Torque

scapaslow

Following on from the recent cadence thread where the following equation came up -

Power = torque x angular pedal velocity

then it seems obvious that given a set cadence at which one is happy to push then in order to increase power you must increase torque.

In my simplistic terms this would mean applying more force to the pedal stroke.

When you increase power by an increase in FTP by x watts over a period of time what physiological adaptations have taken place? Is it simply aerobic capacity increasing or are you also increasing strength by increasing muscles in the legs? What gives you the ability to apply more torque? What exactly is torque in cycling terms?

I'm a bit confused as i'm sure i read on here before that the forces involved in cycling are not sufficient to increase leg strength which seems somewhat counter intuitive.

Alex_Simmons/RST

Well your logic is a little flawed. If you are riding along at a given cadence and then decided to apply more force to the pedals, you will speed up and ride at a higher cadence as well. Until you change gear.

IOW you can't control torque independently of cadence. Nor can you control cadence without a commensurate change in torque. It is the power you produce you control.

The only way to balance one with the other is to change gear.

You know that line I've used ad nauseum:

Cadence is an outcome of the power we produce, the resistance forces acting against us and the gear we happen to be in.

Well...., yep you guessed it.....

Torque is an outcome of the power we produce, the resistance forces acting against us and the gear we happen to be in.


Improved power at threshold is a result of physiological adaptations such as increased muscle mitochondral enzymes and mitochodral density (the energy plants inside our muscle cells), increased muscle capillarisation (able to transport more blood and metobolites to the working muscles), increased cardiac output and VO2 Max (to deliver more oxygen), greater muscle glycogen storage (for instant energy availability and endurance), improved ability to manage higher blood lactate levels (itself a source of fuel).

It however has nothing to do with strength (which is the maximal force generation capacity of a muscle or group of muscles) since as you correctly state, the forces applied when pedalling are very low.

For example, if you were looking to help someone trying to improve strength (let's say their 1 rep max squat), would you suggest they ride a bike (when going hard you have peak forces of ~ 1/4 of your body weight) or do some heavy weight squats of some multiple of your body weight?

SteveR_100Milers

From a Newtonian physics point of view:

For a given resistance, and constant speed, your power must remain constant. If you increase the gearing, your torque increases to offset the reduction in velocity (in this case being angular), as power = force x distance. Conversely, if you reduce the gearing, (i.e. spin faster), then to maintain the same power output your torque decreases. This is why spinning doesnt wreck your knees (low forces) whereas mashing a big gear does (high forces).

So to answer the OP - to increase power you can either increase torque at same cadence, or spin faster at same torque (force). Don't confuse the additional torque required to accelerate to the new velocity. (F=mass x acceleration). What happens physiologiocally and in terms of perceived feel is another story completely well covered I'm sure by Alex!

scapaslow

Thanks for the replies - what you both say makes sense.

Presumably then riders capable of sustained large power outputs have the ability to spin large gears. But how did they get there without wrecking their knees?

I find after a session of trying to sustain an increase in power my knees hurt with the effort (usually around 75/80 rpm) and find it difficult to increase power at high cadence. I find it easier to increase/sustain power when I feel the resistance e.g. going uphill.

Simon Notley

If I understand correctly, the OP is saying that, if you consider a rider with an FTP of 250W and who always pedals at 90rpm who then trains and increases his FTP to 300W and still pedals at 90 rpm then that rider's training must have increased the torque he can produce over a prolonged period, and given that he is still riding the same cranks, he must therefore be exerting a greater force.

The OP is then questioning how this logical (and correct) assumption tallies with the claim that cycling does not build 'strength'. I believe the answer lies in what you refer to as 'strength'. The physiological adapations caused by this cyclist's training regime have enabled him to increase the level of force he can exert for a prolonged period. These adaptations will be things such as hypertrophy of slow twitch muscle fibres which have no bearing on the amount of force the individual can produce in a one-off effort, such as a weighted squat or leg press, so if you judge strength as the maximal amount of force a muscle can exert, then cycling is of little benefit.

So in summary, cycing has not incrased the amount of force the leg muscles can exert in a single effort, but it has incrased the force they can repeatedly exert for a prolonged period.

Of course, if the cyclist is also doing sprint training or other very high intensity effort, there may be some crossover, but this doesn't effect FTP.

SteveR_100Milers

Simon Notley wrote:

If I understand correctly, the OP is saying that, if you consider a rider with an FTP of 250W and who always pedals at 90rpm who then trains and increases his FTP to 300W and still pedals at 90 rpm then that rider's training must have increased the torque he can produce over a prolonged period, and given that he is still riding the same cranks, he must therefore be exerting a greater force.

