The press is a fantastic exercise because it integrates the entire body and creates the largest kinetic chain exercise; everything from the feet articulating with the ground to the hands holding the bar overhead. It’s a significant trunk builder, but press mechanics and strength are better expressed when the trunk is purposely contracted and tightened.
In this video you’ll see an example of a press without trunk tightness followed by reps where an emphasis is placed on tightness.
There’s something I cued her to on a few days later that made an additional impact: I cued contraction of the quadriceps after explaining the importance of making the entire body stable. If the quadriceps have tension, it will prevent the knees from unlocking. If the knees unlock as the press rebounds out of the bottom, the lifter loses some of that force application in the soft, unstable knees. Maintaining quadriceps tension prevents that force loss, but also helps provide a very strong, stable base to press from. Contracting the quadriceps with the entire trunk (with an emphasis on the lower abs) made Aly’s reps much faster and easier, even compared to the final reps in the above video.
Note that this emphasis on trunk stability via tightness and keeping tension on all relevant joints and muscles should be applied into every lift.