The volume (i.e., reps x sets) of each workout is dependent on your experience level as well as fitness goal. For example, beginning trainees aiming to lean out should perform 1 to 3 sets of at least 12 reps whereas those who wish to increase strength should perform 1 to 6 sets of 6 to 8 reps. Those who want to add muscle mass to their body should generally perform 3 to 6 sets of 8 to 12 reps whereas those who want to increase power should perform 1 to 6 sets of no more than 6 reps with heavy loads at slow speeds or more than 30 reps with light loads at quick speeds.
The duration of your total workout (i.e., resistance plus cardio training) may range anywhere between 45 minutes to 2 hours. Working out longer than 2 hours will not provide much added benefit in terms of building lean body mass due to depleted muscle glycogen levels. Your overall energy level drops considerably when working out much longer than 2 hours and you begin to accrue diminishing returns (i.e., onset of muscle catabolism) as a result.
The duration of your cardio training, like resistance training, depends on your experience level as well as fitness goal. Beginners should train from 20 to 45 minutes, intermediates should train from 20 to 90 minutes, and advanced trainees should perform anywhere from 25 minutes to 2 hours of cardio per day. Interval training (i.e., interspersing high- with low-intensity) is an efficient way to workout and is recommended for those whose fitness goal is to burn bodyfat in the shortest amount of time. Durations for each intensity level may vary anywhere between 30 seconds to 5 minutes for total durations between 15 to 60 minutes.
Whatever your training experience level and fitness goal, the important concept here is to get the workout done within the shortest time possible. In other words, get in and out of the gym as quickly as possible! This is a case where less is more. The gym is not the time for social hour--you can chat and catch up on who's dating whom outside of the gym. You should have the mindset that as soon as you step into the door you will perform your intended workout to its fruition and then get out! Nothing else matters while your training. Total focus on your workout is paramount!
So how can you ensure your workout time will be as brief as possible? The key to accomplishing a good hard workout within a relatively short period of time is to lessen your rest periods between each set and/or exercise. Trainees intending to lean out should rest no more than 30 seconds, those aiming to build muscle mass should rest between 30 to 90 seconds, and those wishing to gain strength or power should take anywhere from 2 to 5 minutes rest depending on the loading. My advice is to have a stopwatch or interval timer handy so you can time your rest periods. Trust me--your workouts will be much more efficient as a result and then you can get on with your day.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."