Issue with Swapping Bike mid-plan

I began a new TrainerRoad base program in mid-January but on my old bike because my newer bike was at the LBS getting repaired for 4 weeks (a long story!). I developed a sore arch and tight Achilles and calf muscle on my left leg, which I realised was being caused by the bike fit on my older bike. Now I have the new bike back (which was fitted with a professional bike fit). On my first ride I got a shooting pain on my left leg and have had to get a sports massage to work out the tension. Should I re-start the base plan or swap out a week with lower intensity rides? Any other advice on transitioning from one bike to another (better fitting) bike would be welcome.

I don’t have a good answer on what you should specifically do given your new leg injury, although some time off may be a good idea if the pain is too much, but I routinely swap bikes during my TR
training and haven’t had a problem. Having said that, the two bikes I am swapping right now were both fitted for me by the same person. However, they are pretty different in geometry with one a race bike and one an endurance bike.

When I do something that caused an injury I play it by feel as to what I can get away with. I back off and test myself every few days to see if the injury is getting better. If you go easy and let the calf repair itself that would be best. That’s the tried and true method.
I have ridden in pain where I have to lay the bike down on the ground to get off. ( back issue ) At 72 I know my old body pretty well.
As far as 2 bikes I would try to set up your old one as close to the new one since it was a pro fit. Fitters will tell you to go easy for the first few weeks to let your motor patterns get used to the change in movement.