What happens after you use (contract) a muscle? The quick answer is fatigue! Your muscle gets tired and your performance will slowly decrease. However, that is not always the case. Postactivation Potentiation (PAP) is the exact opposite, whereafter contracting a muscle, the same muscle sees an increase in performance. In order to achieve a PAP response, a strength exercise is done at or above 85% of a single repetition maximum weight, after which an increase in power/velocity is seen for 5 - 20 minutes after the strength exercise. How PAP can affect velocity is divided into two types of speed for this review: linear and change of direction.
Linear velocity is moving in a straight line, typically tested as speed in a forward motion. A couple studies have linked performing a back squat to increase sprint speed. Performing a heavy loaded back squat, of 2 sets of 4 repetitions at 85% maximum weight showed an increase in sprint speed by 3% after 4 minutes of rest. Studies using Deadlift and Power Clean did not show any improvement in sprint speed. The reason for this is that the back squat exercise provides a loaded force, pushing into the ground in order to return to standing, which activates the same muscles used to push into the ground while sprinting. It is noted that PAP is linked to individual reaction, and therefore some people may not find the back squat to increase linear speed. In that case, athlete should try unilateral (single leg) exercises that activates either the pushing force of the run or the forward force.
Change of Direction velocity is the speed in which an individual can move in a new direction, typically tested in a full 180° turn. The two studies reviewed involved a back squat followed by a shuttle run, meaning the change of direction was 180°. Performing a heavy loaded back squat, of 5 sets of 1 repetition at 90% maximum weight showed an increase in shuttle run performance of 1.5%. Results from these studies determined less of an increase in Change of Direction velocity versus the studies done with Linear velocity. A reason for this difference could be the more complicated technique of slowing down and turning involved in performing a shuttle run..
In order to use PAP in your training, you first need to test if it will work for you and which exercises. Engage with your coach or a partner and test out different exercises paired with sprinting. In order to avoid fatigue bias in your results, make sure you test each set of exercises 2-3 days apart.
References
https://journals.lww.com/nsca-scj/Fulltext/2018/02000/Effects_of_Postactivation_Potentiation_on_Linear.9.aspx
