Lower Limb Muscle Groups Research Articles

Walking while resisting a perturbation: Effects on ankle dorsiflexor activation during swing and potential for rehabilitation

Motor control studies have shown that when walking is performed while resisting a perturbation applied to the lower limb, the muscle activation pattern can be temporarily modified. The objective of the present study is to validate if such an approach, targeting the ankle, could specifically promote an increased activation of the ankle dorsiflexor muscles that are of key importance for the rehabilitation of foot drop. Methods12 adults, with no gait deficit, walked on a treadmill for three periods of 5min: before, during and after exposure to a torque perturbation applied by a robotized ankle-foot orthosis that tended to plantarflex the ankle during the swing phase. Spatiotemporal gait parameters, ankle and knee kinematics, and the electromyographic activity of five lower limb muscle groups were recorded. ResultsThe perturbation initially caused a deviation of the ankle towards plantarflexion. This movement error was rapidly reduced and associated with a large increase (78.2%; p<0.001) in tibialis anterior (ankle dorsiflexor; TA) activation, specifically in the stance-to-swing burst. This increase carried over to post-perturbation walking, gradually disappearing over several strides. Interestingly, these aftereffects led to an increase in peak ankle dorsiflexion of approximately 7° during the swing phase. ConclusionsWalking while resisting a torque perturbation applied at the ankle during swing promotes an increase in TA muscle activation that carries over after perturbation removal, leading to an increased ankle dorsiflexion. Training based on this approach may have the potential of improving the gait of persons with foot drop.

Isometric Muscle Strength in Youth Assessed by Hand-held Dynamometry

To determine, with respect to measurement of maximal isometric torque (MIT) using a specific hand-held dynamometer (HHD) protocol, (1) protocol feasibility over a wide age range, (2) intra- and interrater reliability, (3) standard error of measurement, and (4) concurrent validity. The MIT of selected upper and lower limb muscle groups was assessed (n = 74; age = 4-17.5 years) using a standardized, HHD protocol. Testing was repeated in 20 adolescents (n = 10 for each muscle group), who were also assessed with a Cybex dynamometer. The protocol was feasible for all participants. Mean intra- and interrater reliability [intraclass correlation coefficient (ICC)] varied from 0.75 to 0.98, except for ankle dorsiflexor interrater reliability (mean ICC = 0.67). The standard error of measurement varied from 0.5 to 4.9 Nm and was highest for hip extensors. Mean concurrent validity (ICC) varied from 0.78 to 0.93, except for ankle plantar flexors (mean ICC = 0.48). Our HHD protocol was feasible over a wide age range and most MIT values were valid and reliable.

Intra-tester and inter-tester reliability of the MicroFET 3 hand-held dynamometer

Background: The reliability of the MicroFET 3 has not previously been reported in the literature. The aim of this study was to evaluate intra-tester and inter-tester reliability of the MicroFET3 hand-held dynamometer (HHD) in three lower limb muscle groups. Methods: Maximum voluntary isometric contraction (MVIC) of hip extension, knee extension and ankle plantarflexion were measured in 38 healthy participants (males=18, females= 20) by two testers on separate days using the MicroFET3 HHD. The reliability analysis was carried out using intra-class correlation coefficients (ICCs) to measure association and Band and Altman plots to demonstrate agreement. Results: The results showed that intra-tester reliability was moderate to excellent; with associations ranging from ICC 0.56 0.92 and higher agreement for knee and ankle than hip measurements was shown. Inter-tester reliability was lower, with hip and knee associations ranging from ICC 0.60 0.66. Ankle measurements intertester associations were particularly low (ICC 0.23 and 0.15). These values would not be considered acceptable for clinical use. Bland and Altman plots used to demonstrate agreement between testers displayed a considerable lack of agreement with discrepancies of up to 150N noted in measurements. Conclusion: The results suggest that the MicroFET3 HHD displayed moderate to excellent intra-tester reliability and poor to moderate inter-tester reliability and agreement with discrepancies noted between muscle groups. While use of this instrument can be recommended when consistently used by a single tester, further reliability analysis should be carried out before this instrument could be recommended for use by different testers in the clinical setting.

