The effect of two different loading schemes and recovery types on kinematic and kinetic parameters in squat exercise

Understanding the kinematic and kinetic determinants associated with resistanceloading schemes is crucial to maximise neuromuscular adaptations especially musclehypertrophy to resistance training. The main purposes of this research was to determinewhether loading the muscle with lighter load-higher velocity movements would providesimilar or superior kinematics and kinetics to more traditional loading, heavy load-slowvelocity. In addition to understanding the kinematics and kinetics associated with thework period, the effects of exercise such as stretching and aerobic exercise during theinter-set rest period were investigated in the study. This thesis consists of two reviewpapers focused on the inter-set exercises, and five original studies as summarised below. The aim of the first study was to determine the set and session kinematic andkinetic characteristics of two training loads (35%, and 70% 1RM) when equated byvolume. Twelve recreationally trained men were recruited in this acute randomisedwithin-subject crossover design study. Two bouts of a half-squat exercise wereperformed one week apart; one with high load-low velocity (HLLV = 3 sets of 12 repsat 70% 1RM) and the other with light load-high velocity (LLHV= 6 sets of 12 reps at35% 1RM). Variables of interest for the eccentric and concentric phases included timeunder tension (TUT), average force (AF), peak force (PF), average power (AP), peakpower (PP), work (TW) and total impulse (TI), and were compared between loads. Foraverage eccentric and concentric single repetition values, significantly (p(~15-22%) peak power outputs were associated with the LLHV loading, whereassignificantly greater (~7-61%) values were associated with the HLLV condition formost other variables of interest. However, in terms of total session kinematics andkinetics, the LLHV protocol resulted in significantly greater (~16-61%) eccentric andconcentric TUT, PF, AP, PP, and TW. The only variable that was significantly greaterfor the HLLV than LLHV protocol was total impulse (~20-24%). From these results itseems that the LLHV protocol may offer an equal if not better training stimulus formuscular adaptation than the HLLV protocol, due to the greater time under tension,power, force and work output when the total volume of the exercise is equated.The second study compared the same kinematic and kinetic characteristics asthose in the first study between the two training loads (35%, and 70% 1RM) equated bytime under tension (TUT). Twelve recreationally trained men were recruited in thisacute randomised within-subject crossover design study. The 35% and 70% 1RMloading schemes were equated by TUT based on the ground reaction forces data of a half squat exercise. For both eccentric and concentric phases of the squat, variables ofinterest (TUT, AF, PF, AP, PP, TW and TI) were calculated and analysed. Ten out of 12variables were found to be greater in the lighter 35% 1RM loading scheme. The majorfindings were that significantly (Pwere found for both the eccentric and concentric phases for the 35% 1RM loadingscheme. However, significantly greater (~32-34%) eccentric and concentric totalimpulses were found for the heavier loading scheme. It would seem that when equatedby TUT, that lighter loading schemes offer similar peak and average forces but superiorvelocity and power outputs which may have interesting implications for high velocityhypertrophic adaptation. The third study examined if the session kinematics and kinetics of 35% 1RM and70% 1RM loading schemes equated by volume would differ significantly whenstretching (12-15 s static stretching of quadriceps, hamstrings and gluteals) wasundertaken during the inter-set rest periods (90 s). Twelve recreationally trained menwere recruited for this study. Squat AF, PF, AP, PP, TW and TI were quantified duringthe eccentric and concentric phases of two interventions, one involving stretch duringthe inter-set rest period and the other a non-stretch intervention. Total sessionkinematics and kinetics differed by ~0-7% between interventions; however, none ofthese differences were found to be significant (P < 0.05). It was concluded that lowerlimb active inter-set stretching did not adversely affect squat kinematics and kinetics.In the fourth study, the effects of aerobic exercise between sets on the sessionkinematics and kinetics of 35% 1RM and 70% 1RM loading schemes equated byvolume were investigated. Twelve recreationally trained men were recruited for thisstudy, and cycling exercise was undertaken during the 90 s inter-set rest period at a selfselected resistance with velocity between 50 to 70 rpm, corresponding to 50-60% ofmaximum heart rate. Squat AF, PF, AP, PP, TW, and TI were quantified using a forceplate and linear transducer. Blood lactate samples were taken prior to set one, after setone, after set two and after the last set performed. No significant (P9%) in lactate levels were found between the two loading schemes for any of thekinematic and kinetic variables of interest. However, significantly less (5-12%) lactateaccumulation was observed in the 35% 1RM scheme from the inception to thecompletion of loading. It was concluded that active recovery in the form of lowintensity cycling offered no additional benefits in term of lactate clearance andenhancement of set and session kinematics and kinetics. The final study compared between two squat exercises performed with heavy(HLLV; 70% 1RM) or light (LLHV; 35% 1RM) loads for vastus lateralis (VL) fasciclelength, strain, strain velocity and pennation angle changes during exercise. Tenrecreationally trained men performed 10 HLLV and LLHV squat repetitions on separatedays in a counter-balanced and randomised order. Ultrasonography was used to recordVL fascicle length, strain, strain velocity and pennation angle changes during theexercise, whilst vertical ground reaction forces (force platform) and bar displacement(position transducer) were simultaneously recorded. The time taken to complete 10repetitions was significantly (P± 2.4 s) but bar displacement (0.40 m) was the same. Mean fascicle length wassignificantly longer in both concentric and eccentric phases for LLHV and fasciclestrain was greater for LLHV (38.5 ± 8.5 mm) compared to HLLV (30.0 ± 2.8 mm).Fascicle strain velocity in both eccentric and concentric phases for LLHV (118.1 ± 19.1mm·s-1, 162.2 ± 35.2 mm·s-1) was significantly greater than that for HLLV (78.2 ± 17.4mm·s-1, 97.4 ± 25.3 mm·s-1). Pennation angle was significantly smaller for LLHV (12.9± 2.2º) than HLLV (14.8 ± 2.3º) only when measured at the bottom of the movement.These data show substantial fascicle shortening-lengthening behaviour differencesduring the squat exercises performed with different loads but with similar movementkinematics. Based on the study findings, it appears that LLHV loading offers more benefitsin term of velocity-specific hypertrophy compared with a heavier-slower hypertrophyloading that is traditionally prescribed, given that time under tension, force and work arethought critical determinants of hypertrophic adaptation, coupled with the highervelocities and power outputs associated with the 35% 1RM loading scheme. Regardingthe inter-set exercises, no negative effects of stretching on kinematics and kinetics wereevident, therefore there seems compelling reasons to stretch (active and/or passive)during the inter-set rest periods, as it is likely to increase the total time under tension ofthe muscle. Active recovery in the form of low intensity cycling during the inter-setrest period seemed to provide no effects on kinematics and kinetics as well as lactateclearance. However, it is not known whether the aerobic intensity utilised in this studywas optimal, and the effects of the exercise on other metabolic, hormonal, neural andmechanical parameters need to be quantified. More studies to validate results of thepresent study, especially longitudinal (training) studies to investigate the actual effecton muscle hypertrophy should be conducted.

Grantor dc:publisher

Edith Cowan University, Research Online, Perth, Western Australia

Year dc:date

2010

Author dc:creator

• Mohamad, Nur I.

• strength training
• hypertrophy
• heavy load
• resistance training
• Sports Sciences

Repository record dc:identifier

https://ro.ecu.edu.au/theses/145

OAI identifier oai:identifier

oai:ro.ecu.edu.au:theses-1145