Triceps curls or extensions target the muscles in the back of your upper arms, or your triceps brachii, as well as your shoulders and your pectoral muscles. You begin the basic triceps curl by holding a weight with both hands and fully extending your arms directly above your head. You slowly bend your elbows, lowering the weight behind your neck, then straighten your elbows to return the weight over your head with arms extended. This is known as an isotonic exercise because it requires you to open and close the elbow joints, forcing the triceps muscle to shorten and lengthen. Each phase of the triceps curl, however, consists of a different type of muscle contraction.
Isotonic Concentric Contraction
The first phase of the triceps curl exercise is the concentric contraction. This is the motion of raising the weight, usually over your head. As you perform this movement, your triceps muscle shortens as it creates force. Like all muscles, the triceps are weaker during the concentric phase of an exercise. In other words, you can lower weight more easily than you can lift it.
Isotonic Eccentric Contraction
The second phase of the triceps curl exercise is the extension. This can be a confusing term for triceps curls because, although you are not extending your arms, you are still extending the length of the triceps muscle. A study by Dr. Marc Roig and colleagues at the University of British Columbia that was published in the 2009 edition of the British Journal of Sports Medicine concluded that the eccentric phase of a resistance exercise is superior when it comes to building muscle strength and mass.
Often, exercisers who perform triceps curls will pause at the top of the movement, with their arms extended, for a moment to reduce the chance of using momentum during the exercise. During this short pause, the muscle is neither lengthening nor shortening, but it is still working because it is holding up a weight. When the muscle is static but still under tension, it is considered an isometric contraction. A study published in the Journal of Physiology found that there is no significant difference in strength gains between isotonic and isometric resistance training.
Variations of the Triceps Curl
Triceps curls or extensions can be performed in various positions and with the use of a variety of equipment. Traditional free weight extensions are performed with dumbbells, barbells or exercise bands in either a standing position or while lying on a bench. You can also do the extensions with the use of a cable machine. Changing the positioning of your arms, changing the direction your palms are facing during the move or changing the equipment you use will affect which parts of the muscles are worked most.
Andrea Chrysanthou began writing professionally in 1993. Her work has been published internationally by "The Cyprus Mail," MochaSofa and My Favorite Trainer, among other magazines and websites. She holds a Bachelor of Applied Arts in journalism from Ryerson University. Chrysanthou is a certified fitness instructor and personal-training specialist with more than 10 years of experience in the fitness industry.