It's the spring (or springs...) in the pedal that return the beater, and these would be adjusted to the tension needed, depending on how one plays. At first, a fairly strong spring is required, but, as one's finesse increases, the tension is backed off, to enable more 'ghost notes', and a more precise control of the pedal. Too soft, and one gets double strokes and poor rebound control. Too hard, the ankle is fighting for control. Best a bit hard at the beginning; this tones up the muscles involved, which are not used to this stuff yet. Same for the hi-hat; the ankle soon tires, so exercise is needed just to build up the hitherto unused body parts. Yes, drumming becomes quite athletic, and needs preparation and progressive training. Eight-hour sessions are not a good idea at the start..! Medium-short sessions, with rests (or changes of target...) are recommended.