| Background: Mostly occurring in the long head of the biceps femoris,the hamstring strain is one of the most prevalent non-contact injuries in sports field.Studies have shown a negative association between the risk of hamstring strain and the length of muscle bundle.Athletic training can change multiple muscles structure such as fascicle length,muscle thickness and pennation angle,etc.Therefore,in order to prevent hamstring strain,it is important to understand the effect of physical training on muscle function via the change of muscle structure.Purpose: The purpose of this study is to compare the effects of one-time static stretching training and eccentric training on the muscle structure of the hamstring muscles.Additionally,this study aims to access the reliability of ultrasonic detecting which might be a reliable method for the further studies focusing on the risk factors of hamstring strain under living conditions.Results of this study will provide recommendations for prevention of hamstring strain.Method: At the beginning,the reliability of two-dimensional ultrasound evaluation of MAP was tested.The experiment was repeated in two days(daytime test-retest reliability)with three images(intraday test-retest reliability)recorded by detecting each leg of each subject.All the ultrasound images are digitized.After digitization,a clear muscle beam is selected for analysis in each image of front,middle and rear leg position(test-retest reliability at different picture locations).The biceps femoris long legs of 34 male participants were measured by the US GE Vivid i color spectrometer.Interclass correlation coefficient(ICC)and αCronbach were calculated to determine the reliability of measurements.Additionally,standard error of measurement(SEM)and minimum detectable change(MDC)were used to estimate standard error of retest score and measurement error of possible magnitude separately.Exercise intervention was then conducted after obtaining a good retest reliability of ultrasound detecting for MAP.With a crossover design,two intervention trainings including one-time static stretching and one-time Nordic hamstring strength training were conducted among participates.In order to avoid residual effects,the interval between the two types of intervention training was one week.The differences of two intervention training were analyzed by two-way ANOVA.Two factors of repeated measurement are intervention time and intervention method.Bonferroni test was used to compare the differences in muscle structural parameters.All differences and associations were considered significant at the alpha level of 0.05 and the test results were shown as Mean ± SD.Result: The results of MAP accessed through different positions of the same ultrasonic image had good reliability(ICC=0.75-0.99).The retest reliability of intraday muscle structure parameters was excellent(ICC=0.97-0.99).The reliability of muscle structure parameters measured by day was good(ICC=0.64-0.86).The measurement error of fascicle length was 0.35 cm,the measurement error of muscle thickness was 0.09 cm,and the measurement error of pennation angle was 0.72°.There is none statistically significance found among the effects of interaction term(intervention mode x intervention time)on fascicle length,pennation angle and muscle thickness.As a result,the main effect was considered in the internal factors of subjects.The main effects of intervention methods on fascicle length,pennation angle and muscle thickness were not statistically significant(P> 0.05).After intervention there is statistically differences in terms of fascicle length(P <0.001),pennation angle(P <0.001)and muscle thickness(P = 0.017),with differences are 0.5cm,-0.55°and0.04 cm individually.Conclusion: The test-retest reliability of biceps femoris long head muscle structure parameters measured by two-dimensional ultrasound is high;Both static stretching and eccentric training can increase the length of biceps femoris muscle fascicle with the same effect. |
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