These engage most heavily during the "finish" phase of the stroke to push the water back.
Swimming involves nearly every major muscle group working in a synchronized "kinetic chain" to overcome water resistance. Propulsion is generated primarily through the upper body, while the core and legs provide essential stability and positioning. 🦾 Upper Body Propulsion Swimming Anatomy
The chest muscles generate the power needed during the "catch" and initial pull phases. These engage most heavily during the "finish" phase
A strong core is the "transmission" that transfers power between the arms and legs. Swimming Anatomy