Pedal stroke analysis with Powertap advanced metrics

[AlexisBV]

Hello all,

So I finally decided to have a look at the advanced power metrics offered by the Powertap P1 pedals. I installed the Rouvy app on my android phone (since Powertap does not have an android app for those metrics ), and recorded yesterday's workout - a 1 hr indoor ride on a Tacx Neo trainer in Erg mode, following TrainerRoad's Tunnabora workout. The bike is a S30.

Data:

Workout

• AlexisBV
• Jan 30, 2019

And here are the advanced power meter metrics, with a quick explanation of each:

Graph1

• AlexisBV
• Jan 30, 2019

Red color indicates useful force is applied at that point in the pedal stroke (in the direction of rotation). White is neutral, blue means drag, or the foot is actually applying force in the wrong direction, against rotation. The more intense the color, the more intense the force.

The further away the colored band is from the black circle, the more radial force (useless) is being applied.

Graph2

• AlexisBV
• Jan 30, 2019

This one shows the angle of the pedal at each position in the pedal stroke. I'm surprised it indicates the pedal is actually pointing down in the return stroke, which is not the case according to an older video I shot of myself pedalling in slow motion (link at the end of this post), so there's probably some kind of angle offset there.

Graph3

• AlexisBV
• Jan 30, 2019

This graph more explicitely shows the direction of the force being applied on the pedals at each point in the stroke. As in the first graph, we can see that the bulk of the force, which is horizontal (pushing forward), actually happens around the 1 o'clock and 2 o'clock positions in the pedal stroke, so some of that force is being wasted as a radial component ("stretching" the crank).

Analysis:
With the above in mind, it would appear I'm applying force too late in the pedal stroke. Also, during the return stroke, maybe I'm letting too much leg weight onto the pedal, which pushes it against the direction of rotation.

So, on one had, I should improve my pedal stroke (with some focus on the return to do a proper pull and a proper kick upwards at 9 o'clock). But, on the other hand, I'm asking myself if I should stretch the boom a bit further, so that the power stroke happens earlier, nearer to the 12 o'clock position, so more (if not all) of the force is actually in the tangential (useful) direction.

Also, the fact that the chainrings are Qrings might be relevant. They're setup in position 3.

Any thoughts?

FWIW here's the slomo video of the setup, although the video was taken several months ago and I might have tweaked the boom position since.

 

[ed72]

Your pedal stroke looks much better than the data chart would indicate. ?

 

[bladderhead]

Imagine you are riding a scooter. What is the motion of the leg that is propelling you? Imagine a horse pawing the ground.

I hope that is not too "Mr Miyagi" for you. My other bike is a Grasshopper.

 

[AlexisBV]

Thanks, I like the Mr Miyagi advice

I'll try to focus on the movement a bit more tomorrow and see if it changes anything, if not I'll try readjusting the boom.

 

[LarryOz]

Great data Alexis.
From your graphs and your video, it appears to me that your knee is bending at least 70 degrees on your back stoke. You also appear to be fully extended, so you can't really push the boom out at all or you would be hyper-extending you knee. This means to me that you are a candidate for some shorter cranks. What length are you riding with now? I would guess you need to drop 15-20mm. You can then move the boom out 50% of the length that you shorten your cranks by. This will allow you to not have to bend you knee so much on the back-stroke. It has been my experience that you cannot make much power until your knee bend gets past 90 degrees. This means that you foot must move forward enough to go from 70 to past 90 before you can apply much force on the pedals. With a shorter crank you will be able to apply the force quicker. This could also explain why your data is telling you you are resisting the pedal on the back stroke. I think this is due to you knee bending back to 70 degrees also. It doesn't like to do that and is fighting it. When I first started riding a Cruzbike, I had knee pain when my knee bent that much, and it forces me to consider shorter cranks. Good Luck, and again - great data!

 

[ed72]

I looked at that video probably a dozen times and the 70 degree angle at 9 o'clock had me thinking midsole cleat placement could increase the angle a little. It isn't awful but is borderline at 70 degrees. Larry's idea is better.

FWI.....I went with an old Rotor RS4X crank that effectively eliminates the 9-10 o'clock part of the pedal stroke and gained power. I went down this path extensively trying to figure out why I was having trouble getting it over the top and low knee angle. I still might try short cranks but not many good short ones are made. If you look at video of upright cyclists, the hips do not rock side to side but there is sort of a circular motion that can be seen in the head movement. The nexus of motion is the hips; however, this movement is inhibited on a recumbent. At least this is the conclusion I came to and why I have the RS4X cranks. Trying short cranks might be smart.....

