- It's much easier to find 45-60 minutes of free time in your schedule
- Staying focused beyond this time frame can be difficult
- Cortisol (a stress hormone) has been shown to become mass produced after 60 minutes of intense activity (this includes weight training)
The problem with cortisol is that it has both helpful and harmful effects. Without going too much in depth (so no one goes to sleep on me :) just know that having too much can reduce you immune system response, and cause catabolism... which means burning muscle tissue for energy.
So bascially we want to keep our workouts short, intense, and fun... so we can get back home, eat some delicious food (so we can heal and recover), and get back to our awesome, party time lives. In order to do this... we need to get as much exercise bang for our buck as we can.
Wait... what do you mean? You mean like lifting money?
No, I mean like doing movements that involve a number of muscles being used at the same time. If you can do an exercise that works both the butt and quadriceps (the front of your thighs) at the same time, that saves you time, rather than doing both seperately. By stimulating the most muscle at once, we do a bunch of cool things... like release more growth hormones, cause more microtears, increase your overall heartrate and conditioning, and generally get stronger and feel better. We call these "Compound Exercises". They involve more than one muscle group.