William E. Prentice, PhD, PT, ATC, FNATA
After reading this chapter,
the athletic training student should be able to:
- Differentiate between the concepts of an open and a closed kinetic chain.
- Contrast the advantages and disadvantages of using open vs closed kinetic chain exercise.
- Recognize how closed kinetic chain exercises can be used to regain neuromuscular control.
- Analyze the biomechanics of closed kinetic chain exercise in the lower extremity.
- Compare how both open and closed kinetic chain exercises should be used in rehabilitation of the lower extremity.
- Identify the various closed kinetic chain exercises for the lower extremity.
- Examine the biomechanics of closed kinetic chain exercises in the upper extremity.
- Explain how closed kinetic chain exercises are used in rehabilitation of the upper extremity.
- Recognize the various types of closed kinetic chain exercises for the upper extremity.
Through the years, the concept of closed kinetic chain exercise has received considerable attention as a useful and effective technique of rehabilitation, particularly for injuries involving the lower extremity.98 The ankle, knee, and hip joints constitute the kinetic chain for the lower extremity. When the distal segment of the lower extremity is stabilized or fixed, as is the case when the foot is weightbearing on the ground, the kinetic chain is said to be closed. Conversely, in an open kinetic chain, the distal segment is mobile and not fixed. Traditionally, rehabilitation strengthening protocols have used open kinetic chain exercises such as knee flexion and extension on a knee machine.86
Closed kinetic chain exercises are used more often in rehabilitation of injuries to the lower extremity, but they are also useful in rehabilitation protocols for certain upper extremity activities. For the most part, the upper extremity functions in an open kinetic chain with the hand moving freely; however, there are a number of athletic activities in which the upper extremity functions in a closed kinetic chain.97
It must be stressed that both open and closed kinetic chain exercises have their place in the rehabilitative process.22 This chapter clarifies the role of both open and closed kinetic chain exercises in that process.
CONCEPT OF THE KINETIC CHAIN
The concept of the kinetic chain was first proposed in the 1970s and initially referred to as the link system by mechanical engineers.84 In this link system, pin joints connect a series of overlapping, rigid segments (Figure 12-1). If both ends of this system are connected to an immovable frame, there is no movement of either the proximal or the distal end. In this closed link system, each moving body segment receives forces from, and transfers forces to, adjacent body segments and, thus, either affects or is affected by the motion of those components.31 In a closed link system, movement at one joint produces predictable movement at all other joints.84 In reality, this type of closed link system does not exist in either the upper or lower extremity. However, when the distal segment in an extremity (ie, the foot or hand) meets resistance or is fixed, muscle recruitment patterns and joint movements are different than when the distal segment moves freely.84 Thus, 2 systems—a closed system and an open system—have been proposed.
Whenever the foot or hand meets resistance or is fixed, as is the case in a closed kinetic chain, movement of the more proximal segments occurs in a predictable pattern. If the foot or hand moves freely in space as in an open kinetic chain, movements occurring in other segments within the chain are not necessarily predictable.13
To a large extent, the term closed kinetic chain exercise has come to mean “weightbearing exercise.” However, although all weight-bearing exercises involve some elements of closed kinetic chain activities, not all closed kinetic chain activities are weightbearing.82
Because of advancements in our knowledge of biomechanics and its importance in rehabilitation, the concept of the kinetic chain has helped us better understand the underlying science of human movement, thus facilitating the development of new and more rational rehabilitation strategies. The kinetic chain concept has application in a wide spectrum of clinical conditions.47
Muscle Actions in the Kinetic Chain
Muscle actions that occur during open kinetic chain activities are usually reversed during closed kinetic chain activities. In open kinetic chain exercise, the origin is fixed and muscle contraction produces movement at the insertion. In closed kinetic chain exercise, the insertion is fixed and the muscle acts to move the origin. Although this may be important biomechanically, physiologically the muscle can lengthen, shorten, or remain the same length, and thus it makes little difference whether the origin or insertion is moving in terms of the way the muscle contracts.
Concurrent Shift in a Kinetic Chain
The concept of the concurrent shift applies to biarticular muscles that have distinctive muscle actions within the kinetic chain during weightbearing activities.42 For example, in a closed kinetic chain, simultaneous hip and knee extension occur when a person stands from a seated position. To produce this movement, the rectus femoris shortens across the knee while it lengthens across the hip. Conversely, the hamstrings shorten across the hip and simultaneously lengthen across the knee. The resulting concentric and eccentric contractions at opposite ends of the muscle produce the concurrent shift. This type of contraction occurs during functional activities including walking, stair climbing, and jumping and cannot be reproduced by isolated open kinetic chain knee flexion and extension exercises.42
The concepts of the reversibility of muscle actions and the concurrent shift are hallmarks of closed kinetic chain exercises.82
ADVANTAGES AND DISADVANTAGES OF OPEN VS CLOSED KINETIC CHAIN EXERCISES
Open and closed kinetic chain exercises offer distinct advantages and disadvantages in the rehabilitation process. The choice to use one or the other depends on the desired treatment goal. Characteristics of closed kinetic chain exercises include increased joint compressive forces, increased joint congruency (and, thus, stability) decreased shear forces, decreased acceleration forces, large resistance forces, stimulation of proprioceptors, and enhanced dynamic stability—all of which are associated with weightbearing.
