I too have tarsal coalition and was first affected by it when I was 16 years old. I was in pain 24/7 at that time and it affects both feet. For several years during and after college I was actually OK. However, I'm in my 30s now and the pain has become unbearable again. I have tried everything over the years including orthotics (three different times and they were so painful I had to stop), anti-inflammatories (now I have an ulcer from overusage), physical therapy (twice - it did nothing at all for me), and steroid injections (I'm one week after the injections and they are starting to wear off). Now I am afflicted with back, hip, and knee pain as well. At this point I think I am headed for fusion surgery and will be happy when the day comes that my back, hip, knees, and feet are no longer hurting!
By the way, I seriously doubt that working out at the gym will help. I have worked out with trainers and by myself and it has not helped the condition or made it worse.