HMS, BM 2021 HSC 4 MC What is the predominant energy system used by an athlete in a 400-metre running event? Aerobic ATP-PC Phosphate Lactic acid Show Answers Only \(D\) Show Worked Solution D is correct: 400m primarily uses lactic acid system for duration. Other Options: A is incorrect: Too short for predominantly aerobic contribution. B is incorrect: ATP-PC depleted after first 10-15 seconds. C is incorrect: Phosphate system same as ATP-PC system.