The Isometric Horizontal Push Test: Test-Retest Reliability and Validation Study

Background: The planning of training programs is regularly based on assessments of force production tests. Two examples of such tests are the isometric mid-thigh pull (IMTP) and the isometric squat (IS) tests (Comfort et al., 2019). Both require subjects to stand on a force plate and either pull or push a locked in-place barbell as hard and as fast as they can. These tests are valid and reliable, correlated with performance indices, can distinguish between the levels of athletes, and are easy to administer. Although both are extensively implemented, they have two limitations. First, they require a force plate that many cannot afford, and a unique setup to be administered, including a robust weight-lifting cage. Second, they solely measure forces produced vertically, which may limit carryover to forces applied horizontally such as during sprinting activities. Considering these limitations, we designed a new isometric test – the Isometric Horizontal Push Test (IHPT) – that quantifies peak force outputs using a strain gauge. This test does not depend on a force plate, can be easily administered without a complex set up, and assesses the horizontal forces component.

Aims: Our aims were to examine the test-retest reliability of the IHPT peak force outputs across two days, and to establish criterion validity by comparing the results derived from the strain gauge cell to those from a force plate.

Methods: Twenty-four active males with ≥ 3 years of resistance training experience performed two testing sessions of the IHPT, separated by 3-4 days of rest. In each session, subjects performed three maximal trials of the IHPT with 3-min of rest between them. The peak force outputs were collected simultaneously using a strain gauge, and the criterion equipment consisting of a floor-embedded force plate.

Results: The test-retest reliability of peak force values was nearly perfect (ICC ~0.99). Bland-Altman analysis showed excellent agreement between days with nearly no bias for strain gauge 1.2N (95% CI: -3, 6N) and force plate 0.8N (95% CI: -4, 6N). A nearly perfect correlation was observed between the strain gauge and force plate (r= 0.98, p 0.001), with a small bias of 8N (95% CI: 1.2, 15N) in favor of the force plate. The sensitivity of the IHPT was also good, with SWC SEM for both the strain gauge (SWC: 29N; SEM: 17N [95% CI: 14, 20N]) and the force plate (SWC: 29N; SEM: 18N [95% CI: 14, 19N]) devices.

Discussion and Conclusions: The validity, reliability, and sensitivity of the IHPT, coupled with its affordability, portability, ease of use, and time efficacy, point to the potential of the test for monitoring the effects of training interventions, time-course effects of detraining, effects of fatigue on force production capabilities, and preparedness before competition