I think I have a simple question. I’m sure it has a complex answer.
What is the “lay person” definition of metabolic cost?
Context:
I was reading an article recently — and I can no longer find it — about low cadence cycling, and how it (potentially?) had a lower metabolic cost than high cadence cycling.
I am assuming that lower metabolic cost = less recovery time needed (not sure this is correct).
I also think that I think (given identical environmental variables, i.e. I am well rested, well fueled, not stressed, and training at a consistent temperature) that heart rate is a good gauge of metabolic cost. I.E. given the above consistency in environmental variables, a higher HR equals a higher metabolic cost. Is this true? Or could this possibly be true in certain circumstances?
Thus my question is the following … in addition to the questions above:
If it’s (potentially) true that riding for 60 minutes at 250W at a >90 RPM cadence keeps me at a HR of 160 BPM, and riding for 60 minutes at 250W at a <70RPM cadence keeps me at a HR of 150 BPM … does the lower cadence cycling have a lower metabolic cost? And as such, is this training that I could repeat more often because it requires less recovery? And thus in the long term I can train more often at elevated watts because my recovery needs are lower?
TL;DR … what is metabolic cost and is it possible to inform my training with an understanding of it?
To my understanding (very non-scientifically), metabolic cost is the total amount of carbs+fats+whatever else you might be burning to sustain a certain amount of power over a certain amount of time.
For a 60kg climber to sustain 5W/kg will have a lower “metabolic cost” than for a 78kg rouleur to do the same. The latter can’t keep eating enough over a long period of time to be able to maintain that since he’s burning a lot more fuel to do so.
I think lower cadence cycling could lead to a slightly lower metabolic cost since your muscles contract slower and so on, heart rate is lower. But then again the load on your muscles is higher which could cause fatigue and lead to you not being able to maintain the same power at a lower cadence for very long either even though your heart rate and metabolic cost are lower.
Seems like something you shouldn’t target in training. Train yourself to be able to sustain certain power levels at whatever cadence range feels good to you and make sure you learn to ingest enough carbs so that you are able to maintain those efforts and not bonk.
Metabolic “cost” = metabolic rate = rate of energy expenditure = rate of oxidation of carbohydrates, lipids (fats), and protein (the latter almost always representing a minor contribution).
Yes, but no. Not when it comes at the expense of lower cadence. Lower cadence/higher torque recruits more fast-twitch muscle fibers, and those fibers recovers slower than slow-twitch fibers.
Yes, it is true.
Yes, lower metabolic cost. No, you won’t be able to train more. You will in fact need more recovery as it is more taxing on your fast-twitch fibers, and those require more recovery time then slow-twitch fibers.
That article @svens posted was good. The only thing it doesn’t take in account is that people are not built the same.
Your genetics, and training background, is determening factors of what percentage of the different types of muscle fibres you possess. A “fast-twitch” individual might have a different preferred (or most effective) cadence than a “slow-twitch” individual. The first example to come to mind was Alexander Kristoff’s 7km winning solo attack on Scheldeprijs 2022. If you take a look at that attack you will most certainly notice a peculiarly slow cadence compared to what you normally see in a solo attack. He has some fast-twitch fibers to spend compared to the usual solo break winner. As a curiosity, it was his first solo win since Ringerike GP (a UCI cat 1.2 race in Norway) in 2009.
Whether this is true or not is actually equivocal.
Here’s the study normally cited in support of this hypothesis:
However, if you look at the actual data and avoid being sucked in by the somewhat hand-wavy statistics, there really isn’t any difference in the overall pattern of glycogen utilization in the low-cadence and high-cadence conditions.
This outcome may be due to the fact that motor unit recruitment is a function of both force and (intended) velocity, as Henneman himself demonstrated in studying “ramped” vs. “ballistic” contractions.
I’d say that if you are already trained and used to riding below 70 rpms then yes, the cost is lower, but if you are not used to it and it makes your legs sore because of the force and muscle recruitment needed then the cost is higher, at least initially. So you are investing some metabolic cost upfront, for future metabolic savings.
So your assertion/interpretation/understanding of this is that glycogen utilization is the same at low vs high cadence? Thus the metabolic cost is the same?
Not sure if I missed it, but where do you stand on muscle fiber-type recruitment … is low cadence using more fast twitch, in your understanding?
There is a clearly inverted U- or inverted parabolic-shaped relationship between metabolic rate and cadence. IOW, if you pedal too slow or too fast, you will expend more energy and oxidize more fuel (preferentially carbohydrate).
What isn’t really clear, and what I was commenting upon, is what impact cadence has on the pattern of fiber type recruitment. Many people assume that a lower cadence enhanced fast twitch motor unit recruitment, because to generate the same power at a lower cadence requires generating greater force. However, the (intended) speed of movement also plays a role in things, by lowering the degree of central motor drive needed to activate any given motor unit.
Net-net, and looking at the available data, it isn’t clear to me that cadence has any significant influence on how many type II motor units are recruited during cycling.
ETA: Here’s the classic study of the effects of cadence:
