1. The effects of repeated excitation on the compound action potential, or M wave, of mammalian muscle fibres have been investigated in the human biceps brachii. 2. During continuous indirect stimulation at 10 and 20 Hz the mean voltage-time area of the M wave doubled within the first minute, while the mean peak-to-peak amplitude increased by approximately half. The enlargement of the M wave was sustained during stimulation at 10 Hz but not at 20 Hz. Stimulation at 3 Hz caused a small increase which was significant for M wave amplitude only. 3. When the 20 Hz stimulation was performed under ischaemic conditions, the M wave first enlarged and then gradually declined. After 20 Hz stimulation was discontinued, the M wave increased in size; in the ischaemic experiments the release of the cuff produced a further, rapid augmentation. In both the ischaemic and non-ischaemic experiments, the amplitudes and areas of the M waves during the recovery period became significantly larger than the resting values (range, 15-60% at the endplate zone). 4. The mean muscle fibre impulse conduction velocity decreased to less than half the resting value during 20 Hz stimulation, with or without ischaemia, and then increased above the resting value during recovery. 5. On the basis of previous experiments in animals, the augmentation of the M wave was attributed to enhanced electrogenic Na-K+ pumping, and the biceps brachii appeared to be an excellent preparation for studying the time course of this enhancement.

For this population, those with low PAL may also have a high oxygen cost of walking. These individuals' PAL was not related to their peak VO2. Further research is required to determine whether interventions that decrease the oxygen cost of walking also affect PAL and whether changes in PAL affect the oxygen cost of walking.

Elderly persons usually exhibit some degree of muscle atrophy, together with a reduction in voluntary strength, but there is still argument concerning the nature of the cellular events involved. This issue was reexamined by estimating the numbers and relative sizes of motor units in three limb muscles, using a fully automated system (Galea et al., 1993). In 79 healthy volunteers aged 20-98 years, estimations of motor unit numbers were performed on the thenar, biceps brachii, and extensor digitorum brevis muscles. Motor unit populations were noted to decrease significantly with age in the distal muscles but appeared to remain constant in the biceps. The excitable muscle fiber mass, as reflected in the peak-to-peak amplitude and area of the maximum M-wave, was diminished in all three muscles. Although the area of the average motor unit action potential was not significantly different between groups, the ratio of this potential to the M-wave area increased with increasing age. The results suggest that muscle deterioration in the elderly is due to a combination of changes in the muscle fibers and in their nerve supply and that the extent may differ between proximal and distal muscles.

No abstract

Persisting disability in NBPP patients is due, at least in part, to impaired motor unit activation. The authors suggest that the impairment is a form of developmental apraxia caused by defective motor programming in early infancy.

Background: There is a lack of standardized tests that assess functional performance for sustained upper extremity activity. This study describes development of a new test for measuring functional performance of the upper extremity and neck and assesses reliability and concurrent validity in patients with shoulder pathology.

Use of hinged AFO reduces the oxygen and ventilatory cost of walking in children with spastic diplegic CP.

Following obstetrical brachial plexus injury, infants are unable to learn specific patterns of movement due to the disruption of neural pathways. Even with successful reinnervation (spontaneously or post surgical reconstruction), function can be suboptimal due to overactivity in antagonist muscles preventing movement of reinnervated muscles. Botulinum toxin type A (BTX‐A) was used to temporarily weaken antagonistic muscles early in the reinnervation process following brachial plexus injury, with the aim of facilitating functional improvement. A case series of eight children (five females, three males; mean age 12.5mo [SD 6.43]; range 5–22mo) with significant muscle imbalances but evidence of reinnervation were given BTX‐A injections into the triceps, pectoralis major, and/or latissimus dorsi muscles. After a single injection, all parents reported improvement in function. Active Movement Scale total score changed significantly between pre BTX‐A and 1 month (p=0.014), and 4 months (p=0.022) post BTX‐A injection. It is proposed that BTX‐A facilitated motor learning through improved voluntary relaxation of antagonist muscles while allowing increased activity in reinnervated muscles.