Measurement and reproducibility of strength and voluntary activation of lower-limb muscles

Accurate measurement of muscle strength and voluntary muscle activation is important in the assessment of disorders that affect the motor pathways or muscle. We designed a multipurpose system to assess the variability and reproducibility of isometric torque measurements obtained during maximal voluntary efforts of the knee flexor, knee extensor, ankle dorsiflexor, and ankle plantarflexor muscles on each side. It used two isometric myographs mounted on an adjustable frame. Measurements of maximal voluntary torque (range, 25-188 Nm) displayed low variability within a testing session and over five testing sessions (coefficient of variation range, 5-11%). We used the same equipment to measure voluntary activation of the triceps surae muscles. Voluntary activation, measured with a sensitive twitch interpolation method, increased with increasing voluntary contraction torque (P < 0.001) and was very high during maximal efforts (mean, 97.8 +/- 2.1%; median, 98.5%). Furthermore, measurements of voluntary activation during maximal efforts were reproducible across testing sessions with very little variability (coefficient of variation, <2%). The myograph system and the testing procedures should allow accurate measurement of strength and voluntary drive in longitudinal patient studies.     

不同人群踝关节跖屈肌群肌肉形态与力量的相关性

背景：骨骼肌肌肉形态与力量关系密切,采用CT、核磁共振等仪器对人体骨骼肌进行活体形态测量,结合相关肌肉力量测量手段探索两者之间相关关系的报道尚不多见。 目的：对比观察不同人群肌肉形态与力量的差异,探讨踝关节跖屈肌群形态特征与肌肉收缩力量之间的关系。 设计、时间及地点：对比观察,于2006-05/12在中国医科大学附属第二医院完成。 对象：选择普通男性青年学生14人作为对照组,测试前未专门从事过力量训练;另选健将级速滑运动员10人作为运动组。所有测试对象试验期间踝关节均无损伤。 方法：采用螺旋CT对受试对象双侧小腿进行不间断连续扫描,影像分析采用Xiphoid CT专用图像分析软件,由CT图像计算得出小腿围、踝关节跖屈肌横截面积,根据体视学原理采用数值积分法计算跖屈肌群体积。采用CYBEX-NORM型多关节等速测力系统对踝关节跖屈肌群进行60,120,180,240,300 (°)/s不同角速度下的等速测试。 主要观察指标：①各组受试者跖屈肌形态及不同角速度下跖屈峰力矩和跖屈相对峰力矩的变化。②各组受试者不同角速度下跖屈峰力矩与跖屈肌群体积、最大横截面积、小腿围相关性。 结果：①与对照组相比,运动组跖屈肌最大横断面积、体积和小腿围均显著增大(P < 0.05)。在踝关节等速向心测试中,运动组的跖屈向心峰力矩在每一个角速度下均显著高于对照组(P < 0.05),但随着关节运动角速度的增加,对照组和运动组的跖屈向心峰力矩都相应地减小,②在不同的角速度下,跖屈肌群最大横截面积、肌肉体积、小腿围与跖屈峰力矩之间均具有显著的正相关性(r > 0.725,P < 0.05~0.01)。 结论：跖屈肌群峰力矩变化趋势与肌肉形态相一致,肌肉形态可作为观测肌力变化的一个重要参考指标。     

Contributing factors to muscle weakness in children with cerebral palsy

The aim of this study was to determine the extent of ankle muscle weakness in children with cerebral palsy (CP) and to identify potential causes. Maximal voluntary contractions of plantar (PF) and dorsiflexors (DF) were determined at optimal angles in knee flexion and extension in both legs of 14 children with hemiplegia (7 males, 7 females) and 14 with diplegia (8 males, 6 females). Their results were compared to 14 age- and weight-matched control participants (5 males, 9 females). Muscle cross-sectional areas of soleus, posterior, and anterior compartment muscles were determined from MRIs in 14 children with CP (eight diplegia, six hemiplegia) and 18 control children. Specific tension (torque/unit area) of PF and DF was determined from torque and cross-sectional area results. Muscle volumes of PF and DF were also determined in both legs of five control children and five with hemiplegia. Muscle EMG was recorded from soleus, medial gastrocnemius, and tibialis anterior during each maximal voluntary contraction. Mean amplitude was significantly reduced in PF and DF in both CP groups and significantly higher levels of coactivation of antagonists were found compared to control participants. Strength of PF and DF was significantly reduced in both CP groups, but more importantly the muscles were found to be weak based on significantly reduced specific tensions. The PF were most affected, particularly in the group with hemiplegia. It is believed that an inability to maximally activate their muscles contributed to this weakness. A combination of incomplete activation and high levels of PF coactivation are thought to have contributed to DF weakness.     

