Dr. David R Buyer, MD, MBA, FACP

Category: Physical Activity

  • Sedentary Time

    A woman relaxing with her dogOne way to view activity level and health outcome is to measure health outcomes based on amount of non-active time. However, caution must be used in interpretation because moderate activity as recommended is not necessarily the opposite of being sedentary. A meta-analysis assessed sedentary time with risk for disease, mortality and hospitalization. This, in combination with studies on moderate and vigorous activity, helps to provide a more complete picture of activity level and health outcomes.

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    “Maintaining a minimum amount of physical activity and breaking up sedentary time with walks or non-sitting tasks would appear to be beneficial to health.”

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    The study defined being sedentary as less than 1.5 METS (eg. sitting, watching TV, reclining) and evaluated overall hours of sedentary behavior or sitting hours per day or week. Out of almost 21,000 studies 41 met inclusion criteria. The analysis found that greater sedentary time was associated with all-cause mortality, cardiovascular disease incidence, cancer incidence and type 2 diabetes incidence. Of the cancers, breast, colon, colorectal, endometrial and epithelial ovarian cancers showed increased incidence. Further, sitting fewer than eight hours a day had a 14% lower risk for potentially avoidable hospital admissions. When evaluating sedentary time along with level of activity, there was a 30% less relative risk of all-cause mortality in those with high versus low levels of physical activity. It appears that there is an interaction between amount of non-activity and amount of activity, with those who are more physically active having less impact of sedentary time on their health.

    Based on this analysis, both activity and non-activity time is important. Currently guidelines do not state how much sedentary time is “acceptable.” The amount may be different if sitting at work versus sitting in leisure time. We also don’t know if being sedentary and awake longer is better or worse than sleeping more. Much more research is needed. In the meantime, maintaining a minimum amount of physical activity and breaking up sedentary time with walks or non-sitting tasks would appear to be beneficial to health.

  • General Physical Activities Defined by Level of Intensity

    Almost every occupation requires some mix of light, moderate, or vigorous activities, depending on the task at hand. To categorize the activity level of your own position, ask yourself: How many minutes each working day do I spend doing the types of activities described as light, moderate, or vigorous? To arrive at a total workday caloric expenditure, multiply the minutes spent doing activities within each intensity level by the kilocalories corresponding to each level of intensity. Then, add together the total kilocalories spent doing light, moderate, and vigorous activities to arrive at your total energy expenditure in a typical day. Use this handy chart to help calculate the calories burned based on your activities.

    Download the activity guide (PDF file) here |

     

  • Physical Activity Recommendations

    The amount of physical activity recommended for adults is 150 minutes of moderate activity per week, along with muscle-strengthening activity of all muscle groups twice a week. Alternatively, one may get 75 minutes of vigorous activity a week with muscle strengthening twice a week. A mixture of moderate and vigorous activity is also acceptable. Doing ten minutes of activity at a time still counts toward the weekly total. Only 54% of people in Illinois get the recommended amount of physical activity while 24% do not get any leisure-time activity, based on data from 2013.

    So what is moderate and vigorous activity? Activity levels can be roughly assessed using breathing and heart rate. With moderate activity, one can talk in sentences, while with vigorous activity one can only say a few words before needing to take a breath. Using heart rate as a guide, moderate activity is when the heart rate reaches 50–70% of maximum for one’s age, and 70–85% is considered vigorous activity. Maximum heart rate is computed as 220 minus age. Increasing heart rate to the maximum and beyond is not necessary.

    Activities that are considered moderate intensity include walking between 3–4.5 mph, hiking, biking 5–9 mph, yoga and dancing, to name a few. Housework, including scrubbing the floor or bathtub on hands and knees, washing windows and sweeping also are moderately-vigorous activities. Vigorous activity examples include walking, jogging or running more than 5 mph, biking over 10 mph, competitive ballroom dancing and other competitive sports. Household vigorous activity includes moving heavy furniture, carrying 50 pounds or more and shoveling more than 10 pounds a minute. A more extensive list of activities can be found here.

  • Effect of Exercise on Mortality

    Woman doing plank

    Since 2008 the U.S. government has issued activity guidelines. The recommendations are reported in this article. Of the 150 minutes weekly of moderate-intensity activity, vigorous activity can be substituted with a 1:2 ratio of minutes needed. However, cardiorespiratory and metabolic fitness is a better indicator of morbidity and mortality than the amount of time of activity. So despite the recommendations, which are for a minimum amount of activity, is there benefit to more vigorous activity?

    One study evaluated the proportion of moderate or vigorous activity that was accounted for by vigorous activity and whether more vigorous activity decreased mortality. Studies have also examined if there is an upper threshold of vigorous activity that exists such that mortality is not improved or worsened.

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    “Based on these two analysis, increasing activity prolongs longevity and, up to a point, increasing vigorous activity is more beneficial than moderate activity. “

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    The study was performed on 204,000 people in Australia between the ages 45 and 75. This is 10% of the entire population in New South Whales. Self-reported activity intensity is a better predictor of mortality than total amount of activity so self-reported activity data was assessed using a questionnaire. Vigorous activity was defined as “activity that made you breathe harder or puff and pant, like jogging, cycling, aerobics, competitive tennis, but not household chores or gardening.” Moderate activity examples were “gentle swimming, social tennis, vigorous gardening or work around the house.”

