Friday February 1 2013
Vigorous household and garden chores could help your heart
Short bursts of exercise, such as raking the lawn and climbing the stairs, are an excellent way of warding off health problems such as high blood pressure, high cholesterol and diabetes, the Daily Mirror and many global media outlets reported.
The news is based on the results of a cross-sectional study which suggested that even less than 10 minutes of moderate or vigorous activity, such as climbing stairs, ‘count’ and may be as beneficial as longer periods of exercise.
This useful and well-conducted study measured the physical activity of more than 6,000 adults, in addition to measuring various health markers such as blood fats, blood sugar and blood pressure, that are known to be risk factors for chronic conditions including diabetes and heart disease.
The study found that performing moderate or vigorous activity of any duration – either short bursts of less than 10 minutes or for longer – was associated with improved measurements of several cardiovascular risk factors.
The study suggests that even people who do not have time to go to the gym or an exercise class can get many of the health benefits of exercise from adopting an ‘active’ lifestyle.
While the study cannot directly prove cause and effect, it would suggest that any moderate or vigorous exercise you can fit in during the course of a day, benefits your health.
Where did the story come from?
The study was carried out by researchers from Bellarmine University and Oregon State University. The source of funding for this study was not declared.
The study was published in the peer-reviewed American Journal of Health Promotion.
This study was covered by the Daily Mirror and the Mail Online. Although the gist of the story is correct, the researchers looked at short bursts of moderate and vigorous physical activity, rather than the ‘light exercise’ reported in the Daily Mirror and the Mail Online.
What kind of research was this?
This cross-sectional study aimed to determine whether short bursts of physical activity were associated with a decreased risk of metabolic syndrome.
Metabolic syndrome is a term used to describe a combination of related risk factors for chronic conditions such as heart disease and type 2 diabetes – these factors include high waist circumference, blood fats, blood sugar and blood pressure.
The researchers also looked at some additional biological markers known to be risk factors for cardiovascular disease.
They looked at whether there were any differences in risk factors for short bursts of activity versus more prolonged bursts.
Cross-sectional studies have a inherent limitation as they cannot prove causation (a direct cause and effect), they can only highlight possible associations.
So in this case, the researchers cannot conclude that it is the short bursts of activity directly affecting the biological markers measured.
Also, because participants aren’t followed over time we don’t know what came first, so we don’t know:
- if people who exercise a certain way are healthier
- if people who are healthier exercise a certain way
What did the research involve?
The researchers used data collected as part of the US National Health and Nutrition Examination Survey, which collects annual health and nutrition data on a random sample of US citizens. For this study, data from 6,321 non-pregnant adults with data on physical activity from the 2003-2004 and 2005-2006 cycles was used.
A participant’s physical activity was determined by collecting data using an accelerometer. Accelerometers measure the participant’s change in velocity over time (acceleration) allowing the intensity of physical activity to be measured, as well as the duration.
Participants had data on physical activity for at least four days, and at least 10 hours each day. The researchers classified the intensity of physical activity into moderate or vigorous using cut-offs for accelerometry readings.
The researchers also classified activity levels by duration, into two main groups:
- less than 10 minutes duration (‘nonbout’)
- more than 10 minutes duration (‘bout’)
Each period of activity was terminated if accelerometry readings fell below the cut off for three minutes or more.
The researchers also calculated whether a participant met physical activity guidelines, defined as engaging in 150 minutes of moderate-intensity activity or 75 minutes of vigorous-intensity activity or some combination of the two per week, and whether a participant met the criteria by only performing short, less than 10 minute duration ‘nonbout’ periods of activity.
The US National Health and Nutrition Examination Survey also collected data on a participant’s cardiovascular risk factors, including:
- metabolic syndrome – defined as having three or more of the following symptoms: a high waist circumference, a high level of triglycerides (a type of fat), low levels of high-density (‘good’) cholesterol, elevated blood pressure, elevated fasting blood sugar
- systolic and diastolic blood pressure
- blood levels of C-reactive protein (an inflammatory marker), high-density cholesterol, low-density (‘bad’) cholesterol, total cholesterol and blood sugar
- anthropometric measurements including waist circumference, skinfold thickness and body mass index (BMI)
The researchers also collected data on age, gender, smoking status, race/ethnicity, current health status, and whether the participant was taking any medication.
