RESUMEN
BACKGROUND: The benefits of neuromuscular electrical stimulation (NMES) for rehabilitation depend on the capacity to generate functionally relevant torque with minimal fatigability and discomfort. Traditionally, NMES is delivered either over a muscle belly (mNMES) or a nerve trunk (nNMES). Recently, a technique that minimizes contraction fatigability by alternating pulses between the mNMES and nNMES sites, termed "interleaved" NMES (iNMES), was developed. However, discomfort and the ability to generate large torque during iNMES have not been explored adequately. OBJECTIVE: The study objective was to compare discomfort and maximal torque between mNMES, nNMES, and iNMES. METHODS: Stimulation trains (12 pulses at 40 Hz) were delivered to produce dorsiflexion torque using mNMES, nNMES, and iNMES. Discomfort was assessed using a visual analogue scale for contractions that generated 5-30% of a maximal voluntary isometric contraction (MVIC), and for the maximal tolerable torque. RESULTS: Discomfort scores were not different between NMES types when torque was ≤20% MVIC. At 30% MVIC, mNMES produced more discomfort than nNMES and iNMES. nNMES produced the most torque (65% MVIC), followed by iNMES (49% MVIC) and mNMES (33% MVIC); in these trials, mNMES produced more discomfort than nNMES, but not iNMES. LIMITATIONS: The present results may be limited to individuals with no history of neuromusculoskeletal impairment. CONCLUSIONS: In terms of discomfort, there were no differences between mNMES, nNMES, or iNMES for contractions between 5-20% MVIC. However, mNMES produced more discomfort than nNMES and iNMES for contractions of 30% MVIC, while for larger contractions, mNMES only produced more discomfort than nNMES. The advantages and disadvantages of each NMES type should be considered prior to implementation in rehabilitation programs.
Asunto(s)
Articulación del Tobillo/fisiología , Terapia por Estimulación Eléctrica/métodos , Contracción Isométrica/fisiología , Músculo Esquelético/fisiología , Dolor/etiología , Rango del Movimiento Articular/fisiología , Adulto , Terapia por Estimulación Eléctrica/efectos adversos , Femenino , Humanos , Masculino , Torque , Adulto JovenRESUMEN
Neuromuscular electrical stimulation (NMES) generates contractions by activation of motor axons (peripheral mechanism), but the afferent volley also contributes by recruiting spinal motoneurons synaptically (central mechanism), which recruits motoneurons according to Henneman's size principle. Thus, we hypothesized that contractions that develop due to a combination of peripheral and central mechanisms will fatigue less rapidly than when electrically evoked contractions are generated by the activation of motor axons alone. Plantar-flexion torque evoked by NMES over the triceps surae was compared in five able-bodied subjects before (Intact) and during (Blocked) a complete anesthetic block of the tibial and common peroneal nerves. In the Blocked condition, plantar-flexion torque could only develop from the direct activation of motor axons beneath the stimulating electrodes. NMES was delivered using three protocols: protocol A, constant 100 Hz for 30 s; protocol B, four 2-s bursts of 100 Hz alternating with 20-Hz stimulation; and protocol C, alternating 100 Hz bursts (1 s on, 1 s off) for 30 s. The percent change in evoked plantar flexion torque from the beginning to the end of the stimulation differed (P < 0.05) between Intact and Blocked conditions for all protocols (Intact: protocol A = +125%, B = +230%, C = +78%; Blocked: protocol A = -79%, B = -15%, C = -35%). These results corroborate previous evidence that NMES can evoke contractions via the recruitment of spinal motoneurons in addition to the direct recruitment of motor axons. We now show that NMES delivered for periods of up to 30 s generates plantar-flexion torque which decreases when only motor axons are recruited and increases when the central nervous system can contribute.
Asunto(s)
Estimulación Eléctrica/métodos , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Nervios Periféricos/fisiología , Torque , Adulto , Anestesia Local , Anestésicos Locales , Bupivacaína , Combinación de Medicamentos , Electromiografía , Epinefrina , Humanos , Lidocaína , Masculino , Persona de Mediana Edad , Contracción Muscular/efectos de los fármacos , Músculo Esquelético/inervación , Bloqueo Nervioso , Nervios Periféricos/efectos de los fármacos , Reclutamiento Neurofisiológico/efectos de los fármacos , Reclutamiento Neurofisiológico/fisiologíaRESUMEN
Tetanic electrical stimulation applied over human muscle or peripheral nerve generates contractions by depolarizing motor axons beneath the stimulating electrodes. However, the simultaneous depolarization of sensory axons can also contribute to the contractions by the synaptic recruitment of spinal motoneurons. Maximizing this central contribution may be beneficial for reducing muscle atrophy or restoring movement for persons with movement disorders.
Asunto(s)
Trastornos del Movimiento/rehabilitación , Contracción Muscular/fisiología , Músculo Esquelético/inervación , Estimulación Eléctrica Transcutánea del Nervio , Adulto , Axones , Humanos , Trastornos del Movimiento/complicaciones , Músculo Esquelético/fisiopatología , Atrofia Muscular/etiología , Atrofia Muscular/rehabilitación , Nervios Periféricos/fisiopatología , Reflejo/fisiología , Nervios EspinalesRESUMEN
Tetanic neuromuscular stimulation evokes contractions by depolarizing motor axons beneath the stimulating electrodes. However, we have shown that extra torque can develop due to the discharge of spinal neurons recruited by the evoked sensory volley. The present experiments investigated whether extra torque in the ankle plantar- and dorsiflexors was associated with enhanced H-reflexes. The tibial and common peroneal nerves were stimulated using 7-s trains (20 Hz for 2 s, 100 Hz for 2 s, 20 Hz for 3 s). Extra torque was defined as significantly more torque during 20-Hz stimulation after the 100-Hz burst (time2) than before it (time1). In 9 of 11 subjects, extra plantarflexion torque developed during stimulation just above motor threshold. In these nine subjects, torque increased from 8 to 13% MVC (time1 to time2), the soleus H-reflex increased from 13 to 19% Mmax and the M-wave of approximately 2% Mmax did not change significantly. To evoke extra dorsiflexion torque, greater stimulation intensities were required. In 6 of 13 subjects, extra torque developed at intensities that evoked an M-wave of 5-20% Mmax at time1. In these six subjects, torque doubled from 2 to 4% MVC (time1 to time2), whereas tibialis anterior (TA) H-reflexes and M-waves did not change significantly (H-reflex from 0.8 to 2% Mmax; M-wave from 12 to 14% Mmax). In 7 of 13 subjects, extra torque developed at higher stimulation intensities (35-65% Mmax). In these seven subjects, torque increased from 13 to 20% MVC, whereas TA H-reflexes and M-waves were not significantly different (H-reflex from 0.7 to 1% Mmax; M-wave from 49 to 54% Mmax). Thus enhanced H-reflexes contributed to extra plantarflexion, however, other factors generated extra dorsiflexion.