Australasian Science: Australia's authority on science since 1938

Exercise Intensity Counts

By Stephen Luntz

For all the talk that half an hour of gentle exercise per day is all that is required for good health, a new study suggests that getting the heart rate up is important.

Dr Lynda Norton of Flinders University Social Health Sciences studied 620 adults spending either 30 minutes per day walking or doing other moderate intensity exercise, or high intensity exercise for twice as long three times per week.

High intensity exercise was defined as something that pushes the heart rate above 75% of its capacity. The capacity was estimated using the formula 220 beats per minute minus the participant’s age, although Norton says this can vary by 10%.

The regular moderate exercise was helpful for weight, cholesterol and fitness compared with those who did no additional exercise at all, but the high intensity workout proved much more potent.

Norton says the actual activity of each participant was tracked, so the research team had a far wider variation to compare than the simple two categories they had placed people into.

The high intensity workouts were a struggle for most participants, who had previously been sedentary, and Norton says participants started with 2-minute bursts of exercise interspersed with warm-downs. “We found people got most active in team games, and we sometimes had to tell them to slow down as we didn’t want to overextend them.

“Most physical activity guidelines recommend a 30 minute daily walk but we found that it would take 50 hours of walking to achieve the same aerobic fitness that you could get from just 1 hour of high-intensity or vigorous activity,” says Norton.

“When we looked at cholesterol, we found it would take 5 hours of walking to see the same improvements as 1 hour of vigorous exercise, and for body mass index it was the equivalent of about 8 hours of walking.

“Any form of physical activity is better than nothing but you’ll get a lot more bang for your buck if you increase the intensity,” says Norton.

Norton is planning research to see whether intense exercise counteracts long periods of sedentariness. She notes that studies suggesting long periods of sitting are harmful even to those who get plenty of exercise (AS, July/Aug 2011, p. 11) looked at people doing moderate intensity fitness regimes.