all great advice above. as always diff over the net but your physio sounds onto it and may have already checked these anyway. as mentioned does seem neural tension and if your physio is manip trained and if your spine is stiff, then a manip here to either lumbar spine or SIJ (if they are in fact dysfunctional - i have even had results from manip to the cervical spine, thoracic spine if they seem dysfunctional) may help. piriformis can also be involved as can hamstring and calf. also foot biomechanics/shoes/stability etc. can and likely to be complex and combination of a few factors, even get your bike set-up checked to ensure frame and cleats are correctly fitted etc. good luck