1. Figures 3-6. Arm flexion, stride length and frequency and speed.
Introduction
The vacillating action of arm swinging may be a vestigial effect of humans’ prior knuckle-walking locomotor style as Fig. 3 Fig. 4
quadrupeds, and yet to date this has not been examined well. Here we use backpack use to better understand the
evolutionary role of arm swinging as it relates to bipedalism when weight bearing loads are present. Traveling while
carrying more is metabolically expensive; arm swinging serves the function of propelling one forward and thus reduces
the metabolic cost expended by the legs, while also providing leverage in maintaining balance [4]. We predict that weight
bearing loads placed on the dorsal region of our sample subjects will stabilize them by pulling them more upright and that
this stabilizing mechanism will result in less arm swing.
Methods
• Prior to experimentation, height, weight, gender, arm length and leg length for each subject were recorded. Reflective
markers were placed at three locations on subjects for arm swing analysis (Figure 1). Fig. 5 Fig. 6
• Fifteen sample subjects walked on a treadmill at three gradient speeds: 0.7 m/s (1.6 mph), 1.3 m/s (2.9 mph) and 1.8
m/s (4.0 mph).
• Subjects walked at each speed: once with no backpack and then with a backpack weighing 15 pounds.
• Subjects walked for three minutes at each speed in an effort to encourage a habituated, natural arm swing.
• Arm and leg motion were recorded using a video camera (SONY Handicam) at a rate of 60 frame/second (Hz).
• Data were analyzed using DARTFISH TEAM PRO motion analysis (Ver. 6.0) and Microsoft Excel (2010) software.
• Each subject’s arm swing length was recorded.
• For each trial, 10 full arm swings were used to calculate angular displacement of the upper arm and maximum flexion
angle of the lower arm.
• In addition, arm swing frequency (arm swings/sec), stride frequency (strides/sec), and stride length normalized to leg
length (% leg length) were calculated over 20 strides of each trial.
Discussion
Results • Studies indicate that the vacillating act of swinging the arms is not just a passive activity [3] but may
• Across the range of speeds, backpack loading increased upper arm angular displacement and lower arm peak flexion function to improve the efficiency of locomotion and therefore may have played a role in the evolution of
angle but had no effect on arm swing frequency (Figures 2 – 4). bipedalism in humans.
• For both conditions (loaded and unloaded), upper arm angular displacement, lower arm peak flexion angle, and arm • The results of this study show that backpack loading increased upper and lower arm swing. Arm swing
swing frequency increased with speed (Figures 3 and 4). has been shown to counteract the torque created by leg motion during walking [2]. It is possible that
• As speed increased, the backpack related difference in upper arm motion decreased as the difference in lower arm backpack loads accentuated the rotational effect of the legs and thus elicited greater arm swing.
motion increased (Figures 3 and 4).
• Counter swinging of the arms helps to maintain stability. How did this mechanism arise and did it originate
• Backpack loading had no effect on stride frequency or stride length. However, stride frequency increased with speed
as stride length decreased (Figures 5 and 6).
simultaneously with bipedalism? This pendulum like muscle activity could be due to past quadrupedal
• Contrary to our predictions, arm swing frequency was not influenced by the use of the backpack (Figure 2). locomotor patterns. The existence of spontaneous inter-girdle coordinating patterns is subsumed by
neurobiological arguments; in particular these patterns could have resulted from a residual function of
quadrupedal locomotion [1].
Figure 2. Arm frequency and speed. • Though metabolic expenditure was not measured in this study we recommend that it is examined in future
Average Arm Frequency studies relating to the function of bipedalism. Future studies may also employ a slightly heavier backpack
1.20 or a higher range of speeds.
Arm Frequency (arm swings/sec.)
1.00
Acknowledgments
We are grateful to Dr. Justus Ortega for the generous use of his lab and for helping in every stage of this analysis. We also thank our many study
0.80 volunteers, Nicole Anacito, the biomechanics lab coordinator, and several of Dr. Justus Ortega’s graduate students for providing help and instruction in
undertaking the project. We appreciate the support of the Department of Anthropology at Humboldt State University, the College of Arts, Humanities and
Social Sciences, the College of Professional Studies, and the Office of Research.
0.60
NO BACKPACK
WITH BACKPACK
Sources
0.40
[1] Dietz, V., Fouad, K. and Bastiaanse, C.M., 2001. Neuronal coordination of arm and leg movements during human
locomotion. European Journal of Neuroscience 14(11):1906–1914.
0.20 [2] Herr H. and Popovic M. 2008. Angular momentum in human walking. Journal of Experimental Biology 211:467-481.
[3] Jackson K.M., Joseph J., and Wyard S.J. 1978. A mathematical model of arm swing during human locomotion. Journal of
Biomechanics 11:277-289.
0.00
[4] Ortega J.D., Fehlman L.A., and Farley C.T. 2008. Effects of aging and arm swing on the metabolic cost of stability in human
Figure 1. Markers at the 1.6 2.9 4
walking. Journal of Biomechanics 41(16):3303-3308.
shoulder, elbow and hand. Speed (mph)
![Figures 3-6. Arm flexion, stride length and frequency and speed.
