My favorite way to train the core is by doing circuits of the same 3 or 4 or 5 exercises that challenge the core in different ways and only uses 1 piece of equipment. Talk about COVID friendly :)
Exercise 1️: Ball overhead alternating leg drops-Make sure you have STRAIGHT legs
Exercise 2️: Ball to opposite foot sit-up and reach. In the video the guy brings the ball to the floor instead lift the leg that is straight on the ground in the air as you and the medicine ball to that foot. If it's too hard do the modification below in the video.
Exercise 3️: Ball between knee + lemon squeezers
Exercise 4️: Ball under knees + lemon squeezers (knees should touch elbows). Do the same thing as above but place the ball behind the knees and hold it there.
Exercise 5️: Ball overhead core rotation. Instead of having your arms at your side hold the ball or weight straight up overhead while rotating legs to the opposite, then switch arms and rotation of legs.
12-15 reps of each exercise.
4 rounds.
Disclaimer: If you are currently under the care of a PT or MD please consult them before attempting these exercises. These are some general core strengthening exercises, so if any discomfort/pain is felt anywhere please stop and consult a Physical Therapist or your PCP.