Energy expenditure estimated by accelerometry and doubly labeled water: do they agree?

PURPOSE: The purpose of this study was to compare energy expenditure derived from regression equations determined from accelerometry with energy expenditure obtained from the doubly labeled water method (DLW). METHODS: Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Simultaneously, during the 7 d, subjects wore a Tritrac-R3D and an Actigraph (ACT). Pearson and concordance correlations and one-sample t-tests were used to determine the agreement of six Tritrac and eight ACT regression equations that convert body acceleration to energy expenditure with the DLW measurements. RESULTS: Tritrac TDEE determined from the different Tritrac regression equations under- and overestimated TDEE determined with DLW that ranged from -10 to +101%. For ACT, the percent difference between DLW and ACT-TDEE determined with the regression equation developed by Hendelman and Swartz were not statistically significantly different from zero. The mean of the difference was -2 and -4%, but the range of the difference was large for both equations, -29 to +24%. TDEE determined with the six other ACT equations were significantly different compared with DLW. CONCLUSION: Of the 14 different regression equations from the literature, only two developed for ACT compared favorably with DLW; however, the difference in TDEE between these two methods was variable and rather large. These results reemphasize the difficulty in converting body movement into energy expenditure on an individual basis from accelerometry. These results imply that researchers may want to avoid using accelerometers to predict energy expenditure in free-living conditions, instead using these instruments only to measure patterns of physical activity.

Physical activity in physical education: teacher or technology effects.

This study assessed if wearing a heart rate monitor influenced student activity levels in elementary physical education. Data were analyzed for 4 students using an alternating treatment design to assess differential effects between accelerometer activity counts obtained from students when wearing the heart rate monitor and when they were not wearing the monitor. Results show that (a) there was no difference in activity counts between the 2 conditions, (b) boys had higher means than girls, and (c) the variance between more and less active boys was greater than the variance among the girls.

Content analysis of prime-time television coverage of physical activity, 1970-2001.

BACKGROUND: The purpose of this study was to examine how major nightly television networks reported on the health benefits of physical activity. METHODS: A retrospective content analysis of physical activity coverage on four major nightly television networks from 1970 to 2001 was performed. The Vanderbilt Television News Archives were searched for keywords "physical activity," "physical fitness," and "exercise." RESULTS: During the 31-year time period, 111 non-overlapping reports aired on all networks combined. The link between physical activity and health was reported in 53 (47.7%) articles, with general health (n =16, 14.4%) and heart disease (n =12, 12.6%) cited most frequently. Just three broadcasts related to the Surgeon's General Report on Physical Activity and Health were aired following its publication in 1996. CONCLUSIONS: Although the protective health benefits of physical activity are well established, physical activity received a modest amount of television coverage from 1970 through 2001.

Evaluation of a step-counter during treadmill walking in 7-12 year old African-American children.

The primary purpose of this study was to evaluate the accuracy of the Digiwalker step-counter in recording the number of steps by African-American children during level treadmill walking and the accuracy of the Digiwalker when placed inside a pouch at midline rather than when placed at midline of the thigh. A secondary purpose of this study was to examine the relationship between the number of steps and physiological response to walking. Study subjects were a sub-set of thirty-one children recruited from a larger study evaluating the effects of an after school program on cardiovascular risk factors in this population. The Digiwalker was consistent in the steps recorded when time and speed were held constant and the Digiwalker was able to detect increases in steps with small increases in walking speed. In addition, the use of a soft-cased pouch appears to be an appropriate alternate placement site for the Digiwalker.