No abstract

No abstract

A telemetering device is described to record action potentials from muscles of the upper arm and the shoulder during the arm swing of natural walking. The forward swing is caused by activity in some inward rotators, the flexors remaining inactive. The posterior part of the deltoid and some outward rotators are responsible for the backward swing. During walk‐turning electrical activity occurred in flexors inactive during straight walking accounting for the increased excursion of the forward swing which counteracts the torsional movement of the trunk. Step‐related muscular activity persisted even when the arm was prevented from swinging.

Buchthal, P., I?. Erminio and P. Rosekfalck. Motor unit territory in different human muscles. Acta physiol. scand. 1959. 45. 72–47. — The spread of action potentials from motor units of different human muscles was studied by means of a twelve lead multielectrode. The occurrence of a positive‐negative deflection in the potential of less than 0.2 msec duration indicated the presence of active muscle fibres in the immediate vicinity of the recording lead. In this way the fibres of a motor unit were found to be confined to a circular area of 5–7 mm diameter for the muscles of the upper extremities and of 7–10 mm in the lower extremities. Such areas allow space for the fibres of 25 motor units each comprising 500–2,000 fibres. Within the same muscle or the same type of muscle the diameter of the motor unit territory varied by a factor of four. The maximum voltage within the motor unit increased linearly with the territory. The different average values of maximum voltage and territory in different muscles are interpreted in terms of differences in fibre concentration and total number of fibres per motor unit.

No abstract

No abstract

No abstract

The appearance of the action potential of the motor unit, and the development of its mechanical response, depend on the rate of conduction of the excitatory process over its fibres. I n isolated frog muscle fibres, the propagation velocity of the action potential varies proportionally with the circumference of the fibre (H~KANSSON 1954). I n view of the fact that a muscle consists of fibres with largely different diameters, corresponding variations in propagation velocity might be expected, and might explain the variations in action potential duration in different points of a muscle. I n man, propagation velocities have been determined a t voluntary effort (DENSLOW and HASSETT 1943). Ho.wever, the interpretation of the results is complicated by the fact that the motor unit potential represents the activity of many fibres with spatially dispersed end plates. Therefore, in the present study, an attempt was made to measure the propagation velocity of the impulse over as few simultaneously activated fibres as possible. For this purpose, action potentials were recorded a t different distances along the long axis of the muscle from a locally stimulated point. The study was combined with an examination of the distribution of fibre diameters in biopsies from subjects of different age.