AQA A-Level PE Energy Systems Practice Exam

The key idea is that OBLA (the onset of blood lactate accumulation) happens when lactate production outpaces its removal. When the body relies mainly on carbohydrate metabolism, glycolysis runs at a high rate to supply quick energy. If mitochondria can’t oxidize all the pyruvate fast enough, much of it is converted to lactate, and lactate builds up in the blood. A respiratory exchange ratio around 1.0 signals this high carbohydrate, glycolytic state, so lactate production is elevated and OBLA is more likely to occur earlier or at a lower work rate. Higher exercise intensity does push lactate up, but the specific driver here is the substrate use indicated by RER. Slow-twitch fibers are more oxidative and help clear lactate, so their predominance would delay OBLA. Faster lactate removal would also delay OBLA, not increase it.