How Does Golf MTRx Gather Data and Prescribe Steps for Improvement?


Golf MTRx provides clear directions to record a golf swing

Golf MTRx makes use of standard iPhone hardware including the motion sensor gyroscope and accelerometer, the system clock and its timer capabilities, and the system audio microphone and speaker components.

The swing recognition algorithm uses the motion sensor to obtain 3-axis motion data. The clock times the components of the swing. The microphone detects the impact sound of the club hitting the ball. MTRx plays a “ding” sound when each swing is recorded.

How does Golf MTRx recognize a golf swing?

A swing always starts with an address position during which motion is still or minimal. The golfer’s alignment at address is set to zero degrees, the zero line. Setting up open or closed to the target line just moves the zero line from which the hip turn starts.

The backswing starts with a backward turn motion that continues its direction until the top or transition point at the start of the down swing. Turn speed and acceleration during the backswing segment are relatively slow compared with speed and acceleration of the downswing.

The downswing is the start of forward motion from the top of the backswing. Turn speed and acceleration increase rapidly. Impact of the club head with the golf ball happens during the downswing, normally after the hips pass the zero degree position at address.

The motion data can start in either direction depending on the golfer swinging right or left handed. The right handed backswing motion data is the same direction as the left handed downswing, and vice versa.

The swing finish is the point where the hips stop moving forward and either become still or recoil.

How does the app know when impact occurs?

The Golf MTRx swing recognition algorithm determines the impact point using the device microphone by sampling for a spike in peak volume. The recognizer is able to choose the correct impact point from multiple possible sounds from various sources such as other golfers hitting balls nearby, a loud voice, or a car horn in the background.

An impact sound is required for the swing to be recorded; normally the sound of the club hitting the ball. Practice swings that brush the mat or grass with sufficient sound will record; air only swings will not. Hitting a plastic whiffle or soft foam practice ball works well too.

How accurate is the swing data?

Golf MTRx has been designed to report very true unaltered data. There is no interpolation, extrapolation, smoothing, averaging, normalizing, or other manipulation of the motion data. Only the height of the colored speed bars in the charts are amplified slightly for easier viewing.

The accelerometer and gyroscope are independent from the iPhone chips that run the operating system and apps. The iPhone 5 has a faster chip than the iPhone 4 or 4S, yet Golf MTRx obtains identical sampling rates of 100 hz (samples per second) across these devices. A swing that is 2 seconds in duration has about 200 motion samplings, each with three axis angles. With twice as many (400) sound checks, MTRx uses nearly 1000 points of data to recognize a golf swing!


Golf MTRx should be placed in a secure position that allows for a comfortable golf swing

Even though the iPhone constantly monitors phone calls, messages, and other alerts, the timer interval of the sample motion data is very steady resulting in consistent and accurate data. At a top speed of 4

70 degrees per second, a golfer’s hips can rotate about 4.7 degrees between samplings. Microphone sound checks during each sampling interval actually increase the accuracy to about 2 to 3 degrees for the impact turn angles. MTRx also accounts for the time it takes for the impact sound to reach the microphone 3 to 4 feet away, about 6 thousandths of a second.

Consistent and accurate results can best be obtained by securing the iPhone in front, just behind or on either side of the belt buckle, or in back centered over the spine. Choose the location that is comfortable keep it there each time you use Golf MTRx. More information on securing the device for the best possible results can be found on our Getting Started with Golf MTRx page.