My second post on this blog was a suggestion that, when you think about it in detail, there are some problems with the conventional terminology that clinical gait analysts use to divide the gait cycle into phases and that a very simple scheme based upon simple division of the gait cycle into single support, double support and swing might have some advantages. Here is a video I’ve developed to help gait analysts reflect on the issues.
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Walking with Richard 
Hi Richard,
I really like your video on recycling terminology and the logic be hide your gait cycle subdivisions, i would like to know how you would define the events between early-middle and middle-late stages of single support and its twin the swing phase
Dean,
I think the issue here is that single support, double support and swing are qualitatively different biomechanically Ieading to a “natural” sub-division of the gait cycle in terms of gait events. I can’t see any biomechanical reason for further sub-division of single support and swing into distinct phases that are applicable for walking across a range of pathologies. Using events such as tibia vertical as Perry did in swing for example only works for people with a relatively normal gait pattern – in many children with CP walking in a crouch gait pattern the tibia never reaches vertical.
I don’t subdivide single support and swing because I believe there are truly distinct sub-phases but because it is convenient to have words to describe timing within the gait cycle a little more specificity than just single support or swing. In this case an arbitrary division of these phases into three sub-phases of equal duration seems simplest. So in answer to your question these are not differentiate by specific gait events.
I have had a criticism that this is quite easy for instrumented systems outputting gait graphs but doesn’t work as well for observational or video analysis – it would be nice to be able to point to an event in the gait cycle that marked the transition between these sub-divisions that could be seen on the video and didn’t require a mathematical calculation (no matter how simple). I think this is valid and have been thinking about it for some time without coming up with a better solution. So far though I’ve failed.
Given that the system is essentially arbitrary though I think there is an argument that these should be considered as broad terms describing approximate times within the gait cycle and we should not be attempting to apply them to rigidly or precisely. I’d be very wary of a way of describing gait that was based on over-precise definition of these phases.
Hope this is useful. As I’ve said this is not the first time someone has raised this point.