Lis Steidl-Müller*,Crolin HilderndtErich Müller,Christin Fink,Christin Rschner

aDepartment of Sport Science,University of Innsbruck,Innsbruck 6020,Austria

bDepartment of Sport Science and Kinesiology,University of Salzburg,Salzburg 5400,Austria

cResearch Unit for Orthopedic Sports Medicine and Injury Prevention,Institute of Psychology(ISAG),The Health&Life Sciences University(UMIT),Innsbruck 6020,Austria

dGelenkpunkt-Sports and Joint Surgery,Innsbruck 6020,Austria

Abstract Purpose:The aims of this study were to assess differences of limb symmetry index(LSI)in strength-and coordination-related tasks between high-level,competitive,noninjured ski racers of different age-related performance levels and to prospectively assess limb differences as a possible risk factor for traumatic and overuse injury in youth ski racers.Methods:The study(Study 1)included 285 high-level competitive ski racers(125 females,160 males)of 3 age-related performance levels and based on the school system:95 youth(10-14 years,secondary modern school),107 adolescent(15-19 years,grammar school),and 83 elite athletes(20-34 years).To investigate the second aim(Study 2),67 of the 95 youth athletes were included and any traumatic or overuse injuries were prospectively recorded over 2 seasons.All athletes performed 4 unilateral tests(strength related:one-leg counter movement jump(OL-CMJ)and one-leg isometric/isokinetic press strength test(OL-ILS);coordination related:one-leg stability test(OL-ST)and one-leg speedy jump test(OL-SJ)).The LSI was calculated by dividing the dominant leg by the nondominant leg and multiplying by 100.Kruskal-Wallis H tests and binary logistic regression analyses were conducted.Results:There were significant differences between the LSI of the 3 age-related performance-level groups only in the strength-related tests:the OL-CMJ(x2(2,285)=9.09;p=0.01)and the OL-ILS(x2(2,285)=14.79;p＜0.01).The LSI for OL-ILS was found to be a significant risk factor for traumatic injury in youth ski racers(Wald=7.08;p＜0.01).No significant risk factors were found for overuse injuries.Conclusion:Younger athletes display slightly greater LSI values only in the strength-related tests.The cut-off value of limb differences of＜10%for return to sport decisions seems to be appropriate for elite athletes,but for youth and adolescent athletes it has to be critically discussed.It seems to be necessary to define thresholds based on specific performance tasks(strength vs.coordination related)rather than on generalizations,and age-related performance levels must be considered.Limb differences in unilateral leg extension strength represent a significant injury risk factor in youth ski racers.

Keywords:Age-related performance levels;Alpine ski racing;Injury risk;Limb differences;Youth athletes

Table 1Anthropometric characteristics of the participants by performance level(mean±SD)

Fig.1.Percentage of objectively measured right leg as the dominant leg by age-related performance level.OL-CMJ=one-leg counter movement jump;OL-ILS=one-leg isometric/isokinetic press strength test;OL-SJ=one-leg speedy jump test;OL-ST=one-leg stability test.

Table 2 Test values of the dominant and nondominant leg by performance level(mean±SD)

Fig.2.LSI(%)of the 4 test modalities by age-related performance level.*p＜0.05;**p＜0.01.LSI=limb symmetry index;OL-CMJ=one-leg counter movement jump;OL-ILS=one-leg isometric/isokinetic press strength test;OL-SJ=one-leg speedy jump test;OL-ST=one-leg stability test.

Fig.3.Distribution of symmetry and asymmetry in strength-related tests(A)and coordination-related tests(B)by age-related performance level.

Table 3 Occurrence of traumatic and overuse injuries