Motor unit number index examination in dominant and non-dominant hand muscles

This study investigated the effect of handedness on motor unit number index (MUNIX). Maximal hand strength, compound muscle action potential (CMAP) and voluntary surface electromyography (EMG) signals were measured bilaterally for the first dorsal interosseous (FDI) and thenar muscles in 24 right-handed and 2 left-handed healthy subjects. Mean (±standard error) grip and pinch forces in the dominant hand were 43.99 ± 2.36 kg and 9.36 ± 0.52 kg respectively, significantly larger than those in the non-dominant hand (grip: 41.37 ± 2.29 kg, p < .001; pinch: 8.79 ± 0.46 kg, p < .01). Examination of myoelectric parameters did not show a significant difference among the CMAP area, the MUNIX or motor unit size index (MUSIX) between the two sides in the FDI and thenar muscles. In addition, there was a lack of correlation between the strength and myoelectric parameters in regression analysis. However, strong correlations were observed between dominant and non-dominant hand muscles in both strength and myoelectric measures. Our results indicate that the population of motor units or spinal motor neurons as estimated from MUNIX may not be associated with handedness. Such findings help understand and interpret the MUNIX during its application for clinical or laboratory investigations.     

Mechanomyographic and electromyographic responses to eccentric and concentric isokinetic muscle actions of the biceps brachii

The purpose of the present investigation was to examine the effects of forearm angular velocity on the mechanomyographic (MMG) and electromyographic (EMG) responses to eccentric and concentric isokinetic muscle actions. Ten adult male volunteers (mean ± SD age = 23 ± 2 years) performed maximal eccentric and concentric muscle actions of the forearm flexors at 30°, 90°, and 150° s⁻¹. There was no significant (P > 0.05) velocity-related change in peak torque (PT) for the eccentric muscle actions, but there was a significant (P < 0.05) decrease in PT for the concentric muscle actions. For the eccentric and concentric muscle actions, there was a significant (P < 0.05) velocity-related increase in MMG amplitude. There was no significant (P < 0.05) change in EMG amplitude across velocity for the eccentric or concentric muscle actions. The results indicated velocity-related dissociations among the PT, MMG, and EMG responses to maximal eccentric and concentric isokinetic muscle actions. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1438–1444, 1998     

Early Surgical Treatment of Pronator Teres Syndrome

We report a rare case of pronator teres syndrome in a young female patient. She reported that her right hand grip had weakened and development of tingling sensation in the first-third fingers two months previous. Thenar muscle atrophy was prominent, and hypoesthesia was also examined on median nerve territory. The pronation test and Tinel sign on the proximal forearm were positive. Severe pinch grip power weakness and production of a weak "OK" sign were also noted. Routine electromyography and nerve conduction velocity showed incomplete median neuropathy above the elbow level with severe axonal loss. Surgical treatment was performed because spontaneous recovery was not seen one month later.     

Contrasting echogenicity in flexor digitorum profundus–flexor carpi ulnaris: A diagnostic ultrasound pattern in sporadic inclusion body myositis

Introduction: In this study we aimed to clarify whether muscle ultrasound (US) of the forearm can be used to differentiate between patients with sporadic inclusion body myositis (s‐IBM) and those with s‐IBM–mimicking diseases. Methods: We compared the echo intensity (EI) of the flexor digitorum profundus (FDP) muscle and the flexor carpi ulnaris (FCU) muscles in patients with s‐IBM (n = 6), polymyositis/dermatomyositis (PM/DM; n = 6), and amyotrophic lateral sclerosis (ALS; n = 6). Results: We identified EI abnormalities in 100% of patients with s‐IBM, 33% of those with PM/DM, and 33% of those with ALS. An “FDP–FCU echogenicity contrast,” a US pattern involving a higher EI in the FDP than in the FCU, was observed in all patients with s‐IBM, but in none of those with PM/DM or ALS. Conclusions: FDP–FCU echogenicity contrast in muscle US is a sensitive diagnostic indicator of s‐IBM. Muscle Nerve 49 : 745–748, 2014     

