An Evaluation of Select Physical Activity Exercise Classes (PEX) on Bone Mineral Density

INTRODUCTION: According to the National Institute of Health consensus, Osteoporosis causes premature disability in approximately 44 million people (National Institute of Health [NIH], 2001), 80% of this population being women (Ulrich, Georgiou, Gillis, & Snow, 1999). This chronic disease causes 1.5 million fractures annually, 700,000 occurring at the spine (NIH, 2001). One prevention technique developed in recent years is to build a high peak bone mass during growth and in young adult life (Almstedt, Canepa, Ramirez, & Shoepe, 2011). Several publications positively correlate an increase in BMD with increased amounts of exercise. Bone mineral density can be observed through DEXA scans, as well as, by monitoring specific biochemical markers in the blood such as osteocalcin, known to be sensitive to bone formation. PURPOSE: The purpose of this research is to assess the efficacy of select structured physical activity classes. Specifically, we intend to determine the effect of these exercise classes on bone mineral density (BMD) as measured through Dual Energy X-Ray Absorptiometry (DEXA) scans, and analysis of the biochemical marker osteocalcin. METHODS: As part of a prospective cohort study design participants included females, ages 18-35 years, who were enrolled in either a yoga (N=14) or a cardio-kickboxing (N=13) physical activity class both provided by the University of Nevada, Las Vegas (UNLV). Twelve individuals not enrolled in either class served as controls. Participants provided baseline hip, spin, and total body DEXA scans as well as a blood sample to obtain osteocalcin concentrations. Participants were also asked to complete food/medication/supplementation questionnaires concerned with intake prior to and during the study. Previous and current physical activity was also accounted for via questionnaire. Participants were then asked to return for testing after completion of the semester physical activity course to provide post DEXA scans and blood samples. RESULTS: Results suggest no significance observed for BMD by DEXA scans for TB (p= .383), HP (p= .305), or SP (p= .009) sites after completion of a yoga PEX class. In fact, measurements at the SP revealed a significant reduction in BMD (p=.009). Similarly, no significance was observed for BMD by DEXA scans for TB (p= .524), SP (p= .062), or HP (p= .433) after completion of a CKB class. Bone mineral density also failed to be significant across all three groups at each site TB (p= .845), SP (p= .789), and HP (p= .519). However, osteocalcin concentration displayed significance in both yoga (p= .000) and CKB (p= .001) classes but failed to be significant across all three groups including controls (p= .071). DISCUSSION: We can conclude 12 weeks of yoga and CKB classes evoke a significant increase in osteocalcin’s biochemical response. This conclusion could actuate the assumption that biochemical activity is far more sensitive to physical activity than actual bone growth. It is likely that 12 weeks is an insufficient amount of time to induce bone growth, regarding the standard life cycle of bone. Cardio kickboxing is an active physical activity incorporating quick repetitive movements into its curriculum that require the individual to exert force onto an object. This group did not increase BMD, but they did maintain levels at all tested sites. Yoga is a passive physical activity requiring the individual to shift their own body weight through sustained static poses. Force or stress is necessary to induce bone growth. Without an outside stimulus to react against it is reasonable to assume the bone growth response is not initiated. Cardio kickboxing seems to elicit enough force acting against bone to promote maintenance of BMD whereas yoga does not