Effects of muscle kinematics on surface emg amplitude and frequency
during fatiguing dynamic contractions.
Potvin, J. R.
School of Human Biology and Nutritional Sciences, University of
Guelph, Guelph, Ontario, N1G 2W1, (519)-824-4120 ext 4589, fax:
(519)-763-5902, email: jpotvin.ns@aps.uoguelph.ca
APStracts 3:0431A, 1996.
Fifteen male subjects performed a repetitive elbow flexion/extension
task with a 7 kg mass until exhaustion. Average joint angle, angular
velocity and biceps brachii surface EMG amplitude (AEMG) and mean
power frequency (MnPF) were calculated with each consecutive 250 ms
segment of data during the entire trial. Data were separated into
concentric or eccentric phases and into seven 20 degrees ranges from
0 degrees to 140 degrees of elbow flexion. A regression analysis was
used to estimate the rested and fatigued AEMG and MnPF values. AEMG
values were expressed as a percentage of amplitudes from maximum
voluntary contractions (mvc). Under rested dynamic conditions, the
average concentric AEMG amplitude was 10% mvc higher than average
eccentric values. Rested MnPF values were similar for concentric and
eccentric phases although values increased approximately 20 Hz from
the most extended to flexed joint angles. Fatigue resulted in an
average increase in concentric and eccentric AEMG of 35 and 10 %mvc
respectively. The largest concentric AEMG increases (up to 58 %mvc)
were observed at higher joint velocities while eccentric increases
appeared to be related to decreases in velocity. Fatigue had a
similar effect on MnPF during both concentric and eccentric phases.
Larger MnPF decreases were observed at shorter muscle lengths such
that values within each angle range were very similar by the end of
the trial. It was hypothesized that this finding may reflect a
biological minimum in conduction velocity before propagation failure
occurs.
Received 29 April 1996; accepted in final form 30 August 1996.
APS Manuscript Number A409-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996