When I was 11 or 12 I powered an incandescent bulb with an exercise bicycle. I think it was 40 or 60 watts. I can totally understand why that guy was exhausted:

When I was 11 or 12 I powered an incandescent bulb with an exercise bicycle. I think it was 40 or 60 watts. I can totally understand why that guy was exhausted: 60 watts wasn't hard for me, because I used to ride uphill every day after school, but the other kids could only get a dim glow.