Introduction
Human gait is a remarkably intricate process that integrates neural control, musculoskeletal dynamics, and biomechanical coordination [1]. Historically, gait analysis has focused predominantly on lower limb mechanics, with much of the emphasis placed on stride length, cadence, joint kinetics, and energy expenditure in the legs. However, this lower limb-centric perspective overlooks the critical role of upper limb movement—specifically, arm swing—in the regulation of dynamic stability and locomotor efficiency.
Despite its apparent simplicity, arm swing is a coordinated and purposeful component of gait that interacts biomechanically with the trunk and lower extremities [2, 3]. Yet, its role remains underappreciated in both clinical and research contexts. This editorial aimed to reframe the understanding of upper limb swing within the domain of human gait by synthesizing current evidence, highlighting findings from our research, and proposing clinical and investigative pathways for integrating this component into broader models of gait rehabilitation.

Biomechanical significance of arm swing
Arm swing is often mischaracterized as a passive byproduct of locomotion, merely responding to the momentum generated by lower limb movements [4, 5]. Contrary to this outdated assumption, recent studies, including our own, demonstrate that arm swing is an active and functional element of gait. It serves to [6, 7]: 
1) Reduce vertical and mediolateral displacement of the center of mass (COM), thereby stabilizing the trunk and minimizing energy loss through excessive movement; 2) Generate angular momentum that counterbalances lower body motion and limits excessive torso rotation; 3) Enhance intersegmental coordination, contributing to smoother, more energy-efficient gait cycles.
In our study examining the effect of eliminating arm swing, we observed significantly increased three-dimensional COM excursions, particularly in the mediolateral plane [6]. This not only underscores the destabilizing effect of restricted arm motion but also suggests a greater demand on the neuromuscular system to maintain upright posture and forward progression. The implications are especially relevant for clinical populations with balance impairments or neuromotor deficits.
Furthermore, kinematic analyses reveal that upper limb movement is temporally synchronized with lower limb and pelvic motion, contributing to global movement fluidity [8]. Disruption of this synchronization, even in healthy individuals, results in compensatory movement patterns that may predispose individuals to musculoskeletal strain or inefficient gait [9].

Interlimb coordination and mechanical power
The mechanical and neurological coupling between upper and lower limbs reflects a deeply integrated system of motor control. Modifying arm swing—whether through voluntary restriction, splinting, or imposed asymmetry—leads to observable biomechanical consequences in lower limb function [6, 8, 10]: 
1) restriction of arm movement via splinting or immobilization has been shown to reduce peak mechanical power generation in the ankle joint and alter power profiles at the hip and knee. These changes point to a cascade of compensatory strategies that increase the energetic demands of walking [7, 8]; 2) altering the velocity or amplitude of arm swing affects ground reaction forces, cadence, and stride length. Our findings indicate that both excessive and restricted arm swing disrupts the normal timing and amplitude of gait cycles, leading to less efficient locomotion [9]; 3) asymmetrical arm swing, whether due to unilateral pathology or habitual movement patterns, produces measurable changes in contralateral limb kinetics, underscoring the importance of bilateral coordination in gait control.
Collectively, these findings reinforce the view that arm swing is not a redundant or vestigial behavior but a biomechanically essential aspect of functional walking. In clinical assessment, overlooking upper limb dynamics may lead to incomplete diagnoses and suboptimal rehabilitation planning.

Clinical relevance and applications
Impairments in arm swing are not merely incidental but often serve as early markers for pathological gait. They have diagnostic, prognostic, and therapeutic relevance across a range of conditions [8, 11, 12]:
1) Parkinson’s disease (PD): Early asymmetry or reduction in arm swing amplitude can precede more overt motor symptoms. Clinicians often use arm swing as a visual indicator during initial assessments and disease progression monitoring. Reduced arm swing is associated with increased postural sway and fall risk; 2) Post-stroke hemiparesis: Stroke survivors commonly exhibit diminished or delayed arm swing on the affected side, leading to poor interlimb coordination and increased energetic cost of walking. Incorporating arm swing retraining in stroke rehabilitation has demonstrated improvements in gait symmetry and overall mobility; 3) Orthopedic and musculoskeletal conditions: Immobilization following shoulder injury or upper limb surgery can disrupt habitual gait patterns. Prolonged disuse may lead to maladaptive compensations, including altered stride dynamics and increased load on the unaffected side.
In our clinical studies, targeted retraining of arm swing—through functional task practice, cueing strategies, and resistive training—resulted in measurable gains in gait quality [6, 13]. Notably, we observed increased symmetry in mechanical power output and improved balance metrics [9]. These outcomes highlight the need to incorporate upper limb mechanics into holistic rehabilitation protocols.

Future directions in research and rehabilitation
While interest in the role of upper limb dynamics is growing, substantial gaps remain. Addressing these will require interdisciplinary collaboration across biomechanics, neuroscience, and clinical rehabilitation.
1) Normative data: There is an urgent need to establish normative reference values for arm swing parameters (e.g. amplitude, timing, velocity) across different populations, including children, older adults, and individuals with specific diagnoses. Such datasets can inform clinical decision-making and provide benchmarks for recovery; 2) Technology-Assisted Interventions: The development of robotic exoskeletons, functional electrical stimulation (FES), and wearable biofeedback systems offers promising avenues for retraining arm swing. Preliminary studies suggest that augmenting upper limb motion can enhance lower limb engagement, particularly in neurologically impaired populations; 3) Machine Learning and Predictive Analytics: With the advent of wearable IMUs and motion capture technologies, there is growing potential to analyze arm swing patterns in real-time. Machine learning algorithms can be trained to detect deviations from normative patterns and predict fall risk or rehabilitation outcomes; 4) Integration in prosthetics and orthotics: Designing upper limb orthoses that preserve or replicate natural swing patterns could greatly benefit individuals with upper extremity impairments. Similarly, integrating arm swing mechanics into lower limb prosthetic programming may improve balance and reduce metabolic cost.
By advancing these research areas, the biomechanics community can move toward more comprehensive models of human locomotion that reflect the intricate interplay of all body segments.

Conclusion
Arm swing is far more than a byproduct of walking—it is a vital contributor to biomechanical stability, coordination, and energy efficiency. Ignoring its role in gait analysis and rehabilitation neglects a critical dimension of human movement. As clinical biomechanics evolves, our frameworks for understanding and treating gait disorders must also evolve. Integrating upper limb mechanics into clinical practice holds the promise of more effective, individualized interventions and improved patient outcomes across a range of conditions. A paradigm shift is underway—one that recognizes the full-body nature of gait and embraces arm swing as a key player in both research and rehabilitation.




References