This isn’t the first time that footwear designers have come up with curved soles. Some shoes are intentionally wobbly to keep your muscles active. Others, like these, have a ‘rocker bottom’ so that the act of walking propels you forwards, from one step to the next.

Rather than just aping others, Keen has designed the WK400 walking shoe from scratch. Three years, nearly 10,000 hours of design and development, and 5,000 miles of testing contributed to its all-new KEEN.CURVE geometry, with a 3D plate and curved sole.

The full-length plate maintains the shape of the curve and reduces energy loss, while using a high-energy, bouncy EVA midsole. That EVA compound is lightweight and returns energy into your step. The last has a 10mm drop, which is high compared with the trainers that most walkers wear. This is designed to propel you forwards, giving a sense of forward momentum without making you rock backwards. Meanwhile a super-sized 31mm of toe spring – compared...