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At least 1,135 records · Page 63Linked to original sources
PubMed2006

Co-activation: its association with weakness and specific neurological pathology.

BACKGROUND: Net agonist muscle strength is in part determined by the degree of antagonist co-activation. The level of co-activation might vary in different neurological disorders causing weakness or might vary with agonist strength. AIM: This study investigated whether antagonist co-activation changed a) with the degree of muscle weakness and b) with the nature of the neurological lesion causing weakness. METHODS: Measures of isometric quadriceps and hamstrings strength were obtained. Antagonist (hamstring) co-activation during knee extension was calculated as a ratio of hamstrings over quadriceps activity both during an isometric and during a functional sit to stand (STS) task (using kinematics) in groups of patients with extrapyramidal (n = 15), upper motor neuron (UMN) (n = 12), lower motor neuron (LMN) with (n = 18) or without (n = 12) sensory loss, primary muscle or neuromuscular junction disorder (n = 17) and in healthy matched controls (n = 32). Independent t-tests or Mann Witney U tests were used to compare between the groups. Correlations between variables were also investigated. RESULTS: In healthy subjects mean (SD) co-activation of hamstrings during isometric knee extension was 11.8 (6.2)% and during STS was 20.5 (12.9)%. In patients, co-activation ranged from 7 to 17% during isometric knee extension and 15 to 25% during STS. Only the extrapyramidal group had lower co-activation levels than healthy matched controls (p < 0.05). Agonist isometric muscle strength and co-activation correlated only in muscle disease (r = (-)0.6, p < 0.05) and during STS in UMN disorders (r = (-)0.7, p < 0.5). CONCLUSION: It is concluded that antagonist co-activation does not systematically vary with the site of neurological pathology when compared to healthy matched controls or, in most patient groups, with strength. The lower co-activation levels found in the extrapyramidal group require confirmation and further investigation. Co-activation may be relevant to individuals with muscle weakness. Within patient serial studies in the presence of changing muscle strength may help to understand these relationships more clearly.

Journal Article↗
PubMed2003

EMG characteristics of low back and lower limb muscles during forward bending posture.

The study observed forward bending posture and evaluated its effect on muscular activity. The Muscular activity was monitored through the Electromyography (EMG). The objective was to extend the evaluation method of EMG due to muscular load in maintaining the posture and to investigate the existence of muscular coordination between low back and lower limb muscles during the posture. Twelve male subjects were asked to maintain the postures of six stages in bending angles from 0 to 180 degrees. The EMG of erector spinae (ES) at L1 and L5 levels, hamstrings, and gastrocnemius were recorded and analyzed by power spectral density. The characteristics of muscular activities were observed through the EMG power spectrum and the frequency. The activity changes were normalized by the relative presentation and the standardization. The relative presentation showed the level of activity changes in each posture by taking the activity during upright standing as a reference posture, and the standardization was applied to overcome the dependence of the power spectrum and the frequency upon the high standard deviation. A t test with the paired data was also applied to compare the values of EMG of the respective stages of the posture. The results showed that the activity of ES significantly increased during bending posture with an angle up to 45 degrees, and reached silent activity at 90 degrees of flexion. On the other hand, the activity of the hamstrings and gastrocnemius were recognized even when ES activity started and reached the silent activity. The lower limb muscles were considered to be always active during all stages of the posture, and they provided a greater contribution when the ES was in the silent activity.

Adult↗
PubMed1994

EMG profiles of ACL-deficient patients during walking: the influence of mild fatigue.

