Comparison between electrically evoked and voluntary isometric contractions for biceps brachii muscle oxidative metabolism using near-infrared spectroscopy

Myoelectric, Myo-Oxygenation, and Myotonometry Changes during Robot-Assisted Bilateral Arm Exercises with Varying Resistances

Robot-assisted bilateral arm training has demonstrated its effectiveness in improving motor function in individuals post-stroke, showing significant enhancements with increased repetitions. However, prolonged training sessions may lead to both mental and muscle fatigue. We conducted two types of robot-assisted bimanual wrist exercises on 16 healthy adults, separated by one week: long-duration, low-resistance workouts and short-duration, high-resistance exercises. Various measures, including surface electromyograms, near-infrared spectroscopy, heart rate, and the Borg Rating of Perceived Exertion scale, were employed to assess fatigue levels and the impacts of exercise intensity. High-resistance exercise resulted in a more pronounced decline in electromyogram median frequency and recruited a greater amount of hemoglobin, indicating increased muscle fatigue and a higher metabolic demand to cope with the intensified workload. Additionally, high-resistance exercise led to increased sympathetic activation and a greater sense of exertion. Conversely, engaging in low-resistance exercises proved beneficial for reducing post-exercise muscle stiffness and enhancing muscle elasticity. Choosing a low-resistance setting for robot-assisted wrist movements offers advantages by alleviating mental and physiological loads. The reduced training intensity can be further optimized by enabling extended exercise periods while maintaining an approximate dosage compared to high-resistance exercises.

Effects of multicomponent exercise training on muscle oxygenation in young and older adults

Objective

Though multicomponent exercise training was found beneficial in improving the physical functionality, the effects of multicomponent exercise training on muscle oxygenation are still unclear. The purpose of this study was to investigate the effects of multicomponent exercise training on muscle oxygenation in young and older participants.

Methods

In this study, 17 young adults (Y) and 18 healthy older adults (E) were recruited to receive a multicomponent exercise training for 12 weeks, 2-3 sessions per week. Muscle oxygenation, muscle strength, and electromyography data were collected and compared pre- and post-training. Muscle oxygen saturation (SpO₂) during isometric knee extension tests involving voluntary contraction (VOL) and electrical stimulation (ES) was measured by near-infrared spectroscopy. The SpO₂ kinetics in the contraction and recovery phases were calculated using a tangential model to extract ΔSpO₂ and inflection time (IF).

Results

Muscle strength significantly increased in the post-training (234.31 ± 83.2 N·m, p < 0.05). The post-training ΔSpO₂ of the ES in the Y (8.43 ± 5.35%) significantly increased and was higher than that in the E (2.78 ± 3.03%, p < 0.05). In the recovery phase, the post-training IF of VOL (7.07 ± 3.31s) was significantly shorter than that of the pre-training period (8.73 ± 4.46s, p < 0.05). Additionally, the median frequency of electromyography significantly decreased in the post-training period (103.84 ± 21.75 Hz, p < 0.05).

Conclusion

The multicomponent exercise training improved the muscle strength, neuromuscular performance, and muscle aerobic function irrespective of age. The primary adaptation of the muscles to the multicomponent exercise training between the two groups varied.

Electrical-tomographic imaging of physiological-induced conductive response in calf muscle compartments during voltage intensity change of electrical muscle stimulation (vic-EMS)

