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“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Note. This article will be published in a forthcoming issue of the
International Journal of Sports Physiology and Performance. The
article appears here in its accepted, peer-reviewed form, as it was
provided by the submitting author. It has not been copyedited,
proofread, or formatted by the publisher.
Section: Original Investigation
Article Title: A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday
Reliability, Usefulness and the Magnitude of Difference Between Tests
Authors: Claire J Brady1, Andrew J Harrison1, Eamonn P Flanagan2, G Gregory Haff3 and
Thomas M Comyns1
Affiliations: 1Department of Physical Education and Sport Sciences, University of Limerick,
Limerick, Ireland. 2Sport Ireland Institute, IIS Building, National Sports Campus,
Abbotstown, Dublin 15, Ireland. 3Centre for Exercise and Sport Science Research, Edith
Cowen University, Joondalup, Western Australia, Australia.
Journal: International Journal of Sports Physiology and Performance
Acceptance Date: November 9, 2017
©2017 Human Kinetics, Inc.
DOI: https://doi.org/10.1123/ijspp.2017-0480
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
A comparison of the isometric mid-thigh pull and isometric squat: intraday reliability,
usefulness and the magnitude of difference between tests
Submission type: Original Investigation
Claire J Brady1, Andrew J Harrison1, Eamonn P Flanagan2, G Gregory Haff3 and Thomas M
Comyns1
1 Department of Physical Education and Sport Sciences, University of Limerick, Limerick,
Ireland.
2 Sport Ireland Institute, IIS Building, National Sports Campus, Abbotstown, Dublin 15,
Ireland.
3 Centre for Exercise and Sport Science Research, Edith Cowen University, Joondalup,
Western Australia, Australia.
Corresponding Author:
Claire Brady,
Department of Physical Education and Sports Sciences,
University of Limerick,
Limerick,
Ireland
Email: claire.brady@ul.ie
Telephone: +353 85 7321128
Preferred running head: Reliability of isometric strength testing
Abstract word count: 250
Text-only word count: 3678
Number of References: 31
Number of Figures: 5
Number of Tables: 5
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Abstract
Purpose: This investigation examined the reliability and usefulness of the isometric mid-thigh
pull (IMTP) and isometric squat (ISqT) performed at the same knee and hip angles. The scores
produced in each test were compared to determine the magnitude of differences between tests.
Methods: Twenty six male and female athletes (23.6±4.3 y; 1.75±0.07 m; 68.8±9.7 kg)
performed 2 maximal repetitions of the IMTP and ISqT following a specific warm up. Results:
Maximum force, absolute peak force (PF), relative PF, allometrically scaled PF, rate of force
development (RFD) (0 – 200 and 0 – 250 ms) and impulse (0 – 300 ms) were deemed reliable
(ICC ≥ 0.86 and CV ≤ 9.4%) in the IMTP and ISqT based on predetermined criteria (ICC ≥ 0.8
and CV ≤ 10%). Impulse (0 – 200 ms and 0 – 250 ms) were reliable in the ISqT (ICC ≥ 0.92
and CV ≤ 9.9%). Participants produced significantly (p < 0.05) greater PF and impulse (0 –
300 ms) during the ISqT compared with the IMTP. When split by sex, female participants
produced significantly greater PF (p = 0.042) during the ISqT with no significant differences
among male participants (p = 0.245). Both tests are capable of detecting changes in
performance in maximum force and absolute PF. Conclusions: Both tests are reliable for non-
time dependent maximal strength measures when measured at the same knee and hip angles.
The ISqT may be preferred when coaches want to test an athlete’s true maximum lower limb
strength, especially female athletes.
Keywords: isometric strength, force-time curve, maximum strength, explosive strength,
performance testing
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Introduction
Isometric tests such as the isometric mid-thigh pull (IMTP) and isometric squat (ISqT)
allow the assessment of athletes’ strength qualities from a force-time curve and are used to
assess skeletal muscle function.1,2 Buckner, et al. 3 suggested that typical strength assessments
such as 1RM testing are skills and that using multiple measures such as the IMTP or ISqT may
be more advantageous for defining true measures and changes in strength. The IMTP is
designed to replicate the body position at the beginning of the second pull position of the clean
or the snatch.1 The second pull position (130 – 140° knee angle with an upright trunk position1)
is the strongest and most powerful position during weightlifting movements, generating the
highest forces and velocities of any part of the lifts.5 From the force time curve produced in
these tests, there are a number of variables that can be examined. Peak force (maximum force
produced) is indicative of “maximum strength” and rate of force development (RFD) is
indicative of an athletes ability to produce maximal force in minimal time.6 To describe
different portions of the force-time curve, Zatsiorsky 7 calculated the index of explosiveness
(IES), reactivity coefficient (RC), S-gradient and A-gradient. The IES refers to the ability to
exert maximal forces in minimal time and the RC expresses the IES relative to body weight.8
The S-gradient quantifies RFD at the beginning of muscular effort whereas the A-gradient
characterises the late stages.7 While Haff, et al. 9 has applied these to the force-time curve of
an IMTP, they have not yet been applied to the ISqT. Impulse determines the change in
momentum of an athlete and is an important performance related characteristic.
