More and more people around the world are joining in dangerous sports. Some people climbed the highest mountains; some traveled to unknown parts of the world; some sailed small boats across the largest sea. Now some people begin to look for new excitement.

Bungee jumping and motorcycle racing (摩托车赛) are quite thrilling sports. Bungee jumping only lasts for a few minutes or even seconds. You jump from a high place, about 200 meters above the ground, and there is a rubber band (橡胶带子) tied to your legs. When you jump down, the rubber band pulls you up. About 2,000,000 people around the world have tried bungee jumping.

Why do people join in these dangerous sports? Some scientists say that it is because modern life has become safe and it is not interesting. In the past, people lived in danger. They had to go out and look for food, and life was like a fight but was interesting.

Many people think that there is little excitement in life. They live and work in safe places, buy food in shops, and there are doctors and hospitals to look after them if they become ill.

Small amounts of exercise could have a great effect on happiness.

According to a new review of research about good moods and physical activities, people who work out even once a week or for as little as 10 minutes a day tend to be more cheerful than those who never exercise. And any type of exercise may be helpful.

A number of past studies have noted that physically active people have much lower risks of developing depression and anxiety than people who rarely move.

Fewer past studies explored links between physical activity and upbeat emotions, especially in people who already were psychologically healthy, and those studies often looked at a single age group or type of exercise.

So for the new review, the Michigan researchers found, exercise was strongly linked to happiness. The type of exercise did not seem to matter. Some happy people walked or jogged. Others practiced yoga-style posing and stretching. And the amount of exercise needed to influence happiness was slight. In several studies, people who worked out only once or twice a week said they felt much happier than those who never exercised. In other studies, 10 minutes a day of physical activity was linked with happy moods.

But because most of the studies in this review were observational, it is not possible yet to establish whether exercise directly causes changes in happiness or if the two just happen to occur together often. In that case, exercise would not have helped to make people happy; rather, their happiness would have helped to make them exercisers

In a new look at the impact of long-time sitting behavior on health， a new study links time watching television to an increased risk of death.   One of the most surprising findings is that it isn't just couch potatoes who were affected.   Even for people who exercised regularly， the risk of death went up the longer they were in front of the TV.   The problem was the long periods of time spent sitting still.

Australian researchers who tracked 8，800 people for an average of six years found that those who said they watched TV for more than four hours a day were 46% more likely to die of any cause and 80% more likely to die of cardiovascular（心血管的）disease than people who reported spending less than two hours a day in front of TV.

Time spent in front of TVs and computers and video games has come under fire in studies in recent years for contributing to a spread of obesity in the US and around the world.   But typically the resulting public-health message urges children and adults to put down the Xbox controller and remote and get on a treadmill（跑步机）or a soccer field.

The Australian study offers a different view.   "It's not the sweaty type of exercise we're losingsays David Dunstan， a researcher at Baker IDI Heart and Diabetes Institute？ Melbourne？ who led the study.   "It's the incidental moving around？ standing up and using muscles.   That doesn't happen when we are planted on a couch in front of a television.

Indeed？ participants in the study reported getting between 30 and 45 minutes of exercise a day？ on average.

The results are supported by a new field of research that shows how long periods of inactivity can affect the body's processing of fats and other substances that contribute to heart risk.   And they suggest that people can help decrease such risk simply by avoiding extended periods of sitting.

Keeping such processes working more effectively doesn't require constant intense exercise， but consciously adding more routine movement to your life might help？ doctors say.   "Just standing is better than sitting，" says Gerard Fletcher， a cardiologist at Mayo Clinic， Jacksonville， Fla.   ， who works standing up at his computer.   "When you stand up， you wander around a little bit and use muscles not required when you are sitting or lying down. "

Simple strategies for increasing activity include combining household chores such as folding laundry with TV-watching time or getting up to change a TV channel rather than using a remote control.

The report， published Tuesday in the American Heart Association journal Circulation focuses on TV watching partly because it is the main leisure-time activity in many countries？ researchers said， especially in the US.