A new strength measurement device called Accurate Test of Limb Isometric Strength (ATLIS) was developed to precisely and conveniently measure static limb strength in patients with ALS. The investigators will compare ATLIS data with data from two commonly used ALS outcomes measures, the ALS Functional Rating Scale-Revised (ALSFRS-R) and slow vital capacity (SVC) in a prospective, longitudinal study. All three outcomes measures will be performed on 100 subjects collected preferably at bi-monthly clinic visits during the study period.