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Pushing up or pushing out—an initial
investigation into horizontal- versus
vertical-force training on swimming start
performance: a pilot study
Shiqi Thng
1,2
, Simon Pearson
2
and Justin W.L. Keogh
1,3,4,5
1Faculty of Health Sciences and Medicine, Bond University, Gold Coast, QLD, Australia
2Queensland Academy of Sport, Nathan, QLD, Australia
3Sports Performance Research Centre New Zealand, Auckland University of Technology,
Auckland, New Zealand
4Cluster for Health Improvement, Faculty of Science, Health, Education and Engineering,
University of the Sunshine Coast, Sippy Downs, QLD, Australia
5Kasturba Medical College, Mangalore, Manipal Academy of Higher Education, Manipal,
Karnataka, India
ABSTRACT
Background: The block phase in the swimming start requires a quick reaction to the
starting signal and a large take-off velocity that is primarily horizontal in direction.
Due to the principle of specificity of training, there is a potential benefitof
performing a greater proportion of horizontal force production exercises in a
swimmers’dry-land resistance training sessions. Therefore, the purpose of this pilot
study was to provide an insight into the effects of a horizontal- (HF) vs vertical-force
(VF) training intervention on swim start performance.
Methods: Eleven competitive swimmers (six males (age 20.9 ± 1.8 years, body mass
77.3 ± 9.7 kg, height 1.78 ± 0.05 m) and five females (age 21.4 ± 2.0 years, body mass
67.5 ± 7.4 kg, height 1.69 ± 0.05 m)) completed 2 weekly sessions of either a
horizontal- or vertical-force focused resistance training programme for 8 weeks.
Squat jump force-time characteristics and swim start kinetic and kinematic
parameters were collected pre- and post-intervention.
Results: Across the study duration, the swimmers completed an average of nine
swimming sessions per week with an average weekly swim volume of 45.5 ± 17.7 km
(HF group) and 53 ± 20.0 km (VF group), but little practice of the swim start per
week (n= 9). Within-group analyses indicated a significant increase in predicted one
repetition maximum (1RM) hip thrust strength in the HF group, as well as significant
increases in grab resultant peak force but reductions in resultant peak force of the
block phase for the VF group. No significant between-group differences in predicted
1RM hip thrust and back squat strength, squat jump force-time and swim start
performance measures were observed after 8 weeks of training. Significant
correlations in the change scores of five block kinetic variables to time to 5 m were
observed, whereby increased block kinetic outputs were associated with a reduced
time to 5 m. This may be indicative of individual responses to the different training
programmes.
Discussion: The results of this current study have been unable to determine whether
a horizontal- or vertical-force training programme enhances swim start performance
How to cite this article Thng S, Pearson S, Keogh JWL. 2021. Pushing up or pushing out—an initial investigation into horizontal- versus
vertical-force training on swimming start performance: a pilot study. PeerJ 9:e10937 DOI 10.7717/peerj.10937
Submitted 21 September 2020
Accepted 21 January 2021
Published 24 February 2021
Corresponding author
Shiqi Thng,
shiqi.thng@student.bond.edu.au
Academic editor
Tim Doyle
Additional Information and
Declarations can be found on
page 13
DOI 10.7717/peerj.10937
Copyright
2021 Thng et al.
Distributed under
Creative Commons CC-BY 4.0
after an 8-week training intervention. Some reasons for the lack of within and
between group effects may reflect the large volume of concurrent training and the
relative lack of any deliberate practice of the swim start. Larger samples and longer
training duration may be required to determine whether significant differences
occur between these training approaches. Such research should also look to
investigate how a reduction in the concurrent training loads and/or an increase in
the deliberate practice of the swim start may influence the potential changes in swim
start performance.
Subjects Kinesiology, Orthopedics
Keywords Swim start, Swimming, Specificity of training, Force-vector theory, Resistance training
INTRODUCTION
The important role that muscular strength and power play in enhancing swimming
performance has led to the widespread adoption of dry-land resistance training modalities
into a concurrent training model for competitive swimmers (Aspenes et al., 2009;Crowley,
Harrison & Lyons, 2017;Haycraft & Robertson, 2015). While much of the swimming
strength and conditioning research has been on the free swim portion (Crowley,
Harrison & Lyons, 2017), there is now a greater focus on starts and turns since swimmers
have to rapidly apply large forces on the starting block or wall to increase horizontal
impulse and velocity (Born et al., 2020;Jones et al., 2018;Rebutini et al., 2014).
Changes in the starting block and starting technique may have further increased the
importance of lower body strength and power for swim start performance. The OSB11
start block, which was introduced by the International Swimming Federation in 2010, has
an angled kick plate at the rear of the block that enables the swimmer to adopt a kick start
technique (Tor, Pease & Ball, 2015a). The additional kick plate allows for an increased
duration of effective force application (i.e. greater horizontal force component) on the
blocks, which can increase horizontal impulse and take-off velocity (Honda et al., 2010).
