Why leg strength doesn't matter, that much, for road riding - a technical answer

GrasB

Veteran
Location
Nr Cambridge
Let's get some basics out of the way;
  • The average person can easily climb a set of stairs for several min without much problem. They may do this slowly but they can climb stairs. This means that people are regularly pushing down with, considerably, more force than their body weight; if you can't lift more than you weight you'd never climb stairs.
  • A good national level pro/sponsored rider is going to have maximal outputs of around 6.5W/kg for 5 min. A fit, slightly trained rider will be close to 6.5W/kg for 1 min maximal effort & 3W/kg for 5min.
  • A typical trained rider will have a nominal foot speed of 1.25-2.25m/s. On 170mm cranks this equates to approximately 70-125 rpm.
  • The more power you produce the higher your cadence tends to be.
  • Your peek pedal force is approximately 2.1x higher than your average pedal force across the entire pedal revolution. (I know this is true for me I'm not so sure about other people.)
At 6W/kg, & 70 rpm a rider will be applying enough force to lift 53% of their weight over the entire pedal stroke & applying a force to lift 120% of their weight at the point they're applying maximum force on the pedals. This sort of figure is nowhere near the muscular strength limit for a fit person, let alone a trained athlete. To put into context; For Someone who is 12 stone, such as a certain Mr B. Wiggins, 6.5W/kg equates to 495w.

If we drop to a more typical 3W/kg, 230w for someone who tips the scales at 12 stone & the sort of level that I'd expect a faster commuter to be able to produce, even peek pedal pressure is only producing enough force to lift two thirds of your body weight. Do people really think you need a large muscle mass to achieve that sort of force considering how easily most people accelerate their entire body mass up stairs?

Now all this assumes you're at the lower end of the rpm registers when climbing. Say you climb in the low 80rpm range. Even up a 6.5W/kg you're looking at your maximum pedal force being the same as your body weight, something you should easily be achieving. At 3W/kg it's less than half your body weight.

EDITED: make it a bit more readable.
 

T.M.H.N.E.T

Disc brakes - Stopping things since 1902
Location
Northern Ireland
9/10 people will still argue that strength = hillclimbing ease :laugh:
 

ColinJ

Puzzle game developer
I had a friend with enormous legs (he was a bodybuilder) and he insisted on using leg strength to climb in a massive gear, rather than spinning a lower gear. I used to warn him about it but he wouldn't listen and immediately after one such warning, his chain exploded! :eek:
 
I had a friend with enormous legs (he was a bodybuilder) and he insisted on using leg strength to climb in a massive gear, rather than spinning a lower gear. I used to warn him about it but he wouldn't listen and immediately after one such warning, his chain exploded! :eek:
probably more to do with his weight than his power. Anyway, must dash - I'm off to the gym... ;)
 

ColinJ

Puzzle game developer
probably more to do with his weight than his power. Anyway, must dash - I'm off to the gym... ;)
He was actually quite a small man apart from his muscle bulk. He probably weighed several stone less than me!

It was the horrible way in which he mashed the pedals round. He stamped hard twice per revolution of the cranks, rather than turning them smoothly. I could tell that he was going to break something.

It was pretty comical the way it happened ...

Me : "Please use a lower gear and spin your legs more smoothly or you will wreck your bike!"

Bike chain, 2 seconds later: "BANG!"

Me: "Er, just like that!"

:laugh:
 

david1701

Well-Known Member
Location
Bude, Cornwall
Is there not an element of efficiency here?

To supply 300w you need to generate more than 300w. I don't have figures for how much more.

