LACTATE LOCKUP

Amy Mason BSc Sports Science & Physiology

Unisports Centre for Sports Performance Tel 09 521 1210

 

We have all experienced it no matter what our ability. The agonizing feeling that engulfs our legs when we cross our anaerobic/lactate threshold. It feels as though every muscle fibre is being marinated in a bath of hot chilly sauce and there is only one way to alleviate the pain - decrease intensity. And this means one thing: slowing down. This month we are going to introduce the science behind lactate threshold and how you can apply it to training and ultimately improve performance (just to clarify; lactate threshold in this article is the same as anaerobic threshold).

 

Energy (ATP) is essential for muscle contraction, and can be produced via aerobic or anaerobic pathways. One anaerobic pathway provides energy quickly but produces lactate as a by-product. Lactate carries an associated hydrogen ion that decreases muscle pH (acidosis) and inhibits muscle contraction. Therefore it is not the lactate that is detrimental to performance, but the combined production of hydrogen ions.

 

We all produce lactate. At rest or when generally moving about the level of lactate per litre of blood typically ranges from 0.5 to 1.8 mmol.  As we perform more work we produce more lactate, and at maximum generally produce greater than 10 mmol.L-1. However, it is not a straight forward relationship of increasing intensity equals increased lactate. It meanders along at similar levels with an increase in intensity and then all of a sudden shoots up (figure 1), and the point at which it does so is termed lactate threshold. The absolute values produced generally depend on muscle fibre composition. For example track sprinters who have high proportions of fast twitch muscle fibres can produce up to 20 mmol.L-1 in comparison to a slow twitch fibre roadie who would typically max out around the 10 mmol.L-1.  

 

 

Figure 1 – Increase in blood lactate levels with increasing cycling power output.

 

So what does this all mean? At a specific intensity individual to each and every one of us, we will start to accumulate more lactate than we can remove and gradually the by-products of producing this will inhibit muscle contraction, and slow us down. For example, if we have two elite male cyclists with a VO2max of 70 mL.kg-1.min-1, and the same peak power output of 500 watts.  Rider 1’s lactate threshold occurs at 300 watts (60% of peak power output) and rider two’s occurs at 400 watts (80% of peak power output). Who would win a time trial and have the highest chance or winning a road race? Rider 2 because they will be able to sustain a higher power output/speed during the time trial and spend a lesser amount of time above lactate threshold in a road race. Therefore training should be directed towards maximizing the power output (intensity) at which this occurs, and move the lactate curve to the right (figure 2). This means we can ride faster for the same or lower heart rates and blood lactates before our threshold occurs.

 

 

Figure 2 – Rightward shift in the lactate curve with training.  Lactate threshold now occurs at higher power outputs indicating increased sustainable power output.

 

 

How do you determine Lactate threshold?

 

The most accurate way to determine lactate threshold is to have it tested in a sports science laboratory. This involves what is called a “step protocol” where you have to ride at a steady state for multiple stages of ~4+ minutes and a small drop of blood is taken from your fingertip (pictured). The test usually lasts 6 to 9 stages to allow for accurate determination of blood lactate threshold. Heart rate is taken at each stage and this allows heart rate training zones to be applied to training with respect to changes in blood lactate levels. The test commonly costs around $100-200. In the olden days, lactate threshold was estimated using deflection in heart rate to a graded exercise test (the Conconi method). However, this was based on runners, not cyclists and has been shown to inaccurately determine lactate threshold. Along with this only a small percentage of the population exhibit the deflection so beware if anyone tries to test your threshold using this method. Most people show a linear increase in heart rate with increased cycling intensity, as shown in figure 3. Another useful aspect of this test is the determination of aerobic threshold. This is the minimum intensity you should train at to acquire a training effect and any aerobic training below it is effectively a waste of time. In heart rate literature this is typically “65-75% of maximum heart rate” or “when you get up a slight puff and start to sweat.”  However, blood lactate sampling commonly reveals aerobic threshold is typically lower or higher than this, consequently using this estimation, many of us are training too slow or too hard.

 

 

Figure 3 – An example of a blood lactate curve in comparison to heart rate with increasing power output.  Aerobic threshold occurs with a slight increase in blood lactate levels, while lactate threshold occurs with a large jump in blood lactate levels

 

How often should you have it tested?

 

This depends on the type of training you are doing. If you are tested and then do not change your training, then chances are nothing has changed and it is not worth re-testing. However, if you have specifically targeted certain facets of your physiology in training to improve performance, then the minimum time period would be 4 weeks. Ideally throughout the year every 3 months is a good guide to ensure your training is on track for continual improvements.

 

Training to Improve Aerobic and Lactate Threshold

 

The simplest way to improve aerobic and lactate thresholds is to train above them. This requires putting in a little extra effort to push aerobic threshold up. However, training lactate threshold is slightly different. Lactate threshold is essentially our maximum steady state race pace, therefore to push it up we need to train slightly below, on and above it. Long intervals slightly below lactate threshold are useful and can be performed for up to 40 minutes. However intervals on and above lactate threshold should be shorter in duration (<10minutes). This is because you will be producing a large amount of lactate, inhibiting your ability to maintain the same pace. If you carry on training for long durations above threshold while producing high levels of lactate, you are effectively training your body to race slow. Instead you need to keep the intervals short, sharp and at a good pace to not only improve lactate kinetics but also improve race pace.

 

 

References:

 

Astrand, P.O., & Rodahl, K.  (1970).  Textbook of Work Physiology.  McGraw-Hill , New York .

 

Frossard, R.  (1991).  The Use of Lactate Readings in Exercise Prescription.  Bioenergetics, D1-7.

 

Robergs, R.A., & Roberts, S.O.  (1996).  Exercise Physiology: Exercise, Performance and Clinical Applications.  Mosby Inc, St Louis .

 

Weltman, A.  (1995).  The Blood Lactate Response to Exercise.  Monograph 4, Human Kinetics.