With the increased popularity of isometric tests being used to assess strength qualities,
it is important that the data obtained to prescribe, monitor and alter an athletes’ training
programme is reliable. Superior reliability, results in better precision of single measurements
and enhanced tracking of changes in measurement in both research and practical settings.10 To
assess test-retest reliability, it is recommended that the intraclass correlation coefficient (ICC)
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
and the typical error expressed as a coefficient of variation (CV) should be calculated10 along
with 95% confidence intervals (CIs).7 While there are no predetermined standards set for
measurements of reliability in sports science, the literature has commonly used a threshold of
an ICC ≥ 0.80 and a CV ≤ 10%.10
Early research on the IMTP only reported the ICC as the reliability measure and
reported peak force (PF) and peak RFD (pRFD) as reliable.1,11-13 PF is by far the most reliable
variable, with an ICC ≥ 0.92 and a CV ≤ 5% reported in the literature.9,14-16 Research on the
reliability of the ISqT is limited compared to the IMTP, but generally results in PF being the
most reliable variable, with tests performed at various knee angles (ICC ≥ 0.97). 11,17-19
Variables including RFD and impulse have been reported as reliable in the IMTP 9,14-16 and
ISqT.18 There are different methods for calculating the RFD including pre-set time bands, 2,9,20
determining the pRFD across various windows 1,2,9,20,21 and using the slope of the curve from
the initial rise to the maximum force expression (average RFD).9,22 Haff, et al. 9 found that
using selected time bands for the quantification of the RFD offers greater reliability compared
with the quantification of the pRFDs. Average RFD (avgRFD) 9, has been deemed unreliable
and pRFD during a 20 ms sampling window (pRFD20) has only met the ICC criteria for
acceptable reliability (ICC ≥ 0.93 and CV ≥ 12.9%).9,15,16 Maffiuletti, et al. 23 noted that smaller
epochs are more sensitive to changes in the slope of the curve and therefore less reliable.
Nuzzo, et al. 11 reported that male NCAA division 1 American Football players and
track and field athletes produced 12.5% more relative PF during the ISqT when compared with
the IMTP, performed at the same knee angle (140°). Both tests were reported as reliable (r ≥
0.98). There is limited research conducted among female athletes performing an ISqT. Sex
differences in strength exist in the upper body with females demonstrating weakness compared
to their male counterparts.24 The main difference between an IMTP and ISqT is the elimination
of the upper limb during an ISqT and being cued to “push” rather than “pull”. In addition,
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
limited reliability research has been conducted in the ISqT on variables other than PF, such as
RFD (sampling windows), pRFD and impulse.
Once a performance test is determined reliable, the smallest worthwhile change (SWC)
should be calculated and Hopkins 10 suggests using the typical error (TE) alongside the SWC
to allow practitioners to make a well-informed decision on whether a change is both of practical
significance (> SWC) and real (greater than the noise of the test, > TE). This research provides
new information on the usefulness of each test looking at the TE compared to the SWC.
No previous research has compared the reliability and results obtained during the IMTP
and ISqT performed at the same knee and hip angles. Therefore, the aim of the current study
was to determine the intraday reliability of the IMTP and ISqT performed at the same knee and
hip angle, define the usefulness of the tests and determine the magnitude of effect between the
IMTP and ISqT among male and female athletes.
Methods
Participants
Sixteen male (23.0 ±4.8 y; 1.79 ±0.05m; 72.8 ±10.4 kg) and ten female athletes (24.5
±3.1 y; 1.68 ±0.03 m; 62.5 ±3.4 kg) from track & field, boxing, modern pentathlon, canoeing,
rowing, badminton and Taekwondo took part in this study. All participants had at least 6
months of resistance training experience. All participants provided written informed consent
prior to participation in accordance with the ethical requirements of the Research Ethics
Committee.
Study Design
A cross sectional study design with repeated measures was used. This study assessed
the intraday reliability of the IMTP and ISqT performed at the same knee and hip angle to
determine the reliability of maximum force, PF, RFD (sampling windows), pRFD, avgRFD,
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
impulse, IES, RC, S-gradient and A-gradient. The mean scores achieved in each test were
compared. All participants took part in a familiarisation session one week prior to the testing
session. The IMTP/ISqTs were randomised among participants.