The researchers analysed whether there was an association between short ‘nonbout’ periods of activity and longer ‘bout’ periods of activity and cardiovascular risk factors.
They also looked at whether there was any difference in risk factors when physical activity guidelines were only met by performing short ‘nonbout’ periods of activity.
In these analyses, the researchers controlled for age, gender, smoking status, race/ethnicity, and current health status.
What were the basic results?
The researchers found that on average, participants performed 23.6 minutes of moderate-to vigorous-intensity physical activity per day in short, ‘nonbout’ bursts, and 6.6 minutes in 10 minutes or longer bursts (this rather confusing figure is due to some people not doing any moderate to vigorous physical activity in bouts of 10 minutes or longer, during some days).
A total of 42.9% of participants met physical activity guidelines if nonbout physical activity was included, but only 9.7% met guidelines if only 10 minutes or longer periods only were included.
Both ‘nonbout’ and ‘bout’ physical activity were associated with a reduction in cardiovascular risk factors. The associations were strongest when enough activity was performed to meet physical activity guidelines.
The strengths of associations were generally similar for ‘bout’ and ‘nonbout’ physical activity for all risk factors measured, with the exception of BMI.
To make sure the results weren’t due to the fact that people who performed the longer periods of activity were also performing the shorter periods of activity, the researchers repeated the analyses controlling for 10 minutes or longer periods of activity.
Short ‘nonbout’ physical activity was still associated with a reduced risk of metabolic syndrome; favourable levels of C-reactive protein, high density lipoprotein cholesterol, triglycerides; and favourable sized waist circumference, skinfold thickness and BMI.
Again, the associations were strongest when enough ‘nonbout’ physical activity was performed to meet the physical activity guidelines.
Finally, the researchers compared the mean levels of biological markers in people meeting the physical activity guidelines solely through performing short ‘nonbout’ periods of physical activity and those meeting guidelines by performing longer periods of activity.
There was no statistical difference between the level of any marker except for BMI. Participants who met guidelines through longer periods of activity had significantly lower body mass indices (25.85) than those meeting guidelines through short periods of activity (27.49, p<0.0001).
How did the researchers interpret the results?
The researchers conclude that these results show that “with the exception of BMI, meeting physical activity guidelines using an ‘active lifestyle’ approach (nonbout activity) as opposed to a more structured exercise approach (bout activity) resulted in similar health outcomes.”
They suggest that “to reduce levels of adult adiposity (body fatness), adults are encouraged to engage in bouts of physical activity of at least 10 minutes in duration; however, for other health outcomes, an active lifestyle approach (for example, climbing a flight of stairs vs. taking the elevator), particularly of vigorous intensity, may be beneficial for initiating physical activity behaviour among inactive adults as well as being sufficient to elicit improvements in health parameters.”
The results of this study suggests that even short periods of physical activity ‘count’ and are associated with improved levels of several risk factors for cardiovascular disease. The study found that the strength of this association was generally as strong for short periods of activity as longer periods of activity.
This study has strengths and weaknesses. The strengths are that both physical activity and the levels of the biological markers were measured objectively, and did not rely on self-reporting, and that it was performed using a large sample of US adults.
However, it was a cross-sectional study, and cross-sectional studies have the limitation that they cannot show causation, in this case, the researchers cannot conclude whether it is the short bursts of activity that affect the biological markers measured.
Also, because participants aren’t followed over time we don’t know what came first, so we don’t know if people who exercise a certain way are healthier or if people who are healthier exercise a certain way.
However, overall this study supports the suggestion that any level of physical activity is better than no activity.
Even if you don’t feel ready to join your local gym, you can still begin making changes to your lifestyle today to improve your activity levels – read more about how you can get fitter without the gym.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.