A case of ITP with cauda equina syndrome

Dear Editor, A 49-year-old man presented with sudden onset of bandlike numbness in the lower abdomen radiating into the genitalia and buttocks, pain radiating down the lateral aspects of both lower limbs, and widespread petechiae accompanied by an episode of prolonged epistaxis. He had undergone spinal fusion L5-S1 13 years prior following a work-related injury. He had been taking diclofenac for back pain for 3 weeks preceding his presentation. Clinical examination showed decreased sensation in the S1-S2 and saddle regions, with patchy altered sensation in the L2 dermatome. Power was normal in all lower limb muscle groups. Reflexes were preserved. Anal tone was normal. Widespread petechiae were present. A full blood count showed a platelet count of 3×10/L with haemoglobin of 125 g/L and white cell count of 12.4×10/L. Blood film morphology and coagulation screen were unremarkable. A diagnosis of immune thrombocytopenic purpura (ITP) was made. Magnetic resonance imaging of the spine showed a moderate to large epidural/subdural haematoma occupying the entire spinal canal from the L3 to S1 level, with compression of the cauda equina (Fig. 1). There were also subdural collections both ventral and dorsal to the theca sac at the L5-S1 level. The patient was commenced on prednisone (1 mg/kg) and received intravenous immunoglobulin (2 g/kg) over 2 days, resulting in a normalization of the platelet count within 3 days (186×10/L). Platelet function analysis (PFA100TM), performed once the platelets were >200×10/L,

Therapeutic Exercise during Outpatient Radiation Therapy for Advanced Cancer

To characterize the feasibility of delivering a structured physical therapy (PT) program as part of a multidisciplinary intervention to patients undergoing outpatient radiation therapy for advanced cancer. A single-blinded, randomized, controlled trial at a quaternary medical center outpatient clinic. One hundred three adults undergoing radiation therapy for advanced cancer with prognoses > or =6 mos and 5-yr survival estimates < or =50% were randomized to usual care or participation in eight 90-min, multidisciplinary interventional sessions with 30 mins of each session devoted to PT. PT consisted of truncal and limb isodynamic strengthening targeting major upper- and lower-limb muscle groups as well as education and provision with instructional materials. Physical well-being and fatigue were assessed with Linear Analog Scale of Assessment. The Profile of Mood States-Short form, including Fatigue-Inertia and Vigor-Activity subscales, was also administered. PT session attendance was 89.3%. Relative to baseline, mean physical well-being Linear Analog Self Assessment scores at week 4 improved in the intervention group, 0.4 (SD, 23.6), and declined significantly in the control group, -10.0 (SD, 21.5) (P = 0.02). Fatigue and vigor were not significantly different between the groups. All intergroup differences had resolved at 8 and 27 wks. Baseline characteristics were not associated with the magnitude or direction of change in outcomes related to physical functioning. Delivery of a standardized resistive exercise PT intervention is feasible during outpatient radiation therapy and is associated with preserved physical well-being. However, benefits were not sustained, and fatigue was not affected.

Fatiguing intermittent lower limb exercise influences corticospinal and corticocortical excitability in the nonexercised upper limb

