Observation, imagination and execution of an effortful movement: more evidence for a central explanation of motor imagery.

In this study subjects had to imagine, observe and perform a series of 25 squat movements while lifting two dumbbells of 12.5 kg each (one with each hand). This movement is effortful and requires substantial activation of peripheral systems. It was asked whether subjects when they imagined that they were performing the movements or when they observed a model performing the squat movements would show increased activity in EMG, heart rate and respiration compared with a control condition where they sat relaxed in a comfortable chair or a condition where they actually performed the squat movements. Two groups of subjects participated in the experiment: experienced squatters and novices. By employing these two groups we were able to study the differential effect of earlier experience with the target movement on peripheral activation. The results showed that with the exception of respiration no significant peripheral activation could be measured related to motor imagery. Although a clear distinction in experience existed between the experienced squatters versus the novices, no relevant imagery-related differences could be obtained between the two groups. The results are discussed in the light of a central explanation of motor imagery.