  Goal: The countermovement jump (CMJ) is commonly used to measure lower-body
explosive power. 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 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 promising.
  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.