The purpose of this study was to determine muscle activities after ACL rupture during walking and running and to investigate the influence of mild fatigue (10 min walking) on these activities. A group of 12 patients with ACL-ruptures was compared with a control group (healthy volunteers) of 15 persons. Linear envelopes of EMG-activity from vastus medialis, vastus lateralis, biceps femoris and medial hamstrings were measured. Patients and control persons walked on a treadmill at speeds of 1.2 m/s (samples at t = 2 min and t = 12 min) and 2.8 m/s i.e. running (sample at t = 15 min). The patient group showed significantly lower muscle activities of vastus lateralis (p < 0.001) and medial hamstrings (p < 0.05) for both the injured and uninjured leg during running compared to the control group. After 10 minutes walking, the mean-EMG of biceps femoris (p < 0.05) and medial hamstrings (p < 0.01) decreased as did the activity time of biceps femoris (p < 0.05), medial hamstrings (p < 0.01) and vastus medialis (p < 0.001) for the injured leg of the patient group. Control persons showed no significant changes. Thus, mild fatigue did effect only the EMG-pattern of the patients. Patients with ACL-ruptures should be trained not only on strength and stabilisation, but also on endurance. A decrease in hamstrings activity during walking might be a sensitive measure for evaluation of the rehabilitation process, as those muscles may be able to substitute ACL-deficiency.

Anterior Cruciate Ligament Injuries↗
PubMed2000

Gross measures of exercise-induced muscular hypertrophy.

STUDY DESIGN: Pretest-posttest, single factor design. OBJECTIVES: To compare several indices that might be used to depict muscle size. BACKGROUND: The particular strategy used during heavy-resistance training may determine the magnitude of hypertrophic adaptations. At the same time, assorted measures supposedly reflecting muscle size may provide different results. METHODS AND MEASURES: Four groups of men (n = 38, mean age = 21.1 years, SD = 2.1) were exposed to conditions designed to elicit differential hypertrophic adaptations following 21 sessions of squat training. Three of the groups performed 4 sets of multiple repetitions maximum (RM): group I, 3-5 RM; group II, 13-15 RM; and group III, 23-25 RM. A control (C) group did no formal physical training. Tests used to represent muscle size included body weight, thigh girth, net thigh girth, and quadriceps femoris and hamstring thicknesses via B-mode ultrasound. RESULTS: Changes in the groups subsequent to training were similar for body weight and hamstring thickness. Results differed for the remaining 3 dependent variables (mean +/- SD): thigh girth was greater in groups II (1.42 +/- 1.00) and III (1.35 +/- 1.16) than in group C (0.24 +/- 0.69); net thigh girth was greater in groups II (1.33 +/- 0.77) and III (1.40 +/- 1.03) than in group C (0.10 +/- 0.84); and quadriceps femoris thickness was greater in all 3 training groups (I, 0.61 +/- 0.54; II, 0.43 +/- 0.30; III, 0.55 +/- 0.39) than in group C (0.05 +/- 0.11). CONCLUSIONS: Observed muscle mass change following heavy-resistance training is dependent upon both the training intervention and tool used for measurement.

Adult↗
PubMed2003

Botulinum A toxin for treatment of lower limb spasticity in cerebral palsy: gait analysis in 49 patients.

BACKGROUND: Injection of botulinum type A toxin is a new treatment for spasticity. PATIENTS AND METHODS: We evaluated the effect of botulinum A toxin (BTX-A) in the lower limb muscles of patients having cerebral palsy. We tested 49 patients before and, on average, 4 (2-9) months after giving the toxin. The evaluation included 3-dimensional computerized gait analysis, changes in mobility level, using the Gillette Functional Assessment Questionnaire, and gastrocnemius muscle bulk, using ultrasonographic measurements. RESULTS: The patients were divided into 3 groups, according to the site of BTX-A administration (hamstrings, gastrocnemius and multilevel). Those who were injected in the hamstrings showed a significant improvement in only the maximum knee extension angle during the gait cycle. Those with spastic equinus who were injected in the gastrocnemius muscle responded better than the other groups. The ankle angle on the initial contact, terminal stance and pre-swing, maximum dorsiflexion, ankle range of motion, per cent of single support and gait velocity improved significantly. Overall, the patients showed significant improvements in motor skill performance and functional health. INTERPRETATION: Our findings indicate that botulinum type A toxin can be given as an adjuvant to conservative treatment of patients with cerebral palsy.

Adolescent↗
PubMed2006

Distal hamstring lengthening in cerebral palsy: the influence of the proximal aponeurotic band of the semimembranosus.

