Objective. To describe patterns of muscle activation during gait in selected abdominal and
lumbar muscles using cluster analysis.
Participants. A sample of convenience of 38 healthy adult volunteers.
Outcome measures. Electromyographic activity from the right internal and external obliques, rectus
abdominis and lumbar erector spinae were recorded, and the root mean square values
for each muscle were calculated throughout the stride in 5% epochs. These values were
normalised to maximum effort isometric muscle contractions. Cluster analysis was used
to identify groups of subjects with similar patterns of activity and activation levels.
Results. Cluster analysis identified two patterns of activity for the internal oblique, external
oblique and rectus abdominis muscles. In the lumbar erector spinae, three patterns
of activity were observed. In most instances, the patterns observed for each muscle
differed in the magnitude of the activation levels. In rectus abdominis and external
oblique muscles, the majority of subjects had low levels of activity (<5.0% of a maximum
voluntary contraction) that were relatively constant throughout the stride cycle.
In the internal oblique and the erector spinae muscles, more distinct bursts of activity
were observed, most often close to foot-strike. The different algorithms used for
the cluster analysis yielded similar results and a discriminant function analysis
provided further evidence to support the patterns observed.
Conclusions. Cluster analysis was useful in grouping subjects who had similar patterns of muscle
activity. It provided evidence that there were subgroups that might otherwise not
be observed if a group ensemble was presented as the `norm' for any particular muscle's
role during gait.Relevance
The identification of common variations in muscle activity may prove valuable in identifying
individuals with electromyographic patterns that might influence their chances of
sustaining injury. Alternatively, clusters may provide important information related
to muscle activity in those that do well or otherwise after a particular injury.