1. Aerobic activities

Often called cardio or endurance activities, aerobic activities are great for burning calories and paring down unwanted fat. These activities—think of walking, biking, running, and swimming—push large muscles to repeatedly contract and relax. This temporarily boosts your heart rate and breathing, allowing more oxygen to reach your muscles and tuning up cardiovascular endurance.

Experts once believed cardio activities were beneficial only if you kept your heart rate hammering in the aerobic range—70% to 85% of your maximum heart rate—for a specified length of time. (Maximum heart rate is roughly estimated as 220 minus your age.) But research now shows you’re gaining benefits even when working at a more moderate intensity.

How often to perform

The Physical Activity Guidelines for Americans recommend at least 150 minutes of moderate-intensity physical activity (such as a brisk walk) or 75 minutes of vigorous-intensity physical activity per week. You can also perform an equivalent combination of the two intensities. As you start to work out more often, you’ll notice gains as exercises become easier.

2. Strength training

Strength or resistance Training, which typically uses equipment such as weight machines, free weights, and resistance bands or tubing, protects against bone loss and builds muscle. Technically, strength or resistance training takes place any time your muscles face a stronger-than-usual counterforce.

Isotonic actions, such as lifting a dumbbell from knee height to shoulder height, prompt muscles to shorten or lengthen to move the attached joint through its range of motion. The resistance the muscle works against—the dumbbell—is uniform.

Isometric actions, such as pushing against a wall or struggling to lift an extremely heavy weight, force muscles to work against fixed resistance, so no such shortening or lengthening occurs. In fact, there’s no muscle movement, and resistance can vary depending on how hard you push against the wall or pull on the weight. While isometrics are a quick way to build muscle strength within a very limited range of motion, they’re also the most stressful for your heart and circulatory system. You can safely build muscle strength and endurance through isotonic exercise without overtaxing your cardiovascular system.

Strength training with progressively heavier weights or increasing resistance makes muscles bigger—though usually not by much unless genetics allow this and you frequently perform challenging workouts. Even without obvious muscle growth, though, these activities enhance the ability of the nervous system to activate motor units. Aside from toning you, strength training guarantees you’ll have the functional strength to carry out everyday activities—lifting groceries, climbing stairs, rushing for the bus—with ease.

How often to perform

The Physical Activity Guidelines for Americans recommend two sessions a week. But note that your body needs at least 48 hours for recovery and repairs between strength training sessions. So if you do an upper-body strength workout on Tuesday, don’t repeat it before Thursday.

3. Flexibility exercises

Flexibility exercises like stretching, yoga, and Pilates gently reverse the shortening and weak ening of muscles that typically occur as you age. Shorter, stiffer muscle fibers may make you vulnerable to injuries and contribute to back pain and balance problems. Plus, secretions designed to lubricate muscles tend to dry up as you grow older.

The good news? Frequently performing exercises that isolate and stretch elastic fibers surrounding muscles and tendons helps counteract this decline. Encouraging blood flow to muscles makes them more limber. And a well-stretched muscle more easily achieves its full range of motion, which improves athletic performance. If you’re a tennis player, you could reach an overhead you might have missed. Or think about a golfer who is able to swing with greater ease and less restriction. Likewise, reaching, bending, and stooping during daily tasks may be easier, and a hard-to-reach shoelace or fastener may now be within grasp.

At one time, experts prescribed stretching before exercise to help people sidestep injuries. Newer research suggests this does no good. It’s better to stretch when your muscles are warm and pliable by folding flexibility exercises into your post-workout cool-down.

Stretching between exercises may be fine, too, and possibly helps boost flexibility, as shown in a study on lower-leg and ankle stretching sponsored by the American College of Sports Medicine (ACSM).

How often to perform

The ACSM recommends doing flexibility exercises at least two to three times a week. Hold stretches for 10 to 30 seconds, repeating each stretch four times.