Characteristics of open kinetic chain exercises include increased acceleration forces, decreased resistance forces, increased distraction and rotational forces, increased deformation of joint and muscle mechanoreceptors, concentric acceleration and eccentric deceleration forces, and promotion of functional activity. These are typical of nonweightbearing activities.53
From a biomechanical perspective, it has been suggested that closed kinetic chain exercises are safer and produce stresses and forces that are potentially less of a threat to healing structures than open kinetic chain exercises.76 Coactivation or cocontraction of agonist and antagonist muscles must occur during normal movements to provide joint stabilization. Cocontraction, which occurs during closed kinetic chain exercise, decreases the shear forces acting on the joint, thus protecting healing soft tissue structures that might otherwise be damaged by open chain exercises.29 Additionally, weightbearing activity increases joint compressive forces, further enhancing joint stability.
It has also been suggested that closed kinetic chain exercises, particularly those involving the lower extremity, tend to be more functional than open kinetic chain exercises because they involve weightbearing activities.96 The majority of activities performed in daily living, such as walking, climbing, and rising to a standing position, as well as in most sport activities, involve a closed kinetic chain system. Because the foot is usually in contact with the ground, activities that make use of this closed system are said to be more functional. With the exception of a kicking movement, there is no question that closed kinetic chain exercises are more activity specific, involving exercise that more closely approximates the desired activity. For example, knee extensor muscle strength in a closed kinetic chain is more closely related to jumping ability than knee extensor strength in a closed kinetic chain.8 In a clinical setting, specificity of training must be emphasized to maximize carryover to functional activities.82
With open kinetic chain exercises, motion is usually isolated to a single joint. Open kinetic chain activities may include exercises to improve strength or range of motion (ROM).36 They may be applied to a single joint manually, as in proprioceptive neuromuscular facilitation (PNF) or joint mobilization techniques, or through some external resistance using an exercise machine. Isolation-type exercises typically use a contraction of a specific muscle or group of muscles that usually produces single-plane and occasionally multiplanar movement.34 Isokinetic exercise and testing is usually done in an open kinetic chain and can provide important information relative to the torque production capability of that isolated joint.4
When there is some dysfunction associated with injury, the predictable pattern of movement that occurs during closed kinetic chain activity might not be possible because of pain, swelling, muscle weakness, or limited ROM. Thus, movement compensations result, which interfere with normal motion and muscle activity. If only closed kinetic chain exercise is used, the joints proximal or distal to the injury might not show an existing deficit. Without using open kinetic chain exercises that isolate specific joint movements, the deficit might go uncorrected, thus interfering with total rehabilitation.19 The clinician should use the most appropriate open or closed kinetic chain exercise for the given situation.
Closed kinetic chain exercises use varying combinations of isometric, concentric, and eccentric contractions that must occur simultaneously in different muscle groups, creating multiplanar motion at each of the joints within the kinetic chain. Closed kinetic chain activities require synchronicity of more complex agonist and antagonist muscle actions.29
Clinical Decision-Making Exercise 12-1
Following an anterior cruciate ligament surgery, an athletic trainer is ready to incorporate some closed chain exercise into the rehabilitation program. What are some options, and what are advantages of each?