Objectives. The electrical-tomographic imaging has been achieved for exploring differential tendency of physiological-induced conductive response in calf muscle compartments during voltage intensity change of electrical muscle stimulation (vic-EMS).Approach. In the experiments, the differential tendency of conductivity distribution imagesσduringvic-EMS were clearly imaged as three responsive muscle compartments, which are calledM₁compartment composed of gastrocnemius muscle,M₂compartment composed of tibialis anterior, extensor digitorum longus, and peroneus longus muscles, andM₃compartment composed of soleus muscle.Main results. The differential tendency of spatial-mean conductivity 〈σ〉_M1is the same as the differential tendency of venous blood flow velocityv_bland blood lactate concentrationC_blduringvic-EMS by the increased tendency of spatial-mean conductivity difference Δ〈σ〉_M1, venous blood flow velocity difference Δv_bland blood lactate concentration difference ΔC_bl. The 〈σ〉_M1is increased with the increase of voltage intensity from 〈σ^pre〉_M1 = 0.142 [-] to 〈σ^l14 〉 _M1 = 0.442 [-] (pre: pre-training,l14: voltage level duringvic-EMSl = 14) by Δ〈σ^l14-pre〉_M1 = 204.2% (n = 16,p < 0.01). Correspondingly, thev_blandC_blare increased with the increase of voltage intensity by Δv_bl^l14-pre= 1480.5% (n = 16,p < 0.01) and ΔC_bl^l14-pre= 230.1% (n = 16,p < 0.01) respectively.Significance: The reason for the differential tendency of increase in <σ>_M1suggests an increase in muscle extracellular volumes duringvic-EMS due to the co-effect of venous blood flow velocity and blood lactate metabolism. Based on the conductivity second-order difference images∂2σM1φ∂φ2φand spatial-mean conductivity second-order difference∂2σM1φ∂φ2φ,optimum voltage intensityφ_OVIis discussed among sixteen volunteer subjects, which increased with a thicker subcutaneous fat layer.

Neuromuscular electrical stimulation acutely mobilizes endothelial progenitor cells in critically ill patients with sepsis

BACKGROUND

Endothelial progenitor cells (EPCs) have been suggested to constitute a restoration index of the disturbed endothelium in ICU patients. Neuromuscular electric stimulation (NMES) is increasingly employed in ICU to prevent comorbidities such as ICU-acquired weakness, which is related to endothelial dysfunction. The role of NMES to mobilize EPCs has not been investigated yet. The purpose of this study was to explore the NMES-induced effects on mobilization of EPCs in septic ICU patients.

METHODS

Thirty-two septic mechanically ventilated patients (mean ± SD, age 58 ± 14 years) were randomized to one of the two 30-min NMES protocols of different characteristics: a high-frequency (75 Hz, 6 s on-21 s off) or a medium-frequency (45 Hz, 5 s on-12 s off) protocol both applied at maximally tolerated intensity. Blood was sampled before and immediately after the NMES sessions. Different EPCs subpopulations were quantified by cytometry markers CD34(+)/CD133(+)/CD45(-), CD34(+)/CD133(+)/CD45(-)/VEGFR2 (+) and CD34(+)/CD45(-)/VEGFR2 (+).

RESULTS

Overall, CD34(+)/CD133(+)/CD45(-) EPCs increased from 13.5 ± 10.2 to 20.8 ± 16.9 and CD34(+)/CD133(+)/CD45(-)/VEGFR2 (+) EPCs from 3.8 ± 5.2 to 6.4 ± 8.5 cells/10(6) enucleated cells (mean ± SD, p < 0.05). CD34(+)/CD45(-)/VEGFR2 (+) EPCs also increased from 16.5 ± 14.5 to 23.8 ± 19.2 cells/10(6) enucleated cells (mean ± SD, p < 0.05). EPCs mobilization was not affected by NMES protocol and sepsis severity (p > 0.05), while it was related to corticosteroids administration (p < 0.05).

CONCLUSIONS

NMES acutely mobilized endothelial progenitor cells, measures of the endothelial restoration potential, in septic ICU patients.