We undertook a prospective review of 24 children with spastic diplegia treated by distal hamstring fractional lengthening at the Sheffield Children's Hospital. In 14 children (24 limbs) the correction achieved (popliteal angle) was inadequate and in these patients in the operating room a further correction was attained by dividing a tight band palpated in the substance of the semimembranosus muscle. Under general anaesthetic (preoperatively) the popliteal angle (a degrees ) was measured using a goniometer, then again (b degrees ) following distal hamstring fractional lengthening and finally (c degrees ) after surgically dividing the tight band. The mean preoperative popliteal angle (a degrees ) in all 24 limbs was 65 degrees (52-90). Following the standard hamstring fractional lengthening it (b degrees ) measured 37 degrees (35-50) and after division of the tight band it (c degrees ) measured 15 degrees (10-20). The reduction in popliteal angle following release of the tight band (proximal aponeurosis) was statistically significant (P<0.05). We undertook a cadaveric examination of 22 lower limbs and confirmed in all the cases that this band was the proximal aponeurosis of the semimembranosus muscle. The proximal aponeurosis is a well defined band located at the anterior aspect of the semimembranosus muscle where it arises from the tendon of the proximal attachment. It is separate from the distal aponeurosis. Division of the proximal aponeurosis during fractional lengthening of the distal hamstring in patients with cerebral palsy results in a significant reduction in the flexion deformity.

Adolescent↗
PubMed2001

The development of balance control in children: comparisons of EMG and kinetic variables and chronological and developmental groupings.

This cross-sectional study examined electromyographic (EMG) and kinetic variables during reactive balance responses in children grouped according to developmental level as compared with chronological age. Purposes were to explore relationships between the two types of variables and the effectiveness of the two grouping methods. Forty-four children between 9 months and 10 years old were tested for reactive balance control on a moveable platform. Surface electrodes measured EMG activity in the gastrocnemius (GA), hamstrings (HA), paraspinals (PS), tibialis anterior (TA), quadriceps (QA), and abdominal (AB) muscles. Timing and distance of center-of-pressure (COP) movements and peak muscle torques at the ankle, knee, and hip were also examined. Significant relationships and group differences were found between postural muscle activity and both the torque generated in the lower limbs and the timing and distance of COP adjustments employed to restabilize balance. As postural muscle activity increased and became more coordinated in timing, peak torque at the ankle and hip also increased, while the distance of and time to complete COP readjustments decreased. Children in younger/developmentally lower groups had smaller-magnitude and less-synergic muscle activity, lower peak torques, longer times to restabilize the COP, and greater COP paths than older/higher developmental groupings. Grouping by developmental level produced more statistical differences than did grouping by age. The correspondence of GA, HA, and PS muscle activity with COP measures and joint peak torques confirms that these muscles are key contributors to the balance synergy correcting for induced forward sway. Additionally, developmental level appears to be a much better predictor of balance improvement than chronological age.

Age Factors↗
PubMed2005

Identifying the time of occurrence of a hamstring strain injury during treadmill running: a case study.

BACKGROUND: While hamstring strain injuries are common during sprinting, the mechanisms of injury are not well understood. In this study, we analyzed the running kinematics of an athlete obtained at the time of an acute hamstring strain injury. The purpose was to identify the period of the gait cycle during which the hamstring was likely injured, as well as to characterize the biomechanical conditions associated with the injury. METHODS: A male professional skier injured his right biceps femoris long head while running at 5.36 m/s on a treadmill with a 15% incline. Whole body kinematics were recorded at the time of injury. A linear periodic prediction model was used to determine when individual marker trajectories deviated from a cyclic periodic pattern, indicating the mechanical response to injury. A three-dimensional musculoskeletal model was used to compute joint angles and hamstring musculotendon lengths during the injurious running trial. These data were used with estimates of neuromuscular latencies and electromechanical delays to identify the most likely time period of injury. FINDINGS: Based upon the earliest indications in marker trajectories, a 130 ms period during the late swing phase of the gait cycle was identified as the period of injury. During this period, the biceps femoris reached a peak musculotendon length that was estimated to be 12% beyond the length seen in an upright posture and exceeded the normalized peak length of the medial hamstrings. INTERPRETATION: This case provides quantitative data suggesting that the biceps femoris muscle is susceptible to an lengthening contraction injury during the late swing phase of the running gait cycle.

