The Validity and Responsiveness of Isometric Lower Body Multi-Joint Tests of Muscular Strength: a Systematic Review
Drake et al. Sports Medicine - Open
The Validity and Responsiveness of Isometric Lower Body Multi-Joint Tests of Muscular Strength: a Systematic Review
David Drake 0 1
Rodney Kennedy 1
Eric Wallace 1 2
0 Ulster Rugby, Kingspan Stadium , 134 Mount Merrion Avenue, Belfast, Co. Antrim BT6 0FT , UK
1 School of Sport, Ulster University , Jordanstown, Shore Road, Newtownabbey, Co. Antrim BT37 0QB , UK
2 Sport and Exercise Sciences Research Institute, Ulster University , Jordanstown, Shore Road, Newtownabbey, Co. Antrim BT37 0QB , UK
Background: Researchers and practitioners working in sports medicine and science require valid tests to determine the effectiveness of interventions and enhance understanding of mechanisms underpinning adaptation. Such decision making is influenced by the supportive evidence describing the validity of tests within current research. The objective of this study is to review the validity of lower body isometric multi-joint tests ability to assess muscular strength and determine the current level of supporting evidence. Methods: Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were followed in a systematic fashion to search, assess and synthesize existing literature on this topic. Electronic databases such as Web of Science, CINAHL and PubMed were searched up to 18 March 2015. Potential inclusions were screened against eligibility criteria relating to types of test, measurement instrument, properties of validity assessed and population group and were required to be published in English. The Consensus-based Standards for the Selection of health Measurement Instruments (COSMIN) checklist was used to assess methodological quality and measurement property rating of included studies. Studies rated as fair or better in methodological quality were included in the best evidence synthesis. Results: Fifty-nine studies met the eligibility criteria for quality appraisal. The ten studies that rated fair or better in methodological quality were included in the best evidence synthesis. The most frequently investigated lower body isometric multi-joint tests for validity were the isometric mid-thigh pull and isometric squat. The validity of each of these tests was strong in terms of reliability and construct validity. The evidence for responsiveness of tests was found to be moderate for the isometric squat test and unknown for the isometric mid-thigh pull. No tests using the isometric leg press met the criteria for inclusion in the best evidence synthesis. Conclusions: Researchers and practitioners can use the isometric squat and isometric mid-thigh pull with confidence in terms of reliability and construct validity. Further work to investigate other validity components such as criterion validity, smallest detectable change and responsiveness to resistance exercise interventions may be beneficial to the current level of evidence.
Isometric mid-thigh pulls and squats are reliable
tests that can differentiate between strength ability
of participants. These tests can be utilized by both
male and females independent of their training
status or experience.
The isometric squat test can be used to track
progress in muscular strength over time.
Test protocols should be carefully considered and
documented when using isometric multi-joint tests
to ensure repeatability, such as joint angle at which
Commonly isometric multi-joint tests are 5 s in
duration, with two to three trials allowed and 3–5
min recovery between tests.
Testing of specific strength capabilities is a critical
aspect of understanding the strategies that best enhance
muscular strength [1, 2]. In assessing strength, Tillin et
al.  recommended multi-joint rather than
singlejoint testing due to the specific neural and mechanical
conditions in athletic performance tasks such as
sprinting and jumping. Additionally, Gentil et al.  found
no increased motor unit recruitment in single- versus
multi-joint muscle actions. Isoinertial tests such as
repetition maximum back-squats are frequently used to
test lower body multi-joint strength [5–7]. Whilst
isoinertial tests are common, associated methodological
considerations challenge their validity to assess changes
in muscular strength . These considerations include
approaches to squat depth, technical skill required to
complete the range of movement under high external
load as well as the number of trials required to build up
to a maximal test load [9–12]. Previous research has
reported that isoinertial tests lack practicality due to
limitations in using isoinertial repetition maximum tests
with certain populations, such as novice, elderly or
functionally limited participants [6, 8, 13].