If your max supply is 350w then when supplying 300w then you're right at the edge and likely to be less even and less efficient, whereas is your max supply is 600w you are only running at half capacity to provide 300w so should be able to sustain the effort longer as well as not wobbling everywhere on the edge of dying :tongue:
 
If your max supply is 350w then when supplying 300w then you're right at the edge and likely to be less even and less efficient, whereas is your max supply is 600w you are only running at half capacity to provide 300w so should be able to sustain the effort longer as well as not wobbling everywhere on the edge of dying :tongue:
what you have just described is called 'aerobic fitness'... :smile:
 

Hacienda71

Mancunian in self imposed exile in leafy Cheshire
To those in the know. How does Cavendish supply so much power at the end of a 200K stage? To have an output of 1500 watts albeit for a short burst after a long ride seems incredible. I know he is not a great climber no doubt too heavy but what gives a top sprinter the ability to have that output after a gruelling ride.
 
OP
GrasB

GrasB

Veteran
Location
Nr Cambridge
Is there not an element of efficiency here?

To supply 300w you need to generate more than 300w. I don't have figures for how much more.

If your max supply is 350w then when supplying 300w then you're right at the edge and likely to be less even and less efficient, whereas is your max supply is 600w you are only running at half capacity to provide 300w so should be able to sustain the effort longer as well as not wobbling everywhere on the edge of dying :tongue:
At 50rpm I can produce 730-750w of power. That's about my anaerobic neuromuscular limit, that's 85kg ave pedal force & almost 173kg peak pedal force. I can do that for 5, possibly 10 seconds absolute maximum, beyond that my blood can't supply oxygen quickly enough to keep up with that power production & so it drops off very quickly. Down in the 300w range leg strength isn't an issue, it's getting oxygen to the muscles.
 

RecordAceFromNew

Swinging Member
Location
West London
Say you climb in the low 80rpm range. Even up a 6.5W/kg you're looking at your maximum pedal force being the same as your body weight, something you should easily be achieving.
I don't think I can agree with that. Have you unconsciously equated 80rpm at the pedals with full body weight to be about the same as climbing 80 steps of stair per minute?

I have not looked into your maths/assumptions closely, and I do understand pushing at the pedals is not the same as climbing stairs biomechanically, but I often run up long flights of stairs (and occasionally long escalators in London Underground) two steps at a time (such double step would be a little more than the pedal stroke of 2x170mm crank length). My experience tells me I doubt many Joe Blogg commuters can do it at 140/160 such steps a minute (which correspond to 70/80 rpm) for any extended period. If you don't believe me try it (unless you are Wiggo of course... :whistle: ).

As in many assessments in Physics it may be clearer to evaluate in terms of power or energy and see with e.g. 500W how many steps Joe needs to go up in a minute. Since W is kg m^2/s^3, for a 70kg commuter fighting gravity (at say 10 m/s^2) he/she would have to go vertically up at a velocity of 0.71 m/s, which is 43 m/minute, or 214 steps/minute of typical 20cm stair steps. Looking at it in a different way Joe is going vertically up at 2.6kph, or 10.4kph (a very brisk walk) up a 25% (!) incline. Assuming no air/wind resistance, mechanical inefficiency etc. of course.

Actually I think ~10kph was what Berti etc. were doing over the 25% inclines during the past few days in the Vuelta. Now should I be able to "easily" achieve that (even after eating a lot of beef)? :heat: ^_^
 
My experience tells me I doubt many Joe Blogg commuters can do it at 140/160 such steps a minute (which correspond to 70/80 rpm) for any extended period.
they could if they trained themselves to do it...

Actually I think ~10kph was what Berti etc. were doing over the 25% inclines during the past few days in the Vuelta. Now should I be able to "easily" achieve that (even after eating a lot of beef)? :heat: ^_^
Bert didn't 'easily' achieve it either. He trained for it - same as you could, within reason.
 
I believe that was and is my point, per the OP's comment I find difficult to agree with. I also doubt everybody can sustain 500W over extended period even with training, given age, gender, condition etc. all being factors, but that is a different subject.
That's the difference between strength and power. You already have the required strength - but whether you can convert that into sustainable power over a given period of time is a different matter. That was the original point - in the original thread...
 
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