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PubMed1984

Recent advances in the prevention, early diagnosis, and treatment of congenital dislocation of the hip in Japan.

Results of animal experiments and then of clinical study of newborn infants suggested that the main mechanical factor causing hip dislocation is prolonged tension on the hamstrings and iliopsoas and that each of these muscles has a synergistic effect in the production of hip dislocation during the perinatal period. It was, therefore, presumed that the high incidence of congenital dislocation of the hip (CDH) in Japan might be due mainly to the Japanese tradition of forcibly maintaining the legs of infants in an extended position with a "swathing diaper." The incidence of CDH in Japanese infants prior to 1965 was as high as 1.1%-3.5%. In an attempt to reduce the incidence of CDH, examination of newborns was performed on a national scale. However, early screening methods for hip abnormalities were not adequately reliable in Japan to allow identification of conditions that would later become CDH. In 1975 a national campaign to avoid prolonged extension of the hips and knees of infants during the early postnatal period was initiated. As a result, there has been a remarkable reduction in the incidence of CDH in infants, to less than 0.2%.

Animals↗
PubMed2004

Stepping-like movements in humans with complete spinal cord injury induced by epidural stimulation of the lumbar cord: electromyographic study of compound muscle action potentials.

STUDY DESIGN: It has been previously demonstrated that sustained nonpatterned electric stimulation of the posterior lumbar spinal cord from the epidural space can induce stepping-like movements in subjects with chronic, complete spinal cord injury. In the present paper, we explore physiologically related components of electromyographic (EMG) recordings during the induced stepping-like activity. OBJECTIVES: To examine mechanisms underlying the stepping-like movements activated by electrical epidural stimulation of posterior lumbar cord structures. MATERIALS AND METHODS: The study is based on the assessment of epidural stimulation to control spasticity by simultaneous recordings of the electromyographic activity of quadriceps, hamstrings, tibialis anterior, and triceps surae. We examined induced muscle responses to stimulation frequencies of 2.2-50 Hz in 10 subjects classified as having a motor complete spinal cord injury (ASIA A and B). We evaluated stimulus-triggered time windows 50 ms in length from the original EMG traces. Stimulus-evoked compound muscle action potentials (CMAPs) were analyzed with reference to latency, amplitude, and shape. RESULTS: Epidural stimulation of the posterior lumbosacral cord recruited lower limb muscles in a segmental-selective way, which was characteristic for posterior root stimulation. A 2.2 Hz stimulation elicited stimulus-coupled CMAPs of short latency which were approximately half that of phasic stretch reflex latencies for the respective muscle groups. EMG amplitudes were stimulus-strength dependent. Stimulation at 5-15 and 25-50 Hz elicited sustained tonic and rhythmic activity, respectively, and initiated lower limb extension or stepping-like movements representing different levels of muscle synergies. All EMG responses, even during burst-style phases were composed of separate stimulus-triggered CMAPs with characteristic amplitude modulations. During burst-style phases, a significant increase of CMAP latencies by about 10 ms was observed. CONCLUSION: The muscle activity evoked by epidural lumbar cord stimulation as described in the present study was initiated within the posterior roots. These posterior roots muscle reflex responses (PRMRRs) to 2.2 Hz stimulation were routed through monosynaptic pathways. Sustained stimulation at 5-50 Hz engaged central spinal PRMRR components. We propose that repeated volleys delivered to the lumbar cord via the posterior roots can effectively modify the central state of spinal circuits by temporarily combining them into functional units generating integrated motor behavior of sustained extension and rhythmic flexion/extension movements. This study opens the possibility for developing neuroprostheses for activation of inherent spinal networks involved in generating functional synergistic movements using a single electrode implanted in a localized and stable region.

Action Potentials↗
PubMed1989

Muscle afferent contribution to control of paw shakes in normal cats.

