i have long fiber sensory motor axonal neuropathy. I have been getting that heavy feeling in my legs when walking any distance or when i tried to keep running over a decade ago. it feels like i am lugging around tree trunks. i also get the heavy feeling in my arms if i try to use them at or above shoulder level. jy hands also tire quickly but dont feel heavy! After 15 years i probably also have some small fiber involvement but have never been tested for that. it wouldnt make a difference in life style or treatment at this point to have it confirmed. Your electromyography (emg) nerve conduction study (NCS) may give you some answers as to whether you have any large fiber motor nerve involvement