Ankle torque steadiness is related to muscle activation variability and coactivation in children with cerebral palsy

The aims of this study were to: (1) investigate the significance of muscle activation variability and coactivation for the ability to perform steady submaximal ankle torque (torque steadiness) in healthy children and those with cerebral palsy (CP), and (2) assess ankle function during isometric contractions in those children. Fourteen children with CP who walked with equinus foot deformity and 14 healthy (control) children performed maximal and steady submaximal ankle dorsi‐ and plantarflexions. Dorsiflexion torque steadiness was related to agonist and antagonist muscle activation variability as well as the plantarflexor coactivation level in children with CP (r > 0.624, P < 0.03). Moreover, children with CP displayed reduced maximal torque and submaximal torque steadiness of both dorsi‐ and plantarflexion compared with controls (P < 0.05). Both muscle groups may benefit from strength training, as they exhibit poor submaximal control and weakness in children with CP. Muscle Nerve, 2009     

Hyperactive stretch reflexes, co-contraction, and muscle weakness in children with cerebral palsy

The aim of this study was to examine the repeatability of and relationships among spasticity, co-contraction of agonist–antagonist, and muscle strength in children with cerebral palsy (CP). Eight children with spastic diplegic CP (five males, three females; Gross Motor Function Classification System [GMFCS] Levels I–III; mean age 10y 2mo [SD 2y 9mo], range 6–13y) and nine children in a comparison group (six males, three females; mean age 8y 10mo [SD 2y 4mo], range 6y to 12y 6mo) were assessed twice to examine repeatability of Composite Spasticity Scale, soleus stretch reflexes, electromyography (EMG) co-contraction ratio, and torque recorded during maximal isometric voluntary contraction of ankle dorsiflexors and plantarflexors. Sixty-one children with spastic CP, (54 diplegic, seven hemiplegic; 32 males, 29 females; GMFCS levels I–III; mean age 10y 8mo [SD 2y 9mo], range 6–15y) were then assessed to delineate possible correlations among these measures. Intraclass correlation coefficients (0.78–0.97) showed high data repeatability in both groups. Children with spastic CP demonstrated significantly larger soleus stretch reflex/M-response areas smaller torques, but larger EMG co-contraction ratios during both voluntary dorsiflexion and plantarflexion (all p <0.05). Children with spastic CP who had larger soleus stretch reflex/M-response areas demonstrated larger plantarflexion co-contraction ratio ( r = 0.28), and produced smaller plantarflexion and dorsiflexion torques ( r = –0.48 and –0.27 respectively). However, no correlation was noted between soleus stretch reflex and clinical spasticity. Our findings demonstrated that hyperactive soleus stretch reflex affected torque production of ankle muscles. Moreover, the severity of spasticity may not be fully described by either stretch reflex or tone measure alone.     

Attenuation of the effect of remote muscle contraction on the soleus H-reflex during plantar flexion.

