You should stretch all parts. If you are practicing upper limbs, you should stretch your arms and waist.

You can touch the wall with your palm, then straighten your arms and walk to the wall. At this time, you will feel that the muscles inside your arm are stretched. Then hold the left arm and the right arm for 30 seconds each.

At your waist, you can put your hand close to your ear and raise it to your head. Then tilt to the right or left. Be careful not to cross over, that is, to stretch with this opposite force.

You can also raise your hand, then bend it from the elbow, and hold it from the lower waist and upper arm with the other arm. Alternate left and right hands, this action can stretch the muscles on the outside of your big arm.

If you are practicing lower limbs. Then you can stretch the front side of the thigh like this. Stand up straight, then put one leg behind your back and heel close to your ass. Your hands can hold your feet. Left and right legs alternate. For the calf, you can lift your toes to the top of a step and then land your heels. Keep your whole leg upright. Then lean forward. At a small angle to the ankle. The smaller the angle, the greater the tensile strength of your calf. You can stretch the muscles at the back of your thighs by bending down in advance.

If you think these actions need to be counted for a few seconds by yourself, it's too difficult. Try yoga, because every classic yoga posture is stretching a part. Both KEEP and WAKE courses have very good yoga tutorials and that kind of pre-run exercises. By the way, stretching after iron lifting is equally important, and you can also buy a foam shaft to massage your muscles.