    The questionnaire collected data on minutes of walking and minutes of moderate-vigorous physical activity. Covariate analysis with age, sex, education, marital status, urban/rural, BMI, smoking, physical function, alcohol, fruit and vegetable consumption, and total MVPA was also done. The sample was heterogeneous with 64% obese and 55% without any vigorous activity. Sixteen percent of respondents had between 0 and 30% of total activity time being vigorous, and 28% had 30% or more of their activity being vigorous.

    Results are shown in the table below. Increasing amount of time of activity decreases mortality and any report of physical activity decreased mortality 9–13%. This protective effect of activity carried across all subgroups including those with and without cardio-metabolic disease. Another meta-analysis showed that walking pace, not time spent walking, is associated with longevity.

    Effect of Exercise on Mortality — Mortality compared to no activity

    There are a lot of people in the United States doing highly intense physical activity. In 2013, 541,000 people completed a marathon and in 2012 there were 510,000 USA triathalon members. Additionally, there are a lot of people doing high-intensity interval training. If increased intensity activity is beneficial, then is there an upper limit to the amount of vigorous activity, at which point it becomes detrimental?

    An evaluation was done using pooled analysis of 6 cohorts in the National Cancer Institute Cohort Consortium analysis of BMI, physical activity and mortality. Estimated leisure time physical activity (LTPA) based on METs and hours per week of exercise were reported. This was analyzed accounting for covariates of age, sex, race/ethnicity, education, smoking, cancer history, heart disease history, alcohol and marital status. The sample consisted of 661,000 people with median follow up over 14 years. Median age at entry was 62, median leisure-time physical activity (LTPA) was 8 MET hours/week (150 minutes is 7.5 MET hours/week).

    The study showed younger, married, non-smokers, with lower BMI and fewer comorbidities exercised the most. Again, compared to no activity, any level of activity decreased mortality. In subgroup analysis, any level of vigorous activity decreased mortality by 20%, even if less than the recommended amount. The table below shows the decrease in mortality compared with activity level. Cardiovascular death was minimized at 3–5 times the recommended amount of activity and increased again at 10 or more times over the minimum. However, those doing 10 or more times over the minimum recommendation had a 31% lower risk of cancer death.

    Based on these two analysis, increasing activity prolongs longevity and, up to a point, increasing vigorous activity is more beneficial than moderate activity. Although these studies included people with cardiovascular disease, we do not know the severity of this or other illnesses. The results may not be generalizable to people with more severe illness, but the overall recommendation that increasing activity is beneficial seems to make sense for everyone, regardless of overall health.

    Effect of Exercise on Mortality — Amount of physical activity and mortality reduction

  • Activity Monitor Accuracy

    Man with Activity Monitor

    It seems that everyone knows someone who is using an activity monitor these days. They come under a variety of brands including Fitbit, NikeFuel, Jawbone Up and others. Some report steps taken while others are more sophisticated and also report energy expenditure. Accuracy varies among devices and should only be used as a guide.

    The most common way to measure steps is with accelerometry. The device measures change in speed to estimate the number of steps. One study took 16 healthy volunteers and measured activity recorded on various monitors while lying, sitting, standing, walking or shuffling. Error rates were between 4.5–17.2% when compared with manually counted videotaped steps. Error was speed dependent with slow speed having worse accuracy. NikeFuel band underestimated while Jawbone Up overestimated the number of steps at slow speed. Accurately counting steps on stairs was especially difficult for the monitors.

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    “Although these devices are not precise, they provide a reasonable estimate of activity.”

    Energy expenditure reporting is accomplished by converting activity data via an algorithm into energy consumption. This can be done with or without the aid of heart rate, temperature, heat flux or galvanic skin heat response. Monitors were tested in one study using 60 healthy volunteers. Resting energy expenditure was measured and the following week subjects were fitted with multiple monitors. They did activities including being sedentary, walking on a treadmill, jogging/running on a treadmill, and moderate to vigorous activities for 3–5 minutes during measurement. Energy expenditure over the entire duration was examined. Energy consumption estimates were be off by 9–23.5%. Fitbit error was approximately 10%, Jawbone approximately 12%, Nike Fuel 14% and Basis Band 23.5%. However, the standard error of the error measurements was between 6–17% in the study.

    Another study examined shoe-based monitors. These sensed acceleration and foot pressure. Subjects walked in a calorimetric room that measures oxygen and carbon dioxide levels, which is a very accurate way to determine energy expenditure. The shoe-based monitors were accurate within 6% of energy expenditure while commercial monitors such as the Fitbit and DirectLife were off by approximately 14–18%.

    Although these devices are not precise, they provide a reasonable estimate of activity. Effectiveness of the devices to motivate increased activity is an area that is being intensely studied. In the meantime, go ahead and use it if you have one.