I'm not sure what it is but it is also happening to me. I haven't exercised in a while and just started walking again. This same exact thing happened over a year ago after I started exercising and a quit after a while but has come back again now that I have been sedentary for several months. The knot is prominent when in kneeling position or flexed foot. I also experience horrible burning pain in the left calf if I walk over a certain speed. I have been taking some pain medicine and a nitric oxide 25 minutes before walking and have been able to sustain 40 minute walks but only 3.0 speed. (Averages 2 miles in 30 which is way below my goal) I'm going to continue to stay slow and build slowly.. I don't wanna give up. I may change the pain killers to aspirin instead of Excedrin and take away the nitric oxide (cause I'm about out of it anyways and it's hard to find) .. I hope it helps.
Hey Sara!
Well, without a detailed clinical evaluation it would be difficult to determine the cause of the lump. Possibilities that may need to be considered include cysts, growths from the bones/ muscles/ surrounding connective tissue, fractures/ dislocations etc. I would suggest getting this evaluated by a primary care physician initially and depending on the cause diagnosed/ suspected, it can be managed accordingly or specialist care may be sought.
Hope this is helpful.
Take care!