I think a lot of people with incomplete injuries experience the same sensation of weight in the legs. Some of us have great variability in this sensation (a good day might be a 20 pound sensation, a bad day might be 100 pound sensation). I can't offer much other than (1) I use a wheel chair to improve mobility and especially on those 100 lbs days, where mobility can disappear in minutes, (2) exercise seems to help (I use a stationary bicycle).