It has recently been reported that unilateral fatiguing exercise affects not only the motor area innervating the exercising muscle but also the ipsilateral motor area innervating homologous nonexercised muscle. This study was designed to clarify the effects of fatiguing intermittent lower limb exercise on the excitability of the motor cortex representation of nonexercised muscles in the arm. Eight subjects performed an intermittent leg press exercise composed of three bouts of 5-minute leg press (T1, T2, and T3) at 50% of maximal voluntary contraction separated by a 2-minute rest. Motor-evoked potentials (MEP), short interval intracortical inhibition (SICI), and intracortical facilitation (ICF), using paired-pulse transcranial magnetic stimulation, were assessed in two nonexercised arm muscles (first dorsal interosseous muscle: FDI, n = 8; biceps brachii muscle: BB, n = 6) and one exercised leg muscle (quadriceps femoris muscle: QF, n = 6) before and immediately after each bout of exercise and for 30 minutes during recovery after the end of the third exercise bout (Experiment 1). Experiment 2 was the same as Experiment 1, except that the test pulse intensity was adjusted to produce a given amplitude of MEP(TEST) at each time point. MEPs and SICI in the exercised QF muscle were depressed at all time points during and after fatigue. In contrast, MEPs in nonexercised arm muscles were facilitated from T1-T3 (T3, only FDI), but were then depressed for up to 20 minutes in the recovery period. SICI was reduced in both muscles during T1-T3 and remained depressed until 20 minutes into recovery. ICF was unchanged in arm muscles but depressed in QF over T1-T3. The current study indicates that muscle fatigue induced by exercise of a large lower limb muscle group has powerful effects on the excitability of both SICI and the corticospinal projection to muscles of the nonexercised upper limb.

Glucose Uptake Patterns in Exercised Skeletal Muscles of Elite Male Long-Distance and Short-Distance Runners

The aim of this study was to determine glucose uptake patterns in exercised skeletal muscles of elite male long-distance and short-distance runners. Positron emission tomography (PET) using 18F-fluoro-2-deoxyglucose (FDG) was performed to determine the patterns of glucose uptake in lower limbs of short-distance (SD group, n=8) and long-distance (LD group, n=8) male runners after a modified 20 min Bruce treadmill test. Magnetic resonance imaging (MRI) was used to delineate the muscle groups in lower limbs. Muscle groups from hip, knee, and ankle movers were measured. The total FDG uptake and the standard uptake value (SUV) for each muscle group were compared between the 2 groups. For the SD and LD runners, the 2 major muscle groups utilizing glucose during running were knee extensors and ankle plantarflexors, which accounted for 49.3 +/- 8.1% (25.1 +/- 4.7% and 24.2 +/- 6.0%) of overall lower extremity glucose uptake for SD group, and 51.3 +/- 8.0% (27.2 +/- 2.7% and 24.0 +/- 8.1%) for LD group. No difference in muscle glucose uptake was noted for other muscle groups. For SD runners, the SUVs for the muscle groups varied from 0.49 +/- 0.27 for the ankle plantarflexors, to 0.20 +/- 0.08 for the hip flexor. For the LD runners, the highest and lowest SUVs were 0.43 +/- 0.15 for the ankle dorsiflexors and 0.21 +/- 0.19 for the hip. For SD and LD groups, no difference in muscle SUV was noted for the muscle groups. However, the SUV ratio between the ankle dorsiflexors and plantarflexors in the LD group was significantly greater than that in the SD group. We thus conclude that the major propelling muscle groups account for approximately 50% of lower limb glucose utilization during running. Thus, the other muscle groups involving maintenance of balance, limb deceleration, and shock absorption utilize an equal amount. This result provides a new insight into glucose distribution in skeletal muscle, suggesting that propellers and supporters are both energetically important during running. Furthermore, for each unit muscle volume, movers of ankle are more glucose-demanding than those of hip.

The characterisation of gait patterns of people with multiple sclerosis

Background. There are relatively few reports describing gait patterns in multiple sclerosis (MS) and most are confined to the analysis of temporal distance parameters with some assessment of joint range of motion. The aim of this study was to perform a biomechanical characterisation of gait patterns among people with MS across a wide range of severity of ambulatory impairment.Methods. Sixteen patients with MS were recruited for this study. Initially, the spasticity of lower limb muscle groups was measured and ambulatory ability was graded. Patients were then placed in two groups based on the level of severity of ambulatory ability. Kinematic, kinetic and EMG gait data from both MS groups were then compared to a control group of 10 healthy subjects.Results. Patients with MS in both groups were found to walk with reduced gait speed, reduced maximum hip and knee extension, ankle plantarflexion angle and propulsive force compared to the control group. In general, the same gait impairments were found in both MS groups compared to the control group, and were greater for the more severely affected MS patient group.Interpretation. This study highlights typical gait patterns of people with MS and provides an indication of common pathways in the degeneration of ambulatory ability as a consequence of disease progression. This information should enable improved clinical treatment of ambulation, as well as the prescription, or even design, of appropriate assistive devices.

