Purpose:This study aimed to non-invasively test the hypothesis that(a) short-term lower limb unloading would induce changes in the neural control of force production(based on motor units(MUs) properties) in the vastus...Purpose:This study aimed to non-invasively test the hypothesis that(a) short-term lower limb unloading would induce changes in the neural control of force production(based on motor units(MUs) properties) in the vastus lateralis muscle and(b) possible changes are reversed by active recovery(AR).Methods:Ten young males underwent 10 days of unilateral lower limb suspension(ULLS) followed by 21 days of AR.During ULLS,participants walked exclusively on crutches with the dominant leg suspended in a slightly flexed position(15°-20°) and with the contralateral foot raised by an elevated shoe.The AR was based on resistance exercise(leg press and leg extension) and executed at 70% of each participant’s 1repetition maximum,3 times/week.Maximal voluntary isometric contraction(MVC) of knee extensors and MUs properties of the vastus lateralis muscle were measured at baseline,after ULLS,and after AR.MUs were identified using high-density electromyography during trapezoidal isometric contractions at 10%,25%,and 50% of the current MVC,and individual MUs were tracked across the 3 data collection points.Results:We identified 1428 unique MUs,and 270 of them(18.9%) were accurately tracked.After ULLS,MVC decreased by 29.77%,MUs absolute recruitment/derecruitment thresholds were reduced at all contraction intensities(with changes between the 2 variables strongly correlated),while discharge rate was reduced at 10% and 25% but not at 50% MVC.Impaired MVC and MUs properties fully recovered to baseline levels after AR.Similar changes were observed in the pool of total as well as tracked MUs.Conclusion:Our novel results demonstrate,non-invasively,that 10 days of ULLS affected neural control predominantly by altering the discharge rate of lower-threshold but not of higher-threshold MUs,suggesting a preferential impact of disuse on motoneurons with a lower depolarization threshold.However,after 21 days of AR,the impaired MUs properties were fully restored to baseline levels,highlighting the plasticity of the components involved in neural control.展开更多
This study analyzed the difference between using a downward breaststroke kick and a horizontal breaststroke kick in a sample of world class elite swimmers.We compared average muscle activity of the gluteus maximus,qua...This study analyzed the difference between using a downward breaststroke kick and a horizontal breaststroke kick in a sample of world class elite swimmers.We compared average muscle activity of the gluteus maximus,quadriceps femoris(vastus medialis and rectus femoris),hamstring/long head of the biceps femoris,gastrocnemius medialis,rectus abdominal,and erector spinae when using the downward breaststroke kick technique.We find that when this sample of swimmers utilized the downward breaststroke kick,max speed and velocity per stroke increased,measured by 12,788 EMG samples,where the results are highly correlated to duration of the aerodynamic buoyant force in breaststroke kick technique.The increases in performance observed from measuring the world class elite swimmers is highly correlated to the duration of the kick aerodynamic buoyant force.Among this sample of elite swimmers,the longer a swimmer demonstrates a buoyant force breaststroke kick,the lower the time in a 100 breaststroke.展开更多
基金funded by the Italian Space Agency, MARcatori biologici e funzionali per la biomeccanica aStronautica di PREcisione (Project number DC-VUM-2017-006)。
文摘Purpose:This study aimed to non-invasively test the hypothesis that(a) short-term lower limb unloading would induce changes in the neural control of force production(based on motor units(MUs) properties) in the vastus lateralis muscle and(b) possible changes are reversed by active recovery(AR).Methods:Ten young males underwent 10 days of unilateral lower limb suspension(ULLS) followed by 21 days of AR.During ULLS,participants walked exclusively on crutches with the dominant leg suspended in a slightly flexed position(15°-20°) and with the contralateral foot raised by an elevated shoe.The AR was based on resistance exercise(leg press and leg extension) and executed at 70% of each participant’s 1repetition maximum,3 times/week.Maximal voluntary isometric contraction(MVC) of knee extensors and MUs properties of the vastus lateralis muscle were measured at baseline,after ULLS,and after AR.MUs were identified using high-density electromyography during trapezoidal isometric contractions at 10%,25%,and 50% of the current MVC,and individual MUs were tracked across the 3 data collection points.Results:We identified 1428 unique MUs,and 270 of them(18.9%) were accurately tracked.After ULLS,MVC decreased by 29.77%,MUs absolute recruitment/derecruitment thresholds were reduced at all contraction intensities(with changes between the 2 variables strongly correlated),while discharge rate was reduced at 10% and 25% but not at 50% MVC.Impaired MVC and MUs properties fully recovered to baseline levels after AR.Similar changes were observed in the pool of total as well as tracked MUs.Conclusion:Our novel results demonstrate,non-invasively,that 10 days of ULLS affected neural control predominantly by altering the discharge rate of lower-threshold but not of higher-threshold MUs,suggesting a preferential impact of disuse on motoneurons with a lower depolarization threshold.However,after 21 days of AR,the impaired MUs properties were fully restored to baseline levels,highlighting the plasticity of the components involved in neural control.
文摘This study analyzed the difference between using a downward breaststroke kick and a horizontal breaststroke kick in a sample of world class elite swimmers.We compared average muscle activity of the gluteus maximus,quadriceps femoris(vastus medialis and rectus femoris),hamstring/long head of the biceps femoris,gastrocnemius medialis,rectus abdominal,and erector spinae when using the downward breaststroke kick technique.We find that when this sample of swimmers utilized the downward breaststroke kick,max speed and velocity per stroke increased,measured by 12,788 EMG samples,where the results are highly correlated to duration of the aerodynamic buoyant force in breaststroke kick technique.The increases in performance observed from measuring the world class elite swimmers is highly correlated to the duration of the kick aerodynamic buoyant force.Among this sample of elite swimmers,the longer a swimmer demonstrates a buoyant force breaststroke kick,the lower the time in a 100 breaststroke.
文摘目的应用表面肌电技术(sEMG)测定分析重复性操作时上肢肌肉的疲劳状态并探讨指标的适宜性。方法8名男性大学生志愿受试者在实验室(以平均40个/min的速度)连续地抓取、移动和放置零件(5 g),每完成80个零件为1个时间段(约2 min),共4组(约8 min)。同时遥测记录肱桡肌、肱二头肌、三角肌、斜方肌的表面肌电信号,采用时域、频域及肌电术振幅频谱联合分析方法(the joint analysis of EMG spectrum and amplitude,JASA)的指标进行分析。结果4块肌肉肌电的最大自主收缩百分比(the percent of maximal voluntary electrical activation,MVE%)随重复性操作时间延长均呈上升趋势(P>0.05)。中位频率(mean frequency,MF)和平均功率频率(mean power frequency,MPF)降低,即所谓频谱左移,只是在最后一两个时段不再下降,反而升高。所测肌肉肌电频率的斜率在第1时段均为负值,在其余3时段则出现时而为负值、时而又为正值的变动,MF和MPF及其斜率的变化趋势一致。JASA分析表明,上肢肌肉在动态作业过程中呈疲劳、恢复和负荷增加的变动。结论在本例重复性操作中,肌肉呈疲劳、恢复、负荷增加或再次疲劳的变化。累及的肌肉主要是斜方肌、三角肌和肱桡肌,肱二头肌次之。肌电指标(如MVE%,MF,MPF及其斜率)在操作过程中的变化可以反映动态劳动的肌肉疲劳,JASA分析证实了这一点。
