Author and graduation date: Cindy Gail MORGAN, August, 1998

Committee members: Jeanne F. Nichols (Chair), Donna Beshgetoor, James F. Sallis, Karen J. Calfas

Thesis title: Field Validation of the Tritrac-R3D Laboratory Generated Activity Measurement Equation

The purpose of this study was to validate the laboratory generated equation that predicted speed, and indirectly METs, from vector magnitude (VM) counts generated by the Tritac, in a field setting. Thirty non-obese adults (mean age 28 + 5 yr.) were instructed, in randomized order, to "stroll," "walk briskly," and "jog at a comfortable pace" for two laps each around a flat, outdoor, cork 400m track. Exercise bouts were timed and actual speeds calculated. Tritracs were inserted into pouches and securely fastened on the right and left hip at the anterior axillary line. Tritrac data from minutes 2-4 were used for analysis. Projected speeds were calculated using field generated VM data and the laboratory developed regression equation that predicted speed from VM counts. Pearson product-moment correlation demonstrated a strong linear relationship between pooled actual speeds and VM data (r = .95). The results of a two-way repeated measures ANOVA indicated a significant speed effect (p = 0.001), a significant gender effect (p = .019), and a significant interaction between speed and gender (p = .001). The actual speeds were underestimated by 0.69, 0.53, 0.94, and 0.73 mph for the light, moderate, vigorous and total activity. Women ran significantly slower than men during the vigorous activity but VM did not underestimate the speed as it did in men . Using the laboratory developed VM cut-points for light, moderate, and vigorous activity, 40% of the light and 20% of the moderate activity bouts were incorrectly classified. These data may indicate that laboratory developed VM cut-points established to classify activity may provide misleading results in a field setting. Possible differences in the biomechanics of treadmill versus overland walking and running may explain the observed results. A new regression equation that estimated overground walking and running speeds from the VM data was developed and new VM cut-points to classify the intensity of activity as light, moderate, and vigorous activity in a free-living setting were established.

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