It is suggested that isometric multi-joint tests (IMJT)
provide a time efficient assessment of muscular strength
[14, 15] that allows less interruption to training
compared to isoinertial repetition maximum testing. Given
the potential practical merit, it is important to
understand the overall validity of IMJTs. The predominance of
research to date investigating IMJTs has assessed their
specific correspondence to dynamic performance tasks,
such as jump height , change of direction  and
sprint performance . However, this work does not
enhance understanding of IMJTs validity as a measure of
muscular strength. Therefore, research attention is
required to evaluate the evidence directly investigating
validity properties of IMJTs as an assessment tool to
evaluate muscular strength.
Validity of a test refers to the degree to which it
measures what it intends. Many different properties of validity
can be assessed to examine the efficacy of a test. These
properties include face and content validity, based on a
judgement that the test is likely to measure the intended
construct and that the test adequately represents the
construct of interest . Criterion validity is defined as the
extent a test adequately reflects scores on a ‘gold standard’
test measuring the same construct . Construct validity
is the level to which the test measures the intended
construct and the inference that can therefore be made
from the scores. Construct convergent/discriminant
validity relate to the extent to which test scores correlate/or
not with scores on another test of the same construct.
Construct validity for known groups is the degree test
scores differ between groups known to be different on the
variable of interest . Hypothesis testing is the level to
which measured values reflect the pre-defined hypotheses
in terms of expected magnitude and direction of
correlations or differences . Reproducibility refers to the
extent repeated measures (test-retest) provide similar
results and is comprised of both reliability and agreement
parameters . Agreement concerns the intra individual
difference between measurement (absolute
measurement error) and reliability refers to the level of variance
between two or more measurements that is due to the
‘true’ difference . Responsiveness (longitudinal
validity) is defined as the ability of a test to detect change
over a time  and should be described in relation to
the smallest detectable change. The smallest detectable
change can be measured from test-retest studies
provided the length of time between tests is appropriate
and the variable being measured remains stable
between tests . It is important that the defined
components of validity are investigated to understand the
efficacy of tests and for researchers to make appropriate
decisions on their use.
To determine the appropriateness of IMJTs to evaluate
muscular strength and responsiveness to resistance
exercise interventions, knowledge of validity properties is
essential. Noting previous recommendations that validity
is accumulated from multiple studies and cannot be
demonstrated ‘once and for all’ by any single study ,
there is a clear requirement for a synthesis of evidence
for IMJT. As such, the aims of this review were to
determine the current evidence for IMJTs to assess muscular
strength. We hypothesized that IMJT would have strong
evidence in terms of reliability demonstrating intraclass
correlation coefficient (ICC) ≥ 0.70. Additionally, criterion
validity, construct validity and responsiveness to resistance
exercise interventions would have moderate evidence
supporting the validity of IMJT.
The Preferred Reporting Items for Systematic Reviews
and Meta-Analyses (PRISMA) guidelines were followed
. The updated Consensus-based Standards for the
Selection of health Measurement Instruments (COSMIN)
checklist  was applied as a method to critique the
methodological quality and rating of measurement
properties of individual research articles.
The PICO process (PICO acronym stands for P – patient,
problem, population; I – intervention; C – comparison,
control, comparator; O – outcome) was utilized to
develop a search strategy based on the aims of the review.
Initially the term ‘isometric multi-joint test’ was searched
in Google Scholar, with the first 100 articles sorted by
relevance and screened for variations in terminology
within their titles, key words and text terms. All variations
in terminology were recorded into a key terms list to
enable the broadest possible search terms specifically
relevant to the research question and aims of this review.
A validated search method was adapted , and applied
to search electronic databases; Web of Science, CINAHL
and PubMed up to 18 March 2015 (Search terms and
search example provided in Additional file 1). Searches
with each electronic database search were amended for
relevant index terms to reduce the potential of missing
any relevant literature. Articles published in peer reviewed
journals were considered based on title and abstract and
checked for relevance. Secondly, full texts were retrieved
and considered for inclusion against the established
eligibility criteria. Articles that could not be retrieved
electronically were accessed through the British Library
Document Supply Service. Lastly, hand searching of
article reference lists was completed to assess any articles
not successfully retrieved by the search criteria. No time
restrictions were applied to the literature search to ensure
thoroughness of literature included. Following completion
of literature searching, no further studies were considered
for inclusion regardless of relevance.
