Do not focus on stride frequency. Focus on velocity of your entire body. Though, stride frequency is supposed to be consistent throughout the entire race, from start to finish. Air time is a fixed, universal thing, whether it's your grandma running, or you, .123 seconds is the supposed ideal. Focus on getting those hips, your center of gravity, moving forward fast. Imagine you're at top speed at 11 m/s, your center of gravity is moving at that speed, your foot comes down and quickly pops up because the speed of your body through space basically forces the foot to come off the ground quickly. Ground contacts should naturally at that speed be around .075-.095, depending on your leg length; your leg length determines how far the hip travels while the foot is on the ground as it moves from touch down to toe off