Optimization and pose selection for a lindy hop partnered spin

Abstract

Swing dancers often talk about using the laws of physics in performing their physically rigorous jumps, lifts, and spins. Do expert swing dancers physically optimize their pose for a partnered spin? In a partnered spin, two dancers connect hands and spin as a unit around a single vertical axis. We describe the pose of a couple by the angles of their joints in a two-dimensional plane and compare expert and novice dancers' actual poses to the approximately ideal poses generated from a biomechanical optimization model.The optimization objective is to maximize rotational acceleration, by minimizing the resistance to spin, but still producing torque. The model considers only external forces and neglects internal forces. It consists of equations derived from physical principles such as Newton's laws and moment of inertia calculations. Using numerical non-linear optimization we find the pose for each couple that maximizes their rotational acceleration. Different dancers are differently sized, so every couple has a unique optimal pose. Each couple's optimal pose is compared to the pose they actually assumed for the spin.We used motion capture to determine the angles of the joints in the couple's actual pose. The couple's actual pose is used to calculate a predicted rotational acceleration. This predicted acceleration is then compared to the optimal acceleration to determine a fraction of optimal for each couple. We hypothesized that expert swing dancers would achieve a higher fraction of their optimal acceleration than beginners. Our results did not achieve statistical significance with a simplified model and a small sample of 10 couples.