Local Muscle Metabolic Demand Induced by Neuromuscular Electrical Stimulation and Voluntary Contractions at Different Force Levels: A NIRS Study

Functional Muscle metabolic demand during contractions evoked by neuromuscular electrical stimulation (NMES) has been consistently documented to be greater than voluntary contractions (VOL) at the same force level (10-50% maximal voluntary contraction-MVC). However, we have shown using a near-infrared spectroscopy (NIRS) technique that local muscle metabolic demand is similar between NMES and VOL performed at MVC levels, thus controversy exists. This study therefore compared biceps brachii muscle metabolic demand (tissue oxygenation index-TOI and total hemoglobin volume-tHb) during a 10s isometric contraction of the elbow flexors between NMES (stimulation frequency of 30Hz and current level to evoke 30% MVC) and VOL at 30% MVC (VOL-30%MVC) and MVC (VOL-MVC) level in 8 healthy men (23-33-y). Greater changes in TOI and tHb induced by NMES than VOL-30%MVC confirm previous studies of a greater local metabolic demand for NMES than VOL at the same force level. The same TOI and tHb changes for NMES and VOL-MVC suggest that local muscle metabolic demand and intramuscular pressure were similar between conditions. In conclusion, these findings indicate that NMES induce a similar local muscle metabolic demand as that of maximal VOL.

Effects of Increasing Neuromuscular Electrical Stimulation Current Intensity on Cortical Sensorimotor Network Activation: A Time Domain fNIRS Study

Neuroimaging studies have shown neuromuscular electrical stimulation (NMES)-evoked movements activate regions of the cortical sensorimotor network, including the primary sensorimotor cortex (SMC), premotor cortex (PMC), supplementary motor area (SMA), and secondary somatosensory area (S2), as well as regions of the prefrontal cortex (PFC) known to be involved in pain processing. The aim of this study, on nine healthy subjects, was to compare the cortical network activation profile and pain ratings during NMES of the right forearm wrist extensor muscles at increasing current intensities up to and slightly over the individual maximal tolerated intensity (MTI), and with reference to voluntary (VOL) wrist extension movements. By exploiting the capability of the multi-channel time domain functional near-infrared spectroscopy technique to relate depth information to the photon time-of-flight, the cortical and superficial oxygenated (O₂Hb) and deoxygenated (HHb) hemoglobin concentrations were estimated. The O₂Hb and HHb maps obtained using the General Linear Model (NIRS-SPM) analysis method, showed that the VOL and NMES-evoked movements significantly increased activation (i.e., increase in O₂Hb and corresponding decrease in HHb) in the cortical layer of the contralateral sensorimotor network (SMC, PMC/SMA, and S2). However, the level and area of contralateral sensorimotor network (including PFC) activation was significantly greater for NMES than VOL. Furthermore, there was greater bilateral sensorimotor network activation with the high NMES current intensities which corresponded with increased pain ratings. In conclusion, our findings suggest that greater bilateral sensorimotor network activation profile with high NMES current intensities could be in part attributable to increased attentional/pain processing and to increased bilateral sensorimotor integration in these cortical regions.

Mechanisms of Myofascial Pain

Myofascial pain syndrome is an important health problem. It affects a majority of the general population, impairs mobility, causes pain, and reduces the overall sense of well-being. Underlying this syndrome is the existence of painful taut bands of muscle that contain discrete, hypersensitive foci called myofascial trigger points. In spite of the significant impact on public health, a clear mechanistic understanding of the disorder does not exist. This is likely due to the complex nature of the disorder which involves the integration of cellular signaling, excitation-contraction coupling, neuromuscular inputs, local circulation, and energy metabolism. The difficulties are further exacerbated by the lack of an animal model for myofascial pain to test mechanistic hypothesis. In this review, current theories for myofascial pain are presented and their relative strengths and weaknesses are discussed. Based on new findings linking mechanoactivation of reactive oxygen species signaling to destabilized calcium signaling, we put forth a novel mechanistic hypothesis for the initiation and maintenance of myofascial trigger points. It is hoped that this lays a new foundation for understanding myofascial pain syndrome and how current therapies work, and gives key insights that will lead to the improvement of therapies for its treatment.

