Why do you need to let your muscles rest for 24-48 hours? I workout everyday. I usually spend at least 2 hours working arms, legs, tummy, and treadmill. Maybe I should mention too I am a 22 year old female. I really need to get in shape before my dh returns in 2 weeks. Should I slow down? I feel fine, a little sore sometimes, but I can keep going.
You need the break if you are working your muscles hard in a bid to get bigger or stronger. Simply put, your muscles get bigger or stonger in repsonse to stresses placed on them. This happens after you have exercised, not during exercise, and if you don't give them time to recover properly the benefits will not come.
If you are doing lower weights for general conditioning and fat loss, the rest time needed is reduced in comparison to higher weights used to build up strength. I also believe that we all respond differently to exercise and that recovery time can be an individual thing. Some people can work out the same muscles every day while others need 4 or 5 days before repeating a workout - you have to do what works best for you.