The post about Lactate Threshold measuring devices got me thinking about lactate threshold a bit. I thought I would share some info and misconceptions about lactate threshold.
First of all the term lactate threshold is misleading. There really is no "threshold per se." What we define as lactate threshold is the point at which lactic acid begins to rise rapidly in the blood. It is really the point at which production of lactate exceeds the body's ability to clear it. Think about it this way. Lets say we were exercising at 150 watts and our body was producing and clearing 2 units of lactate per minute. We move up to 175 watts and our body is now producing 3 units of lactate but clearing only 2.5 units per minute. Lactic acid begins to slowly accumulate in our bloodstream. Now if we go to 200 wats and our body is producing 3.5 units of lactate per minute and our body is still clearing only 2.5 units per minute, the rate of lactic acid accumulation will double over what it was at the 175 watts level, even though production went up only 17%. There wasn't a sudden global shift towards anaerobic metabolism. There was simply a slight increase in lactate production that outstripped the body's ability to clear it.
Lactic acid is consumed by slow twitch muscles during exercise, regardless of the exercise intensity. Lactic acid levels reflect the balance between this consumption and production. Fast twitch muscles always produce lactic acid, regardless of oxygen availability. This is because fast twitch muscles have tons of lactate dehydrogenase, the enzyme that produces lactic acid. When you get the substrates and enzymes in close proximity, you get the product, in this case lactic acid. Therefore, the production of lactic acid is a result of recruiting fast twitch muscle fibers, not the result of not having enough oxygen available.
Through training you can increase your % of slow twitch fibers. As a result, you do not begin to recurit the large, fast twitch motor units until a higher intensity. That is why your LT increases with training. That and the fact that your aerobic fibers get more aerobic and better at consuming lactate.
People tend to think of LT globally. The real action is inside of the muscle cell. When you recruit fast twitch muscles, they produce lactate. When you recruit slow twitch muscles, they metabolize aerobically and consume lactate. That's where it all happens. There is no general shift from aerobic to anaerobic metabolism that suddenly occurs. It's all about muscle recuritment and muscle fiber type.
Just my $.02 from my grad. student days studying muscle physiology
Mike P.
Simplify, Train, Live
First of all the term lactate threshold is misleading. There really is no "threshold per se." What we define as lactate threshold is the point at which lactic acid begins to rise rapidly in the blood. It is really the point at which production of lactate exceeds the body's ability to clear it. Think about it this way. Lets say we were exercising at 150 watts and our body was producing and clearing 2 units of lactate per minute. We move up to 175 watts and our body is now producing 3 units of lactate but clearing only 2.5 units per minute. Lactic acid begins to slowly accumulate in our bloodstream. Now if we go to 200 wats and our body is producing 3.5 units of lactate per minute and our body is still clearing only 2.5 units per minute, the rate of lactic acid accumulation will double over what it was at the 175 watts level, even though production went up only 17%. There wasn't a sudden global shift towards anaerobic metabolism. There was simply a slight increase in lactate production that outstripped the body's ability to clear it.
Lactic acid is consumed by slow twitch muscles during exercise, regardless of the exercise intensity. Lactic acid levels reflect the balance between this consumption and production. Fast twitch muscles always produce lactic acid, regardless of oxygen availability. This is because fast twitch muscles have tons of lactate dehydrogenase, the enzyme that produces lactic acid. When you get the substrates and enzymes in close proximity, you get the product, in this case lactic acid. Therefore, the production of lactic acid is a result of recruiting fast twitch muscle fibers, not the result of not having enough oxygen available.
Through training you can increase your % of slow twitch fibers. As a result, you do not begin to recurit the large, fast twitch motor units until a higher intensity. That is why your LT increases with training. That and the fact that your aerobic fibers get more aerobic and better at consuming lactate.
People tend to think of LT globally. The real action is inside of the muscle cell. When you recruit fast twitch muscles, they produce lactate. When you recruit slow twitch muscles, they metabolize aerobically and consume lactate. That's where it all happens. There is no general shift from aerobic to anaerobic metabolism that suddenly occurs. It's all about muscle recuritment and muscle fiber type.
Just my $.02 from my grad. student days studying muscle physiology
Mike P.
Simplify, Train, Live