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Biomechanics/Neuromuscular

(14) UNILATERAL AND BILATERAL FORCE PRODUCTION AND MUSCLE EXCITATION DURING MAXIMAL VOLUNTARY ISOMETRIC CONTRACTIONS AND ISOKINETIC LEG EXTENSIONS

Thursday, July 13, 2023
12:00 PM – 1:30 PM East Coast USA Time
Location: Milano III-IV
Abstract Details:
The bilateral deficit (BD) is defined by the force produced during a maximal bilateral (BL) contraction being less than the sum of the force produced by maximal unilateral (UL) contractions of the same muscles. It is unclear whether there are differences in the BD during maximal voluntary isometric contractions (IM) vs. maximal isokinetic (IK) leg extension muscle actions.

Purpose: The purpose of the present study was to examine differences in UL and BL force and muscle excitation during IM vs. IK muscle actions.

Methods: Eleven males (age: 20.8±1.7yrs; height: 179.3±7.1cm; body mass: 84.0±16.2kg), performed separate maximal, UL and BL, IM (6-second hold) and IK leg extensions at 180°s-1 in random order on four separate days (48-hours between). All participants reported being right-leg dominant as determined by kicking preference. Peak force from the non-dominant leg and the electromyographic amplitude (EMG AMP) signal from the vastus lateralis were recorded during the UL and BL muscle actions. Separate 2(Modality: IM vs. IK) x 2(Task: UL vs. BL) x 4(Visits: 1vs.2vs.3vs.4) repeated measures ANOVA were used to examine peak force and EMG AMP. Follow-up post-hoc Bonferroni-corrected pairwise comparisons were conducted when appropriate. Intraclass correlations (ICCs) for all parameters were determined with a 2,1 model with ICCs of 0.75–0.90 considered and ICCs >0.90 considered as excellent. An alpha value of p< 0.05 was considered statistically significant and effect sizes were reported as partial eta-squared (η2p) and Cohen’s d for significant ANOVAs and pairwise comparisons, respectively.

Results: The ICCs for BL and UL IM force (0.844 and 0.896, respectively) and BL and UL IK force (0.834 and 0.887, respectively) were considered good. The ICCs for the BL and UL IM EMG AMP (0.959 and 0.949, respectively) were considered excellent. BL IK EMG AMP (0.893) was considered good, while the UL IK EMG AMP (0.926) was considered excellent. For peak force, there was nonsignificant 3-way interaction but a significant Task x Visit interaction (p=0.001, η2p=0.404) interaction. Post-hoc pairwise comparisons demonstrated that UL (Visit 1: 55.85±14.23kg; Visit 3: 55.43±9.61kg; Visit 4: 60.41±13.75kg) was significantly (Visit 1: p< 0.001, d=0.49; Visit 3: p=0.016, d=0.61; Visit 4: p< 0.001, d=0.69) greater than BL (Visit 1: 48.76±14.55kg; Visit 3: 50.00±8.16kg; Visit 4: 51.69±11.26kg) for most visits. Results for EMG AMP demonstrated no 3- or 2-way interactions, but a main effect for Modality (p< 0.001, η2p=0.896). Post-hoc pairwise comparisons demonstrated that IM EMG AMP (385.2±167.6μV) was statistically different than IK EMG AMP (628.7±211.7μV) (p< 0.00, d=1.46).

Conclusions: The IM and IK peak forces and EMG AMPs exhibited good to excellent reliability. These results demonstrated that regardless of IK or IM modalities, the UL tasks elicited greater force than the BL tasks, thus suggesting a BD for both modalities. The BD, however, was not associated with differences in muscle excitation. PRACTICAL APPLICATIONS: These findings provide practitioners with insights regarding the differences in force and muscle excitation between UL and BL muscle actions. In recreationally trained individuals, practitioners should consider that UL modalities may elicit greater force than BL modalities. For novice or untrained individuals, whose initial strength gains are attributed to neural adaptations, may receive similar benefits from UL and BL training modalities.


Acknowledgements: None