Scott Riewald, PhD, CSCS, NSCA-CPT
Sitting on the couch with a bag of potato chips in hand, a friend of mine commented after watching another contestant lose dramatic amounts of weight on TV show The Biggest Loser, “I could lose all that weight and improve my health if all I had to do each day was work out and someone made all my meals for me.” And in all likelihood, that is true; if he exercised more and ate better, he would be taking proactive steps to ensuring his long-term health. However, it turns out there may be more to improving and maintaining health than just watching what you eat and exercising. Little did he know that what he was doing, simply lounging around and watching TV, can have a negative effect on health as well, even if he was following recommended exercise guidelines. In fact, recent evidence (1) suggests that “sedentary time” may be an independent factor in predicting health outcomes. Active individuals (defined as those engaging in at least 2.5 hours of moderate to vigorous exercise a week), who spend long periods of time being sedentary, exhibit increased risk of developing cardiovascular disease, a higher incidence of type 2 diabetes and obesity, and abnormal glucose tolerance when compared with individuals who do not exhibit less sedentary behavior.
Genevieve et al. (1) at the University of Queensland recently examined the relationship between time watching TV (an indicator they feel is representative of sedentary behavior) and several continuous metabolic risk variables in physically active adults. The results of the study provide support to the hypothesis that sedentary behavior should be treated as an independent risk factor related to health outcomes. Let us look a bit more at the study.
The authors studied 2,031 male and 2,033 female participants (average age 47.3 ± 13.1 and 46.7 ± 12.5 years for men and women, respectively), all of whom engaged in ≥2.5 hours of moderate to vigorous activity each week. After a 10-hour fast, plasma glucose, triglycerides, and cholesterol levels were measured. An oral glucose tolerance test was administered at this time, and the 2-hour plasma glucose level was also recorded. Additional information collected from the participants included waist circumference, resting blood pressure, diet quality (using a validated questionnaire), self-reported TV viewing time, total weekly physical activity, and select demographic information. Data were divided into quartiles (quartile 1 watched the least TV per day and quartile 4 the most) to allow for dose-response relationships to be determined relating TV watching time to the different metabolic risk variables. Statistical analyses were performed to come up with regression coefficients for the standardized and unstandardized data. Data were also adjusted to remove the effects of potentially confounding variables (e.g., income, education, alcohol intake, smoking).
WHAT WAS FOUND?
The investigators found a strong link between TV watching (i.e., sedentary behavior) and increased health risks, even in adults who engaged in regular exercise. A couple of the more notable results are listed below:
- The correlations between TV watching time and physical activity were low for both men and women (r = −0.002 and −0.09, respectively), indicating that these should be treated as independent variables.
- On average, men in this study watched more TV per day (1.85 ± 1.35 hours) compared with women (1.60 ± 1.23 hours) but also demonstrated greater physical activity (9.08 ± 6.30 h/wk for men versus 7.39 ± 5.14 h/wk for women).
- Women, on average, had a significantly better diet quality as assessed by the validated nutrition questionnaire.
- For the women, significant increases in waist circumference, fasting plasma glucose, 2-hour plasma glucose, and triglyceride levels were seen for each increase in TV time compared with the reference group, which watched <2.14 hours of TV a day. Additional significant increases were seen in systolic blood pressure (fourth quartile) and in high-density lipoprotein levels (third and fourth quartiles).
- For the men, significant increases were seen in waist circumference (third and fourth quartiles), systolic blood pressure (third quartile), and 2-hour blood glucose levels (fourth quartile) compared with the reference group, which watched only <0.93 hours of TV a day.
- In general, the strongest associations between TV watching and metabolic variables were seen in men and women in the fourth quartile-those who watched >2.57 and >2.14 hours of TV per day, respectively.
IMPLICATIONS FOR THE STRENGTH AND CONDITIONING COACH/PERSONAL TRAINER
First and foremost, the study provides support to the notion that sedentary behavior, even in individuals who engage in regular physical activity, can contribute to increased health risks. Activity alone, although definitely still recommended and essential for maintaining a healthy lifestyle, may not fully account for the metabolic risks experienced in the adult population. Sedentary behavior and physical activity seem to be independent variables, and the authors make the recommendation that guidelines be developed with regard to sedentary behavior to accompany those presently available for exercise and nutrition. What does this mean for you, the strength and conditioning coach or personal trainer? For one, this study should get you thinking a bit more about how lifestyle effects health and well-being. As someone who interacts with the adult population, it is important to let your athletes and/or clients know the risks that could come with sedentary behavior because most people will feel they are “covered” if they get the recommended amount of physical activity each day or week. In reality, the results of this study indicate that watching TV for more than 2 hours a day can have negative health implications. If you do not think people watch that much TV a day, think again. According to a 2008 American Time Use Survey published by the U.S. Department of Labor (2), in 2007 nearly 80% of the U.S. population watched TV daily, with men and women in this group watching an average of 3.54 and 3.07 h/d, respectively. What type of impact could that amount of TV time have on health?
There are several limitations that should be considered when interpreting the results of this study. First, and foremost, TV time is being used as the sole marker of sedentary behavior and could possibly misrepresent the amount of time spent in sedentary activity. Additionally, all activity and TV watching data were self-reported, and there was no distinction made as to whether the TV watching was done all at once or in smaller increments, both of which carry a level of error. There may also be some questions as to how tightly the study was controlled as it looked only at physically active adults and did not have a nonexercising control group.
In spite of these limitations, the study provides compelling evidence that we need to emphasize staying away from excessive periods of sedentary behavior in addition to promoting physical activity and maintaining a healthy diet.
1. Genevieve NH, Dunstan DW, Salmon J, Shaw JE, Zimmet PZ, and Owen N. Television time and continuous metabolic risk in physically active adults. Med Sci Sports Exerc
40: 639-645, 2008.
2. American Time Use Survey
summary (Table I). Available at: http://www.bls.gov/news.release/atus.nr0.htm
. Accessed: November 21, 2008.