experimental, VT (n = 25) and non-VT (n = 25) groups. A vibrator was used to apply 50 Hz vibration on the left and right quadriceps, hamstring and calf muscles for 1 min in the VT group, while no vibration was applied in the non-VT group. Then, both groups walked downhill on a 10 degrees declined treadmill at a speed of 4 km/hour. The measurements included the isometric maximum voluntary contraction force (IMVC) of left and right quadriceps muscles, pressure pain threshold (PPT) 5, 10 and 15 cm above the patella and mid-line of the calf muscles of both lower limbs before and the day after treadmill walking. After 24 hours, the serum levels of creatine-kinase (CK), and DOMS level by visual analogue scale were measured. RESULTS: The results showed decreased IMVC force (P = 0.006), reduced PPT (P = 0.0001) and significantly increased mean of DOMS and CK levels in the non-VT group, compared to the VT group (P = 0.001). CONCLUSION: A comparison by experimental groups indicates that VT before eccentric exercise may prevent and control DOMS. Further studies should be undertaken to ascertain the stability and effectiveness of VT in athletics.

Adult↗

PubMed2001

Homozygosity and linkage disequilibrium mapping of autosomal recessive distal myopathy (Nonaka distal myopathy).

Autosomal recessive distal myopathy or Nonaka distal myopathy (NM) is characterized by its unique distribution of muscular weakness and wasting. The patients present with spared quadriceps muscles even in a late stage of the disease. The hamstring and tibialis anterior muscles are affected severely in early adulthood. We have localized the NM gene to the region between markers D9S319 and D9S276 on chromosome 9 by linkage analysis. To further refine the localization of the NM gene, we conducted homozygosity and linkage disequilibrium analysis for 14 patients from 11 NM families using 18 polymorphic markers. All of the patients from consanguineous NM families were found to be homozygous for six markers located within the region between markers D9S2178 and D9S1859. We also provided evidence for significant allelic associations between the NM region and five marker loci. Examination of the haplotype analysis identified a predominant ancestral haplotype comprising the associated alleles 199-160-154-109 (marker order: D9S2179-D9S2180-D9S2181-D9S1804), present in 60% of NM chromosomes and in 0% of parent chromosomes. On the basis of the data obtained in this study, the majority of NM chromosomes were derived from a single ancestral founder, and the NM gene is probably located within the 1.5-Mb region between markers D9S2178 and D9S1791.

Adult↗

PubMed1989

Functional electrical stimulation and lower extremity bracing for ambulation exercise of the spinal cord injured individual: a medically prescribed system.

The purpose of this study was to determine whether commercially available electrical muscle stimulators could provide functional ambulation exercise for the spinal cord injured individual. Commercially available electrical muscle stimulators were used for functional electrical stimulation and interfaced with reciprocating gait orthoses so that a new system has been developed. Advantages of the system include commercially available subsystems and subsystems for applications such as gait training. The system involves six electrical stimulation units worn on a belt; controlled by remote switches; and interfacing to electrodes placed over the quadriceps femoris, hamstring, and gluteal muscle groups of each leg. Four electrical stimulation units (for quadriceps femoris muscle stimulation) function primarily for stand-up and sit-down activities. Two other units (for stimulation of the hip extensor muscles) function primarily for ambulation. The system is described for use with a C7-level quadriplegic individual. The patient successfully performed over 20 repetitions of stand-up and sit down exercises with the system. An average walking distance of about 0.8 km was routinely traversed at velocities ranging from 1.2 to 2.0 km per hour. It was concluded that muscle fatigue, rather than battery power, was the functionally limiting factor for the quadriplegic patient. A recommendation is that application of the system for walking exercise should be preceded by a physical conditioning program of functional electrical stimulation. Specific medical criteria should be satisfied prior to formally prescribing the system for an individual. Finally, the steps involved in the writing of the walking system prescription are outlined.

Adult↗

PubMed2004

An analysis of the ratio and relationship between upper body pressing and pulling strength.