Methodology
Participants took part in a familiarisation session that firstly included an explanation of
the study and signing of the informed consent. Participants then performed a general warm up
consisting of 3 minutes of cycling, 10 bodyweight squats, 10 bodyweight walking lunges and
10 glute bridges. Participants were then set in the correct position for the IMTP, which
consisted of a mean knee angle of 136 ± 3° and a hip angle of 137 ± 2°. Participants were
required to maintain the position throughout the test. Knee angles and hip angles were
measured using a hand-held goniometer, grip- and foot- width were measured and remained
consistent between trials. Then each participant performed an IMTP specific warm up
previously reported in the literature 25, which consisted of pulling the IMTP bar for 5 seconds
at a self-directed 50%, 3 seconds at 70 – 80%, 3 seconds at 90% of maximal effort with 1
minute recovery between warm up efforts. Participants completed 3 maximal efforts lasting 5
seconds. During the IMTP, participants used lifting straps to standardise grip strength.25 For
each trial participants were instructed to “pull as hard and as fast as you can, push the ground
away, drive your feet into the ground and the bar from the floor” to ensure maximal force was
achieved.26 Participants were then set in the position for the ISqT, which adopted the same knee
and hip angles attained during the IMTP, with the bar positioned across the shoulders. The
same specific warm up and instruction was given with the exception of “push” instead of “pull”.
One week later, participants completed the testing session. The order sequences of tests
were randomised among participants. Participants completed the general warm up followed by
the specific warm up of the first test to be completed. Participants were then given 2 minutes
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
rest before completing 2 maximal effort trials with 2 minutes between trials. Participants were
instructed to get ready, to pre-tense, and then were given a countdown of “3, 2, 1, PULL!”
Verbal encouragement was provided during each trial. They then rested for 5 minutes before
completing the warm up for the second test (IMTP/ISqT) followed by 2 maximum efforts with
2 minutes rest between trials. Participants completed a third trial if they lost their position or
grip.
All isometric testing was conducted on a custom-made Sorinex isometric rack
(Lexington, South Carolina, USA), allowing the placement of the bar at 0.5 cm intervals
permitting the desired position in each participant. The rack was anchored to the floor and
placed over a Kistler (Winterthur, Switzerland) force platform sampling at 1000 Hz.
Isometric force-time curve analysis
All force-time curves were analysed with the use of a custom built spreadsheet to
determine specific force-time characteristics. The collection period for each trial was set at 12
seconds and a baseline was measured during the 3 second countdown prior to the initiation of
the pull. The criterion onset threshold and onset of the contraction was defined as the point
where the force exceeded 5 SD from baseline.27 The maximum force generated during the 5
seconds was reported as the maximum force. Absolute PF was reported as the maximum force
minus the participant’s body weight. Absolute PF was also reported relative to body mass
(N/kg) and body weight (N/N). Additionally, absolute PF was scaled allometrically (N/kg0.67)
to measure muscle strength independent of body size.12
RFD was analysed with methods previously reported in the literature.9 Precisely, RFD
was calculated (∆Force/∆Time) and was applied to specific time bands (0 – 30, 0 – 50, 0 – 90,
0 – 100, 0 – 150, 0 – 200, 0 – 250 ms). pRFD was then determined as the highest RFD during
a 2- (pRFD 2), 5- (pRFD 5), 10- (pRFD 10), 20- (pRFD 20), 30- (pRFD 30) and 50-millisecond
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
(pRFD 50) sampling windows. AvgRFD was calculated from the PF achieved and the time
elapsed between the initiation of the pull and the PF values. Impulse was measured by average
force divided by the change in time over 100 ms, 200 ms, 250 ms and 300 ms.
The IES is calculated identical to the avgRFD. The RC was calculated using the PF and
time to PF and the participants body weight [PF/ (TPF x BW)]. The S-gradient was calculated
using half the PF (PF0.5) and the time to achieve it (TPF0.5): (PF0.5/TPF0.5). Finally the A-
gradient was calculated by using the PF0.5, TPF and TPF0.5: [PF0.5/ (TPF-TPF0.5)].7
Statistical Analyses
All force-time data were analysed with the use of a custom spreadsheet. Normality of
data was assessed by Shapiro-Wilk statistic. Reliability was calculated by determining the
coefficient of variation (calculated as the typical error and expressed a CV) and the intraclass
correlation coefficient (ICC) and 95% confidence interval (95% CI) using a Microsoft Excel
spreadsheet.28 Acceptable reliability was determined at an ICC ≥ 0.8 and a CV ≤ 10%.10 Paired
t-tests with an alpha level of p ≤ 0.05 were used to determine if differences existed between
mean absolute PF, relative PF (N/kg), allometrically scaled PF, RFD (0 – 200 ms), RFD (0 –
250 ms) and impulse (0 – 300 ms) values produced in the IMTP and ISqT. Participants were
then split by sex for this analysis to determine if sex differences existed. Paired t-test values
were reported with a Holm’s sequential Bonferroni method 29 in order to control for type I
errors. To determine the magnitude of effect within group differences in test scores, a Hedges’
g effect size test was performed between the mean values produced in the IMTP and ISqT. The
magnitude of Hedges’ g was interpreted using Cohen’s scale as trivial (g < 0.2), small (0.2 ≤ g
< 0.5), moderate (0.5 ≤ g <0.8) and large (g ≥ 0.8).30 Typical error (TE) was calculated and the
usefulness of the test was determined by comparing the TE to the smallest worthwhile change
(SWC) calculated on a Microsoft Excel spreadsheet.28 The SWC was determine by multiplying
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
the between-subject SD by 0.2 (SWC0.2) 31, which is the typical small effect or 0.5 (SWC0.5) 30,
which is an alternate moderate effect. If the TE was below the SWC, the test was rated as
“good”, if the TE was similar to SWC it was rated as “ok” and if the TE was higher than the
SWC the test was rated as “marginal”.31
Results
Descriptive statistics for male and female participants for the variables that attained a
criterion of an ICC ≥ 0.8 and a CV ≤ 10% are shown in Table 1 for the IMTP and Table 2 for
the ISqT along with the TE, SWC0.2 and SWC0.5. Figure 1 shows the variables that achieved a
criterion of an ICC ≥ 0.8 and a CV ≤ 10% in either test. While impulse 0 – 200 ms and 0 – 250
ms were determined reliable in the ISqT, they were deemed unreliable in the IMTP (CV >
10%). RFD (0 – 30 ms, 0 – 50 ms, 0 – 90 ms, 0 – 100 ms and 0 – 150 ms), pRFD (2 ms, 5ms,
10 ms, 20 ms, 30 ms and 50 ms), avgRFD, impulse (0 – 100 ms), IES, RC, S-gradient and A-
gradient were deemed unreliable in both the IMTP and ISqT (ICC < 0.8 and/or CV > 10%)
(Figure 2).
