Journal of Strength and Conditioning Research Publish Ahead of Print
DOI: 10.1519/JSC.0000000000001201
The validity and reliability of a portable isometric mid-thigh clean pull
Conducted at School of Human Movement and Nutrition Sciences, University of Queensland,
Australia
By
Lachlan P. James
1
Llion A. Roberts
1
G. Gregory Haff
2
Vincent G. Kelly
1, 3
Emma M. Beckman
1
1
School of Human Movement and Nutrition Sciences, University of Queensland, Australia
2
Centre for Sport and Exercise Science Research, Edith Cowan University, Perth, Australia
3
Brisbane Broncos Rugby League Football Club, Queensland, Australia
Corresponding Author:
Mr. Lachlan P. James, Room 212, Building 26B, School of Human Movement and Nutrition
Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia
Email:
l.james1@uq.edu.au Phone: (+1) 604 726 7782, Fax: (+61) 7 3365 6877
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RUNNING HEAD: A PORTABLE ISOMETRIC MID-THIGH PULL
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ABSTRACT
This study investigated the test-retest reliability and criterion validity of force-time curve
variables collected via a portable isometric mid-thigh clean pull (IMTP) device equipped with
a single-axial load cell. Fifteen males with ≥ 6 months of resistance training experience
attended two testing sessions. In each session, participants performed an IMTP in two
separate conditions in a randomized, counterbalanced manner. The criterion condition
consisted of a closed-chain IMTP configured with a force plate (IMTPf), while the
experimental test was undertaken using a portable IMTP with data acquired via a single-axial
load cell (IMTPl). A very high reliability (CV = 3.10, 90% CI: 2.4 - 4.6%; ICC = 0.96, 90%
CI: 0.90 - 0.98) and acceptable validity (CV = 9.2, 90% CI: 7 - 14%; ICC = 0.88, 90% CI:
0.71-0.95) were found in the experimental condition for the measure of peak force. However,
significant differences were present between the IMTPf and IMTPl (p<0.0001). Alternate
force-time curve variables did not reach acceptable levels of validity or reliability in the
experimental condition. The IMTPl is a valid and highly reliable method for assessing peak
force. This provides evidence supporting the use of an IMTPl as a cost effective and portable
alternative for those who wish to assess maximal force production in a similar fashion to a
traditional IMTP. However, practitioners should be aware that these are slightly different
tests.
Key words: Peak force, rate of force development, field-testing, strength, force-time curve
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RUNNING HEAD: A PORTABLE ISOMETRIC MID-THIGH PULL
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INTRODUCTION
The ability for the neuromuscular system to apply force (strength) is considered as the
primary training factor for many sports (28). This quality is understood to influence a
spectrum of physiological attributes critical to athletic performance such as neuromuscular
power (5), injury prevention (23) and endurance performance (26). Accordingly, maximal
strength is an essential component in performance profiles of athletes from a variety of sports
(28). The effective assessment of the force production capabilities of skeletal muscle forms
the cornerstone of many training plans, in addition to providing valuable information for
research and clinical settings. The isometric mid-thigh clean pull (IMTPf) is a common
method used for the quantification of maximal strength in athletic populations (8, 10, 11, 30).
This test is conducted in a closed chain environment with the athlete assuming an upright
position with a small amount of hip and knee flexion. Such a position is intended to replicate
the beginning of the second pull phase of the clean (11).
The IMTPf provides force-time information through the collection of vertical ground
reaction force (GRF) data, which allows for the calculation of variables such as peak
isometric force (PF), the rate of force development (RFD), and time specific force values.
The PF measure from this test shows high to practically perfect correlations to dynamic
performance variables in common athletic actions such as jumping (8, 11, 19, 25), throwing
(30), change of direction patterns (31) and weightlifting (8, 11, 19, 30), in addition to
effectively detecting training induced changes in force (29). Likewise, RFD measures have
also been related to variables in similar dynamic actions (8, 11, 19, 25). As such, the
quantification of PF and RFD with the use of the IMTPf has become increasingly important
to sports scientists and strength and conditioning coaches who want to evaluate the
neuromuscular characteristics of their athletes. However, the instrumentation required for
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RUNNING HEAD: A PORTABLE ISOMETRIC MID-THIGH PULL
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such a test is expensive and thus poses a considerable limitation for its use in many applied
settings. In particular, the force plate utilized to acquire GRF data can be cost prohibitive and
may lack portability, which limits the performance of the test to laboratory settings. However,
it might be possible to employ more affordable equipment to obtain force-time information.
Specifically, a single axial load cell and accompanying software provides a possible
alternative if the goal is to collect force-time data in only one axis, and likely presents a more
accessible option for many in the field due to its small size and cost effectiveness. Using
commonly available materials, this could be easily configured by the coach to replicate the
laboratory based IMTPf.
For an assessment method to be suitable for use it must first display adequate levels of
reliability. In particular, to effectively monitor the internal response to training interventions
an acceptable absolute reliability as measured by the coefficient of variation (CV) is required
(14, 21). For descriptive variables whereby comparisons within or between groups are
necessary, an intraclass correlation co-efficient (ICC) that reaches satisfactory levels must be
established to ensure relative reliability (1, 14). In addition, these calculations can determine
the extent to which the experimental method simulates the criterion performance, thus
establishing the criterion validity (6).
The purpose of this present experiment was to establish the test-retest reliability and
criterion validity of a custom built portable isometric mid-thigh clean pull utilizing a single-
axial load cell (IMTPl) in comparison to a laboratory based version of the test employing a
force plate (IMTPf) for the assessment of PF. It was hypothesised that the experimental
condition would reach acceptable levels of relative and absolute reliability, thereby proving a
suitable alternative to the IMTPf for this measure. A secondary objective of this experiment
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RUNNING HEAD: A PORTABLE ISOMETRIC MID-THIGH PULL
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was to determine whether RFD and time-point specific force measures attained an acceptable
degree of reliability and validity for the IMTPl.
METHODS
Experimental approach to the problem
Testing sessions were conducted at two time points separated by a minimum of 48
hours and no longer than 7 days apart (mean=3.64 ± 1.95 d). During this period, participants
were instructed to refrain from exercise and alcohol for 48 hours before each session. All
subjects retained the same dietary regime for each testing session. Likewise, nutritional
supplementation, habitual caffeine intake and hydration was monitored to ensure they were
consistent across both testing sessions. Time of day was also held constant ±2h. Testing
sessions required the subjects to undertake the criterion and experimental conditions in a
randomized counterbalanced manner.
Subjects
Fifteen recreationally active males (23.7±3 y; 78.4±10.27 kg; 1.78± 0.06m), with ≥ 6
months of structured resistance training experience, volunteered to participate in this study.
All subjects were made aware of the risks associated with participation in this investigation
and provided written informed consent. This experiment was approved by the University’s
Human Research Ethics Committee.
Procedures
Sessions began with a warm-up involving a series of general dynamic stretches,
followed by 3 sets of 5 repetitions of dynamic mid-thigh clean pulls from the hang position,
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