A Diet and Exercise Program to Improve Clinical Outcomes in Patients with Obstructive Sleep Apnea – A Feasibility Study

To assess the feasibility and efficacy of a novel 16-week exercise and diet program for important clinical outcomes in obstructive sleep apnea (OSA). Cohort study assessing sleep disordered breathing, cardiovascular risk factors, and neurobehavioral function prior to and following completion of the 16-week program. The program used a proprietary very low energy diet (Optifast, Novartis), and subjects participated in a supervised exercise schedule, which included both aerobic and resistance training. Follow-up contact was made at 12 months after program exit. Consecutive patients with newly diagnosed sleep apnea were approached who had an apnea-hypopnea index (AHI) of 10 to 50, a body mass index (BMI) of greater than 30 kg/m2, no significant comorbidities, and able to exercise. All data are presented as mean [SD]. Of 21 patients with OSA who were approached, 12 middle-aged (42.3 [10.4] years old), obese (BMI 36.1 [4.3] kg/m2), and predominantly female (75%) subjects with mild to moderate OSA were enrolled (AHI 24.6 [12.0]). Weight loss was significant (12.3 [9.6] kg, p <0.001), and 5 of the 10 who completed the program were able to independently maintain good weight loss at 12 months. At the 16-week assessment, there was a small nonsignificant fall in the AHI. Six of the 10 subjects had a reduction in sleep disordered breathing, and the AHI was less than 10 in 3 patients. There were significant improvements in neurobehavioral and cardiometabolic outcomes. Snoring improved in most subjects, but the improvement was clinically important (a score of < 2) in only 7. A supportive diet and exercise program may be of benefit to obese patients with mild to moderate sleep apnea. The results of this feasibility study showed significant weight loss and improvement in clinically important neurobehavioral and cardiometabolic outcomes but no significant change in sleep disordered breathing. These promising preliminary results need confirmation with a larger randomized trial.

Voluntary activation of human knee extensors measured using transcranial magnetic stimulation

The aim of this study was to determine the applicability and reliability of a transcranial magnetic stimulation twitch interpolation technique for measuring voluntary activation of a lower limb muscle group. Cortical voluntary activation of the knee extensors was determined in nine healthy men on two separate visits by measuring superimposed twitch torques evoked by transcranial magnetic stimulation during isometric knee extensions of varying intensity. Superimposed twitch amplitude decreased linearly with increasing voluntary torque between 50 and 100% of mean maximal torque, allowing estimation of resting twitch amplitude and subsequent calculation of voluntary activation. There were no systematic differences for maximal voluntary activation within day (mean +/- s.d. 90.9 +/- 6.2 versus 90.7 +/- 5.9%; P = 0.98) or between days (90.8 +/- 6.0 versus 91.2 +/- 5.7%; P = 0.92). Systematic bias and random error components of the 95% limits of agreement were 0.23 and 9.3% within day versus 0.38 and 7.5% between days. Voluntary activation was also determined immediately after a 2 min maximal voluntary isometric contraction; in four of these subjects, voluntary activation was determined 30 min after the sustained contraction. Immediately after the sustained isometric contraction, maximal voluntary activation was reduced from 91.2 +/- 5.7 to 74.2 +/- 12.0% (P < 0.001), indicating supraspinal fatigue. After 30 min, voluntary activation had recovered to 85.4 +/- 8.8% (P = 0.39 versus baseline). These results demonstrate that transcranial magnetic stimulation enables reliable measurement of maximal voluntary activation and assessment of supraspinal fatigue of the knee extensors.