1. The discharge of various hindlimb muscle afferents was recorded during paw shakes in normal cats with the use of floating dorsal root electrodes. 2. Muscle spindle group Ia-afferents and tendon organ group Ib-afferents fired during muscle lengthening, reaching very high peak discharge rates and then silencing at or shortly after the onset of shortening. The timing of Ia firing was consistent with the predictions of a linear model as well as the responses of Ia endings subjected to identical length variations in separate anesthetized cats. 3. In the latter "reconstruction" experiments, waxing and waning dynamic fusimotor action straddling whole paw-shake sequences gave the most consistent matches with the data from the normal cats. The reproducibility of the inferred fusimotor action justifies the inclusion of paw shakes as a class of movement in which fusimotor set is high. 4. The peak ensemble Ia activity from single hindlimb muscles was estimated to be approximately 20 kiloimpulses/s (Kips). Ankle extensor and hamstrings length variations were nearly in phase in the first cycles of a paw-shake sequence. From published data on spindle populations in these muscles, this indicated that peak Ia input to the spinal cord exceeded 0.2 megaimpulses/s (Mips). 5. The phase relationship between origin-to-insertion muscle length and Ia firing during paw shakes was little affected by doubling or tripling the moment of inertia of the foot. We argue that this refutes the notion that in paw shakes phase reversals occur between muscle fibers and tendons in the muscles studied. 6. Inertial loading of the foot led to small but significant reductions in mean paw-shake frequency. This is consistent with an afferent contribution to the generation of these movements. 7. We conclude that in paw shakes in normal cats, the CNS "chooses" to sensitize Ia-afferents to muscle length variations by increasing dynamic fusimotor action. The resulting ensemble Ia input is very large and is likely to play a significant role in reflexly shaping the alpha-motoneuronal activity responsible for the paw shakes.

Action Potentials↗
PubMed1989

[Asymmetrical patchy muscle involvement in manifesting carriers of Duchenne muscular dystrophy--computed tomographical and histological study].

Two cases of manifesting carriers of Duchenne muscular dystrophy (DMD) were described. Case 1. The 41 year-old woman presented gait disturbance at the age of 40. She had two sons. The first son died of pneumonia soon after birth. The second son developed DMD and died of heart failure when he was 17 years old. Neurological examination revealed mild muscle weakness in neck flexors, gluteus maximus (left side dominance) and hamstrings (right side dominance) as well as bilateral calf pseudohypertrophy. Electromyography showed myopathic changes and serum creatine kinase (CK) was elevated (1941IU/l). The karyotype was 46XX. Computed tomography (CT) of skeletal muscles showed that the following muscles were partly replaced by fatty tissue: bilateral paravertebral muscles, left gluteus maximus, left quadriceps femoris, right adductor magnus, long head of right biceps femoris, bilateral peroneus longus and medial head of left gastrocnemius. Histological examination of left quadriceps femoris revealed only minimal change of focal endomysial proliferation and fiber size variation, demonstrating no necrotic fiber or no abnormalities in fiber type. Case 2. The 42 year-old woman was admitted to the hospital complaining of dyspnea and palpitation. The disease was initially diagnosed as myocardial infarction based on cardiomegaly, ECG abnormality (Q in aVL, V5,6., ST depression and negative T in V5,6, ST elevation in I, aVL) and elevated serum CK. However, the diagnosis was rejected due to the lack of subsequent changes in ECG and the continued elevation of serum CK even after her complaints had disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

A strength training program for postmenopausal women: a pilot study.

This pilot study examined a specific exercise program designed for skeletal muscle strengthening in postmenopausal women. The program consisted of patterns of movement using diagonal and spiral patterns, superimposed on a progressive weight-bearing sequence from prone lying to standing. Progressive resistance was provided with the use of progressively thicker elastic straps. Eighteen of an initial 22 healthy volunteer women aged 50 to 64 years completed 8 weekly hour-long group exercise sessions supplemented with twice weekly sessions at home to pilot test the program's safety, acceptability, and effectiveness in changing muscle strength. A physical therapist conducted baseline and final quadriceps, hamstrings, and grip strength assessments using a portable isokinetic dynamometer. Participants achieved a 21% increase in quadriceps (p < or = .001), 9% increase in hamstrings (p < or = .07), and a 14% increase in grip strength (p < or = .002). A positive dose-response relationship was observed between strength gains and compliance with the program. This approach to strength training in postmenopausal women is feasible and effective in increasing muscle strength. It has considerable promise and deserves further testing and evaluation.