Grip and Knee extension muscle strength reflect a common construct among adults

Introduction: Both grip and knee extension strength are often used to characterize overall limb muscle strength. We sought to determine if the measures actually reflect a common construct. Methods: The isometric grip and knee extension strength of 164 healthy men and women (range, 18–85 years) were measured bilaterally using standard procedures. Pearson correlations (r), Cronbach alpha, principal components analysis, and multiple regression/correlation were used to investigate the dimensionality of the measures. Results: Left and right grip forces and knee extension torques were highly correlated, internally consistent, and loaded on a single component. Gender and age explained the variance in both measures, but height added to the explanation of grip strength, whereas weight added to the explanation of knee extension strength. Conclusions: Among healthy adults, grip and knee extension strength reflect a common underlying construct. The measures, however, are affected differently by height and weight. Muscle Nerve 46: 555–558, 2012     

Assessing the accuracy of neuromuscular ultrasound for inclusion body myositis

Introduction: Inclusion body myositis (IBM) can have clinical and electrodiagnostic features similar to other neuromuscular diseases, making it a diagnostic challenge. This prospective study was designed to determine the accuracy of forearm ultrasound for IBM. Methods: Sixty adults were recruited (15 with IBM, 15 with amyotrophic lateral sclerosis [ALS], 15 with other myopathies, and 15 healthy controls), and each underwent ultrasound of the bilateral forearms (imaging the flexor digitorum profundus and flexor carpi ulnaris muscles). Three clinicians with varying ultrasound expertise assigned a diagnosis of IBM, ALS, other myopathy, or control, based on images alone. Results: Intrarater reliability was moderately strong. Interrater reliability varied based on clinician experience. Sensitivity was 73.33% and 66.67% for the expert raters. Specificity was strong for all 3 clinicians (93.33%, 84.44%, and 91.11%). Discussion: Neuromuscular ultrasound of the forearm is reliable and accurate for the diagnosis of IBM, although sensitivity was higher among experienced clinicians. Muscle Nerve 59:478–481, 2019     

Modulation of motor cortex excitability induced by pinch grip repetition

Summary. We examined the influence of right handed pinch grips and the effect of a motor training on motor cortex excitability of the left first dorsal interosseus muscle (FDI). TMS single and paired pulses were applied over the right human motor cortex (M1) during and after right handed pinch grips with low force. In another experiment, these stimulations were performed before and after a 30-minute right handed pinch grip training. Results: MEP amplitudes in left FDI were reduced when TMS single pulses were applied during the pinch grip. Simultaneously, motor cortex excitability was enhanced but returned to baseline after the training period. Conclusion: Phasic pinch grips of the right hand exert an inhibiting effect on the corticospinal excitability of the ipsilateral motor cortex and lead to an increase of intracortical excitability. These changes are distinct and independent of each other. Motor training has an interhemispheric effect on intracortical excitability.     

Skeletal muscle function in primary fibromyalgia. Effect of regional sympathetic blockade with guanethidine

Muscle fatigue is the most disabling symptom in primary fibromyalgia (PF), which in addition is characterized by generalised pain and muscle stiffness. In order to assess whether the fatigue is of central and/or peripheral origin, skeletal muscle function was studied by measuring maximum voluntary hand grip strength, and by measuring various contraction characteristics in the adductor pollicis muscle after electrical stimulation of the ulnar nerve. The PF-patients were also studied after a regional sympathetic blockade of the forearm with guanethidine. A lower hand grip strength was found in the PF-patients compared to the controls, before as well as during the sympathetic blockade. The developed force, measured during electrical stimulation, did not differ between patients and controls. A lower muscle relaxation rate was found in the PF-patients. The relaxation rate increased in the PF-patients during the sympathetic blockade. The results indicate both a central and a peripheral cause of muscle dysfunction. Activity in the muscle sympathetic system may be one link in the chain of events that leads to muscular symptoms in PF.     

