TY - JOUR

T1 - Torque and Discomfort During Electrically Evoked Muscle Contractions in Healthy Young Adults

T2 - Influence of Stimulation Current and Pulse Frequency

AU - Gravholt, Anders

AU - Herskind, Jon

AU - Kloster, Christoffer Tiedemann

AU - Hvid, Lars G

AU - Overgaard, Kristian

N1 - Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.

PY - 2023/3

Y1 - 2023/3

N2 - Objective: To investigate (1) how current and pulse frequency of electrical stimulation (ES) as well as contraction mode (isometric, concentric, and eccentric) influence torque output and discomfort and (2) how familiarization by repeated ES sessions influences ratings of perceived discomfort. Design: An experimental study, 3 sessions. Setting: A university laboratory. Participants: Eight healthy participants (5 men, 3 women; mean age 25.2 years; N=8). Interventions: Participants completed 3 trial days, each including 17 electrically evoked thigh muscle contractions. On each trial day, the first 6 contractions consisted of 2 isometric, 2 concentric, and 2 eccentric muscle contractions randomly ordered with a fixed stimulation current and pulse frequency (200 mA, 20 Hz), while the remaining 11 muscle contractions were all isometric with randomly ordered combinations of current (100-250 mA) and pulse frequency (20-100 Hz). Main Outcome Measures: Torque and perceived discomfort were measured for each ES-evoked contraction. Results: Overall, the findings revealed that a higher stimulation frequency was associated with an increased torque without increased discomfort, while higher currents were associated with increases of both torque and discomfort. Contraction type did not influence level of discomfort, despite eccentric contractions eliciting higher torque compared with concentric and isometric contractions (P<.001). Finally, a significant familiarization to ES (P<.001) was observed after just 1 of 3 identical stimulation sessions. Conclusions: The outlined data suggest that to elicit high torque levels while minimizing levels of discomfort in young subjects, eccentric muscle contractions evoked with a low stimulation current, and a high pulse frequency are preferable. Furthermore, a single familiarization session significantly lowers rating of perceived discomfort during ES.

AB - Objective: To investigate (1) how current and pulse frequency of electrical stimulation (ES) as well as contraction mode (isometric, concentric, and eccentric) influence torque output and discomfort and (2) how familiarization by repeated ES sessions influences ratings of perceived discomfort. Design: An experimental study, 3 sessions. Setting: A university laboratory. Participants: Eight healthy participants (5 men, 3 women; mean age 25.2 years; N=8). Interventions: Participants completed 3 trial days, each including 17 electrically evoked thigh muscle contractions. On each trial day, the first 6 contractions consisted of 2 isometric, 2 concentric, and 2 eccentric muscle contractions randomly ordered with a fixed stimulation current and pulse frequency (200 mA, 20 Hz), while the remaining 11 muscle contractions were all isometric with randomly ordered combinations of current (100-250 mA) and pulse frequency (20-100 Hz). Main Outcome Measures: Torque and perceived discomfort were measured for each ES-evoked contraction. Results: Overall, the findings revealed that a higher stimulation frequency was associated with an increased torque without increased discomfort, while higher currents were associated with increases of both torque and discomfort. Contraction type did not influence level of discomfort, despite eccentric contractions eliciting higher torque compared with concentric and isometric contractions (P<.001). Finally, a significant familiarization to ES (P<.001) was observed after just 1 of 3 identical stimulation sessions. Conclusions: The outlined data suggest that to elicit high torque levels while minimizing levels of discomfort in young subjects, eccentric muscle contractions evoked with a low stimulation current, and a high pulse frequency are preferable. Furthermore, a single familiarization session significantly lowers rating of perceived discomfort during ES.

KW - Electric stimulation

KW - Isometric contractions

KW - Isotonic contractions

KW - Pain

KW - Rehabilitation

KW - Torque

U2 - 10.1016/j.apmr.2022.09.004

DO - 10.1016/j.apmr.2022.09.004

M3 - Journal article

C2 - 36167118

VL - 104

SP - 444

EP - 450

JO - Archives of Physical Medicine and Rehabilitation

JF - Archives of Physical Medicine and Rehabilitation

SN - 0003-9993

IS - 3

ER -