Trials evaluating new therapies for stopping or slowing the progression of ALS depend critically upon the use of outcome measures to assess whether a potential treatment is effective. The more effective an outcome measure, the fewer patients need to be enrolled and the shorter the trial. Many outcome measures have been used over the years, including strength assessments, breathing tests, functional status surveys, and nerve testing, but all are far from ideal. A new method, called electrical impedance myography (EIM) appears to be especially promising in that it provides very consistent data from one testing session to the next, is sensitive to the muscle deterioration that occurs in ALS, and is entirely painless and non-invasive. In this study, investigators from multiple institutions plan to compare several different outcome measures, including EIM, in approximately 120 ALS patients, with each patient being followed for a period of one year. All of these measures will be compared to one another and an assessment of their ability to detect disease progression made. Our goal will be to determine whether EIM can serve as a valuable new outcome measure, ultimately leading to substantially faster, more effective ALS trials requiring fewer patients.