Distribution of motor unit potential velocities in short static and prolonged dynamic contractions at low forces: use of the within-subject’s skewness and standard deviation variables

Abstract

Behaviour of motor unit potential (MUP) velocities in relation to (low) force and duration was investigated in biceps brachii muscle using a surface electrode array. Short static tests of 3.8 s (41 subjects) and prolonged dynamic tests (prolonged tests) of 4 min (30 subjects) were performed as position tasks, applying forces up to 20% of maximal voluntary contraction (MVC). Four variables, derived from the inter-peak latency technique, were used to describe changes in the surface electromyography signal: the mean muscle Wbre conduction velocity (CV), the proportion between slow and fast MUPs expressed as the within-subject skewness of MUP velocities, the within-subject standard deviation of MUP velocities [SD-peak velocity (PV)], and the amount of MUPs per second (peak frequency = PF). In short static tests and the initial phase of prolonged tests, larger forces induced an increase of the CV and PF, accompanied with the shift of MUP velocities towards higher values, whereas the SD-PV did not change. During the Wrst 1.5-2 min of the prolonged lower force levels tests (unloaded, and loaded 5 and 10% MVC) the CV and SD-PV slightly decreased and the MUP velocities shifted towards lower values; then the three variables stabilized. The PF values did not change in these tests. However, during the prolonged higher force (20% MVC) test, the CV decreased and MUP velocities shifted towards lower values without stabilization, while the SD-PV broadened and the PF decreased progressively. It is argued that these combined results reXect changes in both neural regulatory strategies and muscle membrane state. Keywords

Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during prolonged dynamic exercises at low force levels

“…The signal was described by three parameters derived from MUP velocities (MUPVs = peak velocities): the muscle conduction velocity (CV-ipl), the skewness (Sk) and the standard deviation of MUP velocities (SDmup). The MUP-Vs were obtained by the IPL method proposed by Lange and colleagues (Lange et al, 2002) and modified by the authors (Klaver-Król et al, 2007).…”

“…These distribution parameters have not been used that often in the past. Skewness as an sEMG parameter was first described by the present authors (Klaver-Król et al, 2007) and, as far as we know, has only recently been applied by Casale and colleagues who observed different proportions of faster and slower propagating MUPs in fibromyalgie patients compared to a control group, suggesting an aberrant central neural control (Casale et al, 2009).…”

“…A position task involves using an inertial load with the goal of maintaining a target position (Rudroff et al, 2005). However, some dynamic position experiments have been reported sporadically (Klaver-Król et al, 2007;Potvin, 1997;Tax et al, 1989). In the present dynamic position experiment, subjects were required to swing the arm, at a given rate, between two positions.…”

“…inherited) distinguishing muscle characteristics. The experiments were carried out at low force levels, in dynamic conditions, and using a position task procedure (Klaver-Król et al, 2007). The use of low forces, combined with dynamic conditions and a position task, seemed to us to reflect better the natural muscle activities (KroghLund and Jorgensen, 1992;Potvin, 1997).…”

Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during short static contractions at low force levels

“…In a recent study, we introduced a method that used the distribution of motor unit potential (MUP) velocities as a measure of the proportions of faster and slower propagating MUPs in surface electromyography (sEMG) (Klaver-Król et al, 2007). The present study investigates whether the method is able to distinguish between the muscle properties of sprinters and endurance athletes.…”