INFLUENCE OF WEARING A BELT-SUPPORTED ARMORED VEST ON THE ENERGETICS OF OVERGROUND LOCOMOTION

L.M. Whalen1, K.A. Pribanic2, & D.P. Heil1 1Movement Science/Human Performance Laboratory, Montana State University, Bozeman, MT 2Mystery Ranch LTD, Bozeman, MT Standard loads carried by military ground troops on patrol can include a rifle, an operations kit, a loaded backpack, and an armored vest, such as the modular tactical vest (MTV) used in this study. As load mass increases, so does the potential for fatigue and injuries. Finding the most economical load carriage system may allow troops to perform their duties in the safest and most effective manner. PURPOSE: This study assessed the energetic and kinematic effects of supporting an MTV with a backpack-style hip belt during overground hiking. It was hypothesized that the energetics of overground hiking with an MTV would improve with the use of a hip belt. METHODS: Nine women and eight men (Mean±SD: 25±8 years) hiked a 586 m unpaved, outdoor path, carrying a dummy rifle, under three conditions: wearing no MTV (Control); wearing a 17.7 kg MTV (A condition); wearing an MTV with an attached 0.6 kg hip belt (AB condition). Subjects hiked under each condition at three speeds: 67.0 m/min; 80.4 m/min; 93.8 m/min, for a total of 9 trials. Data for stride rate (SR; steps/min), energy expenditure (oxygen uptake, VO2; ml/min), and heart rate (HR; BPM) were measured with accelerometers and a portable metabolic system, then summarized for each trial and analyzed using a multivariate repeated measures ANOVA and Sheffe’s post-hoc at the 0.05 alpha level. RESULTS: At all speeds, SR was always lowest for the Control condition and highest for the AB condition, though not significantly (P\u3e0.05). VO2 and HR were higher for the AB condition than for the Control and A conditions at all speeds, though not significantly (P\u3e0.05). CONCLUSION: The use of an MTV with a hip belt was unexpectedly associated with non-significant trends to increase VO2, HR and SR for all hiking speeds. While many subjects noted greater shoulder comfort when using the hip belt, it is speculated that the belt’s repositioning of the MTV mass necessitated greater balance control during overground hiking, which then caused the observed increases in VO2 and SR. Further research should focus on a similar measurement strategy with attention paid to the mass distribution on the MTV as well as the fit of the MTV with reference to gender and body size of the wearer. Study funded by Mystery Ranch LTD (Bozeman, MT

RELIABILITY AND VALIDITY OF USING A HAND-HELD GPS MONITOR TO CONTROL OVERGROUND HIKING SPEED

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

Sequence‐to‐sequence alignment using a pendulum

Analysing two or more video sequences of dynamic scenes typically requires time synchronisation between sequences, where this alignment is not always possible using hardware. A particular method will most likely process the entire, frequently lengthy, imaged material, requiring additional processing which normally serves for synchronisation only. Software‐based synchronisation methods impose, in basically all cases, certain assumptions about an imaged three‐dimensional (3D) scene and are suited for the already imaged video material in the past. The authors argue that there are applications where the unsynchronised video sequences have not yet been taken. The time‐efficient solution uses a pendulum consisting of a small ball, attached to a 50 cm string and suspended from a pivot so that it can swing freely. The authors estimate the time instant when the ball swings through the equilibrium position. The difference in these times for two cameras yields a subframe time difference between cameras. The proposed method yields subframe differences, statistically no different from ground truth data. 3D reconstruction results for synchronised data clearly outperform those which are unsynchronised. The proposed method relaxes any restrictions and assumptions about the 3D scene that will be imaged later on, yet it allows accurate subframe synchronisation in less than a second