STENSDOTTER, A.-K., P. W. HODGES, R. MELLOR, G. SUNDELIN, and C. HÄGER-ROSS. Quadriceps Activation in Closed and in Open Kinetic Chain Exercise. Med. Sci. Sports Exerc., Vol. 35, No. 12, pp. 2043–2047, 2003.
Purpose: For treatment of various knee disorders, muscles are trained in open or closed kinetic chain tasks. Coordination between the heads of the quadriceps muscle is important for stability and optimal joint loading for both the tibiofemoral and the patellofemoral joint. The aim of this study was to examine whether the quadriceps femoris muscles are activated differently in open versus closed kinetic chain tasks.
Methods: Ten healthy men and women (mean age 28.5 ± 0.7) extended the knees isometrically in open and closed kinetic chain tasks in a reaction time paradigm using moderate force. Surface electromyography (EMG) recordings were made from four different parts of the quadriceps muscle. The onset and amplitude of EMG and force data were measured.
Results: In closed chain knee extension, the onset of EMG activity of the four different muscle portions of the quadriceps was more simultaneous than in the open chain. In open chain, rectus femoris (RF) had the earliest EMG onset while vastus medialis obliquus was activated last (7 ± 13 ms after RF EMG onset) and with smaller amplitude (40 ± 30% of maximal voluntary contraction (MVC)) than in closed chain (46 ± 43% MVC).
Conclusions: Exercise in closed kinetic chain promotes more balanced initial quadriceps activation than does exercise in open kinetic chain. This may be of importance in designing training programs aimed toward control of the patellofemoral joint.
There is a considerable debate regarding the relative efficacy of open (OKC) and closed kinetic chain (CKC) exercise for increased strength and control of the knee muscles. In general, open kinetic chain (OKC) exercises are single joint movements that are performed in nonweight bearing with a free distal extremity. In contrast, CKC exercises are multi-joint movements performed in weight bearing or simulated weight bearing with a fixed distal extremity (22). Although clinical trials suggest that the functional outcome from programs that incorporate these exercise strategies are similar (11), there is a tendency toward better results in terms of strength (2) and functional (28) performance enhancement from CKC exercise. The basis for selection of each exercise regime is based on the hypothesis that there are physiological differences between these strategies and that one strategy may lead to greater improvements in specific physiological variables.
Several rationales for CKC exercises have been presented. First, CKC has been argued to be more “functional” as it simulates the role of lower limb muscles in daily activities (1,6). For instance, rectus femoris (RF) shortens across the knee and lengthens across the hip in walking and climbing stairs due to simultaneous knee and hip extension. Second, it has been argued that proprioceptive feedback differs between CKC and OKC tasks, perhaps due to compression from body mass in CKC (14) and pressure under the foot (13). Third, CKC exercise has been suggested to produce less shear force between the tibiofemoral joint surfaces as co-contraction of the hamstrings will counteract the anterior tibial shear force generated by the quadriceps (16). Thus, from a biomechanical perspective, it is likely that CKC knee exercise places less strain on the anterior cruciate ligament (15,16), although the placement of the body center of mass above the axis of the knee joint determines how the quadriceps and hamstrings co-contract (18,27). Fourth, the interrelationship between patellofemoral joint forces and contact area differs between the two tasks. In closed chain tasks, such as squatting, compressive forces are augmented with increased knee flexion as greater torque develops as a product of the lengthening lever arm between the knee joint and the body’s center of mass when it moves further posterior to the joint axis. However, this compressive force is distributed by greater contact between the patella and femur. In contrast, in OKC exercise the joint stress increases from 90° flexion as the knee extends (5,8) as a result of the greater torque produced by the lengthening lever arm when the center of mass of the leg and eventual load around the ankle moves. Finally, it has been argued that the coordination of the knee muscles may vary between the tasks. For instance, electromyographic activity of vastus medialis has been suggested to be greater in closed chain tasks than in open chain tasks (7). One study has investigated onset times for the different portions of the quadriceps in CKC and OKC under different loading conditions and joint angles but failed to find significant difference (12).
Despite the argument that coordination of the lower limb muscles may be influenced by closed or open chain tasks, for the reasons presented above, there is limited direct evidence of differences in recruitment. The present study was designed to investigate this question by comparison of recruitment of muscles in a simple reaction-time knee extension task performed in both OKC and CKC. This task was selected as it allowed us to control relevant aspects of the activity. Specifically, we were interested in whether the onset and initial amplitude of muscle activity of different portions of the quadriceps would differ between these tasks.