Ground Contact Time
This is the amount of time each foot strike is on the ground in milliseconds. The longer your foot is on the ground, the less efficient you are running. You will typically see this number be higher if your cadence is low. That is because a low cadence can correlate to overstriding. Over Striding makes it more difficult to get your foot off the ground faster.
Ground Contact Time Balance
This will measure how long your left foot is on the ground compared to your right. Ideally, you would want this to be 50/50. Not everyone has perfect biomechanics so you may not be able to have perfect symmetry no matter how hard you try. This is a great metric to monitor because if you see your balance going off, it may be related to an injury coming on or getting worse. Doing proper stretching and drills can help get this number closer to 50/50