Biomechanical Phenomena↗
PubMed2004

In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation.

The function of the anterior and posterior cruciate ligaments (ACL and PCL) in the first 120 degrees of flexion has been reported extensively, but little is known of their behavior at higher flexion angles. The aim of this investigation was to study the effects of muscle loads on the in situ forces in both ligaments at high knee flexion (>120 degrees). Eighteen fresh-frozen human knee specimens were tested on a robotic testing system from full extension to 150 degrees of flexion in response to quadriceps (400 N), hamstrings (200 N), and combined quadriceps and hamstrings (400 N/200 N) loads. The in situ forces in the ACL and PCL were measured using the principle of superposition. The force in the ACL peaked at 30 degrees of flexion (71.7 +/- 27.9 N in response to the quadriceps load, 52.3 +/- 24.4 N in response to the combined muscle load, 32.3 +/- 20.9 N in response to the hamstrings load). At 150 degrees, the ACL force was approximately 30 N in response to the quadriceps load and 20 N in response to the combined muscle load and isolated hamstring load. The PCL force peaked at 90 degrees (34.0 +/- 15.3 N in response to the quadriceps load, 88.6 +/- 23.7 N in response to the combined muscle load, 99.8 +/- 24.0 N in response to the hamstrings load) and decreased to around 35 N at 150 degrees in response to each of the loads. These results demonstrate that the ACL and PCL carried significantly less load at high flexion in response to the simulated muscle loads compared to the peak loads they carried in response to the same muscle loads at other flexion angles. The data could provide a reference point for the investigation of non-weight bearing flexion and extension knee exercises in high flexion. Furthermore, these data could be useful in designing total knee implants to achieve high flexion.

Aged↗
PubMed2005

Muscular activity level during pedalling is not affected by crank inertial load.

The aim of the present study was to investigate the influence of gear ratio (GR) and thus crank inertial load (CIL), on the activity levels of lower limb muscles. Twelve competitive cyclists performed three randomised trials with their own bicycle equipped with a SRM crankset and mounted on an Axiom ergometer. The power output ( approximately 80% of maximal aerobic power) and the pedalling cadence were kept constant for each subject across all trials but three different GR (low, medium and high) were indirectly obtained for each trial by altering the electromagnetic brake of the ergometer. The low, medium and high GR (mean +/- SD) resulted in CIL of 44 +/- 3.7, 84 +/- 6.5 and 152 +/- 17.9 kg.m(2), respectively. Muscular activity levels of the gluteus maximus (GM), the vastus medialis (VM), the vastus lateralis (VL), the rectus femoris (RF), the medial hamstrings (MHAM), the gastrocnemius (GAS) and the soleus (SOL) muscles were quantified and analysed by mean root mean square (RMS(mean)). The muscular activity levels of the measured lower limb muscles were not significantly affected when the CIL was increased approximately four fold. This suggests that muscular activity levels measured on different cycling ergometers (with different GR and flywheel inertia) can be compared among each other, as they are not influenced by CIL.

Adult↗
PubMed1979

Trajectory of group Ia afferent fibers stained with horseradish peroxidase in the lumbosacral spinal cord of the cat: three dimensional reconstructions from serial sections.

