Hey Saunaboy,

Cyclists commonly have tight hip flexors due to the nature of cycling (won't go into detail). Office workers also commonly have tight hip flexors due to the hip being constantly flexed to 90 degrees for ~ 50 hours per week. Tight hip flexors will cause an anterior pelvic tilt (stomach pushed forward) which will further shorten your hip flexors and actually put your hamstrings slightly in a lengthened position. When you have such muscle imbalances you throw off your length/tension relationship (http://www.public.iastate.edu/~zool.255/Nov08_02.pdf) and the muscles become less efficient, which can also lead to injury / overuse or symptoms as you have described (aggravation of the insertion / tendonitis).

As previous physio suggested, a postural assessment is definately in order. Hamstring stretching (light, you do not want to further overtension the insertion, leading the some isolated hamstring strengthening (low grade) if symptom free), hip flexor stretching (more important!!!), and some pilates focusing on posterior pelvic tilt w/ core activation would be where I would start.

This could also explain your cramping in your back, as altered pelvic position can also cause problems with your quadratus lumborum etc. (other lumbar spine muscles) and increased Lx. lordosis due to anterior pelvic tilt will reduce the effeciency of impact loads through the lumbar spine and likely cause protective local muscle activation...? I could go on and on, but correcting the relationship between your hip flexors + extensors will likely help, get out of the chair regularly and stretch hip flexors (i.e. reduce the CAUSE of the imbalance), stretch regularly outside of work, strengthen gluts + abdominals (help bring the pelvis back to an anterior tilt)...

Does this make sense? just typing it all out quickly during lunch.

Let me know if you want more info!