OBJECTIVE: We investigated to what extent the facilitation of the soleus (Sol) Hoffmann (H-) reflex during a phasic voluntary wrist flexion (Jendrássik maneuver, JM) can be modulated by graded plantar flexion force and conditioning wrist flexion force. METHODS: The subjects were asked to perform phasic wrist flexion under a reaction time condition. Sol H-reflex was evoked by stimulating the right tibial nerve at various time intervals (50-400ms) after the 'Go' signal for initiating JM while the ankle was at rest and while plantarflexing. The level of tonic plantar flexion force (isometric contraction of 10, 20 and 30% of maximal EMG) and conditioning wrist flexion (isometric contraction of 30, 50 and 80% of maximum voluntary contraction) during JM was graded systematically. RESULTS: Although JM facilitation could be seen 80-120ms after the flexor carpi radialis (FCR) EMG onset even while plantarflexing, the magnitude of JM facilitation under plantar flexion was significantly decreased compared to that at rest. The degree of decrease in JM facilitation did not depend on the level of plantar flexion force. In contrast, the degree of JM facilitation was proportional to the level of wrist flexion force while the ankle was at rest and while plantarflexing, though the amount of JM facilitation significantly decreased while plantarflexing. CONCLUSIONS: JM facilitation of Sol H-reflex is decreased while performing tonic voluntary contraction of the homonymous muscle. The degree of decrease in JM facilitation is independent of the level of homonymous muscle contraction, but depends on the level of remote FCR contraction. In clinical application, when we intend to elicit a maximum stretch reflex by JM, full relaxation of homonymous muscle should be carefully confirmed. SIGNIFICANCE: Our results provide evidence for better understanding of the features of JM and insight into its clinical application.     

Axonal excitability during ischemia in MELAS

Introduction: We investigated muscle activation strategy and performance of knee extensor and flexor muscles in children and adults with generalized joint hypermobility (GJH) and compared them with controls. Methods: Muscle activation, torque steadiness, electromechanical delay, and muscle strength were evaluated in 39 children and 36 adults during isometric knee extension and flexion. Subjects performed isometric maximum contractions, submaximal contractions at 25% maximum voluntary contraction (MVC), and explosive contractions. Results: Agonist activation was reduced, and coactivation ratio was greater in GJH during knee flexion compared with controls. Torque steadiness was impaired in adults with GJH during knee flexion. No effect of GJH was found on muscle strength or electromechanical delay. Correlation analysis revealed an association between GJH severity and function in adults. Conclusions: The results indicate that muscle activation strategy and quality of force control were significantly affected in adults with GJH during knee flexion, whereas only muscle activation strategy was affected in children with GJH. Muscle Nerve 48:762–769, 2013     

A multilevel approach to botulinum toxin type A treatment of the (ilio)psoas in spasticity in cerebral palsy

In spasticity, flexion deformity of the hip is frequently associated with contracture or hyper-reflexia of the psoas muscle. Botulinum toxin type A (BTX-A) has been used for some considerable time in the management of paediatric gait disorders. We have been using a multilevel approach to manage spasticity in cerebral palsy for several years, the combination of gait analysis and clinical evaluation being important for the selection of target muscles for BTX-A injections. Twenty cerebral palsy children (12 female) with spasticity were treated with BTX-A injections (BOTOX® mean dose, 2 U/kg body weight) into the psoas muscle. Patients were monitored using range of motion measurements of maximal hip extension, clinical estimates of hypertonia in the hip flexors, gait analysis (three-dimensional kinematics and kinetics) and surface electromyography of major lower limb muscles. Full gait analysis was carried out on 12 of the patients. Significant clinical improvements were observed following 15 of the 21 psoas treatments. Furthermore, the kinematics results of gait analysis showed improvement in one or more parameters in nine of the 12 patients. In conclusion, we have demonstrated the value of a multilevel approach to BTX-A treatment in the management of spasticity in children with cerebral palsy.     

Prospective study examining remote effects of botulinum toxin a in children with cerebral palsy

We examined the remote effects on muscle strength and functional decline of lower-extremity botulinum toxin A injections in children with cerebral palsy. This prospective study enrolled 34 children (19 boys, 15 girls; mean age, 7.7 years) diagnosed with spastic cerebral palsy. Patients were examined at baseline and 1 month to determine if they experienced a change in upper-extremity strength (handheld dynamometry) or function (Pediatric Outcomes Data Collection Instrument). Subjects were analyzed in aggregate and by dosing group (low dose, 0-10 U/kg body weight; high dose, 11-25 U/kg) to determine if injection dose was associated with a change in remote muscle strength or function. We measured baseline and 1-month postinjection strength in shoulder flexor, shoulder abductor, elbow flexor, elbow extensor, and finger flexor muscles. None of these remote muscle groups was significantly weaker at 1 month after injection. No correlation was evident between change in muscle strength and toxin dose. These findings indicate that doses of botulinum toxin A in the lower extremities, at up to 21 U/kg, do not affect upper-extremity strength. This information can help guide dosages of botulinum toxin A in the management of spasticity in children with cerebral palsy.     