The following inclusion criteria were established based
on the research question and agreed between authors:
I. Construct: studies with a lower body IMJT. Tests
were maximal effort trials with the duration of the
isometric test greater than 2 s to allow participants
sufficient opportunity to achieve a true maximal
force [9, 24].
II. Target population: studies involved healthy,
uninjured, human participants between the ages of
15–65 years of age. Participants maintained normal
nutritional habits throughout the duration of the
study and were free from supplementation with any
form of ergogenic aid.
III.Measurement instrument: testing was performed
using verifiable isometric testing instruments,
allowing direct measurement of vertical ground
reaction force through a force plate. In accordance
with the recommendations made by James et al.
, force plate derived measurements should not
be interchangeably compared to a load cell device
to reduce potential for systematic error.
IV.Measurement properties: studies involved the
evaluation of any measurement properties relating
to the IMJT (e.g. reliability, validity, responsiveness,
V. Full text: Studies published in English. Adequate
disclosure of information relating the status of
participants and testing methods to enable
assessment of methodological quality was required.
Relevant full-text articles were initially screened by
DD to ensure inclusion criteria was met. The authors
were familiar with the existing literature and had no
conflicting bias with any of the literature screened for
inclusion in the review. Agreement was required by two
authors to exclude any study, a process previously
outlined by Sampson et al. . Two authors (DD and RK)
independently rated included studies methodological
quality and measurement property ratings. Authors
resolved any rating disputes through open dialogue on
how each study met the adapted COSMIN criteria until
agreement was reached.
Methodological Quality Evaluation
Included full-text articles underwent the following process
of review. Firstly, for data extraction purposes, a study
summary table was created outlining the number of
participants and their strength training experience,
description of performance test, measurement equipment
and variables, level of familiarization and instruction, test
position, as well as number of trials, duration and
processing methods. Data extraction for studies included in the
best evidence synthesis is presented in Table 1. All
reviewed full-text articles are presented as author (year),
title and journal in Additional file 2.
Secondly, the methodological quality of each study
was reviewed against the COSMIN four-point scoring
criteria (excellent, good, fair, poor) whereby the worst
score counts in each subsection. The authors made
interpretive adaptations to the protocol and are outline
accordingly below. Box A (internal consistency) and
box E (structural validity) of the COSMIN procedure
were deemed inappropriate for evaluation within this
review as no statistical models were used to analyze
data that was derived through the application of a
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questionnaire. Box F, Hypothesis were evaluated with
specific relevance to multi-joint isometric tests only
within each study. Box G, Cross-cultural validity was
not evaluated, as none of the included studies were
relevant to this section. Box H, criterion validity item 4,
states can the criterion used is considered as a
reasonable gold standard? This item was interpreted by
defining the isoinertial repetition maximum (RM) squat as
the current gold standard for evaluating resistance
exercise. Box I, responsiveness item 7 states, was a
proportion of the patients changed (i.e. improvement or
deterioration)? This item was interpreted by the
authors based on the magnitude of change in the group
mean from baseline (p < .05) or effect size moderate or
large relating only to isometric peak force
measurements . Measurement variables assessed within
studies such as rates of force development or similar
time-dependent variables were excluded from
evaluation within this review. These variables represent a
sub quality of strength as opposed to maximum
muscular strength ability  and may be independently
responsive to resistance exercise interventions .
