Left calf pain during running

Hi I have a case of a 59 year old man who was referred for left calf pain which occurred intermittently and only whilst running.
imaging were negative for any DVT or stress fractures. No pain was felt whilst walking or cycling.

on observation it was noted that he had slight atrophy of left calf, an anterior pelvis tilt and lumbar lordosis. During walking the left lower extremity was excessively rotated externally and a left medial heel turn.

He had a slight right trunk deviation during flexion and hip flexors limitations. In addition repetitive prone lumbar extension caused central low back pain.

What could be the cause of this? I was thinking that it might be a postural syndrome that is leading to a dysfunction syndrome with the main problem being at the back which alters biomechanics of the feet. What are the views on this?

Thanks

From the information I have been able to gather, it seems like a postural syndrome.

I would have a look at the functionality of the left hip initially (along with SIJ function). If the left leg is excessively externally rotated, the likelihood is that the foot will be driven into a pronated position during walking / running. The added speed / ground reaction force the body has to deal with during running may be enough to overload calf to the point of pain. Assessing his running gait would be worthwhile to identify this?