Safety and efficacy of strength training in patients with sporadic inclusion body myositis

We studied the effects of a 12-week progressive resistance strength training program in weakened muscles of 5 patients with sporadic inclusion body myositis (IBM). Strength was evaluated with Medical Research Council (MRC) scale ratings and quantitative isometric and dynamic tests. Changes in serum creatine kinase (CK), lymphocyte subpopulations, muscle size (determined by magnetic resonance imaging), and histology in repeated muscle biopsies were examined before and after training. After 12 weeks, the values of repetition maximum improved in the least weakened muscles, 25–120% from baseline. This dynamic effect was not captured by MRC or isometric muscle strength measurements. Serum CK, B cells, T-cell subsets, and NK cells remained unchanged. Repeat muscle biopsies did not reveal changes in the number and degree of degenerating fibers or inflammation. The size of the trained muscles did not change. We conclude that a supervised progressive resistance training program in IBM patients can lead to gains in dynamic strength of the least weak muscles without causing muscle fatigue and muscle injury or serological, histological, and immunological abnormalities. Even though the functional significance of these gains is unclear, this treatment modality is a safe and perhaps overlooked means of rehabilitation of IBM patients. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1242–1248, 1997     

Grip strength is a representative measure of muscle weakness in the upper extremity after stroke

Background: Muscle weakness is the most common impairment in the upper extremity after stroke, leading to a reduced ability to use the arm and the hand in daily activities. Grip strength is easier to measure than precise, but more time-consuming, isokinetic and isometric arm muscle strength measurements. It would therefore be advantageous in a clinical setting if grip strength could be used as a proxy for muscle strength in the entire upper extremity.

Objective: To investigate the association between grip strength and isometric and isokinetic arm muscle strength in persons with chronic stroke.

Methods: Forty-five persons with mild-to-moderate paresis in the upper extremity, at least 6 months post-stroke participated. Isometric grip strength was measured with a computerized grip dynamometer and arm strength (isometric shoulder abduction and elbow flexion as well as isokinetic elbow extension and flexion) with an isokinetic dynamometer. Pearson’s correlation coefficient was used to determine the association between the muscle strength measurements.

Results: There were significant correlations (p < .0001) between grip strength and all arm strength measurements in both the more affected (r = 0.77–0.82) and the less affected upper extremity (r = 0.65–0.82).

Conclusion: This cross-sectional study showed that grip strength is strongly associated with muscle strength in the arm in persons in the chronic phase after stroke. As grip strength is easy to measure and less time-consuming than arm muscle strength measurements, this implies that grip strength can be a representative measure of muscle weakness of the entire upper extremity in the chronic phase after stroke.     

Negative effect of clenbuterol on physical capacities and neuromuscular control of muscle atrophy in adult rats

Introduction: Clenbuterol has been used to alleviate chronic obstructive pulmonary disease and elicit an anabolic response in muscles. The aim of this study was to determine the influence of muscle mass variation on physical capacities in rats. Methods: The left hindlimbs of Wistar rats were immobilized for 20 days in plantarflexion with a splint and then remobilized for 16 days. The effect of a non‐myotoxic dose of clenbuterol during the immobilization period was evaluated. Physical capacities were coordination, free locomotion, grip strength, and bilateral deficit. Results: Immobilization induced a loss of muscle mass, coordination, and strength without any effect on free locomotion. The positive anabolic effect of clenbuterol did not prevent a loss of physical capacities resulting from immobilization. Conclusions: Muscle mass correlated strongly with coordination and isometric strength in untreated rats. Anabolic effect, fiber phenotype modification, and perturbation in neuromuscular communication with clenbuterol improved muscle mass, but it altered physical capacities. Muscle Nerve 52 : 1078–1087, 2015     

Inclusion body myositis: clinical, morphological, physiological and laboratory findings in 18 cases

Eighteen consecutive patients with inclusion body myositis (IBM) were studied. The mean age of onset of symptoms was 60 years. A typical clinical pattern with insidious onset of muscle weakness in knee extensors and finger flexors combined with dysphagia was observed. Serial measurements of the maximal voluntary muscle strength revealed a mean loss of muscle strength of 1.4% per month. Two of the cases had common variable immunodeficiency, and three cases had reduced levels of the IgG3 subclass. Treatment with prednisone resulted in a temporary improvement of muscle function in three patients. No positive effect of azathioprine or cyclosporine A could be documented. The results show that IBM may be associated with immunodeficiency, and that prednisone treatment may temporarily improve the clinical signs. The results from our studies on the progression of the muscle weakness may provide basis for future studies on treatment of IBM.     