Thirdly, measurement properties including reliability,
measurement error, construct validity, criterion validity
and responsiveness were evaluated in terms of the
quantitative results for each included study using the criteria
‘positive’, ‘indeterminate’ and ‘negative’. In assessing
measurement property rating for responsiveness, we defined
smallest detectable change as the minimal change
required to ensure the observed change is real . Studies
calculating standard error of measurement (SEM) were
accepted as the smallest detectable change (SDC) and
used for assessment. Interpretability was evaluated based
on the requirement the study presented mean and
standard deviation (SD) values for all groups relating to the
isometric tests, allowing for extrapolation of study data.
The final stage of the review process was to synthesize
the evidence, ‘a best evidence synthesis’  performed
by combining the evaluation of the methodological
quality and the quality of measurement properties. Studies of
fair or better methodological quality were included in
the best evidence synthesis. The level of evidence was
classified as “strong” when consistent findings of
multiple good or at least one excellent study was present
and the total sample size of eligible combined studies
was ≥100, ‘moderate’ when consistent findings of
multiple fair or at least one good study was present and the
total sample size ≥50, “limited” when findings of at least
one fair, good or excellent quality study was present and
the total sample size between 25 and 49 and “unknown”
when findings were of indeterminate rating, in studies
with poor methodological quality or with a sample of ≤25
. Where uncertainty in methodological approaches
within studies was found during the review process, direct
email correspondence was made based on the
corresponding author details to request additional details concerning
the study to ensure full evidence was examined.
Classification of Training Status and Resistance Exercise
When reviewing the responsiveness of resistance exercise
interventions, training status of participants is an
important factor to consider given the magnitude of strength
improvements differs considerably between untrained and
trained individuals [33–35]. Classification of training
status has been discussed in a review of strength training
effects by Wernbom et al. . These authors suggest a
lack of studies exist involving participants of different
training status and therefore these should be combined
into one group, encompassing all ‘trained’, ‘advanced’ and
‘elite’ participants across studies. As such, this review
operationally defined participant’s status into two groups, (i)
untrained (less than 6 months resistance exercise
experience) or (ii) trained, relating specifically to their resistance
exercise experience being greater than 6 months.
Trainable characteristics of strength were classified as
muscular strength, muscular hypertrophy and muscular
power with respect to the primary sources of variation
within resistance exercise programs. The variable
components of resistance exercise programs determine the
likely effect of interventions, these include exercise
selection, exercise intensity, exercise volume, repetition
speed/tempo and rest intervals. For a review, see
Ratamess et al. .
One-hundred nine full texts were reviewed with a total
of fifty studies not meeting eligibility criteria for
inclusion (see Fig. 1). A total of fifty-nine articles were
analyzed within this review. Twenty-five studies
investigated isometric squat, 31 investigated isometric
midthigh pulls, 2 investigated isometric leg press and 1
investigated two IMJTs within the same study. The
total number of participants across the included
studies was 1394 with 59% having greater than 6 months’
resistance exercise experience. The mean ± SD age was
21.8 ± 2.7 with nine studies providing a range of ages
to classify participants within their study and three
studies not reporting age. Thirty-nine studies
investigated male participants, 3 females only, 11
investigating a combination of male and female participants and
six studies not disclosing the sex of participants. A
total of 38 studies were included investigating trained
participants with 23 in untrained participants. Two
studies overlapped both trained and untrained
participants (Table 2).
Records identified through database
Web of Science (n = 12,490)
CINAHL (n = 3879)
PubMed (n = 1248)
Records after duplicates removed
(n = 12,025)
(n = 12,025)
Fig. 1 Flow chart of study selection and eligibility criteria
Six of the nine measurement properties outlined in
COSMIN were evaluated across the 59 studies that met
the eligibility criteria. These properties were reliability
(38 studies), measurement error (9 studies), hypothesis
testing (26 studies), criterion validity (9 studies) and
responsiveness (15 studies) (See Fig. 2). All included
studies were deemed excellent in terms of content
validity and therefore this property of validity is not
discussed further within this review.
Methodological Quality Reproducibility
Reliability was assessed in thirty-eight included studies;
three were rated as fair methodological quality for the
isometric mid-thigh pull test [1, 38, 39] and one as good
. Reliability of the isometric squat test was rated fair
in one study  and good in three studies [42–44].