Stroke‐related effects on maximal dynamic hip flexor fatigability and functional implications

Introduction: Stroke‐related changes in maximal dynamic hip flexor muscle fatigability may be more relevant functionally than isometric hip flexor fatigability. Methods: Ten chronic stroke survivors performed 5 sets of 30 hip flexion maximal dynamic voluntary contractions (MDVC). A maximal isometric voluntary contraction (MIVC) was performed before and after completion of the dynamic contractions. Both the paretic and nonparetic legs were tested. Results: Reduction in hip flexion MDVC torque in the paretic leg (44.7%) was larger than the nonparetic leg (31.7%). The paretic leg had a larger reduction in rectus femoris EMG (28.9%) between the first and last set of MDVCs than the nonparetic leg (7.4%). Reduction in paretic leg MDVC torque was correlated with self‐selected walking speed (r² = 0.43), while reduction in MIVC torque was not (r² = 0.11). Conclusions: Reductions in maximal dynamic torque of paretic hip flexors may be a better predictor of walking function than reductions in maximal isometric contractions. Muscle Nerve 51 : 446–448, 2015     

Phenol reduces hypertonia and enhances strength: a longitudinal case study

Phenyl alcohol blocks are used to relieve spasticity. Such nerve conduction blocks result from phenol-induced axonotmesis and could potentially affect muscle properties related to the ability to generate, maximize, and reduce force. This study assessed the 12-week longitudinal effect of phenol on position (stiffness) and velocity (damping) components of hypertonia, in addition to strength (peak torque and times to generate and reduce torque) in an individual with chronic elbow flexor spasticity following stroke. Phenol motor point injections of flexor muscles paradoxically increased the magnitude of flexion torque and decreased the times required to generate and reduce flexion and extension joint torques, in addition to reducing elbow extension stiffness and damping. Large reductions in the velocity-related component of hypertonia (damping changes > 90%) occurred immediately following injection, which is a finding that supports the velocity-dependent definition of spasticity. Although the changes in damping were large and transient, changes in stiffness and strength variables were small, slower to occur, and maintained. This suggests secondary changes following nerve block, possibly facilitated by regular elbow use subsequent to spasticity reduction.     

Reliability of measurements of muscle strength and voluntary activation using twitch interpolation

We investigated the reproducibility of measurements of maximal voluntary torque and maximal voluntary activation using twitch interpolation. On 5 days, each of 5 subjects performed 10 maximal voluntary isometric contractions of their elbow flexors. Single supramaximal stimuli were delivered over biceps brachii at the measured peak torque during each effort, and in the relaxed muscle 5 s later. A voluntary activation score was calculated from the size of twitches evoked by the stimuli (resolution < 0.15 Nm). Although all subjects were able to drive the stimulated elbow flexor muscles maximally in some trials, they did not do so in 75% of all contractions. Maximal voluntary torques did not vary significantly within a subject between sessions. There were consistent differences in the level of maximal voluntary activation between subjects (P < 0.01), but no differences in voluntary activation within an individual across days in 4 of 5 subjects. Failure to drive the stimulated elbow flexor muscles maximally was not associated with inadvertent co-contraction of the antagonist muscles. © 1995 John Wiley & Sons, Inc.     

