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.

Four sites will participate in data collection for this study and will enroll approximately 20-30 subjects per site. Subjects will be tested every 1 to 4 months for up to two years. Subjects will be tested at each visit using ATLIS, ALSFRS-R questionnaire and slow vital capacity testing.

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.

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).

Inclusion Criteria:

• 18 years or older
• clinically possible, laboartory supported probable, probable or clinically definite ALS according to El Escorial Criteria
• capable of providing informed consent

Exclusion Criteria:

• persons with medical conditions that would limit their ability to safely exert maximal force using muscles in their arms and legs (e.g. unstable cardiac, musculoskeletal, or other medical conditions)

Adults with ALS