From the Garmin website:
"Some of Garmin's Fitness devices offer the choice of Smart Recording or Every Second Recording.
Smart Recording records key points where the fitness device changes direction, speed, heart rate or elevation. This recording type allows the user extended recording time given that it is recording less data points, thus taking up less memory.
Every Second Recording records the activities information every second no matter if the device changes direction, speed, heart rate or elevation. This recording type provides a more defined data log of your activity. However, recording time will be reduced given that it taking up more memory.
What does this mean when you upload your workout file to TrainingPeaks?
When there are too many gaps between recorded data points, TrainingPeaks is unable to fully populate workout data from graphs to route maps. If you are seeing gaps in your workout graph and/or an inaccurate route map for your workout, check to see if you have Smart Recording turned on. Turn it off if it is on and see if this resolves your issues.