As someone who has had tight Achilles for yearssssss, this has been a game changer for me and its great for tight calves and plantar fasciitis as well.
The science starts with fascia. For those unfamiliar, fascia is like a net that wraps around your muscles. Over time and for a number of reasons, this fascia gets gunked up and can cause tightness in these areas.
For relief, pay close attention to the picture on the left. You can see my thumb starting at the top of my calf. So for you, use your thumb to SLOWLY slide your way down the calf towards your heel. Cover the entire calf. You should apply medium pressure to this. Remember to go slow.
With your feet, you also want to slide in the direction of your heel. I cover from the balls of my feet to the base of my heel.
What this does is it pushes the fascia towards your heel creating a lot of slack around that turn and giving you a lot more freedom of motion.
I have found the most success using this technique with a Graston tool but the thumb works great also.
The best part about this move is that YOU CAN DO IT YOURSELF!!!!