Lactic Acid and our Muscle
Is lactic acid bad for you?
Lactic acid causes muscle fatigue and the burning sensation when the going gets tough. Right? Wrong. Although it’s seen as the athlete’s enemy, lactic acid – or lactate – isn’t quite the villain it’s been made out to be.
The bad press came from Meyerhoff and Hill’s 1920 study. “They observed an increase in lactate and also observed fatigue, and presumed one caused the other,” says English Institute of Sport senior physiologist Jamie Pringle.
Recent research has shown that rather than causing muscle fatigue, lactic acid is actually a key muscle fuel. “Although people are keen to point the ﬁnger and blame something for fatigue, in reality the main cause of fatigue is the lack of energy and fuel, or speciﬁcally the inability to provide those things at the rate that’s needed to keep up with the muscle contraction,” says Pringle.
In fact, lactate can be oxidised and used to fuel the Krebs Cycle, to release chemical energy, or it can be converted to glycogen in the liver in a process called the Cori Cycle. “When metabolised successfully, the use of lactate as fuel means muscle glycogen stores are actually preserved for longer,” says Pringle. “Muscle lactate concentration does not start to increase until the production rate exceeds the rate of removal.”
This is why working just below this level, known as the lactate turnpoint, can be sustained for so much longer. “This turnpoint, which is around 70-90% of V02 max, is where you have the right balance between lactate production and the rate your muscles can consume it,” says Pringle. “The reason your muscles quickly fatigue above this point is because excess lactate causes your carbohydrate stores to be used up at a much faster rate.”
Lactate threshold: The lactate threshold is a lot lower than most people think, occurring at about 50-70% of V02 max. It marks the ﬁrst increment of lactate concentration in the blood from ‘moderate’ to ‘heavy’.
Lactate turnpoint: The lactate turnpoint happens at 70-90% V02 max and represents a blood lactate concentration shift from ‘heavy’ to ‘severe’. After this point muscles will fatigue signiﬁcantly. “To identify your own lactate turnpoint, perform a time trial of about 60 minutes,” advises Pringle. “As long as you ride at an evenly-paced effort, the average power or heart rate of that will be on or about your lactate turnpoint.”
To increase your lactate turnpoint you should aim to work at the point just below it for three 20- to 30-minute sessions each week. “By doing this you’re pushing the limit up from below,” says Pringle, “and although it’s possible to ‘pull up’ from above by using all-out interval training, this will cause much greater muscle fatigue and will be less effective in the long term.”
Krebs Cycle: This is part of the process of aerobic cell metabolism which can be fuelled by lactate, in which glycogen is broken down to produce the basic muscle energy source adenosine triphosphate (ATP).
Acidosis or ‘The Burn’: ‘The burn’ occurs as a result of a build up of acidity in the blood that causes muscles to contract; severe pain was previously believed to be a result of lactic acid. However, lactic acid immediately splits into lactate and hydrogen in the body and the lactate itself blocks and neutralises the acidic protons in hydrogen, delaying acidosis.