Simply stated, exercises in the open kinetic chain involve the body being supported while the hands or feet are free to move during the exercise (as in a chest fly or a leg curl on a machine). Your body is supported by a piece of equipment so that you do not have to stabilize yourself or work to support your body weight during the exercise.
You also have to overcome a fixed resistance when performing open-chain exercise. On a leg press machine, you have to overcome the resistance selected to get the machine to move and correspondingly increase strength in the targeted muscle or muscle group.
These types of exercise machines facilitate movements that tend to isolate a single muscle group or a single joint. For example, the one joint involved during a leg extension is the knee; this exercise isolates one muscle—the quadriceps.
Open-chain exercises can be done with or without added weight, but when weight is added, it’s usually placed at the distal (far) portion of the limb (such as the ankle). Examples of open-chain exercises are chest presses, biceps curls, and leg extensions.
The disadvantage of open-chain exercises (e.g., knee extensions or hamstring curl exercises performed on machines) is that they can produce shear forces (speed × distance = force), which stress the knee joint (including the vulnerable ligaments such as the ACL, or anterior cruciate ligament) and are more likely to result in injury to vulnerable joints including the knee, shoulder, and hip.
Open-chain exercises are a good choice for beginners, older adults who may need additional support during exercise, and those who are looking to increase the size or strength of a particular muscle. For example, a female bodybuilder may spend more time in open-chain exercise than someone who has a more functional goal and therefore wants a functional approach to a fitness routine.
If you have joint pain (such as knee pain) or a previous injury to a joint, it may be in your best interest to avoid certain types of open-chain exercises on that particular joint. For example, if your knees are bad, you should perform closed-chain exercises such as squats and lunges instead of machine-based leg extensions or leg curls, which are open-chain exercises.
If you have injured your elbow or shoulder joint, you may want to perform push-ups (closed kinetic chain) instead of the flat-bench chest presses (open kinetic chain) or pull-ups in lieu of overhead presses. Although both open- and closed-chain exercises increase strength, there are benefits to open chain exercises. For example, if you were injured and your arm was placed into a cast, the muscles of the arm (biceps and triceps) would atrophy (become smaller).
Performing open-chain exercises such as seated biceps curls or machine biceps curls would be effective for increasing strength and size in that specific muscle. These types of exercises are often selected in rehabilitation programs, beginning strength training programs, and programs geared at increasing size and strength in a particular muscle group.