Introduction: Hockey skates act as an important interface between a player and the ice. As such, the plantar force application within a skate could be an important feature which affects hockey skating. In this study, Principal Component Analysis (PCA, Federolf et al., 2012) was used to (1) determine principal patterns of in-skate force application and (2) distinguish between high and low caliber skating. This approach identifies specific components of force application that can be used to characterize player performance in hockey. Methods: Nine high caliber (25.7±3.7 yrs, 86.2±7.8 kg) and nine low caliber hockey players (35.7±5.7 yrs, 85.7±13.6 kg) performed 15 repetitions of a 30 m sprint whilst plantar pressure was measured in the right skate using pressure sensing insoles. Pressure data from accelerative (ACC) and maximum velocity (MV) strides were extracted and analyzed. Insole pressure was converted to force at the medial and lateral forefoot segments, medial and lateral midfoot segments and heel segment, and subsequently time normalized (0-100%). PCA was applied to all trials of both groups. PCA results in a set of principal components (PC) arranged in descending order according to their explained variance of the original data set. The first component describes the most relevant aspects with respect to in-skate force application. PC scores were obtained by projecting the original data onto the PCs and analyzed for group differences using an independent ttest (á=0.05). Scores were then used to calculate the variance of each group for the PCs. Results: During ACC and MV strides the largest loading on PC1 was the heel segment. PC2 of the ACC stride was represented by medial and lateral forefoot push-off and initial heel contact force. PC2 of the MV stride contained just medial and lateral forefoot push-off. Significantly different PC scores were identified for PC1 and PC2 across calibers during the ACC stride (p<.01). However, during the MV stride a caliber difference was seen only at PC2 (p<.01). The low caliber group represented 64% of the variance contained in PC1 scores. Discussion: This study shows that PCA can be used discriminate high and low caliber skating with respect to in-skate force application. Low caliber players exhibited greater variance in PC1 during ACC, thus caliber differences existed in the most fundamental pressure patterns. This suggests that high caliber players can execute the most important pressure patterns with greater precision and consistency. On the other hand, differences in caliber during MV could only be discriminated at PC2. Therefore as players reach MV, differences in plantar force application become more subtle.
© Copyright 2014 19th Annual Congress of the European College of Sport Science (ECSS), Amsterdam, 2. - 5. July 2014. Veröffentlicht von VU University Amsterdam. Alle Rechte vorbehalten.