A reconstruction was made of the intramedullary trajectory of 23 physiologically identified Ia afferents from cat hind limb muscles (medial gastrocnemius, soleus, plantaris, flexor digitorum-hallucis longus, and hamstring). The afferents were stained by intra-axonally injected HRP. The axons of these afferents were traced over distances of 5.8 mm to 15.7 mm rostrocaudally. In the dorsal funiculus fibers from all the muscles showed a similar course and similarly bifurcated into an ascending and a descending branch. The mean diameters of stem axons, ascending branches, and descending branches were 6.6 micrometer, 5.8 micrometer, and 3.0 micrometer, respectively. Within the analyzed lengths of the spinal cord five to eleven collaterals were given off from the two branches. The distances between adjacent collaterals of the ascending and descending branches averaged 1200 micrometer and 790 micrometer, respectively. The collaterals as a rule passed through the medial half of the dorsal horn before they entered the deeper parts of the gray matter. The terminal distribution areas common to all Ia collaterals were: (1) the medial half of the base of the dorsal horn, mainly lamina VI: (2) lamina VII; and (3) lamina IX. The numbers of terminals were largest in lamina IX and smallest in lamina VII. The density of terminals in lamina IX was highest in the homonymous motor cell column. The terminal distribution areas of adjacent collaterals showed no overlap in the sagittal plane. Terminal branches carried one bouton terminal and up to six boutons en passage with an average of 1.8 terminals per terminal branch. Apparent axosomatic and axodendritic contacts were seen on small-sized and medium-sized neurons in laminae V-VI, medium-sized neurons in lamina VII, and large neurons in lamina IX. One motoneurons was contacted by an average of 3.3 terminals. In addition to the common features, Ia collaterals of various muscles of origin showed some differences in their trajectories in the ventral horn, and in their terminations in the gray matter.

Animals↗
PubMedDate not supplied

Sports injuries in the game of hurling. A one-year prospective study.

A prospective study of hurling injuries was conducted over the 8 months of one season on 74 players. These athletes averaged 4.30 +/- 2.58 hours per week of training and 1.15 +/- 0.21 hours per week of matches. Mean time of injury was 1.20 +/- 2.53 days in the hospital, 20.34 +/- 19.25 days off sport, and 13.34 +/- 17.25 days of restricted activity. Together this injury time amounts to 14.3% of the season. There were 92 match- and 43 training-related injuries, giving 342.47 injuries per 10,000 hours of matches and 43.83 injuries per 10,000 hours of training. Overall, there were 369.9 days of injury per 1000 hours of participation. The most common type of injury was muscle strain (24.4% of the 135 total injuries). The hamstrings was the most common site of strain, accounting for 41% of these injuries. Contusions comprised 16.3% of the injuries and sprains comprised 15.6%. The most frequently injured sites were the finger (13%), hamstrings (12%), back (11%), head (9%), and knee and ankle (9%). Forty-one percent of the injuries were attributed to foul play. The results of the study suggest that the incidence of injuries in hurling is high and may be attributed to poor conditioning, poor protection, and lack of enforcement of the rules.

Absenteeism↗
PubMed2006

Thigh muscle weakness in ACL-deficient knees persists without structured rehabilitation.

UNLABELLED: We evaluated whether quadriceps and hamstrings weakness depended on chronicity in amateur athletes with anterior cruciate ligament deficiencies. We hypothesized that the weakness would not recover to the level of healthy control subjects without structured rehabilitation. Secondarily, we asked whether quadriceps and hamstrings side-to-side percent asymmetry in strength was consistent at different stages of chronicity. Thirty-six male amateur athletes forming equal groups of short, intermediate, and long chronicity (mean, 4, 12, and 56 months, respectively) were tested isokinetically against control subjects at 60 degrees per second. Weakness was substantial in both muscle groups and at all times ranging from 32% to 21% compared with the control subjects. However, side-to-side deficits revealed a linear trend of lessening with time. The quadriceps had greater side-to-side asymmetry that ranged from 23% to 10%, whereas the hamstrings asymmetry ranged from 14% to almost 0%. Acquiring symmetric strength earlier than 1 year after injury only occurred in the hamstrings. It can be inferred that participation in organized rehabilitation would minimize the detrimental effects of anterior cruciate ligament rupture on thigh muscle strength. LEVEL OF EVIDENCE: Prognostic Study, Level II.

Anterior Cruciate Ligament Injuries↗
PubMed2006

Decrease in eccentric hamstring strength in runners in the Tirol Speed Marathon.

