KinX Learning

E-Learning in the Kinesiology of Exercise

Relationships Between the Quadriceps and Hamstrings

Posted by KinX Learning on August 16, 2016 . 0 Comments

It is not uncommon to hear that the strength of the hamstrings must equal that of the quadriceps. Because of this, many personal trainers and strength coaches strive to get an equal balance of strength between these two muscle groups. However, the quadriceps should always be stronger than the hamstrings in almost all instances. The exact ratio should depend on the angle in the knee and the position of the thigh at the hip joint. This view is based on anatomical and physiological data. 

For example, the quadriceps has four separate muscles, three of which are fairly large. The muscle mass of the quadriceps is much greater than that of the hamstrings and their workload is also much greater. The quadriceps are anti-gravity muscles that must contract to not only keep you erect but to move you in walking, running and jumping activities. 

The hamstrings (at the knee joint) are hardly involved in these activities. In regard to size, only one of the hamstrings (the biceps femoris) has two heads and a substantial amount of muscle mass. The semitendinosus and semimembranosus have very small muscle bellies. 

Thus, from the sheer size of the quadriceps and its functions, it stands to reason these muscles should be stronger. Note that at the hip joint the hamstrings are stronger than the one muscle of the quadriceps (rectus femoris). Also, other muscles come into play at the hip joint for both flexion and extension. 

In the knee joint (leg) extension exercise all four heads of the quadriceps are involved. Since the rectus femoris is a two-jointed muscle, the hip end must be placed on stretch for the lower end to act strongly at the knee. If not, the main function of the remaining three heads (vastus lateralis, medialis and intermedius) is knee joint extension. They are not affected by the position of the leg at the hip in order to have an effective or maximal contraction. 

The rectus femoris, the two-jointed muscle of the quadriceps group, plays a major role in knee joint extension when it is placed on stretch at the hip joint. To do this the leg (thigh) must be in line with the body when the knee joint extension takes place. If you are in a seated position (in which most testing and exercise is done) there is slack at the upper end of the rectus femoris. When it then contracts in knee joint extension the initial shortening takes up the slack of the upper muscle tendons and, as a result, its contribution to knee extension is not as great as possible. 

For a stronger contraction of the hamstrings in the knee (leg) curl exercise, the hip joint end of the hamstrings must be placed on stretch (This is why the seated knee curl seems easier than the more popular lying variant). However, the hamstring muscles cannot generate the same amount of strength exhibited by the quadriceps (all other factors being equal). 

More important than being concerned with the strength ratio between the quadriceps and the hamstrings is to develop these muscles as needed for bodybuilding or for sports performance. Keep in mind that as you increase the strength of the quadriceps you are capable of getting greater strength of the hamstrings and vice versa. Thus, both of these muscles should be fully developed (strengthened).