Curls and chinups are exercises that many people perform to work the upper body. These movements are similar in a number of ways, but there are also differences that set them apart. If you perform these exercises in the same workout, it is important to understand the differences and structure your workout accordingly.
Exercise Type
You can classify exercises according to the number of joints at which movement takes place. Isolation exercises involve motion at one joint only. This name is appropriate because these exercises isolate the limited number of muscles involved. Compound exercises are multi-joint movements that target muscles at multiple joints. More muscles contribute to compound exercises and the joint that is weakest will present the limiting factor.
Chin-Ups
A chinup is a bodyweight exercise that involves grabbing an overhead bar with your palms facing back and pulling yourself up. This is a compound exercise because motion occurs at your shoulders and elbows. Movement at each of these joints occurs in the sagittal plane, which is the plane that passes through your body from front to back. The motion at your shoulder is extension, while flexion takes place at your elbow.
Curls
You can perform curls with a barbell, dumbbells or resistance band. You can also use a cable machine with a weight stack or a machine designed for the purpose. Regardless of how you perform them, curls are an isolation exercise because movement occurs at the elbow only. Like chinups, this movement is flexion in the sagittal plane.
Elbow Muscles
Three muscles that cross your elbow -- the biceps brachii, brachialis and brachioradialis -- work together to flex your arm. When you perform curls, your hand position determines which of these is prioritized. Your brachioradialis is primarily a stabilizer and won't contribute appreciably unless your thumbs face forward. This is called a hammer curl. Your biceps brachii is more involved when your palm faces rear, or when you turn it that way as you raise the weight. This is called supination. Your brachialis is equally active no matter what hand position you employ. During chinups, your hands are supinated, so the brachialis and biceps brachii are prime movers for elbow flexion.
Back Muscles
Two muscles that cross your shoulder extend your upper arms while you perform chinups. Your latissimus dorsi, or lats, is a broad muscle that covers most of your back. It is more active during the final 60 degrees of extension. Your teres major is a smaller back muscle that contributes to extension against resistance only. These shoulder extensors are not involved when you perform curls.
Training Shoulder Extensors
Chinups are effective for working your latissimus dorsi and teres major only if your elbow flexors don't give out first. If they do, perform an isolation movement like straight-arm pulldowns prior to chin-ups to pre-exhaust your back. This will render it the weak link during the compound movement. Do not perform curls prior to chinups because doing so increases the likelihood of elbow-flexor fatigue prior to stimulating your back.
Training Elbow Flexors
Work your elbow flexors by performing curls after you've done chinups for back. The chinups will pre-exhaust your elbow flexors, which means you can do less to stimulate them to the same extent. Do not train elbow flexors the day after chinups because they will already be worked and training them again will interfere with recovery. It is important to wait 48 hours for protein synthesis to take place.
References
- "Kinesiology: Scientific Basis of Human Motion; N. Hamilton et al.; 2008
- "American Journal of Physiology"; Mixed Muscle Protein Synthesis and Breakdown after Resistance Exercise in Humans; S. Phillips, et al.; 1997
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