Load Quantification And Force Property Of Velocity Based Unilateral Strength Training

Background: Velocity based training(VBT)is a new method to quantify,monitor and adjust training load based on the strong correlation between movement velocity and intensity(%1RM),repetitions,and fatigue.VBT realizes the real-time monitoring,feedback and adjustment of the load and fatigue of strength training,which meets the development requirements of digital-driven strength training.Unilateral movement is an important part of strength training.However,at present,the available exercises of VBT are concentrated on bilateral,and lack of research on unilateral.it is not clear about the relationship between velocity and load,repletion,fatigue,and the biomechanical property in unilateral VBT.Purposes: The purpose of this study was to explore load quantification and property of typical unilateral movement Bulgarian squat VBT by systematically analysis on the relationship between movement velocity and %1RM(Study 1),the relationship between movement velocity and repetitions(study 2),the relationship between movement velocity and fatigue(study 3),and the kinematic and kinetic characteristics of lower limbs(study 4).Methods:1.The load velocity relationship in unilateral movements VBTA random cross design was used.75 male college athletes volunteered to participate in a total of 8 experiments with 2 familiar tests and 6 incremental load tests(2 devices ×3 exercises,free weight and Smith machine,Bulgarian squat,split squat,and back squat),in which the weight was gradually increased according the repetition velocity change.Gym Aware was used to record the mean velocity(MV)of each repetition.Individual and standard load velocity profile(LVP)were constructed according to the best MV for each load.The real %1RM value obtained by the experiment was used as the gold standard,and the estimated %1RM value was obtained by substituting the corresponding velocity value into each LVP.The value of %1RM was calculated by the interaction of individual LVP obtained by unilateral movement of left and right legs,Smith machine and free weight.A combination of ICC,CV,Bland-Altman,SEM were adopted to assess the validity of each LVP.2.The repetition velocity relationship in unilateral movements VBTA random cross design was used.25 male college athletes volunteered to participate in a total of 8 experiments with 2 familiar tests and 6 loads’ maximum number of repetitions tests of the Bulgarian squat with three(three intensities × two devices,65%,75%,and 85%1RM;free weights and Smith machine).Based on the maximum strength data obtained in Study I to set the load.The MV of each repetition was recorded by Gym Aware,and the maximum number of repetitions was also recorded.The individual quadratic polynomial regression model was constructed according to the velocity loss(VL)and repetition loss(RL)in each load condition.The position of highest repetition velocity and frequency of rebreaking 10,20,30,40%VL were calculated.A combination of T test,ICC,CV,Bland-Altman,SEM were adopted to assess the validity of individual RVP.Chi-square test was used to evaluate the difference of The position of highest repetition velocity and frequency of rebreaking each VL.3.The fatigue velocity relationship in unilateral movements VBTA random cross design was used.19 male college athletes volunteered to participate in a total of 6 tests with 2 familiar tests and four kinds of VL(5%,10%,20%,and maximum VL)tests in Smith Bulgarian squat at 75%1RM.The RPE,VAS,one-leg vertical jump and blood lactate were collected before and after the test.The Vicon 3D motion capture system and Noraxon wireless EMG system were used to record the kinematic(MV,knee Angle)and s EMG data,respectively.The effects of Bulgarian squat with different VL on s CMJ,blood lactic,RPE and VAS fatigue indexes were determined by two-factor(2 times ×4 VLs)repeated measure ANOVA.Pearson correlation coefficient was used to analyze the correlation between the mean power frequency(MF),median power frequency(MPF)of the s EMG and VL in the maximum VL group.4.The kinematic and kinetic property of Bulgarian squat in VBT5.A random cross design was used.The subjects were the same as Study 3.Subjects participated in a total of 4 experiments with 2 familiar tests and 2 formal tests including one different intensity tests(40%,50%,60%,70%,80%,90%1RM)and