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:

  1. deVries, H. A. (1981). Tranquilizer effect of exercise: A critical review. Physician & Sportsmedicine, 9, 47–54.
  2. Jacobson, E. (1932). Electrophysiology of mental activities. American Journal of Psychology, 44, 677–694.
  3. Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1992). A motivational analysis of emotion: Reflex-cortex connections. Psychological Science, 3, 44–49.
  4. Lutz, R. S. (2003). Covert muscle excitation is outflow from the central generation of motor imagery. Behavioural Brain Research, 140, 149–163.
  5. 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.
  6. Weinberg, R. S. (1990). Anxiety and motor performance: Where to from here? Anxiety Research, 2, 227–242.
  7. 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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