With the new OSB11 start block and kick start technique, the swim start may share
some similarities to the sprint start in track and field regarding the starting position,
importance of a quick reaction to the starting stimulus, and the need to produce large
horizontal impulse on the starting blocks (Čoh et al., 2017;Harland & Steele, 1997).
Analysis of the force-time characteristics of swimmers performing the squat jump has
identified concentric impulse as a strong predictor of swim start performance as assessed
by time to 5 m and 15 m (Thng et al., 2020). Further, near perfect correlations (r> 0.90)
between countermovement jump height or take-off velocity and very large correlations
for measures of maximal strength (r= 0.7–0.9) to swim start performance have been
reported in a recent systematic review (Thng, Pearson & Keogh, 2019).
Despite the strength of this cross-sectional literature (Thng, Pearson & Keogh, 2019),
there is relatively little research quantifying the chronic effects of resistance training on
swim start performance. Three studies have utilised jump and plyometric exercise
programmes (Bishop et al., 2009;Rebutini et al., 2014;Rejman et al., 2017), two studies
(Breed & Young, 2003;Garcia-Ramos et al., 2016) used a more general resistance training
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 2/16
programme, and one study (Born et al., 2020) compared the effects of maximal strength
resistance training to plyometrics. The three plyometric studies included adolescent
(Bishop et al., 2009) and national level swimmers (Rebutini et al., 2014;Rejman et al., 2017)
who performed 6–9 weeks of plyometrics, twice a week. Significant improvements in
time to 5 m and 5.5 m, take-off velocity, horizontal forces and impulse were observed
as a result of these plyometric exercise programmes (Bishop et al., 2009;Rebutini et al.,
2014;Rejman et al., 2017). In contrast, the remainder of these plyometric and resistance
training studies typically reported no significant changes in time to 5 m or 15 m, or
any block phase kinetic or kinematic characteristics (Born et al., 2020;Breed &
Young, 2003;Garcia-Ramos et al., 2016). The only exception to this was the significant
improvements in time to 5 m and 15 m observed for the subset of under 17-year-old
swimmers who performed maximal strength training, with no such effects reported for
the under 17-year-old plyometric group (Born et al., 2020).
A possible explanation for the uncertainty regarding whether jump/plyometric or more
general resistance training programmes produces greater improvements in swim start
performance may reflect the direction-specific nature of resistance training. In a review
by Randell et al. (2010) on the specificity of resistance training to sports performance,
it was proposed training adaptations may be direction-specific, and that athletes who
are required to apply forces in the horizontal plane should perform several exercises
containing a horizontal component. More recently, this directional specificity of training
has been referred to as the force-vector theory (Fitzpatrick, Cimadoro & Cleather,
2019), with the hip thrust and prowler push/heavy sled pull being two of the most
commonly used horizontal-force exercises (Contreras et al., 2017;Fitzpatrick, Cimadoro &
Cleather, 2019;Morin et al., 2017;Winwood et al., 2015). A study by Contreras et al.
(2017) using the hip thrust significantly improved 10 m and 20 m sprint running times
(−1.05% and −1.67%, respectively) compared to the front squat, which is a vertical-force
exercise (+0.10% and −0.66%, respectively). The prowler push, which requires the athlete
to push a loaded sled in the horizontal plane, has been shown to closely mimic the
horizontal plane power requirements of sprinting (Tano et al., 2016). A study involving
30 sub-elite rugby players observed that a horizontal-focused resistance training
programme including the prowler push significantly improved performance in a number
of strength, sprinting, and change of direction tests (Winwood et al., 2015). However, no
significant between-group effects were observed between the horizontal-focused and
traditional resistance training programmes (Winwood et al., 2015).
The potential direction specificity of resistance training exercises for improving
aspects of swim start performance has been examined in two jump and plyometric training
studies (Rebutini et al., 2014;Rejman et al., 2017) and two acute training studies
utilising post-activation potentiation (PAP) (Cuenca-Fernandez, Lopez-Contreras & Arellano,
2015;Cuenca-Fernández et al., 2018). Rebutini et al. (2014) and Rejman et al. (2017)
observed a 10.4% and 13.8% increase in take-off velocity in the swim start post 9- and 6-weeks
of plyometric training, respectively, that included a variety of horizontal jumps. Acute
improvements in time to 5 m (Cuenca-Fernandez, Lopez-Contreras & Arellano, 2015;
Cuenca-Fernández et al., 2018) and 15 m (Cuenca-Fernandez, Lopez-Contreras & Arellano, 2015)
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 3/16
after performing PAP protocols that were biomechanically similar to the foot position in
the kick start on the OSB11 start block have also been observed. However, out of these four
plyometric and PAP studies, only one (Cuenca-Fernandez, Lopez-Contreras & Arellano,
2015) utilised the OSB11 start block and the kick start technique currently used by high
performance swimmers.
Therefore, the primary aim of this pilot study was to gain some preliminary insight
into the comparative effects of a horizontal- vs vertical-force resistance training
programme on swim start performance and squat jump (SJ) force-time characteristics.
A secondary aim of the study was to better understand how changes in certain SJ
force-time characteristics may be correlated with the changes in swim start performance in
competitive swimmers.
