Spreading of fatigue-related effects from active to inactive parts in the medial gastrocnemius muscle of the cat

Abstract

In the medial gastrocnemius muscle of the decerebrate cat, the spatial spread of fatigue between active and inactive muscle parts was studied. Conditioning fatiguing stimulation (CFS) was applied to a part of the muscle to test whether it had an effect on the contraction efficiency in an unstimulated part. To exclude somato-sympathetic reflexes during CFS, a full rhizotomy of the lumbo-sacral spinal cord was performed. The same ipsilateral ventral root, either L7 or S1, was divided into seven filaments, one of which was used for the test stimulation, and four or five for CFS. The CFS consisted of 12 s sessions of distributed stimulation of five (or four) filaments at a rate of 40 s(-1), the sessions were repeated, every 40 s, 15 or more times. The test consisted of 12 s of regular stimulation at a rate of 10 s(-1), preceded and followed by a single stimulus. The tests applied just after CFS showed a strong decline of both tension and electromyogram (EMG), amounting to only [mean (SD)] 0.45 (0.18) and 0.51 (0.19) (n = 15), respectively, of the corresponding values in the tests before CFS. It thus turned out that depressive fatigue-related effects could spread within the muscle. At the same time, control reactions recorded in the lateral gastrocnemius during stimulation of its cut nerve did not change. Subsequent repetitions of the tests usually revealed a tendency towards restoration. The EMG reactions recovered more quickly than tension. The depression of EMG after CFS was accompanied by a slowing of the constituent M-waves; their latencies decreased during restoration. Distinct changes in the systemic blood pressure were observed during CFS. These changes were usually correlated well with muscle tension changes. The factors possibly underlying the observed effects may include diffusion of metabolites from active to inactive muscle fibres, lowering of the efficiency of neuro-muscular transmission due to squeezing of efferent motor terminals and changes in outer metabolite content, as well as local hypoxia due to increases in intramuscular pressure.

Conduction Velocity of Quiescent Muscle Fibers Decreases During Sustained Contraction

“…These findings can be explained by the changes that occurred in the extracellular environment during the 3-min subthreshold contraction and indicate that muscle fiber electrophysiological properties are affected by the overall muscle activity, partly independently of the specific fiber activity. This effect was previously advocated as one of the potential mechanisms underlying the modifications in M-wave observed in parts of the gastrocnemius muscle of the cat not elicited by a conditioning fatigue stimulation (Kostyukov et al 2002). This is the first time that an effect of active muscle fibers on membrane properties of nonactive ones is shown in vivo at the level of single motor units.…”

C60 fullerene as promising therapeutic agent for correcting and preventing skeletal muscle fatigue

“…triceps surae under fatigue development before and after C 60 FAS administration. We did not use a level of stimulation above 40 Hz, and the rest period between the experimental series was 15–20 min [2]. This experimental approach allows us to analyse the nature of the muscle contraction force parameter changes under fatigue stimulation before C 60 FAS application (into the left TS ) and directly after F-injection.…”

“…4a–h). It was the result of modified stimulation pattern action, which was due to the influence of the central and peripheral mechanisms of the development of skeletal muscle fatigue [2]. After intramuscular injection of the C 60 FAS partial ipsilateral TS muscle recovery was registered in two rats.…”

An integrative model of motor unit activity during sustained submaximal contractions

“…Small values for DC relative to RC were associated with negligible diffusion between motor units, whereas large values for DC exposed active and nonactive motor units to similar MCs. Experimental findings suggest that the diffusion of metabolites is responsible for the depression of contractile force (48) and changes in membrane properties (36) of inactive motor units. Furthermore, the force-generating capacity and motor unit discharge rates after a 60-s maximum voluntary contraction (MVC) return to baseline after 3 min of rest (70).…”