Electromyography and mechanomyography of elbow agonists and antagonists in Parkinson disease

The purpose of this study was to assess the electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in Parkinson disease patients during maximal isometric elbow contraction in flexion and extension. Ten elderly females with Parkinson disease (average age 75 years) and 10 age‐matched healthy females were tested. The torque and the EMG and MMG signals from biceps brachii and triceps brachii were recorded during sustained maximal voluntary isometric contraction of the elbow flexors and extensors. There were no intergroup differences in the EMG and MMG activities of agonist and antagonist muscles or in torque. This might be because the Parkinson subjects were tested during their medication “ON” phase, or perhaps maximal isometric contraction (MVC) induced greater active muscle stiffness that affected the MMG signal. Muscle Nerve 40: 240–248, 2009     

Meta-analysis of the effect of strengthening interventions in individuals with cerebral palsy

This study aimed to investigate the evidence that strengthening interventions can improve muscle strength and activity in individuals with cerebral palsy. The search focused on studies that employed strength training for children with cerebral palsy for which six electronic databases were used to extract literature published from 2001 to 2012. The key terms used in these searches were combined strength training, strengthening, weight training, weight lifting, resistance, and cerebral palsy. The quality of each study was assessed using the PEDro (Physiotherapy Evidence Database) scale. Thirteen randomized controlled trial studies were selected and divided into categories according to program type, mode, and outcome measures. The overall effect sizes of each study and types of strengthening were large. Strengthening exercise improved muscle strength to a greater degree, when practiced 3 times per week in 40–50 min sessions than in other categories of session length, and greater improvement was observed in younger children than in older. The effect size of the activities and variables related to gait, except for gait endurance, were medium to large. The effect size of individual muscles was large, but the effect sizes for ankle plantar flexor, hip abductor/adductor, and extensor were insignificant. Strengthening interventions are useful for increasing muscle strength in individuals with cerebral palsy, specifically in youth and children, and optimal exercise consisted of 40- to 50-min sessions performed 3 times per week. Although strengthening interventions may improve activities, including gait, more studies that are rigorous are needed to determine the contributions to gross motor function.     

Knee extensor strength, activation, and size in very elderly people following strength training.

Muscle strength, activation, and size were studied in 11 very elderly subjects (8 women and 3 men; age range, 85-97 years) who completed 12 weeks of strength training of the knee extensor muscles. Training increased the maximum amount of weight that could be lifted once (134%; P < 0.05) and maximum voluntary isometric strength, measured as both force recorded at the ankle with the knee flexed 90 degrees (17%, ns) and as torque with the knee flexed 60 degrees (37%; P < 0.05). Anatomical lean quadriceps cross-sectional area (LCSA) measured at midthigh using magnetic resonance imaging increased from 27.5 +/- 9.6 cm2 to 30.2 +/- 10.0 cm2 (9.8%; P < 0. 05) after training. Both before and after training, isometric strength was closely related to LCSA, but training resulted in no significant change in muscle force per unit area of quadriceps muscle. Using the twitch interpolation technique, muscle activation during a maximal voluntary isometric contraction was shown to be incomplete in all subjects before training (ranging from 69% to 93%) and was not significantly increased after training. An increase in skeletal muscle mass may have important functional and metabolic benefits for very elderly people.     

Efficacy of therapeutic ultrasound in the treatment of spasticity: a randomized controlled study

The purpose of this study was to investigate the effect of ultrasound (US) on the spasticity occurring in the ankle plantar flexor muscles after a cerebrovascular event. According to the modified Ashworth scale (MAS), the hemiplegic patients with stage 2-3 spasticity on the ankle plantar flexor muscles were enrolled in the study and divided into two groups. Passive stretching exercise was applied to both groups. Additionally, 10-minute US was applied to one of the groups, using the mode of continuous wave of 1.5w/cm^{2} to the calf muscles before stretching. In order to monitor the efficacy of the treatment in the patients, MAS, Hmax/Mmax ratio, the ankle range of motion (ROM), Functional Independence Measure and Brunnstrom Motor Recovery Stage were evaluated. While a significant recovery was monitored in the MAS and ankle ROM measurements after treatment in both groups, no change was obtained in the other parameters. No significant difference was detected in any of the measurements between the groups. In this study, US treatment applied in combination with the ankle plantar flexor muscles passive stretching exercise was determined to have no effect on the stretching treatment in minimizing the spasticity.     

