Evaluation of Validity and Reliability of Using Video Analysis Method for Calculating Leg Stiffness During Hopping Test

Oral Presentation
Paper ID : 1203-12THCONG
Oral / Poster Presentation File: 1203-12THCONG.mp4 
1Faculty of Physical Education and Sport Sciences, University of Tehran, Tehran, Iran
2Institute of Physical Education and Sport Sciences, Tehran, Iran
Recently “Leg Stiffness” has attracted the attention of many scholars in the field of sport science. Numerous investigations have shown the effect of leg stiffness on injuries and some of performance related conditioning parameters in sport. Moreover, studies suggest that amount of leg stiffness can change and it can be improved through power, strength, and plyometric trainings. It seems that necessity of laboratory conditions and expensive equipment such as force plate limit the usage of this parameter by coaches. This study aims to remove these limitations by evaluating the validity and reliability of video analysis method for calculating leg stiffness.
For validity evaluation, fourteen male athletes performed bilateral hopping test at a frequency of 2.2 Hz. The test was recorded simultaneously by Kistler 9281C force plate and Sony Cyber-shot RxX100IV high speed camera from frontal view with sampling rate of 250 Hz. After extracting contact and flight time from both equipment, leg stiffness for each hop calculated by Dalleau formula. Then validity was tested by Pearson correlation and paired sample t-test.
For testing reliability, 161 sub-elite male soccer players repeat previous hoping test. This time it was recorded only by high speed camera. Afterward, reliability was tested by “Two-way mixed effects, absolute agreement, single rater” ICC (Intraclass Correlation Coeficient) test.
The results of Pearson test demonstrated that amount of leg stiffness calculated by two methods are strongly correlated (r = 0.987, p < 0.001). Furthermore, Paired sample T-test indicated there is no significant differences between two methods (t = 0.135, Pvalue = 0.893). Intraclass correlation coefficient test results showed high amounts of reliability(average measures = 0.969).
Results demonstrated that using the video analysis method for calculating leg stiffness is valid and reliable. Thus traditional method can be replaced by the video analysis method. The advantages of this method compared to force plate method is that it can be performed in the field without using any expensive equipment.