Least useful for a 800-m run in a competitive event would be

800-m run would be over in about 2 min, and it would need a quick burst of activity of the muscle rather than a slow and sustained activity for prolonged periods. Option A: Oxidative phosphorylation generates ATPs in a slow and sustained manner for a low-intensity muscular activity that continues for prolonged periods (e.g., marathon). It will be the least useful of the energy systems for a sho-time event like 800-m run. Option C: LOHMANN REACTION: CREATINE PHOSPHATE - ADP - ATP - UTILIZED For such sho-duration intense muscular activity, pale fibers are more useful as they generate quick ATPs anaerobic glycolysis, using muscle glycogen as the source. Thus, options B and D are useful.