Biomedical subjects

H S Milner-Brown

Publications and source records attributed to H S Milner-Brown.

At least 19 recordsLinked to original sources

PubMed1993

Muscle strengthening in a post-polio subject through a high-resistance weight-training program.

A 48-year-old woman started experiencing increased muscle weakness and fatigue at age 44, 40 years after the onset of acute poliomyelitis. The acute poliomyelitis resulted in severely weak lower limb muscles and as a result, she had used crutches for more than 40 years. Computer-aided force transducer systems were used to determine isometric muscle strength. Both quadriceps and left ankle dorsiflexors were severely weak and could not generate any measurable force. Isometric muscle strength of her right ankle dorsiflexors was 77 Newtons (N) (approximately 1/3 normal); isometric muscle strength of right elbow flexors (171N) and left elbow flexors (160N) were within normal range, although she complained of weakening based on her inability to climb two stairs at a time with crutches as she was used to. She underwent high-resistance weight training of her right ankle dorsiflexors and left elbow flexors for one year. Weight training was three times per week, five sets of ten repetitions per session; total duration of muscle contraction (excluding rest periods) was two and one half minutes per session, 30 minutes per month. Muscle strength (N) was remeasured after four, eight, and 12 months. Muscle strength of right ankle dorsiflexors increased by 61%, whereas that of the left elbow flexors increased by 32% after one year of weight training. She also expressed a subjective feeling of increased muscle strength. High-resistance, short duration muscle strengthening exercise programs should therefore be given a serious consideration in the rehabilitation management of moderately weak muscles of post-polio subjects.

Exercise Therapy↗

PubMed1990

Myotonic dystrophy: quantification of muscle weakness and myotonia and the effect of amitriptyline and exercise.

The purpose of this study was to quantify the degree of muscle weakness and myotonia in 12 patients with myotonic dystrophy (MD), and to quantitatively determine the effects of a four- to six-month therapeutic trial of amitriptyline. Patients had exercised with weights for one or more years. Some had shown initial improvement in muscle strength, but had reached a plateau; others had not improved when the study began. Muscle weakness was quantified by comparing the five-second maximum voluntary contraction (MVC) in newtons (N) per kg (body weight) of 12 patients and 20 healthy subjects. Knee extensor, elbow flexor, and first dorsal interosseous (FDI) muscles were compared. Myotonia was quantified by measuring relaxation times (RTs) at the end of the five-second MVC produced by FDI, as the time taken for the MVC to decrease by 50% and 75% (referred to as 1/2 and 3/4RT). The results were as follows: (1) the mean muscle strength of each of the three muscles of the patients was significantly (p less than .001) reduced compared with healthy subjects; and (2) 1/2 and 3/4RT means of the patients (vs healthy subjects) were significantly prolonged (p less than .01). Eight of the patients participated in a therapeutic trial of amitriptyline. Therapeutic effects were quantified by measuring muscle strength, 1/2 and 3/4RT, and percent change in evoked muscle action potential (MAP) from the FDI muscle after a ten-second MVC, to determine change in excitability. Mean muscle strength of FDI improved from .27 to .33N/kg, (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1989

Increased muscular fatigue in patients with neurogenic muscle weakness: quantification and pathophysiology.

The strength of maximum voluntary contraction (MVC) and muscular fatigue measured from ankle dorsiflexors and knee extensors of 15 patients with neurogenic muscle weakness was compared with those of 20 healthy subjects. Muscle weakness, defined as the failure to generate the expected force, was determined by two methods: (1) manual muscle testing and (2) measurement of MVC using a force transducer. Muscle strength was then quantified as the MVC in Newtons (N)/kg body weight. The percent decrease in both MVC (the Fatigue Index [FI]), and rectified-integrated electromyogram (RIEMG) at the end of 60sec of sustained MVC were computed. There were three main findings. (1) Muscle strength was significantly (p less than 0.001) reduced in both muscles of the patient group: in ankle dorsiflexors, means = 1.62 +/- 0.7N/kg vs 4.8 +/- 0.5N/kg; in knee extensors, means = 3.2 +/- 1.8N/kg vs 7.8 +/- 1.5N/kg. (2) Fatigue was significantly greater (p less than 0.01) in the patient group: for ankle dorsiflexors, means = 50 +/- 15% vs 34 +/- 13%; and for knee extensors, means = 62 +/- 17% vs 46 +/- 15%. There was a negative correlation between muscle strength and FI of only the knee extensors of the patients (r = -0.88, p less than 0.001). (3) The mean decline in RIEMG of the two muscles combined was also significantly greater (p less than 0.001) in the patient group (means = 48 +/- 16% vs 2 +/- 11%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1988

