This small tool will generate JSON out of your Strava activities file. To get your activities from Strava, you shoud go to Settings > My Account > Download or Delete Your Account > Get Started > Request your archive.
Download, unzip it and look for activities.csv file there. It has all your activities in csv format. Paste contents to this tool, adjust the year, activity type and fields you want to be included and you will get JSON which you can use for generating this beautiful chart or for any other purposes. If you are missing something in this parser, fork the pen and adjust it to your needs.