Human Powered Gym- Part 2

In Part 1 we examined the use of cardio machines (specifically a exercise bike) to generate electricity to power various items in the gym.
The conclusion of Part 1 was that a normal gym goer could power the machine, charge his phone and maybe power a light or two. Alternatively, he could power the machine and the stereo system.

That's for one person. What about if we have loads of machines, with some being used by people at a certain time, and others not (i.e a gym)?
Let's take the gym I go to as an example. It's a relatively small gym, with 6 upright bikes, 2 recumbant bikes (which I will regard as equivalent for the energy-generating purpose), 8 treadmills, 6 cross-trainers and 4 rowing machines, along with various weights machines and free weights.

If all of the bikes are used at the same time (they never are, but let's assume) then the total power being produced will be 56 x 8 = 448W.                                  [This 56W value comes from Part 1]

 However, I reckon that on average only about half of the machines are used at any one time. This means that we have half the power (224W) to use.


This will be just about enough to power the 4 machines (80?W), light up some of the gym (assuming 4 20W fluorescent tubes, 80W), power the music system (which is probably more than 30W as there are quite a few speakers- 50W?) and charge any gadgets the users want to (maximum of 8W).

Hang on, I hear you cry- what about the other machines?

Human Powered Gym?- Part 1

I was in the gym the other day, when I thought "hang on a minute, I'm on a cycling machine, which is just basically making a wheel turn (the basis of electricity generation). Why can't we use this to power the gym- lights, the tvs, the radio, the air conditioning and the machines themselves?"

I suppose a more reasonable question is:
Is it economically viable to install generators attached to the machines in a gym? Noting that:

1.  Almost certainly new exercise equipment would be required.
2. All the machines aren't going to be used all time, so either you need a backup supply system (if the average energy output isn't as large as the energy requirement) or a method of storing the energy (if the average energy is larger than the energy requirement).
3. Generators require something spinning, preferably constantly. This is fine on a bike, but rowing machines, treadmills and cross-trainers won't be quite as simple.

 As I imagined, I am not the first person to think of this idea (nice as it would have been!). In fact, there is a gym in Portland across the pond which does exactly this:

http://news.bbc.co.uk/1/hi/technology/7796215.stm

There are also gyms in Hong Kong using this concept:

http://www.inhabitat.com/2007/03/08/human-powered-gyms-in-hong-kong/

And, as a blue sky "gym concept" island:


http://www.alternative-energy-news.info/human-powered-workout-gym-concept/

For this last article, I am not so interested in the article itself, but the comments after it.

This is all very interesting, but let's examine (using the figures found on the companies websites, as well as other sources I will mention) the actual numbers.