Muscle strengthening through electric stimulation combined with low-resistance weights in patients with neuromuscular disorders.

Ten patients with gradually progressive neuromuscular disorders underwent (1) unilateral electric stimulation of anterior tibialis muscles and (2) unilateral stimulation of quadriceps femoris muscles, in combination with voluntary knee extension against ankle weights. After electric stimulation two hours/day, five days/week for two to 14 months, the mean maximum force (muscle strength) of knee extension increased significantly (p less than 0.005), by 108% +/- 56%. The contralateral nonexercised knee extensors also showed some increase in muscle strength. Electric stimulation of ankle dorsiflexors was ineffective; the maximum force of ankle dorsiflexion increased by only 11% +/- 27% (p greater than 0.3). In general, severely weak muscles (less than 10% normal strength) did not improve with either stimulation program. Electric neuromuscular stimulation combined with low-resistance weights can significantly increase muscle strength in patients with neuromuscular disorders if disease progression is gradual and initial muscle strength is greater than 15% normal.

Adolescent↗

PubMed1988

Muscle strengthening through high-resistance weight training in patients with neuromuscular disorders.

The effects of weight training on muscle performance were quantified by measuring (1) maximum force (muscle strength), (2) force-time integral--area under force-time plot during 60 seconds of sustained maximum force (work done), and (3) fatigue index--percentage reduction in maximum force. Subjects included 16 patients with gradually progressive neuromuscular disorders. The muscle strength of these patients ranged from 2% to 75% normal before the program. For patients with markedly to moderately weak muscles, maximum force increased by 80% +/- 48%, force-time integral increased by 132% +/- 93%, and mean fatigue index was significantly reduced from 53% +/- 18% to 34% +/- 7.7% during the study period. Severely weak muscles (less than 10% normal strength) generally did not improve. High-resistance weight training can significantly increase muscle performance of patients with neuromuscular disease if disease progression is slow and initial muscle strength is greater than 15% normal.

Adult↗

PubMed1987

Quantitative correlation between plasma pyridostigmine levels and neuromuscular function in myasthenia gravis.

In 10 patients with myasthenia gravis, we studied the relationship between plasma pyridostigmine levels and five measures of neuromuscular function (NMF) following single oral doses of 60 to 120 mg. The NMF measures were percent decrement of the evoked muscle compound potential, maximum force, force-time integral, vital capacity, and outstretched-arm time. The combined mean improvement was most significant 2 hours after pyridostigmine ingestion and coincided with the peak plasma pyridostigmine levels in eight patients. In seven patients, there was a positive correlation between plasma pyridostigmine levels and the mean percent improvement.

Adult↗

PubMed1986

Muscle membrane excitation and impulse propagation velocity are reduced during muscle fatigue.

In order to determine whether or not impulse propagation was impaired during muscle fatigue, evoked muscle compound potentials (MCP) and twitches were recorded, both before and after fatigue, from the first dorsal interosseus (FDI), adductor pollicis (AP), and anterior tibialis (AT) muscles following supramaximal ulnar and peroneal nerve stimulation, respectively. The muscles were fatigued by maintaining maximum voluntary isometric, index finger abduction, thumb adduction, or ankle dorsiflexion for 1-5 minutes. FDI was most markedly altered, with reduced MCP amplitude (mean 32%) and increased MCP duration (mean 47%) after only 1 minute. After fatigue of longer duration (3-5 minutes), there were corresponding reductions in both the MCP amplitudes and the twitch tensions recorded from both the FDI and ankle dorsiflexors. We conclude that (1) a reduction in both the level of excitation and impulse propagation velocity of muscle membranes occurs during muscle fatigue, and (2) the magnitude of this reduced membrane function and its contribution to the mechanisms underlying fatigue depend both on the duration and degree of fatigue, as well as on the intrinsic properties of the particular muscle.