Inflammatory myopathy with cytochrome oxidase negative muscle fibers: Methotrexate treatment

Inflammatory myopathy with cytochrome oxidase negative muscle fibers (IM/COX−) is characterized by slowly progressive weakness, most prominent in the quadriceps, muscle fibers with reduced COX staining and mitochondrial DNA mutations, and a poor response to corticosteroid treatment. We reviewed records of quantitative measurements of muscle strength in 7 IM/COX− patients to evaluate the outcomes after treatment with oral, once weekly, methotrexate for an average of 15 months. We compared the results to 6 patients with IM/COX− who received no long-term immunosuppression, and to 4 with inclusion body myositis (IBM) who received methotrexate during the same period. Methotrexate treatment of IM/COX− was followed by improved muscle strength in 5 of 7 patients, averaging 17 ± 5%. In contrast, there was no improvement in the strength of 6 untreated IM/COX− patients (−6 ± 4%; P = 0.003), or 4 methotrexate-treated IBM patients (1 ± 2%; P = 0.03). We conclude that, despite clinical similarities to inclusion body myositis, which is usually refractory to immunosuppressive therapy, strength in IM/COX− appears to improve with methotrexate treatment. Biopsy studies of inflammatory myopathies with evaluation of muscle for mitochondrial changes and vacuoles can help to direct the choice of appropriate immunomodulating treatments. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1724–1728, 1998     

Use of human intravenous immunoglobulin in lower motor neuron syndromes

OBJECTIVE: To determine whether patients with the clinical phenotype of multifocal motor neuropathy but without the electrophysiological criteria for conduction block would respond to intravenous immunoglobulin (IVIg). METHODS: Ten patients were selected with a slowly progressive, asymmetric, lower motor neuron disorder, and were treated prospectively with IVIg at a dose of 2g/kg over 5 days. All subjects had neurophysiological testing to look for evidence of conduction block before treatment. Muscle strength was assessed by MRC grades and hand held myometry, measuring pinch and grip strength. A 20% increase in both pinch and grip myometry was considered a positive response. RESULTS: In no patient was conduction block detected. Four of the 10 patients showed a positive response to IVIg, with the best response occurring in two patients who presented with weakness but without severe muscle wasting. Three of the four responders have continued to receive IVIg for a mean period of 17 months (range 15-24 months), with continued effect. The response to IVIg was not related to the presence of anti-GM1 antiganglioside antibodies, but responders had a selective pattern of muscle weakness and normal (>90% predicted) vital capacity. CONCLUSION: The findings suggest that a course of IVIg should be considered in patients with the clinical phenotype of multifocal motor neuropathy but without neurophysiological evidence of conduction block.     

Exercise-induced muscle growth is muscle-specific and age-dependent

Introduction: Sarcopenia, and the importance of satellite cells (SCs) in muscle growth led us to examine the effects of exercise and age on SC activation and gene expression. Methods: Eight‐ and 18‐month‐old mice were either sedentary or underwent 3 weeks of exercise (N = 24). Body mass, distance traveled, and grip strength were recorded at weekly intervals. The extensor digitorum longus (EDL), tibialis anterior (TA), gastrocnemius (GAST), and quadriceps (QUAD) muscles were analyzed along with muscle fiber area, SC activation, neuronal nitric oxide synthase (NOS‐I), MyoD, and myostatin protein content. Results: Older mice demonstrated decreased body mass, grip strength, and fiber area, but these changes were not affected by exercise. The QUAD muscle from young mice demonstrated an exercise‐induced increase in SC activation and NOS‐I and downregulation of myostatin. Conclusions: Exercise‐induced activation of SCs and regulation of gene expression are muscle‐specific and age‐dependent. Perturbed sensitivity to exercise in older mice provides insight into sarcopenia and potential treatments. Muscle Nerve, 2011     

Magnetic resonance imaging pattern recognition in sporadic inclusion‐body myositis

