The document describes three fitness tests and related concepts. It provides details on procedures for a phosphate recovery test, 20m shuttle run test, and suicide run test. It also discusses energy systems, fatigue and recovery mechanisms, and acute responses to exercise for each test. The phosphate recovery test relies predominantly on the ATP-PC energy system due to its maximal 7-second sprints. The 20m shuttle run test relies mainly on the aerobic system due to its sub-maximal intensity over 4 minutes. The suicide run test uses the anaerobic glycolysis system due to its maximal 30-45 second sprints.