“A journey of a thousand miles may begin with a single step, but even if you take just 2,999 more within half an hour, you may be on the road to fitness. A new study finds that people who walk to keep in shape can achieve the right intensity if they take at least 100 steps a minute. The researchers, led by Simon J. Marshall of San Diego State University, equipped volunteers with pedometers that counted their steps as they worked out on treadmills at different speeds. They also measured the participants’ heart rates. A pace of 100 steps a minute or more, they calculated, was enough for the workout to be considered of moderate intensity. The study appears in The American Journal of Preventive Medicine.