MATERIALS AND METHODS
Experimental design
An 8-week training programme sought to examine how a horizontal-force (HF) compared
to vertical-force (VF) oriented emphasis resistance training programme would potentially
alter swim start performance. Participants were randomly assigned to either a HF or
VF training group (HF: n= 6, VF: n= 7), with each group performing two resistance
training sessions per week.
Participants
Thirteen participants (8 males (age 21.0 ± 1.6 years, body mass 78.6 ± 8.3 kg, height
1.80 ± 0.06 m), and 5 females (age 21.4 ± 2.0 years, body mass 67.5 ± 7.4 kg, height
1.69 ± 0.05 m)) volunteered to participate in this study. Participants were national level
swimmers with at least 4 years’experience in competing in national championships and at
least 1 year of land-based resistance training experience that included the barbell back
squat and hip thrust under the supervision of a strength and conditioning coach.
Participants with any known contraindication to maximal training performance and/or
injuries that would interfere with their ability to complete the study or compromise
their health and wellness were excluded. Prior to participating in this study, participants
were briefed on the experimental design and gave written informed consent to participate
in the study. This investigation was conducted in accordance with the Declaration of
Helsinki and approved by Bond University Human Research Ethics Committee (00088).
Assessments were conducted at baseline (week one) and the end of the training
programme (week nine). Participants were instructed to maintain their nutritional and
sleep habits, and to avoid alcohol and caffeine consumption for at least 24 h before
testing sessions. All tests were performed on the same day of the week between 7:00 am and
11:00 am. Participants reported to the gymnasium to perform the squat jump test prior to
the swim start performance test.
Training intervention
The training programme was organised into two phases. In the first phase (weeks one
to four), each group performed three HF and VF lower body exercises, respectively.
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 4/16
A direction specific lower body jump was added in the second phase for each group
(weeks five to eight) (Table 1). The HF training group was prescribed a ‘start jump’
which is a jump for horizontal distance initiated from a mimicked swim start position
(Fig. 1), while the VF training group performed the squat jump. When performing the
jumps, the HF group were instructed to jump as far forward as possible, while the VF
group were instructed to jump as high as possible with each jump.
Participants performed the training programme utilising sets and repetition ranges
typically used for developing maximal strength (Bird, Tarpenning & Marino, 2005).
Participants followed two 4-week mesocycles using a 3:1 loading paradigm, with a
progressive increase in load for the first 3 weeks followed by a reduction in load in the
fourth week (Turner, 2011). This was considered important as the swimmers were still
maintaining high volumes of swimming training throughout the intervention. As the
majority of propulsive forces in the free swim phase comes from the upper body (Morouço
et al., 2015), both groups also performed three sets of several upper body exercises
including pull-ups, bench pull or seated row; and three sets of exercises for the
abdominals/lower back region, as successfully used by Contreras et al. (2017) in a previous
horizontal- vs vertical-force direction study. Sets were separated by a 1-min rest period
(Ritchie et al., 2020). Training records were kept for each participant to analyse the
load progression of the training programme. Predicted one repetition maximum (1RM) of
the hip thrust and barbell back squat was calculated pre- and post-intervention using the
Brzycki equation: Predicted 1RM = weight lifted/1.0278-0.0278 (no. of repetitions)
(Brzycki, 1993). Repetition ranges used in the predicted 1RM was performed during the
first training session (estimated from eight repetitions) and at the last training session
Table 1 An outline of the 8-week intervention programme for the Horizontal-Force (HF; n= 6) and Vertical-Force (VF; n= 5) training group
with weekly sets, repetition, and load progression for the lower body strength and jumping exercises.
Intervention
Group
Day Exercise Training focus
Strength Strength-power
Training week
12345678
Sets ×
reps
Sets ×
reps
Sets ×
reps
Sets ×
reps
Sets ×
reps
Sets ×
reps
Sets ×
reps
Sets ×
reps
HF group 1a Barbell hip thrust 3 × 8 3 × 8 3 × 6 2 × 6 3 × 5 3 × 5 3 × 4 2 × 4
1b ‘Start’jump 3 × 3 3 × 3 3 × 3 2 × 3
2a Prowler push
^
3×83×83×62×63×53×53×42×4
2b Drop vertical jump 3 × 3 3 × 3 3 × 3 2 × 3
VF group 1a Back squat 3 × 8 3 × 8 3 × 6 2 × 6 3 × 5 3 × 5 3 × 4 2 × 4
1b Squat jump 3 × 3 3 × 3 3 × 3 2 × 3
2a Rear foot elevated
split squat
^
3×83×83×62×63×53×53×42×4
2b Drop vertical jump 3 × 3 3 × 3 3 × 3 2 × 3
Note:
^
Repetitions listed are for each leg.
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 5/16
(estimated from four repetitions). Participants were asked to refrain from performing any
additional resistance training and to maintain their current diet for the course of this study.
