Arm swing in human bipedal walking is a natural motion wherein each arm swings with the motion of the opposing leg. Swinging arms in an opposing direction with respect to the lower limb reduces the

angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...

of the body, balancing the rotational motion produced during

walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults o ...

. Although such pendulum-like motion of arms is not essential for walking, recent studies point that arm swing improves the stability and energy efficiency in human

locomotion Locomotion means the act or ability of something to transport or move itself from place to place. Locomotion may refer to: Motion * Motion (physics) * Robot locomotion, of man-made devices By environment * Aquatic locomotion * Flight * Locomoti ...

. Those positive effects of arm swing have been utilized in sports, especially in

racewalking Racewalking, or race walking, is a long-distance discipline within the sport of athletics. Although a foot race, it is different from running in that one foot must appear to be in contact with the ground at all times. Referee, Race judges careful ...

and

sprinting Sprinting is running over a short distance at the top-most speed of the body in a limited period of time. It is used in many sports that incorporate running, typically as a way of quickly reaching a target or goal, or avoiding or catching an op ...

Kinematics

Studies on the role of arm swing consist mainly of analysis of bipedal walking modelsF. C. Anderson, M. G. Pandy (2003). Dynamic Optimization of Human Walking. ''Journal of Biomechanical Engineering'', 123, 381–390. and treadmill experiments on human subjects. Bipedal walking models of various complexity levels provided an explanation for the effects of arm swing on human locomotion. On the course of bipedal walking, the leg swing results in an

that is balanced by the ground reaction moments on the stance foot. Swinging arms create an angular momentum in the opposing direction of lower limb rotation, reducing the total angular momentum of the body. Lower angular momentum of the body results in a decline on the ground reaction moment on the stance foot.J. Park (2008). Synthesis of natural arm swing motion in human bipedal walking. ''Journal of Biomechanics '', 41, 1417–1426. Amplitude or frequency of arm movements is determined by the gait, meaning that the swing motion is adaptive to changing conditions and perturbations.S. F. Donker, Th. Mulder, B. Nienhuis, J. Duysens (2002). Adaptations in arm movements for added mass to wrist or ankle during walking. ''Experimental Brain Research'', 146(1), 26–31. As the walking speed increases, the amplitude of the arm swing increases accordingly. The frequency of the arm movements changes with the speed as well. Studies showed that at speeds lower than approximately 0.8 m/s, the frequency ratio between arm and leg movements is 2:1 whereas above that speed the ratio becomes 1:1.M. P. Ford, R. C. Wagenaar, K. M. Newell (2007). Arm constraint and walking in healthy adults. ''Gait & Posture'', 26, 135–141.

Theories

Stability

Both simulations on skeletal models and experiments on force plate agree that the free arm swing limits the ground reaction moments effective on the stance foot during walking, because the total angular momentum is lowered by the counterbalancing swing of arms with respect to the lower-limb.Yu Li, W. Wang, R. H. Crompton, M. M. Gunther (2001). Free vertical moments and transverse forces in human walking and their role in relation to arm-swing. ''The Journal of Experimental Biology'', 204, 47–58. In other words, a subject exerts less reaction moment to the ground surface when there is arm swing. This implies that the friction force between the stance foot and the ground surface does not have to be as high as without the arm swing.

Energy efficiency

Whether arm swing is a passive, natural motion caused by the rotation of torso or is an active motion that requires active muscle work has been a critical discussion on arm swing that could illuminate its benefit and function. A recent study concentrated on the energy consumption during walking showed that at low speeds arm swing is a passive motion dictated by the kinematics of torso, no different from a pair of pendula hung from the shoulders. Active upper extremity muscle work, controlled by the brain, only takes part when there is a perturbation and restores that natural motion. However, at higher speeds, the passive motion is insufficient to explain the amplitude of the swing observed in the experiments. The contribution of active muscle work increases with the walking speed. Despite the fact that a certain amount of energy is consumed for the arm movements, the total energy consumption drops meaning that arm swing still reduces the cost of walking. That reduction in the energy is up to 12 percent at certain walking speeds, a significant saving.S. H. Collins, P. G. Adamczyk, A. D. Kuo (2009). Dynamic arm swinging in human walking. ''Proceedings of the Royal Society, Biological Sciences '', 276, 3679–3688.

Evolution

The inter-limb coordination in human locomotion, questioning whether the human gait is based on quadruped locomotion, is another major topic of interest. A recent research indicates that inter-limb coordination during human locomotion is organized in a similar way to that in the cat, promoting the view that the arm swing may be a residual function from quadruped gait.V. Dietz (2002). Do human bipeds use quadrupedal coordination? ''Trends in Neurosciences'', 25, No. 9, 462–467. Another work on the control mechanisms of arm movements during walking corroborated the former findings, showing that

central pattern generator Central pattern generators (CPGs) are self-organizing biological neural circuits that produce rhythmic outputs in the absence of rhythmic input. They are the source of the tightly-coupled patterns of neural activity that drive rhythmic and stereot ...

