Relationships among fitness, body composition, and physical activity

Abstract

Purpose: This study was designed to examine the associations of physical activity and body composition with cardiorespiratory fitness in eighth grade girls.

Methods: A random sample of 1440 eighth grade girls at 36 schools participated in this cross-sectional investigation, which represented an ethnically and geographically diverse group. Cardiorespiratory fitness was assessed using a modified physical work capacity test on a cycle ergometer that predicted workload at a heart rate of 170 beats.min. Physical activity was assessed over 6 d in each girl using an accelerometer and body composition was estimated from body mass index and triceps skinfolds using a previously validated equation. Pearson correlations and multiple regression analyses were used to determine the relationships among fitness, physical activity, and body composition.

Results: Significant linear relationships among cardiorespiratory fitness, body composition, and physical activity were found. The combination of fat and fat-free mass along with racial group and a race by fat-free-mass interaction accounted for 18% (R) of the variation in physical fitness. Adding moderate-to-vigorous physical activity to the regression model increased the R to 22%. Black girls had somewhat lower fitness levels (P < 0.05) especially at higher levels of fat and fat-free mass than other racial/ethnic groups.

Conclusions: Physical activity, fat-free mass, and the interaction between fat-free mass and racial group are significantly associated with cardiorespiratory fitness in adolescent girls.

Figures

FIGURE 1

Quintiles of fat mass.

FIGURE 2

Quintiles of fat-free mass.

FIGURE 3

Quintiles of MVPA.

FIGURE 4

Association of fat mass with PWC-170 by racial group.

FIGURE 5

Association of BMI with PWC-170 by racial group.