FWI. Pedal smoothness and uniformity is negatively correlated to power output as many studies have shown. Push hard. Don't listen to the scraping and pulling. It is wrong

https://mypremiertherapy.com/pedaling-techniques-what-does-the-research-say/

 

[Balor]

FWI. Pedal smoothness and uniformity is negatively correlated to power output as many studies have shown. Push hard. Don't listen to the scraping and pulling. It is wrong

On DF. And they are positively correlated at very high cadences and powers - I presume because you no longer have enough 'push' in gravity.
When it comes to recumbents... things might be much more complex than that.

 

[ed72]

On DF. And they are positively correlated at very high cadences and powers - I presume because you no longer have enough 'push' in gravity.
When it comes to recumbents... things might be much more complex than that.

Top cyclists on an upright do not pedal "smoothly"

They push hard.

Take a look at the research referenced in the articles. Or watch the video I posted

 

[ed72]

Pulling and scraping is metabolically inefficient

http://img2.timg.co.il/forums/1_168859045.pdf

http://burnhamcoaching.com/myth-of-pedaling-circles/

 

[Balor]

Top cyclists on an upright do not pedal "smoothly"

I know that for a long time already . I mean people like track sprinters. Very different mode of operation, surely, but still....

 

[Balor]

http://burnhamcoaching.com/myth-of-pedaling-circles/

Yea, I know that 'scraping' or 'pulling' muscles are much less mechanically efficient than 'pushing' muscles.
*Still* I am not familiar with any similar studies for 'top level recumbent cyclists'. I suspect that things *might* be different.

 

[ed72]

Yea, I know that 'scraping' or 'pulling' muscles are much less mechanically efficient than 'pushing' muscles.
*Still* I am not familiar with any similar studies for 'top level recumbent cyclists'. I suspect that things *might* be different.

If anything, the metabolic inefficiency of pulling and scraping is worse for recumbent riders. If I said mechanical efficiency, I apologize. The best study is to read BROL and do the inverse.

 

[LarryOz]

I looked at that video probably a dozen times and the 70 degree angle at 9 o'clock had me thinking midsole cleat placement could increase the angle a little. It isn't awful but is borderline at 70 degrees. Larry's idea is better.

Full disclaimer: I have also moved my cleat to mid-sole, ride XQL Q-rings in pos #1. I think it helps the angle a little, but I mostly like it because the center of pressure is no longer on the ball of my foot (which usually leads to hot foot for ultra cycling distances). I am going to try and capture my own P1 metrics here soon and see what they look like compared what Alexis has posted.

 

[LarryOz]

I still might try short cranks but not many good short ones are made.

Just get a used set of "long" Sram Apex cranks, and drill and tap them to the length you want, then cut off the excess. That is all I have ever done. No need to go the expensive CF route. You will probably be lighter than a normal CF set after you cut off the extra length.

 

[ed72]

PhD thesis comparing upright to recumbent pedaling showing essentially they are similar mechanically although the center of mass movement is different between the two. The pedal motions are so similar between bents and uprights as to almost be identical. EMG studies of others have shown the same.

I have never found a study evaluating metabolic efficiency in the recumbent position although it would not be a hard study to complete with the right equipment and subjects. I would love to be able to measure O2 saturation in the muscle with NIRS (MOXY) but too expensive a toy for me. It is possible that the most effective aerobic pedaling styles between upright and recumbent could be different metabolically due to pressure divergent differentials in the two positions.

https://pdfs.semanticscholar.org/9b97/52bb069813a99cbec038d14181909e6e178d.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3924611/

 

[Balor]

The pedal motions are so similar between bents and uprights as to almost be identical.

Unless you add things like linear drives, K-drive, etc to the mix - they ARE identical.

Now, hip angles and trunk orientation against gravity might be massively different on 'bents' - some are fairly closed, some are extremely open. You really need to reduce the system to it's most basic PHYSIOLOGICAL components (up to muscle fibers, hemodynamics and biochemistry) if you want to build a truly comprehensive model of 'power generation and delivery'. And I daresay this is HARD. VERY hard.

Since our glutes are most perfused muscle groups on a bent, it makes sense to maximise their use.
I've been reading articles on glutes and here is what I've found:

https://www.t-nation.com/training/advanced-glute-training

Rather science-heavy article, but very revealing in terms of how complex biomechanics is.

What is very interesting, however, is this picture:

Does it remind you of something?

Well, it does to me!

