When inactive young people do light cycling, how hard they feel they're working is closely linked to their body switching from burning fat to burning carbs.

If you're out of shape and find light cycling easy, your body burns more fat. But if the same workout feels hard, your body switches to burning more sugar instead.

When inactive young people do light cycling, their bodies burn the most fat at very easy effort levels — but as it starts feeling harder than 'light,' fat burning drops off, showing there's a sweet spot for burning fat during exercise.

When inactive young adults do light cycling, their bodies burn 2 to 4 times more calories than when resting, and they keep burning fat at a high rate even as the effort increases.

People feel much more tired after doing weightlifting with only 1 minute of rest between sets than with 2 minutes of rest, no matter if they’re at high altitude or breathing oxygen-poor air.

When guys who regularly lift weights do more sets of squats and leg exercises in one workout, they feel like they worked harder afterward.