Differences between mean absolute PF, relative PF (N/kg), allometrically scaled PF,
RFD (0 – 200 ms), RFD (0 – 250 ms) and impulse (0 – 300 ms) produced during the IMTP and
ISqT are shown in Table 3. Holm’s Sequential Bonferroni adjusted p-values show significant
differences (p < 0.05) exist between absolute PF (p = 0.006), relative PF (p = 0.006),
allometrically scaled PF (p = 0.006) and impulse (0 – 300 ms) (p = 0.036) values between the
IMTP and ISqT with the ISqT producing significantly higher results than the IMTP (Figure 3).
Figure 4 details the magnitude of effect between the IMTP and ISqT. Participants were split
by sex to determine if sex differences existed between tests. Among males, no significant
differences were detected between any variable (Table 4). Among females, significant
differences were observed between absolute PF (p = 0.042), relative PF (N/kg) (p = 0.042) and
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
allometrically scaled PF (p = 0.042) with the ISqT producing significantly (p < 0.05) higher
results (Table 5). Figure 5 details differences individual and group mean values of the IMTP
and ISqT for male and female participants for measures of absolute peak force, allometrically
scaled PF, RFD 0 – 250 ms and impulse 0 – 300 ms.
Discussion
The aim of this study was to determine the reliability of the IMTP and ISqT performed
at the same knee and hip angles, define the usefulness of the tests and determine the magnitude
of effect between the IMTP and ISqT among male and female athletes and report reference TE
and SWC values. This study provides new information on the reliability and usefulness of both
tests and the mean values produced at the same knee and hip angle. Variables that were reliable
in both tests include, maximum force, absolute PF, relative PF (N/N) and (N/kg), allometrically
scaled PF, RFD (0 – 200 ms and 0 – 250 ms) and impulse (0 – 300 ms) (ICC ≥ 0.8 and CV ≤
10%). Impulse (0 – 200 ms) and (0 – 250 ms) were deemed reliable in the ISqT. All short
sampling windows of RFD (up to 150 ms), pRFD (up to 50 ms), impulse (0 – 100 ms), IES,
RC, S-gradient and A-gradient were deemed unreliable for both tests.
PF has been reported as the most reliable variable measured during an IMTP. Previous
research reported ICCs ≥ 0.92 and CV ≤ 5%9,14-16, which is similar to the results of this study.
However, differences exist in the definition of PF with some research including body weight
in the calculation and other research calculating PF as maximum force minus body weight
Beckham, et al. 2 included body weight in their calculation whereas West, et al. 13 calculated
PF minus the participant’s body weight. Some research does not clearly state whether body
weight was included 12 leaving the interpretation of results confounding for coaches. Previous
research has reported that RFD measures (0 – 200 ms and pRFD) are reliable with ICC > 0.8
even though the CV > 15%.14,16 Haff, et al. 9 reported RFD sampling windows from 0 – 30 ms
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
up to 0 – 250 ms as reliable (ICC > 0.8 and CV < 10%), different to the results found in this
study. Maffiuletti, et al. 23 noted when measuring RFD, familiarisation is very important and
prolonged practice procedures may be required to obtain reliable data. The participants used in
the study by Haff, et al. 9 had a lot of experience in producing force in the second pull position
compared to the participants used in this study and this may explain the difference in results.
To achieve reliable data for RFD measures additional familiarisation session may be required.
Additionally, the method for detecting the onset of contraction used in the study by Haff, et al.
