Rest -you need to give muscles 24hrs to rest. they rebuild over this time, hopefully stronger.
however, a planned week means you can exercises most days. so for example do legs day 1 upper body day 2 and so on OR push exercises day 1 and press exercises day 2. this rests the muscle groups onver 24hrs and leaves other muscles to work the next day. some people do CV work like treadmill (aerobic) and weights (anerobic) im not sure you can isolate the fast and slow twitch muscles that well but might work for you