Exercise, neuromuscular control and performance, and stability of the knee joints
In spite of an accumulating volume of information about injury to the musculoskeletal system in recent years, little scrutiny has been focused on the cause and prevention of injury. The large number of injuries to the knee joint and the anterior cruciate ligament ACL ligament in particular, is an alarming sign of the seriousnesso f this problem facing recreational and athletic people around the world. The large number of injuries appears to arise from an unfavourable interaction between `static' connective tissue-related and 'dynamic' muscle-related stabilisers of the joint system (Gleeson et al., 1998; Myers and Lephart, 2000). The functional stability is mediated ultimately by the neuromuscular system (Myers and Lephart, 2000) and it is important therefore to understand the function of the neuromuscular system as fully as possible in order to affect the aetiology and likelihood of injury favourably. The neuromuscular system includes biological 'machinery' offering capability for neuromuscular control (proprioception) and neuromuscular performance (motor actions). The neuromuscular control was quantified by newly-developed and laboratory-based assessmentsin volving the dynamic muscular reproduction of a `blind' target force and the error associated with such efforts may provide greater efficacy of measurement compared to those tests used in contemporary practice which may not indicate an individual's true functional capability to resist injury threats, in particular, to assessth e muscular dynamic intensity associatedw ith sporting endeavours which may functional capability to resist injury threats may be compromised. This thesis is presented as a series of three studies. The aim of this study was to examine between-day reproducibility and single measurement reliability of objective and self-perceived indices of force error in the knee flexors and extensors in men. Results showed that the reproducibility and single-measuremenrt eliability of objective (CE%, VE %) and self-perceived performance (SPCE% and SPVE %) during between-daya ssessmentso f neuromuscularc ontrol NCA1, NCA2 and NCA3 offered compromised precision and efficacy. These indices of performance should be deployed cautiously within both case-study and inter-individual comparisons and must rely on multiple-trial protocols to achieve acceptable levels of measurement precision in such circumstances. The aim of the second study was to examine the effects of serial bouts of acute fatiguing exercise on objective and self-perceived indices of neuromuscular control and performance of the knee flexors in men. In summary, results showed that despite substantial fatigue-related strength and muscle activation impairments, neuromuscular control as measured objectively by NCAI, NCA3 or RJA was not influenced significantly by the fatigue task intervention and that capability in this aspect of neuromuscular control was preserved in response to this type of exercise stress. Furthermore, constant error associated with self-perceived performance was similarly not influenced significantly by the fatigue task intervention. It is plausible that in ordert o provideo ptimump rotectiono f synovialj oints, neuromusculacro ntrol of the kneef lexorsm ay be preservedp referentiallyt o neuromusculapre rformance whenc hallengedb y fatigue-relatede xercises tresses. The third study assessedc oncomitant effects of an episodeo f muscle damage interspersed amongst serial bouts of fatigue on objective and self-perceived indices of neuromuscular control and performance of the knee flexors. This type of exercise perturbation reflects that associated with acute, transient and metabolically-focused effects (fatigue) and that during a more prolonged, mechanical type of disruption to the muscle (EIMD). It was likely to mimic some of the patterns of exercise inherent in sports and training practice and may serve to disrupt dynamic stabilization around the knee joint. Results showed that despite substantial EIMD and fatigue-related strength impairments (the former confirmed in this experiment by means of indirect physiological descriptive variables including a reduced range of movement and an increase in pain upon active movement of the affected limb), neuromuscular control as measured by objective and self-perceived indices of constant and variable error in assessment protocols NCA 2, NCA3 and DNCA was not influenced significantly by the EIMD and fatigue task intervention. It was notable that capability in this aspect of neuromuscular control was preserved in response to this type of exercise perturbation in the three different modes of objective assessments of neuromuscular control used in this study.