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PubMed1992

Foot trajectory in human gait: a precise and multifactorial motor control task.

The trajectory of the heel and toe during the swing phase of human gait were analyzed on young adults. The magnitude and variability of minimum toe clearance and heel-contact velocity were documented on 10 repeat walking trials on 11 subjects. The energetics that controlled step length resulted from a separate study of 55 walking trials conducted on subjects walking at slow, natural, and fast cadences. A sensitivity analysis of the toe clearance and heel-contact velocity measures revealed the individual changes at each joint in the link-segment chain that could be responsible for changes in those measures. Toe clearance was very small (1.29 cm) and had low variability (about 4 mm). Heel-contact velocity was negligible vertically and small (0.87 m/s) horizontally. Six joints in the link-segment chain could, with very small changes (+/- 0.86 degrees - +/- 3.3 degrees), independently account for toe clearance variability. Only one muscle group in the chain (swing-phase hamstring muscles) could be responsible for altering the heel-contact velocity prior to heel contact. Four mechanical power phases in gait (ankle push-off, hip pull-off, knee extensor eccentric power at push-off, and knee flexor eccentric power prior to heel contact) could alter step length and cadence. These analyses demonstrate that the safe trajectory of the foot during swing is a precise endpoint control task that is under the multisegment motor control of both the stance and swing limbs.

Adult↗

PubMed1994

Experimental Chagas' disease: electrophysiology and cell composition of the neuromyopathic inflammatory lesions in mice infected with a myotropic and a pantropic strain of Trypanosoma cruzi.

C3H/HeN mice infected with the pantropic/reticulotropic Trypanosoma cruzi RA strain disclosed electromyographic signs (EMG) of neuropathic damage, while those infected with the myotropic CA-I strain showed EMG suggestive of primary muscle involvement. Although both strains induced inflammatory infiltrates in hamstring muscles (HM), damage was more severe in mice infected with CA-I. In sciatic nerves (SN) of mice infected with the RA strain, increased inflammatory changes, amastigote nests, and myelin digestion chambers were consistently found during the course of infection. On the other hand, the CA-I strain produced minor inflammatory changes without detectable amastigotes in such tissue. The RA strain induced chronic leptomeningitis in spinal cord (SC), while infiltrates were limited to spinal roots and dorsal ganglia in animals infected with CA-I. In mice infected with RA, phenotypic analysis of inflammatory lesions showed a consistent predominance of CD8+ T cells in nervous tissue throughout the course of infection and in HM during the chronic phase whereas natural killer cells were detected at 120 and 270 days pi. In mice infected with CA-I, a predominance of CD8+ cells in SN was only detected during the acute phase and in HM during the late chronic phase; B lymphocytes bearing surface IgM were present in all studied tissues at 270 days pi. In addition, positive fluorescence for mouse IgG was observed at 120 days pi in muscle interstitium. These results strongly suggest that T. cruzi strain-dependent mechanisms are involved in the development of neuromyopathic damage.

Animals↗

PubMed1997

The effect of pedaling rate on coordination in cycling.

To further understand lower extremity neuromuscular coordination in cycling, the objectives of this study were to examine the effect of pedaling rate on coordination strategies and interpret any apparent changes. These objectives were achieved by collecting electromyography (EMG) data of eight lower extremity muscles and crank angle data from ten subjects at 250 W across pedaling rates ranging from 45 to 120 RPM. To examine the effect of pedaling rate on coordination, EMG burst onset and offset and integrated EMG (iEMG) were computed. In addition, a phase-controlled functional group (PCFG) analysis was performed to interpret observed changes in the EMG patterns in the context of muscle function. Results showed that the EMG onset and offset systematically advanced as pedaling rate increased except for the soleus which shifted later in the crank cycle. The iEMG results revealed that muscles responded differently to increased pedaling rate. The gastrocnemius, hamstring muscles and vastus medialis systematically increased muscle activity as pedaling rate increased. The gluteus maximus and soleus had significant quadratic trends with minimum values at 90 RPM, while the tibialis anterior and rectus femoris showed no significant association with pedaling rate. The PCFG analysis showed that the primary function of each lower extremity muscle remained the same at all pedaling rates. The PCFG analysis, which accounts for muscle activation dynamics, revealed that the earlier onset of muscle excitation produced muscle activity in the same region of the crank cycle. Also, while most of the muscles were excited for a single functional phase, the soleus and rectus femoris were excited during two functional phases. The soleus was classified as an extensor-bottom transition muscle, while the rectus femoris was classified as a top transition-extensor muscle. Further, the relative emphasis of each function appeared to shift as pedaling rate was increased, although each muscle remained bifunctional.

