The 2 keys to arm strength are ground force and rotational force. Ground force is made by pushing off of your back leg but not just your leg, the inside arch of your back foot. So if you were wearing Nikes, you would push off the swoosh in the middle of the shoe on the inside. Now the other thing having to do with ground force is you need to keep a slight bend in your knees throughout the motion. Start with a good base like you are surfing or riding a skateboard with bent knees and good posture. Don’t be narrow. Strike the ground with a slight bend in your front leg, don’t extend it or strike the ground heel toe. That kills all of the force you have produced from your legs. It will shoot back into your body. The second key is rotational force. Which is produced by torque. Study Tom Brady’s motion to better understand what I’m about to say. You want to keep your shoulders back as your hips go forward. Bring your back hip the middle of your body almost pivoting off your back foot after you push. Keep your front arm tight and have your front hand somewhere in front of your face on the throw. This creates almost a bow and arrow effect. This gives you a lot of torque. Lastly you want to finish with the back of your throwing shoulder on the target to ensure you got full rotation on the throw. If you have any questions on this, you can message me on any one of my social media platforms.