Sitting with a small ball placed behind the knee, in the popliteal fossa, and rolling gently over it releases tightness where the hamstring and calf tendons meet. This spot gets skipped by most foam rolling routines even though it's a common source of stiffness behind the knee.
Log your roll ball popliteal sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.