Can Your GPS Watch Help Predict Injury?

Of course not! That is just a clickbait title. 

There are two types of runners: 

One that stops their run and immediately decides what caption and picture to pair with it on Strava, and the other that sifts through all of the data with a fine-tooth comb. Personally I am the former, but in the case that you are the latter, I wanted to explain some of the common data that we see on our GPS watches.

1. Ground Contact Time: This is how long you spend on the ground per individual foot strike. In general, a shorter GCT is preferable, because the longer our feet are on the ground, the more force (ground reaction force) our bodies absorb. This can also be correlated with cadence, with a lower cadence causing a longer GCT, and vice versa. In general GCT will also be lower with faster paces. If there are asymmetries between sides (Your GCT graph looks like a zigzag), this indicates that there is an imbalance that could lead to injury if it goes uncorrected. There are more sophisticated ways to measure this that require specific sensors - either a chest strap or a foot pod - that will tell you the percentage of GCT per side, with 50%/50% being ideal.

2. Vertical Oscillation: This is how much your body translates up and down with each stride. This is measured using motion detecting sensors in your watch or HR chest strap. The chest strap is thought to be more accurate because it measures bodily movement close to the center of mass. Vertical oscillation can be seen as a measure of efficiency, with less vertical oscillation indicating a more efficient stride pattern. Less than 10cm of vertical oscillation is ideal, whereas more could indicate that there is room for improvement. Ways to improve vertical oscillation include, but are not limited to: increased cadence, improved forward lean posture, and improved ankle/hip mobility. 

3. Power: Running power is a measure of the mechanical work you are doing to overcome gravity, forward motion, and wind resistance. It is another measure of effort, similar to HR or pace, but quantifies real-time effort while taking into account terrain. Keep in mind that this is an indirect method of measuring power using algorithms, unlike a power meter on a bike. Watches or pods use the accelerometer (to measure changes in movement), barometer (changes in altitude), and GPS (pace/distance) to calculate the power graphs you see post run. Certainly using HR or pace is just fine to measure effort, but running power can help you gauge the evenness of your effort over hills - a handy tool here in ATL! 

4. Heart Rate Variability: Some watches have the ability to measure heart rate variability (HRV), which is a measure of nervous system strain (if you wear it to sleep at night). Your watch will tell you “balanced” or “unbalanced”. A lower HRV suggests increased strain - which could be caused by poor sleep, stress, training, or illness. Keeping an eye on HRV can help you monitor how your body is responding to stress and training - informing your workout decisions to avoid overtraining. As with all wearable technology, we have to integrate the data with how we feel in our own bodies (instead of blindly following the metrics), but it can be helpful to look at trends and changes over time. 

Our watches give us so much data - perhaps too much data, but having a good understanding of the metrics can help us get the most out of the technology available to us. Always remember to keep it fun and don’t get too bogged down by the data! 

Keep going, you got this!

Dr. Kacy Seynders