Muscle Overuse Research Articles

Tl-201 Scintigraphy in Muscle Trauma

Muscle uptake of Tl-201 thallous chloride in the larger or more major groups, particularly the legs, chest, and upper limb areas, is not uncommonly observed in healthy persons. However, as illustrated in three patients, such uptake, when localized or asymmetric, may provide evidence of unrecognized traumatized muscle, resulting from more chronic or subacute muscle overuse than the acute muscle insult that produces the marked uptake of Tc-99m phosphates associated with frank rhabdomyolysis.

Age-related changes in muscle fiber regeneration in the human thyroarytenoid muscle.

Muscle fiber regeneration is essential to maintain normal muscle fiber populations and muscle mass by continuous replacement of fibers lost to acute muscle injury or overuse. However, the extent of ongoing muscle fiber regeneration in the laryngeal muscles is unknown. The present study provides statistically unbiased, quantitative estimates of the content of regenerating fibers in the human thyroarytenoid muscle over the adult lifespan. In the adult, only regenerating muscle fibers express the developmental myosin isoform. Therefore, regenerating fibers were identified using immunohistochemical techniques. The content of regenerating muscle fibers in the entire muscle volume was then estimated using stereological techniques. Through the use of a computer-automated sampling protocol, stereological data were collected from sets of isotropic uniform random cryostat sections. Overprojection error was minimized by using a confocal laser-scanning microscope to image thin optical sections for use as sample fields. Eight autopsy cases, subjects ranging in age from 19 to 81 years. The summed length of fibers expressing developmental myosin increased significantly (P=.02) with age when compared with the overall muscle fiber length. This finding indicates that muscle fibers maintain the capability for spontaneous regeneration, and that the proportion of regenerating fibers increases as the thyroarytenoid muscle ages. This increase is possibly a compensatory response to an age-related increase in muscle fiber injury or death.

Neuromuscular function of the latissimus dorsi muscle in goats after dynamic cardiomyoplasty.

Skeletal muscle deterioration is emerging as a limitation to long-term cardiac assist by dynamic cardiomyoplasty. Chronic electrical stimulation of in situ skeletal muscle showed that ischemia, decreased muscle preload, muscle overuse, and chronic electrical stimulation are factors for muscle deterioration. Transposition around the heart has been associated with signs of muscle denervation after chronic electrical stimulation. To evaluate latissimus dorsi muscle neuromuscular function after longterm dynamic cardiomyoplasty, we performed neuromuscular functional analysis and histology on the latissimus dorsi muscle and thoracodorsal nerve of six normal goats and six goats after 6 months of dynamic cardiomyoplasty. Electromyographic analysis showed positive sharp waves and fibrillation potentials in the latissimus dorsi of three goats from the dynamic cardiomyoplasty group. Conduction velocity of the thoracodorsal nerve of goats from the dynamic cardiomyoplasty group (58.32+/-9.80 m/s) was reduced compared to the goats from the control group (71.48+/-5.71 m/s, P = 0.02). Histologic changes in skeletal muscle were compatible with denervation. Loss of myelin sheaths, collapse of endoneurial connective tissue, and solitary foci of axonophagia and myelinophagia further documented severe injury to the thoracodorsal nerve in goats from the dynamic cardiomyoplasty group. The latissimus dorsi muscle wrap was denervated after long-term dynamic cardiomyoplasty. Traction on the neurovascular pedicle at each contraction of the transposed muscle may induce afferent axonal injury of the thoracodorsal nerve resulting in diminished muscular function.

Exercise-Induced Signs of Muscle Overuse in Children

Exercise-Induced Signs of Muscle Overuse in Children

Emotional sources of dysfunctional breathing

Inappropriate alterations in breathing such as breath-holding, mouth breathing, thoracic breathing and increased depth and rate are discussed in light of their role in physical survival situations. The drawbacks include disrupted oxygen delivery to the brain, respiratory alkalosis, overuse of accessory breathing muscles and weakening of the diaphragm. Pavlovian conditioning can initiate these breathing reactions, linking contextual cues or emotional aspects of a traumatic experience with associated breathing changes. The process of generalization further broadens the pool of emotional and situational triggers, and emotional states such as grief, suppressed anger, frustration and anxiety may maintain dysfunctional breathing patterns indefinitely.

