Effects of Backpack Load and Load Height on Arm Reaching Ability in Several Directions

Abstract

PURPOSE: The ability to reach with the arm has not been examined during load carriage with a backpack, or with the load distributed high or low in the backpack. METHODS: Arm reach was tested using the Functional Reach Test (Forward), Multi-directional Reach Test (Backward, Right, Left), Upward Reach Test (Upward) at a 50° angle, and Forward Reach to the Floor Test (Low). Subjects were healthy males (n=7) and females (n=2), 19-21 years, who wore a hiking backpack and performed using the dominant arm. Subjects were tested with no backpack, and then (in random order on different days) with the backpack empty, or load (weight) equivalent to 10, 30, and 50% of bodyweight in the bottom of the backpack. Trials were repeated with the load high in the backpack using a custom designed box. Three trials were completed for each reach. Mean values were analyzed with repeated measures ANOVA and Tukey’s post-hoc test with significance level p < 0.05. RESULTS: (Data are presented as reach in cm normalized for arm length, mean ± SD). When compared to no backpack, load high (30, 50% BW) in the backpack resulted in significant reductions in arm reach (all directions; Low = 140.5±13.8 vs 124.3±6.7, 115.5±7.7; Upward = 165.1±10.7 vs 159.9±9.3, 155.3±12.9; Left = 196.2±8.5 vs 181.6±7.3, 173.4±4.5; Right = 194.0±8.9 vs 181.7±8.0, 175.5±8.4; Backward = 180.2±9.1 vs 160.9±5.7, 153.5±7.9; Forward = 218.2±10.8 vs 208.9±8.1, 200.9±10.1) and load low (all loads) in the backpack resulted in significant reductions in arm reach for backward reach only (180.2±9.1 vs 176.8±8.1, 169.5±9.5, 164.5±1.3). When compared to empty backpack, load high (30, 50% BW) in the backpack resulted in significant reductions in arm reach (all directions; Low = 137.1±1.1 vs 124.3±6.7, 115.5±7.7; Up = 163.9±10.6 vs 159.9±9.3, 155.3±12.9; Left = 194.3±8.6 vs 181.6±7.3, 173.4±4.5; Right = 194.7±8.7 vs 181.7±8.0, 175.5±8.4; Backward = 177.9±7.4 vs 160.9±5.7, 153.5±7.9; Forward = 215.1±11.3 vs 208.9±8.1, 200.9±10.1) and load low (50% BW) in the backpack resulted in significant reductions in backward reach only (177.9±7.4 vs 164.5±1.3). CONCLUSIONS: Backpack load weight and height differentially affects arm reach. This project was funded in part by the Douglas A. & Phyllis G. Smith Student Faculty Collaborative Research Fund.