Abstract / Summary
IntroductionMaximal shoulder external rotation strength may not fully reflect force regulation during sustained submaximal contractions.This exploratory study examined whether shoulder external rotation force steadiness, quantified by force variability during 20% and 40% maximal voluntary contraction (MVC) tasks, was associated with normalized medial, superolateral, and inferolateral reach distances on the upperextremity Star Excursion Balance Test (UE-SEBT) in healthy young adults.MVC peak force was also examined to compare maximal force-generating capacity with submaximal force regulation. Materials and methodsTwenty-six healthy young adults participated in this cross-sectional study.Shoulder external rotation MVC peak force and force steadiness at 20% and 40%MVC were assessed using a pull-type handheld dynamometer (Mobie Z; Sakai Medical, Japan).Force variability was quantified using the standard deviation (SD) and coefficient of variation (CV) from the five-second window with the lowest SD during a 15-second submaximal task.Medial, superolateral, and inferolateral UE-SEBT reach distances were normalized to upper-limb length.Raw correlation p-values were adjusted using the Benjamini-Hochberg false discovery rate procedure.Exploratory body-mass-adjusted partial correlations were calculated for selected variables. ResultsBefore correction for multiple comparisons, 20%MVC SD correlated negatively with medial reach (ρ=-0.503,raw p=0.009) and superolateral reach (ρ=-0.528,raw p=0.006).The 20%MVC CV correlated negatively with medial reach (r=-0.421,raw p=0.032) and MVC peak force with superolateral reach (r=-0.484,raw p=0.012).None remained statistically significant after Benjamini-Hochberg false discovery rate correction.Exploratory body-mass adjustment attenuated the MVC peak force correlation but minimally changed the 20%MVC force variability correlations.Force variability during the 40%MVC task showed no consistent associations with UE-SEBT reach distances. ConclusionsIn healthy young adults, selected shoulder external rotation force variability indices showed moderate negative correlations with UE-SEBT reach distances before correction for multiple comparisons.None remained statistically significant after false discovery rate correction.These findings are exploratory and hypothesis-generating rather than confirmatory.