Effect of prior activity on properties of different types of motor units.

Physiological types and histochemical profiles in motor units of the cat gastrocnemius

“…In the absence of contrary evidence, we have assumed that the actual relative frequencies of the different unit types is about the same in all normal adult cats, and this assumption is implicit in giving the average frequencies above. The relative frequency of slowly contracting type S units in the present sample population was not much different from that found in previous samples drawn from the medial gastrocnemius muscle unit pool, making allowances for differences in experimental techniques (Burke, 1967;Olson & Swett, 1971;Wuerker et al 1965).…”

“…Burke, 1967;Olson & Swett, 1971;Wuerker et al 1965). Early in the course of the present work it became apparent that muscle unit twitch characteristics showed marked dependence on the stimulus history, in particular exhibiting considerable post-tetanic potentiation of twitch tension in many units (cf.…”

“…3). There is evidence that slowly contracting muscle units in the gastrocnemius and soleus muscles of the cat may exhibit repetitive firing to single volleys in the motoneurone axon in the aftermath of a prolonged high-frequency tetanus, with consequent tension augmentation (Olson & Swett, 1971;Standeart, 1964). Such repetitive firing was not observed in any of the type S units in the present experiments, presumably because intermittent and relatively short tetani were used to produce PTP.…”

“…Each of the physiological categories of muscle units exhibited a corresponding INTRODUCTION Since Ranvier's observation that the colour and histological features of whole muscles are in many cases correlated with their speed of contraction (Ranvier, 1874), it has become generally accepted that the increasingly well-studied morphological and histochemical characteristics of individual muscle fibres must be related in some way to the physiological properties of the same fibres (e.g. Henneman & Olson, 1965;Olson & Swett, 1971; see review by Close, 1972). However, experimental evidence supporting the above hypothesis, while considerable and intuitively satisfying, has until recently been indirect and in some respects contradictory (DennyBrown, 1929;Gauthier, 1969;Hall-Craggs, 1968;Nystr6m, 1968).…”

Behaviour of human motor units in different muscles during linearly varying contractions

“…The potentiation of motor-unit twitch tension after repetitive stimulation has been well documented (for a review, see De Luca, 1979) and seems a likely mechanism to explain this phenomenon. Olson & Swett (1971) have localized twitch potentiation to fatigue-resistant muscle fibres having slow-twitch characteristics. Since the deltoid of long-distance swimmers has been shown to have a significantly higher percentage of these fibres than that of powerlifters (Gollnick, Armstrong, Saltin, Saubert, Sembrowich & Shepherd, 1973), the probability of detecting potentiation is greater and one could expect a more pronounced decline in firing rate from recruitment to decruitment (to produce an equivalent force output).…”