Scapula winger's brace: A case series on the management of long thoracic nerve palsy

Objective: To evaluate the clinical utility of a new scapula winger's brace. Design: A case series. Setting: A tertiary military clinic serving a young population. Participants: Fourteen patients referred to the clinic for thoracic nerve palsy of a least 3 months' duration. Outcome Measures: Manual muscle tests with and without the brace and patients' compliance/satisfaction with brace as measured by personal interview during follow-up. Results: Muscle strength increased by one grade with brace application; patients who maintained compliance ( n = 6) recovered their brace-free shoulder flexion strength and/or had reduced pain at the last follow-up (1 to 7 months after brace). All patients reported a subjective feeling of increased shoulder flexion strength and decreased pain with brace application. Conclusion: The scapula winger's brace is a useful tool for physiatrists in the management of scapular winging secondary to long thoracic nerve palsy. Additional studies are needed to confirm the conclusion that the device's benefits derive from proprioceptive feedback that prevents muscle overuse or over-stretch and from its transfer of contralateral shoulder protraction force to the affected scapula.

Biomechanical abnormalities of post-polio patients and the implications for orthotic management

Muscle weakness resulting from the combined effects of acute and late motor neuron pathology is the basic cause of post-polio dysfunction. Through their normal sensation and moter control, post-polio patients minimize their disability by useful substitutions. Orthoses are needed only when these substitutions either are inadequate or result in muscle or joint overuse. The areas most commonly showing late disability are the lower extremities, shoulders and low-back. In the lower extremities, the major muscle groups are the hip extensors and abductors, the knee extensors (quadriceps), ankle plantar flexors and dorsi flexors. Each group has a specific function which relates to one of the basic tasks of walking, weight acceptance, single limb support and swing. To determine orthotic needs, polio gait deviations representing useful substitutions must be differentiated from symptomatic dysfunction. Weight acceptance utilizes the quadriceps, hip extensors and hip abductors to establish a stable limb and provide shock absorbing mechanics. Substitutions to preserve weight bearing stability include sacrifice of normal shock absorbing knee flexion for quadriceps weakness, backward or lateral trunk lean for hip extensor and abductor weakness. Knee pain, excessive hyperextension and flexion contractures are indications for orthotic assistance with a KAFO. Orthotic designs relate to the type of knee joint (off-set, free, locked) and completeness of the AFO component. Low-back pain from hip substitutions or over use of the hip muscles requires a walking aid. Single limb support is the period when the limb and body advance over the supporting foot. The key muscle group is the soleus-gastrocnemius complex. Swing involves lifting and advancing the unloaded limb. While all three joints flex simultaneously, the hip flexors and ankle dorsi flexors are the critical muscles. A drop foot from ankle dorsiflexor weakness is the common disability. Excessive hip flexion is the usual substitution. An orthosis which assists dorsiflexion without obstructing loading response plantar flexion is the most functional design.

Children Are Less Susceptible to Exercise-Induced Muscle Damage than Adults: A Preliminary Investigation

The aim of the present study was to investigate whether children showed similar signs of muscle overuse like adults after intense exercise. One child group (n = 10) and one adult group (n = 10) of males both had to perform five series of bench press exercises at an intensity of 80% of maximum strength until exhaustion. Maximum isometric strength, subjective perception of muscle pain, was measured before, immediately after, 48 hr, 72 hr, and 1 week after the exercise. Serum creatine kinase (CK) activity was measured before, 48 hr, 72 hr, and 1 week after the exercise. The adults showed all symptoms of muscle overuse: reduced strength, muscle pain, and elevated CK activities until 3 days after the exercise. In contrast, the children experienced only some light muscle pain, but neither showed reduced strength nor elevated CK activities. It is concluded that children’s muscles can easier withstand physical stress than adult muscles.

