Facial electromyography as a measure of effort during physical and mental tasks

Facial electromyography (EMG) is a psychophysiological technique that has been used in the study of emotions. However, there is also some research employing this technique to study the facial expression of effort. Using facial EMG, it has been shown that facial muscle activity is related to effort during mental tasks. It was found that facialEMG amplitude increases with task difficulty and with time on task during a two-choice serial reaction task. However, a relationship between facial EMG and effort has not always been found during mental tasks. Recently, we have started to employ facial EMG to study effort during physical tasks. We have found, by manipulating exercise intensity and muscle fatigue during a leg-extension task, that facial EMG correlates positively with effort during weightlifting exercise. We have also demonstrated that facial EMG reflects exercise intensity during constant-workload cycling to exhaustion. Interestingly, we found that facial EMG increases significantly with exercise duration during high-intensity cycling, but not during moderate-intensity cycling. A plausible neurobiological mechanism that might explain the relationship between facial EMG and effort is motor overflow. Motor overflow refers to involuntary muscle contractions that may accompany voluntary muscle contractions. This is thought to be caused by spreading of excitation in the motor cortex, because of increased excitability. In healthy adults, motor overflow is usually seen only during tasks that require considerable (physical) effort. This might explain the difference between high-intensity exercise, where the relationship between facial EMG and effort is strong and consistent, and moderate-intensity exercise or mental tasks, where a relationship between facial EMG and effort has not consistently been found. Facial EMG may be used in the future alongside rating of perceived effort as an extra, more objective measure of effort. This might have additional value in groups of people who have difficulties with rating effort, or when it is hard to obtain ratings, for example during maximal efforts of a few seconds and very high-intensity exercise of short duration. An additional benefit of facial EMG as a measure of effort is that it is a continuous measure. © 2012 by Nova Science Publishers, Inc. All rights reserved.