Titled "Dynamic fit adjustment for wearable electronic devices", the patent begins by highlighting the cumbersome nature of existing fastening methods, which can be inconvenient to adjust or require special tools to achieve the desired fit, and often fail to offer fine-grained adjustment.
The patent goes on to note that not only can a sub-optimal fit be uncomfortable, it also risks decreasing the sensitivity of onboard biometric sensors and reducing their measurement accuracy. These potential problems are often exacerbated by sweat and motion during exercise, the document notes.
A number of possible solutions are offered, using variations of a built-in tensioner mechanism that adjusts automatically or at the wearer's request, tightening or loosening as required. Variations include embedded shape memory wire, internal ratcheting apparatus, gas or fluid bladders, retractable band elements, and even extendable portions of the device housing.
As always with patents, it's not known whether the inventions will ever be used in Apple's consumer product line-up, but the designs clearly relate to potential future models of Apple Watch or watch band, the latest being the Sport Loop with hook-and-loop fastener.