Cadence, heart rate and power: do I need to do high power intervals at high cadence? and why?

Today I started power build and did Williamson+2. (Williamson +2 consists of 4 sets of 6 descending-duration/ascending-intensity intervals from 115% FTP for 2 minutes to 150% FTP for 30 seconds. Recovery between intervals matches the duration of the preceding interval - work for 2 minutes, rest for 2 minutes).

The instructions (not in session) said do the intervals at 100rpm plus. This is not an issue for me as I am happily doing spin ups at 120-130, and have also played on the track. Also even in TTs I tend to average 92rpm. However higher cadences do affect my heart rate.

In this session for the first two sets spinning at an average of around 100-103rpm, my Hr was hitting over 150 and averaging 141 for an interval. So for sets 3 and 4 I dropped the cadence to average c94/95, with the result was that my Heart Rate was far lower and it was far easier for me to get through the set. My average HR for the latter intervals was 135 and I was peaking at mid 140s.

To my question: I was wondering what value the training effect of completing these Aerobic Capacity intervals at a higher cadence was. I can see it for the final sprint interval of the set. I am still training to produce these power outputs, but not a such a high cadence.

Thoughts please you cadence/power experts.

I suspect that the primary aim of the higher cadence is probably to ensure that the rider taxes the lungs and heart as opposed to the muscles. This would correlate with the changes in HR that you noticed.

In a similar workout i did recently, the in-ride instructions stated that the higher cadence aimed to do what i described above and ensured that the lungs and heart and therefore fat burning side of things was dominating the power production as opposed to the muscles (sugar burning) that will fatigue quicker

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I’ve been experimenting with cadence during the anaerobic TR workout intervals. On ERG mode, the faster you spin, the less the resistance you feel and I find this to be efficient (+100 RPM), but on a 3 min interval I tend to start gassing out and tend to slow down cadence which causes the resistance to increase, sometimes significantly enough to slow me to a crawl. If i can’t get the spinning back, I’m screwed. I guess the idea here is to find a balance of the highest maintainable RPM’s and HR effort. Mashing gets you there, but the resistance can kill your leg muscles depending on the duration of the interval and the recovery time.

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When you are outside and really going for a sprint, any shifting is going to waste time. Also, power is basically the amount of force (torque on pedals) multiplied by velocity (cadence).

If you can put down 100 pounds of force on the pedal, you will generate more power at 120rpm than at 100rpm. Assuming I correctly recall and understand the physics.

In other words, if you are going to train max power output then train it at higher cadences. At the tail end of my 10-week resistance training, I’ve seen my max power output move to higher cadences (roughly 115-125rpm). And when sprinting on the trainer its better to use resistance.

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how do you change the trainer mode from ERG to resistance in the middle of the workout? do you stop and reset? or do you set it up on resistance mode before starting the workout?

If the goal is V02 Max training, maybe you could disregard the power target, and keep the higher gear with the lower cadence, but increase cadence and thus power, which would elevate your heart rate?

I’m mostly training outside, and so when on the trainer I’ve been using resistance mode just to keep everything the same. I’ve got a Kickr direct-drive, and found standard/level mode to be better than resistance.

If you want to switch during a workout, on TR mobile its a hassle and on TR desktop its as easy as tapping the keyboard.

on the desktop app you can simply toggle between ERG/ Resistance/Standard in the middle of a workout using the tab on the bottom of the screen. It usually takes a few seconds to change but is otherwise really straightforward. I do a lot of work in ERG mode but almost always switch to standard mode ahead of any short bursts for more control and a more realistic sensation.

… surely, then, for any given power, (as I am in erg mode and hitting a specific target) if I lower my cadence I am increasing my force… which is no bad thing… and I can always increase my cadence as well if I like at a later stage…

@GYM5825

On a keyboard (PC version) simply press T to swap modes. I suggest however you preset the resistsnce level you want using the arrows. I can’t erecall which do which but I think up/down affect erg mode and left right affect resistance.

Personally with my kickr core I am happy staying in erg mode for shorter intervals.

A higher cadence is less force on the legs but stresses your aerobic system (heart and lungs) hence higher HR

A slower cadence (at the same watts) needs more muscular force but lower aerboic stress hence lower HR

Muscular endurance is a finite resource, but as long as you are fuelled the aerobic system can go for much longer, I think this is why a faster spin is favoured.

However having said that I also mix it up with faster / slower spining, I don’t want to become good a just a high cadece as I’m sure therre will be a time on a ride where I will need to use a low cadence.

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Williamson is a bit of a mystery to me, as I’m only familiar with doing max efforts to increase anaerobic capacity. Here are the goals:

And I did NOT look at the workout notes to see if there was any Coach Chad commentary about reason for higher cadence. In general Coach Chad pushes for higher rpms on a lot of workouts, and sometimes the reasoning is explained during the workout.

If it was me and I wanted an answer, I’d file a support request and ask the TR support team for clarification on difference between doing them at lower cadence versus suggested cadence.

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Thanks, @bbarrera Yes, I had looked at those (as W+2 omits Chad’s helpful voice along the way) but as you say it does not really explain why do them at say 103 vs 95.

Also its the first time I have used “General power build”. Previously I was using “Sustained power build” for my TTing, but decided this year over winter, to do General power build 1/2, then sustained 1/2, to give me a richer base.

I will follow your recommendation, thanks.

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