Development and Field Evaluation of a Bolt-Type Force Measurement System for Sport Climbing Holds

Quantitative measurement of forces applied to climbing holds is important for biomechanical analysis and technique assessment in sport climbing. Existing measurement systems often require dedicated instrumented holds or force sensors inserted between the hold and the wall, which can restrict the selection of hold shapes or alter the wall–hold geometry. This study developed a bolt-type force measurement system in which strain-gauge-based sensors replace the bolts used to secure climbing holds. The sensor wiring passes through the bolt shaft and is routed to the rear side of the climbing wall, thereby reducing interference with the climber while preserving the external shape of the hold. Two bolt-type force sensors were calibrated using a reference six-axis force sensor and installed in two footholds on a standardized speed climbing wall. Within the calibration dataset, the error ratios in the principal loading direction, Fy, were 2.9% and 5.1% for Foot 1 and Foot 2, respectively, whereas the error ratios in the least-loaded Fx direction were higher, at 11.8% and 27.1%. Because the same calibration data were used to select the calibration matrices and calculate these errors, these values represent in-sample agreement rather than independent validation performance. A supplementary two-way hold-out analysis produced larger and split-dependent errors; for the principal loading direction, Fy, the hold-out MAE ratios ranged from 3.5% to 7.5% for Foot 1 and from 7.4% to 11.3% for Foot 2, whereas the corresponding Fx ratios ranged from 8.0% to 26.8% and from 45.9% to 87.5%, respectively. Field measurements were then conducted during 27 start trials performed by five competitive climbers. The system operated throughout all trials and recorded time-varying three-axis force estimates from both footholds without exposed wiring on the climbing side. For Foot 1, the estimated force components could be interpreted together with the observed start motion. For Foot 2, the climber’s foot may also have contacted the adjacent wall surface, so the sensor did not necessarily capture the entire foot reaction force. These results demonstrate the feasibility of deploying and operating the proposed system under actual speed-climbing conditions and provide a basis for future field-based biomechanical analyses.