Accurate Test of Limb Isometric Strength (ATLIS) in ALS

Inclusion criteria: * Subjects 18 years or older diagnosed with clinically possible, laboratory supported probable, probable or clinically definite ALS according to the World Federation of Neurology Revised El Escorial Criteria. * Capable of providing informed consent and complying with trial procedures. * Active movement of at least two limbs at the time of study entry * Intend to routinely attend clinic for neurological care at the clinical site Exclusion criteria: * Patients, judged by the site clinical investigator to have medical conditions that may limit their ability to safely exert maximal force using the muscles in their arms and legs will be excluded from this study (e.g. unstable hypertension, significant cardiac disease, significant musculoskeletal disorders, or other medical conditions). * Patients judged by the site clinical investigator to have significant clinical evidence of unstable medical or psychiatric illness will be excluded.