Warming up to start your workout is important for several reasons. Firstly to stretch out your body and to warm up your muscles and core temperature. Warm ups will help you to remove or loosen up any stiff or soreness from muscles before you get into your workout. The increase in blood flow to your muscles to bring in nutrients and remove waste will help warm your core temperature (this can help especially if the water is a bit cold!).

Warm up should not be hard or strenuous and your RPE should be around 3-4. You don't want to bring your Heart Rate up too high so if you do, that means that you have done too much. Keep things easy. You shouldn't be out of breath during this first 10 minutes or so.

Warming up your muscles and bringing up your core temperature as well as your cardiovascular system means that your body is ready to do harder work in the Workout part of your session.

You will know you have warmed up successfully because you will feel warmer (core temperature higher), your muscles will be supple and you will have a good range of motion in your joints. You should feel warmed up and smiling. You will have a slightly higher cardiovascular system (maybe harder or faster breathing rate and higher heart rate).

If you are out of breath or sore, then you may need to check your warm up was appropriate.