Findings in post-poliomyelitis syndrome. Weakness of muscles of the calf as a source of late pain and fatigue of muscles of the thigh after poliomyelitis.

The purpose of this study was to identify overuse of muscles and other alterations in the mechanics of gait in twenty-one patients who had muscular dysfunction as a late consequence of poliomyelitis. All of the patients had good or normal strength (grade 4 or 5) of the vastus lateralis and zero to fair strength (grade 0 to 3) of the calf, as determined by manual testing. Dynamic electromyography was used, while the patients were walking, to quantify the intensity and duration of contraction of the inferior part of the gluteus maximus, the long head of the biceps femoris, the vastus lateralis, and the soleus muscles. Patterns of contact of the foot with the floor, temporal-spatial parameters, and motion of the knee and ankle were recorded. The principal mechanisms of substitution for a weak calf muscle fell into three groups: overuse of the quadriceps (twelve patients) or a hip extensor (the inferior part of the gluteus maximus in eight patients and the long head of the biceps femoris in four), or both; equinus contracture (twelve patients); and avoidance of loading-response flexion of the knee (five patients). Most patients used more than one method of substitution. These observations support the theory that post-poliomyelitis syndrome results from long-term substitutions for muscular weakness that place increased demands on joints, ligaments, and muscles and that treatment--based on the early identification of overuse of muscles and ligamentous strain--should aim at modification of lifestyle and include use of a brace.

Activity recognition in long‐term electromyograms

Long-term electromyography with portable recorders allows the study of muscle activity in the natural environment to investigate whether muscle overuse or oral habits may contribute to initiate or perpetuate a myoarthropathy of the masticatory system. At present, little is known about the behaviour of masticatory muscles over long time periods. The aim of this preliminary study was to define parameters which allow the automatic recognition of different types of oral activities from the electromyogram form. A programme with functional and parafunctional activities was performed by four volunteers (total of 333 functional and 82 parafunctional recordings). Electromyograms of the masseter and temporal muscles were recorded by means of a self-developed portable intelligent solid state recorder. Signal mean level (mw) and dynamics (dw) within a sliding window were determined. Temporal muscle recordings allowed better discrimination between function and simulated parafunction. The average of mw for clenching was 51.4 +/- 3.5% and for tooth grinding 21.2 +/- 2% of the peak electromyogram value at maximum voluntary clench. At 0.96 s sliding window duration, clenching, tooth grinding and chewing signals had maximum separation, using dw/mw as parameters (average: 0.16 +/- 0.01 for clenching, 0.39 +/- 0.01 for teeth grinding and 0.88 +/- 0.01 for chewing).

Epidemiology of injuries associated with physical training among young men in the army

It is widely acknowledged that musculoskeletal injuries occur as a result of vigorous physical activity and exercise, but little quantitative documentation exists on the incidence of or risk factors for these injuries. This study was conducted to assess the incidence, types, and risk factors for training-related injuries among young men undergoing Army infantry basic training. Prior to training we evaluated 303 men (median age 19 yr), utilizing questionnaires and measurements of physical fitness. Subjects were followed over 12 wk of training. Physical training was documented on a daily basis, and injuries were ascertained by review of medical records for every trainee. We performed univariate and multivariate analyses of the data. Cumulative incidence of subjects with one or more lower extremity training-related injury was 37% (80% of all injuries). The most common injuries were muscle strains, sprains, and overuse knee conditions. A number of risk factors were identified, including: older age, smoking, previous injury (sprained ankles), low levels of previous occupational and physical activity, low frequency of running before entry into the Army, flexibility (both high and low), low physical fitness on entry, and unit training (high running mileage).

