Hi guys,

A somewhat strange question here, where I don’t know where this will be headed: what are the pro’s / cons of “spikey” vs. steady power, and what effects/physiological costs do these have?

Some background: my girlfriend and I both enjoy riding our bikes, and dabble into (gasp!) Zwift racing every now and then for some fun short all-out efforts.

I have noticed that my girlfriend’s power output is very different than mine. She tends to spike her power repeatedly (as in every 10-20 seconds or so) then drop below sweet spot. So she’ll typically be sitting at 150W-170W and spike to 200-250W, rinse and repeat. She refuses to do a FTP test, but she has held 192W average (3.4W/kg) for an hour in a race so she’s no slouch on the bike.

For my part, I tend to be more of a “pick your power ad sit there” kind of guy, and I only spike when I intend to (e.g. climb / attack / losing the wheel).

We are using the exact same setup (swapping our bikes on a Wahoo Kickr), so that’s not an equipment artifact.

So what do you guys think is causing this very different approach to putting down power on the bike, and what are the pro’s / cons of both?

Illustration: typical girlfriend’s race, note the jagged power

Illustration: typical for my races, note the steady power line

The exact same thing is happening when we are riding outside too, see screenshot of a ride we did together (both on identical power meters):

Girlfriend’s power graph

My power graph

Is she newer to cycling? Holding steady power is a skill and can be practiced and improved

Your Y axes are wildly different. Small variations in power will necessarily look more dramatic when the Y axis is double the resolution between graphs.

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are you both using the same power meter / smart trainer (with same smoothing settings) and are both zwift accounts set up to same smoothing average?

Strava’s auto-scaling makes it hard to compare. Regardless her power looks normal. And the scaling makes it look like your HR is oddly all over the place for such a steady effort. But your HR probably looks worse due to Strava auto-scaling. Strava is really a poor tool for analyzing data for several reasons, starting with having no control over the graphs.

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Funnily enough I have been toying on adding a question about the same thing. During long steady climbs I find I have to sit way above threshold in order to move at a reasonable pace (for me anyway) and on very steep climbs I have no choice other than to ride at way over threshold just to move along (I am 85kg)

At this power output I likely wouldn’t last the full climb so in order to reach the top I spike my power so I can have what I call “micro rests” these help my legs to not fatigue to the point of stopping. I have been doing this for a couple of years now and it works for me but one day I hope to be able to hold a decent consistent power for the full length of any climb.

Even though the power graphs may look the same, there are two distinct kinds of spiky power. One is unintentional meaning you are unable to hold a steady power and the second is the on-demand spiky power that is very common in actual bike races.

If it’s just happening by accident, it’s bad. Its either a sign you can’t ride steady or, you’re starting to get in over your head on pace and starting to struggle. Spiky power is less efficient than a steady power. However, if you are you going to do hard competitive group rides or especially if you’re going to race, the ability to output repeated spiky power efforts over a longer period of time is fundamental to succeed in competitive cycling.

All that being said, her power graphs look pretty normal for an outdoor ride (or hard Zwift ride)

Just by way of example re: axes, here’s my cadence and heart rate over 12-minute intervals from a year and a half ago:

and here’s some that are more recent:

My heart didn’t magically get better at beating; the vertical resolution halved.

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Thanks for all the comments about scaling and graph range. They are valid points, but I don’t think that’s the only difference at play here.

Just to illustrate, compare with GF’s race on Zwift (172W average) to my ride outside (216w average), so there is less of a scaling disparity:

GF on Zwift

Me outside

If you ignore the last 30km of my ride outside where I did some crazy stuff, the difference in spikes is still there despite the fact that it’s way easier for her to keep steady output on Zwift than it is for me to do the same outside.

Formulated differently: there is no way I could do what she does, spiking to 120-130% FTP (and often higher still) every 20 seconds for an hour! I’d be lucky to last 10 minutes at that. I think that exact thing when I watch her race and focus on the power reading, along with “would she be faster still if she didn’t do that, or is it this something that I could train”?

The Y axis on your girlfriend’s graph is 0 to 407:

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Also, the X-axis on hers is 1 hr while yours is 100+km (so probably like 3.5hrs). So that, along with the difference in y-axis, will make comparing the data pretty hard.

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Right, one final attempt at clearing up the illustrations (I seem to be making a terrible job out of it )

Here are the first two graphs (zwift races), where I divided the power in the file by the average power for each ride, so it is somewhat normalized per rider. Can’t see how I could make the comparison any closer (same setup, same power meter, same smoothing, normalized power).

To me it looks like my GF’s power (in blue) is much, much spikier than mine. I have rises in there, but they are much slower, and much lower. This pans out as well if you look at the standard deviation for both graph: 0.17 for mine, and 0.23 (35% higher) for my GF. And she can spike at a frequency I can’t even dream of…

And I know this is not a graph artifact because I can clearly see it when I watch her race in real time: the rate and height of her spikes (relative to FTP) isn’t something I could match, ever. I just try using the graphs to try and show that.

But forget about the graphs for a second, my main question is still: why are some people able/willing to spike continuously way above FTP while that would kill some of us? Is that a thing that can be trained? I’m sure If I could spike to 400W+ every 20 seconds and recover at 290W I would drop anyone in my local group rides in no time!

It’s called variability index (VI), shows normalized / average power. You can check it in https://intervals.icu (it fetches data from Strava).

And yes, can be learned: when started doing workouts outdoors, it was initially ~1.07, after 3 months exactly 1 (per interval, not whole ride)

Variabilty index isn’t quite the same as standard deviation @svens, although it does try to capture the same thing. The math is just a little different, and I can’t do VI in excel

But standard deviation / VI is only part of the story. I can match her VI when I am doing intervals. What I cannot do is what she is doing, which is essentially VO2max - threshold intervals at a crazy high frequency. That’s like doing Spanish needle for an hour, without the long breaks, and sped up 10 times (shorter work, shorter rest).

I just pointed out that you can prove using VI that spikiness is not graph scale issue but real difference between you and your girlfriend. As your original question about whether higher VI has some physiological effect, I don’t know.

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To me a key question is are there differences in how you do the races? Are you keeping steady power to keep a steady position in the pack? Is she dropping to the back of a pack, surging to the front and dropping back again?

How you move around the pack can have a dramatic effect on power output. When I first started zwift racing it took me a little while to get on board with pack dynamics and drafting. I would lose focus and drift to the back then punch it to get to the front and drift back, etc. Now my power output is steadier and I can better control where I am in the pack. I also accept that if I go to the front I will naturally drift back after some time and when I’m at the back if power is high enough I will eventually drift forward (as long as my power isn’t low enough for me to pop off the back.).

That said, I have seen some people ride in very surgy manners during zwift group rides. Maybe it works for them based on their particular strengths, but it would not work for me. In a group ride situation it also negatively impacts the group dynamic when one person is riding at 2wkg (pack is around 3.2-3.5) and then spikes to 8-10wkg then drops to <2wkg when they hit the front. For racing, go for it, the goals are different.

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