The OP is then questioning how this logical (and correct) assumption tallies with the claim that cycling does not build 'strength'. I believe the answer lies in what you refer to as 'strength'. The physiological adapations caused by this cyclist's training regime have enabled him to increase the level of force he can exert for a prolonged period. These adaptations will be things such as hypertrophy of slow twitch muscle fibres which have no bearing on the amount of force the individual can produce in a one-off effort, such as a weighted squat or leg press, so if you judge strength as the maximal amount of force a muscle can exert, then cycling is of little benefit.

So in summary, cycing has not incrased the amount of force the leg muscles can exert in a single effort, but it has incrased the force they can repeatedly exert for a prolonged period.

Of course, if the cyclist is also doing sprint training or other very high intensity effort, there may be some crossover, but this doesn't effect FTP.

Only if the resistance changes! Such as going up hill, or going faster. In both cases, for a fixed cadence, the force at the pedals must increase. I suspect (from trying to do circuit training) that the actual differences in forces required are low, indeed in overall terms the actual foprces required to cycle normal terrain use relatively lower forces (try doing star jumps for more than a minute when you weigh 100Kgs).

Alex_Simmons/RST

SteveR_100Milers wrote:

From a Newtonian physics point of view:

For a given resistance, and constant speed, your power must remain constant. If you increase the gearing, your torque increases to offset the reduction in velocity (in this case being angular), as power = force x distance. Conversely, if you reduce the gearing, (i.e. spin faster), then to maintain the same power output your torque decreases. This is why spinning doesnt wreck your knees (low forces) whereas mashing a big gear does (high forces).

Since the forces are quite low, even at low cadences, I would suggest that knee problems are more likely to do with improper set up and/or inherit problems than the speed at which you happen to turn the cranks.

SteveR_100Milers wrote:

So to answer the OP - to increase power you can either increase torque at same cadence, or spin faster at same torque (force).

But the issue remains, you can't control one independently of the other. It is impossible to apply more torque without also changing cadence.

IOW it is only the power we produce and the gear we ride in that we have control over. We can't independently control cadence or torque. We can make large step changes in both when we change gears but that's a gear choice.

SteveR_100Milers

Alex_Simmons/RST wrote:

But the issue remains, you can't control one independently of the other. It is impossible to apply more torque without also changing cadence.IOW it is only the power we produce and the gear we ride in that we have control over. We can't independently control cadence or torque. We can make large step changes in both when we change gears but that's a gear choice.

Oh but you can, and do regulaly - its called a headwind or an incline. You need to do more work (incease power output) to maintain the same speed (cadence), thus you will increase the force on the pedals. Of course, on the flat, say on the track, and of course if you do not change the gearing, then increasing the force will increase cadence, after all its how you accelerate (where a= Force/mass from Newton again).

The point is that you can achieve the same power output either from high force / low cadence or low(er) force / high cadence. Your point fo gearing ratio is valid of course, in effect the torque/cadence setting is intuitive, we select the appropriate gearing to give us our personal optimum engine.

Alex_Simmons/RST

What you are controlling is your power output and gear.

You are not "controlling" torque independently. Nor cadence. They are just outcomes of the the power and gear plus the resistance forces acting against us.

But I can see it's not quite getting through, so I'll leave it at that.

just pedal and pick a gear that feels good. it's not complicated

SteveR_100Milers

Alex_Simmons/RST wrote:

What you are controlling is your power output and gear.

You are not "controlling" torque independently. Nor cadence. They are just outcomes of the the power and gear plus the resistance forces acting against us.

But I can see it's not quite getting through, so I'll leave it at that.

just pedal and pick a gear that feels good. it's not complicated

I read it and initially agreed, but thinking about it more - surely when you pedal, you deliberately (i.e. initiate a physical response) press harder to go faster or to go uphill at the same speed. You instruct your leg muscles to exert more force (which surely is the same as any voluntary muscular reaction). Power is simply a measure of work done per unit time (joules per second, or watts), work is the total amount of energy expended (joules). So, yes you can *control* the rate at which you do work, but surely the primary control parameter is the force of muscular contraction (Newtons). Your legs dont produce power, unless the force they create moves an object.

That said, that is only a simple Newtonian analysis, the bit I am not sure about is the physiological measurement of the what is going on the leg, for exmaple if you stationary squats, you are not technccally producing any power, but something is going oin the muscle in the form of chemical processes that are generating static forces that must burn energy. Is this what you refer to?