USING CLOSED KINETIC CHAIN EXERCISES TO REGAIN NEUROMUSCULAR CONTROL
Chapter 6 stressed that proprioception, joint position sense, and kinesthesia are critical to the neuromuscular control of body segments within the kinetic chain. To perform a motor skill, muscular forces, occurring at the correct moment and magnitude, interact to move body parts in a coordinated manner.69 Coordinated movement is controlled by the central nervous system, which integrates input from joint and muscle mechanoreceptors acting within the kinetic chain. Smooth, coordinated movement requires constant integration of receptor, feedback, and control center information.69
In the lower extremity, a functional weight-bearing activity requires muscles and joints to work in synchrony and in synergy with one another. For example, taking a single step requires concentric, eccentric, and isometric muscle contractions to produce supination and pronation in the foot; ankle dorsiflexion and plantar flexion; knee flexion, extension, and rotation; and hip flexion, extension, and rotation. Lack of normal motion secondary to injury in one joint will affect the way another joint or segment moves.69
To perform this single step in a coordinated manner, all of the joints and muscles must work together. Thus, exercises that act to integrate, rather than isolate, all of these functioning elements would seem to be the most appropriate. Closed kinetic chain exercises, which recruit foot, ankle, knee, and hip muscles in a manner that reproduces normal loading and movement forces in all of the joints within the kinetic chain, are similar to functional mechanics and would appear to be most useful.69
Quite often, open kinetic chain exercises are used primarily to develop muscular strength, while little attention is given to the importance of including exercises that reestablish proprioception and joint position sense.1 Closed kinetic chain activities facilitate the integration of proprioceptive feedback coming from Pacinian corpuscles, Ruffini endings, Golgi-Mazzoni corpuscles, Golgi tendon organs, and Golgi ligament endings through the functional use of multi-joint and multiplanar movements.13
BIOMECHANICS OF OPEN VS CLOSED KINETIC CHAIN ACTIVITIES IN THE LOWER EXTREMITY
Open and closed kinetic chain exercises have different biomechanical effects on the joints of the lower extremity.18 Walking along with the ability to change direction requires coordinated joint motion and a complex series of well-timed muscle activations. Biomechanically, shock absorption, foot flexibility, foot stabilization, acceleration and deceleration, multiplanar motion, and joint stabilization must occur in each of the joints in the lower extremity for normal function.35,69 Some understanding of how these biomechanical events occur during both open and closed kinetic chain activities is essential for the athletic trainer.
Foot and Ankle
The foot’s function in the support phase of weightbearing during gait is 2-fold. At heel strike, the foot must act as a shock absorber to the impact or ground reaction forces and then adapt to the uneven surfaces. Subsequently, at push-off, the foot functions as a rigid lever to transmit the explosive force from the lower extremity to the ground.94
As the foot becomes weightbearing at heel strike, creating a closed kinetic chain, the subtalar joint moves into a pronated position in which the talus adducts and plantar flexes while the calcaneus everts. Pronation of the foot unlocks the midtarsal joint and allows the foot to assist in shock absorption. It is important during initial impact to reduce the ground reaction forces and distribute the load evenly on many different anatomical structures throughout the lower extremity kinetic chain. As pronation occurs at the subtalar joint, there is obligatory internal rotation of the tibia and slight flexion at the knee. The dorsiflexors contract eccentrically to decelerate plantar flexion. In an open kinetic chain, when the foot pronates, the talus is stationary while the foot everts, abducts, and dorsiflexes. The muscles that evert the foot appear to be most active.94
The foot changes its function from being a shock absorber to being a rigid lever system as the foot begins to push off the ground. In weightbearing in a closed kinetic chain, supination consists of the talus abducting and dorsiflexing on the calcaneus while the calcaneus inverts on the talus. The tibia externally rotates and produces knee extension. During supination, the plantar flexors stabilize the foot, decelerate the tibia, and flex the knee. In an open kinetic chain, supination consists of the calcaneus inverting as the talus adducts and plantar flexes. The foot moves into adduction and plantar flexion, around the stabilized talus.94 Changes in foot position (ie, pronation or supination) appear to have little or no effect on the electromyogram (EMG) activity of the vastus medialis or the vastus lateralis.39
It is essential for the athletic trainer to understand forces that occur around the knee joint. Palmitier et al proposed a biomechanical model of the lower extremity that quantifies 2 critical forces at the knee joint65 (Figure 12-2). A shear force occurs in a posterior direction that would cause the tibia to translate anteriorly if not checked by soft tissue constraints, primarily the anterior cruciate ligament (ACL).14 The second force is a compressive force directed along a longitudinal axis of the tibia. Weightbearing exercises increase joint compression, which enhances joint stability.
In an open kinetic chain seated knee-joint exercise, as a resistive force is applied to the distal tibia, the shear and compressive forces would be maximized (Figure 12-3A). When a resistive force is applied more proximally, shear force is significantly reduced, as is the compressive force32 (Figure 12-3B). If the resistive force is applied in a more axial direction, the shear force is also smaller (Figure 12-3C). If a hamstring cocontraction occurs, the shear force is minimized (Figure 12-3D).
Closed kinetic chain exercises induce hamstring contraction by creating a flexion moment at both the hip and the knee, with the contracting hamstrings stabilizing the hip and the quadriceps stabilizing the knee.89 A moment is the product of force and distance from the axis of rotation. Also referred to as torque, it describes the turning effect produced when a force is exerted on the body that is pivoted about some fixed point (Figure 12-4). Cocontraction of the hamstring muscles helps to counteract the tendency of the quadriceps to cause anterior tibial translation.88 Cocontraction of the hamstrings is most efficient in reducing shear force when the resistive force is directed in an axial orientation relative to the tibia, as is the case in a weightbearing exercise.65 Several studies have shown that cocontraction is useful in stabilizing the knee joint and decreasing shear forces.38,46,67,83
The tension in the hamstrings can be further enhanced with slight anterior flexion of the trunk.58 Trunk flexion moves the center of gravity anteriorly, decreasing the knee flexion moment and, thus, reducing knee shear force and decreasing patellofemoral compression forces.64 Closed kinetic chain exercises try to minimize the flexion moment at the knee while increasing the flexion moment at the hip.
