Your quads produce power and if they are stiff with a limited range of motion, then all muscle fibres can’t fire properly and you won’t pedal to your full potential. If you want to prevent that, then assume the position in the picture below and stretch your quad by bringing your ankle closer to your butt. Try to keep your knees as close together as possible and your body upright.
If your hamstrings are properly stretched out, they will let your pelvis tilt forward on the saddle, allowing for a more aerodynamic position. This also allows your most powerful muscles, the glutes, to be more involved in pedalling. You can stretch your hamstring either by leaning towards a single straight leg as showed in the first picture. Or you can use a band or a towel to bring a straight leg towards you while lying on the floor as seen in picture two.
Glute and hip flexor stretch
This stretch targets your gluteus medius and maximus, your lower back, and also your hip flexors. It is extra important for those who experience lower back pain after long or intense rides. All you need to do is to get into the position you see in the picture. If you want to increase the intensity of the stretch, just pull your knee towards your stomach.
Before you start stretching remember two things. First, hold each stretch for at least 30 seconds on each side, that’s the minimum effective dose. And second, always stretch after your ride. Pre-exercise stretching won’t improve your performance, and studies have shown that it may actually increase the chances of injury. Just warm up before and you’re good to go.