9 was different and this may impact reliability. Haff, et al. 9 visually identified the start point
and in this study the point was defined at the point where the force exceeded 5 SD from
baseline. Haff, et al. 9 deemed pRFD sampling windows unreliable except for pRFD 20,
however the CV was 12.9%, which would be unreliable based on the criteria set in this study.
All measures of pRFD were deemed unreliable in this study. Similar to the results of this study,
Haff, et al. 9 deemed avgRFD unreliable. Impulse at 100 ms, 200 ms and 300 ms has been
reported as reliable in previous research (ICC ≥ 0.86 and CV ≤ 8.4%) 14-16, in line with the
results of this study, except for impulse at 100 ms which was deemed unreliable.
The TE was less than the SWC0.2 for maximum force and absolute PF in both tests, and
in the IMTP, the TE of relative PF (N/kg) was less than SWC0.2 demonstrating that the test is
useful in detecting if a “meaningful change” in performance has occurred for these variables.
All other variables in both tests were rated as “marginal” or “ok”. The TE was below the
SWC0.5 for each variable for each test rating the usefulness as “good”. Where the TE is above
the SWC0.2, coaches and practitioners can use SWC0.5 to provide context of “meaningful
change” to group analysis since the SWC0.2 may lack the sensitivity.
Participants produced significantly greater absolute PF, relative PF (N/kg) and
allometrically scaled PF in the ISqT compared to the IMTP with a moderate effect size. In
addition, participants also produced significantly greater impulse (0 – 300 ms) with a small
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
effect size. However, when participants were split by sex, there were no significant results for
males, also having a small effect size. By comparison, significant differences were seen for
female participants for absolute PF, relative PF (N/kg) and allometrically scaled PF with a large
effect size. Results are similar to Nuzzo, et al. 11 who found that males produced an additional
12.5% relative PF (N/kg) in an ISqT. Males produced an additional 9.5% relative PF and
females produced an additional 28.5% relative PF during an ISqT compared with the IMTP.
This may be due to the elimination of the use of upper extremity force during the ISqT
compared with the IMTP, providing a potential advantage to athletes with weakness or
dysfunction in their upper extremity. Females have shown to be weaker in the upper extremity
compared to their male counterparts 24, possibly leaving females at a disadvantage in
demonstrating lower extremity strength when performing an IMTP compared to the ISqT. In
addition, participants in this study had at least 6 months of resistance training experience, and
not all were familiar with weightlifting movements. More recently, Beckham, et al. 4 noted that
those with less experience in weightlifting movements have spent less time overloading the
power position and would not be expected to show the effect of training in this position. This
lack of experience in this position may also affect the reliability results. 4
Results suggest that the IMTP and ISqT are reliable for comparable variables, with the
IMTP appearing to be more reliable when examining pRFD and the ISqT more reliable when
examining impulse. When determining the reliability the ICC and CV should be measured with
the CIs giving a clearer understanding of the level of reliability. Significant differences exist
between the IMTP and ISqT, and this difference is greater for female athletes compared to
males.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Practical Applications
The present study demonstrated that the IMTP and ISqT are reliable for maximum
force, absolute PF, relative PF, RFD (0 – 200 ms and 0 – 250 ms) and impulse (0 – 300 ms).
Impulse (0 – 200 ms and 0 – 250 ms) is reliable in the ISqT. Variables of maximum force and
absolute PF are useful in detecting meaningful change in both tests (SWC0.2). Where the TE is
above the SWC0.2, coaches and practitioners can use SWC0.5 to provide context of “meaningful
change” for all other variables in both tests. Significant differences exist between the IMTP
and ISqT for measures of absolute PF, relative PF, allometrically scaled PF and impulse (0 –
300 ms). If coaches and practitioners are looking to measure an athlete’s true maximum
strength, the ISqT may be the preferred test, especially among female athletes. The ISqT may
be a truer reflection of the athletes maximum lower extremity strength compared with the
IMTP. Future research should determine if different knee and hip angles in the ISqT produce
higher forces than those used in this study.
Conclusions
Results suggest that the IMTP and ISqT are reliable for maximum force, absolute PF,
relative PF, RFD (0 – 200 ms and 0 – 250 ms) and impulse (0 – 300 ms). The ISqT may be
useful for measures of impulse. Both tests are useful in detecting the smallest worthwhile
change for maximum force and absolute PF. The ISqT produces significantly higher absolute
and relative PF among female athletes.
Acknowledgements
The authors would like to thank all athletes who participated in this study. The authors have no
conflicts that are directly relevant to the content of this article. This research is supported by
the Irish Research Council and Sport Ireland Institute.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
References
1. Haff G, Stone M, OʼBryant HS, et al. Force-Time Dependent Characteristics of
Dynamic and Isometric Muscle Actions. J Strength Cond Res. 1997;11(4):269-272.
2. Beckham G, Mizuguchi S, Carter C, et al. Relationships of isometric mid-thigh pull
variables to weightlifting performance. J Sports Med Phys Fitness. 2013;53:573-581.
