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Abstract
This study attempted to assess and compare the amount of cocontraction present in
thigh and leg muscles in three groups of children during treadmill walking and running.
Thirty children, aged 7-8 (n = 10), 10-12 (n = 10) and 15-16 (n = 10) years, performed
4-min bouts of submaximal treadmill exercise at two walking and four running speeds,
assigned in a randomized order. Three seconds of EMG data were collected during the
final minute of each bout from the vastus lateralis (VL), hamstrings (H), tibialis
anterior (TA) and soleus (S). The processed linear envelopes of VL and H, and likewise
of TA and S, were overlapped and a cocontraction index calculated (area of overlap
divided by the number of data points) for thigh and leg segments, respectively. Cocontraction
was highest for the youngest children and lowest for the oldest, for both thigh and
leg, whether expressed in terms of absolute speed or as a percentage of each child's
VO(2 max). Larger amounts of cocontraction may help to explain the higher metabolic
cost of locomotion for younger children, when compared with adolescents and adults.