Cell Membrane Permeability↗

PubMed1986

Prednisone-induced worsening of neuromuscular function in myasthenia gravis.

In patients with myasthenia gravis who received single doses of prednisone orally (40 to 100 mg), we found acute inhibition of neuromuscular function as manifest by increased decremental responses to repetitive nerve stimulation, reduced twitch tension, and lowered maximum voluntary contraction strength. The time course of these changes correlated with plasma methylprednisolone levels, implying direct drug effects on neuromuscular function.

Action Potentials↗

PubMed1986

Quantifying human muscle strength, endurance and fatigue.

Physiologic methods have been developed to objectively quantify muscle strength, endurance, and fatigability. Isometric force and rectified/integrated electromyogram were simultaneously recorded during the three phases of a recording session: pre-fatigue, fatigue (1 min duration) and post-fatigue recovery (up to 10 min). Five parameters of muscle performance were computed: Maximum force (MF) exerted during isometric voluntary contraction (muscle strength); Force-time integral--area under force-time plot (endurance); Fatigue index (FI) (% reduction in MF); Neuromuscular efficiency (force/mV of EMG recruited), and Recovery time (RT). Normal values based on data from 20 normal subjects were determined for four muscles: index finger abductor, elbow flexors, knee extensors, and ankle dorsiflexors. Neuromuscular efficiency (NME) decreased significantly (20 to 70%) at the end of the fatigue phase; it generally increased to the pre-fatigue level in 2 to 10 min, during the recovery phase. The period needed to reach pre-fatigue level was referred to as RT. The elbow flexors had the highest mean FI (48%) and the longest RT (greater than 6 min); the ankle dorsiflexors had the lowest mean FI (34%) and the shortest RT (1.5 min). These methods have been used also to evaluate the effects of weight training in two patients with neuromuscular disorders.

Adolescent↗

PubMed1982

Time course of improved neuromuscular function following plasma exchange alone and plasma exchange with prednisone/azathioprine in myasthenia gravis.

Ten patients with myasthenia gravis (MG) were treated with weekly plasma exchange (PE) in combination with prednisone and azathioprine; 4 of the patients were treated with 3-6 PE alone, before instituting prednisone/azathioprine. Four clinico-physiological parameters of neuromuscular function as well as the anti-acetylcholine receptor antibody (anti-AChRAb) titers were measured 1-3 times per week. Evidence of improved neuromuscular function (NMF) was based on: (1) reduced % decrement of the maximum muscle compound potential following 2/s supramaximal nerve stimulation; (2) increased maximum force; (3) increased outstretched arm time, and (4) increased vital capacity. An early improvement in NMF occurred within the first 2 weeks (sometimes as early as 1-2 days), which was quantitatively comparable in patients treated with PE alone and PE plus prednisone/azathioprine. This early improvement reached a plateau, and was subsequently maintained for 3-4 weeks, followed by a later substantial improvement after 8-12 weeks of combined PE plus prednisone/azathioprine.

Adult↗

PubMed1980

"Turns" analysis in the physiological evaluation of neuromuscular disorders.

