Purpose： The aim of this study was to compare mechanical muscle function in the eccentric/concentric phases of vertical bilateral jumping in anterior cruciate ligament-reconstructed （ACLR）, elite （ELITE）, and ado...Purpose： The aim of this study was to compare mechanical muscle function in the eccentric/concentric phases of vertical bilateral jumping in anterior cruciate ligament-reconstructed （ACLR）, elite （ELITE）, and adolescent （ADOL） alpine ski racers and ski cross athletes. Methods： Alpine ski racers/ski crossers （ACLR： n = 12, age = 26.7 ± 3.8 years; ELITE： n = 12, age = 23.9 ± 3.0 years; ADOL： n = 12, age = 17.8 ± 0.7 years; females： n = 6 per group, males： n = 6 per group） performed 5 maximal countermovement jumps （CMJs） and 5 squat jumps. The ground reaction forces for each limb were analyzed using dual force plate recording to obtain body center of mass （BCM） velocity, displacement, and power. The eccentric deceleration （ECC） and concentric phases were determined from BCM velocity. CMJ net concentric and ECC impulses were calculated （body mass normalized） along with the peak and mean BCM power and maximal vertical jump height. CMJ lower limb stiffness （LLS） was determined by the slope of the ground reaction forces vs. the BCM displacement curve over the ECC phase. Concentric and ECC asymmetry indices were calculated for each leg, and the left vs. right LLS was compared. Outcome measures （reported as mean ± SD） calculated as a 5-jump mean were normalized to body mass and compared using an analysis of variance. Results： No between-group differences were found for peak and mean power or jump heights. There were no group differences for LLS or net concentric phase impulse, but the net ECC impulse was lower in the ADOL group compared with ELITE skiers （ADOL： 1.33 ± 0.32 Ns/kg; ELITE： 1.59 ± 0.16 Ns/kg; p 〈 0.05）. Although no group differences were found for ECC asymmetry indices, a group × limb interaction was found for LLS （p 〈 0.01）, which was systematically higher in the right vs. the left limb of ADOL skiers （right： 54.1 ± 17.9 N/m/kg; left： 48.7 ± 15.7 N/m/kg;p 〈 0.01）. Conclusion： ADOL skiers demonstrated decreased ECC impulse and systematic right limb dominance in LLS compared with ACLR and ELITE skiers. The implication of these findings for injury and performance are unknown, but further investigation into these potential relationships is warranted.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.展开更多
The aims of this study were(a)to investigate the effects of a unilateral training program in reducing inter-limb asymmetry in male soccer players;(b)to explore such effects on measures of physical performance and unil...The aims of this study were(a)to investigate the effects of a unilateral training program in reducing inter-limb asymmetry in male soccer players;(b)to explore such effects on measures of physical performance and unilateral inter-limb asymmetry.Twenty-four soccer players,randomly assigned to a 6-week unilateral strength and power training(UNI)(n=12)or a control group(CON)(n=12),performed single countermovement jump(SLCMJ),single leg broad jump(SLBJ),single leg drop jump(SLDJ),10-m sprint,and 505 change of direction(COD)speed test.Raw jump scores revealed small to large improve-ments in SLCMJ,SLBJ,and SLDJ reactive strength index(RSI)(g=0.46 to 1.66)in the UNI group,whereas negligible changes were found in the CON group(g=−0.31 to 0.33).Asymmetry indexes showed a moderate significant reduction in the SLDJ(RSI)and in the SLDJ stiffness(K)(g=1.00 to 1.11)in the UNI group.The between-group comparison indicated a significant change in the SLDJ(RSI)and in the SLDJ(K)(g=1.01 to 1.07)in favour of the UNI group.Thus,a unilateral training program seems to be able to reduce between-limb imbalances and foster improvements in jump performance,without any detrimental effects on linear or COD speed times.Given the importance of these physical characteristics for soccer,it is suggested that unilateral strength and power training are incorporated into strength training routines for players of all levels.展开更多
基金the Killam Foundation provided funding for this research
文摘Purpose： The aim of this study was to compare mechanical muscle function in the eccentric/concentric phases of vertical bilateral jumping in anterior cruciate ligament-reconstructed （ACLR）, elite （ELITE）, and adolescent （ADOL） alpine ski racers and ski cross athletes. Methods： Alpine ski racers/ski crossers （ACLR： n = 12, age = 26.7 ± 3.8 years; ELITE： n = 12, age = 23.9 ± 3.0 years; ADOL： n = 12, age = 17.8 ± 0.7 years; females： n = 6 per group, males： n = 6 per group） performed 5 maximal countermovement jumps （CMJs） and 5 squat jumps. The ground reaction forces for each limb were analyzed using dual force plate recording to obtain body center of mass （BCM） velocity, displacement, and power. The eccentric deceleration （ECC） and concentric phases were determined from BCM velocity. CMJ net concentric and ECC impulses were calculated （body mass normalized） along with the peak and mean BCM power and maximal vertical jump height. CMJ lower limb stiffness （LLS） was determined by the slope of the ground reaction forces vs. the BCM displacement curve over the ECC phase. Concentric and ECC asymmetry indices were calculated for each leg, and the left vs. right LLS was compared. Outcome measures （reported as mean ± SD） calculated as a 5-jump mean were normalized to body mass and compared using an analysis of variance. Results： No between-group differences were found for peak and mean power or jump heights. There were no group differences for LLS or net concentric phase impulse, but the net ECC impulse was lower in the ADOL group compared with ELITE skiers （ADOL： 1.33 ± 0.32 Ns/kg; ELITE： 1.59 ± 0.16 Ns/kg; p 〈 0.05）. Although no group differences were found for ECC asymmetry indices, a group × limb interaction was found for LLS （p 〈 0.01）, which was systematically higher in the right vs. the left limb of ADOL skiers （right： 54.1 ± 17.9 N/m/kg; left： 48.7 ± 15.7 N/m/kg;p 〈 0.01）. Conclusion： ADOL skiers demonstrated decreased ECC impulse and systematic right limb dominance in LLS compared with ACLR and ELITE skiers. The implication of these findings for injury and performance are unknown, but further investigation into these potential relationships is warranted.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.
文摘The aims of this study were(a)to investigate the effects of a unilateral training program in reducing inter-limb asymmetry in male soccer players;(b)to explore such effects on measures of physical performance and unilateral inter-limb asymmetry.Twenty-four soccer players,randomly assigned to a 6-week unilateral strength and power training(UNI)(n=12)or a control group(CON)(n=12),performed single countermovement jump(SLCMJ),single leg broad jump(SLBJ),single leg drop jump(SLDJ),10-m sprint,and 505 change of direction(COD)speed test.Raw jump scores revealed small to large improve-ments in SLCMJ,SLBJ,and SLDJ reactive strength index(RSI)(g=0.46 to 1.66)in the UNI group,whereas negligible changes were found in the CON group(g=−0.31 to 0.33).Asymmetry indexes showed a moderate significant reduction in the SLDJ(RSI)and in the SLDJ stiffness(K)(g=1.00 to 1.11)in the UNI group.The between-group comparison indicated a significant change in the SLDJ(RSI)and in the SLDJ(K)(g=1.01 to 1.07)in favour of the UNI group.Thus,a unilateral training program seems to be able to reduce between-limb imbalances and foster improvements in jump performance,without any detrimental effects on linear or COD speed times.Given the importance of these physical characteristics for soccer,it is suggested that unilateral strength and power training are incorporated into strength training routines for players of all levels.
