American Fitness Professionals & Associates

By Paul Sorace, M.S., RCEPsm, CCS (Ph.D. Student) AFPA Faculty

People who strength train often times have a habit of “doing the exercise”. For example, people “do” chin-ups because “it” targets the back with some assitive work from the biceps. Depending on your strength, chin-ups can either be performed with your bodyweight, additional weight attached to you, or on a machine (i.e.- Gravitron) that has a counter weight to assist you.

Chin-ups are more difficult than pulldowns. A good rule of thumb is to perform pulldowns with a supinated grip (palms forward) until you can use 10% more than your bodyweight for reps.

At that point, you should be ready to perform chin-ups with your bodyweight. People who don’t know how the body works are the ones that are likely to do the exercise improperly. That is why the fitness professionals are the ones to seek regarding proper exercise form and technique. Someone who doesn’t know biomechanics will likely pull up until his or her chin is above the bar. Believe me, many do just this. Is this the end point of the concentric (lifting) phase? For some individuals, it may be.

For most, however, it won’t be. Why? Well, this exercise requires shoulder extension, scapular retraction \ depression, and elbow flexion.
The major movement is shoulder extension, which is performed primarily by the latissimus dorsi.

This is the prime mover here (FYI- other muscles involved in shoulder extension include the posterior deltoids, teres major, long head of the triceps, and the sternal head of the pectoralis major). Full contraction in shoulder extension is when the upper arm (humerus) is atleast in line with rib cage and many times the arm will need to go past the torso for full contraction. Almost always with a chin-up, this will occur when the chest hits the bar and not the chin. With only the chin over the bar, the humerus will usually be several inches forward of the torso. “Doing” the exercise this way neglects a full range of motion (ROM). Lacking a full ROM will create a muscle imbalance within the muscle. The muscle(s) will not be strengthened in the fully contracted position and joint flexibility can be reduced.

Another function to look at here is the biceps. Remember that since the biceps muscle is the largest elbow flexor, it is the main assistor in a chin-up. Many have a tendency to start this exercise by pulling with their biceps.

They do this typically by thinking about initiating the movement with their hands. This is not the best way to perform this exercise. Since the back muscles are the prime mover here, you should initiate this movement by pulling with your elbows and retracting your shoulder blades (scapula). This is because the “lats” insert on the upper arm (proximal anterior \ medial aspect of the intertubercular groove for you experts). Using the biceps should be secondary. After we initiate the pull with the elbows and the shoulder blades, the elbows will then bend (flex) as the pull continues.

If you perform the exercise properly, the biceps will naturally come into play after the back. Another aspect of biomechanics to look at here is the grip used. We all can do more chin-ups or pulldowns with the palms facing you (supinated) compared to palms forward (pronated). What’s the difference? The biceps, along with flexing the elbow, also supinate the hand. The biceps contraction will be greater with this grip. This is because the biceps muscle is lengthened in the supinated position. The tension potential states that a muscle can contract more forcefully in a slightly stretched position. When slack is placed on a muscle, the contractile ability is reduced. Hand supination lengthens the biceps and hand pronation puts slack on the biceps.

We are about 15% stronger in pulling motions with a supinated grip as apposed to a pronated grip. A supinated grip places your biceps in a position of strength. You will be able to achieve more reps \ weight and ultimately work your back muscles to a deeper level of fatigue. The biceps will inevitably fatigue first during this exercise no matter what grip is used. So why make a bad situation worse by placing the biceps in a weaker position. A supinated grip is more desirable.                                                  

Knowing biomechanics will enable you to perform an exercise properly and avoid “doing the exercise”. After all, it’s not because of chin-ups that we work our back and biceps but rather because of our back and biceps muscles that we can perform chin-ups.