3. Buckner SL, Jessee MB, Mattocks KT, et al. Determining strength: a case for multiple
methods of measurement. Sports Med. 2017;47(2):193-195.
4. Beckham GK, Sato K, Mizuguchi S, Haff GG, Stone MH. Effect of Body Position on
Force Production During the Isometric Mid-Thigh Pull. J Strength Cond Res.
2017;ahead of print.
5. Garhammer J. A Review of Power Output Studies of Olympic and Powerlifting:
Methodology, Performance Prediction, and Evaluation Tests. J Strength Cond Res.
1993;7(2):76-89.
6. Stone M, Moir G, Glaister M, Sanders R. How much strength is necessary? Phys Ther
Sport. 2002;3(2):88-96.
7. Zatsiorsky V. Science and practice of strength training. Champaign, IL: Human
Kinetics; 1995.
8. Harris NK, Cronin J, Taylor K-L, Boris J, Sheppard JM. Understanding position
transducer technology for strength and conditioning practitioners. Strength Cond J.
2010;32(4):66-79.
9. Haff G, Ruben RP, Lider J, Twine C, Cormie P. A comparison of methods for
determining the rate of force development during isometric midthigh clean pulls. J
Strength Cond Res. 2015;29(2):386-395.
10. Hopkins WG. Measures of reliability in sports medicine and science. Sports Med.
2000;30(1):1-15.
11. Nuzzo JL, McBride JM, Cormie P, McCaulley GO. Relationship between
countermovement jump performance and multijoint isometric and dynamic tests of
strength. J Strength Cond Res. 2008;22(3):699-707.
12. Stone M, Sands WA, Carlock J, et al. The importance of isometric maximum strength
and peak rate-of-force development in sprint cycling. J Strength Cond Res.
2004;18(4):878-884.
13. West DJ, Owen NJ, Jones MR, et al. Relationships between force time characteristics
of the isometric midthigh pull and dynamic perfromance in professional rugby league
players. J Strength Cond Res. 2011;0(0):1-6.
14. Beckham G, Suchomel TJ, Bailey CA, Sole CJ, Grazer JL. The relationship of the
reactive strength index-modified and measures of force development in the isometric
mid-thigh pull. Paper presented at: Proceedings of XXXIInd International Conference
of Biomechanics in Sports2014; Johnson City, TN.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
15. Thomas C, Comfort P, Chiang CY, Jones PA. Relationship between isometric mid-
thigh pull variables and sprint and change of direction performance in collegiate
athletes. J Trainol. 2015;4:6-10.
16. Thomas C, Jones PA, Rothwell J, Chiang CY, Comfort P. An investigation into the
relationship between maximum isometric strength and vertical jump performance. J
Strength Cond Res. 2015;29(8):2176-2185.
17. Blazevich AJ, Gill N, Newton RU. Reliability and Validity of Two Isometric Squat
Tests. J Strength Cond Res. 2002;16(2):298.
18. Bazyler CD, Beckham GK, Sato K. The use of the isometric squat as a measure of
strength and explosiveness. J Strength Cond Res. 2015;29(5):1386-1392.
19. Cormie P, McCaulley GO, McBride JM. Power versus strength-power jump squat
training: influence on the load-power relationship. Med Sci Sports Exerc.
2007;39(6):996-1003.
20. Leary BK, Statler J, Hopkins B, et al. The relationship between isometric force-time
curve characteristics and club head speed in recreational golfers. J Strength Cond Res.
2012;26(10):2685-2697.
21. Haff G, Carlock JM, Hartman MJ, et al. Force time curve characteristics of dynamic
and isometric muscle actions of elite women olympic weightlifters. J Strength Cond
Res. 2005;19(4):741-748.
22. Khamoui AV, Brown LE, Nguyen D, et al. Relationship between force time and
velocity time characteristics of dynamic and isometric muscle actions. J Strength Cond
Res. 2011;25(1):198-204.
23. Maffiuletti NA, Aagaard P, Blazevich AJ, Folland J, Tillin N, Duchateau J. Rate of
force development: physiological and methodological considerations. Eur J Appl
Physiol. 2016;116:1091.
24. Yanovich R, Evans R, Israeli E, et al. Differences in physical fitness of male and female
recruits in gender-integrated army basic training. Med Sci Sports Exerc.
2008;40(11):S654-S659.
25. Beattie K, Carson BP, Lyons M, Kenny IC. The Effect of Maximal- & Explosive-
Strength Training on Performance Indicators in Cyclists. Int J Sports Physiol Perform.
2016:1-25.
26. Halperin I, Williams K, Martin DT, Chapman DW. The effects of attentional focusing
instructions on force production during the isometric mid-thigh pull. J Strength Cond
Res. 2015;30:919-923.
27. Dos’Santos T, Jones PA, Comfort P, Thomas C. Effect of Different Onset Thresholds
on Isometric Mid-Thigh Pull Force-Time Variables. J Strength Cond Res. 2016;Epub
ahead of print.