Adult↗

PubMed1981

The sizes of motoneurons supplying hindlimb muscles in the mouse.

Motoneurons supplying identified muscle groups in the mouse spinal cord were labelled by retrograde transport of horseradish peroxidase. The size of motoneurons was estimated by measuring perimeter and cross-sectional area at the level of the nucleolus for the following seven major muscle groups: quadriceps femoris, adductors and gracilis, gluteal musculature, hamstring muscles, posterior crural musculature, anterolateral crural musculature and intrinsic musculature of the foot. The qualitative observation of two size ranges of motoneuron was supported by the measurements. Frequency distribution histograms of motoneuronal cross sectional area were bimodal for all motoneuronal groups except for the foot musculature. The population parameters and proportions for the six bimodal histograms were estimated by the method of maximum likelihood. It was found that the mean area of the small neuron component, which were presumed to be gamma motoneurons, was similar for the six bimodal systems. In contrast to this the mean area of the large neuron component, presumed to be alpha motoneurons, was found to be different for the six bimodal systems; motoneurons supplying more proximal muscles showed a larger mean area than those supplying distal muscles. The mean area of both components was unaffected by survival time and this was interpreted as indicating that changes in survival time did not label greater numbers of small or large motoneurons. The proportion of motoneurons in the small neuron component was found to vary from 9 to 27%.

Animals↗

PubMed1990

Surgical treatment of knee dysfunction in cerebral palsy.

The prerequisites for normal gait are: (1) stability in the stance phase of gait, (2) clearance of the foot in the swing phase, (3) proper foot preposition in swing, and (4) an adequate step length. In the stance phase, the knee provides shock absorption and energy conservation; in the swing phase, it allows foot clearance. To accomplish these functions, the knee must extend fully in stance and flex approximately 60 degrees in swing. Consequently, balanced muscle action at the hip, knee, and ankle joints, combined with adequate acceleration from the hip flexor and triceps surae muscles, is essential. In the crouch gait of spastic cerebral palsy, hamstring lengthening alone often converts the flexed-knee gait to an extended-knee, stiff-legged gait with inadequate swing-phase knee flexion. This unwanted conversion is due to cospasticity of the quadriceps and hamstring muscles. Restoration of normal knee function in patients with spastic paralysis is more successful when fractional hamstring lengthening is combined with a transfer of the distal rectus femoris tendon to either the iliotibial band or the distal tendon of the semitendinosus.

Biomechanical Phenomena↗

PubMed1995

Loss of power during fatigue of human leg muscles.

1. We have investigated the loss of power seen during high-intensity exercise of human leg muscles such as might occur during sprinting. Subjects exercised the quadriceps and hamstring muscle groups using a Cybex dynamometer at an angular velocity of 90 deg s-1 once a second for 6 min. At 1 min intervals the quadriceps were electrically stimulated via the femoral nerve to produce an isometric contraction which was then released into an isokinetic shortening contraction at 90 deg s-1. 2. The extent of central fatigue was assessed by comparing the force of a voluntary isokinetic contraction with that elicited by electrical stimulation during isokinetic releases. Two subjects were repeatedly tested. In the first series of experiments, exercising the quadriceps of one leg, the instantaneous power fell to about 50% over the course of 2 min and remained constant for the rest of the exercise. For one subject the voluntary and electrically stimulated forces declined in parallel while for the second subject the voluntary force was 10% less than the stimulated force at the end of the exercise. These results show that central fatigue represented a minor factor contributing no more than one-fifth of the total loss of power in these circumstances. 3. In a second series of experiments the subjects alternately contracted the quadriceps and the hamstrings of both legs in an exercise which had a high rating of perceived exertion and entailed considerable respiratory and cardiovascular effort. The time course and proportionate loss of power were very similar to those seen with the one-leg exercise and neither subject showed evidence of significant central fatigue. The pattern of force loss was very similar for the hamstrings. We conclude that, for determined subjects, afferent feedback from muscles, tendons and joints or from the respiratory and cardiovascular systems does not have a major role in inhibiting voluntary activation of the quadriceps during heavy exercise. 4. In both series of experiments the power output during electrically stimulated isokinetic contractions was reduced to 50% of the initial value after 2 min of exercise while the isometric force, measured immediately before the release, fell to only 75%. This suggests that fatigue affects isometric and shortening contractions to different extents and the loss of power may be due to a combination of factors, only one of which is evident in the loss of isometric force.

