General fitness monitoring has very successfully made the leap from professional to personal, with the use of apps that log exercise or dedicated gadgets watching everything from the number of steps you’ve taken to your heart rate and blood pressure almost becoming the norm.

The latest enhancement for modern fitness gear, just published in Advanced Materials Technologies, is an optical waveguide-based strain sensor that can gauge how hard you’re exercising just by strapping it over your muscles.

The device is based on low-cost, easy-to-work-with, silicone-clad urethane fibre cabling, capable of flexing and stretching when pressure is applied. In the application demonstrated by its creators from the University of Louisville and Cornell University in the USA, the fibres are sewn onto athletic tape using a sewing machine couching foot, which shows how easily they could be incorporated into almost any kind of garment or accessory.

A 100 Mbps, 870 nm LED was connected to one end of the fibre and a sensor to the other, and changes in muscle thickness were tracked as the volunteer wearing the athletic tape shifted weight from one leg to the other. The response was transmitted wirelessly and recorded as a change in voltage over time, producing a distinct signal (see image). Being able to show direct feedback from the muscles like this without applying electrodes to the skin is an important step for such sensing devices.

The fibres, with their surprisingly simple build, could also be used for gait or joint angle sensing and could be applied to physical therapy as much as to sports applications.

See the detailed discussions on the potential causes of signal loss and how easily they were handled here.