28. Hopkins WG. Spreadsheets for analysis of validity and reliability. Sportscience.
2015;19:36-42.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
29. Holm S. A simple sequentially rejective multiple test procedure. Scandinavian journal
of statistics. 1979:65-70.
30. Cohen J. Statistical power analysis for the behavioural sciences. Hillside. NJ: Lawrence
Earlbaum Associates. 1988.
31. Hopkins WG. How to interpret changes in an athletic performance test. Sportscience.
2004;8(1):1-7.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Figure 1: Reliability measures of the intraclass correlation coefficient of the variables attaining
an ICC > 0.8 in either the IMTP or ISqT and CV of each variable. °/* = ICC; error bars indicate
95% confidence limits. Grey shaded area = zone of acceptable reliability (ICC > 0.8). Max
force = maximum force; PF = absolute peak force; RPF (N/N) = PF relative to body weight,
N/N; RFP (N/kg) = PF relative to body mass; AlloPF = allometrically scaled PF. RFP 0 – 200
= rate of force development 0 – 200 ms sampling window; RFD 0 – 250 = rate of force
development 0 – 250 ms sampling window. Impulse 0 – 200 = impulse 0 – 200 ms sampling
window; impulse 0 – 250 = impulse 0 – 250 ms sampling window; impulse 0 – 300 = impulse
0 – 300 ms sampling window.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Figure 2: Reliability measure of the intraclass correlation coefficient of the variables deemed
unreliable in the IMTP and ISqT (ICC < 0.8 and/or CV > 10%). ᵒ/▪ =ICC; error bars indicate
95% confidence limits. Grey shaded area = zone of acceptable reliability (ICC > 0.8). A = ICC
RFD windows, B = CV%: RFD 0 – 150 = rate of force development 0 – 150 ms sampling
window RFD 0 – 100 = rate of force development 0 – 100 ms sampling window; RFD 0 – 90
= rate of force development 0 – 90 ms sampling window; RFD 0 – 50 = rate of force
development 0 – 50 ms sampling window; RFD 0 – 30 = rate of force development 0 – 30 ms
sampling window. C = ICC pRFD windows, D = CV%: pRFD 50 = peak rate of force
development 50 ms sampling window; pRFD 30 = peak rate of force development 30 ms
sampling window; pRFD 20 = peak rate of force development 20 ms sampling window; pRFD
10 = peak rate of force development 10 ms sampling window; pRFD 5 = peak rate of force
development 5 ms sampling window; pRFD 2 = peak rate of force development 2 ms sampling
window. E = ICC impulse and Zatsiorsky RFD measures, F = CV%: RC = reactivity
coefficient; IES = index of explosiveness; avgRFD = average rate of force development;
impulse 0 – 100 ms = impulse 0 – 100 ms sampling window.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Figure 3: A, B, C and D = Individual and group mean values of the IMTP and ISqT. A =
absolute peak force, B = impulse 0 – 300 ms, C = RFD 0 – 200 ms, D = RFD 0 – 250 ms.
Single dots represent the mean of the two trials of each participant for each test, straight line
links to their corresponding score on the ISqT. *Significantly different using Holm’s Sequential
Bonferroni adjusted p-value, p < 0.05.
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Figure 4: Results of Hedges g with 95% CIs calculated for between tests. The shaded area
detail Cohen’s scale which was interpreted as trivial (g < 0.2), small (0.2 ≤ g < 0.5), moderate
(0.5 ≤ g < 0.8) and large (g ≥ 0.8).
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Table 1: Descriptive statistics for male and female participants for the IMTP and within session reliability variables attaining a criteria of an ICC
> 0.8 and a CV < 10%.
95% CI
95% CI
Variables
Mean ± SD
ICC
Lower
Upper
CV%
Lower
Upper
TE
SWC
(0.2)
Rating
SWC
(0.5)
Rating
Max force (N)
2669 ± 599
0.98
0.96
0.99
3.4
2.6
4.7
89
120
good
301
good
Absolute PF (N)
1994 ± 513
0.97
0.94
0.99
4.6
3.6
6.4
89
103
good
259
good
RPF (N/N)
2.9 ± 0.4
0.93
0.84
0.97
4.6
3.6
6.4
0.1
0.1
ok
0.2
good
RPF (N/kg)
28.7 ± 4.4
0.93
0.84
0.97
4.6
3.6
6.4
1.3
0.9
good
2.2
good
AlloPF (N/kg0.67)
116 ± 20.9
0.95
0.88
0.98
4.6
3.6
6.4
5.1
4.2
marginal
10.6
good
RFD 0 – 200 ms (N/s)
5623 ± 1447
0.89
0.77
0.95
9.6
7.4
13.5
509
298
marginal
746
good
RFD 0 – 250 ms (N/s)
4919 ± 1286
0.86
0.77
0.95
9.6
7.5
13.6
458
265
marginal
663
good
Impulse 0 – 300 ms (N.s)
344 ± 108
0.92
0.82
0.96
9.4
8.8
16
33
22
marginal
55
good
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Table 2: Descriptive statistics for male and female participants for the ISqT and within session reliability variables attaining a criteria of an ICC
> 0.8 and a CV < 10%.
