Does stimulus pulse width influence contraction fatigability during neuromuscular electrical stimulation?

• Author / Creator

  Chen, Meng

• Neuromuscular electrical stimulation (NMES) is used to generate contractions of muscles for rehabilitation after injury or disease to restore functional movements or reduce secondary complications of disuse. However, due to the unnaturally high discharge rates and random recruitment order of motor units (MUs) during conventional NMES (NMESCON), contraction fatigability, which is the significant decline in torque over time, occurs rapidly, limiting the duration and intensity of NMES-based programs. It has been reported that sequential NMES (NMESSEQ) can produce less contraction fatigability than NMESCON by reducing MU discharge rates. It has also been suggested that delivering NMES using relatively long pulse widths reduces contraction fatigability by recruiting MUs in their natural order via central pathways through the spinal cord. Therefore, the present study explored the effect of pulse width on contraction fatigability of the quadriceps muscles during both NMESSEQ and NMESCON. Twelve participants (6 males and 6 females, age: 30.8  11.7) with no known neurological or musculoskeletal injury volunteered for the project and took part in 6 sessions. In the different sessions, NMESSEQ was delivered using a 0.2, 0.5, 1, or 2 ms pulse width and NMESCON was delivered using a 0.2 or 1 ms pulse width. Each session was separated by a minimum of 48 hours. During each experimental session, three different NMES trains were delivered before the fatigue protocol as an assessment of contribution of central pathways to contractions. Then a fatigue protocol was delivered which consisted of 100 contractions (1 s on/1 s off) generated by NMES delivered at 40 Hz. Current was adjusted to generate contractions of 20 % maximum voluntary isometric contraction (MVIC) at the beginning of each fatigue protocol. The contribution of central pathways was quantified as the increase in torque over the course of each type of NMES train. Contraction fatigability was quantified as the percent decline in torque from the beginning to the end of the fatigue protocols. Pulse width did not affect how torque changed during NMES trains (p > 0.05) and we found little evidence of a central contribution to contractions. Contraction fatigability was not different between pulse widths (p > 0.05). However, NMESSEQ produced less contraction fatigability (26  13 %) than NMESCON (43  9 %) (p < 0.001). Our results suggest that both NMES delivered over the quadriceps muscles, regardless of pulse width or NMES type, generated contractions predominantly by peripheral pathways, and thus pulse width did not influence contraction fatigability. However, NMESSEQ produced less contraction fatigability than NMESCON. These findings reaffirm that using NMESSEQ would increase the benefits of NMES-rehabilitation programs by reducing contraction fatigability.

• Subjects / Keywords

  • Contraction fatigability
  • Pulse width
  • Quadriceps muscles
  • Sequential electrical stimulation
  • Neuromuscular electrical stimulation

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-e6r6-et43

• License

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