Title

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

Date of Award

2010

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Exercise, Biomedical and Health Sciences

Faculty

Computing, Health and Science

First Advisor

Professor John Cronin

Second Advisor

Professor Ken Nosaka

Abstract

Understanding the kinematic and kinetic determinants associated with resistance
loading schemes is crucial to maximise neuromuscular adaptations especially muscle
hypertrophy to resistance training. The main purposes of this research was to determine
whether loading the muscle with lighter load-higher velocity movements would provide
similar or superior kinematics and kinetics to more traditional loading, heavy load-slow
velocity. In addition to understanding the kinematics and kinetics associated with the
work period, the effects of exercise such as stretching and aerobic exercise during the
inter-set rest period were investigated in the study. This thesis consists of two review
papers 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 and
kinetic characteristics of two training loads (35%, and 70% 1RM) when equated by
volume. Twelve recreationally trained men were recruited in this acute randomised
within-subject crossover design study. Two bouts of a half-squat exercise were
performed one week apart; one with high load-low velocity (HLLV = 3 sets of 12 reps
at 70% 1RM) and the other with light load-high velocity (LLHV= 6 sets of 12 reps at
35% 1RM). Variables of interest for the eccentric and concentric phases included time
under tension (TUT), average force (AF), peak force (PF), average power (AP), peak
power (PP), work (TW) and total impulse (TI), and were compared between loads. For
average eccentric and concentric single repetition values, significantly (p(~15-22%) peak power outputs were associated with the LLHV loading, whereas
significantly greater (~7-61%) values were associated with the HLLV condition for
most other variables of interest. However, in terms of total session kinematics and
kinetics, the LLHV protocol resulted in significantly greater (~16-61%) eccentric and
concentric TUT, PF, AP, PP, and TW. The only variable that was significantly greater
for the HLLV than LLHV protocol was total impulse (~20-24%). From these results it
seems that the LLHV protocol may offer an equal if not better training stimulus for
muscular 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 as
those in the first study between the two training loads (35%, and 70% 1RM) equated by
time under tension (TUT). Twelve recreationally trained men were recruited in this
acute randomised within-subject crossover design study. The 35% and 70% 1RM
loading 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 of
interest (TUT, AF, PF, AP, PP, TW and TI) were calculated and analysed. Ten out of 12
variables were found to be greater in the lighter 35% 1RM loading scheme. The major
findings were that significantly (Pwere found for both the eccentric and concentric phases for the 35% 1RM loading
scheme. However, significantly greater (~32-34%) eccentric and concentric total
impulses were found for the heavier loading scheme. It would seem that when equated
by TUT, that lighter loading schemes offer similar peak and average forces but superior
velocity and power outputs which may have interesting implications for high velocity
hypertrophic adaptation.

The third study examined if the session kinematics and kinetics of 35% 1RM and
70% 1RM loading schemes equated by volume would differ significantly when
stretching (12-15 s static stretching of quadriceps, hamstrings and gluteals) was
undertaken during the inter-set rest periods (90 s). Twelve recreationally trained men
were recruited for this study. Squat AF, PF, AP, PP, TW and TI were quantified during
the eccentric and concentric phases of two interventions, one involving stretch during
the inter-set rest period and the other a non-stretch intervention. Total session
kinematics and kinetics differed by ~0-7% between interventions; however, none of
these differences were found to be significant (P < 0.05). It was concluded that lower
limb 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 session
kinematics and kinetics of 35% 1RM and 70% 1RM loading schemes equated by
volume were investigated. Twelve recreationally trained men were recruited for this
study, 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% of
maximum heart rate. Squat AF, PF, AP, PP, TW, and TI were quantified using a force
plate and linear transducer. Blood lactate samples were taken prior to set one, after set
one, 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 the
kinematic and kinetic variables of interest. However, significantly less (5-12%) lactate
accumulation was observed in the 35% 1RM scheme from the inception to the
completion of loading. It was concluded that active recovery in the form of low
intensity cycling offered no additional benefits in term of lactate clearance and
enhancement 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) fascicle
length, strain, strain velocity and pennation angle changes during exercise. Ten
recreationally trained men performed 10 HLLV and LLHV squat repetitions on separate
days in a counter-balanced and randomised order. Ultrasonography was used to record
VL fascicle length, strain, strain velocity and pennation angle changes during the
exercise, whilst vertical ground reaction forces (force platform) and bar displacement
(position transducer) were simultaneously recorded. The time taken to complete 10
repetitions was significantly (P± 2.4 s) but bar displacement (0.40 m) was the same. Mean fascicle length was
significantly longer in both concentric and eccentric phases for LLHV and fascicle
strain 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 ± 19.1
mm·s-1, 162.2 ± 35.2 mm·s-1) was significantly greater than that for HLLV (78.2 ± 17.4
mm·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 differences
during the squat exercises performed with different loads but with similar movement
kinematics.

Based on the study findings, it appears that LLHV loading offers more benefits
in term of velocity-specific hypertrophy compared with a heavier-slower hypertrophy
loading that is traditionally prescribed, given that time under tension, force and work are
thought critical determinants of hypertrophic adaptation, coupled with the higher
velocities and power outputs associated with the 35% 1RM loading scheme. Regarding
the inter-set exercises, no negative effects of stretching on kinematics and kinetics were
evident, 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 of
the muscle. Active recovery in the form of low intensity cycling during the inter-set
rest period seemed to provide no effects on kinematics and kinetics as well as lactate
clearance. However, it is not known whether the aerobic intensity utilised in this study
was optimal, and the effects of the exercise on other metabolic, hormonal, neural and
mechanical parameters need to be quantified. More studies to validate results of the
present study, especially longitudinal (training) studies to investigate the actual effect
on muscle hypertrophy should be conducted.

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