Plyometrics is the way of the future. More and more information about the positive effects of plyometrics and jumping workouts are coming out. This is a great way to improve your vertical displacement and it increased neural pathways in the brain for running specific movements. Many times, people ask when is the best time to incorporate a plyo workout. The Journal of Sports Science recently published research on the changes in vertical jump mechanics after a half-marathon race.
The researchers in this study performed a vertical hop test pre-Race as well as directly post race and 5 minutes post race. Interestingly, there was a significant decrease in vertical distance in the second post test, but not the first post test. There was not significant change in displacement of the jump, eccentric power, concentric power.
Runners are perfectionists. We want to do everything perfectly but in actuality, we learn more from our mistakes than from out perfections. This principle is true for exercise. Performing strengthening is beneficial when you are tired just as much as when you are fresh. As long as your are watching your form, performing plyometric exercises when your legs are tired can help strengthen muscles that are fatigued (a trait you need toward the end of a marathon) allows neural pathways to connect when the body is tired and also works on your endurance of holding your alignment.
Don't worry about scheduling your workouts perfectly, fit them in when you can. You just might learn a lot about your own strength and endurance if you push yourself when you are tired.
Rousanoglou, E. Et. Al. Alterations of Vertical Jump Mechanics after a Half-Marathon Mountain Running Race. Journal of Sports Medicine. 2016(15). 277-286.