Validity of an Isometric Midthigh Pull Dynamometer in Male Youth Athletes

Abstract

Till, K, Morris, R, Stokes, K, Trewartha, G, Twist, C, Dobbin, N, Hunwicks, R, and Jones, B. Validity of an isometric midthigh pull dynamometer in male youth athletes. J Strength Cond Res 32(2): 490-493, 2018-The purpose of this study was to investigate the validity of an isometric midthigh pull dynamometer against a criterion measure (i.e., 1,000-Hz force platform) for assessing muscle strength in male youth athletes. Twenty-two male adolescent (age 15.3 ± 0.5 years) rugby league players performed 4 isometric midthigh pull efforts (i.e., 2 on the dynamometer and 2 on the force platform) separated by 5-minute rest in a randomized and counterbalanced order. Mean bias, typical error of estimate (TEE), and Pearson correlation coefficient for peak force (PF) and peak force minus body weight (PFBW) from the force platform were validated against peak force from the dynamometer (DynoPF). When compared with PF and PFBW, mean bias (with 90% confidence limits) for DynoPF was very large (-32.4 [-34.2 to -30.6] %) and moderate (-10.0 [-12.8 to -7.2] %), respectively. The TEE was moderate for both PF (8.1 [6.3-11.2] %) and PFBW (8.9 [7.0-12.4]). Correlations between DynoPF and PF (r 0.90 [0.79-0.95]) and PFBW (r 0.90 [0.80-0.95]) were nearly perfect. The isometric midthigh pull assessed using a dynamometer underestimated PF and PFBW obtained using a criterion force platform. However, strong correlations between the dynamometer and force platform suggest that a dynamometer provides an appropriate alternative to assess isometric midthigh pull strength when a force platform is not available. Therefore, practitioners can use an isometric midthigh pull dynamometer to assess strength in the field with youth athletes but should be aware that it underestimates peak force.

Lower limb force‐production capacities in alpine skiing disciplines

“…Our portable IMTP system was selected to improve the accessibility of isometric assessments, given the cost and ungainly nature of force‐plate systems. However, while similar systems provide accurate F max with some systematic bias, 34‐37 the one report of RFD validity that exists depicts poor agreement compared to fixed‐bar force‐plate systems 35 . Our system overcomes several critical limitations of previous designs that feasibly improve RFD accuracy (eg, rigid base‐plate [wood vs reinforced steel], high sampling frequency [< 100 vs 1000 Hz], and rigid tether [material lashing strap vs hardened metal chain]), and might be considered a different assessment than the criterion solution since they are fixed vs open chain.…”

“…Athletes performed the IMTP using a portable dynamometer consisting of an Olympic lifting bar with its ends and bearings removed (7.5 kg), attached to a rigid platform via a heavy‐duty chain (see Figure 1). The portable system is a more advanced alternative to those presented in the literature, 34‐37 which have provided acceptable measurement of peak force capacities but limited and mixed results for RFD (discussed in the limitations) 35 . For the test, the athletes were instructed to set themselves in a position where they felt comfortable to present maximum effort (ie, like that of the second pull of the “clean‐pull” movement, commonly used by alpine skiers 14 and other athletes).…”

The anthropometric and physical qualities of women’s rugby league Super League and international players; identifying differences in playing position and standard

“…To assess muscular strength, the IMTP was performed using a dynamometer (T.K.K.5402, Takei Scientific Instruments Co. Ltd, Niigata, Japan) sampling at 122 Hz, which was attached to a wooden platform, a chain and a latissimus pulldown bar. The test protocol outlined by Till et al, (2018) was utilised in which participants were positioned by standing with their feet approximately shoulder width apart with the chain length adjusted so that the bar was positioned at the mid-thigh. Participants were instructed to maintain a flat back position with their head up and arms straight.…”

Intra-Trial Reliability and Usefulness of Isometric Mid-Thigh Pull Testing on Portable Force Plates

“…While peak force was reported as highly reliable with a conventional force platform (ICC 0.88, CV 9.2% and ICC 0.96, CV 3.10% respectively), the rate of force development and force at selected time points did not reach acceptable levels of reliability compared to the force platform (ICC ≤ 0.31, CV ≥ 17.3% and ICC ≤ 0.31, CV ≥ 16.2%, respectively) (James et al, 2017). Similarly, research using a custom built IMTP dynamometer against a criterion measure (i.e., 1,000-Hz force platform) for assessing muscle strength in male youth rugby league athletes (Till et al, 2018) reported underestimated peak force and peak force/body mass obtained using a criterion force platform, but with strong correlations between the dynamometer and the force platform. While single load cells and dynamometers can be used to quantify peak forces, other variables such as force, impulse and rate of force development, require force plates to offer more in-depth analysis of physical qualities at the recommended sampling frequency of 1000 Hz (Bartlett, 2007).…”