- Training
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When you train intensively, the muscles you’ve worked may feel sore in the days that follow, and you might think that lactic acid – which builds up in the blood after a very intense workout – is to blame. But this is not correct. Let’s look at what lactic acid is and when it is produced.
Lactic acid is a by-product of anaerobic lactic metabolism which causes muscle fatigue, as its molecular structure leads to a drop in blood pH and thus creates a purely acidic environment that prevents further activity. In this article, we’ll debunk the myth that lactic acid is responsible for DOMS, or delayed-onset muscle soreness.
How is lactic acid formed?
The energy used to enable muscle contraction comes from a molecule called ATP. To have energy available, muscle cells must continuously produce ATP, and they do so by using three energy systems:
- aerobic system
- lactic anaerobic system
- alactic anaerobic system
When intense exercise lasts for more than 10 seconds, the alactic anaerobic system is no longer sufficient to produce energy (phosphate reserves are depleted), which is why the lactic anaerobic system takes over. In order to produce energy in the absence of oxygen, through a series of processes that take place during glycolysis, it converts pyruvate into lactic acid. If we also take the initial phase into account, this system reaches its peak – that is, maximum lactic acid production – approximately 30 to 40 seconds after the start of the activity. Prolonged exertion, however, requires a reduction in exercise intensity or a halt to the activity. The anaerobic lactic system is the energy system used in activities that require strength and endurance for around one minute.
For example, during a bench press, the anaerobic lactic system kicks in when there is insufficient oxygen to produce ATP via the aerobic system. It becomes active after 7 to 8 seconds of intense physical exercise. Its build-up in the muscles and blood causes acidosis, which prevents the bench press from being continued due to the onset of physical fatigue.
The ability to sustain this system depends on the amount of lactic acid the muscle can tolerate, and this tolerance threshold can only be improved through training and, to some extent, with certain dietary supplements, such as creatine, which have a buffering effect.
In a muscle under strain, the production of lactic acid is particularly evident in white or fast-twitch fibres, i.e. the fibres that work in the absence of oxygen and have a reduced content of haemoglobin and mitochondria.
But if lactic acid is produced during training, what causes the soreness felt for a few days afterwards?
The soreness felt after an intense workout is not caused by a build-up of lactic acid, as this is completely cleared within 2 to 3 hours of the workout, unlike the peak of delayed onset muscle soreness (DOMS), which occurs 24 to 48 hours after the workout. There is therefore no correlation between lactic acid and muscle soreness.
DOMS is in fact caused by damage resulting from muscle contractions, as well as by microtrauma that is perceived as pain.
The significance of lactic acid
This naturally raises the question: is the production of lactic acid important or not?
It should be noted that lactic acid should not be regarded as a harmful substance, as it contains energy that is captured and utilised by various organs, particularly the liver – where it is converted into glucose via the Cori cycle – and the heart, which uses it for energy. Furthermore, it strongly stimulates the secretion of anabolic hormones such as GH and testosterone, which is why high-intensity weight training is recommended for increasing muscle hypertrophy. As well as the Cori cycle, there are other buffering systems that prevent the build-up of lactic acid in the muscles and enable intense exertion to be sustained for longer: the most common of these are carbon dioxide and bicarbonate.
Notes
When a blood chemistry test is carried out after or in the days following a training session, it may be observed that post-exercise muscle inflammation can affect CPK levels, which may then be higher. Creatine phosphokinase (CPK) is an enzyme found in muscle tissue, cardiac fibres, the brain and the lungs. It is therefore advisable to carry out routine blood tests after at least 5 days of physical rest.
