Author(s): RASP, D., VOGL, A., KIEßLING, E., STOCKERTS, A., BURKERT, F., PATERNOSTER, F., Institution: TECHNICAL UNIVERSITY OF MUNICH, Country: GERMANY, Abstract-ID: 2547

INTRODUCTION:

Isokinetic trunk flexion (FLEX) and extension (EX) strength is commonly assessed in performance diagnostics [1]. Devices assessing isokinetic trunk strength (ITS) contain a rigid bar that subjects move during FLEX and EX. The bar itself and the subject’s trunk cause additional torque, which must be overcome. Numerous studies, however, do not report whether and how this additional torque was compensated for [2,3]. This study examined the effect of two different gravity compensation (GC) approaches on peak torque (PT), angle of peak torque (APT), and work (W) during FLEX and EX.

METHODS:

32 healthy subjects (25.4 ± 4.2 years; 72 ± 11.7 kg; 1.77 ± 0.08 m) performed five maximal concentric FLEX and EX repetitions on an isokinetic dynamometer (IsoMed2000) at 60°/s over a range of motion (RoM) of -20° to 40°, where 0° indicated upright sitting with vertical spine. In addition, subjects were passively moved by the device across the RoM to quantify the gravitational torque of the device’s bar and subject’s trunk (GCT). This procedure was repeated with the bar only (GCB). We then subtracted the passive torque of GCT and GCB from the actively generated torque. Repeated measures ANOVA tested the effect of GC (GC_NONE vs. GCB vs. GCT) on PT, APT, and W (α = 0.05, Bonferroni-corrected post-hoc tests). Cohen’s d (d) quantified the differences between GC conditions; asterisks indicate significance (p < 0.001: ***; p < 0.01: **; p < 0.05: *).

RESULTS:

In FLEX, ANOVA revealed a significant GC effect on all parameters (η² > 0.32***). PT in GC_NONE was significantly lower than in both GCB (d = -0.61***) and GCT (d = -0.85**), while a tendency was observed between GCB and GCT (d = -0.25; p = 0.069). The APT in FLEX was significantly more positive in GC_NONE than in GCB (d = 1.71**) and GCT (d = 1.88***), with no significant difference between GCB and GCT. W showed significantly lower values in GC_NONE than in GCB (d = -0.60***) and GCT (d = -0.63***), while no significant difference was present between GCB and GCT.
In EX, ANOVA detected a significant GC effect on all outcome parameters (η² > 0.30***). GC_NONE presented lower PT than GCB (d = -0.11; p = 0.067) and GCT (d = -0.26***), with PT in GCB lower than in GCT (d = -0.15**). Regarding APT, GC_NONE displayed significantly lower angles than GCB (d = -1.08***) and GCT (d = -1.28***), with no significant difference between GCB and GCT. W in GC_NONE was significantly lower than in GCB (d = -0.07***) and GCT (d = -0.15***), while a tendency was present between GCB and GCT (d = -0.08; p = 0.056).

CONCLUSION:

We recommend performing GCT to account for passive torque of the device’s bar and subject’s trunk. The effect sizes indicated a more pronounced effect of GC in FLEX than EX. Neglecting GC may hence result in misleading inter- and intra-individual comparisons when trunk weight changes.

LITERATURE:
[1] Zouita et al., 2020, Int J Sports Phys Ther.
[2] Barbado et al., 2016, PLoS One.
[3] Helge & Kanstrup, 2002, Med Sci Sports Exerc