Building strength for sprinting without using weights.
One way in which strength converts to sprinting speed is in the ability to move the limbs fast and suddenly change direction. If the arm is moving forward and is gradually slowed to change direction, it has taken too much time to change direction. It is moving more slowly and the legs will also slow down.
When the arm is moving forward at a high speed, more strength is required to stop the arm and move it backward than if it were moving forward slowly. This strength can be developed with weights, but why not use movements more specific to running? Strength can be improved without using weights. Shoulder strength can be developed just by moving the arms fast. This can be done while standing, and several variations can be used. I think the movement that is best for building strength is keeping the arms slightly bent but almost straight. The arms swing to about a 45 degree angle in front and back. Do this as fast as possible for a given number of repetitions - maybe the number of strides that are required in a 100 m. race. Emphasize the sudden change of direction in front and back to create the most vertical force. After several weeks, enough strength and timing may have developed to lift the body when the arms change directions.
Hip flexor and glute strength can be developed by moving the thigh fast through the cycle used in sprinting. Begin with only bringing the knee up quickly and pulling it back down quickly with the glutes. Anticipate activating the glutes as the knee rises so that there is a sudden change in direction rather than a gradual deceleration or a pause before the thigh rotates down and back. Ensure that the thigh is rotating through its vertical position by scraping the ball of the foot on the ground rather than stomping on the ground. After this is comfortable, add the hamstring curl and pull the knee forward and up in one cycling motion. Suddenly pulling the knee down with the glutes should still be the main emphasis in the cycle. Don’t let the leg straighten too early before the foot contacts the ground, and make sure that the contact does not occur too far in front of the body. If you have a problem with over-striding, this is a controlled movement in which you can try to contact behind the body as a way to over correct to retrain the nerves and muscles to stop over-striding.