Power Measurement in the Weights Room

In what seems like no time at all we have our second guest blog ready for consumption (if you fancy writing something get in touch). This piece discusses a piece of sports technology to measure power in weight lifting, enjoy!

Power is the most desired physical quality for a number of sports because it entails both force (strength) and velocity (speed) aspects.”[1]

Dan Baker – President of the ASCA Brisbane Broncos Strength and Conditioning Coach

Why do we need to measure power in an athlete’s performance? Well, Dan Baker also says:

“Once adequate levels of strength have been attained, training priorities may focus more on increased power… “[2]

Over the past two decades, sports scientists have used a variety of methods and instruments to quantify power in an athlete. While these early methods were successful in a research setting where skilled users were available to operate and calibrate the equipment, they have not translated well to the coal face of training rooms; performance staff and trainers are just too busy to perform complicated setups and calibrations. Training rooms need simple performance tests that can be done in minutes by ‘non-scientific’ staff. When the performance testing is done, trainers and coaches need instant answers to inform their immediate training decisions.

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GymAware Power Tool 5 combines a highly accurate digital position and time measurement, accelerometer (measuring angle of lift) and state of the art signal processing which automates analysis of the individual lifts – read more to find out why this is important.

The Power Tool connects via Bluetooth to any of the Apple iOS devices (iPad/iTouch/iPhone) with one of two apps: Gym Aware and Gym Aware Lite.

Designing for Sport

One of the big challenges in making the Power Tool work in sport was to maintain system accuracy when pursuing ease of use.

It had to be:

● exceptionally robust in the face of rough handling by athletes

● zero drift, as calibration is not an option

● accurate enough to provide useful data

● able to measure a broad range of movements

We use a tethered LPT and not a wireless accelerometer because better met our needs for accuracy and simplicity. With an inboard triaxial accelerometer included in every phone there is a lot of potential to build some pretty cool apps, but these can be a bit gimmicky, we have prioritised simplicity and accuracy (accelerometers are notoriously bad at measuring accurate displacement due to their integration drift – to measure power: power = force x displacement / time). A tethered LPT gives a very accurate measure of displacement. When you combine this with accurate time stamping of each position you can calculate velocity and acceleration. By adding a measure for the mass of the system you can then calculate force and power using kinematics.

Encoding technology

LPTs convert linear motion to rotary motion that can be measured in a number of ways. Older systems use a rotary potentiometer to produce an analog voltage while modern systems are usually based on some form of digital encoding technology. For the Power Tool, we use a reflective optical encoder built in to the LPT spool assembly, this gives us a non-contacting low power, zero drift method of detecting movement of the tether.

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A major advantage of this system is that data is only recorded when a movement is detected (by the encoder count changing), this Variable Rate Sampling (VRS) is discussed in more detail here and here. The VRS data is very compact and requires no further filtering making it ideal to collect on mobile devices and send over the internet.

Angle of lift

Most of the exercises used for measuring an athletes performance have a vertical and a horizontal component. For our kinematic calculations we only want the vertical component, which we get by measuring the angle of lift. This Angle lift measurement is found by mechanically coupling a triaxial accelerometer to the tether to measure tilt with respect to gravity. Once we know the angle of the tether we can use a polar to rectangular conversion to calculate the vertical component of the lift.

By combining the advantages of the tethered LPT, digital optical encoding and VRS, with measurement of angle, we can produce a very simple, accurate power and velocity measuring device. With the simple user interface, bomb proof construction, and plenty of under the hood automation we have built a system that is ready for use in any professional sports performance program.

About Rob Shugg

Rob Shugg has over 20 years experience in a range of sports science technology research and development projects, including 12 years working with sports physiology at the Australian Institute Sport (AIS). He co-founded Kinetic Performance in 2000.


[1] Combining scientific research into practical methods to increase the effectiveness of maximal power training ASCA

[2] Baker, D. Comparison of maximum upper body strength and power between professional and college-aged rugby league football players. J. Strength Cond. Res. 15(1): 30-35. 2001.

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