Recovery of electromyograph median frequency after lumbar muscle fatigue analysed using an exponential time dependence model

Abstract

The recovery of the median frequency of the power spectrum of the electromyogram (EMG) after fatigue has been studied to obtain reference data for healthy subjects (n = 55). In a seated position, the subjects performed a 45 s isometric back muscle contraction at 80% of maximal voluntary contraction, followed by 5 s contractions after 1, 2, 3, and 5 min in the recovery phase. In an additional reliability study (n = 11), this was performed six times. Surface EMG was recorded on four sites, namely, bilaterally from the lumbar muscles at the level of the first (L1) and fifth (L5) vertebrae. By non-linear regression, an exponential time dependence model was used to analyse the recovery of median frequency, giving recovery half-time as a resulting measure. Agreement with exponential time dependence was very good (coefficient of determination r(2) = 0.98) in the analysis of mean data (n = 55), with recovery half-times in the range 32-39 s on the four recording sites. Analysis of individual recordings, for which r(2) values in general were lower, revealed further details. Median values of the half-times in general agreed well with the half-times obtained from the analysis of mean data. Recovery half-time and median frequency slope during contraction were not correlated; this is in agreement with what may be expected from an exponential time dependence. Non-significant negative slopes occurred on apparently randomly selected sites, possibly indicating varying muscle coordination in the seated test method. The reliability of the half-time was not sufficient to allow for follow-up measurements on individuals, due to the fluctuations of the recovery data in recordings from individuals.

Temporal strategy and performance during a fatiguing short-cycle repetitive task

“…Over the entire 1-h task we observed a cumulative increase in perceived fatigue and EMG amplitude but not a consistent decrease in the MPF, which is in line with several previous studies which have found that MPF recovery is fast after exercise (e.g. Elfving et al 2002).…”

EMG recovery and ratings after back extensor fatigue in patients with lumbar disc herniation and healthy subjects

“…When a subject rests after a fatiguing contraction, the median frequency measured from back and extremity muscles recovers to the initial level following an exponential curve function of time (Broman et al 1985;Kuorinka 1988;Vestergaard-Poulsen et al 1995;Alfonsi et al 1999;Elfving et al 2002). An exponential (non-linear) model is superior to models anticipating linearity in the analysis of metabolic changes during muscle contraction and recovery (Simond et al 2001).…”

Electromyography for Assessment of Pain in Low Back Muscles

“…12 Although intracellular acidosis is considered to contribute to muscle fatigue, it also plays a role in preserving excitability when depolarization occurs within the muscle during activity; that is, intracellular acidosis has a protective effect during muscle fatigue. 23 Considering recovery capacity (ie, a return to a nonfatigue condition 24 ) as an important tool in the analysis of neuromuscular function and low back pain, we also used REC to evaluate low back muscle performance in the present study. In contrast to our initial expectations, the results demonstrated higher values for MFr and, consequently, for REC in subjects with pain than in subjects without pain (Tabs.…”