Amyotrophic lateral sclerosis is a progressive neurodegenerative disorder selectively affecting motor neurons, resulting in progressive weakness. Currently there is no known cure and a specific cause has not been identified. Creatine is a nutritional supplement that improves mitochondrial function and has been shown to protect motor neurons in animal models of ALS. Preliminary research indicates that creatine may also improve strength in patients with ALS. This study will determine the effect of creatine treatment on short-term muscle strength and long-term muscle deterioration in patients with ALS.