It has been posited that certain balances in strength should exist for opposing muscle groups (e.g., hamstrings and quadriceps) or actions (e.g., internal and external rotation of the shoulder) to improve sports performance or limit the likelihood of injury. Typically, expensive laboratory equipment such as isokinetic devices has been used to evaluate strength balances. The purpose of this study was to determine if two popular field tests of strength could be used to assess a concise strength balance in roughly opposing muscle actions for the shoulder girdle. The two opposing movement actions of pressing away from the shoulder girdle and pulling in towards the shoulder girdle were assessed via the 1 repetition maximum bench press (1RM BP) and 1 repetition maximum pull-up (1RM PU), respectively. Forty-two rugby league players, comprising 21 national league (NRL) and 21 state league (SRL) players, who regularly performed both exercises in their training, served as subjects in this investigation. The equivalence of the strength ratio (BP/PU x 100) and correlation between tests were also examined. The pooled data exhibited a strength ratio of 97.7% (9.0%) and correlation of r = 0.81 between the 1RM BP of 130.1 +/- 20.2 kg and 1RM PU of 133.1 +/- 17.1 kg. The small standard deviation exhibited tends to indicate that athletes should exhibit a concise ratio of around 100% if pressing and pulling strength have been addressed fairly equally in training. However, some athletes may have body types, preexisting injuries, or training histories that predispose them to either excelling or performing poorly during strength activities for either upper body pressing or pulling actions, with differences in strength of up to 15% existing in some individuals. These factors need to be taken into account when prescribing training based upon the strength ratio between pressing and pulling strength.

Adult↗

PubMed1996

Hamstrings and psoas lengths during normal and crouch gait: implications for muscle-tendon surgery.

Crouch gait, one of the most common movement abnormalities among children with cerebral palsy, is characterized by persistent flexion of the knee during the stance phase. Short hamstrings are thought to be the cause of crouch gait; thus, crouch gait is often treated by surgical lengthening of the hamstrings. In this study, a graphics-based model of the lower extremity was used in conjunction with three-dimensional kinematic data obtained from gait analysis to estimate the lengths of the hamstrings and psoas muscles during normal and crouch gaits. Only three of 14 subjects with crouch gait (four of 20 limbs with knee flexion of 20 degrees or more throughout stance) had hamstrings that were shorter than normal by more than 1 SD during walking. Most (80%) of the subjects with crouch gait had hamstrings of normal length or longer, despite persistent knee flexion during stance. This occurred because the excessive knee flexion was typically accompanied by excessive hip flexion throughout the gait cycle. All of the subjects with crouch gait had a psoas that was shorter than normal by more than 1 SD during walking. These results emphasize the need to consider the geometry and kinematics of multiple joints before performing surgical procedures aimed at correcting crouch gait.

Adolescent↗

PubMed1998

Models of ensemble firing of muscle spindle afferents recorded during normal locomotion in cats.

1. The aim of this work was to compare the ability of several mathematical models to predict the firing characteristics of muscle spindle primary afferents recorded chronically during normal stepping in cats. 2. Ensemble firing profiles of nine hamstring spindle primary (presumed group Ia) afferents were compiled from stored data from 132 step cycles. Three sets of profiles corresponding to slow, medium and fast steps were generated by averaging groups of step cycles aligned to peak muscle length in each cycle. 3. Five models obtained from the literature were compared. Each of these models was used to predict the spindle firing profiles from the averaged muscle length signals. The models were also used in the reverse direction, namely to predict muscle length from the firing profiles. A sixth model incorporating some key aspects of the other models was also included in the comparisons. 4. Five of the models predicted spindle firing well, with root mean square (r.m.s.) errors lower than 14 % of the modulation depth of the target profiles. The key variable in achieving good predictions was muscle velocity, the best fits being obtained with power-law functions of velocity, with an exponent of 0.5 or 0.6 (i.e. spindle firing rate is approximately proportional to the square root of muscle velocity). The fits were slightly improved by adding small components of EMG signal to mimic fusimotor action linked to muscle activation. The modest relative size of EMG-linked fusimotor action may be related to the fact that hamstring muscles are not strongly recruited in stepping. 5. Length was predicted very accurately from firing profiles with the inverse of the above models, indicating that the nervous system could in principle process spindle firing in a relatively simple way to give accurate information on muscle length. 6. The responses of the models to standard ramp-and-hold displacements at 10 mm s-1 were also studied (i.e. velocities that were an order of magnitude lower than that during stepping). In these cases components of spindle primary response related to length as well as velocity were needed for good fits. Because these length-related components detracted from rather than improved predictions of the step cycle data, an attenuation of length dependence at high muscle velocities emerged as a possibility. 7. We conclude that in this study we have identified models and parameters that may be used to predict spindle afferent firing from the time course of muscle length in the cat step cycle.

