I. Dominguez, D. Bell, A. Fijalka, K. Woodworth, B. Higginson

Gonzaga University, Spokane, WA

Hiking is not only a recreational pursuit but is used in extreme sports and professional settings such as mountaineering and the military, and those pursuing the activity experience varying terrain with changes in grade. Regardless of the purpose behind hiking, almost all long-distance hikers have a common way of storing their items: backpacks. PURPOSE: The purpose of this study was to observe the effects of slope grade and backpack load on muscle activation and trunk angle while carrying a backpack. METHODS: Participants (n=18) walked on a treadmill at 2.5 mph for a total of ten trials, five of which were performed with an unloaded backpack and five with a loaded backpack at 30% of the subject's body weight. Subjects walked at grades of -5%, 0%, 5%, 10%, and 15% for each condition. Surface EMG electrodes were attached to the muscle bellies of select lower extremity muscles: tibialis anterior (TA), soleus (Sol), lateral gastrocnemius (LG), biceps femoris (BF), vastus lateralis (VLO), and rectus femoris (RF) muscles. Also, trunk angle was measured throughout all trials. To examine the effects treadmill grade and backpack load had on muscle activation, a within-in subjects repeated-measures analysis of variance (ANOVA) was used. ANOVA was also run to examine the effects of treadmill inclination and backload load has on muscle activation. The level of significance was set at p<0.05. RESULTS: Muscle activation of almost all of the lower extremity muscles measured (TA, Sol, LG, VLO, and RF) were significantly greater for the loaded backpack condition compared to the unloaded condition. Furthermore, there was an interaction effect between backpack load and treadmill grade on the activation of the Sol (p=0.001), LG (p=0.000), and VLO (p=0.000), in which these muscles were activated to a greater magnitude with a load than without a load across an increasing grade. Forward lean (trunk angle) progressively and significantly (p<0.05) increased as treadmill inclination increased, and it was significantly greater in the loaded condition than the unloaded condition by - 6.971°, p=0.000. CONCLUSIONS: Forward trunk lean was greater with a weighted backpack, which may result as a compensation to center the total mass of the trunk and pack to the position of the unloaded condition, allowing the individual to walk more efficiently. Because carrying a weighted backpack over increasing grades yielded greater increases Sol, LG, and VLO activation than when equipping an empty one, hikers planning expeditions with steep inclines may want to train these specific muscles for strength and endurance more than others.

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