Lactate Threshold: Muscular or Cardiovascular Phenomenon?
We answer a lot of questions for athletes (you can ask yours here) and share some of the more notable ones on the Train Right Blog to provide the answers to more athletes. Recently we received the question below about the relationship between heart rate and power output.
Question:
So I have been in a debate with a friend about the use of heart rate vs. power in training. He says that power will be power regardless of how your body is acting physiologically that day. I don’t dispute that, but what I say is that why, if you are having one of those days when your HR is elevated, would you want to train using only power and possibly exceed a HR zone? Say, for example, you want to sit just under LT. If you used only power and were having an elevated HR day, would you potentially be unknowingly riding in an anaerobic state, thus diminishing the training benefit of the day? Said otherwise, could you be in an aerobic power state but an anaerobic HR state?
So the question that I have is: Does HR really drive the difference between aerobic and anaerobic that closely? If so, it seems like using power blind of HR could be detrimental. And if that is true, that HR is the one that fluctuates, if you had to use one wouldn’t it be more prudent to use HR as the measure of what your body is capable of that day, and train to it? – John M.
Answer:
John,
It’s a good debate, and we like how you’re approaching it. The idea that power today is power tomorrow is correct, but you’re also correct in that power needs to be considered in context with both heart rate and perceived exertion. Where we need to clarify is the idea of HR driving the difference between aerobic and anaerobic efforts. Lactate threshold happens at the muscle level, not the cardiovascular level. It is often observed at the cardiovascular level because we know there is a cardiovascular response (increased blood lactate levels) to an athlete reaching lactate threshold at the muscular level. That’s why we say that power is a direct measure of the work being done, and heart rate is the observed response to that work. You reach lactate threshold when the mitochondria in your muscle cells have to use a metabolic shortcut to partially break down carbohydrate rather than breaking it down completely. The partially metabolized carbohydrate (lactate) will be reintegrated into normal aerobic metabolism once your intensity drops a bit and your demand for energy slows. Then it’s processed through the mitochondria and completely broken down.
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We associate a heart rate with this threshold point because there’s a good correlation between an athlete’s heart rate intensity and the point at which we see elevated lactate in the blood. However, as you’ve noted, many factors can influence heart rate. If you’re fatigued, dehydrated, overheated, or excited, heart rate response to exercise at a given power output will fluctuate. The question, though, is: does heart rate matters if power output is known?
Power is the primary number you should use for guiding your training intensities, but heart rate provides important context. Let’s say you have SteadyState intervals today and tomorrow. Today you go out and nail the power numbers and the heart rate numbers are where you expect them to be. Tomorrow you go out and do the same exact interval set, and you can achieve the power numbers but your heart rate is suppressed (about 5beats) and your perceived exertion is higher. We would look at that and say you’re most likely a little fatigued. You’d expect to see the perceived exertion be elevated on the second day, but the heart rate and power output should stay pretty consistent from the first to second day. Nevertheless, the workout was still good and effective. On the plus side you’re showing signs of stressing the system. On the cautious side, it probably means a third day of SteadyState intervals probably wouldn’t be a good idea. Another sign of fatigue would be an elevated heart rate and an inability to reach the desired power output.
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Comments 17
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Sherrill are you referring to the question Robbie Ray asked … my answer to RR is that muscle fatigue on the second day of intervals prevents you from being able to push hard enough to be able to get your HR up… leave a day in between and the muscles have recovered and then you can get the HR up…. this is a function of age and probably does not apply to the under 40 crowd
I am 66 and elite level for my age. One cannot over estimate the power of rest. I raced last Sunday, finished a very close 2nd, did an extra lap in prep for a longer race coming up and finished with a TSS if 258. It took me to Thursday to fully recover. Getting the balance right between intensity and endurance is very difficult as we get older. Everyone is different as well.
Useful info, to be sure, but did not seem to answer the question. John asked about elevated, not suppressed, HR. Other CTS literature correctly emphasizes that elevated resting HR can be a symptom of overtraining, which could be exacerbated by blindly forging ahead with the usual power-based intervals. I have been in that situation myself and have learned to read “professional” advice very carefully.
I started cycling about 20 years ago and about 2 years ago I quit smoking and drinking (better late than never) and started to take it a bit more seriously. I am now 73 and I bought a Wahoo Kickr one year ago. Using the Kickr I established my FTP at 237 on TrainerRoad and started doing workouts and a training plan based on that FTP. I found some hard and some very hard, but looking at others doing the same workouts I was better than most regarding completion and having to lower intensity. I have not tested my FTP since, but I am a better cyclist on the road. Quite simply I can hit my targets better if I rest properly for a few days, but I like to do a bit most days. My resting HR Is close to 50 most mornings
I am 71 and find that consecutive days of high intensity intervals are not good for me. I like to do these intervals about twice a week with fast paced group rides about 2days a week. I have a friend who rides hard a lot and can’t understand why he loses energy and can’t stay with me. I convinced him to cut back and when he did his performance improved. At my age going hard too often is detrimental to any gains I hope to attain. Also, I do some easy rides with my wife on non hard effort days and that works for me.
Interesting comment Ray. I’m 72, this year riding around 200 kms a week with around 4,000 metres of climbing. Just a recreational rider, don’t do any structured training, though the hills where I live impose some kind of structure. Last year I was riding closer to 300 kms pw, and watching myself get slower, extremely frustrating. The decline seems to have leveled off, but it’s hard to tell. But I certainly feel like I need a 2 or 4 days to recover after a hard ride.
I don’t think there are improvements in the pipeline – so just appreciate what is, I guess..
Also don’t forget, The really important side of the cardiovascular equation is cardiac output. It is comprised of HR x SV (Stroke Volume). You can have the same CO over a range of HR values depending on what volume of blood is ejected with each beat. Don’t get too caught up in the HR value as an absolute number.
Would seem that HR would be elevated on that second day of intervals rather than suppressed: Heart working harder to maintain 02 levels at the given power. Obviously, I am wrong. Why?
Would you say that weight training is important for muscular endurance?
I’m considering starting a weight training protocol during my off season
Hi … I find your articles most interesting and informative however being older (almost 65) I find there is very little SPECIFIC information available for older “Hard Core cyclists”.. I measure both power and HR and can go hard and stick with the younger guys (mostly in the draft) on the Saturday 100k ride with normalized power around 225 with 1- 3 min short hills or sprints around 300-350W BUT the next day my HR is 20 BPM lower and hard to hold 200W … maybe most guys have quit by the time they are 65 but hard to find any specifics as to how much to rest and how much to push.
Well I an 67 and feel like I am experiencing the same set of facts/issues. I seem to have peaked my FTP at around 228W. I can’t seem to make gains above this although my endurance certainly has improved. For example, I recently did some 6 minute intervals trying to reach 240W – but can only reach 225 to 234W. I think my problem is the amount of rest after hard intervals and the type (intensity and duration) of intervals I am doing. Or perhaps I am never going to get any better do to my age etc. I have a coach and am using TP but I am not getting good insight/analysis into what is going on. I have always felt there is opportunity for improvement at any age!
Hi DE..
What is ‘TP’?
On your numbers, my understanding is that FTP is the power you can maintain for an hour, and that one way of estimating it is to do a 20′ max effort and subtract 5%. So if your FTP is 228 that would correspond with 240 for 20′, so you certainly should be able to achieve that for 6′. Have I misunderstood?
TP = Training Peaks software. Plus I mistated FTP – it is 217 or 5% below 228.
Any chance to try the BSX insight lactate monitor yet?
http://www.dcrainmaker.com/2014/09/bloodless-lactate-threshold.html