SPORTS REHABILITATION

training load such that you can have a reasonably clear picture of how hard each particular muscle group is working and this can be set to suit your training goals. This is one of the reasons behind the popularity of isokinetic exercises.

It has also been suggested that single joint motions have limited functionality (7). If you consider the normal range of activities for the lower limb it is difficult to think of too many examples where we perform isolated movements at a single joint. It is much more common to see two or more joints acting in a co-ordinated fashion as in the triple flexion/extensions involved in stepping, jumping, reaching etc. In these combination movements the patterns of muscle activation are consider- ably different to the isolated pattern. Generally there is greater involvement of uni-articular muscles in single limb motions with a reduced role for the important bi-articular muscles.

During multi-segment movements the task requires the generation of some ‘net-force’ through a combination of torques at each of the involved joints. Since the net-force generated is a composite of each of the separate joint contributions it is not possible to easily establish how much each part contributes to the whole. As a consequence of the number of unknowns, the best we can do is gain an overall impression of the contribution from each joint (8). As the joints are arranged in series, the effectiveness of the limb system is determined by the strength of the weakest element. Thus when setting train- ing loads for multi-joint movements the magnitude of the training stimulus will vary for each of the tissues involved, typically it will only be the weakest tissues which are optimally trained.

So where does this leave us? I hope that through this discussion I have been able to set out a clear case against the use of the concept of ‘open’ and ‘closed’ chains to differentiate exercises. The idea is flawed mechanically and unhelpful in furthering our knowledge of the impact of different exercises on the rehabilitation process. I thus exhort you to abandon this terminol- ogy and to focus on what really matters. The critical differences between the exercises described in the majority of the literature is not that they are ‘open’ or ‘closed’ but that they involve either a

20 single joint or a combination of joints.

There are many interesting studies which set out the relative merits of different exercise modes and their conclusions can be used to inform the single ‘v’ multi-joint exercise discussion. These different exercise modes result in different training stimuli and the selection of exercise mode should bear these differences in mind. Generally, the literature suggest that:

■ single joint movements result in lower co-contraction and consequently greater shearing forces than multi-joint move- ments at similar joint positions (6, 10,13)

■ the patterns of muscular activation are different between the two exercise modes (4)

■ single joint motions permit easier inter- pretation of the specific tissue and joint loads whilst multi-joint motions identify only the ‘net’ effect of all involved joints

■ multi-joint movements involve a greater contribution from bi-articular muscles which are known to be important for co-ordination and control (8)

■ multi-joint movements are generally considered to be more functionally relevant (5).

References 1. Wilk K. Rehabilitation of isolated and com- bined posterior cruciate ligament injuries. Clinics in Sports Medicine 1994;13:649-77 2. Cohen Z, Roglic H, Grelsamer R, Henry J, Levine W, Mow V and Ateshian G. Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simula- tion. American Journal of Sports Medicine 2001;29:480-7 3. Enocson A, Berg H, Vargas R, Jenner G and Tesch P. Signal intensity of MR-images of thigh muscles following acute open- and closed chain kinetic knee extensor exercise – index of muscle use. European Journal of Applied Physiology 2005;94:357-63 4. Stensdotter A, Hodges P, Mellor R, Sundelin G and Hager-Ross C. Quadriceps activation in closed and in open kinetic chain exercise. Medicine and Science in Sports and Exercise 2003;35:2043-7 5. Mellor K and Hodges P. Motor unit synchro- nization of the vasti muscles in closed and open chain tasks. Archives of Physical Medicine and Rehabilitation 2005;86:716-21 6. Balzopoulos V, Eston R and McLaren D. A comparison of power outputs on the Wingate test and a test using an isokinetic device.

Ergonomics 1988;31:1693-1699 7. Bynum E, Barrack R and Alexander A. Open versus closed kinetic exercises after anterior cru- ciate ligament reconstruction. A prospective ran- domized study. American Journal of Sports Medicine 1995;23:401-406 8. Pandy M and Zajac F. Optimal muscular co- ordination strategies for jumping. Journal of Biomechanics 1991;24:1-10 9. Savelberg H and Meijer K. Contribution of mono- and biarticular muscles to extending knee joint moments in runners and cyclists. Journal of Applied Physiology 2003;94:2241–2248 10. Hefzy M, al Khazim M and Harrison L. Co- activation of the hamstrings and quadriceps dur- ing the lunge exercise. Biomedical Sciences Instrumentation 1997;31:360-365 11. Kibler W. Closed kinetic chain rehabilitation for sports injuries. Physical Medicine and Rehabilitation Clinics of North America 2000;11:369-384 12. Kibler W, McMullen J and Uhl T. Shoulder rehabilitation strategies, guidelines and prac- tice. Orthopedic Clinics North America 2001;32:527-538 13. Lutz G, Palmiter R, An K and Chao E. Comparison of tibiofemoral joint forces during open-kinetic-chain and closed-kinetic-chain exercises. Journal of Bone and Joint Surgery 1993;75:732–739

THE AUTHOR

Dr Neil Fowler PhD is the head of the depart- ment of Exercise and Sport Science at MMU where he teaches applied biomechanics at both undergraduate and post graduate level to exercise and sport science and sports medicine students. He is a member of BASES and has held both research and support accreditation since 1995. He has been the chair of both the Biomechanics Section and Education and Training Committee of BASES. In providing applied biomechanics support to athletes Neil has worked with the British Athletics and Target Shooting teams at National, European, World and Olympic competitions.

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