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STUDENT : KARENINA ARRAIS GUIDA MODESTO PRADO
DATE: 22/12/2023
TIME: 14:00
LOCAL: Ambiente virtual Teams
TITLE:

Neuromuscular Electrical Stimulation: Comparison of carrier frequencies, burst durations, and duty cycles in evoked torque generation, sensory discomfort, muscle fatigue, and peripheral oxygen extraction.

KEY WORDS:

Electrical stimulation, Duty cycle, Burst.

PAGES: 110
BIG AREA: Ciências da Saúde
AREA: Educação Física
SUMMARY:

Neuromuscular Electrical Stimulation (NMES) aims to generate muscle contractions to counteract atrophy and enhance performance. NMES has been utilized for over 40 years, demonstrating muscle strengthening benefits across diverse populations. Kilohertzfrequency currents are commonly employed in clinical practice for this purpose. However, the relationship between their physical parameters and stimulation efficiency, including torque generation, sensory discomfort, and muscle fatigue, remains unclear due to a lack of standardization. Studies suggest that lower carrier frequencies allow for increased torque generation, yet results vary across different frequencies. Duty cycles below 50% appear more favorable for torque enhancement and discomfort reduction. The impact of burst duration on torque, discomfort, and, particularly, muscle fatigue is still underexplored. The absence of standardization in NMES parameters may account for inconsistent findings regarding torque generation, discomfort, and muscle fatigue. Little is known about the influence of these parameters on metabolic demand during NMES, crucial for improving strength and muscle hypertrophy. This study aimed to understand the effects of carrier frequency, burst duration, and duty cycle on torque generation, discomfort, fatigue, and metabolic demand. It is anticipated that these results will contribute to optimizing NMES rehabilitation protocols, fostering more efficient therapeutic benefits and encouraging patient adherence to this form of therapy. Objectives Artigo 1: We investigated the effects of carrier frequency, burst duty cycles, and burst durations on evoked torque, perceived discomfort, and muscle fatigue. Artigo 2: Compare Aussie currents with 1000 Hz and Russian currents with 2500 Hz, hypothesizing lower frequencies and shorter duty cycles improve torque and efficiency without increased discomfort. Artigo 3: Investigated the effects of four different NMES protocols applied to the triceps surae muscle on maximum evoked torque, fatigue muscle, efficiency, sensory discomfort and spinal excitability. Methods: Artigo 1: A search across eight data sources by two independent reviewers led to the selection of 13 peer-reviewed studies following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, and they were assessed using the PEDro scale to evaluate the methodological quality of the studies. Artigo 2: Using a cross-over design, kHz frequency alternating currents (KFAC) with 1 kHz (10% and 20% of duty cycle) and 2.5 kHz, (10% and 20% of duty cycle) were randomly applied on triceps surae of healthy participants with a minimum of seven days between sessions. The NMES-evoked torque, NMES-efficiency, NMES-intensity, and NMES-discomfort were measured in maximum and submaximum conditions. Statistics were conducted using a two-way mixed-model ANOVA with repeated measures [two levels: currents (Aussie and Russa) X duty cycle (10% and 20%)], followed by Tukey post-hoc. Artigo 3: A cross-over design, using a kHz frequency alternating currents (KFAC) with 1 kHz (10% and 20% of duty cycle) and 2.5 kHz, (10% and 20% of duty cycle) were randomly applied on triceps surae of healthy participants with a minimum of seven days between sessions. The maximum evoked torque (MEC), fatigue muscle (total TTI, decline of TTI, fatigue index and number of contraction), efficiency, sensory discomfort and spinal excitability were measured. Statistics were conducted using a two-way mixedmodel ANOVA with repeated measures [three levels: currents (aussie and russa) X duty cycle (10% and 20%) X time (pre and post] followed by Tukey post-hoc. Results: Artigo 1: Most studies showed that carrier frequencies up to 1 kHz elicited higher torque, while frequencies between 2.5 and 5 kHz resulted in lower perceived discomfort. Additionally, most studies indicated that shorter burst duty cycles (10% to 50%) induced higher evoked torque and lower perceived discomfort. Methodological quality scores ranged from 5 to 8 on the PEDro scale. Artigo 2: Forty-four participants (age 25.65 ± 6.55 years) were included. Aussie currents produced a higher evoked torque and efficiency in maximum and submaximum conditions. Duty cycle 20% produced a highest efficiency in submaximum conditions. Aussie currents presented a lower minimization of intensity usage in maximum and submaximum conditions. Duty cycle 20% presented lower minimization of intensity usage in submaximum condition. Aussie currents produced a higher discomfort in maximum condition, however, there was no difference in submaximal conditions. Artigo 3: Were included forty-four participants (age 25.65 ± 6.55 years). The Aussie current produced higher evoked torque and TTI values. Aussie currents showed a higher total sum for TTI with a lower decline in TTI and fatigue index. The Aussie current takes more contractions for a noticeable drop in torque generation. Only the soleus showed a decrease between pre and post assessments for RMS and FM. The gastrocnemius muscles showed a reduction between pre and post assessments for RMS and higher values for the 20% duty cycle for FM. The Aussie current demonstrated higher efficiency, regardless of pre and post assessments, as well as during fatigue. The Aussie current resulted in higher overall discomfort. Discomfort during fatigue is higher at the beginning of the protocol compared to the end. Conclusion: Article 1: We concluded that kilohertz-frequency alternating current generates greater evoked torque for carrier frequencies between 1 and 2.5 kHz and burst duty cycles below 50%. Lower perceived discomfort was generated using kilohertz-frequency alternating currents between 2.5 and 5 kHz and burst duty cycles below 50%. Article 2: The Aussie current demonstrates superior performance in eliciting higher evoked torque, enhanced efficiency, and reduced current amplitude when compared to the Russian current, irrespective of whether assessed under maximal or submaximal conditions. While the Australian current induces greater discomfort during maximal conditions, no significant disparity is observed when compared to the Russian current under submaximal conditions. Furthermore, a 20% duty cycle exhibits enhanced efficiency and utilizes lower current intensity in submaximal conditions. Article 3: The Aussie current presented superior performance in evoked torque generation and muscular efficiency. Regarding muscle fatigue, the Aussie current appears to induce less muscular fatigue compared to the Russian current, with 10% duty cycles resulting in higher fatigue. Although the Aussie current is more uncomfortable in terms of total discomfort, there is no significant difference in discomfort between the currents during the fatigue protocol, except that discomfort decreases over time.

COMMITTEE MEMBERS:
Externo à Instituição - BRUNO MANFREDINI BARONI - UFCSPA
Externo à Instituição - DENIS CÉSAR LEITE VIEIRA - UBFC
Externo à Instituição - IVO VIEIRA DE SOUSA NETO - USP
Presidente - 1567105 - JOAO LUIZ QUAGLIOTI DURIGAN
Interno - 2174703 - MARTIM FRANCISCO BOTTARO MARQUES