Adult↗

PubMed2001

Semitendinosus muscle in anterior cruciate ligament surgery: Morphology and function.

PURPOSE: To evaluate the fate of the hamstring muscles in general and the semitendinosus muscle in particular, after anterior cruciate ligament (ACL) reconstruction with an autologous semitendinosus tendon graft from the ipsilateral side. TYPE OF STUDY: Prospective consecutive case series investigation. METHODS: Included were 16 consecutive patients, 14 male and 2 female, with a mean age of 26 years. The inclusion criterion was chronic unilateral ACL insufficiency with no concomitant knee ligament injuries. ACL reconstruction was performed with a quadruple semitendinosus tendon graft using the EndoButton technique (Acufex, Mansfield, MA). Intraoperatively, muscle specimens were taken from the semitendinosus muscle on the harvested side. Follow-up at a minimum of 6 months included clinical examination, isokinetic strength performance, magnetic resonance imaging (MRI) of the thigh and knee, and ultrasound-guided muscle biopsy procurement from the semitendinosus muscle for histochemical and enzymatic analyses. RESULTS: Of the patients, 75% showed regeneration of their semitendinosus tendons. The neotendons all inserted below the knee joint where they had fused with the gracilis tendon to a conjoined tendon inserting in the pes anserinus. The semitendinosus muscle had a smaller cross-sectional area on the operated side but none showed total atrophy. Less atrophy was present in the patients with a regenerated semitendinosus neotendon compared with those without regeneration (P =.029). In the latter group the semimembranosus muscle seemed to compensate for this with hypertrophy (P =.019). Cross-sectional muscle fiber areas, the relative number of each fiber type and oxidative potential as estimated by citrate synthase activity, showed no significant differences between the operated and nonoperated legs. The isokinetic strength of the hamstrings and quadriceps was significantly lower in the operated leg than in the nonoperated leg. CONCLUSIONS: With this surgical technique, the semitendinosus muscle can recover and the tendon has, according to the MRI images, a great potential to regenerate after its removal.

Adolescent↗

PubMedDate not supplied

Hamstrings in cerebral palsy crouch gait.

After observing patients with increased anterior pelvic tilt following medial hamstring lengthening in cerebral palsy crouch gait, we became concerned that the hamstrings may be functionally important hip extensors. To evaluate this, we studied the three-dimensional motion of the hip and knee, calculated hamstring muscle length, and evaluated dynamic electromyography (EMG) of the medial hamstrings in 16 patients with diplegic cerebral palsy and crouch gait to determine if the hamstrings were extending the hip. Twelve of 16 patients exhibited marked prolongation of electrical activity in the medial hamstrings, and in eight of these 12, the hamstrings were contracting concentrically, thus aiding in hip extension during gait. Hamstrings may be important hip extensors in some cerebral palsy patients with crouch gait; however, other deformities contributing to crouch (such as hip flexion contracture) need to be considered before isolated hamstring lengthening is performed in these patients.

Adolescent↗

PubMed1993

Biomechanical analysis of the knee extension exercise.

A mathematical analysis of knee extension and flexion exercise is presented to determine effectiveness in strengthening the quadriceps and hamstring muscles. A quantitative relationship between the quadriceps force and the hamstring force is obtained for several variations of the exercises. The theoretical results are supplemented with experimental studies performed on subjects exercising with the Tekdyne Incentive Dynamometer.

Biomechanical Phenomena↗

PubMed1992

Isokinetic exercise system modification for short below-the-knee residual limbs.

The use of isokinetic exercise has been shown to be an effective way of strengthening debilitated muscles. In the below the knee amputee, significant quadriceps and hamstring muscle wasting has been documented. Although isokinetic strengthening of the debilitated knee extensors and flexors in the below the knee amputee would be beneficial, there are no fully described isokinetic equipment modifications in literature that would allow a short below the knee amputee to effectively use isokinetic equipment. This article describes such a modification.

