Injecting plyometric exercises help to tune the body's (muscle-tendon) elasticity to be more springy. This ability helps to recoil the impact force from the pounding and recycle it back into kinetic energy (motion). In layman term the body becomes a better spring so less energy is wasted, imagine dropping a tennis ball and it just keeps on bouncing. For longer distance running you want to keep recycling the energy so that you save enough to push for the later half of the race.
However you don't want to bounce too much vertically otherwise this excessive displacement is also considered inefficient. For the rule of 'specificity' you want to focus bouncing more horizontally and less vertically which is more useful for running. A good gadget to measure your vertical oscillation (movement) are the Garmin watches. They are equipped with the dynamic index that can tell you vertical oscillation, stride length and cadence (step per minute). In general low value for vertical oscillation is better meaning you are not bouncing too much up and down.
For a runner that has a high "VO" you may want to check if your SL and cadence which these data might give away some clues. (1) A low SPM with long SL may results in a floating gait and increase the vertical height. Increasing the cadence may help to reduce this extended vertical float because the foot need to quickly contact with the ground. (2) Muscular weakness of the hip extensor (primary the glut max) means the propulsion is mainly driven by the secondary muscles like hamstring and glut med or even overworked the calves. (3) Posture that is too upright may leads to a higher vertical displacement. By leaning forward slightly from the ankle-hip-head like a "falling tree" may help to lower the displacement value.
I just uploaded a basic plyo-workout that I typical do for beginner to intermediate level. I don't do very explosive drills at this point (10wks from key marathon) and as a marathoner I prefer more repetitive sets but less explosive for endurance and muscle memory purposes. Let me know if you know other alternative tips or advises and share in the comment section.
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