Thesis (MHSc--Health Science) -- Auckland University of Technology, 2005. / Also held in print (xvi, 130 leaves, ill., 30 cm.) in Akoranga Theses Collection. (T 613.718 DOM)

A Research Report submitted to the Faculty of Health Sciences, University of the Witwatersrand Gauteng, 2017 / Background Soccer is a sport that is gaining in popularity in the elite and non-elite populations worldwide. As a result, the number of injuries in soccer is increasing. Hamstring injuries in particular, with a reported incidence rate as high as 63%, are of significant concern. Most hamstring injuries tend to occur during the swing phase of sprinting when hamstring activity is at its highest. As the speed of sprinting increases, greater mobility in the lumbo-pelvic area is required to maximise sprinting efficiency. Any abnormal or dysfunctional lumbo-pelvic movement during this phase could induce pain and hamstring injury. Lumbo-pelvic movement control dysfunction may therefore indirectly link abnormal lumbar spine movement to lumbo-pelvic pain and hamstring injury. The first aim of this study was to compare the performance of the erector spinae, gluteus maximus, hamstrings (biceps femoris) and quadriceps (rectus femoris) muscles in soccer players, with and without recent hamstring injuries, while performing isometric contractions, a functional squat and sprinting. The study’s second aim was to compare lumbo-pelvic movement control in soccer players with and without recent hamstring injuries. Method Thirty soccer players were selected to participate in this study. Fifteen were assigned to the injured group and 15 to an uninjured group. The injured group comprised players who had sustained a hamstring injury six months prior to the research and who had partially returned to training, and the uninjured group comprised players with no recent hamstring injuries and who were actively involved in full training. Players were matched in respect of age, height, weight and playing position. All players gave informed written consent, completed the physical activity, training and injury questionnaire, and the Oslo hamstring injury questionnaire. Physical tests, which included isometric contraction of the erector spinae, gluteus maximus, hamstrings (biceps femoris) and quadriceps (rectus femoris) muscles, a functional squat and a thirty-metre sprint were done. Muscle activity during these tests was recorded via electromyography (EMG). To determine the lumbo-pelvic movement control of the players, the dorsal pelvic tilt, waiter’s bow, one leg stand and prone knee bend tests were used. Cohen's d (parametric) and Spearman’s correlation coefficient (nonparametric) were used to calculate the effect size, and the Chi-square test and Fisher’s exact to analyse the lumbopelvic movement control data. To establish a statistical significance, the p-value of the study was set at p<0.05. Results EMG muscle activity during isometric contractions was lower in the erector spinae muscles (p=0.04) and biceps femoris muscle (p=0.02) of the injured group. Both these findings were statistically significant. There was no statistically significant difference in muscle activity during the functional squat between the study and uninjured groups. The results of the EMG activity in the thirty-metre sprint were determined to be significant as they demonstrated that the hamstring muscle (p=0.01) activation in the injured group was decreased in comparison with the uninjured group. During the performance of the lumbo-pelvic test, no association was found between the two groups in the dorsal pelvic tilt and one leg stand. The performance of the waiter’s bow (p=0.01) and prone knee bend (p=0.004) revealed statistically significant differences between the study and uninjured groups. The majority of the players in the injured group performed both of these functional tests incorrectly (WB n=10; PKB n=14). Conclusion The study found that the hamstring muscle is at great risk of injury during eccentric contraction of the hamstring muscles. This can be associated with poor lumbo-pelvic movement control, as the load on the hamstring muscle is increased to provide intersegmental stability around the neutral zone, the area of high spinal flexibility. / MT2017

