Time‐dependent effects of pre‐conditioning activation on muscle fiber conduction velocity and twitch torque

Abstract

In this study we investigate the range of interstimulus intervals influencing the recovery functions for conduction velocity (velocity recovery function, or VRF) and twitch torque (twitch torque recovery function, or TRF) of muscle fibers. We studied the tibialis anterior muscle of 8 healthy men by varying the time interval between a pair of stimuli in the range of 4-1000 ms, with (triplet) and without (doublet) a preconditioning stimulus. For triplet stimulations, the interval between the first and second stimulus or between the second and third stimulus was fixed, and the other interval was varied. VRF and TRF were influenced by a preconditioning stimulus only when it was delivered within 125 ms and 30 ms, respectively, before the doublet stimulation. The results provide evidence of the range of preconditioning intervals influencing the VRF and TRF; this is relevant for understanding the mechanisms of force generation and for standardizing compound action potential measurements.

Do muscle fiber conduction slowing and decreased levels of circulating muscle proteins represent sensitive markers of steroid myopathy? A pilot study in Cushing's disease

“…Physiological values of MFCV estimated from surface EMG signals detected during electrically elicited muscle contractions (i.e. the average conduction velocity of all the muscle fibers that are excited by the externally imposed electrical field) ranged from 4.0 to 6.0 m/s for the vastus lateralis and medialis muscles (5,13,18,19) and from 3.5 to 5.5 m/s for the tibialis anterior muscle (5,20,21).…”

Sympathetic activation by the cold pressor test does not increase the muscle force generation capacity

“…The protocol adopted in the present study included electrical stimulation by paired stimuli at varying ISI within the range 4 -1,000 ms. This stimulation pattern was previously employed for the investigation of the velocity recovery function of muscle fibers (18) and of twitch summation (17). It was adopted in the present study for two reasons: 1) the response to the doublet at short ISI is stronger than the single twitch and thus provides an improved signal-to-noise ratio for the detection of changes in muscle contractility; and 2) possible increase/decrease in twitch duration, resulting in increased/decreased twitch fusion, would have been evidenced by rightward/leftward shift of the torque amplitude vs. ISI curve in this stimulation pattern.…”

“…The stimulation pattern for single stimuli and doublets consisted of a sequence of 22 alternated single and paired pulses separated by 1-s interval. The paired pulses (doublets) had an interspike interval (ISI) ranging between 4 and 1,000 ms (4,8,12,15,20,30,50,75,100,125,150,175,200,225,250, 300, 400, 500, 750, and 1,000 ms) according to a protocol adopted in previous studies (17,18). This sequence of pulses was followed by four pulse trains of 5 s in duration, separated by 5-s intervals.…”

Physiological consequences of doublet discharges on motoneuronal firing and motor unit force

“…Such effects have been frequently observed in experiments with doublets of pulses (in a range of 5–10 ms) on isolated fast or slow MUs of hind limb muscles of cat (Burke et al, 1976; Stein and Parmiggiani, 1979; Zajac and Young, 1980a) and rat (Hennig and Lømo, 1987; Celichowski and Grottel, 1998). A potentiation of MUs force in response to doublet has resulted from non-linear summation of twitch forces (Duchateau and Hainaut, 1986a) and could be twice to three times higher than the force of a twitch evoked by a single pulse (Parmiggiani and Stein, 1981; Kamavuako and Farina, 2010). …”