Acute microcirculatory effects of medium frequency versus high frequency neuromuscular electrical stimulation in critically ill patients - a pilot study

BACKGROUND

Intensive care unit-acquired weakness (ICUAW) is a common complication, associated with significant morbidity. Neuromuscular electrical stimulation (NMES) has shown promise for prevention. NMES acutely affects skeletal muscle microcirculation; such effects could mediate the favorable outcomes. However, optimal current characteristics have not been defined. This study aimed to compare the effects on muscle microcirculation of a single NMES session using medium and high frequency currents.

METHODS

ICU patients with systemic inflammatory response syndrome (SIRS) or sepsis of three to five days duration and patients with ICUAW were studied. A single 30-minute NMES session was applied to the lower limbs bilaterally using current of increasing intensity. Patients were randomly assigned to either the HF (75 Hz, pulse 400 μs, cycle 5 seconds on - 21 seconds off) or the MF (45 Hz, pulse 400 μs, cycle 5 seconds on - 12 seconds off) protocol. Peripheral microcirculation was monitored at the thenar eminence using near-infrared spectroscopy (NIRS) to obtain tissue O2 saturation (StO2); a vascular occlusion test was applied before and after the session. Local microcirculation of the vastus lateralis was also monitored using NIRS.

RESULTS

Thirty-one patients were randomized. In the HF protocol (17 patients), peripheral microcirculatory parameters were: thenar O2 consumption rate (%/minute) from 8.6 ± 2.2 to 9.9 ± 5.1 (P = 0.08), endothelial reactivity (%/second) from 2.7 ± 1.4 to 3.2 ± 1.9 (P = 0.04), vascular reserve (seconds) from 160 ± 55 to 145 ± 49 (P = 0.03). In the MF protocol: thenar O2 consumption rate (%/minute) from 8.8 ± 3.8 to 9.9 ± 3.6 (P = 0.07), endothelial reactivity (%/second) from 2.5 ± 1.4 to 3.1 ± 1.7 (P = 0.03), vascular reserve (seconds) from 163 ± 37 to 144 ± 33 (P = 0.001). Both protocols showed a similar effect. In the vastus lateralis, average muscle O2 consumption rate was 61 ± 9%/minute during the HF protocol versus 69 ± 23%/minute during the MF protocol (P = 0.5). The minimum amplitude in StO2 was 5 ± 4 units with the HF protocol versus 7 ± 4 units with the MF protocol (P = 0.3). Post-exercise, StO2 increased by 6 ± 7 units with the HF protocol versus 5 ± 4 units with the MF protocol (P = 0.6). These changes correlated well with contraction strength.

CONCLUSIONS

A single NMES session affected local and systemic skeletal muscle microcirculation. Medium and high frequency currents were equally effective.

Investigating the adaptation of muscle oxygenation to resistance training for elders and young men using near-infrared spectroscopy

PURPOSE

The purpose of this study was to investigate the differences in resistance training adaptation on muscle oxygenation between young and elderly subjects. Groups of eleven trained young, untrained young, trained elderly, and untrained elderly (UTE) were recruited.

METHODS

Muscle oxygenation of the vastus lateralis muscle during 20 % maximal voluntary isometric contraction was observed using near-infrared spectroscopy. The oxygen saturation (SpO2) kinetics in the contraction and recovery phases was modeled with a tangential model to extract ΔSpO2 and inflection time (IF). The median frequencies of SpO2 data representing the change of tissue oxygenation oscillation were compared.

RESULTS

The ΔSpO2 values for the trained groups (12.00 ± 7.86%) were significantly higher than those for the untrained groups (5.91 ± 4.36%, P < 0.05), and those for the young groups (11.63 ± 7.52%) were significantly higher than those for the older groups (6.29 ± 4.70%, P < 0.05). In the recovery phase, the IF was significantly longer for the elderly groups (10.32 ± 4.39 s, P < 0.05) than that for the young groups (6.31 ± 3.69 s). The median frequency of tissue oxygenation oscillation was significantly lower for the TE group (0.41 ± 0.12 Hz, P < 0.05) than that for the UTE group (0.57 ± 0.13 Hz).