Animals↗

PubMed1999

Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight-bearing flexion.

Strengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight-bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings force significantly reduced internal rotation (p<0.0001) and anterior translation (p<0.0001), increased quadriceps force (p<0.0001) and normal resultant force on the tibia (p<0.0001), and reversed the direction of the shear force on the tibia (p<0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament-deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.

Aged↗

PubMed1985

Muscular activity during ergometer cycling.

The aim of the study was to quantify the activity as recorded by electromyography during ergometer cycling in eleven different muscles of the lower extremity. Eleven healthy subjects rode in twelve different ways at different work-load, pedalling rate, saddle height and pedal foot position. Vastus medialis and lateralis, gastrocnemius medialis and lateralis and the soleus muscle were the most activated muscles. Changes in muscle activity during different calibrations were studied in eight of the eleven muscles. An increase in work-load significantly increased the mean maximum activity in all the eight muscles investigated. An increase of the pedalling rate increased the activity in the gluteus maximus, gluteus medius, vastus medialis, medial hamstring, gastrocnemius medialis and soleus muscles. An increase of the saddle height increased the muscle activity in the gluteus medius, medial hamstring and gastrocnemius medialis muscles. Use of a posterior pedal foot position increased the activity in the gluteus medius and rectus femoris muscles, and decreased the activity in the soleus muscle.

Adult↗

PubMed1994

Instrumental straight-leg raising: results in patients.

Straight-leg raising is used as a diagnostic test for both elastogenic (passive muscle stretch test) and nonelastogenic (Lasègue's test) pathology in patients unable to bend forward from the standing position while holding the knees in extension. The test assessment is based on the range of the leg excursion and the type of pain that is provoked. An instrumental version of Lasègue's test (instrumental straight-leg raising) provides information about the extensibility, elasticity and electrical activity of the hamstrings and back muscles and about pelvic rotation. To investigate the diagnostical value of the additional information, both clinical and instrumental straight-leg raising was done by 30 patients who were unable to touch the ground while bending forward from the standing position with the knees extended. In one group of patients, the electrical activity of the muscles was comparable to that observed in the muscles of a control group of healthy volunteers; in a second group, however, the electrical muscle activity was aberrant. Muscle extensibility and passive muscle elasticity was comparable in patients in the first group and the healthy controls. In the patients with aberrant muscle activity, the elasticity of the passive muscles was not different from the control group, but both leg excursion and muscle extensibility were much smaller. Comparison of the clinically and experimentally diagnosed cause (elastogenic or non-elastogenic) of the movement restriction showed a remarkable discrepancy. We conclude that instrumental straight-leg raising provides valuable additional diagnostical information.

Adolescent↗

PubMed2004

Knee joint laxity affects muscle activation patterns in the healthy knee.

This study investigated the effects of anterior knee joint laxity on muscle activation patterns prior to and following a lower extremity perturbation. Participants were subjected to a forward and either internal (IR) or external (ER) rotation perturbation of the trunk and thigh on the weight-bearing shank. Pre-activity (%MVIC) before the perturbation, and reflex time (ms) and mean reflex amplitude (%MVIC) following the perturbation were recorded via surface electromyography (sEMG) in the medial and lateral gastrocnemius, hamstring and quadriceps muscles. Twenty-one NCAA DI intercollegiate female athletes with below average anterior knee laxity (3-5 mm) were compared to 21 with above average anterior knee laxity (7-14 mm) as measured by a standard knee arthrometer. Groups differed in reflex timing by muscle (P = 0.013), with females with above average knee laxity (KT((>7 mm))) demonstrating a 16 ms greater delay in biceps femoris reflex timing compared to females with below average knee laxity (KT((<5 mm))). Groups also differed in muscle activation amplitude by response, muscle and direction of rotation (i.e. a 4-way interaction; P = 0.027). The magnitude of change from pre to post perturbation was significantly less in KT((>7 mm)) vs. KT((<5 mm)) for the medial (MG) and lateral (LG) gastrocnemius muscles, primarily due to higher levels of muscle preactivity while awaiting the perturbation (MG = 20% vs. 12% MVIC, P = 0.05; LG = 33% vs. 21% MVIC, P = 0.11). Further, KT((>7 mm)) demonstrated higher activation levels in the biceps femoris than KT((<5 mm)) (47% vs. 27% MVIC; P = 0.025) regardless of response (pre vs. post perturbation) or direction of rotation. These findings suggest females with increased knee laxity may be less sensitive to joint displacement or loading (delayed reflex), and are more reliant on active control of the gastrocnemius and biceps femoris muscles to potentially compensate for reduced passive joint stability.

