21 - 26 MD SCREEN 19/7/06 12:10 pm Page 22 THE PERFORMANCE MATRIX

ent proprioceptive system along with many psycho-social factors. Hypertrophy is a peripheral structural adaptation in muscle to demand, along with central ner- vous system neural adaptation, and is the result of overload training (3). Hodges (4) argues that strengthening the muscles of range and force potential, and motor con- trol training of deeper (force inefficient) muscles, are two distinctly separate processes, both of which are required to perform to high levels of activity such as during competitive sport.

PAIN AND RECRUITMENT There is consistent evidence of altered recruitment in the presence of pain. Pain affects slow motor unit recruitment more significantly than fast motor unit recruit- ment. Pain does not appear to significant- ly limit an athlete's ability to generate power and speed as long as they can mentally 'put the pain aside'. It has been suggested anecdotally that up to 90% of sporting world records are broken by ath- letes with a chronic or recurrent musculo- skeletal pain problem.

Recent research on musculoskeletal pain has focused on motor control changes associated with the pain state. This research has provided important new information regarding chronic or recurrent musculoskeletal pain. A large number of independent research groups are all reporting a common finding in their stud- ies. They have consistently observed and measured that in the presence of chronic or recurrent musculoskeletal pain, sub- jects change the patterns or strategies of synergistic recruitment that are normally used to perform low load functional move- ments or postures (4-18). They demon- strate that these subjects employ strate- gies or patterns of muscle recruitment that are normally reserved for high load function (eg. lifting, pushing, pulling, throwing, jumping, running) for normal postural control and low threshold func- tional activities.

These altered strategies or patterns have been described in the research and clini- cal literature as 'substitution strategies’, ‘compensatory movements’, ‘muscle imbalance’ between inhibited/lengthened stabilisers and shortened/overactive mobilisers, ‘faulty movements’, ‘abnormal dominance of the mobiliser synergists’, ‘co-contraction rigidity’ and ‘control

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(a) Prone knee extension (14): ideally, there should be approximately 120º knee flexion without significant lumbo- pelvic motion.

(Reproduced with permission Kinetic Control)

Figure 1a and 1b: Relative flexibility showing possible lumbar extension weak link impairments’.

Altered control strategies (stability dysfunction) The concept of muscle imbalance and its relationship to treating established mus- culoskeletal pain is not new (10,11,14, 15,17,19,20), but the concept of linking it to injury prediction is a more recent development (21).

There is frequently (but not always) a relationship between the loss of range of movement at one or more motion seg- ments, and the development of compen- satory excessive movement at adjacent segments. Relative flexibility is a concept that links movement dysfunction to pathology (22). During functional multi- joint movements a relatively stiffer joint or muscle tends to resist movement, but function is maintained by another joint increasing motion to compensate. Once a joint has developed abnormal compen- satory motion, the stabilising muscles and supporting structures (eg. ligaments) around these joints become too flexible, more lax and have more ‘give’.

The concept of relative flexibility should be qualified by the site and direction of compensation or ‘give’. For example, the lumbar spine may be more flexible relative to the hips in extension due to the rela- tively stiff hip flexors providing greater resistance to hip extension than that pro- vided by the abdominals to lumbar exten- sion (Figure 1). The site of greatest rela- tive compensation is at the lumbar spine during trunk extension movement. Therefore during gait, at push off, exces- sive lumbar extension is used because it is easier than hip extension. The result is compensatory lumbar extension and a potential lumbar extension ‘weak link’.

Functional testing for altered con- trol strategies (dissociation) During all normal functional activities, muscles co-activate in integrated patterns to maintain stability. All functional activ- ities impose stress and strain forces on the movement system in varying loads and in all three planes or directions of motion. Normal functional movements rarely eliminate motion from one joint system while others move. Functional movement rarely occurs in only one plane. However, everybody has the ability to per- form patterns of movement that are not habitually used in ‘normal function’ (eg. pat the head and rub the stomach). Some of these patterns of movement are unfa- miliar and feel ‘unnatural’ precisely because they are not habitual patterns of recruitment.

Performance of some of these unfamiliar movements is a test of motor control (skill and co-ordination). The ability to activate muscles to isometrically hold position or prevent motion at one joint system, while concurrently actively producing a move- ment at another joint system in a specific direction is a test of motor control known as dissociation. Even though it is accept- ed that these direction control or ‘dissoci- ation’ patterns are not ‘normal’ or ‘natural’ functional movements, they are however, movement skills and motor patterns that everybody normally has the ability to per- form, so long as they are taught and understand the movement pattern (24).

An example of a flexion dissociation test involves producing a movement pattern of keeping the back straight (preventing any flexion/bending) and bending forward by hinging solely at the hips (Figure 2). This is a motor control test and can also be

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(b) Lumbar extension weak link (prone knee extension) (23): If the rectus femoris is stiffer than the abdom- inals, then during knee flexion the pelvis tilts anteriorly and the spine extends.