生体力学：つま先の上がった靴を履くと必要な筋肉の仕事量が減る

Wearing footwear with an upward curvature at the front of the shoe ― known as the toe spring ― requires less work from the muscles of the feet to walk than shoes with a flatter sole, according to an experimental study published in Scientific Reports.

Toe springs keep the toes continually elevated above the ground in a flexed upwards position to help the front part of the foot roll forward when walking or running and are present in most modern athletic shoes. However, their effect on natural foot function and the vulnerability of the feet to injury has not been widely studied.

Freddy Sichting, Dan Lieberman, Nicholas Holowka and colleagues investigated the effects of toe springs on foot biomechanics using a controlled experiment in which 13 participants walked barefoot on a treadmill at a comfortable walking pace. The participants were then asked to repeat the process wearing four different pairs of specially designed sandals with varying upward curvature of the toe region in order to simulate the curvature of modern athletic footwear. 3D motion data were captured using markers placed on each subject’s knee, ankle and foot.

The authors found that toe springs decrease the work of the muscles around the joints that connect the toes to the foot bones. The higher the upwards curve of the toes with respect to the rest of the foot, the less work the foot muscles had to perform to support the joints when walking.

The findings explain why toe springs are so comfortable and popular but suggest that shoes with toe springs may contribute to weakening of the foot muscles with long-term use. This may increase susceptibility to common pathological conditions, such as plantar fasciitis (inflammation of the part of the foot that connects the heel bone to the toes), according to the authors.