Performance and perturbation tests in elite Paralympic sit-skiers

INTRODUCTION: In cross-country sit-skiing athletes are grouped in 5 different classes (LW10-LW12) on the basis of their ability to control the trunk. The greater trunk stability and trunk flexion angle during the pushing phase are, the higher is the performance effectiveness (Rapp et al.,2016),(Schillinger et al.,2016). Since the aim of classification process is to move from functional to evidence-based classification, the purpose of this study is to design a new testing device and assess its reliability in measuring athletes sport-specific force production and trunk control. METHODS: The testing device is composed of a chair surrounded by an aluminum frame and fixed to a motorized sledge. Two force sensors are mounted in anterior and posterior backrests of the chair. Two force sensors are embedded in a couple of ropes fixed at the frame top. Athletes performance was tested by 3 maximal voluntary contraction tests: simulated bench press by pushing with (Pw), without (Pwo) back support and simulated poling by pulling (P); while athletes trunk control was assessed by unpredictable forward and backward perturbations. To assess reliability 12 sit-ski athletes classified LW10.5-LW12 performed each test twice in 3 days. The following variables were considered to test reliability: anterior force in Pwo, anterior and posterior force in Pw, pulling force in P and ratio between anterior force in Pwo and Pw. Perturbation data is yet to be analyzed. RESULTS: Considering all the athletes, all variables showed a high ICC (0.93, p<.001 anterior force Pwo; 0.98, p<.001 anterior force Pw; 0.95, p<.001 posterior force Pw; 0.93, p<.001 pulling force P; 0.77, p<.03 anterior force ratio Pwo/Pw). No significant differences were observed between the two tests in any of the measured force variables. When class LW10.5 (N=1) was combined with LW11 (N=2) the ratio Pwo/Pw (mean of two measurements) was lower (0.39 vs 0.53) than in combined LW11.5 (N=3) and LW12 (N=6). DISCUSSION: The high repeatability in sport-specific tests suggests consistent measurement conditions, thus the device can be recommended for force measurements in sit-ski athletes. Lower force ratio in lower classes supports the importance of trunk muscles. This implies also that the new device can separate athletes with different impairment level. CONCLUSION: The next step is to evaluate if unpredictable perturbation test gives as good repeatability results as performances tests and if a trunk control-performance relationship is present. REFERENCE: Rapp, W., Rosso, V., Ohtonen, O., Gastaldi, L., Vanlandewijck, Y., Lindinger, S., Linnamo, V. (2016). Role of muscle activation in the sit-skiing performance and classification process. In Science and Nordic Skiing III (pp. 165–172). Schillinger, F., Rapp, W., Hakkarainen, A., Linnamo, V., Lindinger, S. (2016). A descriptive video analysis of classified Nordic disabled sit-skiers during the Nordic World Championship 2013. In Science and Nordic Skiing III (pp. 173–179).