Intermuscle differences in activation

The objective of this study was to investigate differences within individual subjects in the ability to activate the quadriceps, plantar flexors (PF), dorsiflexors (DF), and elbow flexors (EF) during isometric contractions. Twelve male subjects performed submaximal and maximal voluntary isometric contractions, and maximal tetanic contractions were also induced by electrical stimulation. The interpolated twitch technique was used to gauge the extent of muscle inactivation or inability to produce maximum force. Measurements included torque output, absolute and relative rate of force development (RFD), and percentage of muscle inactivation. The quadriceps exceeded all other muscle groups in voluntary and tetanic torque output, voluntary absolute RFD, and absolute and relative tetanic RFD. The quadriceps also exceeded the PF and DF in voluntary relative RFD and had greater muscle inactivation (15.5%) than the EF (5.0%), PF (5.0%), and DF (1.3%). Although the higher RFD may suggest a higher percentage of type II fibers in the quadriceps, their higher threshold of recruitment leads to greater difficulty in fully activating the quadriceps.     

Effects of a Nintendo Wii exercise program on spasticity and static standing balance in spastic cerebral palsy

ABSTRACT

Objective: This study sought to evaluate the effects of a Nintendo Wii Balance Board (NWBB) intervention on ankle spasticity and static standing balance in young people with spastic cerebral palsy (SCP). Methods: Ten children and adolescents (aged 72–204 months) with SCP participated in an exercise program with NWBB. The intervention lasted 6 weeks, 3 sessions per week, 25 minutes for each session. Ankle spasticity was assessed using the Modified Modified Ashworth Scale (MMAS), and static standing balance was quantified using posturographic measures (center-of-pressure [CoP] measures). Pre- and post-intervention measures were compared. Results: Significant decreases of spasticity in the ankle plantar flexor muscles (p < 0.01). There was also a significant reduction in the CoP sway area (p = 0.04), CoP mediolateral velocity (p =0.03), and CoP anterior–posterior velocity (p = 0.03). Conclusion: A 6-session NWBB program reduces the spasticity at the ankle plantar flexors and improves the static standing balance in young people with SCP.     

Effects of imagery motor training on torque production of ankle plantar flexor muscles

The aim of this study was to investigate in control subjects the effect of imagery training on the torque of plantar-flexor muscles of the ankle. Twenty-nine subjects were allocated to one of three groups that performed either imagery training, low-intensity strength training, or no training (only measurements). The low-intensity training served as an attention control group. Plantar-flexor torques were measured before, during, directly after, and 4 weeks after the training period. At the end of a 7-week training program, significant differences were observed between the maximal voluntary torque production of the imagery training group (136.3 +/- 21.8% of pretraining torque) vs. the low-intensity training group (112.9 +/- 29.0%; P < 0.02) and the control group (113.6 +/- 19.2%; P < 0.02). The results of this study show that imagery training of lower leg muscles significantly increased voluntary torque production of the ankle plantar-flexor muscles and that the force increase was not due to nonspecific motivational effects. Such muscle strengthening effects might be beneficial in rehabilitation for improving or maintaining muscle torque after immobilization.     

Impaired “natural reciprocal inhibition” in patients with spasticity due to incomplete spinal cord injury

Experiments were performed to compare the ability of normal subjects and patients with spinal spasticity to suppress antagonist H reflexes during isometric ankle contractions. Soleus H reflex suppression was examined during tonic pretibial muscle contractions in which the torque levels were constant and during dynamic pretibial muscle contractions in which the torque followed a predetermined ramp. As well, subjects were instructed to alternately contract ankle plantarflexors and dorsiflexors at various frequencies to examine patterns of EMG activity during rhythmically alternating isometric contractions in antagonist muscles. Patients with incomplete spinal cord injury demonstrated reduced ability to suppress soleus H reflexes during pretibial muscle contraction. At slow speeds of alternating contraction, spinal cord injured patients retained the ability to perform alternating isometric pretibial/soleus muscle contractions. The patients demonstrated abnormal coactivation in soleus muscle during faster alternating isometric ankle muscle contractions. Furthermore, the patients who demonstrated the greatest impairment in natural reciprocal inhibition, also displayed the largest amount of coactivation. In general, the results would suggest that impairment of natural reciprocal inhibition is correlated with an increase in the amount of antagonist muscle coactivation seen during alternating isometric muscle contractions.