Changes in masseter inhibitory reflex responses in patients with diffuse sclerosing osteomyelitis of the mandible

Masticatory inhibitory mechanisms were studied in 10 patients treated for diffuse sclerosing osteomyelitis of the mandible. Their masseter inhibitory reflex responses were provoked electrically by mental nerve stimulation during maximal clenching of the teeth. The masseter inhibitory reflex was normal in two patients and significantly abnormal in eight patients. The two patients with a normal masseter inhibitory reflex were free of complaints, whereas, of the eight patients with an abnormal masseter inhibitory reflex, two were free of complaints and six had moderate to severe symptoms. In three patients, spasms and involuntary bursts of electromyographic activity were found. The abnormal masseter inhibitory reflex consisted of a loss of early and late components in four patients or a loss of the late component with a normal early one in four patients. These findings seem to support the hypothesis that diffuse sclerosing osteomyelitis of the mandible is a chronic tendoperiostitis caused by muscle overuse. It is suggested that this overuse is caused by central hyperexcitability of trigeminal motoneurons.

Exertional muscle injuries

Exertion-related muscle pain is frequent in athletes and patients alike; however, its severity and significance may be difficult to assess clinically. MRI can be used to evaluate myalgia, strains, delayed-onset muscle soreness, chronic muscle overuse syndromes, muscle contracture, and sequellae of muscle injuries such as myositis ossificans and compartment syndrome. MRI documents the distribution of affected muscles, the presence of focal hematoma, fascial herniation, and subsequent healing, fibrosis, or fatty infiltration. MRI is useful in evaluating acute and delayed exertional muscle injuries.

A RAT MODEL OF THE POST-POLIO MOTOR UNIT

We examined the long-term effects of muscle usage on a rat model of the post-polio motor unit. Isometric tensions, type I and type II muscle fiber areas, the incidence of collateral sprouting, and motor endplate morphology were examined following 1, 3, 6, and 9 months of partial denervation in rat plantaris muscle. Full morphologic and functional stability of the expanded motor units occurred at 6 months post-partial denervation. Fiber hypertrophy was observed, possibly the result of compensatory work hypertrophy due to muscle overuse. Following 9 months of partial denervation and muscle overuse, the twitch and tetanic tensions and type I and type II muscle fiber areas were significantly reduced as compared to sham controls; angulated myofibers and group atrophy also were seen. The percent collateral sprouting, the number of terminal branches per endplate, and the endplate area were all increased, possibly a compensatory response to a decreased synthesis of neurotrophic factor(s) and/or transmitter-related components. These aging-like changes seem to occur earlier in chronically stressed, overenlarged, and overworked motor units.

Exertional muscle injuries

Exertion-related muscle pain is frequent in athletes and patients alike; however, its severity and significance may be difficult to assess clinically. MRI can be used to evaluate myalgia, strains, delayed-onset muscle soreness, chronic muscle overuse syndromes, muscle contracture, and sequellae of muscle injuries such as myositis ossificans and compartment syndrome. MRI documents the distribution of affected muscles, the presence of focal hematoma, fascial herniation, and subsequent healing, fibrosis, or fatty infiltration. MRI is useful in evaluating acute and delayed exertional muscle injuries.

A COMPARISON OF CONTRACTILE PROPERTIES IN THE PREFERRED AND NONPREFERRED LEG IN A MIXED SAMPLE OF DYSTROPHIC PATIENTS

No study of how muscle contractile function is related to limb preference in human muscular dystrophy is presently available. The purpose of this study was to determine if the ankle plantarflexor (PF) and dorsiflexor (DF) muscle groups of the preferred leg are more or less affected than the nonpreferred one in a mixed sample of myotonic and limb-girdle patients. Measurements of lower limb preference were made as well as of PF and DF evoked and voluntary contractile responses. Isometric contractile properties and peak values for torque production during maximum isometric twitch and voluntary contractions were measured. No significant difference was found in terms of contractile properties between the preferred and nonpreferred leg for both DF and PF muscle groups, except for the large PF twitch torque observed in the nonpreferred side (P less than 0.05). These results, however, reveal a clear tendency for both muscle groups on the preferred side to be weaker than those on the nonpreferred side. This last finding, in conjunction with the equally if not presumably stronger PF/DF muscles on the preferred leg of healthy adult subjects, would suggest that the equivalent bilateral muscle force observed in the present study may be interpreted as giving support to the hypothesis that overwork or overuse of dystrophic muscles may be harmful in weakening the musculature.

