Hello. i am a 26 years old male, have problems with really dark brown urine when i am very active, and my stool is thin and yellow and small. i am als?

Please see a doctor: This is not ALS, but dark urine is a symptom with a wide differential ranging from post-traumatic over-exertion hematuria to issues with kidney (IgG nephropathy) to muscle problems from either an inborn error of metabolism (metabolic myopathies) or mitachondrial disease. You could go into kidney failure with some of these conditions. Please see your doctor for further evaluation.