When Spencer is running, he doesn't lift his knee as high as the true elites, hence his stride length is a little shorter than optimum.
3 things can improve this: flexibility, lower leg/ foot strength and core
1. Flexibility. The hamstrings, hip flexor, quads and glutes all need to be worked on for maximum mobility.
2. Lower leg / foot strength. This comes from running hard and running on grass. It has to be developed over time.
3. He looks tight across the shoulders. A stronger core will give him a more relaxed look at faster paces.
Spencer has an efficient stride at the moment, but a longer, stronger and more fluid stride will help him improve his times.