Everything you need to know about lactate: your burning questions answered by an exercise physiologist

Lactate is produced during exercise when the body breaks down carbohydrates. It is now known that lactate is not a waste product but an energy source – it can be ‘recycled’ back into pyruvate for energy. Public perception is yet to catch up with the science: lactate is still widely accused of causing fatigue and soreness.  

Though increased fatigue and soreness is associated with high lactate values measured in the blood, this is not a causal link – lactate is not solely to blame. Exactly what causes the burning sensation in fatiguing muscles is unknown. 

Dr Richard Ferguson told us: “Lactate used to be considered a waste product of metabolism and a major player in the fatigue process during high-intensity exercise. However, this is no longer the case. Indeed, lactate is now seen to be a critical metabolite that has an important role as a fuel source, even playing a part in the cell signalling and adaptive process, and critically, has no role in fatigue.” 

So lactate is not causing the burning feeling in your legs – but that doesn’t stop WorldTour pros. Even in this year’s Tour de France, Wout van Aert commented in post-stage interviews that he could “feel the lactate in the legs”. In fact, this feeling is not caused by lactate. 

Lactate values, measured at various intensities, indicate the metabolic stress your body is under – even if lactate is not the cause of the fatigue. At altitude, lactate values will be higher than at the same power at sea level. The ability of a lactate measurement to reflect ‘stress’ in a different way to power, heart rate and perceived effort is the reason for its usefulness. Lactate gauges the metabolic stress of the exercise being undertaken and therefore also the metabolic efficiency of the athlete.  

No, though it was previously believed that far more lactate was produced during ‘anaerobic’ (without oxygen) processes. Dr Ferguson explained: “Lactate production occurs continuously under fully aerobic [low-intensity] conditions, and not as traditionally thought only under anaerobic conditions. Indeed, skeletal muscle is never really anaerobic, even during the most strenuous exercise.”  

Lactate can be measured with a small hand-held device, such as the Lactate Plus, which uses a pin prick of blood and a paper strip. Establishing your personal lactate curve is a great way to set training zones. Power is increased and lactate measured every four to 10 minutes. Blood lactate values (in mmol/L) are plotted against power and heart rate to create the curve. Sport scientists regard measuring lactate during a ramp test as the ‘gold standard’ for setting cycling training zones. 

Once you have three data points (power, heart rate and lactate), you have a much fuller metabolic picture, compared to using power and heart rate only. As amateurs, we don’t really need to train with lactate, but it does help us control intensity more precisely.

The Cori cycle, also known as the lactic acid cycle, is a staple for biology students. Muscles break down glucose via glycolysis into ATP and pyruvate. The ATP is used for energy, and the pyruvate is turned into lactate. 

Dr Ferguson explained: “Most of the lactate produced, 75- 80 per cent, is readily transported out of muscle cells and shuttled to adjacent muscle cells or around the body via the bloodstream. This circulating lactate is taken up by other muscles and organs, where it is converted back to pyruvate and used for aerobic energy production. Lactate that makes it to the liver undergoes a process called gluconeogenesis, where it is turned into glucose.” 

We know that lactate doesn’t cause fatigue or pain, but it remains a very important biomarker. An athlete’s lactate curve is a good proxy for mitochondrial function and density without doing further, more invasive, testing. With a simple pin prick blood test, we’re able to ascertain how quickly we’re metabolising glycogen. If pyruvate is not being transported to the mitochondria quickly enough, blood lactate accumulates. As an athlete develops their aerobic ability, their mitochondrial density increases and so lactate can be processed more quickly. This means more energy over any given period of time.  

The two key lactate thresholds are commonly called LT1 and LT2. The first threshold, LT1, is the top of Zone 2 (in the five-zone model). It’s defined as, “the lowest intensity at which there is a sustained increase in blood lactate concentration above resting values.” A male professional cyclist weighing around 70kg is typically able to sustain around 300W at LT1 and can churn out this intensity for upwards of three hours. LT2 is reached at the top of Zone 4 and is often referred to as the lactate turnpoint. This is the point beyond which lactate accumulates rapidly. It roughly corresponds to FTP intensity. LT1 is often referred to as ‘aerobic’ and LT2 as ‘anaerobic’, which is a hangover from earlier, more rudimentary understanding. 

Your personal lactate curve should inform your training, allowing you to focus on specific points on the lactate curve to raise your thresholds. The intensity at which you train determines how the shape of the lactate curve develops. The aim is to produce more power for a given lactate value, to put off the tipping point where lactate begins to accumulate rapidly. By raising your thresholds, you can push more watts while paying less of a metabolic cost. This means a lower impact of punching over climbs, sprinting out of corners or being able to ride at higher power for sustained periods.  

Testing the lactate curve used to be the preserve of professional cyclists, but as more and more sports science labs have begun offering lactate tests, the price has come down. At Southampton Solent University, for example, a lactate test costs around £150. The whole process takes about two hours. Alternatively, you could attempt the DIY option by buying a lactate meter, available from a number of pharmaceutical companies online, and testing yourself – provided you have a smart trainer and a friend to assist.  

Across the board, endurance sports scientists agree that consistently accumulating lots of low-intensity hours – plus a sprinkling of quality sessions during key periods – is the most effective formula. Specifying the exact combination of sessions for optimum results is much more difficult. Many athletes take too shortterm an approach; endurance fitness continues to grow over many years. Even if you have a limited amount of time available, you should still do a large proportion of your riding at lower intensities. This is because, at low intensities, we increase mitochondrial density. As we now know, mitochondria are the cellular ‘energy factories’ that turn glucose into energy. More mitochondria equals higher sustained power. 

It depends. If you’re training heavily with lactate as a guide, you might want to check your thresholds every six to eight weeks as part of your cycling training plan. If you just want to see how your fitness has changed during the course of a larger training cycle, two to four tests a year is sufficient.  

Conventional wisdom suggests using lower-intensity, longer intervals, further out from your first race. As your racing season comes around, use higher-intensity intervals (HIIT workouts). Typically this means doing lots of riding at around LT1 in the base phase, then shifting the focus to 95-105 per cent of LT2 as the season approaches. If you’re training for 10 hours a week, no more than two hours in total per week should be ridden at above LT1.  

Among the supplements for cyclists are lactate buffers, most of which contain relatively large amounts of sodium bicarbonate, which is alkaline – the idea being that it neutralises acidity levels in muscles. Does it stack up? A 2020 study in the Human Kinetics Journal tested the effect of topical (Amp Human PR lotion) sodium bicarbonate on exercise performance, and found no improvement. In fact, no published studies have shown any meaningful effect from this type of product. 

The technology for wearable lactate sensors already exists. Wearables that can measure blood biomarkers in non-invasive ways – patches and watchlike devices – will be available in the coming years. Pin-prick blood lactate testing will soon be a thing of the past, and lactate monitoring will be another string to the bow of the best smartwatches for cycling - but just for now, we'll have to wait.