Electromyographic activity of the human extensor carpi ulnaris muscle changes with exposure to repetitive ulnar deviation

Abstract

With little known about the changes in muscle physiology due to repetitive work during an 8 h workday, our objective was to quantify the changes in muscle activity due to this type of work. Using a repeated measurements design, 13 healthy women participated in three conditions, each lasting 2 days: a control condition where they remained inactive, and two repetitive work conditions involving repeated ulnar deviation of the wrist at 20 and 25 repetitions a minute at workloads which they themselves had deemed acceptable for 8 h through a psychophysical protocol. Electromyographic (EMG) activity of the extensor carpi ulnaris muscle was recorded during voluntary isometric contractions (20% and 60% maximal voluntary contraction) eight times throughout the work and control days at 0, 2, 4.25, 6.75, 8, 9, 10, and 11 h. The amplitude of the EMG signal was lower on workdays compared to the control days. Although power was significantly reduced in all spectrum bands of the EMG power spectra, the reductions were not uniform across the entire frequency range, giving rise to different shapes of the EMG power spectra. Initial median frequency of the EMG signal showed no change between the control and workdays (P = 0.51); however, the decline of the median frequency with respect to time over the course of each isometric contraction was steeper during workdays compared to control days (P = 0.003). These changes suggest that the muscles are in an early stage of fatigue when working for an 8 h day.

Assessment of muscle fatigue in low level monotonous task performance during car driving

“…Through the isometric measurements they could conclude that the muscles were fatigued faster in working days. Other reports in literature can be found on the increase and decrease of EMG amplitude during fatigue [3,9,10,13]. …”

“…But also the RMS values dropped. Traditional fatigue measurements would suggest that if the muscle was fatigued, the EMG amplitude would increase and MF would decrease [3,34]. With a decreasing EMG amplitude according to the JASA principle there would be a force decrease of the muscles [28].…”

The forearm positioning changes electromyographic activity of upper limb muscles and handgrip strength in the task of pushing a load cart

“…In view of this, one can say that the handgrip movement involves the finger flexion performed by the flexor muscles (Hagg and Milerad, 1997). However, Bennie et al (2002) also reported that extensor muscles are activated to oppose the flexion torque in order to keep the wrist in neutral position. Because it is known that handgrip requires the action of the flexor and extensor muscles of wrist and fingers, it is necessary to quantify the degree of electromyographic activity of each muscle group so that one can obtain an indication of the potential risk of musculoskeletal lesion, thus suggesting a causal relationship between labour activity and occupational diagnosis of lateral or medial epicondylitis.…”

Electromyographical manifestations of muscle fatigue during different levels of simulated light manual assembly work

“…our assembly task), factors that can hardly be controlled (such as muscle length, muscle-electrode distance and movement velocity) may lead to erroneous interpretation of the EMG signals (Madeleine et al, 2001). Therefore, previous studies introduced isometric test contractions to be performed at specific time points during the dynamic task to study the development of fatigue (Suurkü la and Hägg, 1987;Mathiassen and Winkel, 1996;Bennie et al, 2002;Søgaard et al, 2003;Bosch et al, 2007). An isometric test contraction allows the recording of stationary signals that are likely to be produced by the same pool of motor units in every measurement.…”

“…In studies on other muscles than the upper trapezius muscle, manifestations of muscle fatigue due to isolated activities were studied (Bennie et al, 2002;Dennerlein et al, 2003;Søgaard et al, 2003). Objective signs of manifestations of fatigue were found, but it remains questionable whether these results can be extrapolated to the fatigue development in the shoulder muscles in more natural tasks.…”