en بيومکانيک ورزشی و شاخه‌های وابسته بدان Sport Biomechanics and its related branches مقاله اصیل Original Article <div style="text-align: justify;"><strong>Background. </strong>Movement assessment is vital in physical therapy for injury prevention. Although 3D motion capture provides precise measurements, its high cost and complexity limit its practical application. Inertial measurement units (IMUs) present a more feasible alternative; however, their reliability in complex movements, such as the countermovement jump (CMJ), remains underexplored.<br> <strong>Objectives. </strong>To assess the reliability and concurrent validity of IMUs in measuring maximum lower limb angles during CMJs compared to 3D motion analysis.<br> <strong>Methods. </strong>An observational cross-sectional design was employed, involving 36 participants (18 males and 18 females; mean age, 23.25 years). Participants performed CMJs while fitted with reflective markers for 3D analysis and IMUs. Peak joint angles were measured in the sagittal, frontal, and transverse planes. Reliability was assessed using intraclass correlation coefficients (ICCs), and concurrent validity was determined through Pearson correlation coefficients.<br> <strong>Results. </strong>Results indicated moderate to excellent reliability for joint angle measurements, with ICCs ranging from 0.51 to 0.95 across planes. Concurrent validity demonstrated moderate to high correlations, particularly in the sagittal (hip: r = 0.74, knee: r = 0.73) and frontal planes (ankle: r = 0.94). However, lower correlations were noted in the transverse plane for the ankle (r = 0.40).<br> <strong>Conclusion. </strong>These findings suggest that while IMUs are effective for assessing joint angles during CMJs, caution is warranted when interpreting transverse plane data, particularly for the ankle. This study underscored the potential of IMUs as a practical alternative to 3D motion analysis in clinical and athletic settings</div> Inertial Measurement Units, Three-Dimensional Motion Analysis, Countermovement Jump, Kinematic Assessment 0 0 http://aassjournal.com/browse.php?a_code=A-11-1927-3&slc_lang=en&sid=1 Chuanpis Boonkerd chuanpis.b@allied.tu.ac.th 100319475328460017245 100319475328460017245 No Department of Physical Therapy, Faculty of Allied Health Sciences, Thammasat University, Pathum Thani, Thailand Thanawat Kitsuksan thanawat.k@allied.tu.ac.th 100319475328460017246 100319475328460017246 No Department of Physical Therapy, Faculty of Allied Health Sciences, Thammasat University, Pathum Thani, Thailand Suteera Jaidee suteera.j@allied.tu.ac.th 100319475328460017247 0009-0003-4986-7959 No Department of Physical Therapy, Faculty of Allied Health Sciences, Thammasat University, Pathum Thani, Thailand Teerapat Laddawong teerapat.l@allied.tu.ac.th 100319475328460017248 100319475328460017248 Yes Department of Physical Therapy, Faculty of Allied Health Sciences, Thammasat University, Pathum Thani, Thailand