Adult↗
PubMed2005

Early changes in muscle activation patterns of toddlers during walking.

Early locomotor behavior has been the focus of considerable attention by developmentalists over several decades. Few studies have addressed explicitly patterns of muscle activity that underlie this coordination pattern. Our purposes were to illustrate a method to determine objectively the onset and offset of muscle firings during early walking and to investigate the emergence of patterns of activation of the core locomotor muscles. We tested eight toddlers as they walked overground at walking onset (max. of 3-6 independent steps) and after three months of walking experience. Surface electrodes monitored activity of the gastrocnemius, tibialis anterior, quadriceps, and hamstrings. We reduced EMG signals to a frame-by-frame designation of "on-off," followed by muscle state and co-contraction analyses, and probability distributions for each muscle's activity across multiple cycles. Our results clearly show that at walking onset muscle activity was highly variable with few, if any, muscles showing recurring patterns of behavior, within or among toddlers. Variability and co-activation decreased with walking experience but remained inconsistent, in contrast to the significant increase in stability shown for joint coordination and endpoint (foot placement) parameters. We propose this trend emerges because of the high number of options (muscle combinations) available. Toddlers learn first to marshal sufficient force to balance and make forward progress but slowly discover how to optimize these resources.

Analysis of Variance↗
PubMed2001

Arthroscopic-assisted simultaneous reconstruction of the posterior cruciate ligament and the lateral collateral ligament using hamstrings and absorbable screws.

Arthroscopic-assisted simultaneous reconstruction of the posterior cruciate ligament (PCL) and the lateral collateral ligament (LCL) using hamstring tendon grafts is described. The femoral tunnel is drilled through an incision over the medial femoral condyle and the tibial tunnel through the same skin incision used for harvesting the tendon graft. PCL reconstruction is performed using a 4-strand hamstring tendon graft and absorbable screw fixation. The tendon of the semitendinosus muscle of the uninvolved knee is used as a lateral loop for LCL reconstruction. After pulling the transplant through the fibular head, femoral fixation of the loop is made with an absorbable screw.

Absorbable Implants↗
PubMedDate not supplied

Accuracy of intramuscular injection of botulinum toxin A in juvenile cerebral palsy: a comparison between manual needle placement and placement guided by electrical stimulation.

Most clinicians who perform botulinum toxin A injections for children with cerebral palsy do so using the "free-hand" or manual technique without using radiologic or electrophysiologic guidance to aid needle placement. The objective of this study was to investigate the accuracy of manual needle placement compared with needle placement guided by electrical stimulation. A total of 1,372 separate injections for upper and lower limb spasticity were evaluated in 226 children with cerebral palsy. The accuracy of manual needle placement compared with electrical stimulation was acceptable only for gastroc-soleus (>75%); it was unacceptable for the hip adductors (67%), medial hamstrings (46%), tibialis posterior (11%), biceps brachii (62%), and forearm and hand muscles (13% to 35%). The authors recommend using electrical stimulation or other guidance techniques to aid accurate needle placement in all muscles except the gastroc-soleus. Further study is needed to determine whether more accurate injecting will lead to better functional outcomes and more efficient use of botulinum toxin A.

Adolescent↗
PubMed2006

A risk-factor model for anterior cruciate ligament injury.

The incidence of non-contact anterior cruciate ligament (ACL) injury is reported to be 6-8 times greater in females than males competing in the same activities. Injury to the ACL occurs as a result of insufficient stability of the tibiofemoral joint, which fails to prevent posterior dislocation of the femur on the tibia. The stability of the tibiofemoral joint is maintained by passive (non-contractile) and dynamic (contractile) mechanisms. The passive mechanisms include the shape of the articular surfaces, the menisci, the ligaments and the joint capsule. The dynamic mechanisms consist of the muscle-tendon units that cross the joint, in particular, the quadriceps and hamstrings. The relative significance of the various passive and dynamic mechanisms in maintaining the stability of the tibiofemoral joint is not clear. A number of intrinsic and extrinsic risk factors have been proposed to account for the sex difference in the incidence of ACL injuries. However, most of the proposed risk factors have arisen from univariate correlation studies based on relatively small samples.

