Body composition, neuromuscular function, and physical activity among adolescent African-American females
Williams, Richard Hadley
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Problem: American adults are facing two major lifestyle-related problems that have surfaced during the previous two-to-three decades: an epidemic of increasing adiposity and a deteriorating pursuit of physical activity. These lifestyle traits, which emerge prior to adolescent growth and development, are culturally linked. The literature suggests that this “weight plague” and “inactivity lifestyle” both have a gender bias and are ethnically prevalent. In particular, the African-American race and the female gender are associated with propensity for this combination. Additionally, the literature suggests that risks for various debilitating diseases are more pronounced as fat mass increases and activity level decreases. Therefore, what consequence, if any, do these trends have on the neuromuscular characteristics of adolescent African-American females? Procedures: Thirty-two subjects were randomly selected to participate in a seven week protocol that encompassed analysis of body composition, indices of skeletal muscular strength, and questionnaires which quantified time spent in leisure, occupational, and/or structured physical activity endeavors. In order to illustrate comparisons, subjects were grouped as “low-risk” or “high-risk,” depending upon their body mass index (BMI<22.5= “low-risk” and BMI>22.5= “high-risk,” respectively). Results: There was no sound evidence that suggests lessening of neuromuscular function among subjects. Although possessing significantly greater total body fat-freemass (p=0.029), leg fat-free mass (p=0.041), arm fat-free mass (p=0.025), and thigh extensor absolute-strength (p=0.013), the “high-risk” individuals demonstrated less attributable variance in their muscular strength and size indices. Surprisingly, the “highrisk” subjects were more active (kcal/d, p=0.042 and 5 day pedometer readings, p=0.0001) than their “low-risk” counterparts according to self-report measures of physical activity. However, the pursuit of hard-to-vigorous physical activities was almost non-existent between both groups (1.88 and 2.56 hrs/wk for “low-risk” and “high-risk” respectively). Conclusion: Although groups differed in body composition, muscular strength, and activity durations, altered neuromuscular function among subjects were not present. Given the minimal pursuit of hard-to-vigorous activities, more time engaging in these activities may be the critical element in offsetting premature neuromuscular disorders, although not observed. Moreover, more research in needed that focuses on adolescent skeletal muscular characteristics and their relation to physical activity durations. Additionally, developing ways to enhance hard-to-vigorous activities is strongly encouraged.