Squat jump test
The SJ test was collected as previously described by Thng et al. (2020). All participants
completed a standardised dynamic warm-up consisting of a predetermined series of
dynamic joint ranges of motion of the upper and lower body under the supervision of a
strength and conditioning coach. Participants were then given two practice SJs before the
test was conducted. All SJs were performed on a force platform (FD4000; ForceDecks,
London, United Kingdom), with a sample rate of 1,000 Hz. Participants started in an
upright standing position with their hands on their hips and were instructed to keep their
hands on their hips to prevent the influence of any arm movements for the jump trials.
All participants were instructed to adopt a squat position using a self-selected depth
that was held for 3 seconds before attempting to jump as high as possible (Mitchell
et al., 2017). A successful trial was one that did not display any small amplitude
countermovement at the start of the jump phase on the force trace (Sheppard & Doyle,
2008). All participants performed three maximal effort SJs with a 30-s passive rest between
each effort. The SJ trial with the highest jump height was kept for data analysis. Jump
height was determined by the flight-time method (Jump height = gt
2
/8, where gis the
Figure 1 Initial positioning of the ‘start’jump for the Horizontal-Force (HF) training group.
Full-size
DOI: 10.7717/peerj.10937/fig-1
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 6/16
acceleration due to gravity and tis the flight time) (Linthorne, 2001). Ground reaction
force data from the SJs were analysed using the commercially available ForceDecks
software (ForceDecks, London, United Kingdom). A description of the SJ variables that
were identified by Thng et al. (2020) as significant predictors of swim start performance
were extracted for analysis are provided in Table 2.
Swim start performance test
Swim starts were collected using methods as described by Thng et al. (2020). Prior to the
swim start test, all swimmers completed a pool-based warm-up based on their usual
pre-race warm-up routine. Participants then performed three maximal effort swim
starts to 15 m with their main swim stroke (front crawl (n= 8), butterfly(n= 3), or
breaststroke (n= 2)) and preferred kick plate position, which was recorded to ensure
consistency between testing sessions. Trials were started as per competition conditions
and swimmers were instructed to swim to a distance past the 15 m mark, in order to ensure
that representative values at the 15 m distance were obtained (Barlow et al., 2014).
Two-minutes of passive recovery were given between each trial (Tor, Pease & Ball, 2015b).
The start with the fastest 15 m time was selected for further analysis. Swim starts were
Table 2 Description of squat jump variables obtained from the ForceDecks force platform, and the swim start variables obtained from the
KiSwim Performance Analysis System.
Variable Description
ForceDecks SJ
variables
Concentric impulse (N.s.) Net impulse of vertical force during the concentric phase
Concentric mean power (W) Mean power during concentric phase
Concentric rate of power
development (RPD) (W/s)
Rate of power development between start of concentric phase to peak power
Jump height (cm) Jump height calculated from Flight Time (time between take-off and landing) in centimetres
Reactive strength index
modified (RSImod) (m/s)
Jump height (Flight Time) divided by contraction time
KiSwim swim start
kinetic variables
Average acceleration (m/s/s) Horizontal take-off velocity/seconds from starting gun to take-off
Average power (W/kg) The average power relative to the swimmers’body mass produced from the starting signal to
when the swimmer leaves the starting block. This was calculated as the product of
(absolute force × absolute velocity)/body mass
Horizontal take-off velocity
(m/s)
The horizontal take-off velocity calculated by integrating horizontal acceleration
Work/kg (J/kg) Average power × seconds from the starting gun to take-off
Front horizontal peak force (N) Peak horizontal force on the front plate of the starting block (grab bar component not
subtracted)
Grab resultant peak force
(N/BW)
Peak grab bar resultant force
Rear horizontal peak force (N) Peak horizontal force on the foot plate (grab bar component not subtracted)
Total resultant peak force (N) Peak resultant force (grab bar component subtracted)
Rear resultant average force
(N/BW)
Average resultant force on the foot plate (grab bar component not subtracted)
Swim start
performance times
Time to 5 m and 15 m (s) Time from the starting signal to a swimmers’head crossing the 5 m and 15 m mark. This is
digitised at the point where the centre of the swimmers’head crosses 5 m and 15 m
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 7/16
collected using a Kistler Performance Analysis System—Swimming (KiSwim, Kistler
Winterthur, Switzerland), which utilises a force instrumented starting block, constructed
to match the dimensions of the Omega OSB11 block (KiSwim Type 9691A1; Kistler
Winterthur, Switzerland). Time to 5 m and 15 m were collected using five calibrated
high speed digital cameras operating at 100 frames per second, synchronised to the
instrumented KiSwim starting block. One camera was positioned 0.95 m above the water
and 2.5 m perpendicular to the direction of travel to capture the start and entry of
swimmer into the water, while the other three cameras were positioned 1.3 m underwater
at 5 m, 10 m and 15 m perpendicular to the swimmer to capture the time to 15 m.
The times to 5 m and 15 m were defined as the time elapsed from the starting signal until
the apex of the swimmer’s head passed the respective distances (Tor, Pease & Ball, 2015b).
An Infinity Start System (Colorado Time Systems, Loveland, CO, USA) provided an
audible starting signal to the athletes and an electronic start trigger to the KiSwim
system. Kinetic and kinematic variables of block performance extracted for analysis were
identified by Thng et al. (2020) as key predictors of time to 5 m and 15 m (Thng et al., 2021,
unpublished data). A description of the swim start variables analysed are provided in
Table 2.