Use of hand-held dynamometry in the evaluation of lower limb muscle strength in people with Huntington’s disease

Sub-clinical muscle involvement, including myopathic changes and mitochondrial dysfunction of skeletal muscle, has been reported in people with Huntington's disease (HD). Muscle strength was evaluated using a hand-held dynamometer. Reliability and validity in people with HD were determined. Isometric muscle strength of 6 lower limb muscle groups was measured in 20 people with HD and matched healthy controls. People with HD were evaluated with the Unified Huntington's Disease Rating Scales (UHDRS). Within session reliability using intra-class correlation coefficients (ICC) was calculated. Discriminant and convergent validity was also evaluated. UHDRS motor scores of people with HD ranged from 28 to 80. Reliability of strength testing was excellent (ICC 0.86 to 0.98). People with HD had on average about half the strength of healthy matched controls. UHDRS motor scores and strength scores were significantly correlated (convergent) providing a further indication of validity of strength testing. The hand-held dynamometer is a reliable and valid measurement tool to detect strength differences between people with HD and a matched control group. There is significant reduction in lower limb muscle strength in HD which does not appear to have been described previously.

Walking ability is related to muscle strength in children with cerebral palsy

The purpose of this study was to assess the relation between muscle strength and walking ability in children with bilateral spastic cerebral palsy at GMFCS levels I–III. 55 children (mean age 10.7, range 5–15) were tested for muscle strength in eight lower limb muscle groups with a handheld myometer. They were also tested with the Gross Motor Function Measure domains for standing and walking, running and jumping. Muscle strength in the legs was below normative predicted value in most of the children, with muscle weakness most pronounced around the ankle, followed by the hip muscles. There was a significant difference in muscle strength between GMFCS levels. There was also a moderate to high correlation between muscle strength and the GMFM, indicating that muscle weakness affects walking ability. Independently walking children had more than 50% of predicted muscle strength values.

Recovery of muscle strength following multi-level orthopaedic surgery in diplegic cerebral palsy

Muscle strength changes following multi-level surgery in cerebral palsy and the impact of rehabilitation on functional recovery are largely unknown. The aim of this study was to quantify lower limb muscle strength changes in children with spastic diplegia after multi-level orthopaedic surgery and to compare the efficacy of progressive resistance strengthening (RS) versus active exercise (AE). Twenty children with spastic diplegia (mean age 12.5 years) participated in this prospective randomised controlled trial. Participants underwent multi-level orthopaedic surgery. Routine physiotherapy commenced immediately after surgery. At 6 months post-operatively, children were randomly assigned to the resistance strengthening RS ( n = 11) or active exercise AE ( n = 9) group and received intensive physiotherapy for 6 weeks. Gait, motor function and maximum isometric muscle strength in five lower limb muscle groups were measured pre-operatively and at 6 months (before and after intensive physiotherapy) and 12 months. As part of the study, we developed and validated a myometry protocol. Despite kinematic improvements, there was significant reduction of muscle strength ( p < 0.05) in all muscle groups at 6 months post-operatively. Following 6 weeks of intensive physiotherapy, both groups showed significant improvement in muscle strength, GMFM scores and gait parameters. Resistance training showed some advantages over active exercise. At 1 year after surgery, strength did not reach pre-operative values in some muscle groups but the benefit from physiotherapy was maintained. In conclusion, we quantified objectively the reduction in muscle strength 6 and 12 months following multi-level surgery. Furthermore, we demonstrated significant improvement in muscle strength, gait and function following post-operative strength training.