Adult↗

PubMed1996

Proprioceptive mechanisms in the cruciate ligaments: an electromyographic study on reflex activity in the thigh muscles.

The hypothesis of a proprioceptive mechanism arising from mechanoreceptors in the cruciate ligaments and with efferences to the thigh muscles is investigated in an animal model. Electromyographic (EMG) studies of the quadriceps and hamstrings muscles were performed in six sheep anesthetized by intravenous injection of chloralose on applying static and dynamic shear forces to isolated fascicle bundles in the anterior (ACL) and posterior (PCL) cruciate ligaments at 200 to 500 N and 50 to 200 N/sec, respectively. With the help of an external fixator, the knee joint position was varied at 25 to 150 degrees. The relative preload of the anteromedial and posterolateral fascicles in the ACL and the anterior and posterior fascicles in the PCL induced by variation of the joint angle was measured with the help of strain gages. By static and dynamic loading of the anteromedial group of the ACL, EMG activity in the hamstrings increases significantly to 159 +/- 22 and 257 +/- 46 microV seconds, respectively (p < 0.001), with a simultaneous suppression of the quadriceps activity. Static and dynamic loading of the posterolateral ACL group results in a significant excitation of the quadriceps with mean potentials of 142 +/- 29 and 173 +/- 23 microV seconds, respectively (p < 0.001). Mechanical shear applied both to the anterior and posterior fascicles of the PCL induces a significant activation of the ipsilateral quadriceps muscles with a simultaneous inhibition of the hamstrings (p < 0.001). The quality of mechanical loading, i.e., static or dynamic shear, determines the degree of muscular recruitment significantly (p < 0.01). The joint angle contributes to a modulation in the quantitative EMG excitation. Linear regression analysis of the integrated EMG potential values and the amount of passive preload induced by the respective joint position results in a close correlation (r = + 0.78 to + 0.86). The results lead to the conclusion that a proprioceptive mechanism exists that arises from the cruciate ligaments and influences the tone in the thigh muscles. The degree of muscle excitation on mechanical ligament loading is modulated by the amount of preload in the ACL and PCL and the quality of load applied.

Animals↗

PubMed1987

Spinal cord projections from hindlimb muscle nerves in the rat studied by transganglionic transport of horseradish peroxidase, wheat germ agglutinin conjugated horseradish peroxidase, or horseradish peroxidase with dimethylsulfoxide.

The spinal cord projections of four different groups of hindlimb muscle nerve branches--the medial and lateral gastrocnemius nerves, muscle branches of the deep peroneal nerve, muscle branches of the femoral nerve, and a nerve to the hamstring muscles--were studied with transganglionic transport of horseradish peroxidase (HRP) in the rat. The influence of varying the postoperative survival (3, 6, and 10 days) and of using wheat germ agglutinin-HRP conjugate (WGA-HRP), or HRP with dimethylsulfoxide (DMSO) instead of free HRP was studied for the gastrocnemius nerves. After 3 days' survival following application of HRP to the gastrocnemius nerves, fine granular labeling was found mainly in lamina V in L4-5, and coarse granular labeling was found in Clarke's column as far caudally as L2, and in laminae VI and VII predominantly in Th12-L2. After 6 or 10 days' survival, the fine labeling in lamina V was sparse or absent, whereas the coarse labeling appeared to remain or to be only slightly reduced in Clarke's column and in laminae VI and VII. No labeling suggestive of terminals was observed in laminae I-III from the gastrocnemius nerves. Except for sparse labeling in lamina I in some of the cases and some minor differences rostrocaudally, the spinal distribution of labeling was similar to that from the other nerves investigated. The distribution of labeling obtained after application of WGA-HRP or HRP with DMSO to the gastrocnemius nerves was very similar to that obtained with free HRP after 3 days' survival. The results indicate that the spinal cord projections of hindlimb muscle nerves in the rat distribute mainly in the deep part of the dorsal horn and in the intermediate zone. Furthermore, the lack of labeling suggestive of terminals in laminae I-III from the gastrocnemius nerves suggests, in conflict with earlier findings in the cat, that primary afferent fibers from muscles do not necessarily terminate in these laminae in the rat. The results suggest, furthermore, that fine granular labeling found in lamina V represents fine-calibered afferent fibers. Finally, the similar spinal projection patterns of the different muscle nerves investigated suggest either a less developed or an essentially different somatotopic organization for muscle afferents compared to cutaneous afferents, as revealed in earlier studies.