Statistical analysis
Descriptive statistics are reported as mean ± SD for normally distributed continuous
variables and frequencies for categorical variables. Normality was checked using
histograms, normal Q–Q plots, and the Shapiro–Wilk test. A paired sample t-test was used
to determine whether statistically significant differences were found between pre- and
post-test means within each group. Independent t-tests were carried out to test for the
difference in change in the outcome between intervention groups. Effect sizes (ES) with
95% confidence intervals (95% CI) were reported in standardised (Cohen’s d) units as the
change in mean to quantify the magnitude of differences within (i.e. post-intervention—
pre-intervention results) and between the two intervention groups (i.e. HF and VF).
Criteria to assess the magnitude of observed changes were: 0.0–0.2 trivial; 0.20–0.60 small;
0.60–1.20 moderate; and >1.20 large (Hopkins, 2002). Effect sizes were calculated using a
programme created by Lenhard & Lenhard (2016).
To gain some preliminary insight into how changes in the SJ force-time characteristics
may be correlated with the changes in swim start performance, the association between the
change scores (calculated as the difference between each individuals’pre- and post-test
scores) for these outcomes were assessed by Pearson’s product-moment correlation
coefficient (r). Data were analysed with SPSS version 23.0.0 (SPSS Inc., Chicago, IL, USA).
P-values < 0.05 were deemed to indicate statistical significance.
RESULTS
Training compliance
Of the 13 initial participants, 11 participants completed the training study (Table 3).
Two participants were removed due to moving to another swim squad (n= 1) and
non-adherence to the training protocol (n= 1). Participants completed a total of 14 ± 3 out
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 8/16
of 16 training sessions, with the primary reasons for missed training sessions being
short-term illness or domestic competitions. A summary of the within-group and
between-group changes are provided in Table 4.
Within-group changes post-intervention
Only three significant within-group differences were observed across both groups. For the
HF group, a significant increase in predicted 1RM hip thrust strength (p= 0.04) was
observed. The VF group had a significant increase in KiSwim grab resultant peak force
(p= 0.007) and a significant decrease in KiSwim resultant peak force (p= 0.02).
Between-group changes post-intervention
A greater increase in predicted 1RM strength for the hip thrust was observed in the HF
training group (50%) than the increase in back squat strength for the VF training
group (18%) after 8 weeks of training (ES = 1.36). Moderate effect sizes were observed in
two SJ force-time variables and five KiSwim variables (Table 4). Specifically, moderate
effect size improvements in SJ jump height and three swim start kinetic measures were
observed in the HF group. In the VF group, SJ concentric RPD and two swim start kinetic
measures favoured moderate effect size improvements in the VF group.
When looking at individual changes across both groups, no significant correlations were
observed between the change scores in any of the ForceDecks outcome measures and time
to 5 m or 15 m. Similarly, there were no significant correlations in the change score
correlations between the KiSwim outcomes and time to 15 m. However, significant
correlations between the change scores for five KiSwim outcomes and time to 5 m
were observed. These were average acceleration (r=−0.82, p= 0.02), horizontal take-off
velocity (r=−0.81, p= 0.03), average power (r=−0.77, p= 0.05), work (r=−0.74, p= 0.01)
and rear resultant average force (r=−0.71, p= 0.02).
DISCUSSION
The present pilot study was designed to provide some insight into the potential directional
specificity of resistance training (now referred to as the force-vector theory) on swim start
performance and squat jump (SJ) force-time characteristics in competitive swimmers.
This was achieved by examining the within- and between-group training-related changes
in swim start performance for two groups of competitive swimmers, who differed on
Table 3 Physical characteristics of participants (N= 11).
Variables HF group (n= 6) VF group (n=5)
Age (years) 21.3 ± 1.7 21.0 ± 2.2
Sex (male/female) 3/3 3/2
Body mass (kg) 74.3 ± 10.5 70.0 ± 10.3
Height (m) 1.73 ± 0.06 1.74 ± 0.08
Weekly in-water training volume (km) 45.5 ± 17.7 53.0 ± 20.0
Weekly number of swim starts performed 9 ± 2 9 ± 2
Note:
All data, apart from the sex of the participants are presented as means and standard deviations.
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 9/16
Table 4 Pre- (week 1) and post- (week 9) measures of squat jump force-time variables and swim start kinetic and kinematic parameters for the
horizontal-force (HF) and vertical-force (VF) training groups. Results are presented as mean ± SD except for effect sizes and change scores.
