Inactivity – a public health problem
Obesity is on the rise both in Norway and the world at large. As a consequence, the incidence of a variety of lifestyle-related diseases also increases. Lack of physical activity plays an important part in many of these diseases. Physical inactivity can be considered an independent risk factor of the same magnitude as hypertension, smoking, and an unhealthy cholesterol profile.
Inactivity increases the risk of both cardiovascular disease and obesity, and individuals with low activity levels are more likely to be overweight. Inactivity is responsible for many needless deaths every year, and can be considered one of the silent killers of our time. The U.S. Department of Health and Human Services believes that 30 percent of all American deaths are caused by inactivity, making it the nation's most common cause of death.
The exact mechanism of how inactivity causes disease remains unknown. In a study where healthy, young people transitioned from an active to an inactive lifestyle, researchers found an increase in abdominal fat and a reduced insulin response after only a fortnight. Both of these are characteristics of the metabolic syndrome, a clustering of risk factors for cardiovascular disease.
A fatter world
Obesity is no longer a problem exclusive to developed countries. On a global basis, overweight and obesity kill more people than underweight. In 2010, the World Health Organization (WHO) reported that 65 % of the world's population lived in countries where obesity was a more frequent cause of death than underweight.
It would be natural to assume that the rise of obesity is a result of people exercising less. However, that is not actually the case. According to the Nord-Trøndelag health study (HUNT), it appears that people are exercising more now than they did in the 1980s. Additionally, many have increased the intensity of their workouts. Yet, over the course of the same timespan, the same population got substantially fatter.
So how can people get fatter when they appearantly exercise more? The reason is probably not that people are eating more than before. It is more likely that people are inactive more of the time when they aren't working out. A couple hours of exercise each week is inadequate if the remainder is spent at rest. Daily activity levels have probably declined significantly over the past years. We spend too much time in front of a screen or in our cars.
Inactivity is unhealthy even without obesity
Inactivity is not just a problem because it makes people fatter, which in turn causes more disease from obesity. Researchers have also found an inverse relationship between physical activity and all-cause mortality independent of fatness. This relationship remains regardless of whether test subjects are normal weight, overweight or obese.
People who exercise regularly live longer and have reduced risk of multiple diseases, so it's worthwhile to stay fit. The Norwegian Directorate of Health recommends that adults should be in moderate physical activity at least 150 minutes a week, or at least 75 minutes if the activity is of high intensity. Children and adolescents should have double dose. Everyone should reduce sedentary behavior. The Norwegian recommendations correspond to international guidelines for physical activity.
Even a little exercise matters!
Although 150 minutes every week might not sound like much, a large segment of the population still find it overwhelming. In an American study where physical fitness was objectively measured by accelerometer less than 5 percent of adults met the recommended half hour every day.
Inactivity carries clear health risks, but the good news is that there is a significant health benefit from just a little physical activity. One of our newer studies showed that for moderately trained people, 1x4 interval training might have similar impact on cardiac health and fitness as 4x4 interval training. This is a good example of how just a few minutes can make a big difference. Moreover, another study from CERG, including people with the metabolic syndrome, showed that the greatest reduction in mortality was found in individuals who maintained a low level of physical activity, compared to none at all.
The intensity of the physical activity also matters. Research has show that high-intensity training reduces the risk of disease more than physical activity of a lower intensity. Some studies have also been able to show that this risk reduction actually stems from the increased intensity, not just the higher energy expenditure from high-intensity exercise. This means that while high-energy workouts are good for you, high-intensity workouts are even better.
Our exercise advice
High-intensity exercise is definitely a research focus at CERG, and we recommend 4x4 interval training as part of your personal fitness plan. We have compared high-intensity interval training to continuous moderate exercise in multiple contexts, and found that aerobic interval training more effectively improves physical fitness. For instance, we showed that patients with myocardial infarction recover better with interval training compared to continuous moderate exercise both in the short and longer terms.
To read more about publications from CERG, please see our research news. To learn more about 4x4 interval training, please see our general exercise advice and answers to common questions, and try our 7-week fitness program that you can use to get fit fast.
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NTNU, Fakultet for medisin og helsevitenskap
Institutt for sirkulasjon og bildediagnostikk
St. Olavs Hospital
Prinsesse Kristinas gt. 3
Akutten og Hjerte-lunge-senteret, 3. etg.