Author(s): VOGL, A., STOCKERT, A., KIEßLING, E., BURKERT, F.M., PATERNOSTER, F.K., RASP, D.M., Institution: TECHNICAL UNIVERSITY OF MUNICH, Country: GERMANY, Abstract-ID: 2642

INTRODUCTION:
Isokinetic (ISO) testing of concentric trunk flexion (FLEX) and extension (EX) strength is an essential and widely used procedure in performance diagnostics across many elite sports [1]. However, considerable methodological heterogeneity exists among ISO devices used to measure trunk strength. Devices differ in the body position of the subjects (standing, semi-standing, sitting) [2-4] and in whether the feet are placed on a footplate (FP), on firm ground, or are unsupported. In semi-standing testing, the use of a FP has been shown to significantly increase EX peak torque (PT) compared to testing without a FP (WFP), whereas FLEX PT remained unaffected [4]. To date, no study has examined the influence of a FP on PT production during ISO trunk strength testing in a seated position. Moreover, the effect of a FP on work (W) has not yet been investigated, irrespective of body position. Therefore, the present study aimed to examine the impact of testing ISO FLEX and EX with vs. without a FP on PT and W in a seated position.
METHODS:
17 females and 15 males completed five consecutive ISO concentric trunk FLEX and EX repetitions in the FP and WFP condition (CON) (counter-balanced randomized order) in a seated position on the IsoMed 2000 dynamometer (Angular velocity 60°/s). The neutral position (0°) was defined as an upright vertical sitting posture. From this position, subjects performed trunk movements over a range of -20° to +40°. PT and W were extracted from the respective ISO phases of each FLEX and EX, of which the peak values of each parameter and CON were normalized to body mass and statistically compared via two-tailed paired-samples t-tests (FP vs. WFP) – or Wilcoxon signed-rank test – at an alpha level of 0.05.
RESULTS:
PT Ex (p=0.036, d=0.387) and W Ex (p=0.003, d=0.569) were significantly higher in FP than in WFP. PT FLEX did not reveal significant differences between CON (p=0.577). FLEX/EX PT Ratio (p=0.019, d=-0.439) was significantly lower in the FP than in the WFP CON. FLEX W and the FLEX/EX W Ratio were not directly comparable between CON, as the range of the ISO phases during FLEX differed significantly (p=0.006, rank-biserial r=0.563).
CONCLUSION:
The use of a FP during seated ISO trunk testing increases EX outcomes, while FLEX outcomes remain unchanged. By actively pressing against the FP, subjects may generate a counterforce that enhances force transmission and thereby enables greater EX strength production. In contrast, during FLEX, the lower extremities may not contribute to force transmission to the same extent due to the opposite direction of force application. Consequently, trunk strength values and ratios are only comparable across ISO devices with identical testing configurations. This is particularly important for longitudinal monitoring and inter-device comparisons.

[1] Zouita et al., 2020, Int J Sports Phys Ther
[2] Findley et al., 2000, J Strength Cond Res
[3] Hildebrandt et al., 2017, J Hum Kinet
[4] Porto et al., 2015, Isokinet Exerc Sci