This question about following a weight training schedule is asked quite often, and the answer is surprisingly simple.
When using weight training as your means of developing and maintaining strength, the fundamental principle is that muscles should not be worked every day. A muscle should be rested for at least 48 hours between workouts. The best news is that there is no scheduling excuse to not weight train other than planning to work the muscles two or three times per week.
So, divide your workouts so they fit into YOUR schedule each week.
Personally, I separate my workouts into upper and lower body so that I work each group twice per week. Sometimes, I will add a third workout for a muscle group just to mix it up a bit -- higher reps with lighter weights or lower reps with heavier weights. You may prefer to do your entire body in one workout.
No matter how you approach it, you must bear in mind the three principles phases of weight training discussed below.
Muscle develops because this form of exercise creates microscopic tears in the muscle, and that trauma sends signals that the tissue needs to be repaired.
This principle has been around since the late 1940s.
In weight training, you must repeatedly place a demand on the muscle for a minimum number of reps and sets in order for it to grow. Increased strength and growth is the result of the muscle adapting to that demand over time.
For upper body, that would be a weight that you can control for 8 - 12 repetitions.
For the lower body, use a weight that you can lift with control for 12 – 15 repetitions.
If you can do more than 12 repetitions on the upper body or more than 15 on the lower body, it’s time to slightly increase the weight you are using for that body part to keep the repetitions within that range.
Do more than one set. Studies show that 3 sets are better than one for maximal strength gain.
Having to increase the weight means that your muscle has adapted to the demand you are placing on it, and you are making progress. Increasing resistance over time is essential.
I often see people in the gym rest for long periods between sets. Unless you are a power lifter or Godzilla, you are missing out on some great gains in muscle adaptation.
My rule of thumb – Rest for 45 to 60 seconds between each set. You want the muscle to rest, but you don't want it to recover. Recovery is a totally different phase.
For a refresher on the meaning of the terms "set" and "repetition," check out Weight Training For Beginners.
I cannot stress this phase enough. It is especially important as we age.
Never lift weights for any body part two days in a row. As stated previously, and worth the emphasis, our weight training schedule should allow at least 48 hours of rest for each muscle group.
Working a muscle two times each week is sufficient to make gains if you are working the muscles with sufficient intensity.
Rest, and proper nutrition, allow the muscles to heal and adapt to the demands you have placed on them -- making them stronger over time.
Don't let your training out-pace your recovery time.
Remember that it is YOUR weight training schedule, and this website is a no-excuses website.
If all you can do is one session on a particular week for any and all muscle groups, increase the intensity of your training on that day. Instead of three sets, do four or five sets. Do pyramids or hundreds to mix it up a bit. Muscles tend to respond very well to this approach.
Weight training is an efficient use of your time, leaving you more time for other things during your week. You can complete a full-body workout in about 45 minutes if you use your time wisely.
Mix it up! Keep it fun!