Activities recorded with a Garmin device can become merged into the same file if the user does not "Reset" the Garmin between activities.
The "Reset" function can be performed on the Garmin device when the "Reset" button is pressed and held down for 3 seconds. When the Garmin is reset, the finished activity is saved to the Garmin's memory, and the timer clears for the recording of a new activity.
When you plug in or otherwise connect the Garmin device to your computer for upload, or plug in the Garmin device to be charged, the Reset function occurs automatically.
Instructions on how to get your Activity file Split into multiple parts:
Unlike the Crop tool, the Split Activity tool is not yet available to our users. It currently exists as an admin tool only.
First, upload your activity file to Strava. You will notice that the activities are merged on the Activity page, often designated by a very large "total elapsed time," cumulative distance, and other merged stats.
Start a new support ticket on the Strava Support site, titled "Activity Split Request."
Include the link to the Strava activity in the body of the email. Also include any special instructions.
Strava Support will split your activity into the requested parts.
This can also be performed for multisport files if you would like your swim/bike/run or bike/run files split into individual activities on Strava.