4. Balance exercises

Want to improve stability, which tends to erode as you age? Balance exercises can help you do just that. They offer an excellent defense against falls, which can be far more dangerous than you might imagine. Often, falls cause head injuries and temporarily or permanently disabling bone fractures. Balance typically worsens over time, compromised by medical conditions, medications, changes in vision, and lack of flexibility. Activities that enhance balance include tai chi, yoga, Pilates, and numerous exercises in this report designed to challenge stability.

How often to perform

Two to seven days a week.

5. Relaxation exercises

Relaxation exercises are not, strictly speaking, a component of most fitness programs. Yet stress reduction enhances quality of life and health. Some disciplines like Pilates, yoga, and tai chi meld tension-melting movements with mental focus and meditation. While improving strength, flexibility, and balance, practitioners ease stress, relieve pain, and gain an overall sense of well-being. Even walking can be a meditative practice. Stretching, too, releases muscle tension and promotes inner calm.

How often to perform

Incorporate a daily dose of relaxation.

Five Ways to Juice Up a Workout

1. Power training

Muscle power is the intersec- tion of speed and strength: how quickly you can exert a given force to produce a desired movement. Strength in your leg muscles helps you walk across a four-lane intersection; speed moves you swiftly enough to beat the light. When not tuned up, speed ebbs even more quickly than muscle strength as you age. That means to maintain power over the years, it’s important to focus on speed in at least some of your workouts. Power training may hinge on fast, explosive moves like the plyometric jumps in the “Power challenge workout”, or require you to do exercises at your usual pace while wearing a weighted vest. Athletes often use power moves tailored to their sports in order to bump up their game.

2. Interval training

Interval training consists of bursts of vigorous activity alternating with lower-intensity activity. You might jump rope for a minute, then walk briskly for three minutes, then repeat the pattern. Or break up your usual walk by jogging—or sprinting—at regular intervals. Interval training alternates aerobic activities, which use oxygen to turn stored glycogen into energy, and anaerobic activities, which don’t need oxygen to make the energy conversion. Training this way delivers cardiovascular benefits and challenges muscles sufficiently to strengthen them. Additionally, it can bump you up to the next level if your exercise reaches a plateau.

3. Periodization

Periodization is a training technique based on the idea that muscles adapt to challenges. A weight that’s initially hard to lift becomes less challenging as your muscle grows stronger. If you keep using the same weight or doing exactly the same exercise routine, for example, your muscles stop improving.

Periodization helps you avoid overuse injuries and improve fitness by changing up your workout periodically—every five to six weeks is typical, but time frames vary from person to person. Switching to a new workout challenges different muscle groups and often builds different components of fitness.

An equally important reason is compliance. It’s easy to get bored by an exercise routine. Creating variety makes exercise more interesting and fun. Fitness pros and athletes use periodization in very specific ways to train for sports events.

4. Task-specific training

Often, exercises are designed to isolate specific muscles—biceps, let’s say, or knee extensors—to work on building them up. Task-specific training takes a different approach by working multiple muscle groups through dynamic movements similar to those you might make in sports or daily life. Depending on its focus, task-specific training can bolster athletic performance or basic abilities. Many of the workouts in this report include this type of training. An exercise in which you swing your arm up while rotating at the waist helps hone muscle sets you might use in golf, tennis, squash, or volleyball. Explosive jumps from one side of a rope to the other build muscles used in skiing, basketball, and soccer. Meanwhile, squats and chair stands strengthen muscles that allow you to sit, rise from a seat, and walk up stairs—all tasks important for independent living.

5. Complex workouts

These workouts braid together two or more exercises into a single sequence. Flowing from one exercise—and muscle group—to the next without pausing for a rest between each exercise delivers a strong, time-efficient workout. For example, one set might be eight to 12 reps of a sequence requiring a bridge, leg extension, and hamstring curl, followed by a rest before starting a second set. Complex workouts are an excellent way to add variety to your exercise routine, often while increasing the challenge.

Adapted with permission from Workout Workbook: 9 Complete Workouts to Help You Get Fit and Healthy by Harvard Health Publications.