A previously described technique of automatic analysis of the electromyogram during isometric voluntary contraction has been used to investigate the biceps and triceps muscles of 18 patients with various neuromuscular disorders. Three modifications in the method were made: at each electrode position the data were computed at 10%, 20%, 30% and 50% of the maximum force; the duration of contraction was reduced from 5 s to 2 s; and the diagnosis was based on analysis of the plots of turns and mean amplitude per turn versus percentage of maximum force. These modifications resulted in increased sensitivity, the ability to evaluate motor unit abnormality at different force levels, and a quantitative assessment of the degree of involvement of antagonist muscles. The data indicate that motor units recruited at lower force levels may be involved preferentially in myopathies, and also that the involvement of pairs of flexor and extensor muscles in neuromuscular disorders is not always uniform.

Adult↗

PubMed1979

Electrical properties of motor units in Parkinsonism and a possible relationship with bradykinesia.

The electrical activity of single motor units was recorded from the first dorsal interosseous muscles of nine patients with Parkinson's disease. Six of these patients had a combination of the following abnormal motor unit properies: (1) a variable delay period of 20 seconds to 3 minutes between the initiation of voluntary effort and the recruitment of the first group of motor units; (2) after recruitment, some of the motor units stopped firing for durations of 10s, 40s, 75s... 3 min.; (3) some of the motor units fired at abnormally low frequencies of 2-3 per second. All these six patients had slowed finger movement, and five of the six were studied while off levodopa for two to seven days. One of these patients, reinvestigated after levodopa therapy had been restarted, demonstrated improvement in motor unit control. The three remaining patients who were studied while on uninterrupted levodopa therapy could make rapid finger movements, could recruit motor units without delay, and could fire recruited motor units continuously at normal frequencies of 6-14 per second. These results suggest that levodopa therapy is effective in Parkinson's disease at least partly because of its ability to correct abnormalities in the recruitment of motor units. Levodopa also corrects the abnormal motor unit firing pattern. The abnormal motor unit properties found in these patients could account for some aspects of bradykinesia.

Action Potentials↗

PubMed1979

Pathophysiological mechanisms in cerebral palsy.

To investigate some of the pathophysiological mechanisms in cerebral palsy, surface electromyograms (EMG) were recorded from pairs of flexor/extensor muscles during both voluntary and passive flexion/extension of upper and lower limbs of 20 patients. Elbow, knee, or ankle joint angles were measured simultaneously, as well as the force required to flex/extend the limbs passively at frequencies of 0.1--1.0 Hz. In addition, single motor units were recorded from the first dorsal interosseous muscles of six of the patients. Almost all patients showed resistance to passive movements (hypertonia). This hypertonia did not necessarily impair voluntary flexion/extension movements if alternating EMG activity was maintained in at least one of the pairs of flexor/extensor muscles involved in the movement. In six severly involved patients, there was a complete breakdown in the reciprocal relationship between reciprocally acting pairs of flexor/extensor motoneurones, which resulted in synchronous activation (co-contractions) of flexor/extensor muscles during both voluntary and passive movements. In these patients the hyperactive segmental reflex added to the disabling effects of co-contractions during voluntary movements. Single motor units recorded from patients with dystonic movements were recruited with variable delays (2--10 s) and usually discharged intermittently at high frequencies (60--120/s). This abnormla motor unit discharge pattern may relate to pathology of the basal ganglia.

Adolescent↗

PubMed1976

Multiple point electrical stimulation of ulnar and median nerves.

A computer-assisted method of isolating single motor units (MUs) by multiple point stimulation (MPS) of peripheral nerves is described. MPS was used to isolate 10-30 single MUs from thenar and hypothenar muscles of normal subjects and patients with entrapment neuropathies, with the original purpose of obtaining a more representative mean motor unit potential for estimating the number of MUs in a muscle. The two important results that evolved from MPS however, were: (1) in the absence of 'alternation' MUs were recruited in an orderly pattern from small to large, and from longer to shorter latencies by graded electrical stimulation in both normal and pathological cases, (2) a comparison of the sizes of MUs recruited by stimulation proximal and distal to the elbow suggested that axonal branching can occur in the forearm 200 mm or more proximal to the motor point in intrinsic hand muscles.

Adult↗

PubMed1976

Some electrical properties of motor units and their effects on the methods of estimating motor unit numbers.