Fatigability of Lower Limb Muscles during Walking in Chronic Obstructive Pulmonary Disease

Background: Patients with chronic obstructive pulmonary disease (COPD) perceive much less quadriceps fatigue during walking compare to cycling. Whether other lower limb muscles could develop fatigue during walking is unknown. The purpose of this study was to assess the electrical activity of five lower limb muscles during a 6-minute walking test in 11 healthy subjects and in 10 patients with COPD matched for age and activity level. &#x0D; &#x0D; Methods: Surface electromyographic (EMG) data were recorded in five muscle groups (soleus, gastrocnemius (GM), tibialis anterior, vastus lateralis and rectus femoris) of the right leg during the walking test. The EMG median frequency of all contractions at minute 2 and 6 were averaged for each muscle group. Ventilation, oxygen consumption and CO2 production were also continuously measured throughout the test. &#x0D; &#x0D; Results: Although the walking distance (494 ± 116 vs. 625 ± 50 m; P &lt; 0.01) and the walking speed (1.7 ± 0.4 vs. 2.1 ± 1.2 m·s-1; P &lt; 0.01) were reduced in COPD compared with controls, patients worked at a higher percentage of their estimated maximum voluntary ventilation during the test (118 ± 32 % vs. 51 ± 14 %; P &lt; 0.01). The time course of the EMG median frequency from minute 2 to 6 differed between patients with COPD and healthy controls for the soleus, GM and tibialis anterior suggesting the occurrence of a muscle fatiguing profile in COPD. &#x0D; &#x0D; Conclusions: Evidences of a fatiguing profile was found in three lower limb muscle groups during walking in COPD despite a slower walking speed compared to healthy controls.

Initiating extension of the lower limbs in subjects with complete spinal cord injury by epidural lumbar cord stimulation.

We provide evidence that the human spinal cord is able to respond to external afferent input and to generate a sustained extension of the lower extremities when isolated from brain control. The present study demonstrates that sustained, nonpatterned electrical stimulation of the lumbosacral cord--applied at a frequency in the range of 5-15 Hz and a strength above the thresholds for twitches in the thigh and leg muscles--can initiate and retain lower-limb extension in paraplegic subjects with a long history of complete spinal cord injury. We hypothesize that the induced extension is due to tonic input applied by the epidural stimulation to primary sensory afferents. The induced volleys elicit muscle twitches (posterior root muscle-reflex responses) at short and constant latency times and coactivate the configuration of the lumbosacral interneuronal network, presumably via collaterals of the primary sensory neurons and their connectivity with this network. We speculate that the volleys induced externally to the lumbosacral network at a frequency of 5-15 Hz initiate and retain an "extension pattern generator" organization. Once established, this organization would recruit a larger population of motor units in the hip and ankle extensor muscles as compared to the flexors, resulting in an extension movement of the lower limbs. In the electromyograms of the lower-limb muscle groups, such activity is reflected as a characteristic spatiotemporal pattern of compound motor-unit potentials.

Centre of mass motion during gait in persons with myelomeningocele

The movement of the centre of mass in the vertical and lateral directions during gait in children with myelomeningocele was analyzed. The children were classified into five groups depending on the successive paresis of lower limb muscle groups and compared to a control group. In the groups with dorsi- and plantarflexor weakness, the excursions increased and an anterior trend in the centre of mass was observed. In the groups with additional abductor paresis, the lateral excursion was highest and the vertical excursion low due to increased transverse and frontal motion and reduced sagittal motion. With further paresis of the hip extensors, the centre of mass was more posteriorly positioned due to compensatory trunk extension. Improved understanding of individual children's solutions to their muscle paresis can be obtained by visualizing the centre of mass relative to the pelvis. Centre of mass analyses in myelomeningocele offer an important complement to standard gait analysis.

Interventions for preventing lower limb soft-tissue injuries in runners.

