JOINT STABILISATION

pre-activation was shown in this study, preliminary data suggest confidence in performing follow up work to examine specific pre-activation change under cognitive loads.

Role of muscle stiffness in preactivation Another contributing factor using the somaosensory system to manipulate muscle activation is the stiffness of muscle. Stiffness specific to a joint, can be affected by joint capsule and pressure from within the joint, as well as the soft tissue crossing the joint. Stiffness in muscle is defined as the resistance to force resulting in length changes. Muscle, fascia, and tendon stiffness will have impact on mechano-receptors, such as golgi tendon organs and muscle spindles, contributing to afferent neural mechanisms in turn leading to changes in muscle parameters. For example, stiffness may lead to improved regulation of pre-activation by creating a pre-tensioned muscle which can lead to reduced electromechanical delay.

These factors will improve response time, and more importantly improve congruency of the joint.

While the evidence suggests changing pre-activation levels in a variety of tasks, development of paradigms to control or enhance pre-activation is required to use this aspect of muscle function as a way to prevent injury. The task then becomes relevant to how more pre-activation can be generated to help stabilisation of the joints.

PREHABILITATION There are two good examples of injury prevention programs that use exercise. The first, 'prehabilitation' method was based on strength development, decreasing atrophy, and acute care management (10). The second injury prevention program is a lower extremity landing programme (11). ‘Pre-hab’ developed from the finding that some reduction in post-surgery rehabilitation time would occur following a reduction in swelling and improvement in strength prior to surgery. Similarly, if some training occurs to help joint and limb function post surgery, training effects could be beneficial as a preventative strategy. Pre-hab has grown to include the post-injury and pre-surgery techniques, and now incorporates strategies for injury prevention. Specifically, one popular pre-hab is designed for muscles surrounding the joint shoulder consistent with the function of throwing. Not an entirely new strategy, the Hewitt11 landing programme for ACL injury prevention puts great emphasis on position. Taking into account the anatomy of the ACL, and consistent with the typical landing characteristics of female landing, Hewitt designed a program to eliminate compromising positions, namely a valgus motion. This is a prime example of how a repetitive position exercise program will change habits. The following paradigm to this statement is that a therapist must assess posture and movement patterns to establish if there is uneven distribution of forces through the stabilising structures.

To assess abnormal forces throughout the body, we can employ traditional orthopaedic testing procedures. Using manual muscle testing and postural analysis, muscle strength, length, and shortness are determined. As with most activities, however, it is necessary to understand the effects of movement, force development, and absorption on the soft tissue structures. Additional movement analysis methods are useful for this assess- ment. Sahrmann (12) proposes a ‘movement system balance’ approach, where precise movement of segments are required for efficiency and longevity of the biomechanical system. Without the

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precise movement, which is within the kinesiological norm of the joint, degeneration of the joint will occur. This paradigm can be expanded to include other soft tissue outside of hyaline cartilage to suffer injury, such as acute or overuse muscle or tendon tears. This will occur through imbalance of muscle function. For exam- ple, secondary movers will accept more tension from the motion when a primary mover is either inappropriately contracting, whether from lack of force or onset timing. Sahrmann proposes other familiar methods of joint dysfunction, such as hyper- and hypomobility (from myofascial or capsular faults) or instability in the absence of muscle control. Flexibility and range of motion from muscular contribution is therefore important to the movement balance, but the focus of this article is to understand the musculature’s aid in joint stability and function.

The ‘functional movement analysis’ by Cook (13) is another system to assess muscle function and control of movement patterns. This system uses a series of exercise tests to determine a score of functional ability. Exercises include squat, lunge, hurdle, shoulder ROM, modified push up, straight leg raise, and trunk rotation. Additionally, step up and down and two foot and single foot box drop landings for advanced testing are completed. This system uses a similar approach of correcting faults in the movement pattern to reduce or balance stress through the soft tissue.

An often used functional movement test is the ‘overhead double leg squat’ to identify functional compensations and motion restrictions. This is a standing squat test, while keeping the arms forward flexed overhead. Usual deviations include positions of toe out, flattening of medial longitudinal arch, knee valgus, arms falling forward, and excessive trunk lean. These dysfunctions will contribute to the methods of losing normal kinesiological motions as described above, and necessary restorative exercises are required to rehabilitate the client. For the purpose of injury prevention using muscle activation, the therapist can use this test to ensure appropriate flexibility of tissue (correct if limiting), and provide corresponding corrective exercise(s) to strengthen the muscle in the acceptable ROM. Repetition of the functional movement pattern will be an important final step to ensure transition to learned and therefore experienced based pre-activation.

Livingston (14) identified a training pyramid to improve the association between active movement specificity and training specificity. As modification (13) he suggests that the fundamental movement make up 40% of the training program, where the traditional rehabilitation method includes closer to 15%. The reduction of sports-specific work (15%), general fitness work (25%) and performance fitness work (20%) are reduced from the traditional level to allow more emphasis on fundamental movement. Similarly to Sahrmann and Cook, Livingston believes that the foundation exercises need to put the client in the cor- rectly aligned position. The literature previously cited agrees, if working on flexibility, one must ensure that there are not com- pensatory movements at other joints. Similarly, for strength work, those muscles which are assessed as long need to be corrected in a shortened position. This can be aided by using proprioceptive and kinesthetic feedback measures, but ultimately the client needs to be able to perform this movement independently. The exercise must be performed in a quality manner, not necessarily of quantity. Speed will also be an important consideration, in that

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