How much force is a bicycle pedal stroke?

offwidth

Level 9 Valued Member
Ah.... OK that makes sense. So with cycling, more of the work goes directly to making you go, whereas in running it might be moving the arms, bobbing up and down, etc.



Also makes sense. Sounds like this is the efficiency that increases in runners as their tissues become more adapted to running, so an experienced runner of the same bodyweight puts out less work to go the same distance. And this doesn't apply so much in cycling.

Thanks, Mike!

So, a follow-up question... If I run for an hour with my HR at 140, and cycle for an hour with my HR at 140, have I likely done the same amount of work and/or burned the same amount of calories?
You may or may not have done the same amount of work. Recall that the way we define work is basically force x speed. Heart rate is only tangentially related to that.

But you raise an interesting question, and you could add less common activities like rowing, cross country skiing, etc, where a given participant could perform for an hour at a given HR.
 

krg

Level 5 Valued Member
Recall that the way we define work is basically force x speed.
Yep.

You can imagine trying to lift up your car for an hour - it won't move at all so formally no work done - but you'll use some calories.

The comparable HR across exercises is an interesting point. I can elevate my HR off a spectacularly slow run, to achieve the same HR elevation on a bike I'd have to push much harder (in terms of perceived exertion) unless I was going uphill. No idea if I'd burn the same calories or not.
 

Steve Freides

Staff
Senior Certified Instructor
Elite Certified Instructor
My bikie friends always told me that one of the reasons I rode pretty well was because I was also a runner.

All other things being equal, I always felt like your RPE had to be higher on the bike to get the same amount of cardio training and calories burned and all that.

JMO.

-S-
 

mprevost

Level 6 Valued Member
So, a follow-up question... If I run for an hour with my HR at 140, and cycle for an hour with my HR at 140, have I likely done the same amount of work and/or burned the same amount of calories?
Not exactly, but pretty close.
 

Deleted member 5559

Guest
Where does momentum play a role in efficiency? Does that help explain why cycling requires more perceived effort to reach the same level of work?
 

Deleted member 5559

Guest
Not directly, just the first pedal stroke requiring more force than subsequent strokes. The fact you can coast seems like an underlying factor. When you stop running, you stop. When you stop pedaling you coast. That ability allows momentum to be conserved.
 

Anna C

Level 9 Valued Member
Elite Certified Instructor
Where does momentum play a role in efficiency?
I think that might expand the definition of efficiency as provided by @mprevost:

Efficiency is just energy expended/work completed. We can measure your calorie expenditure while cycling and also measure your power output and therefore your total work. If we convert calories to joules and total work to joules, we can simply divide total work/total calories.
Momentum would not factor into this definition because no power is being generated while coasting.
 

offwidth

Level 9 Valued Member
Efficiency in cycling can be affected by many variables.
Rider based:
  • Pedaling style
  • Aerodynamic position
  • Positioning on bike (bike fit)
  • Cadence
Bike based: (bank account based)
  • Aerodynamic Frame and components
  • Lightweight Frame and components (especially rotating weight)
  • Crank arm length
  • Rolling resistance of all rotating components
  • Pedals/cleats
That being said Vincenzo Nibali is still going leave me in the dust if he was riding a rusty bike found at a garage sale...
 

Anna C

Level 9 Valued Member
Elite Certified Instructor
Efficiency in cycling can be affected by many variables.
Rider based:
  • Pedaling style
  • Aerodynamic position
  • Positioning on bike (bike fit)
  • Cadence
Bike based: (bank account based)
  • Aerodynamic Frame and components
  • Lightweight Frame and components (especially rotating weight)
  • Crank arm length
  • Rolling resistance of all rotating components
  • Pedals/cleats
That being said Vincenzo Nibali is still going leave me in the dust if he was riding a rusty bike found at a garage sale...
I agree! But here again, we're talking about a different definition of efficiency.

In @mprevost's definition, it's the rider's effort (calories burned) relative to how many watts of power makes it to the pedal.

In your definition, it's how many watts of power is on the pedal relative to how far/fast that makes the rider go.
 

offwidth

Level 9 Valued Member
Not really Anna. The more 'efficient' the whole system is, is what counts. It's physics. The riders effort will be less when there are better efficiencies in the bike, riding position etc.

Bicycling would not be efficient at all if we were pedaling 100lb bikes, with rusted bearings. Imagine the calories burned doing that! :)

The main reason it's efficient is because of the design of the bike. Again, it comes down to physics.
 

Anna C

Level 9 Valued Member
Elite Certified Instructor
I understand what you're saying, @offwidth, but I still think it's two different definitions.

In your example of the 100 lb bike with rusted bearings (and many other examples of less than ideal equpment), the rider has to generate more power to make the bike go. But that would not change the ratio of energy expended/work completed, where work completed is power to the pedal.

Perhaps @mprevost can clarify.
 

offwidth

Level 9 Valued Member
Efficiency is the effectiveness of a system in transforming the energy and power input into the system into some output force / movement.

Bicycles are very efficient machines...

I didn't become a mechanical engineer for nothing:)

I'm not even sure I know what we are discussing anymore :)

I might go for a ride...
 

krg

Level 5 Valued Member
Not directly, just the first pedal stroke requiring more force than subsequent strokes. The fact you can coast seems like an underlying factor. When you stop running, you stop. When you stop pedaling you coast. That ability allows momentum to be conserved.
F = m x a
When you are accelerating then you require a lot of force to speed up (depending on mass), once you're at constant speed you only need enough force to overcome resistance (wind, tyres, gradient).
 

offwidth

Level 9 Valued Member
F = m x a
When you are accelerating then you require a lot of force to speed up (depending on mass), once you're at constant speed you only need enough force to overcome resistance (wind, tyres, gradient).
This is one of the reasons rotating weight is so important, and why wheels are one of the most significant upgrades one can make to a bike...
 

krg

Level 5 Valued Member
This is one of the reasons rotating weight is so important, and why wheels are one of the most significant upgrades one can make to a bike...
Which must explain the frankly absurd prices people will pay for bike wheels....
 

offwidth

Level 9 Valued Member
Indeed and... Guilty as charged.

I did a fun little calculation...

If I wanted to go the lightest (safe) wheels for my bike; I took the price of the proposed new wheels and divided into that the weight difference between my current wheels and the proposed new wheels. Giving me dollars / pound.

The 'upgrade' would cost about $18,000/lb
 
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mprevost

Level 6 Valued Member
The biggest inefficiency is the simple conversion of carbon based compounds to ATP and then the hydrolysis of the ATP to produce force. That's where we lose about 80%. Most is lost a heat production. When we measure cycling efficiency in the lab, we do it on a stationary bike, where bike frictional losses (which are minimal) are the only real issue. Pedaling style, cadence etc... accounts for maybe 5% difference.

All of the stuff offwidth mentions are a big deal on the open road though. But they are generally considered separately from the 20% figure I mention.
 

mprevost

Level 6 Valued Member
Where does momentum play a role in efficiency? Does that help explain why cycling requires more perceived effort to reach the same level of work?
This is where specific definitions become important. Although you are moving forward while you are coasting, you are producing zero work. So momentum contributes to going forward but not work or power, or efficiency.
 
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