Chief of Sports Science, Dr. Phil Cheetham, talks about Sportsbox AI's accuracy, sharing graphs and data along the way.
Introduction
Sportsbox 3D Golf is a software application that runs on iOS, Android and Windows platforms. It is a single camera video-based application that allows users to video a golf swing. From this video it creates a 3D dynamic model of the swing using artificial intelligence. Key biomechanics parameters were then calculated from this dynamic model throughout the swing.
This paper reviews the accuracy tests that Sportsbox performs on a regular basis. Sportsbox does these tests by comparing swings that were captured simultaneously on the AMM3D system and the Sportsbox iPhone app. AMM3D is an electromagnetic sensor-based motion capture system that, over the last 20 years, has become one of the gold standards in golf swing biomechanics analysis.
Methods
Over the past year Sportsbox has done several studies where both AMM3D and Sportsbox have been used to capture swings simultaneously. For the purpose of this accuracy study, Sportsbox and AMM3D data were collected for a set of 30 golfers with one swing each. We performed our captures with both AMM3D and Sportsbox simultaneously, with attention to detail consistent with scientific rigor. Golfers signed a consent form before data collection. Best practices were followed. Cameras and the AMM3D transmitter were set up perpendicular to the target line, lighting was good, and a high-speed shutter was used on the cameras to help freeze the motion in each frame and avoid motion blur, especially of the club. The golfers were of varying skill levels, including both amateurs and professionals. Golfers hit balls indoors and outdoors, using both 7 irons and drivers.
From these studies swings have been selected to represent a variety of conditions, including, drivers and irons, indoors and outdoors, males and females. Table 1 outlines these conditions.
An assessment comparing AMM3D and Sportsbox for their equivalences and differences is now provided. Of the over 200 indicators Sportsbox provides to describe a golf swing, a few principal ones, representing both linear and angular measures, will be presented.
Quantitative Research
For the accuracy results we calculated the absolute difference between the values collected by AMM3D and Sportsbox. The results are provided in Table 2.
We calculated the absolute differences for angular and linear values at three key positions in the golf swing: address, top of backswing, and impact. The chosen indicators are the main ones used in typical golf swing analysis sessions. Angular parameters include chest turn, pelvis turn, chest side bend, pelvis side bend and chest forward bend. As indicated in Table 2, the average difference between AMM3D and Sportsbox for each of the angular parameters combined is 2.2 degrees, 2.5 degrees, and 2.0 degrees for the address, top, and impact positions, respectively.
The same procedure was used for linear measures, but only for the top of backswing and impact positions, because by definition address is set to the zero position. The linear parameters evaluated were chest sway, pelvis sway, chest lift, and pelvis lift. For top of backswing the overall average was 0.6 inches, and for impact it was 0.2 inches. 
Qualitative Results
It is also instructive to compare the data in the form of the graphs, with one curve from AMM3D and one from Sportsbox for a representative swing. This swing was from a former LPGA tour pro with a 7 iron.
From the graphs in Figure 1, it can be seen that the curves from both AMM3D and Sportsbox overlay each other closely and show similar motion characteristics.
Summary
Sportsbox data is very similar to the data from AMM3D, one of the accepted gold standards in golf swing motion analysis. It must be remembered however that achieving the best accuracy requires best practices to be followed, that includes correct camera placement, correct video set up (exposure, frame rate etc.), avoidance of complicated backgrounds where possible, and good lighting. In these conditions it is possible to capture accurate 3D swing data with the Sportsbox AI single cameral system.
Takeaway
For the angular measurements, including turn, bend and side bend of the chest and pelvis, and of the set of 30 swings tested, we found that the absolute average difference between AMM and Sportsbox was approximately 2 degrees at the key positions of address, top and impact.
For the linear measurements of sway and lift the absolute average difference between AMM and Sportsbox for top of backswing and impact combined was 0.4 inches.