Reliability & linearity of an electronic body protector employed in taekwondo games: a preliminary study

Abstract

An official electronic body protector (EBP) requires both, the necessary degree of accuracy and consistency in securing the same result under similar conditions. The purpose of this study was to assess the repeatability and linearity of a taekwondo EBP. A commercially available EBP that registers the energy (E) of a hit in Joules was placed unfolded on a hard non-deformable surface. Ten potential "hit" areas were marked on the EBP's surface. To simulate kicking conditions a 4 kg iron shot attached to a switch operated electromagnet was systematically released against the EBP from three randomly selected heights (1.78m, 1.92m, and 2.00m). The shot was released 5 times repeatedly from each height on each of the 10 areas. The procedure was repeated after a 30min interval. Reliability was assessed by the test-retest method using Chronbach's alpha, Guttman split half and ICC, and the coefficient of variation (%CV). The overall (10 sites pooled together) CV was 4.8%. Τhe CV’s for the three heights of release were 5.47%, 4.77%, and 4.18%, respectively. For the 10 separate analyses (one for each of the 10 EBP sites) CV ranged from 2.5% to 11.6%. For the 10 separate analyses (one for each of the 10 trials) CV ranged from 6.8% to 11.6%. The overall reliability between the 30 trials (across the three heights of release) was: Chronbach's α = 0.979, single measure ICC = 0.572, average measure ICC = 0.976 (p<0.001). Testing revealed that the inter-trial and inter-site reliability of the EBP is poor. Further research is required in testing the reliability of a variety of body protectors used in official competitions today so as to assure fairness among contestants.