Realising a biomimetic low-Vogel-exponent aquatic training device

Aquatic resistance training is a key technique within both sports training and osteomuscular rehabilitation, typically featuring the use of devices such as swimming parachutes to augment the hydrodynamic drag of the trainee. Conventional swimming parachutes, however, are limited by the classical strong (quadratic) scaling of drag force with velocity: to maintain a consistent target resistance, the swimmer must maintain a constant speed and the parachute size must be closely adjusted to this speed. In this work, we present and evaluate a bio-inspired approach to overcome these limitations. Many flexible biological structures, both terrestrial and aquatic, show weakened drag-velocity scaling, and thereby more consistent drag loading: an effect measured by the Vogel exponent (Ѵ). We design a swimming parachute with squid-inspired morphology that uses structural flexibility to weaken drag-velocity scaling, and evaluate it experimentally under the hydrodynamic conditions associated with crawl swimming. This evaluation confirms low Vogel exponent (-0.9<Ѵ<-1.3), corresponding to linear-to-sublinear scaling of drag force with velocity, across several different morphological configurations. This demonstration of improved resistance load consistency via flexible bio-inspired morphology has the potential to reduce the risk of injury in aquatic resistance training, and provides a novel connection between biological fluid-structure interaction and biomedicine.