Keyboard operating posture and actuation force: Implications for muscle over-use

A substantial proportion of the problems in keyboard operator ‘Over-use Syndromes’ occur in the wrist and finger extensor muscle group. Biomechanical analysis shows these muscles to be subject to substantial sustained static (isometric) muscle contraction during the work task. This study measured the maximum relaxed finger press forces for 60 subjects in three arm support methods, in order to predict what the minimum keypress force should be to permit finger support sufficient to facilitate relaxation of finger extensor muscles. It was postulated that the minimum key activation force should accommodate the 95 percentile predicted population relaxed finger weights. The predicted force of 0.8 newton is within limits previously proposed for performance criteria, and which have been found practical commercially.

Creatine kinase and fibrillation potentials in patients with late sequelae of polio

The incidence of an elevated creatine kinase (CK) in a group of polio patients with delayed weakness (15/29) did not differ from polio patients without delayed weakness (9/31) or others with amyotrophic lateral sclerosis (ALS; 10/21). Mean CK in polio patients without delayed weakness (151 IU/L) was lower than the CK in those with delayed weakness (270 IU/L) or ALS (224 IU/L) (P less than 0.05). An elevated CK in polio patients with delayed weakness did not correlate with new or residual weakness. These findings suggest that muscle overuse is either not important or inadequately measured by CK. Widely distributed fibrillations were associated with an elevated CK for all polio patients combined (P less than 0.01). Fibrillations occurred in more muscles of polio patients with delayed weakness (P less than 0.01) and implies that late denervation may play a role in the development of new weakness in some polio patients.

Symptoms and clinical impressions of patients seen in a postpolio clinic.

A retrospective study was performed to identify symptoms and clinical findings in postpolio patients seen in a postpolio clinic. Charts of 79 consecutive patients (28 men and 51 women) with histories and examinations compatible with the diagnosis of poliomyelitis were reviewed. The average current age of our patients was 47.3 +/- 10.4 years; the average age at onset of acute polio was 10.4 +/- 9.4 years; and the average number of years since function was first noticed to decline was 7.8 +/- 6.4 years. The most common symptoms acknowledged were progressive weakness (87%), muscle pain (86%), fatigue (86%), decreased activity level (78%), joint pain (77%), and back pain (70%). The clinical impression in most of these patients was arthritis/arthralgia (71% of the patients) or muscle overuse or myofascial pain (71%). Eleven (14%) had evidence of nerve compression, although 39% complained of sensory loss. Five patients had respiratory problems that required evaluation. Recommendations proved helpful for 78% of those seen at follow-up. These recommendations included pacing, energy conservation (planning, use of wheelchair or motorized scooter), gentle stretching or strengthening exercise, use of orthotic devices, weight loss or nutritional counseling, gentle aerobic exercise, use of a cane, and use of adaptive equipment.

Serum Creatine Kinase in the Post-Polio Population

Elevated creatine kinase (CK) levels may be noted in neuromuscular patients as a result of muscle damage and necrosis. We measured the serum CK levels of 62 post-polio patients with chronic neurologic disease (Neuro) and 13 post-polio patients with no evidence of neurologic compromise (Control). Patient groups were comparable for age, gender and years since onset of poliomyelitis. The Neuro group had substantially increased CK levels compared with the Control group, 211 +/- 19.0 IU v 114 +/- 26.2 IU (mean +/- 1 SE; P less than 0.05). Of the Neuro group, 40% had abnormally elevated CK values, compared with 8% of the Control group. Within the Neuro group, there was a robust correlation between elevated CK values and self-reports of strenuous work and level of community ambulation (P less than 0.05). These findings support the hypothesis that chronic muscle overuse may be a contributing factor to the advanced senescence reported by post-polio patients with neuromuscular compromise.