Effect of intermittent sub-maximal exercise on percent body fat using leg-to-leg bioelectrical impedance analysis in children.

The purpose of this investigation was to determine the effect of intermittent sub-maximal exercise on percent body fat (%BF) estimated by leg-to-leg bioelectrical impedance analysis (LBIA) in children. Fifty-nine children (29 girls; 30 boys) mean age 9.0 ± 1.3 years participated in this study. LBIA measured %BF values were obtained immediately before and within five minutes after completing an intermittent exercise protocol consisting of three 8-minute sub-maximal exercise bouts (2.74 km·hr-1, 0% grade; 4.03 km·hr-1, 0% grade; and 5.47 km·hr-1, 0% grade) each separated by a 5-min seated rest period. The three exercise bouts corresponded to 56%, 61% and 71% of maximal heart rate. Significant differences (p < 0.001) were observed for fat mass, fat free mass, total body water, and body weight, post-exercise in both groups. Significant reductions (p < 0.001) in %BF were observed post-exercise in the female (23.1 ± 9.9 vs. 21.8 ± 9. 9 %) and male (23.3 ± 10.5 vs. 21.8 ± 10.2 %) children when compared to pre-exercise values. However, for the majority of the subjects (females = 86%; males = 73%) the decrease in %BF post- exercise was less than 2.0 %BF. These data indicate that sub-maximal intermittent exercise, that may be representative of daily free-form activities in children, will most likely have a limited impact on %BF estimates when the assessment is performed immediately post-exercise. Key Points LBIA measures of body weight, percent body fat, fat mass, fat free mass and total body water were significantly lower after the intermittent sub-maximal exercise. The reductions in percent body fat for girls (1.4%) and boys (1.5%) compare favorably to previous investigations. Intermittent exercise, that may be representative of daily free-form activities in children, will most likely have a limited impact on LBIA percent body fat estimates Key words: Bioelectrical impedance analysis, body fat, sub-maximal exercise, children Introduction Leg-to-leg bioelectrical impedance analysis (LBIA) is a fast, easy to administer, and relatively inexpensive method of evaluating body composition. The LBIA method introduces a low level electrical current into the body and measures the lower-body impedance, or resistance to the current flow as the individual stands on a scale-like platform (Nunez et al., 1997). Fat-free mass, due to its fluid and electrolyte content, is an excellent conductor of electrical current (i.e., low impedance), while adipose tissue which contains little water is a poor conductor (i.e., high impedance). From impedance, fat-free mass and percent body fat (%BF) can be estimated using equations developed for adults and children (Heyward and Wagner, 2004). The LBIA method differs considerably from the traditional bioelectrical impedance analysis (TBIA) method, which measures whole-body impedance (arm-to-leg) and requires the specific anatomical placement of gel electrodes. Due to the ease of operation, interest in using LBIA to estimate %BF has grown, especially in settings where body composition assessments are often performed without the benefit of properly-trained personnel (e.g. school districts). To increase the accuracy of the measurement, it is recommended that clients adhere to a series of pre-testing guidelines which are designed to control for fluctuations in hydration status. Previous research examining TBIA (arm-to-leg) has demonstrated that the increased blood flow to skeletal muscle and skin, and sweating during aerobic exercise can influence impedance measurements (Kushner et al., 1996). As such, it is currently recommended that no exercise be performed within 12 hours of the test (Heyward and Wagner, 2004). However, little evidence exists examining the effect that aerobic exercise has on the relatively new LBIA technology. If necessary, stringent pre-testing guidelines may significantly limit the practicality of utilizing LBIA as a body composition assessment method in children. Research examining the effect of exercise on estimated %BF using LBIA in children is limited. Goss et al., 2003 examined the effect of progressive cycle ergometry exercise to VO2peak in male and female children (age; 10.9 ± 0.8, 11.5 ± 0.7 years, respectively) using a common LBIA analyzer (Tanita: Model TBF-305). Relatively small decreases in %BF (≤ 1.2%) were observed post-exercise (Goss et al., 2003). The authors noted that the changes in %BF post-exercise were similar to the day-to-day variability of the LBIA system (Goss et al., 2003). Recently, Andreacci et al., 2006 examined the effect of maximal treadmill exercise on LBIA (Tanita: Model TBF-300A) %BF in male and female children (age; 9.1 ± 1.0 years). Comparable to Goss et al., 2003 similar reductions in %BF were observed in both groups (mean difference: females = 1.6%, males = 1. 5%). Collectively, the %BF reductions observed following maximal/peak exercise tests were relatively small and may have little practical significance in the assessment of %BF in children (Andreacci et al., 2006; Goss et al., 2003). However, children tend to demonstrate daily physical activity patterns that consist of multiple intermittent bouts of sub-maximal effort rather than a single maximal effort (Robertson et al., 2001; Sleap and Tolfrey, 2001; Sleap and Warburton, 1996). To our knowledge, the effect of intermittent sub-maximal exercise on %BF estimates determined by LBIA has yet to be explored in children. As such, the purpose of this investigation was to determine the effect of intermittent sub-maximal exercise on %BF estimated by LBIA in children.