This is from my article “Bench press battlefield”
It’s well documented that intense stretching prior to a muscle contraction greatly reduces the force production potential from that contraction. That’s one of the reasons why it’s best to stretch after a workout rather than before it.
We can use this little tidbit of information to our advantage. There’s this thing called antagonist co-contraction which can actually reduce our capacity to lift big weights. How? It’s fairly simple to understand: if an antagonist muscle (a muscle of the opposite function than the target muscle) has a lot of tension in it, it’ll take more force for the agonist muscle to produce a certain movement. For example, if your triceps are contracting, it’ll be harder to curl big weights. The triceps are elbow extensors while the biceps are elbow flexors; the contraction of an extensor will make the flexion harder to do.
So if we can reduce the contraction potential of the antagonist muscles, their level of co-contraction will be less. As a result, the inhibitory effect of the antagonist will be reduced, thus allowing you to lift more weight. If the antagonists are contracting, not only do you have to fight the barbell, you have to fight the antagonist muscles too!
In the bench press, the prime movers and synergists (agonists) are: the anterior deltoids, the triceps, and the pectorals/serratus. So we can conclude that the antagonists are the posterior deltoids, the biceps, and the latissimus dorsi/rhomboids. Now we know that stretching a muscle will reduce its capacity to contract, so stretching the antagonists right before attempting a bench press will facilitate the action of the prime movers and synergists!