HF group (n= 6) VF group (n= 5) Between-group differences
Week 1 Week 9 Change
scores
Within-group
ES (95% CI)
Week 1 Week 9 Change
scores
Within-group
ES (95% CI)
Mean difference
(95% CI)
ES (95% CI)
Predicted 1RM strength
Hip thrust (kg) 78.5 ±
15.0
118.3 ±
26.9
39.8 ±
16.6**
1.83
[−0.08 to 3.73]
Barbell back squat
(kg)
70.6 ±
27.0
85.20 ±
38.67
14.6 ±
20.8
0.44
[−1.34 to 2.21]
25.23
[−0.23 to 50.70]
1.36
[0.04–2.67]
SJ force-time variables
Jump height (cm) 28.4 ± 7.5 29.1 ± 7.0 0.8 ± 3.1 0.11
[−1.50 to 1.71]
29.0 ±
10.7
27.1 ± 8.3 −1.9 ±
2.9
−0.19
[−1.95 to 1.56]
2.63
[−1.50 to 6.76]
0.87
[−0.37 to 2.11]
Concentric impulse
(N.s.)
183.2 ±
46.2
182.3 ±
49.4
−0.9 ± 7.6 −0.02
[−1.62 to 1.58]
167.3 ±
43.3
165.3 ±
44.1
−2.0 ±
8.4
−0.05
[−1.80 to 1.71]
1.06
[−9.84 to 11.97]
0.14
[−1.05 to 1.33]
RSImod (m/s) 0.79 ±
0.16
0.73 ±
0.21
−0.07 ±
0.10
−0.32
[−1.93 to 1.29]
0.75 ±
0.30
0.73 ±
0.33
−0.02 ±
0.14
−0.06
[−1.82 to 1.69]
−0.04
[−0.20 to 0.12]
−0.42
[−1.62 to 0.78]
Concentric mean
power (W)
1414.2 ±
387.6
1442.0 ±
527.8
27.8 ±
174.6
0.06
[−1.54 to 1.66]
1268.0 ±
437.5
1241.0 ±
587.7
−27.0 ±
254.8
−0.05
[−1.81 to 1.70]
54.8
[−238.3 to 347.9]
0.26
[−0.94 to 1.45]
Concentric RPD
(W/s)
11986.3 ±
2879.3
10130.6 ±
3817.3
−1,855.6 ±
1921.3
−0.55
[−2.18 to 1.08]
10216.0 ±
5333.5
10874.5 ±
6109.3
658.4 ±
3017.4
0.12
[−1.64 to 1.87]
−2,514.1
[−5896.6 to 868.3]
−1.02
[−2.28 to 0.24]
KiSwim kinetic variables
Average Power
(W/kg)
19.66 ±
3.33
19.52 ±
2.94
−0.15 ±
0.63
−0.05
[−1.65 to 1.56]
20.65 ±
5.42
19.91 ±
5.05
−0.74 ±
0.97
−0.14
[−1.90 to 1.61]
0.59
[−0.50 to 1.68]
0.74
[−0.49 to 1.97]
Average Acceleration
(m/s/s)
6.20 ±
0.80
6.15 ±
0.64
−0.04 ±
0.22
−0.07
[−1.67 to 1.53]
6.42 ±
1.14
6.26 ±
1.04
−0.16 ±
0.26
−0.15
[−1.90 to 1.61]
0.12
[−0.21 to 0.45]
0.50
[−0.70 to 1.71]
Work/kg (joules) 13.83 ±
2.00
13.91 ±
1.93
0.08 ±
0.43
0.04
[−1.56 to 1.64]
13.73 ±
2.68
13.57 ±
2.51
−0.16 ±
0.39
−0.06
[−1.82 to 1.69]
0.24
[−0.32 to 0.80]
0.58
[−0.63 to 1.79]
Horizontal take-off
velocity (m/s)
4.36 ±
0.38
4.38 ±
0.36
0.03 ±
0.14
0.05
[−1.55 to 1.66]
4.29 ±
0.46
4.29 ±
0.41
0.00 ±
0.09
0.00
[−1.75 to 1.75]
0.03
[−0.13 to 0.19]
0.25
[−0.94 to
−1.44]
Total resultant peak
force (N/BW)
1.73 ±
0.21
1.68 ±
0.19
−0.05 ±
0.07
−0.25
[−1.86 to 1.36]
1.95 ±
0.53
1.84 ±
0.55
−0.11 ±
0.06*
−0.20
[−1.96 to 1.55]
−0.06
[−0.15 to 0.03]
0.91
[−0.33 to 2.16]
Front horizontal peak
force (N/BW)
0.69 ±
0.07
0.70 ±
0.05
0.02 ±
0.05
0.16
[−1.44 to 1.77]
0.73 ±
0.05
0.72 ±
0.09
−0.01 ±
0.05
−0.14
[−1.89 to 1.62]
−0.03
[−0.09 to 0.04]
0.60
[−0.61 to 1.81]
Rear horizontal peak
force (N/BW)
0.90 ±
0.19
0.88 ±
0.16
−0.02 ±
0.05
−0.11
[−1.72 to 1.49]
0.91 ±
0.16
0.92 ±
0.15
0.01 ±
0.05
0.06
[−1.69 to 1.82]
0.03
[−0.03 to 0.10]
−0.60
[−1.81 to 0.61]
Rear resultant average
force (N/BW)
0.58 ±
0.10
0.58 ±
0.09
−0.01 ±
0.03
0.00
[−1.60 to 1.60]
0.58 ±
0.13
0.57 ±
0.13
−0.01 ±
0.03
−0.08
[−1.83 to 1.68]
0.00
[−0.04 to 0.04]
0.00
[−1.19 to 1.19]
Grab resultant peak
force (N/BW)
38.67 ±
7.76
38.83 ±
7.65
0.17 ±
4.17
0.02
[−1.58 to 1.62]
36.20 ±
7.92
38.80 ±
8.26
2.60 ±
1.14**
0.32
[−1.44 to 2.09]
2.43
[−1.95 to 6.81]
−0.76
[−1.99 to 0.47]
Swim start performance times
T5 m (s) 1.60 ±
0.15
1.61 ±
0.14
0.02 ±
0.03
0.07
[−1.53 to 1.67]
1.59 ±
0.19
1.61 ±
0.19
0.02 ±
0.03
0.11
[−1.65 to 1.86]
0.00
[−0.04 to 0.04]
0.00
[−1.19 to 1.19]
T15 m (s) 7.33 ±
0.69
7.32 ±
0.57
−0.01 ±
0.19
−0.02
[−1.62 to 1.59]
6.82 ±
0.91
6.85 ±
0.88
0.04 ±
0.08
0.03
[−1.72 to 1.79]
−0.04
[−0.28 to 0.19]
−0.33
[−1.53 to 0.86]
Notes:
*
p< 0.05.
