Is it better to run fast or slow?

VLast week I was visiting a friend who lives in Brooklyn, New York. On the first day I started jogging, still a bit lost, disoriented, past Polish bakeries, greengrocers and a small flea market. Then I followed another jogger who led me to a tartan track. I entered the oval, lined up and felt safe in unfamiliar surroundings.

Some runners just walked side by side, others did tempo runs. I forgot the jet lag, the slight nausea, and started running 200 meters faster, trotting in between, and running 200 meters fast again. I had almost forgotten that this was the time I had the most fun. And asked myself: Should I do this more often again? Do you prefer to run short and fast instead of slow and long?