Goal: The countermovement jump (CMJ) is commonly used to measure the explosive power of the lower body. This study evaluates how accurately markerless motion capture (MMC) with a single smartphone can measure bilateral and unilateral CMJ jump height. Methods: First, three repetitions each of bilateral and unilateral CMJ were performed by sixteen healthy adults (mean age: 30.87 $\pm$ 7.24 years; mean BMI: 23.14 $\pm$ 2.55 $kg/m^2$) on force plates and simultaneously captured using optical motion capture (OMC) and one smartphone camera. Next, MMC was performed on the smartphone videos using OpenPose. Then, we evaluated MMC in quantifying jump height using the force plate and OMC as ground truths. Results: MMC quantifies jump heights with MAE between 1.47 and 2.82 cm, and ICC between 0.84 and 0.99 without manual segmentation and camera calibration. Conclusions: Our results suggest that using a single smartphone for markerless motion capture is feasible. Index Terms - Countermovement jump, Markerless motion capture, Optical motion capture, Jump height. Impact Statement - Countermovement jump height can be accurately quantified using markerless motion capture with a single smartphone, with a simple setup that requires neither camera calibration nor manual segmentation.

翻译：目标：下蹲跳（CMJ）常用于测量下肢爆发力。本研究评估使用单智能手机进行无标记动作捕捉（MMC）量化双侧与单侧下蹲跳高度的准确性。方法：首先，十六名健康成年人（平均年龄：30.87 $\pm$ 7.24 岁；平均BMI：23.14 $\pm$ 2.55 $kg/m^2$）在测力台上分别完成三次双侧和单侧下蹲跳，并同步使用光学动作捕捉（OMC）和单台智能手机相机进行记录。其次，通过OpenPose对智能手机视频进行MMC处理。随后，以测力台和OMC为基准，评估MMC量化跳高高度的性能。结果：在不需手动分割和相机标定的情况下，MMC量化跳高高度的平均绝对误差（MAE）介于1.47至2.82厘米之间，组内相关系数（ICC）介于0.84至0.99之间。结论：结果表明使用单智能手机进行无标记动作捕捉具有可行性。关键词：下蹲跳；无标记动作捕捉；光学动作捕捉；跳跃高度。影响声明：通过单智能手机无标记动作捕捉，可在无需相机标定和手动分割的简易设置下准确量化下蹲跳高度。