CONCLUSIONS

The increased ΔSpO2 in trained groups during muscle contraction may be due to lower microvascular O2 pressure. The lower median frequency for the TE group indicates that tissue oxygenation oscillation significantly trended toward low-frequency oscillation, possibly resulting from the enhancement of vascular function.

Lack of functional effects of neuromuscular electrical stimulation on skeletal muscle oxidative metabolism in healthy humans

A recent study has demonstrated that neuromuscular electrical stimulation (NMES) determines, in vitro, a fast-to-slow shift in the metabolic profile of muscle fibers. The aim of the present study was to evaluate if, in the same subjects, these changes would translate, in vivo, into an enhanced skeletal muscle oxidative metabolism. Seven young men were tested (cycle ergometer) during incremental exercises up to voluntary exhaustion and moderate and heavy constant-load exercises (CLE). Measurements were carried out before and after an 8-wk training program by isometric bilateral NMES (quadriceps muscles), which induced an ∼25% increase in maximal isometric force. Breath-by-breath pulmonary O2 uptake (V̇o2) and vastus lateralis oxygenation indexes (by near-infrared spectroscopy) were determined. Skeletal muscle fractional O2 extraction was estimated by near-infrared spectroscopy on the basis of changes in concentration of deoxygenated hemoglobin + myoglobin. Values obtained at exhaustion were considered “peak” values. The following functional evaluation variables were unaffected by NMES: peak V̇o2; gas exchange threshold; the V̇o2 vs. work rate relationship (O2 cost of cycling); changes in concentration of deoxygenated hemoglobin + myoglobin vs. work rate relationship (related to the matching between O2 delivery and V̇o2); peak fractional O2 extraction; V̇o2 kinetics (during moderate and heavy CLE) and the amplitude of its slow component (during heavy CLE). Thus NMES did not affect several variables of functional evaluation of skeletal muscle oxidative metabolism. Muscle hypertrophy induced by NMES could impair peripheral O2 diffusion, possibly counterbalancing, in vivo, the fast-to-slow phenotypic changes that were observed in vitro, in a previous work, in the same subjects of the present study.

Biceps brachii muscle oxygenation in electrical muscle stimulation

The purpose of this study was to compare between electrical muscle stimulation (EMS) and maximal voluntary (VOL) isometric contractions of the elbow flexors for changes in biceps brachii muscle oxygenation (tissue oxygenation index, TOI) and haemodynamics (total haemoglobin volume, tHb = oxygenated-Hb + deoxygenated-Hb) determined by near-infrared spectroscopy (NIRS). The biceps brachii muscle of 10 healthy men (23-39 years) was electrically stimulated at high frequency (75 Hz) via surface electrodes to evoke 50 intermittent (4-s contraction, 15-s relaxation) isometric contractions at maximum tolerated current level (EMS session). The contralateral arm performed 50 intermittent (4-s contraction, 15-s relaxation) maximal voluntary isometric contractions (VOL session) in a counterbalanced order separated by 2-3 weeks. Results indicated that although the torque produced during EMS was approximately 50% of VOL (P<0.05), there was no significant difference in the changes in TOI amplitude or TOI slope between EMS and VOL over the 50 contractions. However, the TOI amplitude divided by peak torque was approximately 50% lower for EMS than VOL (P<0.05), which indicates EMS was less efficient than VOL. This seems likely because of the difference in the muscles involved in the force production between conditions. Mean decrease in tHb amplitude during the contraction phases was significantly (P<0.05) greater for EMS than VOL from the 10th contraction onwards, suggesting that the muscle blood volume was lower in EMS than VOL. It is concluded that local oxygen demand of the biceps brachii sampled by NIRS is similar between VOL and EMS.