The Research Of Optimal Eccentric Load With Increasing Lower Limb Power

Objective:To observe the effects of load vertical jump(LVJ)with reducing the load in eccentric stage on lower limb power output and lower limb muscle activation,and to develop a new LVJ training method that can further improve the power output in traditional LVJ,at the same time,reducing the ground reaction force when landing.Methods:Sixteen young male athletes with long-term training experience were recruited as subjects.To test the maximum voluntary contraction(MVC)of the lower limbs in the semi-squat position with force plate and a fixed barbel.Then vertical jump with 10%,20%,30%,40%and 50%MVC,respectively,to measure the peak power of the LVJ,so as to obtain the optimal load(OL)of the subjects when the maximum peak power occurred.Each subject started LVJ with OL as the load,at the same time reduced the load in eccentric stage by 25%,50%,75%,100%OL respectively through computer-assisted barbell training system.At the same time maintain the concentric load is still the OL.Using force plate to test the ground reaction force under reducing different kinds of load in eccentric stage;Using red motion capture system measure the vertical jump height,the center of gravity vertical velocity,in the process of computing the peak power;Using wireless surface electromyography system to record the iEMG of gulteus maximus(GM),biceps femories muscle(BF),lateral gastrocnemius(LG),rectus femories(RF),vastus lateralis muscle(VLO),vastus medialis muscle(VMO)during LVJ.SPSS 21.0statistical software and Excel were used to analyze the data.Single-factor repeated measurement analysis of variance was used to compare each load in the group in pairs,with Bonferomi correction.The statistical results were expressed as (?)±sd,and the significance level was defined as P<0.05.Results:1.Under the load of 30%MVC(61.14±7.55w/kg),the peak powe was significantly higher than 10%MVC(58.28±6.55w/kg,P<0.05),20%MVC(59.04±7.80w/kg,P<0.05),50%MVC(56.29±7.02w/kg,P<005).2.LVJ with reducing load in eccentric stage:(1)The height of reducing 25%(037±0.06m,P<0.05),50%(038±0.06m,P<0.05),75%(0.37±0.05m,P<005),100%(037±0.06m,P<0.05)OL in eccentric stage was significantly higher than traditional LVJ(the eccentric and concentric load was the same,0.33±0.06m).(2)The peak power of reducing 50%(55.41±7.83w/kg,P<0.05)OL in eccentric stage was significantly higher than the traditional LVJ(51.95±7.62w/kg).(3)The maximal ground reaction force of reducing 25%(34.75±8.68N/kg,P<0.05),50%(29.81±4.55N/kg,P<0.05),75%(25.46±5.00n N/kg,P<0.05),100%(23.39±4.08N/kg,P<0.05)OL in eccentric stage was significantly higher than the traditional LVJ(44.8±8.0N/kg).(4)The iEMG in VLO of reducing 75%(87.30±44.95 u V·s,p<0.05),100%(89.55±45.27,u V·s,P<005)OL in eccentric stage were significantly higher than the traditional LVJ(109.04±52.82u V·s).The iEMG in VMO of reducing 100%(121.44±71.37u V·s,P<0.05)OL in eccentric stage were significantly higher than the traditional LVJ(149.34±80.81u V·s,P<0.05).Conclusion:The LVJ with the load in eccentric stage reduced can reduce the ground reaction force and increase the peak power further compared with traditional LVJ,which is a more safe and effective way to develop power.