Can BlazePose accurately assess joint angles in outdoor running environments?

Study aim: Accurate measurement of joint angles during running is crucial for performance optimisation and injury prevention. Traditional methods are often expensive or impractical for outdoor settings, making pose estimation techniques a promising alternative. This study aims to validate and evaluate the accuracy of BlazePose for measuring hip, knee, and ankle joint angles at key gait events, initial contact (IC), midstance (MS), and toe-off (TO) in outdoor running.

Material and methods: Sixteen male athletes participated in this study. Joint angles were measured using BlazePose and compared to manual measurements obtained with Kinovea software. Statistical analysis, including paired t-tests, Pearson correlation coefficients (r), Bland-Altman plots, mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE), was performed to assess BlazePose’s validity, agreement, and accuracy.

Results: BlazePose demonstrated a strong to very strong correlation with Kinovea (r: 0.70-0.97). Bland-Altman plots indicated good precision with minimal bias (average MAE: 2.11°, MAPE: 1.57%, RMSE: 2.63°). Ankle joint measurements were the most accurate across all joints and events, followed by the hip joint, particularly during midstance. Knee joint measurements had slightly higher errors but remained within an acceptable range.

Conclusions: BlazePose is a valid tool for measuring joint angles during outdoor running, providing an affordable alternative for biomechanical analysis. The findings are specific to the outdoor conditions under which the study was conducted, highlighting the necessity of validating pose estimation techniques in diverse environments and populations for broader applicability.