Spend some time stretching your short adductors (groin muscles) and your hip flexors. If you have a stand up alternative to the bike, that may also be influencing some anterior hip tightness and anterior pelvic tilt or an anteriorly positioned innominate (one side of your pelvis rotates forward compared to the other side).
In extreme hip flexion positions (lowered sitting), you can impinge the soft-tissues or bursae that sits just below the pointy bone in the front of your hip.
Bill
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