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
• 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.

Types of skeletal muscle fibres

• Slow twitch muscle fibres contract relatively slowly, but can sustain contractions for longer.
• They are useful for endurance activities such as long distance running, cycling or cross-country skiing.
• Slow twitch muscle fibres 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 of slow twitch muscle fibres is fats.
• Fast twitch muscle fibres contract relatively quickly, over short periods.
• They are useful for activities such as sprinting or weightlifting.
• Fast twitch muscle fibres can generate ATP through glycolysis only and have fewer mitochondria and a lower blood supply compared to slow twitch muscle fibres.
• The major storage fuel of fast twitch muscle fibres 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.