Scientists studied more than 1,000 healthy joggers and non-joggers over a 12-year period.

科学家们对1000多名身体健康的慢跑者和不跑步的人进行研究，追踪时间超过12年。

Those who jogged at a steady pace for less than two and a half hours a week were least likely to die in this time。

慢跑速度较为稳健，且每周慢跑时间不超过两个半小时的人猝死的可能性最小。

But those who ran more than four hours a week or did no exercise had the highest death rates。

而一周跑4个小时以上或者从不锻炼的人则有着最高的死亡率。

'Upper limit'

“上限”

Analysing questionnaires filled out by all the people in the Danish study, scientists concluded the ideal pace was about 5mph (8km/h) and that it was best to jog no more than three times a week or for 2.5 hours in total。

在丹麦进行的研究中，科学家通过分析所有参与者的问卷得出结论：理想的运动速度大约是每小时5英里(约8公里/小时);每周的运动次数不超过3次或者时长累计为2.5小时。

People who jogged more intensively - particularly those who jogged more than three times a week or at a pace of more than 7mph - were as likely to die as those who did no exercise。

进行更为密集的慢跑，尤其是那些一周跑3次以上或者速度超过每小时7英里的人，其死亡几率和那些不运动的人相差无几。

Researcher Jacob Louis Marott, from the Frederiksberg Hospital in Copenhagen, said: "You don't actually have to do that much to have a good impact on your health。

来自哥本哈根腓特烈斯贝医院的研究人员雅各布·路易斯·马罗塔(Jacob Louis Marott)说：“其实你不必强求，为自己的健康做太多。”

"And perhaps you shouldn't actually do too much。

“或许事实上你不应该做太多。”

"No exercise recommendations across the globe mention an upper limit for safe exercise, but perhaps there is one."

“目前，全球尚无有关安全锻炼的上限建议，但或许应该有一个。”

Scientists are not yet sure what is behind this trend - but they say changes to the heart during extreme exercise could contribute。

科学家还不能确定潜在的趋势——但他们说极端运动改善心脏状况可能有所帮助。

'Brisk walking'

“快走”

In their report, they suggest: "Long-term strenuous endurance exercise may induce pathological structural remodelling of the heart and arteries."

在调查报告中，他们提出：“长期从事剧烈的耐力运动可能会改变心脏和动脉的病理结构。”

Maureen Talbot, senior cardiac nurse at the British Heart Foundation, said: "This study shows that you don't have to run marathons to keep your heart healthy。

英国心脏基金会高级心脏护士莫林·托尔伯特(Maureen Talbot)说：“这项研究表明，你不必为保持心脏健康去跑马拉松。

"Light and moderate jogging was found to be more beneficial than being inactive or undertaking strenuous jogging, possibly adding years to your life。

“少量、适度的慢跑被认为比不运动或进行高强度慢跑更有益，或可延长你的寿命。”

"National guidelines recommend we do 150 minutes of moderate-intensity activity a week。

“国家指南推荐我们每周进行150分钟的中等强度的活动。”

"It may sound like a lot, but even brisk walking is good exercise. And if you're bit of a couch potato, this is a good place to start."

“这听起来可能很多，但即使快走也是很好的锻炼。如果你有点宅，这对你来说是一个很好的开始。”