T.K. Vetrone, L.Whalen, K.A. Pribanic, & D.P. Heil

Montana State University, Bozeman, MT

To accurately control locomotion speed and grade, load carriage studies are commonly performed in lab settings. However, it may be more appropriate to perform these same studies in outdoor settings. For example, a recent study in our lab assessed the energetic and kinematic effects of hiking with an armored tactical vest commonly worm by active military ground troops. To control outdoor hiking speed, a hand-held GPS monitor was used by investigators to pace the test subjects as they hiked a level trail under different load carriage conditions. The accuracy and repeatability of this technique for controlling outdoor hiking speed, however, has never been evaluated. PURPOSE: To determine the validity and reliability of using a hand-held GPS monitor to control overground hiking speed of subjects performing outdoor load carriage studies. METHODS: Nine women (mean±SD: 27±7 years; 163.1±6.1 cm; 62.5±10.3 kg) and eight men (24±4 years; 179.5±6.0 cm; 81.7±12.5 kg) performed outdoor hiking tests as part of a larger study of wearing a Modular Tactical Vest (MTV) both with and without a hip belt. The three hiking conditions (hiking without MTV; hiking with MTV; and hiking with MTV plus a hip belt) were each performed at three goal speeds: 67.0m/min (2.5mph); 80.4m/min (3.0mph); 93.8m/min (3.5mph), for a total of 9 trials. For each trial, subjects followed an investigator (i.e. pacer) with a hand-held GPS monitor with instructions to stay within 1-2 m of the pacer at all times. Actual speed for each lap was computed from the time required to complete each 293 m lap. Reliability of actual speed between the two laps was assessed using a two-factor repeated measures ANOVA (α=0.05), the intraclass correlation coefficient (Rxx), and the standard error of measurement (SEM). Validity was assessed by comparing the goal speeds to the 95% confidence intervals for each trial speed. RESULTS: Reliability results were mixed: ANOVA for all 9 trials were non-significant; Rxx values ranged from low to high (0.27-0.87); SEM for each of the 9 trials was consistently low (±0.47 to ±1.02 m/min; or ±0.02 to ±0.04mpg). Lastly, the goal speeds were all within the 95% CIs for each of the 9 trials. CONCLUSIONS: Based on the collective reliability and validity results, the method of using a hand-held GPS monitor to control overground hiking speed was both reliable and valid and should be considered for future outdoor overground locomotion studies.

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