**
p< 0.01.
BW, bodyweight; 95% CI, confidence interval of the differences within and between measures; ES, effect size; RPD, rate of power development; SD, standard deviation; SJ,
squat jump.
For within group effects, a positive change score and effect size indicated that the post test score was larger than the pre-test score. For between group effects, a positive
effect size indicated that the HF group had a larger change than the VF group.
Bolded values indicate an effect size difference of moderate or large.
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 10/16
whether they performed a horizontal- or vertical-force oriented emphasis resistance
training programme.
Relatively few significant within-group changes in any outcome measures were
observed, with the non-significant changes being trivial to small in their effect sizes.
The three significant within-group changes included significant increases in predicted
1RM hip thrust strength for the HF group as well as significant increases in swim start grab
resultant peak force but reductions in resultant peak force for the VF group. No significant
between-group differences were observed between the HF and VF groups in predicted
1RM strength, SJ force-time and swim start performance measures post-intervention.
However, seven moderate between-group effect size differences were observed, with
four outcome measures favouring greater improvements for the HF group and three
outcome measures favouring the VF group. As such, this current study has been unable to
determine whether the inclusion of horizontally oriented exercises has any clear benefitto
swim start performance over more conventional vertically oriented exercises.
Possible explanations for our lack of significant within- or between-group
improvements may include the small number of participants and short duration of the
training intervention, inclusion of plyometric and non-plyometric jumps in only the last
four of 8 weeks of training, the interference effect due to concurrent training and the
relative complexity of the swim start. Regarding the length of the intervention, the absence
of any significant improvements in swim start performance in the current study was
consistent with some studies involving 21 (Born et al., 2020)or23(Breed & Young, 2003)
participants performing 6–8 weeks of resistance training, but inconsistent with other
plyometric training studies of 6–9 weeks involving nine (Rejman et al., 2017), 10 (Rebutini
et al., 2014)or22(Bishop et al., 2009) participants.
The potentially greater adaptations in swim start performance observed in previous
plyometric studies may reflect the between study differences in plyometrics training
volume. The present study only included 33 jumps, compared to previous successful
plyometric studies (Bishop et al., 2009;Rebutini et al., 2014;Rejman et al., 2017), which
included ~484–883 jumps across the study. Interestingly, even though Born et al. (2020)
included comparable volumes of plyometrics in their training study (~360–588 jumps) to
those of the successful studies, the plyometric training group reported no significant
improvements in swim start performance. While it cannot be discounted that the present
study included an insufficient volume of plyometric exercise, the lack of any widespread
changes in lower body force-time characteristics and swim start performance metrics
observed in the present study and some of the literature (Born et al., 2020;Breed & Young,
2003), may be indicative of the challenges coaches face in making any substantial
improvements in strength and power characteristics that transfer to improved sporting
performance within such short periods of concurrent training.
Concurrent training is complex in that both swim training and resistance training
impose different acute stresses on the body that elicit distinct adaptations. In particular, the
concurrent development of both muscular strength/power and aerobic endurance
from resistance training and swimming training respectively can lead to conflicting
neuromuscular adaptations (Garcia-Pallares et al., 2009). In the current study, participants
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 11/16
were primarily middle to long distance swimmers, who performed nine in-water sessions
weekly (HF: 45.5 ± 17.7 km and VF: 53 ± 20.0 km per week). The sessions had an
average swimming volume of 5.1 km and 5.8 km for the HF and VF group per session, with
two swimming sessions a day performed several days per week. In contrast, the resistance
training programme was only performed twice per week. The interference effect from
concurrent training is more likely observed with ≥three sessions of high volume
endurance training weekly (Bishop et al., 2019). Therefore, the high aerobic training
volume for the participants in the present study likely attenuated any resistance
training-induced adaptations. Consistent with this view, Haycraft & Robertson (2015)
recommend swim training volumes be reduced ≤5 km per day to enable maximal strength
and power gains and minimise neuromuscular fatigue.