Animals↗

PubMed2001

Selective thigh muscle atrophy in trans-tibial amputees: an ultrasonographic study.

In trans-tibial amputees, PTB (patellar tendon bearing) prostheses provide almost physiological mobility of the knee joint in the sagittal plane. Nevertheless, there are characteristic adaptations of the knee joint muscles. Myosonography is a suitable method for depicting muscle atrophy and hypertrophy due to muscle dysfunction. The present study was intended to assess anatomical alterations of thigh muscles in trans-tibial amputees wearing a PTB prothesis. Thicknesses and cross-sectional areas of the quadriceps femoris, sartorius, gracilis, semitendinosus and biceps femoris muscles were determined ultrasonographically on both limbs in 17 amputees with a PTB prothesis. The gait was analysed using an optoelectronical system, force plates and surface electromyography of the vastus lateralis and biceps femoris muscles. Quadriceps femoris and sartorius muscles of the amputated extremity exhibited significant atrophy compared with the contralateral limb (reduction of muscle thickness ranged between 11.7% and 30.4%), whereas the gracilis and hamstring muscles were not significantly affected. Even the quadriceps femoris muscle of the non-amputated limb showed a slight atrophy compared with a reference group. Increased echointensities were found predominantly in the quadriceps muscle on the amputated leg. During gait, electromyographical activity within the amputated limb was reduced in the vastus lateralis and increased in the biceps femoris muscle. Even long-term adaptation to PTB prostheses results in characteristic deviation from normal gait. Atrophy occurs in the ventral thigh muscles, predominantly on the amputated leg, whereas the dorsal thigh muscles are hardly affected, probably due to compensatory hyperactivity.

Adolescent↗

PubMed1992

Vestibular-evoked postural reactions in man and modulation of transmission in spinal reflex pathways.

1. The effects of galvanic stimulation of the vestibular apparatus (with electrodes on the mastoid processes) have been studied in standing human subjects. With the head turned to one side, subjects swayed towards the anode. 2. Forwards sway was preceded by electromyographic (EMG) activity in quadriceps and tibialis anterior muscles. Backwards sway was preceded by EMG activity in soleus and hamstring muscles. 3. Using the method of H reflex conditioning, forward sway was found to be preceded by inhibition of soleus motoneurones. 4. Interaction between the vestibular-evoked inhibition of soleus motoneurones preceding forwards sway and peripheral reflex inhibition was examined by a spatial facilitation method. 5. Interaction was found between vestibular-evoked inhibition and Ia reciprocal, group I non-reciprocal and group Ia-Ia presynaptic inhibitory pathways. It is concluded that vestibular signals converge on spinal interneurones subserving these inhibitory actions. 6. A 'decoupling' of soleus motoneurons and soleus-coupled Renshaw cells was found in the period of soleus activation preceding backwards sway.

Adult↗

PubMed1995

The control of mono-articular muscles in multijoint leg extensions in man.

1. Movements often require control of direction and a magnitude of force exerted externally on the environment. Bi-articular upper leg muscles appear to play a unique role in the regulation of the net torques about the hip and knee joints, necessary for the control of this external force. 2. The aim of this study was to test the hypothesis that the mono-articular muscles act as work generators in powerful dynamic leg extensions, which means that they should be activated primarily in the phases during which they can contribute to work, irrespective of the net joint torques required to control the external force. 3. Cycling movements of six trained subjects were analysed by means of inverse dynamics, yielding net joint torques as well as activity patterns and shortening velocities of four mono- and four bi-articular leg muscles. 4. The results show that the mono-articular muscles exert force only in the phase in which these muscles shorten, whereas this appears not to be the case for the bi-articular muscles. 5. Reciprocal patterns of activation of the rectus femoris and hamstring muscles appear to tune the distribution of net joint torques about the hip and knee joints, necessary to control the (changing) direction of the force on the pedal. 6. An analysis of running in man and additional related literature based on animal studies appears to provide further support for the hypothesis that mono- and bi-articular muscles have essentially different roles in these powerful multijoint leg extension tasks.

