Humans evolved to walk with an extra spring in our step

Newswise — A recent study indicates that humans might have developed a spring-like curve to facilitate bipedal movement. Researchers, who have been investigating the evolution of two-legged walking, traditionally believed that the elevated curve in the foot aids walking by functioning as a lever, propelling the body forward. However, an international group of scientists has now ascertained that the flexible arch's rebound effect repositions the ankle to an upright position, enhancing walking efficiency. The impact is more pronounced during running, implying that the capacity to run effectively could have exerted selective pressure for a flexible arch, subsequently enhancing walking efficiency as well. This revelation could potentially assist medical professionals in enhancing treatments for contemporary patients with foot ailments.

Dr. Lauren Welte, the primary researcher of the study published in Frontiers in Bioengineering and Biotechnology, explained, "Initially, we believed that the spring-like arch assisted in raising the body for the subsequent step. However, we have discovered that, in fact, the spring-like arch rebounds to aid the ankle in lifting the body." Dr. Welte conducted this research during her time at Queen's University and is currently associated with the University of Wisconsin-Madison.

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The development of our feet, characterized by the elevated medial arch that distinguishes us from great apes, plays a vital role in bipedal locomotion. The raised arch is believed to provide hominins with enhanced leverage during upright walking. While the precise mechanism remains uncertain, it is observed that restricting arch motion leads to increased energy expenditure during running. The recoil of the arch has the potential to improve our running efficiency by propelling the body's center of mass forward or compensating for mechanical work that would otherwise be performed by muscles.

In order to explore these hypotheses, the research team recruited seven individuals with different degrees of arch mobility. These participants underwent walking and running sessions while their feet were recorded using high-speed x-ray motion capture cameras. The researchers measured the height of each participant's arch and performed CT scans of their right feet. Rigid models were constructed and compared to the actual motion of the foot bones to assess the impact of arch mobility on neighboring joints. Additionally, the scientists determined the joints that contributed the most to arch recoil and evaluated the influence of arch recoil on the center of mass and ankle propulsion.

Leaning into bipedalism

Contrary to their initial expectations, the researchers found that arch recoil played a different role than anticipated. They discovered that a rigid arch lacking recoil had unfavorable consequences. It either caused the foot to lift off the ground prematurely, potentially reducing the efficiency of the calf muscles, or resulted in excessive forward inclination of the ankle bones. This forward tilt resembled the walking posture of chimpanzees rather than the upright stance observed in human gait. However, the presence of a flexible arch assisted in realigning the ankle to an upright position, enabling more effective propulsion during leg push-off from the ground. Notably, this effect was even more pronounced during running, suggesting that the evolution of a flexible arch may have been influenced by the selective pressure for efficient running.

Furthermore, the researchers made an important observation regarding the joint between two bones within the medial arch, namely the navicular and the medial cuneiform. They identified that this specific joint played a vital role in the flexibility of the arch. Alterations or changes to this joint could potentially provide valuable insights into the evolution of bipedalism when studying hominin fossil records.

Dr. Michael Rainbow, the senior author of the study from Queen's University, emphasized the significance of foot mobility in enabling upright walking and running. He stated, "The mobility exhibited by our feet appears to be a key factor in allowing us to walk and run in an upright position, rather than adopting a forward crouch or prematurely propelling into the next step."

Therapeutic potential

These findings also imply potential therapeutic options for individuals with rigid arches caused by injury or illness. Promoting arch flexibility might enhance overall mobility, offering new avenues for treatment.

"Our study indicates that enabling arch movement during propulsion enhances movement efficiency," Welte explained. "If we limit the motion of the arch, it is probable that it will affect the functioning of other joints accordingly."

"At this juncture, our hypothesis necessitates additional testing to confirm whether variations in foot mobility among the general population result in the observed changes, considering the limitations of our small sample size," Rainbow stated. "Nevertheless, our research establishes a promising foundation for an intriguing and innovative line of inquiry."