Date of Award

3-2010

Degree Name

MS in Kinesiology

Department

Kinesiology

Advisor

Ann Yelmokas McDermott

Abstract

This observational study investigated whole body and regional differences in bone mineral density and soft tissue amounts (fat mass versus lean mass) among collegiate runners and swimmers using dual energy X-ray absorptiometry (DXA) for body composition measurement. A data subset was gathered for post-hoc analysis on a group of Caucasian male Cal Poly swimmers (n=20) and Cal Poly track and field runners (n=20) of similar age (18-25 years) and race. In addition to their sport-specific training, both teams had engaged in free weight training and running for approximately 12 weeks prior to their DXA scans. Group mean values for total body and regional bone mineral density (BMD) and percent body fat (% BF) were then compared, as were ratios for soft tissue distribution among the athletes. Multiple correlations between BMD, age, body weight (BW), fat mass (FM), lean tissue mass (LTM) and sport grouping were also determined.

Results for bone mineral differences between the two groups were consistent with past literature, as the runners had significantly greater total body BMD (p=0.000), and regional BMD of the legs (p=0.000). Swimmers possessed significantly greater total % BF (p=0.004), and legs % BF (p=0.004), despite having a greater lean torso-to-legs (LTL) ratio than the runners (p=0.000). However, even though the swimmers exhibited the greater average BW of the two groups, the runners actually had more measured LTM (in kg) located in the legs than the swimmers. The track runners had a greater FFM/FM ratio, but this value narrowly missed significance (p=0.012) after Bonferroni correction for multiple test comparisons lowered the level of significance (p<0.0083). The FFM/FM ratio was not correlated to the BMD among all subjects.

Several significant correlations were found among the body composition and group descriptive variables. Total BMD was predicted by BW (Pearson r=0.421, p=0.007) and whole-body LTM (r=0.468, p=0.002) among both groups. The strongest correlation was displayed between LTM and BW for both groups (r=0.932, p=0.000). While much is known in the research about the relationship between BW and load-bearing forces among weight-bearing and non-weight-bearing athletes, these data findings suggest that soft tissue distribution differences among such athletes should be further evaluated. Future research conducted with larger athlete sample sizes may possibly be able to determine what other physiological factors (age, hormonal and metabolic variations, muscular contractions, etc.) have the most influence on such differences in body composition.

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