Just walk, at a reasonably vigorous clip (3 m. p. h. - 4 m. p. h.) for half an hour or so, maybe five or six times a week.

就以适度有力的步伐(每小时3 ~ 4英里)走上半个小时左右，每周五六次。

youdao

At low speeds, below about 15 miles per hour (m.p.h.), risks are low and increase relatively slowly with small increments in speed.

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