A Harvard doctor says these are the best exercises for your body

If you think running a marathon is the quickest ticket to a rock-hard body, I-Min Lee, a professor of medicine at Harvard Medical School, has news for you: That classic feat isn't as good for your body as it seems.

Instead of long-distance running, which can be hard on your joints and digestive system, Lee recommends five other types of workouts. They generate benefits that range from weight loss and muscle building to protecting your heart and brain and strengthening your bones.

The findings are detailed in a Harvard Medical School health report called "Starting to Exercise" which recommends some of the best exercises for your body.

Here they are.

1. Swimming

"You might call swimming the perfect workout," write the authors of the Harvard Healthbeat newsletter, which summarizes the report's key takeaways and gives insight from Lee.

In addition to working nearly every muscle in your body, swimming can raise your heart rate to improve heart health and protect the brain from age-related decline. Plus, being afloat makes this type of exercise nearly strain-free. "Swimming is good for individuals with arthritis because it's less weight-bearing," Lee said in the newsletter.

When you swim regularly for at least 30 to 45 minutes at a time, you're doing aerobic exercise — a type of workout that a spate of recent research suggests could help battle depression, lift your mood, and reduce stress, among other benefits.

2. Tai chi

Tai chi — also called tai chi chuan — is a Chinese martial art that combines a series of graceful, flowing movements to create a sort of moving meditation. The exercise is performed slowly and gently with a high degree of focus and a special attention paid to breathing deeply. Since practitioners go at their own pace, tai chi is accessible for a wide variety of people — regardless of age or fitness level.

Tai chi "is particularly good for older people because balance is an important component of fitness, and balance is something we lose as we get older," Lee said.

3. Strength training

At its most basic, strength training involves using weight to create resistance against the pull of gravity. That weight can be your own body, free weights like barbells or dumbbells, elastic bands, or weighted ankle cuffs.

Research suggests you can use either heavy weights and a small number of reps or lighter weights and more reps to build stronger, more sturdy muscles.

Chris Jordan, the exercise physiologist who came up with the viral 7-minute workout (officially called the "Johnson & Johnson Official 7 Minute Workout"), told Business Insider that healthy adults should incorporate resistance training on two to three of the four to five days per week that they work out.

You can also use high-intensity interval training (HIIT), which combines the cardiovascular benefits of cycling or running with resistance training, to achieve the same or similar results. If you like HIIT, the 7-minute workout is a great place to start.

Whichever workout you try, the most important thing is to keep doing it.

"To achieve results, consistency is key," Jordan said.

4. Walking

It might sound insignificant, but walking can be powerful medicine.

Several studies suggest that walking for at least 30 minutes — even at a moderate or leisurely pace — can have benefits for the brain and body. One recent study found that in adults ages 60 to 88, walking for 30 minutes four days a week for 12 weeks appeared to strengthen connectivity in a region of the brain where weakened connections have been linked with memory loss. And a pilot study in people with severe depression found that just 30 minutes of treadmill walking for 10 consecutive days was "sufficient to produce a clinically relevant and statistically significant reduction in depression."

If you don't currently exercise regularly, the folks at Harvard recommend starting your walking routine with 10-15 minute treks and building up to 30 or 60-minute hikes.

5. Kegel exercises

Kegel exercises are important for both men and women because they help to strengthen a group of muscles commonly referred to as the "pelvic floor." As we age, these muscles — which include the uterus, bladder, small intestine, and rectum — can start to weaken. But keeping them resilient can have important benefits, ranging from preventing embarrassing accidents like bladder leakage to the accidental passing of gas.

The right way to do kegels involves squeezes the muscles you'd use to hold in urine or gas, according to the folks at Harvard. They recommend holding the contraction for two to three seconds, releasing, and repeating 10 times. For the best results, do them four to five times a day.

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