Hi Robert, thanks for the post. I have to say right now it feels like perhaps unrelated pieces might have been put together to to form a jigsaw diagnosis, which is not unreasonable. By that I mean there might be one or two things going one which are indirectly related but not necessarily Wikipedia reference-linkclaudication even at a mild level. A vascular insufficiency could give these symptoms and a 'flushing' sensation would be felt as the blood flow is restored to normal.

I cycle a lot myself and found I developed a numb left foot for a long time. In fact it has been really hard to work that one out despite looking intensively as the foot, lower leg and low back. Thing thing that in fact helped the most was a new par of shoes with more room and some arch supports inside them. This in fact really helped gain more strength during the push on the cranks.

Now that may or may not be involved. The pars defect and bilateral nature of your symptoms is an interesting one. It is very common in young bowlers and can result in intermittent, ongoing annoyance. A defect could indicate that you have an unstable segment which tends towards a small Wikipedia reference-linkSpondylolisthesis. Now that might only be symptomatic after a period of loaded flexion, such as rowing or cycling. Once you become upright things pinch for a time and then return to normal. It would be a good idea to perhaps mimic a routine and see if you can provoke the symptoms in clinic and then your local physio can do more assessment.

You could also provoke symptoms and then get a plain x-ray in flexion to see if there is any malalignment at that time. The problem with supine MRI's it that the spine is loaded and if things are mobile they should return to a resting position during the scan.

Another thing to check is the pedal pulses in the foot/ankle area when the numbness if there and compare to when things are normal. This could also be done in the clinic if you can provoke symptoms at that time. In general if it is a mechanical cause then 'hammering' out physio in the beginning is not really the concept. Working on core stabilisation, movement correction and improving fatigue resistance will all help and it sounds like you are doing some of that already.

Perhaps if you can consistently provoke the symptoms then you can let us know a pattern and the pattern and timing of the symptomatic behaviour during that process, e.g. what gets numb first, any areas of pain, right side vs left side etc. I am sure others will have ideas so this is a nice place to discuss.

One last point that I might mention is that i did see a fighter pilot for a long time following numbness in the feet pulling a several G turn. It seems like blood flow but eventually we nailed it down to the harness he was wearing and possible the seat of the plane. I say this also as if you are regularly jumping you will have both pulling on your harness on your pelvis and well as some forceful loads as you land. That could easily cause a milalignment of the pelvic bones and disruption to the normal tone of muclses in the buttocks, e,g. piriformis. An insufficiency there could well lead to symptoms like those you are experiencing as well. So ask the physio to assess your pelvic symmetry as well.

Look forward to other peoples input.