Multifocal tDCS Targeting Lower-Limb Cortical Areas Preserves Late-Stage Endurance and Tunes Phase-Specific Coordination During Incremental Cycling

Zhiqiang Liang^1,2,3Perianen Ramasawmy⁴Xue Guo⁴Yufei Fang^5*Andrea Antal^4*YU LIU^6*

• ¹Research Academy of Medicine Combining Sports, Ningbo No 2 Hospital, Ningbo, China
• ²Faculty of Sports Science, Ningbo University, Ningbo, China
• ³Key Laboratory of Exercise and Health Sciences of Ministry of Education, Shanghai University of Sport, Shanghai, China
• ⁴Universitatsmedizin Gottingen, Göttingen, Germany
• ⁵Department of Rehabilitation Medicine, Ningbo No 2 Hospital, Ningbo, China
• ⁶Shanghai University of Sport, Shanghai, China

Background: Multifocal transcranial direct current stimulation (m-tDCS) may modulate distributed motor networks in a polarity- and task-state–dependent manner to support performance near exhaustion. The aim of this study is to test whether m-tDCS targeting lower-limb-specific cortical areas could optimize late-stage performance and phase-specific muscle coordination during cycling. Methods: Two independent trials were conducted: (i) a tolerability assessment (Trial 1) and (ii) a randomized, double-blind, sham-controlled parallel study (Trial 2). In Trial 1, participants completed tolerability test as well as recorded pain and side effects during 21 min stimulation. In Trial 2, healthy adults performed an incremental cycling test; late-stage performance was operationalized a priori as the 85–100% peak power output (PPO) phase, during which time-to-exhaustion (TTE), work (W), mean power (P), revolutions per minute (RPM), heart rate (HR), blood lactate (ΔL), ratings of perceived exertion (RPE), and EMG-derived muscle contribution ratio (MCR) and knee co-activation index (CAI) were analyzed across propulsion and pull. Results: (1) m-tDCS was well tolerated; pain ratings declined progressively across the stimulation, with typical transient sensations. (2) In the 85–100% PPO phase, m-tDCS increased W and RPM relative to sham without altering mean power or ΔL; HR decreased after m-tDCS, and RPE rose only after sham. (4) At the coordination level, m-tDCS preserved quadriceps MCR during propulsion and reduced antagonistic activation during pull, preventing the CAI increase observed in the Sham. Conclusion: m-tDCS did not augment peak mechanical output but preserved late-stage endurance via phase-specific coordination tuning—consistent with improved neural efficiency near exhaustion. These findings refine mechanistic interpretations of tDCS effects on endurance and support m-tDCS as a safe, coordination-centric adjunct for high-intensity cycling.