Many training courses consist of strength training or cardio or a combination of the two. Stretching is often overlooked...
Short and stiff muscles can prevent you from doing some of the exercises properly and so influence the progress that you (don't) make.
The good news: if you spend some time stretching after each workout, you'll get as flexible as a yoga master. (Okay, that's an exaggeration, but it helps!)
Important stretching exercises
See below for important stretching exercises that can improve your flexibility. Do 2 or 3 after your workout. Stretch the muscles that you have trained or that are most stiff. Hold each stretch for 30 to 60 seconds and keep breathing calmly.