Adding wall sits to the end of every run will strengthen your quads, hamstrings and glutes, improving your speed and endurance. Lean against a wall with your feet shoulder-width apart, then squat until your knees are bent at 45 degrees. Hold for 30 to 60 seconds; work up to doing 10 sets. Add a challenge by including heel raises: Lift your left heel, then the right, then lift both together twice.