Introduction
The vacillating action of arm swinging may be a vestigial effect of humans’ prior knuckle-walking locomotor style as Fig. 3 Fig. 4
quadrupeds, and yet to date this has not been examined well. Here we use backpack use to better understand the
evolutionary role of arm swinging as it relates to bipedalism when weight bearing loads are present. Traveling while
carrying more is metabolically expensive; arm swinging serves the function of propelling one forward and thus reduces
the metabolic cost expended by the legs, while also providing leverage in maintaining balance [4]. We predict that weight
bearing loads placed on the dorsal region of our sample subjects will stabilize them by pulling them more upright and that
this stabilizing mechanism will result in less arm swing.
Methods
• Prior to experimentation, height, weight, gender, arm length and leg length for each subject were recorded. Reflective
markers were placed at three locations on subjects for arm swing analysis (Figure 1). Fig. 5 Fig. 6
• Fifteen sample subjects walked on a treadmill at three gradient speeds: 0.7 m/s (1.6 mph), 1.3 m/s (2.9 mph) and 1.8
m/s (4.0 mph).
• Subjects walked at each speed: once with no backpack and then with a backpack weighing 15 pounds.
• Subjects walked for three minutes at each speed in an effort to encourage a habituated, natural arm swing.
• Arm and leg motion were recorded using a video camera (SONY Handicam) at a rate of 60 frame/second (Hz).
• Data were analyzed using DARTFISH TEAM PRO motion analysis (Ver. 6.0) and Microsoft Excel (2010) software.
• Each subject’s arm swing length was recorded.
• For each trial, 10 full arm swings were used to calculate angular displacement of the upper arm and maximum flexion
angle of the lower arm.
• In addition, arm swing frequency (arm swings/sec), stride frequency (strides/sec), and stride length normalized to leg
length (% leg length) were calculated over 20 strides of each trial.
Discussion
Results • Studies indicate that the vacillating act of swinging the arms is not just a passive activity [3] but may
• Across the range of speeds, backpack loading increased upper arm angular displacement and lower arm peak flexion function to improve the efficiency of locomotion and therefore may have played a role in the evolution of
angle but had no effect on arm swing frequency (Figures 2 – 4). bipedalism in humans.
• For both conditions (loaded and unloaded), upper arm angular displacement, lower arm peak flexion angle, and arm • The results of this study show that backpack loading increased upper and lower arm swing. Arm swing
swing frequency increased with speed (Figures 3 and 4). has been shown to counteract the torque created by leg motion during walking [2]. It is possible that
• As speed increased, the backpack related difference in upper arm motion decreased as the difference in lower arm backpack loads accentuated the rotational effect of the legs and thus elicited greater arm swing.
motion increased (Figures 3 and 4).
• Counter swinging of the arms helps to maintain stability. How did this mechanism arise and did it originate
• Backpack loading had no effect on stride frequency or stride length. However, stride frequency increased with speed
as stride length decreased (Figures 5 and 6).
simultaneously with bipedalism? This pendulum like muscle activity could be due to past quadrupedal
• Contrary to our predictions, arm swing frequency was not influenced by the use of the backpack (Figure 2). locomotor patterns. The existence of spontaneous inter-girdle coordinating patterns is subsumed by
neurobiological arguments; in particular these patterns could have resulted from a residual function of
quadrupedal locomotion [1].
Figure 2. Arm frequency and speed. • Though metabolic expenditure was not measured in this study we recommend that it is examined in future
Average Arm Frequency studies relating to the function of bipedalism. Future studies may also employ a slightly heavier backpack
1.20 or a higher range of speeds.
Arm Frequency (arm swings/sec.)
1.00
Acknowledgments
We are grateful to Dr. Justus Ortega for the generous use of his lab and for helping in every stage of this analysis. We also thank our many study
0.80 volunteers, Nicole Anacito, the biomechanics lab coordinator, and several of Dr. Justus Ortega’s graduate students for providing help and instruction in
undertaking the project. We appreciate the support of the Department of Anthropology at Humboldt State University, the College of Arts, Humanities and
Social Sciences, the College of Professional Studies, and the Office of Research.
0.60
NO BACKPACK
WITH BACKPACK
Sources
0.40
[1] Dietz, V., Fouad, K. and Bastiaanse, C.M., 2001. Neuronal coordination of arm and leg movements during human
locomotion. European Journal of Neuroscience 14(11):1906–1914.
0.20 [2] Herr H. and Popovic M. 2008. Angular momentum in human walking. Journal of Experimental Biology 211:467-481.
[3] Jackson K.M., Joseph J., and Wyard S.J. 1978. A mathematical model of arm swing during human locomotion. Journal of
Biomechanics 11:277-289.
0.00
[4] Ortega J.D., Fehlman L.A., and Farley C.T. 2008. Effects of aging and arm swing on the metabolic cost of stability in human
Figure 1. Markers at the 1.6 2.9 4
walking. Journal of Biomechanics 41(16):3303-3308.
shoulder, elbow and hand. Speed (mph)](https://image.slidesharecdn.com/tiaandvinceposterfinal-130402002454-phpapp01/85/Tia-and-vince-poster-final-1-320.jpg)
