(11) DIFFERENCES IN EXERCISE-INDUCED FATIGABILITY AND NEUROMUSCULAR RESPONSES TO UNILATERAL, BILATERAL, AND MIXED ISOKINETIC LEG EXTENSIONS

Exercise-induced fatigability, as determined by declines in peak force, is modality-specific and characterized by a greater fatigability during unilateral (UL) than bilateral (BL) tasks. It has been hypothesized that interhemispheric inhibition (IHI) may reduce cortical activation during BL compared to UL tasks, resulting in a BL force production deficit. No studies, however, have examined the influence of IHI under fatiguing conditions.

Purpose: The purpose of this study was to compare the patterns of responses for peak force, electromyographic (EMG) amplitude (AMP) and mean power frequency (MPF) during fatiguing UL-only, BL-only, UL followed by BL, and BL followed by UL isokinetic leg extensions.

Methods: Eleven recreationally trained men (MEAN±SD; age = 20.8±1.72 yrs; body mass = 84.0±16.2 kg; height = 179.3±7.2 cm) performed fatiguing tasks consisting of either 50 UL, 50 BL, 25 UL followed immediately by 25 BL (ULBL), or 25 BL followed immediately by 25 UL (BLUL) maximal, isokinetic leg extensions at 180°·s^-1 in random order on separate days. For peak force, EMG AMP, and EMG MPF, every 5 of the 50 repetitions were averaged, normalized to the value at repetition 5, and examined with 4 (Condition [UL, BL, ULBL, BLUL]) × 10 (Repetition [5-50]) repeated measures ANOVAs. Follow-up repeated measures ANOVAs and paired samples t-tests were performed when appropriate. An alpha of p < 0.05 was considered significant.

Results: The results for peak force, EMG AMP, and EMG MPF exhibited significant Condition by Repetition interactions (p < 0.001-0.027; η²_p = 0.141-0.370). For peak force compared to the value at repetition 5, UL exhibited declines at repetitions 25-50 (p < 0.001); ULBL exhibited significant declines at repetitions 20-50 (p < 0.001- 0.029); BL exhibited declines at repetitions 30 and 35 (p = 0.017-0.033); and BLUL exhibited declines at repetitions 45-50 (p = 0.001). For EMG AMP compared to the value at repetition 5, UL exhibited an increase at repetition 15 (p = 0.043); ULBL exhibited no significant changes; BL exhibited an increase at repetition 50 (p = 0.043); and BLUL exhibited increases at repetitions 15 and 30-45 (p = 0.018-0.045). For EMG MPF compared to the value at repetition 5, UL exhibited declines at repetitions 40-50 (p = 0.003-0.008); ULBL exhibited no significant declines; BL exhibited a decline at repetition 40 (p = 0.026); and BLUL exhibited declines at repetitions 45-50 (p = 0.002-0.024).

Conclusions: The findings of the present study suggested that the UL and ULBL modalities exhibited earlier and greater exercise-induced fatigability than the BL and BLUL modalities. Additionally, when compared to the BL condition, the BLUL exhibited a sustained decline in peak force. These differences, however, were generally not associated with similar patterns of responses for EMG AMP and EMG MPF. Thus, it remained unclear whether differences in UL and BL modalities were associated with IHI. Practical Applications: These findings provide practitioners insights regarding differences between training modalities, characterized by the UL modality eliciting a greater exercise-induced fatigability than the BL modality. Practitioners working with novice athletes, whose adaptations are initially associated with neuromuscular adaptations, should consider the implementation of both BL and UL modalities due to their generally similar patterns of neuromuscular excitation.

Acknowledgements: NONE