Lactic acid starts to accumulate in the muscles once you start operating above your anaerobic threshold. This is normally somewhere between 85% and 90% of your maximum heart rate (MHR).
If your lactate threshold (LT) is reached at low exercise intensity, it often means that the "oxidative energy systems" in your muscles are not working very well. If they were performing at a high level, they would use oxygen to break lactate down to carbon dioxide and water, preventing lactate from pouring into the blood.
If your LT is low, it may mean that:
- You are not getting enough oxygen inside your muscle cells.
- You do not have adequate concentrations of the enzymes necessary to oxidize pyruvate at high rates.
- You do not have enough mitochondria in your muscle cells.
- Your muscles, heart, and other tissues are not very good at extracting lactate from the blood.