INTRODUCTION: Alpine skiing performance requires eccentric muscular contractions to resist the gravity and the centrifugal force during the turning phases or to absorb the irregularities of the terrain. For this reason, the measure of eccentric strength is highly relevant in alpine skiers. Isokinetic open-chain tests are traditionally used to measure the eccentric strength. However, the open-chain muscular actions required by these tests are different compared to the closed-chain nature of actual ski performance. To verify if the use of open-chain isokinetic tests can be an acceptable alternative to closed-chain measurements, we examined the relationship between the eccentric strength assessed using an open-chain isokinetic dynamometer and a motorized leg press. METHOD: Nineteen male and 16 female of the Italian National Alpine Ski team were involved in the study. Participants completed an isokinetic strength test for the assessment of eccentric strength of the knee extensors using a Cybex Norm dynamometer (Humac, CA) at an angular velocity of 60°/s. In a separate occasion, subjects completed a test on a motorized leg press modified to measure the eccentric strength. The linear velocity was selected to obtain a mean knee angular velocity as close as possible to 60°/s. Similar ranges of motion were also selected (80°). RESULTS: The relationship between open- and closed-chain eccentric measurements was not significant in female (r=0.32; P=0.23; R2=0.10), while a significant but low correlation was found in male (r=0.50; P=0.03; R2=0.25). A significant Pearson's r was found using the pooled data, that is increasing the spread of the data (Figure 1). DISCUSSION: The results of this study showed that the evaluation of eccentric strength of the knee extensors using open-chain tests is not a valid alternative to closed-chain assessments (10 to 20% of common variance). Indeed, while the leg press measures the vertical component resulting from the contractions of three muscular groups (calf, quadriceps and gluteus), the traditional isokinetic dynamometers measure the strength of the quadriceps only. CONCLUSION: Given the closed-chain nature of alpine skiing performance, the assessment of eccentric strength should be performed using closed-chain tests.
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