Long train (50) electrical pulses were applied to the ulnar, median, and deep peroneal nerves. The probability of firing, or firing index, of the first motor units (MU) recorded by surface and needle electrodes in the first dorsal interosseous, thenar, and extensor digitorum brevis muscles varied from 0-100% as the stimulus was increased from a minimum threshold voltage (V) to V + delta V (delta V = 2-4 volts). The voltage interval, delta V (firing level range), of even the first few MU recruited greatly overlapped in normal subjects, but may overlap less in some neuromuscular disorders such as amyotrophic lateral sclerosis. The mean size of the single MU isolated by (1) isometric voluntary contraction method, (2) F recurrent discharge method, and (3) stimulation at multiple locations along the nerve, were more than twice as large as the mean size of the incremental steps evoked by graded electrical stimulation. These results suggest that methods of estimating the number of MU in a muscle should incorporate a correction for the fluctuations in excitability and overlap in firing levels of MU, and in addition should include larger MU in the estimation of the mean MU potential.

Axons↗

PubMed1976

New methods of estimating the number of motor units in a muscle.

Two electrophysiological methods have been described for estimating the number of motor units (MU) in a muscle. The methods are based on the original methods of Mc Comas and others, which involve dividing the maximum compound potential (MCP) of muscle evoked by supramaximal electrical stimulation of nerve by a mean motor unit potential (MMUP). The important modifications in the methods are the incorporation of the fluctuations in the response of MU to electrical excitation and a possible correction for the overlap in the firing levels of motor axons. The methods have been used in the estimation of the number of motor units in the first dorsal interosseous, thenar, hypothenar, and extensor digitorum brevis muscles of normal subjects and patients with various neuromuscular disorders. The results indicate that previous motor unit estimates were in general erroneously high.

Axons↗

PubMed1975

Synchronization of human motor units: possible roles of exercise and supraspinal reflexes.

Some normal human subjects show definite synchronization of the motor units in hand muscles (i.e., the impulses from two or more motor units coincide in time more frequently than expected for independent random processes). Subjects who show synchronization tend to use their hands to exert large, brief forces, either in their work (e.g., manual laborers) or recreational activities (e.g., weightlifters). In this study all seven weightlifters examined showed a significant degree of synchronization. Furthermore, after 6 weeks of using the first dorsal interosseus muscle of the hand to exert maximal, voluntary contractions, the level of synchronization increased substantially in four control subjects, and the average level became significantly different from zero. Weightlifters also showed greater late reflex responses than control subjects, but no significant difference in earlier spinal reflexes. Two late reflex waves are described which probably involve fast pathways to and from motor cortes. We suggest that supraspinal connections from motor cortex directly to spinal motoneurons may be enhanced as a result of training to the point where they produce a significant synchronization of motor units during steady, voluntary contractions.

Electric Stimulation↗

PubMed1975

The relation between the surface electromyogram and muscular force.

1. Motor units in the first dorsal interosseus muscle of normal human subjects were recorded by needle electrodes, together with the surface electromyogram (e.m.g.). The wave form contributed by each motor unit to the surface e.m.g. was determined by signal averaging. 2. The peak-to-peak amplitude of the wave form contributed to the surface e.m.g. by a motor unit increased approximately as the square root of the threshold force at which the unit was recruited. The peak-to-peak duration of the wave form was independent of the threshold force. 3. Large and small motor units are uniformly distributed throughout this muscle, and the muscle fibres making up a motor unit may be widely dispersed. 4. The rectified surface e.m.g. was computed as a function of force, based on the sample of motor units recorded. The largest contribution of motor unit recruitment occurs at low force levels, while the contribution of increased firing rate becomes more important at higher force levels. 5. Possible bases for the common experimental observation that the mean rectified surface e.m.g. varies linearly with the force generated by a muscle are discussed. E.m.g. potentials and contractile responses may both sum non-linearly at moderate to high force levels, but in such a way that the rectified surface e.m.g. is still approximately linearly related to the force produced by the muscle.

Action Potentials↗