Reliability of the isometric leg press was evaluated in
one study  rated as poor methodological quality. The
primary rationale for poor methodological quality in
Table 2 Summary of best evidence synthesis
Type of test Validity Level of
Criterion validity Responsiveness
Fig. 2 Rating distribution of included studies for methodological quality
reliability studies was due to insufficient participant
numbers. ICC reliability values for peak force in the seven
noted studies ranged from ≥0.80 to 0.99 [1, 38–43], all
rating positive in terms of measurement properties.
Measurement error was evaluated in nine studies [15, 46–53]
rated as poor methodological quality due to insufficient
participant numbers to satisfy better rating classification.
Construct Validity and Hypothesis Testing
Twenty-six studies were rated; individual studies utilizing
the isometric mid-thigh pull test were rated fair  and
good . Ratings for the isometric squat test of fair 
and good  methodological quality were found within
the included studies. All four studies performed
hypothesis testing with one study additionally investigating
construct validity for known positional groups in rugby union
players . Evaluation of measurement properties for
construct validity revealed one study for the isometric
squat test rated positive , one as indeterminate 
with two other studies using the isometric mid-thigh pull
test rating indeterminate [38, 54]. Twenty-two studies
rated as poor in methodological quality [15, 16, 45–47, 50,
52, 53, 55–68] were limited due to insufficient participant
numbers or lacked clarity in their hypotheses generation.
Of these 22 studies, 7 rated positive [15, 45, 46, 50, 52, 56,
62] and 15 indeterminate [16, 47, 53, 55, 57–61, 63–68]
for measurement properties.
Nine studies were rated as poor for methodological quality
[14–16, 46, 50, 67, 69–71] due to insufficient participant
numbers to satisfy a higher rating and one study did not
assess the correlation between isometric squat and the
criterion test 1RM squat . Four studies of poor
methodological quality [14, 16, 70, 71] investigated the
isometric mid-thigh pull test and four investigated the
isometric squat test [15, 46, 50, 69], with one further study
investigating both the isometric mid-thigh pull and
isometric squat test . Seven studies of poor
methodological quality were rated positively [14–16, 46, 50, 70, 71]
in terms of methodological properties with correlation
≥0.70 with the gold standard test, with one indeterminate
 and one negative rating .
In total, 15 studies were evaluated with only studies of
poor methodological quality for isometric mid-thigh
pull [24, 29, 60, 72, 73] found within included studies,
two studies were rated fair for the isometric squat test
[69, 74] and one as poor for the isometric leg press
. Both studies rated fair in methodological quality
were rated as indeterminate for measurement
properties due to no smallest detectable change being
assessed. Studies assessed for intervention
responsiveness varied in duration from 5 to 28 weeks, mean 10.6
± 6.84 SD weeks and a mean frequency of 2.7 ± 0.916
SD sessions per week across interventions. Ten studies
had longitudinal interventions [24, 29, 45, 46, 55, 60,
69, 72–74] and five studies investigated acute
responses [41, 64, 75–77]. Included studies varied in
resistance exercise protocol with Alegre et al.  using
the half-squat exercise at an intensity between 50 and
60% 1RM for three sets of 6–10 reps. Significant
changes in peak isometric force were found compared
to the control group (≥4.77% increase, d ≥ 0.11, p ≤ 0.05).
Wilson et al.  used the back-squat exercise,
completing between 3 and 6 sets of 6–10 repetitions at a
RM intensity in each respective set. Significant
improvements were found in this study corresponding to
increases in peak isometric force ≥14.5% (d ≥ 0.30,
p ≤ 0.05). Eight studies of poor methodological quality
[24, 29, 45, 46, 55, 60, 72, 73] were limited by
insufficient participant numbers to satisfy rating
classification as fair in addition to four of the mentioned
studies investigating acute responsiveness [41, 75–77],
therefore not enabling assessment of longitudinal
Whilst not being rated within methodological quality
rating, interpretability is an important characteristic of
any measurement instrument across the included studies.