Introduction: In sporadic inclusion‐body myositis (IBM), additional tools are needed to confirm the diagnosis, particularly in clinically atypical or pathologically unproven patients. The aims of this study were to define the pattern of muscle MRI in IBM and to assess its accuracy in differentiating IBM from other myopathies that overlap with it clinically or pathologically. Methods: Blind assessment was done on the scans of 17 definite IBM, 2 possible IBM, and 118 patients with other myopathies. Results: The diagnostic accuracy to detect definite IBM was 95% for the typical pattern (with 100% specificity) and 97% for both typical and consistent patterns (with 97% specificity). Conclusions: Muscle MRI is an accurate tool for diagnostic work‐up of suspected IBM patients and may be particularly helpful in patients with early disease or who lack the classical IBM pathology. Muscle Nerve 52 : 956–962, 2015     

Identification of dynapenia in older adults through the use of grip strength t‐scores

Introduction: The aim of this study was to generate reference values and t‐scores (1.0–2.5 standard deviations below average) for grip strength for healthy young adults and to examine the utility of t‐scores from this group for the identification of dynapenia in older adults. Methods: Our investigation was a population‐based, general community secondary analysis of cross‐sectional grip strength data utilizing the NIH Toolbox Assessment norming sample. Participants consisted of community‐dwelling adults, with age ranges of 20–40 years (n = 558) and 60–85 years (n = 390). The main outcome measure was grip strength using a Jamar plus dynamometer. Results: Maximum grip strengths were consistent over the 20–40‐year age group [men 108.0 (SD 22.6) pounds, women 65.8 (SD 14.6) pounds]. Comparison of older group grip strengths to those of the younger reference group revealed (depending on age strata) that 46.2–87.1% of older men and 50.0–82.4% of older women could be designated as dynapenic on the basis of t‐scores. Conclusions: The use of reference value t‐scores from younger adults is a promising method for determining dynapenia in older adults. Muscle Nerve 51 : 102–105, 2015     

Skeletal muscle changes following stroke: a systematic review and comparison to healthy individuals

Background: Despite extensive study of the impact of stroke on muscle and functional performance, questions remain regarding the extent to which changes are due to the neurological injury vs. age-related loss of morphology and force production.

Objectives: To synthesize available evidence describing post-stroke changes in lower extremity muscle size and strength compared to healthy adults.

Methods: Scientific literature was searched up to April 2016 to identify studies that included lower extremity muscle size and strength measures in individuals with chronic stroke. Lower extremity muscle size and strength data from healthy controls were sought for comparison. Relative differences were calculated between paretic, nonparetic, and control limbs.

Results: Fifteen studies with 375 participants (61% male; age = 62 ± 5 years; time since stroke = 60 ± 42 months) were included. The paretic limb exhibited deficits of ~13% in thigh muscle size, ~5% in lower leg muscle size, and ~8% in lean leg mass compared to the nonparetic limb. Paretic plantarflexor and knee extensor strength were 52 and 36% lower, respectively, compared to the nonparetic limb. When compared to age-matched control data, both paretic and nonparetic limbs showed deficits in muscle size and strength.

Conclusions: Age-related differences support the impact of stroke-related sarcopenia as a contributor to hemiparetic muscle dysfunction. Understanding these muscular changes is necessary for designing appropriate exercise interventions aimed at restoring muscle function.     

Doxycycline ameliorates the dystrophic phenotype of skeletal and cardiac muscles in mdx mice

Introduction: We examined whether doxycycline, an antibiotic member of the tetracycline family, improves the histopathology and muscle function in mdx mice, the experimental model of DMD. Methods: Doxycycline was administered for 36 days (starting on postnatal day 0) and for 9 months (starting at 8 months of age) in drinking water. Histopathological, biochemical (creatine kinase), and functional (forelimb muscle grip strength) parameters were evaluated in limb, diaphragm, and cardiac muscle. Results: Doxycycline significantly minimized the dystrophic phenotype of skeletal and cardiac muscles and improved forelimb muscle strength. The drug protected muscle fibers against myonecrosis and reduced inflammation. Furthermore, it slowed the progression of myocardial fibrosis. Conclusions: This study provides evidence that doxycycline may be a potential therapeutic agent for DMD. Muscle Nerve 46: 400-406, 2012.