How Good is My Fitness Watch at Measuring What It Claims to Measure?

As a runner I have been interested in the evolving technology in fitness watches, but have been hesitant to purchase one due to questions about accuracy of the measurements.  And, other than getting to wear a cool looking watch, how do these measures benefit me?  A great study was recently published in the Journal of Orthopedic and Sports Physical therapy which addresses this issue.  The measures in question are defined as and include:

Cadence:  steps per minute

Vertical Oscillation:  Measured in centimeters, vertical body translation during each step/stride

Ground Contact Time:  Measured in seconds, the amount of time the foot is on the ground

The answer is to the above question of “how do these measures benefit me” are as follows.  Running is a repetitive movement and small changes in your movement can have overall large effects on the cumulative impact on your body.  For example changing of Cadence can reduce the hip adduction angle, hip rotation, vertical loading and knee joint loads.  In essence optimizing these measurements decrease stressful forces on your body.  Decreasing Vertical Oscillation can decrease ground reaction forces which again decreases stressful forces on the body.  The fitness watch in this study of 20 runners did find the Cadence and Vertical Oscillation measure to be both reliable and valid against the gold standard of a motion capture system.  Valid meaning it measures what it says it is measuring and reliable meaning it is consistent in its measurement.

Ground Contact Time relates to running in that as your pace increases, ground contact time decreases.  The study found that for Ground Contact Time validity was low, but that it was reliable or consistent in its measurement.

The Verdict:  I hope Santa manages to slip a fitness watch into my stocking!

The watch used in this study was the Garmin Fenix 2. 



Adams D, Pozzi F, Carroll A, Rombach A, Zeni J.  J Orthop Sports Phys Ther. 2016 Jun;46(6):471-6. 

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