A flexion moment is also created at the ankle when the resistive force is applied to the bottom of the foot. The soleus stabilizes ankle flexion and creates a knee extension moment, which again helps to neutralize anterior shear force (see Figure 12-4). Thus, the entire lower extremity kinetic chain is recruited by applying an axial force at the distal segment.
In an open kinetic chain exercise involving seated leg extensions, the resistive force is applied to the distal tibia, creating a flexion moment at the knee only.85 This negates the effects of a hamstring cocontraction and produces maximal shear force at the knee joint. Shear forces created by isometric open kinetic chain knee flexion and extension at 30 and 60 degrees of knee flexion are greater than those with closed kinetic chain exercises.55 Decreased anterior tibial displacement during isometric closed kinetic chain knee flexion at 30 degrees when measured by knee arthrometry has also been demonstrated.95
The effects of open vs closed kinetic chain exercises on the patellofemoral joint must also be considered. In open kinetic chain knee extension exercise, the flexion moment increases as the knee extends from 90 degrees of flexion to full extension, increasing tension in the quadriceps and patellar tendon.6 Thus, the patellofemoral joint reaction forces are increased, with peak force occurring at 36 degrees of joint flexion.26 As the knee moves toward full extension, the patellofemoral contact area decreases, causing increased contact stress per unit area.7,40
In closed kinetic chain exercise, the flexion moment increases as the knee flexes, once again causing increased quadriceps and patellar tendon tension and, thus, an increase in patellofemoral joint reaction forces.62,75 However, the patella has a much larger surface contact area with the femur, and contact stress is minimized.7,26,40 Closed kinetic chain exercises might be better tolerated in the patellofemoral joint because contact stress is minimized.104
CLOSED KINETIC CHAIN EXERCISES FOR REHABILITATION OF LOWER EXTREMITY INJURIES
For many years, athletic trainers have made use of open kinetic chain exercises for lower extremity strengthening. This practice has been partly a result of design constraints of existing resistive exercise machines. However, the popularity of closed kinetic chain exercises can be attributed primarily to a better understanding of the kinesiology and biomechanics, along with the neuromuscular control factors, involved in rehabilitation of lower extremity injuries. For example, the course of rehabilitation after injury to the ACL has changed drastically over the years. (Specific rehabilitation protocols are discussed in detail in Chapter 21.)
Technologic advances have created significant improvement in surgical techniques, and this has allowed athletic trainers to change their philosophy of rehabilitation. A number of studies published in the early 1990s provided support for accelerated rehabilitation programs that recommend the extensive use of closed kinetic chain exercises.9,15,20,26,56,76,90,99 However, the most recent systematic reviews in the literature have found that there is no clear consensus on whether closed or open kinetic chain exercises should be the intervention of choice following an ACL injury or reconstruction.44 While several recent studies have recommend closed kinetic chain exercises as the most effective for improving knee function following ACL injury,21,41,51,93,105 others have suggested that using a combination of both open and closed kinetic chain exercises is most effective both in ACL rehabilitation28,54,78 and in treating patellofemoral pain syndrome.43,62 Further, since closed kinetic chain exercises appear to reduce anterior shear of the ACL, promote dynamic early joint stability, and stimulate proprioceptors, it was suggested that closed chain exercises can be safely used early in the postoperative period, while the use of open kinetic chain exercises should occur later in the rehabilitative process,28,57,59 although the safest point in time to start open kinetic chain exercises remains uncertain.72
Several different closed kinetic chain exercises have gained popularity and have been incorporated into rehabilitation protocols.49 Among those exercises commonly used are the mini-squat, wall slides, lunges, leg press, stair-climber and elliptical machines, lateral step-up, terminal knee extension using tubing, stationary bicycles, slide boards, Biomechanical Ankle Platform System (BAPS; Spectrum Therapy Products) boards, and the Fitter (Fitter International, Inc.).
Mini-Squats, Wall Slides, and Lunges
The mini-squat (Figure 12-5) or wall slide (Figure 12-6) involves simultaneous hip and knee extension and is performed in a 0- to 40-degree range.89 As the hip extends, the rectus femoris contracts eccentrically while the hamstrings contract concentrically. Concurrently, as the knee extends, the hamstrings contract eccentrically while the rectus femoris contracts concentrically. Both concentric and eccentric contractions occur simultaneously at either end of both muscles, producing a concurrent shift contraction. This type of contraction is necessary during weightbearing activities.77 It will be elicited with all closed kinetic chain exercises and is impossible with isolation exercises.84