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Power Generated During Exercise And The Possibility Of Human-Powered Flying Machines

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Contributor:
Phil Stewart
Phil Stewart

One of the best measures of athletic performance is power output. Measured in watts, it’s exactly equivalent to the power that lights a bulb or moves a car. Tour de France cyclists run at about 500 watts for hours on end, and can hit output of 1500 watts in short bursts. How does this compare to you and I?

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Whereas VO2 max measures the potential of an athlete, power measures the actual energy being created by an athletic motion. Creating this athletic power is a process that begins with chemical reactions in the body. Your body uses oxygen and food to create a chemical called ATP. ATP is the ‘fuel’ of your muscle cells, stimulating muscular contraction and creating movement. Movement of your body can then be applied to your self (like in running) or to things (like a bike). What your personal athletic power is applied to will determine how fast you go.

The power output of yourself or these things can be measured to see how much work you are actually doing.
Athletic power of the people is generally measured in watts per kg of bodyweight. We can therefore expect heavier people to be (potentially) able to generate more power.
 
How much can we generate?

For sustained periods – let’s say about an hour – here’s the athletic power output for different types of people:

The average fit person can produce about 3 watts/kg
top amateurs produce 5 watts/kg and
elite athletes achieve 6 watts/kg

So, all things being equal, if you weigh 80kg you can generate more power than if you are 70kg. Which is all well and good. But if you are heavier you have more weight to move around, so your actual performance is likely to be affected. That is, you have to work harder to move your increased bulk, or you might end up going slower than a lighter person for the same power output.

If I weigh 90kg let’s say I can produce 90 x 3 = 270 watts constantly.

If you weight 80kg let’s say you produce 80 x 3 = 240 watts constantly.

Who wins a race between us?

It depends on how we are racing. If it’s on a bike, it might be close: I have more power, but I have more weight to pull around. If it’s an uphill race, you will win, as my extra weight becomes more influential.

If we are on a rowing machine, I’ll put my money on me – weight doesn’t come into the equation as much, simply because the machine doesn’t require me to carry my weight.
 
What you are doing makes a difference

On firm, flat, ground, a 70 kg person requires about 100 watts to walk at 5 km/h.

If that same person applies 100 watts of effort on a bicycle, they can average 25 km/h.

So that says a bike is about 5 times as efficient. Or, put another way, the energy efficiency of biking is 5 times that of walking.

I like the rowing machine for cardio over winter when I can’t go and run in sunshine. How efficient is the rowing machine? To create 100 watts of power on the machine requires that I move at 2 min 30 secs per 500m. Quick calculation says this is 12 km/hr. So efficiency of this machine is in-between walking and cycling.

What’s not efficient? Swimming. To move at the same speed as walking, swimming requires about 4.5 times the power output.

Think about the triathalon or ironman – the swimming leg is much shorter than the running leg, which itself is much shorter than the cycling leg. We do the hardest event over a shorter distance because it’s slower at the same level of effort.

cycling 

Cycling is efficient so it's easier to go further
 
Short Bursts of Power

What is really impressive is our ability to create very high levels of power during short bursts.

Elite track sprinters are able to attain an instantaneous maximum output of around 2,000 watts, or in excess of 25 watts/kg.

Elite road cyclists may produce 1,600 to 1,700 watts as an instantaneous maximum in their burst to the finish line at the end of a five-hour long road race.

On the rowing machine, I can create up to 320 watts when I’m rowing at 1 min 45 secs per 500m (my fast speed). I can hold this comfortably for a few minutes at a time. Over 17 minutes of interval-training cardio, I’m averaging 240 watts.