(CPG) might be involved in cyclic arm swing. However, these findings do not imply vestigiality of arm swing, which appears to be debateful after the 2003 evidences on the function of arm swing in bipedal locomotion.E. P. Zehr, C. Haridas (2003). Modulation of cutaneous reflexes in arm muscles during walking: further evidence of similar control mechanisms for rhythmic human arm and leg movements. ''Experimental Brain Research'', 149, 260–266.

Athletic performance

Energy efficiency of arm swing and its potential in adjusting the momentum of the body have been utilized in sports. Sprinters make use of the contribution of arm swing on the linear momentum in order to get a higher forward acceleration. Racewalkers are also utilizing the arm swing for its energy efficiency. Rather than the rhythmic movements during walking, swinging arms in the right way helps athletic performance in different disciplines. Standing long jump performance is shown to be improved by swinging arms forward during the onset of the jump and back-and-forth during landing since the linear momentum of the body can be adjusted with the help of moving arms.B. M. Ashby, J. H. Heegard (2002). Role of arm motion in the standing long jump. ''Journal of Biomechanics '', 35, 1631–1637. Use of arms in adjusting the rotational and linear momentum is also a common practice in somersaulting and gymnastics.K. B. Cheng, M. Hubbard (2008). Role of arms in somersaulting from compliant surfaces: A simulation study of springboard standing dives. ''Human Movement Science'', 27, 80–95.

Robotics

The literature on the arm swing is partly created by robotics researchers as the stability in locomotion is a significant challenge especially in humanoid robots. So far although many humanoid robots preserve static equilibrium during walking which does not require arm swing, arm movements has been added to a recent humanoid robot walking in dynamic equilibrium.Archived a
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The pendulum-like motion of arms is also utilized in passive dynamic walkers, a mechanism that can walk on its own.S. Collins, A. Ruina, R. Tedrake, M. Wisse (2005). Efficient Bipedal Robots Based on Passive-Dynamic Walkers. "Science", 307, 1082.

Neuromechanical considerations

Understanding the underlying neural mechanisms on the organization of rhythmic arm movement and its coordination with the lower limb could enable development of effective strategies for rehabilitation of spinal cord injury and stroke patients. Rhythmic arm movements for different tasks -arm swing during walking, cycling arms while standing and arm swing while standing- were investigated in this perspective and the results pointed a common central control mechanism.M. D. Klimstra, E. Thomas, R. H. Stoloff, D. P. Ferris, E. P. Zehr (2009). Neuromechanical considerations for incorporating rhythmic arm movement in the rehabilitation of walking. ''Chaos'', 139. Performing the left-lateralised

Stroop task ---- ---- Naming the font color of a printed word is an easier and quicker task if word meaning and font color are congruent. If two words are both printed in red, the average time to say "red" in response to the written word "green" is ...

while walking on a treadmill tends to reduce arm swing on the right, particularly in older people, suggesting a significant supraspinal contribution to its maintenance.Killeen T, Easthope CS, Filli L et al (2017). Increasing cognitive load attenuates right arm swing in healthy human walking, http://rsos.royalsocietypublishing.org/content/4/1/160993. While men of all ages demonstrate this interference effect between cognitive load and right arm swing, women appear to be resistant until the age of 60.

Medical science

The role of arm movements in unhealthy subjects is another popular direction investigating the strategies adopted by patients in order to maintain stability in walking. As an example, children with hemiparetic CP showed substantial increases in angular momentum generated by the legs, which were compensated by increased angular momentum of the unaffected arm showing the way arm swing is utilized in order to balance the rotational motion of the body.S. M. Bruijn, P. Meyns, I. Jonkers, D. Kaat, J. Duysens (2011). Control of angular momentum during walking in children with cerebral palsy. ''Research in Developmental Disabilities'', 32, 2860–2866. Reduction in bilateral arm coordination may contribute to clinically observed asymmetry in arm swing behavior which could be a sign of Parkinson's disease.X. Huang, J. M. Mahoney, M. M. Lewis, G. Du, S. J. Piazza, J. P. Cusumano (2012). Both coordination and symmetry of arm swing are reduced in Parkinson’s disease. ''Gait & Posture'', 35, 373–377. A quantitative study on the level of asymmetry in arm swing is considered to have utility for early and differential diagnosis, and for tracking Parkinson's disease progression.M. D. Lewek, R. Poole, J. Johnson, O. Halawa, X. Huang (2010). Arm swing magnitude and asymmetry during gait in the early stages of Parkinson’s disease. ''Gait & Posture'', 31, 256–260.

References

External links

Arm Swinging – Experiment
* ttp://www.chirunning.com/chi-library/article/arm-swing-maximize-your-upper-body-and-reduce-your-legwork/ Arm Swing: Maximize Your Upper Body and Reduce Your Legworkbr>How Important is Arm Swing to Running Form and Speed?Scientists find a reason for arm-swinging as you walk
Walking