Muscles: Quadriceps, gluteus maximus, soleus and all the back muscles (especially the back muscles: muscles of the spine).
What you need to do: knee flexion (this movement is called: squat) is the king of motion-exercises. It is working all the muscles of the thighs, but also many of the rest of the body muscles.
Stand with feet shoulder width apart basin, a straight bar resting on the back of the shoulders (you can equip your bar with a foam sleeve that makes the most comfortable position). Hands are spaced shoulder width apart.
Bend your knees and buttocks down to the ground. Your heels should not be off the ground during the descent. When your thighs are parallel to floor, slowly return to the starting position with the strength of your thighs and glutes. Flexibility in working smoothly. To keep your back straight when performing this exercise, look ahead (do not look at your feet).