Overall, 48 were rated positive and 11 as negative.
Best Evidence Synthesis
For the best evidence synthesis studies of fair or better
methodological quality were considered and summarized
for IMJTs combined. Additionally, the level of evidence
for each individual isometric test is reported. No studies
were included in the best evidence synthesis for either
measurement error or criterion validity. No studies within
the best evidence synthesis used the isometric leg press
and therefore were classified as unknown in terms of the
level of evidence supporting the use of this test.
With respect to reliability, there was strong evidence
for combined IMJTs. There was moderate evidence for
isometric mid-thigh pull and strong for isometric squat
test. Evidence for hypothesis testing was found to be
strong for combined IMJTs. Isometric mid-thigh pull
and isometric squat tests individually have moderate
level evidence supporting their use. Finally, there was
moderate evidence for responsiveness of the isometric
squat test and unknown evidence for the isometric
midthigh pull and leg press test.
Assessment of physiological mechanisms and adaptations
associated with resistance exercise is critical to improve
understanding and efficacy of interventions . The
practical benefits of isometric multi-joint tests to assess
resistance exercise interventions have been previously
discussed [14, 15, 47, 56]. The aims of this review were to
determine the level of evidence for IMJTs in their
assessment of muscular strength.
Strong evidence was found for reliability of combined
IMJTs including strong evidence for the isometric squat
test and moderate evidence for the isometric mid-thigh
pull independently. ICC values for reliability of peak force
in the seven studies included in the best evidence
synthesis ranging from ≥0.80 to 0.99, well above the acceptable
threshold for ICC >0.7 as discussed in Baumgartner
and Chung . Researchers and practitioners can be
confident with the reliability of IMJT measures of
muscular strength. All best evidence synthesis inclusions
within this review used a repeated trials design conducted
on the same day. No studies to the authors knowledge
used a day-to-day variability in measurements design
(stability reliability) as defined by Baumgarter . Atkinson
and Nevill  have previously cautioned that exercise
performance tests are affected by systematic bias. As such,
reliability investigations may benefit from greater than one
day between tests to get a true measurement on day to
day variability. This review therefore highlights that
stability reliability warrants further investigation, whereby
studies using experimental designs account for day-to-day
variability in measurements.
Our results demonstrate strong evidence to support
construct validity (hypothesis testing) for combined
isometric multi-joint tests, with moderate evidence for
the isometric squat test and isometric mid-thigh pull,
respectively, as independent tests. Primarily, the
experimental design of three studies in the best evidence
synthesis were correlational [38, 43, 54] with one study
implementing an acute responsiveness design. No
studies within the best evidence synthesis employed a study
design assessing IMJTs discriminant validity, to
investigate the difference between known groups. This is an
additional aspect of validity that requires further
exploration to fully understand the efficacy and
application of IMJTs.
It was hypothesized that criterion validity would be
supported with moderate level evidence based on
knowledge of existing literature examining the relationship of
isometric tests to dynamic performance tests.
Additionally, Juneja et al.  suggests isometric strength testing
has a strong potential to predict dynamic performance in
strength based activities. Contrary to our hypothesis and
previous suggestions , no appropriate evidence
supporting the criterion validity of IMJTs was found. With
nine studies in the overall review rated as poor
methodological quality for criterion validity, none were accepted
into the best evidence synthesis. Within this review, the
isoinertial repetition maximum was defined as the gold
standard comparison. As such, findings are not equally
comparable with previous work by Juneja et al.  who
evaluated criterion validity with various dynamic
performance tests. This review highlights a paucity of evidence to
support criterion validity of IMJTs relating to isoinertial
repetition maximum performance. The current lack of
evidence for criterion validity of IMJTs is due to eight
studies within this review rated poor in methodological
quality based on insufficient participant numbers to satisfy
a higher rating. However, seven of these studies were rated
positive for measurement properties with correlations
≥0.70 with the gold standard test. This demonstrates a
likelihood of strong evidence for criterion validity where
future research investigating this critical component of
validity satisfies key methodological criteria, such as
appropriate participant numbers.