BACKGROUND: The local muscular endurance of knee flexors, during eccentric work in particular, is important in preventing or delaying kinematic changes associated with fatigue during treadmill running. This result, however, may not be transferable to overground running. OBJECTIVE: To test the hypothesis that overground running is associated with eccentric hamstring fatigue. METHODS: Thirteen runners (12 male and one female) performed an isokinetic muscle test three to four days before and 18 hours after a marathon. Both legs were tested. The testing protocol consisted of concentric and eccentric quadriceps and hamstring contractions. RESULTS: There were no significant differences between peak torque before and after the race, except that eccentric peak hamstring torque (both thighs) was reduced. CONCLUSION: Overground running (running a marathon) is associated with eccentric hamstring fatigue. Eccentric hamstring fatigue may be a potential risk factor for knee and soft tissue injuries during running. Eccentric hamstring training should therefore be introduced as an integral part of the training programme of runners.

Adult↗
PubMedDate not supplied

[Proprioceptive deficit following cruciate lesions--afferent disorder or compensatory mechanism?].

It was suggested that the ACL has not only mechanical functions but also acts as proprioceptive organ. In cruciate deficient knees pathological patterns of muscle control were found. These findings could be caused by a disturbed afferent signal from the disrupted ACL or by secondary changes in muscle innervation, which shall protect the instable knee against subluxation. 33 patients with unilateral operative ACL repair (21 cases with primary suture, 12 cases with autogenous ligamentum-patellae-reconstruction; average post op 36.5 yr) were examined clinically and with the KT 1000 arthrometer (MEDMETRIC Inc.). Patients history was evaluated by using the LYSHOLM score. During a cycling task the electromyographic activity was monitored from the thigh muscles (M. vastus lat. and med., lat. and med. hamstrings). In comparison to the ACL deficient patients, we tested 25 healthy subjects of same age and activity level. In the ACL group the following differences to the normals were found: the M. vastus lat. showed a significantly delayed onset, earlier end and shorter duration. M. vastus med. had the same pattern; the delayed begin of activity and the shorter duration were statistically significant. M. biceps femoris showed a significant later onset and shorter duration. So did the medial hamstrings; the differences, however, were not statistically significant. There was no significant difference between operated and healthy leg in the ACL group. By comparing the primary sutures and the ligamentum-patellae-reconstructions no significant differences were found. The instable patients (KT 1000 > 3 mm) of the ACL group showed more distinct differences in the EMG pattern than the patients with stable knee joints.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1980

Electromyographic investigation of muscle stretching techniques.

Myotatic reflexes can be enhanced following brief static contractions. Since static contractions are often used as precursors to muscle stretch, rationale underlying these techniques were questioned and re-examined through electromyography (EMG). Twenty-one female gymnasts performed three methods to produce hamstring stretch: static (S), contract-relax (CR), and contract-relax with agonist (hip flexors) contraction (CRAC). Hip joint angles and intra-individual electromyograms were statistically compared across stretch conditions. In 12 subjects, the CRAC method elicited significantly greater hamstring EMG activity (P < 0.05) than the other techniques. A higher level of muscle activation was associated with the S method in only one subject. No significant differences in EMG activity across stretch conditions were found in eight subjects suggesting that the relative effectiveness of the stretch techniques varied across individuals. Involuntary paroxysmal tremor activity was occasionally visible in EMG records of most subjects at the low levels of muscle activation. While apparently contributing to increased muscle stiffness, the CRAC technique produced the largest gains in hip flextion. Rank orderings of minimum pain and maximum perceived stretch effectiveness were significantly related with one another, and with decreasing EMG activity, but not with range of motion.

Adolescent↗
PubMed1978

Activities of pongid thigh muscles during bipedal behavior.