Adult↗

PubMed2005

The relationship between quadriceps muscle force, knee flexion, and anterior cruciate ligament strain in an in vitro simulated jump landing.

BACKGROUND: An instrumented cadaveric knee construct was used to quantify the association between impact force, quadriceps force, knee flexion angle, and anterior cruciate ligament relative strain in simulated unipedal jump landings. HYPOTHESIS: Anterior cruciate ligament strain will correlate with impact force, quadriceps force, and knee flexion angle. STUDY DESIGN: Descriptive laboratory study. METHODS: Eleven cadaveric knees (age, 70.8 [19.3] years; 5 male; 6 female) were mounted in a custom fixture with the tibia and femur secured to a triaxial load cell. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated using pretensioned steel cables (stiffness, 7 kN/cm), and the quadriceps tendon force was measured using a load cell. Mean strain on the anteromedial bundle of the anterior cruciate ligament was measured using a DVRT. With the knee in 25 degrees of flexion, the construct was vertically loaded by an impact force initially directed 4 cm posterior to the knee joint center. Tibiofemoral kinematics was measured using a 3D optoelectronic tracking system. RESULTS: The increase in anterior cruciate ligament relative strain was proportional to the increase in quadriceps force (r(2) = 0.74; P < .00001) and knee flexion angle (r(2) = 0.88; P < .00001) but was not correlated with the impact force (r(2) = 0.009; P = .08). CONCLUSION: The increase in knee flexion and quadriceps force during this simulated 1-footed landing strongly influenced the relative strain on the anteromedial bundle of the anterior cruciate ligament. CLINICAL RELEVANCE: These results suggest that even in the presence of knee flexor muscle forces, the increase in quadriceps force required to prevent the knee from flexing during landing can place the anterior cruciate ligament at risk for large strains.

Aged↗

PubMed2005

Quadriceps femoris muscle morphology and function after ACL injury: a differential response in copers versus non-copers.

The morphology (volume and peak cross-sectional area) and voluntary muscle control of 27 athletic people were evaluated with magnetic resonance imaging (MRI) and an established method of testing neuromuscular control in order to explain why some people are able to cope with anterior cruciate ligament (ACL) injury (copers), whereas most cannot (non-copers). Axial spin-echo T1 weighted MRI images were acquired from the level of the ankle mortise to the iliac crest. The subjects' quadriceps, hamstrings, and gastrocnemius muscles were digitally reconstructed from the MRI images. The volume and peak cross-sectional area (CSA) of each muscle were then calculated. Voluntary muscle control was evaluated using an established target-matching protocol that requires subjects to produce and modulate force with control over a range of directions. Electromyographic signals were collected from seven muscles as the subjects performed the experiment. Circular statistics methods were used to calculate a specificity index that describes how focused the activity pattern of each muscle was with respect to its principal direction of action. The results of the non-copers, copers, and uninjured subjects were then compared. The non-copers displayed significantly greater quadriceps atrophy than the copers. The most profound differences were observed in the vastus lateralis muscle. The non-copers also displayed diminished vastus lateralis and lateral gastrocnemius muscle control. Little differences were observed in the results of the copers and uninjured subjects. In general, the copers' results fell between those of the non-copers and uninjured subjects. The results of this study suggest that quadriceps muscle function is a critical factor in the differential response to ACL injury.

Adolescent↗