What do you mean by ‘short-term’ here? 5 seconds? 10, 20 etc? And does it matter how far your power fluctuates? It would be good to know if I’m worrying too much about the details of my power fluctuations as I start to take my workouts outside.
The half-life for changes in muscle energy metabolism is about 25 seconds. Thus, fluctuations in power over durations shorter than that have limited influence. In fact, now-classic studies by Birgitta Essen showed that the metabolic (and cardiovascular, etc.) responses to 15 s on/off efforts at 300 W were nearly identical to continuous exercise at 150 W…about the only thing that really differed was the fiber type recruitment pattern.
There are also various studies out there using ‘sinusoidal’ exercise, i.e., continuous cycling with the power varying in a sine-wave fashion, over various periods that lead to a similar conclusion.
Given that it’s hard (impossible, in fact) to vary your power by more than +/- 100% of the average, the studies by Essen et al. also address your second question.
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Back when I had more of a kick, I’ve always wondered if I could ride a short TT as 30/30s or similar. Seems maybe 15/15s would have been the way to go? Never tried it it though…
Don’t ignore this part, WRT to trying to do that for an extended duration and having the same or better performance. Fatigue resistance in certain fibers would matter a whole lot, IME.
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Yep. But for something like a 5 mile or 10 mile TT, so 12 or 25 minutes of effort…maybe? If you’re an anaerobically strong rider?
I don’t think I could do it now, but it used to sound less horrendous to me than trying to sit at constant power for the duration.
(There are other reasons that would make that a bad tactic for a TT. You’re likely less aero, and your avarage speed is likely less.)
I’ve done 40/20 sets of 15 minutes in length, like 400W and coasting, and I would have to go look but it certainly didn’t feel as fast as a 15 min all out at ~300W, and it was absolutely more taxing! Granted 40s you’re above that half life…
Just looked and while you can’t control for everything, on the same stretch of road:
15 min 40/20 set, NP: 281W, 23.4mph avg (about six weeks ago)
15 min threshold interval, NP: 292W, 24.6mph avg.
FWIW, the first workout was on a Venge frame, second on my Chapter 2 Toa which is less aero, but everything else (wheels, helmet, etc.) was the same, and same time of day and weather, so wind was probably similar given it’s a coastal environment.
Interesting to look at.
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Yes, I think it would be slower. I can’t imagine that you can keep your position as aero when doing intermitted high-power efforts, for instance. Also I might have that wrong, but I think the repeated accelerations to faster speeds mean working against more air resistance, which isn’t fully balanced by coasting at lower speeds.
100%. Inertia is a thing.
Yep. Drag is exponential. Riding 30 minutes at 22 mph and 30 minutes at 24 mph through whatever combination of 30/30 or 15/15s takes more energy than 60 minutes at 23 mph would despite getting to the end at the same time. The accelerations themselves wouldn’t matter b/c you get the energy back when you start coasting (though, it seems like it’d be awfully annoying).
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Don’t think drag is exponential, but the drag force is at least proportional to the square of speed, and power at least the cube of the speed.
In any case, it’s non-linear, and the over-under approach takes more power than riding a constant average.
Still think it is interesting from a physiological (and maybe psychological too) aspect, for riders that struggle with prolonged constant efforts.