Bicycling↗

PubMedDate not supplied

The soleus muscle acts as an agonist for the anterior cruciate ligament. An in vitro experimental study.

BACKGROUND: Although the quadriceps muscles are known antagonists for the anterior cruciate ligament and the hamstring muscles are known agonists, the influence of the calf muscles on knee stability is not well understood. HYPOTHESIS: The soleus muscle acts as an anterior cruciate ligament agonist and the gastrocnemius muscle acts as an anterior cruciate ligament antagonist. STUDY DESIGN: Controlled laboratory study. METHODS: Six cadaveric knees were tested with individual and combined activation of the gastrocnemius and soleus muscles to determine the influence of simulated muscle contraction on tibiofemoral motion. RESULTS: At all flexion angles, applying the soleus muscle force tended to translate the tibia posteriorly, whereas applying the gastrocnemius muscle force tended to translate the tibia anteriorly. Applying the soleus and gastrocnemius muscle forces together also tended to translate the tibia anteriorly. The average anterior and posterior tibial translations were greatest at 50 degrees of flexion. CONCLUSIONS: The soleus muscle is capable of acting as an agonist for the anterior cruciate ligament and the gastrocnemius muscle can act as an antagonist. CLINICAL RELEVANCE: A better understanding of the agonistic behavior of the soleus muscle on the anterior cruciate ligament may lead to the development of training and rehabilitation strategies that could reduce the incidence of injury and improve function in both patients with anterior cruciate ligament deficiency and patients who have undergone anterior cruciate ligament reconstruction.

Aged↗

PubMedDate not supplied

Anterior cruciate ligament reconstruction with multistranded autogenous semitendinosus tendon.

We evaluated 41 knees 24 to 48 months after anterior cruciate ligament reconstruction was performed using multiple autogenous semitendinosus tendons. The ipsilateral free semitendinosus tendon was tripled or quadrupled to make a graft 7 to 10 mm in diameter and more than 60 mm long. When the diameter of the graft was less than 7 mm, an ipsilateral doubled gracilis tendon was also used (in seven cases). Twenty-three patients (56%) returned to their preinjury activity levels. According to the patients' subjective assessment, 34 (83%) graded themselves as normal or nearly normal. No patient reported giving way of the knee or limitation of knee motion. The average anterior laxity difference between the involved knee and contralateral uninjured knee was 1.5 mm at 200 N. Twenty-nine patients (71%) demonstrated an anterior laxity difference of 3 mm or less when the involved knee was compared with the contralateral uninjured knee. Quadriceps muscle strength was 90% compared with the contralateral healthy limb, and hamstring muscle strength was equivalent to the contralateral limb. In our study, tripled or quadrupled semitendinosus free tendons were excellent anterior cruciate ligament grafts for restoring knee stability, recovering thigh muscle power, and preserving knee motion.

Adolescent↗

PubMed1983

Thigh muscle atrophy in below-knee amputees.

The atrophy was evaluated by using muscle biopsies, computed tomography and measuring tape. Ten well functioning below-knee amputees with a mean age of 56 years participated. The amputees had 33 per cent type I fibres in the amputated leg compared to 38 per cent in the non-amputated leg, the difference not being significant. In the amputated leg there was less type IIA fibres (p less than 0.01), more type IIB (p less than 0.05) and type IIC fibres (p less than 0.01) than in the non-amputated leg. Atrophy (single fibres or groups of 4-5 small fibres) of both type I and type II fibres were seen in most patients. The mean muscle fibre area of the vastus lateralis of the amputated leg was 74 per cent of that of the non-amputated leg (p less than 0.05). In both legs the area of type II fibres was larger than that of type I fibres. The cross-sectional area of the whole thigh in the amputated leg was 86 per cent (p less than 0.05), of the quadriceps muscles 66 per cent (p less than 0.01) and of the hamstring muscles 80 per cent (p less than 0.05) of the area of the non-amputated leg. It was not possible to demonstrate if there was a reduction in the total number of muscle fibres. This indicates that the main cause for the reduction of muscle volume is the reduction in fibre sizes. There was no significant difference in circumference measurements when using computed tomography or measuring tape.

Adult↗