Optimal Velocity Loss For Inducing Post Activation Potentiation In 85% 1RM Squat

Objective: Post-activation potentiation(PAP)is a physiological phenomenon caused by the acute increase of muscle force speed or explosive force caused by the maximum intensity resistance exercise for a short time in advance.The discovery of PAP provides a new way for athletes to improve their explosive power,which can benefit from the events such as sprint,long jump,throwing and so on.However,the existing PAP protocols all adopt the traditional weight-based load design,which has the defects of lack of accuracy and lack of individualization of fatigue control.In recent years,Velocity-Based Training(VBT)has been widely concerned by strength practitioners because of its advantage of accurate load.VBT is a method to monitor and adjust the resistance load in real time by using the strong correlation between action speed and% 1RM and the number of repetitions.Through the strong correlation between the percentage of velocity loss(VL)and the repetitions,VL is used to measure the load.Compared with the traditional method of measuring the load by the repetitions,the method of measuring the load by VL can not only ensure the accurate match between the real intensity of training and the target intensity,but also control the fatigue degree of each group,avoid excessive fatigue and achieve the same level of stimulation among individuals.However,the VL that causes the best PAP effect is not clear.Therefore,the purpose of this study is to explore the optimal VL to induce squat PAP.This study assumes that a lower VL will result in a better PAP.Methods: Twenty-two high-level track and field athletes from Shanghai University of Sport were selected(age 21.1 ±2.0yrs,training years 5.8 ±2.6yrs,1RM / body mass1.9 ±0.2).Using crossover design,subjects voluntarily participated in one squat 1RM test and four 85%1RM squat PAP tests.The interval of 5 tests were more than 48 hours,and all of them were carried out at the same time.Subjects were prohibited from strenuous exercise and drinking foods containing alcohol or caffeine within 24 hours before the experiment.Before the formal experiment,all the subjects were familiar with the site equipment and experimental process,and the 1RM squat test was performed one week before the squat PAP test.The test adopts incremental load test,and the squat movement standard refers to the(NSCA)neck back squat technical standard of the International Weightlifting Federation.In this study,the same squat rack and barbell were used to ensure the consistency of the test.Gym Aware Power Tool tachometer(Kinetic Performance Technologies,Canberra,Australia)was used to monitor the squatting speed of each squatting PAP activation test in real time.The subjects performed three reverse longitudinal jumps(Counter Movement Jump,CMJ)after 10 min standardized warm-up(5min’s 1km average speed warm-up run and 5min dynamic stretching activity)and sit-in 5min,and the best value was recorded.After that,the subjects took a 3-minute break and began to PAP protocols.In order to ensure the squatting range of the subjects,an elastic band was set at the height of the tuberosity of the tibia,and the buttocks were required to touch the elastic band when squatting.4 times of PAP protocols were carried out randomly,and the VL was 5%,10%,15% and 20% VL,respectively.2 groups were performed each time,and intermittent 1min was performed between groups.The squatting was ended when the actual VL ≥ specified value,and three times of CMJ(interval 10s)were performed at 10 s,4min,8min,12 min and 16 min after PAP protocol.The jump height,peak output power and impulse of each optimal CMJ,as well as the times of squatting during PAP protocol were recorded.The ambient temperature of the test was 20-24℃,and oral encouragement was given to the subjects throughout the process.All data were expressed by mean ±standard deviation(X ±SD).Excel was used for summary,and SPSS26.0,was used to repeatedly measure the jump height,peak output power and momentum of CMJ,and one-way ANOVA was used to analyze the number of squats.Results: The jump height,peak output power and impulse of subjects’ CMJ were analyzed by repeated measurement analysis of variance.The results showed that 10 s after PAP protocol,the jump height(P>0.05),peak output power(P>0.05)and momentum(P>0.05)of CMJ were lower than those of pretest(but not significant).The fatigue effect after protocol was not obvious.At 8 minutes after PAP protocol,the jump height(ES=0.73,P=0.038),peak output power(ES=0.73,P=0.038)and momentum(ES=0.72,P=0.041)of CMJ were significantly higher than those of pretest,and the PAP was obtained.When 10%,15% and 20%VL were used,10 s after PAP protocol,the jump height(P<0.001),peak output power(P<0.001)and momentum(P<0.001)of CMJ were significantly lower than those of pretest,and the fatigue effect was significant.The jump height(P>0.05),peak output power(P>0.05)and momentum(P>0.05)of CMJ at each time point after PAP protocol were higher than those of pretest(but not significant),and no PAP was obtained.The analysis of variance of squatting repetitions corresponding to different VL showed that the repetitions of the first group with 5%VL were significantly lower than those of20%VL(P<0.001),and 20%VL was significantly higher than that of 10%VL(P<0.001)and 15%VL(P=0.002).In the second group,the repetitions in 5%VL group was significantly lower than that in 15%VL(P=0.040)and 20%VL(P<0.001),and that in 20%VL was significantly higher than that in 10%VL(P=0.023),and the total repetitions in 5%VL was significantly less than that in 15%VL(P=0.003)and 20%VL(P<0.001),and 20%VL was significantly higher than that in 10%VL(P<0.001)and15%VL(P=0.002).Conclusions: When using 5%VL,85%1RM PAP protocol successfully induced PAP at 8 minutes after protocol,while 85%1RM squatting failed to induce PAP after protocol at 10%,15% and 20%VL.In addition,the repetitions corresponding to 10%,15% and 20% VL,5% VL are significantly less,and the PAP efficiency is higher.5%VL may be the best VL for squatting-induced PAP under 85%1RM intensity.