Ans. is 'a' i.e., Glycogen Source of energy for muscular activityo The immediate source of energy for all muscle contraction is ATP, followed immediately by creatine phosphate.o In stemous exercise ATP store is sufficient only for 1-2 seconds and creatine phosphate for another 5-7 seconds.o Thus, energy rich phosphagen stores (ATP and creatine phosphate) permit severe muscle contraction for 8-10 seconds only.o After this, energy is obtained from the metabolism of stored glycogen or from circulating glucose and free fatty- acids, depending upon the availability of oxygen.o Energy source during in exercise can be summarized by : -Short burst of intense activity (e.g., 100 meter sprint or weight lifting) : - All energy comes from ATP and creatine phosphate. Breakdow n of these compound is an anaerobic processes. Little longer intense exercise (e.g., 200 meter sprint or 100 meter swim)Besides ATP and creatine phosphate, glycogen is metabolised by anerobic glycolytic pathways to provide a ready source of energy. So, muscle work is anaerobic.Longer duration exercise (e.g., jogging, marathon run) : - The muscle work is aerobic and energy comes from aerobic utilization of glucose and free fatty acids. More glucose is utilized at the initial stage, but as the exercise is prolonged, free fatty acids become the predominant fuel. Immediate energy systemAnerobic glycolytic systemOxidative (aerobic) systemSubstratesATP, creatine phosphateGlucose or glycogenGlucose or glycogen, fatty acidsEnergy' productionVery fastFastSlowrPeak at0-30 sec.20-180 sec.>3 minLimiting factorDepletion of CrP. ATPLactic acid accumulationGlycogen depletionActivity examplePowerlifting & weight lifting, short sprintsJumping, throwingLonger sprintsMiddle distance team sportsBall games (Soccer, rugby)Endurance eventsTeam sportsBall games (Soccer, field hockey)