You could probably get electrical energy that is needed to run a gym (lights, accountant pc, vending machine) if you just install generators in all of this gym's exercise equipment

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70 W is very casual riding, anyone actually taking will be more in the 100-150 W range. My fridge uses 70 W as an example, and only when actively running, with a duty cycle of 40% or so. Obviously this isn't an industrial fridge or freezer.

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The energy used probably wouldn’t even heat the water for the showers though.

Not even close. Someone posted a video of an Olympic cyclist going all out running a 700 Watt toaster for 2 minutes, and he was exhausted after that. A water heater would be like 3000 Watts and would need to run for a long time to heat up an entire tank of water, which would last for just a couple quick showers.

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I’ve considered instead of energy generation which is pretty hard for human biomechanics to do, we could have a gym where you build stuff. Like today’s workout is you have to build a wall.

Carry a bunch of wood around (squat, deadlift, carries ).
Do some sawing (row, push up).
Lift wood overhead (press).

And at the end of the workout you’ve got a wall!

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but if you want the fridge you need five cyclists

Your numbers suggest the fridge uses 5 * (30 to 70), or 150 to 350 watts. Which are reasonable numbers when the compressor is running.

But, the duty cycle of a fridge is typically less than 30%. It only draws a couple watts with the compressor off and the door closed.

In a long enough "race", two cyclists should be able to drive the electric meter backward faster than the fridge drives it forward.

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My first factory job was a workout. I spent all day taking bundles of ice cream products off a conveyor and placing them on skids. I liked that aspect of the job, or any job that involves physical activity.

The first week was brutal with muscle pain, but then my body got used to it.

I do white collar work now but kinda wish I could do that kind of work like one day a week or something.

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It's a tough ask. A bicycle generator will be 70% efficient, and a healthy amateur could do 100w over an hour of effort generating 70w. A treadmill would have a lot more friction, and a rowing machine gets nowhere near the power you can generate from your legs. A linear "foot press" exercise machine is not as efficient as the circular motion of cycling.

Power requirements of a gym might also include music systems, outside lighting. Heat/hot water could come from gas.

It can still be worth adding generators and wiring to exercise machines to offset energy consumption, including batteries to prevent peak TOU rates. But it is a tough ask to disconnect from grid, without solar.

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but a relay team could do 600watts "continuous".

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It would have to be a pretty big relay team. The recovery time for 2 minutes of all-out power exercise is pretty long.

Look at the size of this guy's thighs. He's a freak of nature (in the positive sense of the term) who trains for this specific type of exercise and had to stop after 2 minutes because he was in so much pain. I can't imagine he'd be ready for another all-out run in less than a couple hours, and after two in a day, probably would need a day's rest.

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Something like this has been prototyped by a group including the peeps behind low tech magazine: https://www.humanpowerplant.be/
It's really cool!

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Have you watched Nathan For You?

Nathan for You - Wikipedia

(en.wikipedia.org)

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6 guys simultaneously doing 100w for an hour has a much larger "relay pool" of available athleticism.

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That's fair. But that's still a lot of work for so little work, if that makes sense. Which is kind of what the demonstration showed.

A man at the peak of human athletic capability could barely put in enough energy on his own to slightly toast a piece of bread. Of course 6 people could put in one sixth of the effort, but that's six people still working such a small output.

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For a 2 slice toaster, they could make 60 toast per hour. Primitive human hunters had an endurance advantage over all prey, as sweat is a cooling system. They could run long enough to exhaust the prey. I still imagine horses could produce more electricity. Though apparently a horse can travel just 20-30 miles per day, while an average cyclist could do 60+.

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That's 1440 slices of toast per day. Using random numbers from google, that's 110k Calories worth of plain white bread. Assuming 6 people putting in the work, that's a bit over 18k per cyclist for 24 hours cycled, who each would require about 12k Calories for the work put in.

However, this is just to toast the bread, not to make the bread. I'm being a little dumb and taking this hypothetical a bit too far.

HubertManne

yeah. it still amazes me how much it takes to actually burn calories and its mostly heart rate that does it. I was thinking how you won't get anything from the free weights or aerobics classes along with swimming and heating pools, sauna, hot tub is not insignificant. I think it could be done as long as what the gym offers is limited and it uses very energy efficient things.

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Eh if you want to go real efficient you just drop the heating music and light and have only non electric machines and voilà! 0W used

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At the door there’s a bike. Start peddling to turn the lights on.

After a quick warmup, you can find your way to the rest of the gym. All the other machines also power the lights, air conditioning, showers etc.

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What if you have anxiety?

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There is a YouTube video around of a sprint cyclist powering a toaster and he can barely do it. I don't think you could do it "reasonabley".

DankOfAmerica

I do! How did you know?? I'm stressing out