Impact of an Acute Bout of Low- and High-Frequency Neuromuscular Electrical Stimulation on Voluntary Muscle Fatigue and Antioxidant Response

Neuromuscular electrical stimulation (NMES) is an intervention used for promoting skeletal muscle contraction, strength, and hypertrophy, particularly in populations with limited voluntary exercise capacity. Stimulation frequency is a key NMES parameter that may influence force production, fatigue development, and biological markers involved in skeletal muscle health, muscle growth and general physical health. PURPOSE: The purpose of this study was to investigate the acute effects of a single bout of high-frequency (60 Hz) versus low-frequency (20 Hz) NMES on skeletal muscle fatigue and antioxidant biomarkers in healthy, young adults. METHODS: Fifteen participants (9 females, 6 males; mean age 23.9 ± 4.3) completed this randomized crossover design study. The student was conducted over 3 study days: On Day 1 Maximal Voluntary Contractions (MVCs) of both legs were performed and on Day 2 and 3 NMES treatments of 20 Hz and 60 Hz were applied to both legs in randomized order. Each leg received a 60-minute NMES treatment with on-off cycle of 10s on and 15s off, and pulse width of 200 μs with stimulation intensity set at 15% of MVC, with ≥1-week washout period between each treatment sessions to mitigate any effects from first treatment day. Heart rate and perceived muscle fatigue were recorded pre-, during, and post-stimulation every 15 minutes (15, 30,45,60). MVC torque was measured immediately after each NMES treatment (explain WHY). Blood samples were collected pre- and 5-minutes post-NMES to assess superoxide dismutase (SOD) concentration response to the NMES treatments RESULTS: Both NMES protocols (20 Hz and 60 Hz) resulted in progressive increases in perceived fatigue and percent maximal heart rate over the 60-min protocol. Statistical analysis showed a significant main effect of time for perceived fatigue (p < 0.001) and percent maximal heart rate (p = 0.004), with no significant effect of frequency or frequency × time interaction (p > 0.05). MVC torque decreased significantly from pre- to post-NMES following both the 20 Hz (p < 0.001) and 60 Hz protocols (p = 0.007), with no difference in the percent reduction in maximal torque between frequencies (p = 0.940). A significant main effect for Time for SOD concentration was observed following the NMES treatment (p = 0.004), indicates SOD concentration significantly decreased post NMES, independent of stimulation frequency. These findings indicate that NMES produces comparable muscle fatigue, cardiovascular responses, and a decrease in the antioxidant, SOD, concentration following NMES treatment, with no difference between 20 Hz and 60 Hz stimulation frequency. CONCLUSION: Both 20 Hz and 60 Hz NMES effectively induced muscle fatigue, with similar MVC reductions Perceived leg fatigue and percent maximal heart rate increased progressively during the session, demonstrating that both stimulation frequencies effectively induced muscle fatigue during the 60-min protocol. SOD activity decreased pre-, reflecting a transient reduction in antioxidant defense consistent with hormesis. Overall, NMES elicits consistent fatigue and cardiovascular responses, with stimulation frequency having minimal impact on these acute outcomes. Clinically, these findings indicate that NMES can reliably produce meaningful neuromuscular fatigue and metabolic stress regardless of stimulation frequency, providing clinicians with flexibility to select frequencies based on patient tolerance, comfort, and rehabilitation goals while still achieving an effective therapeutic stimulus

Name thesis:degree_name

Master of Science

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Exercise Science

Grantor

Texas State University

Year dc:date.issued

2026

Author dc:creator

• Khan, Khizra

Advisor dc:contributor.advisor

• Mettler, Joni A.

Committee members dc:contributor.committeemember

• Miller, Kevin
• McAllister, Matt

• neuromuscular electrical stimulation
• NMES
• oxidative stress
• reactive oxygen species (ROS)
• antioxidant enzymes
• superoxide dismutase (SOD)
• redox signaling
• musle fatigue
• neuromuscular fatigue
• electrical stimulation
• exercise physiology
• rehabilitation
• skeletal muscle health
• Miller, Kevin

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10877/24778

OAI identifier oai:identifier

oai:digital.library.txst.edu:10877/24778