Objective To compare the effect of transcranial direct current stimulation(tDCS),functional electrical stimulation(FES)of the forearm flexors,and their combined intervention on grip strength and cerebral cortical activation in healthy young adults.Methods From December,2024 to March,2025,twelve healthy right-handed young volunteers aged 20 to 23 years were recruited from the Fifth Hospital of Xiamen.They were randomly assigned to receive tDCS alone(tDCS group),FES alone(FES group),or simultaneous tDCS-FES(Sim group)in a crossover design.For tDCS,synchronous bihemispheric stimulation of the primary motor cortex(M1)was applied(anode on the left/cathode on the right).FES was delivered to the right flexor carpi radialis and flexor digitorum superficialis muscles.Isometric maximal grip strength was measured before and after each intervention,and functional near-infrared spectroscopy(fNIRS)was used to synchronously monitor oxyhemoglobin(HbO2)during grip strength tasks.Results A case dropped down.The effect of time on grip strength was significant(F=3.964,P=0.048);Post-hoc tests revealed that grip strength significantly increased after intervention in both FES group and Sim group(P<0.05).The effect of groups was significant on HbO2 of the left prefrontal cortex(PFC)and left premotor and supplemen-tary motor cortex(PMC)(F>3.613,P<0.05);Post-hoc tests revealed that the HbO2 of the left PFC and left pri-mary sensory cortex was higher in FES group than in Sim group,while the HbO2 of the left PMC and right PMC was higher in tDCS group than in Sim group(all P<0.05).Correlation analysis indicated that the grip strength was positively correlated with the HbO2 of the bilateral M1 only in Sim group(r>0.694,P<0.05).Conclusion For healthy young adults,tDCS alone mainly activates motor-related brain regions such as PFC and PMC,while FES alone directly enhances peripheral muscle force output and activates the left PFC to participate in mo-tor regulation.The combined intervention achieves the maximum gain in grip strength through a brain-limb inte-grated regulation mechanism,which may be associated with optimization of neural resource and M1 activity.

Objective To compare the effect of transcranial direct current stimulation(tDCS),functional electrical stimulation(FES)of the forearm flexors,and their combined intervention on grip strength and cerebral cortical activation in healthy young adults.Methods From December,2024 to March,2025,twelve healthy right-handed young volunteers aged 20 to 23 years were recruited from the Fifth Hospital of Xiamen.They were randomly assigned to receive tDCS alone(tDCS group),FES alone(FES group),or simultaneous tDCS-FES(Sim group)in a crossover design.For tDCS,synchronous bihemispheric stimulation of the primary motor cortex(M1)was applied(anode on the left/cathode on the right).FES was delivered to the right flexor carpi radialis and flexor digitorum superficialis muscles.Isometric maximal grip strength was measured before and after each intervention,and functional near-infrared spectroscopy(fNIRS)was used to synchronously monitor oxyhemoglobin(HbO2)during grip strength tasks.Results A case dropped down.The effect of time on grip strength was significant(F=3.964,P=0.048);Post-hoc tests revealed that grip strength significantly increased after intervention in both FES group and Sim group(P<0.05).The effect of groups was significant on HbO2 of the left prefrontal cortex(PFC)and left premotor and supplemen-tary motor cortex(PMC)(F>3.613,P<0.05);Post-hoc tests revealed that the HbO2 of the left PFC and left pri-mary sensory cortex was higher in FES group than in Sim group,while the HbO2 of the left PMC and right PMC was higher in tDCS group than in Sim group(all P<0.05).Correlation analysis indicated that the grip strength was positively correlated with the HbO2 of the bilateral M1 only in Sim group(r>0.694,P<0.05).Conclusion For healthy young adults,tDCS alone mainly activates motor-related brain regions such as PFC and PMC,while FES alone directly enhances peripheral muscle force output and activates the left PFC to participate in mo-tor regulation.The combined intervention achieves the maximum gain in grip strength through a brain-limb inte-grated regulation mechanism,which may be associated with optimization of neural resource and M1 activity.