Objective To explore the effect of exercise-induced fatigue on intra-and interhemispher-ic functional connectivity of the primary motor cortex during unilateral ankle plantar-dorsiflexion.Meth-ods Twenty-four healthy adult males(age:21.6±2.2 years;all right-side dominant)were selected as participants for the study.They ran on a treadmill at an individualized constant speed until fatigue.Fatigue was determined when all the following criteria were met:(1)participants failing to maintain the individualized constant speed despite the strong verbal encouragement from the experimenters;(2)reaching a rating of perceived exertion(RPE)score of at least 19;and(3)their heart rate reaching 90%of their age-predicted maximal heart rate(220-age).Moreover,EEG signals from four channels(C1,C2,C3,and C4)of the primary motor cortex were collected during unilateral ankle dorsi-plan-tarflexion movements before and after fatigue,followed by EEG coherence analyses on the collected da-ta.Results Compared to the pre-fatigue state,the coherence values of the intra-hemispheric primary motor cortex electrode pairs C1-C3 and C2-C4 during unilateral ankle plantar-dorsiflexion decreased significantly in the alpha and gamma bands after fatigue(both P<0.05).Conversely,the value of the interhemispheric primary motor cortex electrode pair C1-C2 increased significantly in the beta band(P<0.05).Conclusion Exercise-induced fatigue significantly weakens the intra-hemispheric functional con-nectivity of the primary motor cortex during unilateral ankle plantar-dorsiflexion.However,it may en-hance the interhemispheric functional connectivity and potentially collaborate to strengthen the regula-tion of fatigued muscles.

Objective To explore the effect of exercise-induced fatigue on intra-and interhemispher-ic functional connectivity of the primary motor cortex during unilateral ankle plantar-dorsiflexion.Meth-ods Twenty-four healthy adult males(age:21.6±2.2 years;all right-side dominant)were selected as participants for the study.They ran on a treadmill at an individualized constant speed until fatigue.Fatigue was determined when all the following criteria were met:(1)participants failing to maintain the individualized constant speed despite the strong verbal encouragement from the experimenters;(2)reaching a rating of perceived exertion(RPE)score of at least 19;and(3)their heart rate reaching 90%of their age-predicted maximal heart rate(220-age).Moreover,EEG signals from four channels(C1,C2,C3,and C4)of the primary motor cortex were collected during unilateral ankle dorsi-plan-tarflexion movements before and after fatigue,followed by EEG coherence analyses on the collected da-ta.Results Compared to the pre-fatigue state,the coherence values of the intra-hemispheric primary motor cortex electrode pairs C1-C3 and C2-C4 during unilateral ankle plantar-dorsiflexion decreased significantly in the alpha and gamma bands after fatigue(both P<0.05).Conversely,the value of the interhemispheric primary motor cortex electrode pair C1-C2 increased significantly in the beta band(P<0.05).Conclusion Exercise-induced fatigue significantly weakens the intra-hemispheric functional con-nectivity of the primary motor cortex during unilateral ankle plantar-dorsiflexion.However,it may en-hance the interhemispheric functional connectivity and potentially collaborate to strengthen the regula-tion of fatigued muscles.

Objective To investigate the effects of high-definition transcranial direct current stimulation(HD-tDCS)on the modulation of the H-reflex and M-wave during ankle dorsiflexion-plantar flexion fatigue tasks to provide direction for the application of HD-tDCS in mitigating neuromuscular fatigue.Methods Twenty healthy young male participants were recruited and randomly assigned to either the real stimulation or sham stimulation group,with 10 participants in each group.The intervention consisted of a 5-day single-blind HD-tDCS application(duration:20 min;intensity:2 mA;target:Cz).Baseline measurements of the H-reflex and M-wave under resting conditions,M-wave during maximal voluntary isometric contraction(MVIC)of the dorsiflexor muscle,and MVIC torque of the dorsiflexor and plantar flexor muscles were obtained.An ankle dorsiflexion fatigue task was performed to determine the time to achieve fatigue for the task.The same fatigue task was repeated and evaluated one day after the intervention.A repeated-measures two-factor(stimulation condition x pre/post fatigue)analysis of variance(ANOVA)was used to analyze the effects of independent variables on the mechanical properties of the muscles and α-motoneuron conduction characteristics.Results After fatigue,voluntary activation(VA),maximal H-reflex(Hmax),maximal M-wave(Mmax),and dorsiflexor and plantar flexor MVIC torques in both groups were significantly reduced compared with pre-fatigue levels(P＜0.05).However,compared to the real stimulation group,the sham stimulation group showed a more significant decline in VA and plantar flexor MVIC torque(P＜0.05).Conclusions A continuous 5-day HD-tDCS intervention can effectively increase α-motoneuron activity at the spinal segment.It can also exert an inhibitory effect on reducing information transmission capacity at the peripheral neuromuscular junction under the ankle dorsi-plantarflexion fatigue task.