1 . Running is often tiring and a lot of hard work, but nothing beats the feeling you get after finishing a long workout around the track.

But while it’s long been believed that endorphins (内啡肽) —chemicals in the body that cause happiness—are behind the so-called “runner’s high”, a study suggested that there may be more to this phenomenon than we previously knew.

According to a recent study published by a group of scientists from several German universities, a group of chemicals called endocannabinoids (内源性大麻素) may actually be responsible for this familiar great feeling.

To test this theory, the scientists turned to mice. Both mice and humans release high levels of endorphins and endocannabinoids after exercise. After exercising on running wheels, the mice seemed happy and relaxed and displayed no signs of anxiety. But after being given a drug to block their endorphins, the mice’s behavior didn’t seem to change. However, when their endocannabinoids were blocked with a different drug, their runners’ high symptoms seemed to fade.

“The long-held notion of endorphins being responsible for the runner’s high is false. Endorphins are effective pain relievers, but only when it comes to the pain in your body and muscles you feel after working out,” Patrick Lucas Austin wrote on science blog Lifchacker.

Similar studies are yet to be carried out on humans, but it’s already known that exercise is a highly effective way to get rid of stress or anxiety. The UK’s National Health Service even prescribes (开药 方) exercise to patients who are suffering from depression. “Being depressed can leave you feeling low in energy, which might put you off being more active. Regular exercise can improve your mood if you have depression, and its especially useful for people with mild to moderate (中等的) depression,” it wrote on its website.

It seems like nothing can beat that feeling we get after a good workout, even if we don’t fully understand where it comes from. At least if we’re feeling down, we know that all we have to do is to put on our running shoes.

When I was four, my seven-year-old brother received a baseball glove for his birthday. Every night. as we went to sleep. I’d listen to him throwing a ball into the glove over and over to soften the leather. I wanted a glove so much that I almost cried. But, back then, girls didn’t play sports; they played with dolls (洋娃娃).

Fast-forward twenty-six years. Now a thirty-year-old mother of two boys and a girl, I happened to sec a notice in my local paper: “Women’s Baseball League opens soon. Anyone interested, sign up at the community service center.” I cut it out and set it on the kitchen table, Could I? After all these years?

I looked at that notice on my table every day. l thought of a thousand reasons I couldn’t play. But the idea of playing baseball stuck in my head and wouldn’t go away. Finally, 1 gathered up my courage and signed up. Since I wasn’t a member of any team, they told me I’d be assigned (分配) to one. Two weeks passed before they gave me the name of the team to look for. Since my husband worked Monday nights, I arranged for a babysitter. It was a luxury (奢侈) but, at that moment in my life, a necessity.

On Monday, heart pounding, I walked through the park filled with women of all ages practicing. It took me a while to find my team. They were all high-school girls, seventeen and eighteen years old! I waited a couple of minutes before approaching the coach. He had put together top athletes for his team, and he didn’t want some old lady messing things up. He looked me over. His girls had fine gloves and metal cleats (棒球钉鞋). They looked like players. I had no glove and wore an old T-shirt and gym shoes. I didn’t care. I wanted to play. That first day, he had me run bases (跑垒). I never got a chance to bat or play the field. I just ran bases all night. The next morning, I could hardly stand.

When I showed up the next Monday, the coach was clearly surprised.

“Impressive catch!” my teammates cheered for my performance after the training.

5 . Race walking shares many fitness benefits with running, research shows, while most likely contributing to fewer injuries. It does, however, have its own problem.

Race walkers are conditioned athletes. The longest track and field event at the Summer Olympics is the 50-kilometer race walk, which is about five miles longer than the marathon. But the sport’s rules require that a race walker’s knees stay straight through most of the leg swing and one foot remain in contact (接触) with the ground at all times. It’s this strange form that makes race walking such an attractive activity, however, says Jaclyn Norberg, an assistant professor of exercise science at Salem State University in Salem, Mass.

Like running, race walking is physically demanding, she says, According to most calculations, race walkers moving at a pace of six miles per hour would burn about 800 calories(卡路里) per hour, which is approximately twice as many as they would burn walking, although fewer than running, which would probably burn about 1,000 or more calories per hour.

However, race walking does not pound the body as much as running does, Dr. Norberg says. According to her research, runners hit the ground with as much as four times their body weight per step, while race walkers, who do not leave the ground, create only about 1.4 times their body weight with each step.

As a result, she says, some of the injuries associated with running, such as runner’s knee, are uncommon among race walkers. But the sport’s strange form does place considerable stress on the ankles and hips, so people with a history of such injuries might want to be cautious in adopting the sport. In fact, anyone wishing to try race walking should probably first consult a coach or experienced racer to learn proper technique, she says. It takes some practice.