The effect of vibration and static stretches on dynamic knee range of motion and lower limb function
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For many athletes, static stretches are used prior to sporting activity to increase the length of the muscle. This increase in available range is proposed to reduce the risk of injury, and to prepare the entire muscle for activity. Static stretching has been recognised to produce significant increases in ROM when applied in acute and long term training studies. This change has been attributed to viscoelastic and myogenic (i.e. stretch tolerance) influences. However, some authors have found static stretches to be detrimental to explosive performance tasks, which could be damaging for high performance athletes (e.g. sprinters), where every bit of force and power generated is crucial. As a result there has been great interest in dynamic stretching techniques for changing range of motion (ROM), which are proposed to enhance muscle extensibility, but not negatively influence performance measures. With regards to measuring ROM, static assessment techniques are most commonly used, where in most cases a goniometer is used to measure a static hold at the end range of the muscle. However, such techniques have limitations in regards to assessing dynamic movement. As the majority of functional movement is dynamic, there is a need for an accurate measurement technique to identify dynamic ROM. This will allow analysis of functional ROM during an activity/task and the ability to assess the effects of various acute and chronic interventions on dynamic ROM. One intervention that may have interesting implications for acute and chronic changes in ROM is vibratory stimulation. The effect of vibration on the human body has been researched in detail over the last decade, namely in occupational studies. More recently, sports and exercise scientists have begun to investigate the effect of whole body vibration on muscle performance and ROM. These studies have found acute enhancing effects of vibration on strength, force, power, and jump height. One study has investigated the effect of vibration on ROM, finding it beneficial for increasing knee ROM in a three week training study. Vibration has been proposed to affect these changes as a result of altered neural sensitivity through a variety of central and peripheral mechanisms, or viscoelastic changes through increased temperature and blood flow. There is also debate as to the influence of compliance on the musculotendinous unit in response to vibration, where increased temperature could reduce stiffness, whilst enhanced neural sensitivity and activation could increase stiffness. There is a need for further research to determine the effect of vibration on ROM, and observe if it has a role as a potential substitute, or compliment, to static stretching. Additional research may also clarify the mechanisms behind any such change. The purpose of this thesis therefore was to identify a new and reliable dynamic knee extension measurement technique, determine the effect of different vibratory parameters on knee ROM, and compare any such change with a static stretching protocol. The new, non weight-bearing, dynamic ROM measurement technique used video-camera footage, digitisation, and analysis with the siliconCOACH computer programme. It consisted of ten repetitions of dynamic knee extension at one second intervals, which were followed by three, three second static knee extensions. Dynamic ROM was measured first to limit any effect of the sustained static holds on knee ROM. Video-analysis provided a comparison of congruency and accuracy between dynamic and static active knee extension measurements. The testing was repeated on four separate occasions to determine test-retest reliability of the assessment procedure. The ROM technique was then used to analyse the effects of different vibratory parameters (i.e. amplitude, frequency, acceleration), to identify the optimal parameters for changing ROM. A randomised cross-over experiment used these vibration parameters to compare knee ROM following vibration, static stretching, and a combination of vibration and static stretching protocol, on three separate occasions. The duration of any such effect was investigated with a repeated ROM measure ten minutes after testing. Repeated counter-movement jumps were also performed following each ROM assessment to evaluate the impact of these interventions on performance. Three jump heights, within one centimetre of each other, were recorded on each testing occasion. It was hypothesised that vibratory stimulation could provide a method for optimally preparing a muscle for performance, without negatively influencing explosive tasks and muscle performance. It was observed that the proposed video-analysis ROM technique was a reliable method for measuring dynamic knee ROM. The technique had high intra-class coefficients (0.89) and low coefficients of variation (2.08%), representing a high degree of stability. It was found to be comparable with reliability tests of other static ROM measures, and no significant (p< 0.05) differences were found between static and dynamic measurements used in this study. Of the vibration machine settings, three of the four settings trialled significantly increased knee ROM, with parameters of 3-5 mm amplitude, 24-44 Hz frequency, and acceleration of 33.2-49.4 m.s². The vibratory stimulation resulted in greater effect sizes compared to other studies investigating ROM due to lower variance between measures. However, when vibration was used as an intervention (30 second application, three times) there was no significant increase in dynamic ROM. The static stretching intervention was found to create a significant increase (2% or 3º) in dynamic ROM, which remained significant ten minutes after the intervention. The combination of static stretches and vibration did not significantly change ROM, although was a significant difference between ROM measures of the combined intervention and the vibration intervention groups after 10 minutes (p=0.01). No intervention affected jump height significantly. It was concluded that the new dynamic knee measurement technique was just as reliable as recognised static assessment techniques for the knee. However, further research is warranted on the measurement of other joints and during a functional task. Although vibratory stimulation was found to cause a small change in ROM of the knee, additional research is required to determine the effect of different vibration parameters, such as duration, and application types (i.e. segmental versus whole body vibration) on ROM, including that of different joints. The proposed mechanisms behind ROM changes could also be explained with future research assessing electromyography and force generation measurements during stretches and vibration. The use of vibration could also be integrated into long term studies, to see if vibration can have an influence on ROM over a long term programme.