Anterior Cruciate Ligament↗
PubMed1990

Posterior femoral cutaneous nerve conduction.

The posterior femoral cutaneous nerve is a sensory nerve comprised of fibers originating from the anterior and posterior divisions of the first three sacral segments. It exists the pelvis distal to the piriformis muscle and proceeds distally, superficial to and between the medial and lateral hamstring musculature. The nerve's major cutaneous distribution is the posterior aspect of the thigh and a variable area of the posterior calf. An electrophysiologic technique to assess the peripheral axons of the posterior femoral cutaneous nerve is described. A recording electrode is placed 6cm proximal to the midpopliteal fossa and the nerve is stimulated supramaximally 12cm proximally on a line between the active electrode and the ischial tuberosity. A ground electrode is placed just proximal to the active recording electrode. The lower extremities of 40 individuals with a mean age of 34 years (20 to 78 years) were examined. The mean peak latency of the response is 2.8 (2.3 to 3.4) msec +/- 0.2msec with a mean amplitude of 6.5 (4.1 to 12.0) microV +/- 1.5 microV. This technique may facilitate the proximal evaluation of lower extremity peripheral neuropathies, lesions of the posterior femoral cutaneous nerve, or the assessment of the peripheral nervous system in persons with lower extremity amputations.

Action Potentials↗
PubMed1994

Proprioception enhancement for anterior cruciate ligament deficiency. A prospective randomised trial of two physiotherapy regimes.

We performed a prospective, double-blind, randomised, clinical trial to investigate the efficacy of two regimes of rehabilitation for knees with anterior cruciate ligament deficiency (ACLD). Fifty ACLD patients were randomly allocated to one of two treatment groups: a programme of muscle strengthening (T) or a programme designed to enhance proprioception and improve hamstring contraction reflexes (P). An indirect measure of proprioception, the reflex hamstring contraction latency (RHCL), and a functional scoring system were used to record the status of the knee before and after the 12-week course of physiotherapy. Sagittal knee laxity was also measured. There was improvement in mean RHCL and in the mean functional score in both groups after treatment. The improvement in group P was significantly greater than that in group T. There was no significant change in joint laxity after treatment in either group. In both groups there was a positive correlation between improvement in RHCL and functional gain.

Adolescent↗
PubMed1988

Effects of joint angle, electrodes and waveform on electrical stimulation of the quadriceps and hamstrings.

Isometric twitch moments of the quadriceps and hamstrings were recorded in 20 normal subjects at 40 cells of a superimposed grid. Results were compared at 15, 45, and 75 degrees of knee flexion. Bipolar stimulation at 6 pairs of cells was performed to determine the effect of electrode size, waveform, and polarity on moments. The quadriceps had one region of excitability over the femoral nerve and a second broader region of excitability over the muscle mass. Neither location was significantly affected by knee flexion. Regions of excitability for the hamstrings demonstrated more individual variation and were affected by knee angle. Electrode size had little effect on moments produced with monopolar or bipolar stimulation. When monophasic waveforms were used, reversing polarity generally caused changes in moments of greater than 20%, whereas polarity had no significant effect when using biphasic waveforms. Moments produced with biphasic waveforms were always greater (by 20-25%) when compared with monophasic waveforms. During monopolar, monophasic stimulation, the anode, often termed the "indifferent" electrode, produced nearly 70% of the moment produced by the cathode.

Adult↗
PubMed1999

Muscle preactivity of anterior cruciate ligament-deficient and -reconstructed females during functional activities.