Electromyographic recordings were taken from 12 thigh muscles (or major parts of them) in a gorilla, from 6 thigh muscles in a chimpanzee, and from 2 thigh muscles in an orangutan as they engaged in bipedal positional behavior, including stance, reaching overhead, lunging, leaping and walking. In the African apes, symmetric bipedal stances with hindlimb flexure were accompanied by notable EMG potentials generally increased to or remained at moderate and high levels. Our studies on the gluteal (Tuttle et al., '78) and thigh muscles of African apes partly confirm Kummer's ('75) prediction that considerable gluteal and hamstring activity would be required in order for them to stand bipedally with flexed hip and knee joints. The gorilla's thigh muscles exhibited considerable EMG activity during the stance phase and remarkably little activity during the swing phase of bipedal steps. The activity patterns of most thigh and gluteal muscles (Tuttle et al., '78) in the African apes are much more similar to those of bipedal gibbons than to their counterparts in man. The bipedal locomotor cycles of human subjects are accompanied by many more biphasic and triphasic EMG patterns in the thigh muscles than the locomotor cycles of other anthropoid primates are. The evolutionary anthropological significance of these findings should become clearer when they are complemented by EMG studies on human running, arboreal bipedalism and vertical climbing in apes, and central pattern generation in man and apes.

Animals↗
PubMed1987

Lower extremity antagonist muscle response following standing perturbation in subjects with cerebrovascular disease.

The onset, amplitude, and relative timing of opposing muscle groups during forward and backward body sway were investigated in standing subjects with hemiplegia and a normal control group. The agonist was the first muscle stretched by platform perturbation and the antagonist was the opposing muscle passively shortened by the movement stimulus. Tibialis anterior (T), quadriceps (Q), gastrocnemius (G) and hamstrings (H) were simultaneously monitored bilaterally for burst activity. During rotational (toe up/down) and horizontal perturbations in normals, two distinct muscle responses were observed--an initial long-latency response (LLR) in the agonist and a subsequent response in the antagonist muscle group. Hemiplegics showed early activation of the antagonist response (AR) with respect to the initial LLR and frequent coactivation of synergists (T-Q or G-H). Although the AR was tightly coupled to the initial LLR in both hemiplegic lower limbs, initiation of the distal LLR-AR sequence was significantly delayed in the paretic extremity by 25-40 ms. In addition, the distal AR amplitude was suppressed in the paretic limb. The number of AR defaults in hemiplegics for all perturbation modes was significantly greater than normal. Therefore, unilateral cerebrovascular disease may reduce the occurrence of antagonist muscle activation and alter the latency, amplitude and phasing of passively shortened antagonist muscles.

Central Nervous System↗
PubMed2002

Muscle activity damps the soft tissue resonance that occurs in response to pulsed and continuous vibrations.

This study tested the hypotheses that when the excitation frequency of mechanical stimuli to the foot was close to the natural frequency of the soft tissues of the lower extremity, the muscle activity increases 1) the natural frequency and 2) the damping to minimize resonance. Soft tissue vibrations were measured with triaxial accelerometers, and muscle activity was measured by using surface electromyography from the quadriceps, hamstrings, tibialis anterior, and triceps surae groups from 20 subjects. Subjects were presented vibrations while standing on a vibrating platform. Both continuous vibrations and pulsed bursts of vibrations were presented, across the frequency range of 10-65 Hz. Elevated muscle activity and increased damping of vibration power occurred when the frequency of the input was close to the natural frequency of each soft tissue. However, the natural frequency of the soft tissues did not change in a manner that correlated with the frequency of the input. It is suggested that soft tissue damping may be the mechanism by which resonance is minimized at heel strike during running.

Adult↗
PubMed1993

Electromyographic analysis of the anterior cruciate ligament-deficient knee.

The protective relationship of the human anterior cruciate ligament (ACL) by active contraction of the hamstring musculature has been known and understood by sports orthopedists and physical therapists for many years. Rehabilitation programs for patients with torn ACLs as well as those treated with ligament reconstruction have always stressed hamstring strengthening. Research in this area during the past decade has begun to define the proprioceptive mechanism that governs this relationship as well as the actual recording of dynamic muscle firing patterns in pre- and postoperative subjects. Laboratory studies suggest that altered hamstring activity may help these subjects compensate for a knee that is lax because of ACL damage.

Anterior Cruciate Ligament Injuries↗