Regarding free-weight training, which of the following is the most accurate statement?

Building and maintaining muscle is necessary for all of us, especially as we age. And the earlier we start, the better.

According to the American Council on Exercise, most adults lose nearly a half pound of muscle per year starting around age 30, mostly because they aren’t as active as they were when they were younger. Losing muscle at the same time that metabolism starts to slow down is a recipe for weight gain and the health issues that can accompany it.

Building stronger muscles isn’t just about vanity, either. According to the Mayo Clinic, strength training not only helps with weight control, but also stops bone loss and can even build new bone.

This can reduce the risk of fractures from osteoporosis. It also improves balance and boosts energy levels.

A significant amount of evidence exists to support the overall health benefits of strength training. And there’s been some quite convincing research on the subject recently:

• A study published in Cancer Epidemiology Biomarkers and Preventionsuggested that the more muscle men have, the lower their risk of death from cancer.
• A study published in BMJsuggested that weight training can improve long-term balance in older adults.
• A 2017 study in the Journal of Endocrinology suggested that having muscle can improve insulin sensitivity and glucose tolerance.

The amount of weight you use depends on how many repetitions you’re aiming for. You want to lift enough weight so that the last repetition is really tough and you feel like you couldn’t do one more. Naturally, you’ll need to use a heavier dumbbell for 6 repetitions than you will for 12, even though you’re doing the same exercise.

Never lift so much weight that it causes pain. You are better off lifting too little than too much as your body gets used to weight training. Also, unless you are working out with a spotter, use machines with safety stops in place to prevent injury.

The best exercises depend on your goals and how much time you have. You can do one exercise per body part or you can do six. You can do exercises that focus on one muscle group or exercises that work several at the same time.

The key is balance. It doesn’t look too good to have a huge chest and a weak back, and it’s also not healthy. When you work on one muscle, make sure you also schedule time to work on the opposing muscle.

All muscles are broken into pairs consisting of an extensor muscle and a flexor muscle. These muscles complement each other and work in opposition to one another, flexing while the other is extending and vice versa. Some muscle pairs relevant to weight training are:

Here’s a workout designed for novices. All it takes is at least two half-hour sessions each week.

For each of the following exercises:

• Start with one set of 8 to 12 repetitions (reps) for the first four weeks. When choosing weight, remember that the last 2 or 3 reps should be very difficult.
• Increase to 12 to 15 reps for the next four weeks.
• When performing 15 reps becomes easy, add a second set of reps (doing the same number of reps per set) or use a heavier weight.

Be sure to take deep breaths while you are doing these exercises. Always exhale during the exertion part (the “lifting” phase) of the move.

Dumbbell chest fly (targets chest)

• Lie on your back with support under your head, shoulders, and upper back.
• Hold a dumbbell in each hand. (Start with 2- to 5-pound dumbbells.)
• Push your arms straight up until your elbows are almost entirely extended, palms facing each other. The weights should be directly above your shoulders.
• Inhale and slowly lower your arms out to the side, keeping your elbows slightly bent.
• Continue to lower your arms until your elbows are slightly below your shoulders.
• Pause, exhale, and slowly close your arms back to the starting position.

Dumbbell overhead triceps extension (targets triceps)

• Stand with your feet shoulder-width apart.
• Hold a dumbbell in each hand with your arms extended overhead. (Start with 2- to 5-pound dumbbells.)
• Without moving your elbows, slowly lower the right dumbbell behind your neck, pause, and then lift it to the starting position.
• Repeat with the left hand.

Dumbbell shoulder press (targets shoulders)

• Sit on a chair with back support and put your feet flat on the floor.
• Hold a dumbbell in each hand. (Start with 2- to 5-pound dumbbells.)
• Bend your arms so the weights lightly rest on your shoulders, palms facing forward.
• Push the weights up until your arms are straight, pause, and slowly return to the starting position.

Single-leg squat (targets buttocks, quadriceps, and calves)

• Stand with your feet shoulder-width apart and your arms out to the side, raised to shoulder height.
• Lift your right leg out in front of you and slowly squat down, stopping when you feel like you’re losing your balance. (If you need help balancing, brace yourself by placing one hand on a wall.)
• Contract your leg and buttocks muscles to push yourself back to the starting position.
• Complete reps, switch legs, and repeat.

People do the exact same routine in the exact same order for years. It can be comforting to master your program, but the problem is that your muscles adapt and get bored — and so will you.

Every six to eight weeks, tweak your workout. Change things like the number of sets and reps, rest periods, angles, sequence, and type of equipment. Also keep the following tips in mind for a safer and more effective workout.

Never skip a warm-up

It’s tempting to go straight from the locker room to the bench press, but you’ll be able to lift more if you warm up your muscles with five minutes of aerobic exercise. Also, go easy on your first set of each strength-training exercise.

Don’t let momentum do the work

When you lift weights too fast, you develop momentum, which can make the exercise too easy on your muscles. People are especially lax on the return phase of a lift: they’ll often hoist the dumbbells up slowly and then let them come crashing down.

To guard against that, take at least two seconds to lift, pause for a second or two at the top of the movement, and take a full two seconds to return the weight to the starting position.

Don’t hold your breath

People often forget to breathe when they lift. You need as much oxygen as possible when lifting. Holding your breath or taking breaths that are too shallow can increase your blood pressure and zap your energy. Breathe through your mouth rather than your nose.

For most exercises, exhale when you lift or press the weight and inhale when you lower it. For exercises that expand your chest cavity (such as upright or seated rows), it’s more natural to inhale as you lift and exhale as you release.

Mix it up

To keep making gains, you must vary your routine every six to eight weeks. For instance, increase the amount of weight you lift (increase by no more than 10 percent at a time), increase the number of repetitions, and reduce the rest time between sets.

How many repetitions are enough? You should be lifting enough weight that the last two or three repetitions are very challenging. For most people that’s in the 12- to 15-pound range.

With a good strength-training routine, you may see results in just a few short weeks. Keep up the effort, and more-defined muscles, better balance, and improved overall health will be the result.