Hearing the term blood lactate, or as it’s more commonly known, lactic acid, sends shivers down the spine of any athlete. For years it has been portrayed as the stuff of nightmares and depending on how apparently sadistic you are, you either avoid it like the plague or embrace it as an unconquerable challenge just so that you can “feel the burn”. However, as always, science has come to our rescue and has started to dispel the myths surrounding lactic acid.
So what actually is lactic acid? Technically, blood lactate and lactic acid are two different things. Blood lactate is a by-product of exercise metabolism. However, when lactate disappearance equals lactate production, blood lactate should not rise at all and you should not feel any sensation from this (Mann, 2016). Lactate is used in a number of ways by our bodies during exercise.
Firstly, lactate is oxidised and is converted into pyruvate and used as a substrate for aerobic respiration. For the endurance athletes out there, as long as exercise intensity (explained below) and blood lactate are monitored, this should be music to your ears. Secondly, under aerobic conditions, meaning that oxygen is present, lactate can be converted into muscle and liver glycogen (how our body stores glucose) and amino acids (the building blocks of our cells and muscle tissue). You’re probably thinking now, well what’s all the fuss about? This lactate stuff is brilliant!
Aerobic exercise uses oxygen to enable the athlete to perform whatever exercise they’re doing for a prolonged period of time depending on glycogen availability, hydration levels, endurance capacity and various other things. The presence of oxygen allows any blood lactate to be oxidised and the relatively low exercise intensity allows our body to remove lactate as it’s produced. However, when our exercise intensity increases, we start to work on ~50-75% of our aerobic capacity, thus, lactate production surpasses lactate oxidation or removal. This is where you need to worry.
The relative low tissue oxygen, our reliance on glycolysis (providing our muscles with energy without oxygen), activation of our fast twitch muscle fibres and reduced lactate removal are all factors that will lead to the classic painful experience of lactic acid.
So lactic acid is building, what now? Well, if you continue to increase your exercise intensity or remain training at the intensity at which you can no longer get rid of lactate at the same rate you are producing it, hydrogen ions and lactic acid will start to build up. Our bodies are absolutely majestic but incredibly sensitive and have a very specific range in which they can carry out metabolic processes.
At rest, our blood pH is ~7.2-7.5, so slightly above neutral. The same pH you’d expect from a bottle of mineral water. This allows the enzymes involved in respiration to work optimally so that your body can support whatever activity it is that you’re doing. As the hydrogen ions and lactic acid start to build, the pH of your blood starts to decrease and becomes slightly acidic at ~6.8. Your body can no longer work in these conditions and your exercise intensity will drop and you’ll start to feel that infamous “burn” (McArdle, Katch & Katch, 2010).
So, if you’re training in a gym where your coach has prescribed an absolute smash of a session and then proceeds to shout at you for not putting any effort in when you need to take a rest, find a new gym. You’re physiologically incapable of continuing until you have shuttled the hydrogen ions and lactic away and restored a more optimal pH for respiration to occur. Unfortunately, mind over matter won’t work. Nature always wins, always.
However, there are benefits of training at an intensity just shy of your lactate threshold at a stage called lactate turn point and aerobic training below any intensity that induces a build-up of lactate. Your ability to produce, dispose of and clear blood lactate increases (Messonnier, Emhoff, Fattor, Horning, Carlson & Brooks, 2013). Interval training at a high intensity can also increase both submaximal and maximal performance measures (Seiler, Joranson, Olesen & Hetlelid, 2011) and increase mitochondrial density within the muscle, meaning you have more power stations in your muscle to further enhance your performance (Neal et al, 2012).