 

[ed72]

Glutes should be primarily activated coming over the top of the pedal stroke......not scraping and pulling back unless one is trying to "sprint" or trying to achieve peak torques. Muscles work in combination or in pairs. Engaging the glutes, hip flexors, and psoas on one side by pulling back will suboptimize the powerful downwards thrust of the other leg. I know, if say the vastus lateralis is limited by delivery of oxygen due to local effects (not lungs or heart), it is quite possible that I am wrong and the optimal recumbent recruitment pattern for the most effective pedaling is indeed different. This is why I want a 3 sensor MOXY unit to measure metabolic function real-time. Stick one on my ass, one on my VL, and the other on the vastus medialis. I listened to a podcast presentation by Coggan and as a consumer level product, it is very sensitive to even light movements of the leg.

Since cycling is mostly aerobic, metabolic efficiency is more important than mechanical efficiency. Some studies have shown equivalent peak power generation from supine to upright position (I can't replicate it myself). I recall seeing one study showing that 30 degrees reclined is the lowest for relative equivalence to an upright position with respect to RER and also, aerobic output power. The only tools I have to measure are HR, power, and lactate levels but they are insufficiently precise and slow to respond to stimulus. I can say this for sure. Once I stopped with trying to emulate the bent legs scraping dogma and simply pushed really hard doing tabata intervals, things got better for my outputs. I say dogma because I have never seen a study with data. None. I have looked. The anecdotes are the opposite.

Of course this is way too much information for the OP, but it is not so simple a matter.

 

[Balor]

Few things are simple when it comes to biomechanics, and individuals vary hence you may never know if even a large sample size, properly conducted research results (which are frankly rare in sports medicine) would apply to YOU.
nnmbent on BROL keeps point out that 'top athletes' are self-selected and, hence, study conducted on those is prone to, well, selection bias. Still, is better to emulate fast people than slow people, just don't take that that you'll get same results for granted.

(To clarify, just like it is clear that while there are no schizophrenics in heavy machinery works, it does not mean that operating heavy machinery is neuroprotective, hence might simply mean that people to whom 'push style' pedalling works best become top athletes... and if it does not - than not. Far-fetched to be fair, bust still possible!)

 

[Balor]

I know, if say the vastus lateralis is limited by delivery of oxygen due to local effects (not lungs or heart), it is quite possible that I am wrong and the optimal recumbent recruitment pattern for the most effective pedaling is indeed different.

Which really makes sense both anecdotally and from perfusion POV, doesn't it?

 

[ed72]

Few things are simple when it comes to biomechanics, and individuals vary hence you may never know if even a large sample size, properly conducted research results (which are frankly rare in sports medicine) would apply to YOU.
nnmbent on BROL keeps point out that 'top athletes' are self-selected and, hence, study conducted on those is prone to, well, selection bias. Still, is better to emulate fast people than slow people, just don't take that that you'll get same results for granted.

(To clarify, just like it is clear that while there are no schizophrenics in heavy machinery works, it does not mean that operating heavy machinery is neuroprotective, hence might simply mean that people to whom 'push style' pedalling works best become top athletes... and if it does not - than not. Far-fetched to be fair, bust still possible!)

I like the studies that use decent or slight above average athletes. I don't care about sedentary results to be frank. Populations of a study need to be comparable, which is why inclusion and exclusion criteria are very important during design. Since I am average, I like average studies from average athletes. There just are not a lot of recumbent studies period. Naturally, study results from average athletes may not necessarily be applied to those with impairments or disabilities. But the results are generally applicable when applying to similar populations .....or one can just constantly throw the baby out with the bathwater and cling to dogma.

I don't believe in that British fellow's snowflake model as if the water in England is especially wet or the roads are especially steep or his pavement is especially rough or English wind is stronger or lung function of Welch sheep are particularly limited due to sniffing coal dust or the wax from their bees is especially viscous and so on. Having come from the Pharma world and having more than just seen plenty of clinical, preclinical, and nonclinical studies, I can appreciate sample sizes and confidence levels as well as the cost to do a real study. However, this misguided notion that we are always and forever unique and special is silly. Almost as silly as finding fault in every study w/o even trying to emulate the process that generated results. Sometimes there is always a problem to every solution. Sure, outliers exist. When I bought my bike, Bram told me "don't push here" and then said, "Never mind, you are an engineer and wouldn't do something so stupid"....of course, you know these things, too. Some things are obvious. Pushing against one's lard and/or impinging on the lung expansion, for instance. Pedaling technique is up there with chain lubes in terms of controversy.

I have never read a study showing pedaling in circles is more metabolically efficient than just push hard. More effective in terms of peak power? Yes. Efficient? No. I keep looking, so, am I excluded from operating heavy equipment?