Overuse musculoskeletal injuries occur frequently in runners. Suggestions for prevention have focused on stretching exercises, modifying training schedules and the use of protective devices such as braces and insoles. To date, no systematic analysis of the literature on the effectiveness of these strategies in the prevention of overuse injuries has been published. The objective of the review was to evaluate the evidence from randomised controlled trials on the prevention of lower limb soft-tissue running injuries. An electronic database search included The Cochrane Musculoskeletal Injuries Group specialised register (date of last search October 2000), The Cochrane Controlled Trials Register (The Cochrane Library, Issue 3, 1999), MEDLINE (from 1966), EMBASE (from 1980), SPORT Discus (1975-2000), HERACLES (1975-2000), ATLANTES (1980-1996), BIOSIS, CINAHL, SCISEARCH, Current Contents, Index To Theses and Dissertation Abstracts. Date of last search for these databses: May 2000. Any randomised or quasi-randomised trials evaluating interventions to prevent lower limb soft-tissue running injuries. All trials fulfilling the selection criteria were assessed by two reviewers independently. Data were also extracted independently by the two reviewers using a pre-derived data extraction form. Exploratory analyses, including pooling of results from groups of trials of similar designs were undertaken, using a fixed effects model. Results were reported as relative risks (RR) with 95 per cent confidence intervals (95% CI). Twelve trials with 8,806 participants were included. In one trial, a single control group was matched to three different included intervention groups. The effectiveness of stretching exercises (5 trials, 1944 participants in the intervention groups, 3159 controls), and of insoles and footwear modification (5 trials, 903 participants in the intervention groups, 3006 controls) in the prevention of lower extremity soft tissue injuries associated with running is unknown. Reducing the distance, frequency and duration of running may be effective in the prevention of lower extremity soft tissue injuries associated with running (3 trials, 514 participants in intervention groups, 1663 controls). Wearing a knee brace with a patellar support ring may be effective in the prevention of running-associated anterior knee pain (1 trial, 27 participants in the intervention group, 33 controls). This review provides some evidence for the effectiveness of the modification of training schedules, but there is insufficient evidence to determine the effectiveness of stretching exercises for major lower limb muscle groups in reducing lower limb soft-tissue running injuries. More studies are required to confirm that knee braces may prevent knee pain, to clarify the role of stretching, and to quantify optimal training loads. Generalisability of the results may be limited by the intensive nature of military training (the context for most of the studies) and the inclusion of only small numbers of women.

Botulinum toxin A in cerebral palsy: Functional outcomes

Botulinum toxin A in cerebral palsy: Functional outcomes

Contractile properties of two human lower limb muscle groups: The quadriceps and triceps Surae

The purpose of this study was to differentiate between the contractile characteristics of the quadriceps femoris (QF) and triceps surae (TS) muscle groups within the same individual independently of volitional effort. Electrically evoked isometric contractions of the QF and TS muscle groups were recorded from the dominant leg of 13 men and women (28.8 ±2.1 years). The electrical stimulation protocol performed included: supramaximal twitches; contractions evoked at 10, 20, 50 and 100 Hz stimulation; and a two minute fatigue test. Compared with the QF, the TS contractile properties were found to have: (1) prolonged twitch TPT and ½RT; (2) a larger relative torque production at low frequencies of stimulation; and (3) a greater resistance to fatigue. These results indicate: (1) that the TS is a functionally slower and less fatiguable muscle group than the QF; and (2) that electrical stimulation is a sensitive and non‐invasive technique for determining the contractile characteristics of human muscle.

Consistency of multi-channel surface EMG recordings: Application in spinal cord injured subjects

We evaluated the consistency of serial polyelectromyographic recordings of altered motor control in spinal cord injured (SCI) individuals. Using 12 pairs of surface electrodes placed over major muscle groups of lower limb and trunk, we examined voluntary and involuntary and phasic and tonic features of motor control using a standardized protocol for brain motor control assessment (BMCA). The surface electromyographic (EMG) data were digitized and analysed on the basis of the root mean square (RMS) envelope of activity, with the exception of phasic tendon tap responses which were evaluated from full bandwidth EMG data. The average amplitudes of responses were calculated. The median correlation of the results from two successive examinations 1–2 weeks apart for all subjects was 0.98. Further analysis was based on ratios of corresponding elements from the two studies. Noise from null responses was suppressed by incorporating a threshold parameter T set to 1 μV RMS. With this value, pairs of studies in 52 subjects were virtually identical (mean ratio of 1.02 ± 0.1). Z-scores from two case studies in which pharmacological and physiological interventions changed motor control demonstrated the utility of the procedure. This method offers a reliable and appropriate means of studying altered motor control which is sensitive to changes induced after interventions.