Dynamic testing to determine and predict trampoline function

Abstract

Safety standards for domestic trampolines are based on static-load testing using a factor of five times the maximum intended user mass. This paper presents a dynamic test method for trampolines, and provides measures of the users’ performance (e.g., peak acceleration, Accmax) and injury risk (e.g., mean rate of change of acceleration, Jerkmean). Uniform masses (41–116 kg) were dropped from 0.66 m onto the bed centre of nineteen different trampolines. Trampoline bed and spring stretches, mass flight time (FlightT) and accelerations were recorded using motion capture and accelerometers. Thirty-seven percent of trampolines exceeded the static safety standard bed deformation limits (80% of frame height) by 11 ± 6% with dynamic testing (mean ± standard deviation). Across all trampolines and masses dropped, the Accmax ranged from 5.1 to 7.6 g, suggesting the factor of five used in static-loading safety standards needs reviewing. Statistically significant negative correlations (p < 0.05) were found between trampoline bed diameter and Accmax (r = – 0.88), Jerkmean (r = – 0.77) and FlightT (r = – 0.82). Furthermore, significant correlations (p < 0.05) were also found between the mass dropped and Accmax (r = – 0.27), Jerkmean (r = – 0.59) and FlightT (r = 0.25). The combined effects of the spring constants, number of springs, bed diameters and masses dropped were described in predictive multivariate equations for Accmax (explained variance, R2 = 95%) and maximum vertical bed deformation (R2 = 85%). These findings from dynamic testing may assist manufacturers in designing trampolines that meet safety standards while maximising user performance and reducing injury risk.