You can become very strong and grow large muscles just by lifting a single set of 6 to 12 repetitions of a weight that is 75 percent of your maximum, three times a week (Sports Med, Apr 2020;50(4):751-765). You need to lift a weight heavy enough to damage muscle fibers to make a muscle bigger and stronger, but causing more damage than that increases your chances of injuring yourself.

Basic Principles
• You will not become any stronger or grow larger muscles by lifting weights six times a week than you will by lifting three times a week, as long as you do the same volume of lifts (J Strength Cond Res, Jul 2019;33 Suppl 1:S122-S129; J Strength Cond Res, May 2018;32(5):1207-1213).
• You will not become stronger by lifting all muscle groups five days a week than by doing only one muscle group a day for five days as long as you do the same number of sets (10-15 sets), same number of exercises, same number of 6-12 repetitions maximum, at 70-80 percent of your one-repetition maximum (J Strength Cond Res, Jul 2019;33 Suppl 1:S130-S139).
• As long as you train to failure (which means you are lifting to the point of fatigue), you can gain about the same amount of strength and muscle size either by lifting heavy weights a few times or by lifting lighter weights many more times (J Strength Cond Res, Oct 2015;29(10):2954-63).
• Taking longer rest periods between sets will cause greater gains in strength and muscle size, because increased rest between sets allows you more time to recover for your next set (J Strength Cond Res, July 2016;30(7):1805-12).

How Muscles Become Stronger
Muscles are made up of thousands of fibers just as a rope is made of threads. Each fiber is made up of blocks called sarcomeres joined end to end at the Z-lines like a line of bricks. Muscles contract only at each Z-line, not along the entire length of a fiber. There is a diagram showing sarcomeres and Z-lines here. Intense workouts cause muscle damage, which can be seen as bleeding into the muscles themselves and disruption of the Z-lines that hold the sarcomeres together. Significant increases in muscle strength and size come only with workouts intense enough to break down muscle Z-lines, without causing the fibers to separate. See Delayed Onset Muscle Soreness (DOMS). When muscles heal they become stronger and larger.

My Recommendations
• Before you start a program of lifting heavy weights, you should lift light weights. Most novice lifters do better with strength machines (rather than lifting free weights) because the machines guide your motions, which helps to prevent injuries.
• For each exercise, pick a light weight resistance that you can lift at least 10 times in a row comfortably without straining. Start out with only one set. Do this three times a week, never on consecutive days.
• As you become stronger, increase the repetitions and stop each set when you tire or start to feel a burning in your muscles.
• When you can lift a weight 30 or more times without straining, you should increase the weight on your next workout, and lift that weight repeatedly until you start to feel a burn.
• This program will make you stronger and help you to grow larger muscles.
• If you really want to become much stronger, get instructions from an experienced lifter on doing single set training to failure. You don’t have to do multiple sets unless you want to become very strong, have exercised regularly for months, are in very good shape and do not have any health conditions that might be harmed by this type of exercise.

Note (3/28/20): Diana and I are trying to find ways to stay fit through this time of restrictions, when we have no access to our regular gym, dancing, and other physical activities. My article above goes over some principles of weight training that you can use at home. Without gym-quality weight training equipment, you may need to get creative about ways to maintain (or start) your resistance exercise program. You can put cans or other heavy objects into shopping bags to use for weights, or you may want to go on Amazon or other online shopping options and order yourself some home equipment. Exercises that use your own body weight for resistance, such as stair-stepping, sit-ups or push-ups, can also be used as part of your weight training program.

Whatever else you are doing, try to get at least 30 minutes of exercise each day and include both aerobic and resistance activities. Most “stay home” restrictions allow you to go outside for exercise, so you can walk, jog or cycle, as long as you follow the “social distance” requirements. Stay well and be safe!