It should also be acknowledged that the swim start is a discrete skill, requiring a
quick reaction to the starting stimulus and the ability to effectively coordinate hand and
foot forces to optimise horizontal impulse and take-off velocity. Unfortunately, the
swimmers in the present study only performed a small number of swim starts per week
(n= 9 ± 2), with this performed either during regular swim training or at the end of the
session. It was also interesting to observe that Born et al. (2020) also reported a low volume
of swim starts (n= 16) performed per week. Breed & Young (2003) emphasised that a
higher skill component is involved in executing the swim start in comparison to
vertical jump. This may reflect the requirement for how the ankle, knee, and hip joint
moments needs to be coordinated effectively with those of the upper body during the block
phase to maximise horizontal take-off velocity. Further, minimising the time to 15 m
also requires a clean entry into the water and a streamlined glide position with undulatory
leg kicks to minimise velocity loss while transitioning into the break-out of full swimming
and stroking after 15 m (Vantorre, Chollet & Seifert, 2014). The relative absence of
deliberate practice of the swim start coupled with performing the starts in a fatigued state
may also help explain the minimal transfer of the resistance training interventions to
improved swim start performance in the current study and that of Born et al. (2020).
However, significant correlations in the change scores of five block kinetic variables to time
to 5 m were observed in the current study, whereby an increase in block kinetic variables
was associated with a decrease in time to 5 m. Such correlations suggest that the
longitudinal tracking of individual swimmers’SJ force-time characteristics may provide
some insight into their potential improvements in swim start performance.
Due to the demands of competitive swimming, it seems necessary that a targeted
approach of both resistance training and deliberate practice of the swim start is
required across the annual periodisation plan to improve swim start performance. This is
especially important to minimise the potential adverse effects of concurrent training
and maximise skill acquisition, particularly for swimmers who need to improve
aspects of their swim start technique, given the complexity of the swim start. Practical
recommendations include a targeted block of resistance training focused on improving
the strength and power characteristics required forthe swim start in a low swimming volume
phase such as pre-season for a longer duration than used in the present study. Specifically,
extended intervention periods >6 months have been suggested for an optimal transfer of
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 12/16
strength and power qualities to performance in well-trained endurance athletes (Beattie
et al., 2014). Incorporating greater amounts of deliberate practice of swim starts, especially
at the beginning of each training session when the swimmer is mentally and physically fresh
would appear to be beneficial for skill acquisition (Branscheidt et al., 2019).
CONCLUSION
There were very few significant differences observed, either within or between the HF and
VF groups after an 8-week training intervention on swim start performance. Despite
exploring the inclusion of a higher proportion of horizontally oriented exercises based
on the force-vector theory, the current study did not observe a transfer to improved swim
start performance. However, this should not discount the potential value of including
horizontally directed exercises to improve swim start performance, given the results were
similar to those from more traditional vertically oriented exercises. Future studies should
consider an extended training intervention completed during a phase of lower swim
training volume to enable strength and power adaptions to occur.
ACKNOWLEDGEMENTS
This work was supported by the Queensland Academy of Sport’s Sport Performance
Innovation and Knowledge Excellence Unit in conjunction with Bond University Faculty
of Health Sciences and Medicine. The authors would like to acknowledge Mr. Andrew
Pyke for his assistance with data collection and coach Mr. Adam Mallet for allowing his
athletes to be a part of this study. The authors also wish to thank Ms. Evelyne Rathbone for
her statistical assistance in this study and resulting manuscript. There is no conflict of
interest related to the content of this article.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
This work was supported by the Queensland Academy of Sport’s Sport Performance
Innovation and Knowledge Excellence Unit in conjunction with Bond University Faculty
of Health Sciences and Medicine. The funders had no role in study design, data collection
and analysis, decision to publish, or preparation of the manuscript.
Grant Disclosures
The following grant information was disclosed by the authors:
Bond University Faculty of Health Sciences and Medicine.
Competing Interests
Justin W.L. Keogh is an Academic Editor for PeerJ.
Author Contributions
Shiqi Thng conceived and designed the experiments, performed the experiments,
analysed the data, prepared figures and/or tables, authored or reviewed drafts of the
paper, and approved the final draft.
Thng et al. (2021), PeerJ, DOI 10.7717/peerj.10937 13/16
Simon Pearson conceived and designed the experiments, performed the experiments,
analysed the data, authored or reviewed drafts of the paper, and approved the final draft.
Justin W.L. Keogh conceived and designed the experiments, analysed the data, authored
or reviewed drafts of the paper, and approved the final draft.
Human Ethics
The following information was supplied relating to ethical approvals (i.e. approving body
and any reference numbers):
Bond University Human Research Ethics Committee approved this research (00088).
Data Availability
The following information was supplied regarding data availability:
Raw data, including pre- and post-intervention measures of squat jump force-time
measures and kinetic and kinematic variables of the swim start, are available as a
Supplemental File.
Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.10937#supplemental-information.
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