Here is a quick yet effective routine to do 1-2 times a week. Get yourself a mat, sliders, 1 dumbell, and a timer and have at it
1)Russian twist (optional weight)
2) Cross Body Mtn Climber with Sliders
3) Prone Bird Dog
4) Mtn Climber with Sliders
5) Flutter Kick on the Stomach
6) Flutter Kick on the Back
I created this combo to work on connecting abdominal strength with the legs which you’ll need for swimming the freestyle stroke and doing the 2 beat/pendulum legs. You will also be working your shoulder strength while doing the exercises, also helpful for swimming freestyle.