HMS, BM 2016 HSC 2 MC What is the most likely cause of fatigue in a runner completing a 100 m sprint? Dehydration Accumulation of lactic acid Depletion of muscle glycogen Depletion of phosphate creatine Show Answers Only \(D\) Show Worked Solution D is correct: 100m sprints primarily use ATP-PCr system which fatigues from phosphocreatine depletion. Other Options: A is incorrect: Dehydration unlikely in such short duration activity. B is incorrect: Lactic acid builds up but PCr depletion occurs first. C is incorrect: Glycogen depletion occurs in longer duration activities.