one 75%1RM to fatigue test at the maximum deliberate velocity.The Vicon three-dimensional motion capture system was used to obtain the barbell velocity and knee joint Angle.The Noraxon wireless EMG system was used to obtain the EMG amplitudes of the vastus lateralis,biceps femoris and gluteus maximus muscles of both legs.Two Kistler force tables were used to obtain the vertical ground reaction of the front and rear legs.Two-factor repeated measure ANOVA was used to analyze the relevant data.Results:1.Similar to the bilateral squat,the MV of Bulgarian squat and split squat of both devices were very high to practically perfectly correlated with %1RM(r >-0.88,p = 0.001),and the validity of %1RM of individual LVP was acceptable(ICC ≥ 0.75,CV < 10%).The validity of standard LVP was unacceptable(ICC ≥ 0.75,CV > 10%),and individual LVP was not interoperable between devices(CV: 12.18-16.67%),the predictive validity of the nonlinear equation was slightly better than that of the linear equation.The individual LVP of Bulgarian squat and split squat could not be interused between limbs(SEM > 5%1RM).2.The Bulgarian squat VL and RL were highly correlated with each other.The validity of 6 RVPs for predicting RL in Bulgarian squatters(3 loads × 2 devices,65%,75%,85%1RM,free weights and Smith frame)was acceptable,but it could not be used interoperable between devices and in 65%1RM of free weight.When ≥ 75%1RM,the highest MV in the group was mainly distributed in the first and second repetition(≥ 87.5%),and most of the MV in the first repetitionand the lowest MV in the group was mainly distributed in the last repetition.When ≤65%1RM,the distribution of the highest MV were relatively dispersed.With the increase of intensity and VL,the frequency of MV rebreaking threshold gradually decreased.Under the same load and VL,the threshold breaking ratio of free weight barbell was higher than that of Smith machine Bulgarian squat.3.5%,10%,20% and maximum VL all cause significant changes in fatigue levels.With the increase of VL,the fatigue levels of s CMJ,blood lactate,RPE and VAS increased,but there were differences in the acute response of different indexes.Blood lactate changed significantly with the increase of VL(p = 0.001),but s CMJ did not change significantly when the difference of VL was less than 10% (p ≥ 0.2).However,RPE and VAS had no significant change after VL≥20%(p ≥ 0.73).There is a significant high and moderate correlation between VL and the trend of MF(r: 0.55-0.64)and MPF(r: 0.31-0.44)of s EMG,respectively.4.Vastus lateralis in the foreleg,vastus lateralis in the rear leg,gluteus maximus and biceps femoris in the foreleg are the main muscle groups in the Bulgarian squat.With the increase of relative load and fatigue,the repetition MV decreased linearly and significantly,the maximum Angle of the concentric phase of the foreleg knee joint decreased gradually,and the EMG amplitude of the main muscle groups showed a nonlinear change,but showed a downward trend.There was no significant change in EMG amplitude at ≥50%1RM and at each stage of fatigue group.With the increase of load,the ground reaction force of the front leg increases significantly,while the ground reaction of the rear leg increases gently and significantly.The proportion of ground reaction force in front and rear legs remained stable(about 8:2).Conclusions: The movement velocity of unilateral movement is closely related to %1RM,repetitions and fatigue,which can be used to quantify the load of strength training in VBT.The LVP is individualized,and cannot be inter-used between free weights and Simth machine,left and right limbs.Low load,low VL and free weight interact to influence the accuracy of VL determination.The neuromuscular,metabolic,and subjective fatigue induced by VL were asynchronous.Bulgarian squat has obvious unilateral property,the force ratio of the front and rear legs,the activation level of the main muscle groups are less affected by load and fatigue.The asymmetrical force property and the knee joint stable requiements could not influence the movement velocity with load and fatigue.When performing unilateral VBT,practitioners should select appropriate LVP according to different populations,set VL according to different fatigue caused by VL,and pay attention to the accuracy of VL judgment when bearing low load,low VL threshold and free weight.