Electromyography

Electromyography (EMG) is an electrical record of muscle activation. It is a measure that is recorded by placing sensors on the skin of a participant and monitoring changes in the electrical activity of the underlying musculature relative to movement. Greater levels of activation occur as motor unit recruitment increases in order to perform movements successfully. EMG provides a useful window into mind–body relationships, both within exercise and sport domains. While the use of EMG in sport and exercise psychology has been fairly sporadic, there are pockets of research in both exercise and sport where the use of EMG has provided valuable insights into the mind–body relationship.

One area in which EMG has been used with interesting results is in the study of the tranquilizer effect of exercise. More specifically, the study of the anxiolytic (anxiety-reducing) properties of exercise has been a popular topic for decades. Anxiety is a psychophysiological construct, having both psychological (e.g., feelings of worry, fear, apprehension) and physiological (e.g., increased heart rate and respiration, increased muscle tension) manifestations. As such, if one operationalizes anxiety as being reflected as increased muscle tension, EMG can be used to examine changes in that tension before and after exercise. One scientist, who made significant advances in this area, indeed coining the phrase tranquilizer effect of exercise, was Herbert deVries. In a series of studies beginning in 1968, deVries demonstrated that muscle tension was significantly reduced following aerobic exercise. This effect proved fairly robust, occurring for relatively brief bouts of exercise in college-age students, in older adults recruited for having elevated levels of resting muscle tension and being superior to tranquilizer medication, and at different levels of the skeletal muscular signal (innervation of muscle fiber, innervation of muscle spindle). This effect has been shown by others as well, with some finding the tension-reducing effect of leg cycling exercise to be specific to the soleus muscle and not to other muscle groupings like flexor carpi radialis. Furthermore, the tension reducing effect has been shown to occur following both active and passive leg cycling exercise.

Relatively little work has tried to examine the relationship between the physiological reduction in muscle tension and self-reported tension, namely state anxiety (assessed via questionnaire). In one of the few studies, Robert Motl and Rod Dishman examined the effects of moderate intensity leg cycling on muscle tension in the soleus, reflected through the Hoffmann reflex (H-reflex; index of motor neuron excitability), and self-reported state anxiety. Further, using an interesting approach, they manipulated anxiety by having participants ingest a relatively large dose of caffeine (based on body weight) prior to exercise. Muscle tension was reduced following exercise regardless of whether caffeine or placebo was used, but self-reported anxiety was reduced only following the exercise + caffeine condition (exercise + placebo did not result in self-reported anxiety reduction). They also showed no significant relationship between changes in muscle tension (H-reflex) and changes in state anxiety. Finally, in an approach using the startle probe paradigm developed by Peter Lang and Margaret Bradley, the relationship between changes in facial muscle tension, specifically the musculature surrounding the eyes (corrugator superciilii), and different intensities of leg cycling exercise has been examined. An overall reduction in EMG activity followed both low and moderate-intensity exercise compared to seated quiet rest. There was no relationship between the reductions following exercise and self-reported anxiety changes, as anxiety was reduced following both exercise and quiet rest. Self-reported anxiety reductions were largest following quiet rest and smallest following moderate-intensity cycling, but EMG reductions were largest following moderateintensity cycling and smallest following quiet rest (exactly opposite of what would be expected if the two were related).

Clearly, more work is needed to better understand the relationship between muscle activity and affective responses, particularly with respect to exercise. Most of the work to date has focused only on self-reported anxiety, but other measures of affect related to anxiety, such as tension, tiredness, and calmness, should also be investigated. Furthermore, timing of measurements of both the physiological and psychological events is crucial to uncovering any relationship between the two, should they in fact exist.

The relationship between muscle tension (using EMG) and motor performance has also been a topic of interest in sport psychology. In an initial study in 1976, Robert Weinberg and Valerie Hunt measured self-reported anxiety and EMG activity during a task involving throwing a tennis ball at a target. Participants completed trials without feedback and then completed trials where they were given failure feedback meant to induce pressure. Participants who had higher levels of anxiety had EMG patterns reflecting longer contractions of both the biceps and triceps than those who had lower anxiety. This high-anxious pattern was interpreted as reflecting a reduction in muscular efficiency. Although it did not have negative influence on performance, the low-anxiety group did show performance improvement (greater accuracy) when given failure feedback, as it was thought that the high-anxiety group could have performed better if muscle tension had not increased under pressure. Subsequent work has essentially replicated these findings. More recent work, using golf putting as the motor task, has examined the effects of performance pressure on anxiety, effort, and EMG activity during the putt swing. Increasing pressure resulted in worsening performance (fewer putts made), increased anxiety, and increased sense of effort. Like the original Weinberg and Hunt study, the patterning of EMG activity was indicative of inefficient use of muscular energy.

Another area of sport and exercise psychology where EMG has shown promise is in the area of imagery, mental practice, or visualization. Whereas imagery has been shown to result in improved performance, the reason for this improvement has been elusive. One explanation for the improvement in physical performance following mental practice has been termed the inflow explanation. In essence, the inflow explanation, captured in psychoneuromuscular theory, proposes that EMG activity should be similar in patterning during imagined movements as it is during the actual movement as it activates the same motor structures as the actual movement. Dating back to Edmund Jacobson’s pioneering work in the 1930s, researchers have sought to determine whether muscle activation (EMG) during imagery is similar to that obtained during the actual movement. This inflow explanation was supported in work by some, but not by others. More recent studies seem to suggest that the EMG activity seen during imagery is more an outcome of the imagery rather than what causes the imagery or its benefits.

It is actually rather surprising, given the results from studies like those presented, that the use of EMG as a physiological measure has not occurred more frequently. As measurement technology continues to improve, allowing more real-time assessments to take place, it would be worthwhile to see the extent to which some of the findings presented above can be replicated in more natural settings, both in the exercise and sport domains. Although it would certainly require background and training in psychophysiology, the yields of such research could be fruitful indeed.

References:

deVries, H. A. (1981). Tranquilizer effect of exercise: A critical review. Physician & Sportsmedicine, 9, 47–54.
Jacobson, E. (1932). Electrophysiology of mental activities. American Journal of Psychology, 44, 677–694.
Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1992). A motivational analysis of emotion: Reflex-cortex connections. Psychological Science, 3, 44–49.
Lutz, R. S. (2003). Covert muscle excitation is outflow from the central generation of motor imagery. Behavioural Brain Research, 140, 149–163.
Motl, R. W., & Dishman, R. K. (2004). Effects of acute exercise on the soleus H-reflex and self-reported anxiety after caffeine ingestion. Physiology & Behavior, 80, 577–585.
Weinberg, R. S. (1990). Anxiety and motor performance: Where to from here? Anxiety Research, 2, 227–242.
Weinberg, R. S., & Hunt, V. V. (1976). The interrelationships between anxiety, motor performance and electromyography. Journal of Motor Behavior, 8, 219–224.

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