The objective of this study was to investigate the influence of cyclic loading on the extensibility of hamstring muscle-tendon units in vivo.Study Design: A test-retest randomised controlled trial with repeated measures was undertaken.Background: Stretching has been commonly promoted to increase the passive extensibility of the muscle-tendon units, yet the mechanism behind its proposed effects remains ambiguous. In vivo studies of stretching have mostly been limited to the viscoelastic characteristic of stress-relaxation. Few studies have investigated the characteristic of creep. Animal and cadaver in vitro creep experiments have consistently shown increases in the length of the soft tissues, with associated changes in their resistance and stiffness. These results however, might not be representative of human muscle-tendon units under in vivo conditions. Additionally, those in vivo human studies that have investigated creep phenomenon have contrasting results. To date, no known in vivo study has examined passive cyclic loading of human hamstrings to a constant load level.Method: Using a repeated measures design the extensibility of the hamstring muscles were assessed by a passive knee extension test (PKE) to maximal stretch tolerance using a KinCom® dynamometer. Those participants in the intervention group underwent 45 continuous passive cyclic loadings as the KinCom® dynamometer moved the knee joint into extension until torque reached 85% of maximal passive resistance torque measured in the passive knee extension test. The control group sat quietly relaxed during the intervention period. Measurements of hamstring passive extensibility using the PKE test were repeated at the end of the intervention.Results: Following the intervention, the PKE test showed for the cyclic loading group there was a significant (p < 0.05) increase in both maximal passive resistance torque (mean 23%) and knee joint angle (mean 6.3%). A significant (p < 0.05) decrease in passive resistance torque (mean 11.8%) when re-measured at the baseline position of maximal passive knee angle was observed. A significant increase (p < 0.05) was found for passive stiffness over the final 10% of the knee torque-angle curve. No significant difference (p > 0.05) was found for passive stiffness for the full (100%) of the torque-angle curve. Of the control group, no significant differences (p > 0.05) were observed for all variables of the PKE test. Analysis of cycle one compared to forty-five of the cyclic loading intervention procedure showed a significant (p < 0.05) increase in both passive knee joint angle (mean 5.2%) and passive stiffness (mean 28.6%) over the final 10% of the knee joint torque-angle. No significant difference (p > 0.05) was found for passive stiffness across the full (100%) knee joint torque-angle.Conclusion: The findings of the current study demonstrated that after cyclic loading the hamstring muscles lengthened and became stiffer over the final gained range of knee joint motion. Although the current study cannot determine the mechanism behind the changes in the variables of interest, these findings do provide some evidence that most likely a combination of altered stretch tolerance and local mechanical effects within the muscle-tendon unit, i.e. creep lengthening were responsible.

The objective of this study was to investigate the influence of cyclic loading on the extensibility of hamstring muscle-tendon units in vivo.Study Design: A test-retest randomised controlled trial with repeated measures was undertaken.Background: Stretching has been commonly promoted to increase the passive extensibility of the muscle-tendon units, yet the mechanism behind its proposed effects remains ambiguous. In vivo studies of stretching have mostly been limited to the viscoelastic characteristic of stress-relaxation. Few studies have investigated the characteristic of creep. Animal and cadaver in vitro creep experiments have consistently shown increases in the length of the soft tissues, with associated changes in their resistance and stiffness. These results however, might not be representative of human muscle-tendon units under in vivo conditions. Additionally, those in vivo human studies that have investigated creep phenomenon have contrasting results. To date, no known in vivo study has examined passive cyclic loading of human hamstrings to a constant load level.Method: Using a repeated measures design the extensibility of the hamstring muscles were assessed by a passive knee extension test (PKE) to maximal stretch tolerance using a KinCom® dynamometer. Those participants in the intervention group underwent 45 continuous passive cyclic loadings as the KinCom® dynamometer moved the knee joint into extension until torque reached 85% of maximal passive resistance torque measured in the passive knee extension test. The control group sat quietly relaxed during the intervention period. Measurements of hamstring passive extensibility using the PKE test were repeated at the end of the intervention.Results: Following the intervention, the PKE test showed for the cyclic loading group there was a significant (p < 0.05) increase in both maximal passive resistance torque (mean 23%) and knee joint angle (mean 6.3%). A significant (p < 0.05) decrease in passive resistance torque (mean 11.8%) when re-measured at the baseline position of maximal passive knee angle was observed. A significant increase (p < 0.05) was found for passive stiffness over the final 10% of the knee torque-angle curve. No significant difference (p > 0.05) was found for passive stiffness for the full (100%) of the torque-angle curve. Of the control group, no significant differences (p > 0.05) were observed for all variables of the PKE test. Analysis of cycle one compared to forty-five of the cyclic loading intervention procedure showed a significant (p < 0.05) increase in both passive knee joint angle (mean 5.2%) and passive stiffness (mean 28.6%) over the final 10% of the knee joint torque-angle. No significant difference (p > 0.05) was found for passive stiffness across the full (100%) knee joint torque-angle.Conclusion: The findings of the current study demonstrated that after cyclic loading the hamstring muscles lengthened and became stiffer over the final gained range of knee joint motion. Although the current study cannot determine the mechanism behind the changes in the variables of interest, these findings do provide some evidence that most likely a combination of altered stretch tolerance and local mechanical effects within the muscle-tendon unit, i.e. creep lengthening were responsible.