Response to Letter Regarding Article, “Body Mass Index and Vigorous Physical Activity and the Risk of Heart Failure Among Men”
We thank Hansel and Simon for their interest in our article1 and for raising some concerns, all pertaining to the semantics of physical activity. Hansel and Simon propose to replace the term “vigorous physical activity” with “self-reported physical inactivity” in the title of our article.1 Such a change would make the title imprecise because the information on all of the 3 variables—value of body mass index, frequency of vigorous physical activity, and diagnosis of heart failure (HF)—mentioned in the title was based on self-reports by physician participants. Furthermore, it may be inaccurate to assume that participants who rarely or never vigorously exercised were physically inactive because nonvigorous (light or moderate intensity) physical activity was not ascertained at baseline. Therefore, we believe that the title of our article is appropriate as is.
Our statement that “any vigorous physical activity is an indicator of healthier lifestyle in men at risk of developing HF” should be interpreted in the milieu of a reduction in the risk of HF even among participants who reported exercising vigorously enough to work up a sweat at a frequency as low as 1 to 3 times a month (multivariable 22% reduced risk of HF compared with rarely or never group; Table 2).1 We speculate that the effect of low-frequency vigorous exercise alone would not likely explain the extent of the reduction in HF risk. We suggest, therefore, that any observed frequency of vigorous physical activity, beyond rarely or never, may also represent a healthier set of behavioral and dietary factors, a potential source of residual confounding in our study.
In human physiology experiments, physical training has been shown to increase sweating responsiveness2 and decrease sweating threshold.3 The rate of sweating increases with increasing intensity of isometric (static)4 as well as isotonic (dynamic)5 exercise. Thus, in epidemiological investigations, such as the present one, it is reasonable to include “breaking a sweat” as a component of vigorous physical activity. Whether well-conditioned participants underreport their frequency of vigorous physical activity is speculative or unknown. We disagree with the interpretation of Hansel and Simon that our definition of vigorous physical activity and categorization of its frequency did not distinguish the degrees of HF risk among our study participants. To the contrary, in multivariable models assessing for linear trends, increasing frequency of vigorous physical activity was associated with a graded reduction in the risk of HF (P value for trend ranging from <0.001 to 0.016; Table 2).1 Additional studies using various alternative definitions of physical activity are warranted to confirm, refute, or build on our findings.
In essence, we emphasize the beneficial effect of vigorous physical activity in lowering the risk of HF; however, Hansel and Simon highlight the harmful influence of the lack of vigorous physical activity in elevating the risk of HF. Whereas we infer that vigorous physical activity is an indicator of healthier lifestyle, Hansel and Simon imply that physical inactivity is an indicator of unhealthier lifestyle. Both of these statements are logically equivalent.
Sources of Funding
The study was supported in part by grants HL-26490 and HL-34595 from the National Heart, Lung, and Blood Institute, Bethesda, Md, and grants CA-34944, CA-40360, and CA-097193 from the National Cancer Institute, Bethesda, Md. The sponsoring organizations played no role in the design and conduct of the study; in the collection, management, analyses, and interpretation of data; or in the preparation, review, and approval of the correspondence.
Kenchaiah S, Sesso HD, Gaziano JM. Body mass index and vigorous physical activity and the risk of heart failure among men. Circulation. 2009; 119: 44–52.
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