Glycolysis

Glycolysis is the breakdown of carbohydrate, from muscle glycogen or blood glucose, to replenish ATP.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} Its many enzyme-driven steps occur in the sarcoplasm, supplying ATP more slowly than the one-step phosphagen system.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} Its capacity is much larger because glycogen and glucose stores far exceed creatine phosphate stores.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} Glycolysis nets two ATP per molecule of glucose and three from glycogen.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 45.}

The fate of pyruvate, its end product, distinguishes fast from slow glycolysis.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} Under high energy demand, as in resistance training, pyruvate is mostly converted to lactate, allowing faster ATP production for a shorter time.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} When demand is lower and oxygen is available, pyruvate enters the mitochondria for further oxidation.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.} Glycolysis itself doesn’t depend on oxygen, so the NSCA describes the labels “anaerobic glycolysis” and “aerobic glycolysis” as imprecise.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 62.},^{3Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 43.}

In practice

• Carbohydrate is the only macronutrient that can supply energy without oxygen directly involved, making it critical during anaerobic metabolism.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 60.},^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 61.}
• To stress fast glycolysis, the NSCA’s interval table lists efforts of 15 to 30 seconds at 75 to 90% of maximum power, with work-to-rest ratios of 1:3 to 1:5.^{6Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 76.}
• The NSCA’s program design guide reports higher glycolytic enzyme levels after training with bouts of 15 to 30 seconds or longer; one study found changes within two weeks.^{7Hoffman, NSCA’s Guide to Program Design, p. 142.}