Tour de France cyclist Floyd Landis has been recorded spending nearly four hours straight at a power output of more than 500 watts.  That's a maximum-effort sprint that can only be held for a few seconds to most recreational riders. For top athletes, it's the ability to ride at this stratospheric level that sets them apart.

cycling2 

Tour de France cyclists generate lots of power for long times
 
Peak Power and Long Distance

Over longer distances, you would imagine that peak power becomes less useful as a predictor of abilities. Peak power is largely anarobic (non-oxygen fuel supply), while most types of exercise or events rely mainly on aerobic (oxygen fuel supplies) ability. But this is not so. If you have a high peak power, you generally have great endurance too. Peak power has been proven to be one of the best predictors of 2000 m times in studies on stationary rowers (source – Ed McNeely of The Rowing News)
 
Caffeine Can Improve Your Peak Power

On stationary rowing machines, researchers have seen a 1.2% improvement in 2000 m time and a 2.7% increase in mean power with caffeine ingestion. Another similar study observed most improvements in time came during the first 500 m of an event – and indication anaerobic peak power is being influenced. The start of the event is largely anaerobic, as is peak power, so this suggests that caffeine influences peak power rather than endurance.

A study on cycle performance found that in test subjects peak power increased from 864W to 940W (9% increase) after ingesting a controlled amount of caffeine.

I insist on taking a short black coffee before every workout. Good to know it’s useful for fat loss and power.
 
What Can You Power?

Here are some common items that can be powered, and some power that can be created:

Power users:

Laptop     40 watts
Desktop computer     120 watts
TV     150 watts
Coffee maker     800 watts
Toaster      1000 watts
Microwave    1200 watts

Power suppliers:

Domestic solar panel     50 watts
(Me) Stationary rowing full-out      320 watts
Tour de France cyclist constant speed      500 watts
Tour de France cyclist sprinting      1600 watts
Olympic 100m sprinter first 30 m     2000 watts
1.8 l toyota carolla engine      100,000 watts
6 l V12 Ferrari 599 engine     462,000 watts

ferrari 

Me vs Ferrari 599: one creates 1400 times more power than the other
 
Me vs the Train Part II

Do you know that I once raced an Auckland commuter train to see who could get cross-town faster? It was a fairly close race over a distance of around 7 km.

The question is, how much energy did I use, and how much did the train?

Running at a speed of about 11 km /hr, let’s say I’m producing 3 watts/kg (as above). At 90 kg, that’s 270 watts – which means 270 J (of energy) per second. So over the 40 minutes of my run, that’s a total of 648 kJ of energy.  That’s about the energy two bananas can give me.

The train, however, requires a lot more energy. Our DFT-class locomotives in Auckland produce 1,800,000 W. In my train-race, actual moving time of trains amounted to only 14 minutes. Let’s say the locomotive is averaging only 1,000,000 W for that time (it’s not running at full power). During 14 minutes, the energy required by the locomotive to move the train was 1000000 joules per second for 14 minutes: a total of 840,000 kJ. That is 1300 times the energy I produced. Or equal to the energy of 2600 bananas.

Or put another way: moving the train and the passengers took 1300 times more energy than to just move me.

The question than becomes, how many people were on the train? If there were about 1300 onboard, the energy exerted would (on a pure energy-conservation level) be justified.  But what say there were only 50 people onboard? Do we see the energy used to move the train as being somewhat wasteful? Could that energy be spent elsewhere?

train

The power required to move a train is best spent when the train is full
 
Energy of Man and Machine Part II

A Japanese study called ‘Man as Locomotive Engine’ by Kazuho KAWAI and Masashi HARADA takes man-machine-energy analysis many steps further. These two researchers investigated a human-powered flying machine, where the power created to flap oversized wings is provided by the pilot pulling on a stationary rowing machine.

Yes.

Tiny, propeller-driven conventional aircraft have been proven to fly a person requiring only 200W of power. But what about being propelled by a flapping wing you ask? That's what they were checking out.
Here’s what was concluded:

“The maximal power of rowing is much more than 200 W. We suppose that by using the locomotive movement of a man, the flight with flapping wing is possible as long as the wing is designed appropriately. We should never give up on human flight similar to that of a bird.”

That will do me.

windmill

Source: Body Transform

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