Calibration of a novel instrumented mounting screw for monitoring sport climbing on artificial climbing walls

Sport climbing has become an Olympic sport, which has fostered interest in advanced monitoring of climber performance. Our research focuses on developing an unobtrusive sensor within an instrumented mounting screw (IMS) for assessing climber performance in real-world conditions. The IMS comprises single or double triplet configuration strain gauges bonded to modified mounting screws. Calibration of force magnitude, using known weights, was compared between an analytical approach and a machine learning neural network (NN) algorithm approach. Additionally, force directions in the coronal (frontal) and sagittal (side) planes relative to the climbing hold were determined analytically and compared to reference angles. Results demonstrated that the IMS could measure force magnitude and direction on climbing holds. In the double triplet configuration (six strain gauges), NN-based calibration showed more accurate results in estimating force magnitude compared to the analytical solution, with a relative error of 6% and 20%, respectively. For the single triplet configuration (three strain gauges), the NN method showed an accuracy of 14%. Similar trends were observed when the center of pressure (COP) was varied on the climbing hold, with higher root mean squared error (RMSE) for configurations with fewer strain gauges. In the coronal plane, force direction errors in angle were below 5°, while in the sagittal plane, errors reached 10° for angles above 25°. Thus, larger sagittal plane angles only indicate direction, and do not provide precise measurement. In conclusion, the developed unobtrusive IMS presents a promising method for assessing climbing performance on existing climbing walls.