The power of lactate testing
As many of us enter the offseason now is a good time to look back at how the season panned out, what went well and what could you have gone or been done better, particularly in the context of any goals that you set yourself.
It’s also a good time to think about how you can better define your training going forwards to ensure you maximise your available time, one way of achieving this is through understanding your lactate profile.
Similar to both heart rate and power, the use of lactate testing allows you to understand what is going on in the body from a metabolic perspective, in simple terms this metabolic biomarker helps us get some insight into what proportion of fuels (Fat & Carbs) are being used at a given intensity.
In the same way that heart rate is useful to understand how hard the cardiovascular system is working and power is useful to know what your output is and how that is evolving over time relative to say heart rate and time generally - the power duration curve.
Lactate testing provides further useful insight into how your body is reacting to the loads being placed on it during a given effort. Increased lactate levels were often confused with the term lactic acid which was originally thought of as a byproduct of exercise that led to that burning sensation in the muscles and then ultimately fatigue.
Not to get too technical it is a byproduct of utilising carbohydrates (glycogen) during exercise but this isn’t what causes the muscle fatigue sensations, it is actually a fuel source that is consumed by various parts of the body, such as the brain, heart and vital organs as well as the muscles themselves through a process known as the krebs cycle.
In simple terms lactate will or should be stable at rest and also during very easy walking, running or cycling. As the speed or intensity increases so will the production of lactate. The increase in lactate during exercise is in response to the shift from being primarily aerobic – utilizing mainly fats to becoming more anaerobic which utilizes glycogen without the need for oxygen. Knowing the point at which we start to see these increases in lactate is how we can then better define our training so we are working at the right intensity levels during a particular training session.
Chances are during your longer endurance rides you’re often riding too hard for extended periods of time which then has a subsequent knock on effect on recovery and then your ability to complete harder interval session in the days ahead. Similarly you might be riding too easy too often and not stressing your slow twitch fibers enough to get the maximum training response.
So how do you find those key lactate thresholds or turn points.
The testing protocol seems to vary quite a bit, having had testing done myself in a lab for both lactate and Vo2 max and then subsequently from my own research I can say that the intervals need to be of sufficient length in order to get a reliable data set. Unlike power which is instant, we know that heart rate takes time to catch up as there is a delay. Similarly lactate has an even slower response time than heart rate so the minimum accepted interval length seems to be around 4-5 mins. Anything less than this is going to give misleading data. The same goes for the increase in intensity for each step, this needs to be gradual so as not to miss the critical changes in lactate levels.
What we are aiming to obtain from the testing is where the significant changes in the lactate profile occur relative to heart rate, power and also your own RPE (rate of perceived exertion). From this we can then plot a graph similar to that shown which indicates the key turn points LT1 and LT2.
LT1 is considered the first significant increase in lactate compared to resting levels and indicates the point at which lactate is starting to rise, it’s at this point that we would then look at your HR and Power to get a sense of where your longer aerobic sessions should be targeted. LT2 is the point at which blood lactate is now beginning to accumulate faster than it can be cleared and with it other metabolites which cause that burning sensation in the legs, this is often referred to as your anaerobic threshold or in power terms FTP.
Looking at the example I would say this athlete would be looking to ensure the longer rides which we want to keep relatively easy should be aiming for a 114-126 heart rate for the majority of the ride. At this intensity lactate is likely to remain low and from a metabolic perspective it’s primarily fat being used by the slow twitch muscles. I wouldn’t focus on power during these rides, that would be something to look at after each ride and then track over time.
At the upper end I’d suggest any threshold sessions are kept between 220-240 watts and I’d use heart rate as the limiter, if they start going much above 155 then they will likely be working too hard and the session becomes too anaerobic and in all likelihood they might struggle to complete the session adequately. Or if they do complete the session the recovery period in the days after will likely be extended and then potentially compromise future sessions.
Over time by training in this controlled manner will ensure that you maximise the balance between stress response and fatigue management / recovery. The key word here is control.
Also by narrowing the focus of your training in these lower zones has a number of potential benefits, namely that you become more efficient at preserving glycogen as you begin to produce more power at those LT1 levels.
In an ideal world, in the same way you get to see your HR track it would be great to see how your lactate levels are moving during a session. Unfortunately these constant lactate monitors are not widely available so stand alone one off test is the next best thing. You can then periodically have follow up tests to see how your levels are changing, ideally you want that lactate curve shifting to the right so that you are producing more power at the same or lower lactate levels.
If this is something you think might be of interest to you I’m now able to offer a lactate testing service please get in touch to find out more.
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