OBJECTIVE: Underlying the ability of the hamstrings to decrease tibial anterior shear is the time of firing in comparison with the quadriceps. This timing may be aided by neural programming during a planned or expected activity. It is theorized that individuals who have better programming ability will suffer fewer anterior cruciate ligament (ACL) injuries due to joint protection through muscular stabilization. A component of this dynamic restraint is the development of muscular tension before the knee is loaded. The objective of our study was to compare the muscular activity before footstrike in ACL-deficient (ACL-D), ACL-reconstructed (ACL-R), and control (C) females during functional activities. DESIGN AND SETTING: Active females were divided into groups based on their ACL status. The study was conducted in a neuromuscular research laboratory. SUBJECTS: Twenty-four female subjects (ACL-D = 6, ACL-R = 12, C = 6). MEASUREMENTS: Integrated electromyographic (IEMG) activity from the thigh (vastus medialis obliquus [VMO], vastus lateralis [VL], medial hamstring, and lateral hamstring) and leg (medial gastrocnemius and lateral gastrocnemius [LG]) and footswitch signals were recorded during downhill walking (15 degrees at 0.92 m/s), running (2.08 m/s), hopping, and landing from a step (20.3 cm). IEMG activity was normalized to the mean amplitude of the sample and analyzed for area and mean amplitude for 150 milliseconds before heelstrike. Side-to-side differences were determined by t tests, and separate one-way analyses of variance (ANOVA) were used to detect differences among the 3 groups for each muscle of each activity. RESULTS: IEMG area side-to-side differences for the ACL-D group appeared in the LG (involved [I] = 36.4 +/- 19.7, uninvolved [U] = 60.1 +/- 23.6) during landing, in the VMO (I = 11.4 +/- 3.8, U = 7.2 +/- 3.1) and VL (I = 13.3 +/- 2.7, U = 8.9 +/- 1.9) during running, and in the VMO (I = 9.2 +/- 4.2, U = 19.5 +/- 7.3) during downhill walking. IEMG mean amplitude side-to-side differences for the ACL-D group appeared in the LG (I = 79.7 +/- 30.3, U = 122.3 +/- 34.9) during downhill walking and in the VMO (I = 78.6 +/- 23.2, U = 45.8 +/- 18.9) during the run; IEMG mean amplitude side-to-side differences for the ACL-R group appeared in the LG (I = 74.7 +/- 40.0, U = 52.8 +/- 14.3) during the hop. The ACL-D group had higher IEMG means than control in the VL (ACL-D = 12.9 +/- 5.8, C = 7.1 +/- 3.9), but lower in the VMO (ACL-D = 9.2 +/- 4.2, C = 15.7 +/- 3.6). CONCLUSIONS: The side-to-side differences of the ACL-D and ACL-R groups, as well as the group differences between ACL-D and control, suggest that different muscle activation strategies are used by females when performing different dynamic activities. Therefore, muscle unit differentiation may be the cause of our results. These changes appear to be reversed through surgery or the associated postoperative rehabilitation.

Journal Article↗
PubMed2005

Females recruit quadriceps faster than males at multiple knee flexion angles following a weight-bearing rotary perturbation.

OBJECTIVE: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10 degrees, 20 degrees, and 30 degrees. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles. DESIGN: A repeated-measures design. SETTING: Motion analysis laboratory. PARTICIPANTS: Twenty (10 female; 10 male) healthy, recreationally active volunteers. INTERVENTIONS: A rotary perturbation in single leg stance. OUTCOME MEASUREMENTS: Response times of the medial and lateral quadriceps, hamstrings, and gastrocnemius. RESULTS: There was a trend toward faster response times for all muscles closer toward extension. A consistent neuromuscular recruitment pattern for both males and females was evident for each knee angle tested. Females, however, contracted their quadriceps faster than males at all knee flexion angles. CONCLUSIONS: Small changes in knee angle near extension do not alter muscle response times and hence neuromuscular recruitment patterns in males and females. Regardless of knee flexion angle, following a perturbation in single leg stance, females contract their quadriceps faster than males. CLINICAL RELEVANCE: Earlier contraction of the quadriceps in females may increase anterior tibial translation and hence anterior cruciate ligament strain, thereby heightening injury risk.

Adult↗