# The impact of testing-parameter variability on force production in the isometric single-leg long-lever bridge: implications for training and testing rigor in sporting environments

## TL;DR

This study shows that small changes in knee angle during a strength test significantly affect force measurements, suggesting the need for strict control in athletic testing.

## Contribution

The study quantifies how knee angle variability impacts force production in a specific isometric exercise, offering practical guidelines for testing rigor in sports.

## Key findings

- Large variance in force outputs was observed across different knee angles.
- Significant differences in force production were found between all tested knee angles.
- Rigorous control of knee angle is necessary for accurate and consistent testing results.

## Abstract

The aim of this study was to determine the impact of knee angle variability on force production outcomes during the single-leg isometric long-lever bridge, thus providing monitoring guidelines for testing rigor with direct implications for feasibility across a variety of high-performance sporting environments.

Thirty men (age: 19.4 ± 1.3 years; height: 179.8 ± 6.3 cm; body mass: 80.4 ± 10.3 kg) and 14 women (age: 20.0 ± 1.3 years; height: 166.9 ± 7.2 cm; body mass: 64.4 ± 7.4 kg) all of whom were Division 3 athletes with no recent injury history volunteered to participate in the study. All participants completed three testing sessions over five days in randomized order, with knee flexion angles of 15°, 30°, or 45° degrees. Each session consisted of three unilateral maximal voluntary isometric contractions (MVIC), with the athlete’s heels positioned on force plates, shoulders elevated on a 15.24 cm box, and hips secured using a rigid barbell. All data was analyzed to assess net force production comparisons between knee angles at 50, 100, 150, 200, 250 ms and peak force (N).

Large variance in force outputs were observed ranging between 0.30 and 0.82 (male ηp²), and 0.52–0.76 (female ηp²), and significant differences observed between all knee angles (p < 0.05). Pairwise comparisons revealed effect sizes ranging between small-large for males (Hedge’s g = 0.27–1.84) and moderate to very large for females (g = 0.51–2.18) across individual force-time points.

These findings indicate that the knee angle must be rigorously controlled when performing the single-leg isometric long-lever bridge to mitigate unwanted variability and to accurately assess the intended musculature, especially for longitudinal monitoring.