SPORTS REHABILITATION

WHEN CHAINS JUST DON’T LINK UP

INTRODUCTION

This opinion paper sets out the argument that the common practice of classifying movements as either ‘Open’ or ‘closed’ chains is inappropriate and distracts us from the real differences between various exercises. It is explained why this classifica- tion system is thought to be flawed, and the rationale for it questioned. The paper then moves on to reinterpret some of the common outcomes of studies purporting to compare ‘open’ and ‘closed’ chain movements. It is suggested that, in the major- ity of studies, the actual comparison being made is between single and multi-joint movements and that it is this which is important when designing rehabilitation programmes. Readers are encouraged to abandon the use of the conceptually flawed concept of ‘open’ and ‘closed’ chains and to focus upon the important differences between exercises using single or multiple joints.

By Dr Neil Fowler

One need not look too hard to find guidance in the published literature concerning the appropriate order for the use of ‘open’ and ‘closed’ kinetic chain exercises in the rehabilitation process. Most commonly, but by no means univer- sally, the literature suggests that ‘closed chain’ exercises should precede ‘open chain’ movements (1,2). This advice is predicated on assumptions about the effects of these different exercise modes upon the involved tissue structures. The research data variously suggest:

■ Greater recruitment of vastii during isolated ‘open chain’ knee extension exercises (3)

■ Better co-ordination during ‘closed chain’ exercises (4,5)

■ Lower joint shear forces in ‘closed chain’ exercises (6)

■ Greater functionality in ‘closed chain’ exercises (7).

For the most part, the science underpin- ning these studies is sound. Many different assessment techniques have been used to evaluate the merits of these different exercise modes, including isokinetic and isometric dynamometry, EMG, biomechani- cal modelling and MRI. Although the sample sizes in these studies have often been small, limiting their statistical power, one must trust in the integrity of the

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review process to accept that the studies are suitably robust in their methods and sample size to allow conclusions to be drawn.

So we begin with an acceptance that the body of literature is based on reasonably robust methodology. But, and this is a very big BUT, the problem with most of this body of work does not lie with methods, but with the way that the exercises are classified and differentiated.

The very notion of a kinetic chain deserves some consideration, just what do we mean when we consider the body as either an ‘open’ or a ‘closed’ chain? Clearly anatomi- cally, the body can be thought of a series of rigid or semi-rigid segments (the limbs) joined by a set of links (the joints). These links and segments can then be considered to form a chain when several segments are joined, in series, with a number of links. Both the upper and lower limbs could be seen as chains comprising four segments and three links: foot, shank, thigh, pelvis/trunk joined by ankle, knee and hip; hand, fore-arm, upper-arm, scapula/trunk joined by wrist, elbow and shoulder. Such an approach has merit in that it simplifies the body into a more manageable form for analysis but it does not really represent the true complexity of the body or how we move.

If, for the time-being, we accept that a

link-segment (chain) model is a useful way to consider the body, the next step is to address the definition of ‘open’ and ‘closed’ chains. This is where we start to run into problems. The differentiation into ‘open’ and ‘closed’ chains is normally based upon whether the joints within the chain are able to act independently (‘open’) or if they are constrained to function in a predictable interactive pattern (‘closed’). These two situations can be exemplified by considering how the joints of the lower limb work during the swing and stance phases of gait.

During the swing phase, the distal end of the segment is free to move in space with no external constraint upon its path. The ankle could, theoretically, be plantar- flexed or dorsi-flexed at any point in the swing independent of the knee angle. In the same way knee extension or flexion can be created at any point in the cycle of hip motion. Such a chain is categorised as ‘open’.

Stance, by contrast, is considered as a ‘closed’ chain, as the distal segment is fixed by virtue of the contact between the foot and the floor. This results in a more predictable interaction between the joints. In order to maintain balance it is important for the centre of mass to remain above the base of support, therefore move- ment at any one of the lower limb joints will necessitate adaptation at one or more

sportEX medicine 2008;35(Jan):18-20