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Low frequency fatigue in human quadriceps is fatigue dependent and not task dependent
Journal article   Open access   Peer reviewed

Low frequency fatigue in human quadriceps is fatigue dependent and not task dependent

Masaki Iguchi, Kris Baldwin, Charles Boeyink, Carol Engle, Michael Kehoe, Anish Ganju, Andrew J Messaros and Richard K Shields
Journal of electromyography and kinesiology, Vol.18(2), pp.308-316
2008
DOI: 10.1016/j.jelekin.2006.09.010
PMCID: PMC2963071
PMID: 17157533
url
http://doi.org/10.1016/j.jelekin.2006.09.010View
Open Access

Abstract

It is well accepted that a low intensity/long duration isometric contraction induces more low frequency fatigue (LFF) compared to a high-intensity/short-duration contraction. However, previous reports examined the intensity/duration of the contraction but did not control the level of fatigue when concluding fatigue is task dependent. The purpose of this study was to determine whether a long duration/low intensity fatiguing contraction would induce greater LFF than a short duration/high-intensity contraction when the quadriceps muscle was fatigued to similar levels. Eighteen healthy male subjects performed quadriceps contractions sustained at 35% and 65% of maximal voluntary contraction (MVC) on separate days, until the tasks induced a similar amount of fatigue (force generating capacity = 45% MVC). Double pulse torque to single pulse torque ratio (D/S ratio) was obtained before, immediately and 5 min after fatigue along with the electromyographic (EMG) signal from vastus medialis (VM) and rectus femoris (RF). The D/S ratio significantly ( p < 0.05) increased by 8.7 ± 8.5% (mean ± SD) and 10.2 ± 9.2% after 35% and 65% tasks, respectively, and remained elevated 5 min into recovery; however, there was no significant difference in ratio between the two sessions immediately or 5 min post-fatigue ( p > 0.05) even though the endurance time for the 35% fatigue task (124 ± 39.68 s) was significantly longer ( p = 0.05) than that of the 65% task (63 ± 17.73 s). EMG amplitude and median power frequency (MPF) analysis also did not reveal any significant differences between these two sessions after fatigue. These findings indicate that LFF fatigue is fatigue dependent as well as task intensity/duration dependent. These findings assist us in understanding task dependency and muscle fatigue.
 Double/single ratio Electrical stimulation Excitation–contraction coupling Task dependency Equivalent fatigue

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