95% CI
95% CI
Variables
Mean ± SD
ICC
Lower
Upper
CV%
Lower
Upper
TE
SWC
(0.2)
Rating
SWC
(0.5)
Rating
Max force (N)
2997 ± 784
0.98
0.96
0.99
3.5
2.7
4.8
110
147
good
368
good
Absolute PF (N)
2322 ± 709
0.97
0.94
0.99
4.6
3.6
6.4
110
131
good
327
good
RPF (N/N)
3.5 ± 0.6
0.95
0.88
0.98
4.6
3.6
6.4
0.2
0.1
marginal
0.3
good
RPF (N/kg)
33.3 ± 7.5
0.95
0.88
0.98
4.6
3.6
6.4
1.5
1.3
marginal
3.2
good
AlloPF (N/kg0.67)
134.9 ± 33.1
0.96
0.9
0.98
4.6
3.6
6.4
6.2
5.7
marginal
14.3
good
RFD 0 – 200 ms (N/s)
5879 ± 1891
0.91
0.8
0.96
9.9
7.7
14
578
365
marginal
911
good
RFD 0 – 250 ms (N/s)
5083 ± 1566
0.91
0.8
0.96
9.8
7.5
15.4
488
306
marginal
764
good
Impulse 0 – 200 ms (N.s)
212 ± 74
0.92
0.84
0.97
9.9
7.9
14.3
21
15
marginal
37
good
Impulse 0 – 250 ms (N.s)
294 ± 99
0.95
0.88
0.98
8.1
6.3
11.4
24
20
marginal
49
good
Impulse 0 – 300 ms (N.s)
379 ± 124
0.96
0.91
0.98
6.7
5.2
9.4
26
25
ok
62
good
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Table 3: Comparison of variables deemed reliable in the IMTP and ISqT for male and female
participants.
All Participants
95% CI
Variables
p
g
lower
upper
Absolute PF (N)
0.006*
0.52
-0.03
1.07
RPF (N/kg)
0.006*
0.74
0.18
1.30
AlloPF (N/kg0.67)
0.006*
0.67
0.11
1.23
RFD 0 – 200 ms (N/s)
0.708
0.15
-0.39
0.69
RFD 0 – 250 ms (N/s)
0.708
0.11
-0.43
0.66
Impulse 0 – 300 ms (N.s)
0.036*
0.30
-0.25
0.84
*Statistically different using Holm’s Sequential Bonferroni adjusted p-value, g = Hedges g for magnitude of
effect.
Table 4: Descriptive statistics for male participants and comparison of variables deemed
reliable in the IMTP and ISqT.
IMTP
ISqT
95% CI
Variables
Mean ± SD
Mean ± SD
p
g
lower
upper
Absolute PF (N)
2225 ± 493
2466 ± 761
0.222
0.37
-0.33
1.07
RPF (N/kg)
30.4 ± 3.8
33.3 ± 7.0
0.245
0.50
-0.20
1.21
AlloPF (N/kg0.67)
125 ± 18.5
137.6 ± 33
0.245
0.46
-0.25
1.16
RFD 0 – 200 ms (N/s)
6077 ± 1502
6044 ± 2090
1.000
-0.02
-0.71
0.68
RFD 0 – 250 ms (N/s)
5392 ± 1301
5297 ± 1701
1.000
-0.06
-0.75
0.63
Impulse 0 – 300 ms (N.s)
383 ± 119
407 ± 142
0.555
0.18
-0.52
0.87
“A Comparison of the Isometric Mid-Thigh Pull and Isometric Squat: Intraday Reliability, Usefulness and the Magnitude of
Difference Between Tests” by Brady CJ et al.
International Journal of Sports Physiology and Performance
© 2017 Human Kinetics, Inc.
Table 5: Descriptive statistics for female participants and comparison of variables deemed
reliable in the IMTP and ISqT.
IMTP
ISqT
95% CI
Variables
Mean ± SD
Mean ± SD
p
g
lower
upper
Absolute PF (N)
1624 ± 285
2090 ± 578
0.042*
1.81
0.77
2.85
RPF (N/kg)
26 ± 4.1
33.4 ± 8.7
0.042*
2.06
0.98
3.15
AlloPF (N/kg0.67)
101.6 ± 16.3
130.6 ± 34.6
0.042*
2.07
0.98
3.15
RFD 0 – 200 ms (N/s)
4895 ± 1049
5614 ± 1589
0.156
1.10
0.16
2.04
RFD 0 – 250 ms (N/s)
4162 ± 857
4741 ± 1335
0.156
1.05
0.11
1.98
Impulse 0 – 300 ms (N.s)
283 ± 46
333 ± 75
0.051
1.28
0.32
2.25
*Statistically different using Holm’s Sequential Bonferroni adjusted p-value, g = Hedges g for magnitude of
effect.
