Yes, you are able to backup your data onto your SD Card.
To back up your JEFIT data to your SD card, you will want to open up your app and click the slider navigation button on the top left hand corner of the screen.
After which you will click on the "Settings" tab which will open up your preferences page.
Once on the preferences page, you will scroll down to the bottom of the page until you notice the section that states "Backup", once in this section you will want to click on the button labeled as "Backup"
By clicking on this button, you will be prompted to either backup your existing data either from JEFIT to your SD card.