Moderate evidence was found supporting
responsiveness for combined IMJTs in keeping with our hypothesis.
Surprisingly this evidence was found only in studies using
the isometric squat test [69, 74]. The principal reasons for
studies not being included in the best evidence synthesis
were due to insufficient participant numbers or absence of
longitudinal interventions to assess responsiveness. Whilst
multiple studies in this review [41, 63, 64, 76, 77] use
acute response designs and receive poor methodological
quality rating, they may have some generalizable merit for
sports medicine and science readers. Given the resistance
exercise intervention used by Alegre et al.  was
classified as a muscular power intervention, only one study
within the best evidence synthesis has examined
responsiveness to a muscular strength intervention using
highintensity loading. Therefore, the use of moderate and high
intensity loading schemes within resistance exercise
interventions warrant further investigation to assess
responsiveness of IMJTs.
Common methodological protocols for IMJTs are
apparent amongst the best evidence inclusions (see
Table. 1). Typically, studies use a 5-s test duration, 2–3
trials per testing session and between trials recovery
time of 3 to 5 min. The instruction given to participants
is consistently to push or pull as ‘hard and as fast as
possible’ dependent on the type of the test, in all but one
included study . Methodological approaches to
familiarization of participants, instruction around
pretension and the processing of the trials was found to be
variable within current literature. Joint angle at which
the isometric test occurs is another methodological
variation amongst studies, although inclusions within
the best evidence synthesis in this review utilize a knee
angle approximately 120° of flexion with one study
using a 90° knee angle .
Whilst the COSMIN protocols have been applied in
reviewing the methodological quality of performance
tests in sports medicine and science research [32, 82,
83], they were not specifically designed for appraisal of
performance tests. As such, several interpretive
amendments were required by the authors as outlined in our
methodology section. Participant numbers is a
consistent limitation to study quality within the COSMIN
protocols and may benefit further consideration given the
tendency for sports medicine and science research to
have relatively small participant groups. This is
particularly the case in longitudinal studies where practical
considerations in studying large participant numbers is
an added challenge. Moreover, eligibility criteria were
established to only include full-text articles published
in English and therefore a possibility exists that
appropriate research may have been missed due to
publication in another language.
IMJTs have been utilized as a measurement tool within 59
studies analyzed within this review. Researchers and
sports practitioners based on strong evidence supporting
their efficacy can confidently utilize isometric multi-joint
tests with respect to reliability and construct validity. The
findings of this review are generalizable to male, female,
trained and untrained participants. IMJTs have
demonstrated moderate responsiveness to resistance exercise.
Future work to investigate this component of validity
would further the understanding of current evidence.
Despite the plethora of investigations examining critical
aspects of validity, caution is urged in the application of
IMJTs in relation to measurement error and criterion
validity. Variability in test protocols must be carefully
considered when interpreting IMJTs outcomes; therefore,
authors are encouraged to provide comprehensive details
on their respective testing protocols.
Additional file 1: Search terms and search example. (DOCX 51 kb)
Additional file 2: Full text inclusion study table. (DOCX 59 kb)
The authors wish to acknowledge Marie Rose Holman, Subject Assistant
Librarian, Ulster University, for her assistance in search strategy development.
No sources of funding were used to assist in the design, collection, analysis,
interpretation of data or in writing of this manuscript.
David Drake contributed to the planning, literature appraisal and writing of this
study. Dr Rodney Kennedy contributed to the planning, literature appraisal and
writing of this study. Professor Eric Wallace contributed to the planning and
writing of this study. All authors read and approved the final manuscript.
David Drake, Dr Rodney Kennedy and Professor Eric Wallace declare that
they have no conflicts of interests relevant to the content of this review.
Ethical Approval and Consent to Participate
Springer Nature remains neutral with regard to jurisdictional claims in
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