Perception of effort is the feeling of how heavy and strenuous a
physical task is. This perception has important implications for health
and physical performance. To date , it has been studied mainly from an
exercise physiological and a psychophysical point of view. There is a
lack of psychophysiological research in this area. The general theme
of the thesis was therefore to study perception of effort by using a
psychophysiological approach. The first aim was to establish whether
perception of effort correlates with central motor command to the
active muscles and the second aim was to establish whether frowning
muscle activity reflects perception of effort during exercise.
In chapter 2 we show during elbow flexion exercise that movement related cortical potential (MRCP) amplitude and perception of effort
are augmented by an increase in exercise intensity and they are also
augmented for the same exercise intensity during muscle fatigue.
Across these two manipulations, we found a significant correlation
between perception of effort and MRCP amplitude at the vertex during
the first 1000 ms of movement execution. This is the first
neurophysiological evidence that perception of effort correlates with
central motor command to the active muscles. Interestingly, we did
not find effects of our manipulations on MRCP amplitude during
movement preparation.
In chapter 3 we corroborate and extend the findings of chapter 2. We
demonstrate during isometric leg-extension exercise that MRCP
amplitude at the vertex during the first 1000 ms of movement
execution also reflects the reduction in perception of effort caused by
caffeine intake. MRCP amplitude and perception of effort were both
reduced after caffeine intake compared to placebo , in the absence of
changes in motor neuron output and force output. Furthermore, we
found an effect of exercise duration on perception of effort and MRCP
amplitude at the vertex during the first 1000 ms of movement
execution. Both variables were significantly higher during the second
block of 50 trials compared to the first block of 50 trials of the
isometric leg-extension protocol, despite the fact that there was no
muscle fatigue.
In chapter 4 we show during leg-extension exercise that facial
electromyogram (EMG) amplitude of the corrugator supercilii muscles
increases with increases in exercise intensity, and it is also augmented
for the same exercise intensity during muscle fatigue. We found
significant correlations between facial EMG amplitude and perception
of effort. This study demonstrates for the first time that frowning
muscle activity reflects perception of effort during a physical task.
In chapter 5 we corroborate and extend the findings of chapter 4. We
show that facial EMG also reflects exercise intensity during aerobic
exercise. Facial EMG and perception of effort were significantly
higher in the severe-intensity group compared to the heavy-intensity
group. We also found an increase in facial EMG amplitude with
exercise duration during severe-intensity cycling. However, during
heavy-intensity cycling, we found a dissociation between perception
of effort and facial EMG.
By using two psychophysiological measures to study perception of
effort, we have provided valuable new evidence and interesting new
insights about the neurophysiological bas is and the facial expression
of effort. First of all, we have provided the first neurophysiological
evidence that perception of effort reflects central motor command to
the active muscles, and secondly, we have shown that facial EMG of
the frowning muscles reflects perception of effort during intense
exercise, but not during lower-intensity exercise