1.8

• Lactate metabolism

  During vigorous exercise, the muscle cells do not get sufficient oxygen to support the electron transport chain. Under these conditions, pyruvate is converted to lactate. This conversion involves the transfer of hydrogen from the NADH produced during glycolysis to pyruvate in order to produce lactate. This regenerates the NAD needed to maintain ATP production through glycolysis. Lactate accumulates and muscle fatigue occurs. The oxygen debt is repaid when exercise is complete. This allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver.
• NAD must be present to enable glycolysis to continue to produce more ATP
• Pyruvate conversion

  1. Aerobic - Oxygen present, Acetyl

  2. Fermentation - Insufficient Oxygen present, Lactate
• Slow twitch muscle fibres

  Contract relatively slowly, but can sustain contractions for longer. Useful for endurance activities. Rely on aerobic respiration to generate ATP and have many mitochondria, a large blood supply, and a high concentration of the oxygen-storing protein myoglobin. The major storage fuel is fats.
• Fast twitch muscle fibres

  Contract relatively quickly, over short periods. Useful for activities such as sprinting or weightlifting. Can generate ATP through glycolysis only and have fewer mitochondria, a lower blood supply compared to slow-twitch muscle fibres. The major storage fuel is glycogen.
• Most human muscle tissue contains a mixture of both slow and fast twitch muscle fibres
• Athletes show distinct patterns of muscle fibres that reflect their sporting activities