Comparison between electrically-evoked and voluntary wrist movements on sensorimotor and prefrontal cortical activation: A multi-channel time domain functional NIRS study

Neuromuscular electrical stimulation (NMES) has been consistently demonstrated to improve skeletal muscle function in neurological populations with movement disorders, such as poststroke and incomplete spinal cord injury (Vanderthommen and Duchateau, 2007). Recent research has documented that rapid, supraspinal central nervous system reorganisation/neuroplastic mechanisms are also implicated during NMES (Chipchase et al., 2011). Functional neuroimaging studies have shown NMES to activate a network of sub-cortical and cortical brain regions, including the sensorimotor (SMC) and prefrontal (PFC) cortex (Blickenstorfer et al., 2009; Han et al., 2003; Muthalib et al., 2012). A relationship between increase in SMC activation with increasing NMES current intensity up to motor threshold has been previously reported using functional MRI (Smith et al., 2003). However, since clinical neurorehabilitation programmes commonly utilise NMES current intensities above the motor threshold and up to the maximum tolerated current intensity (MTI), limited research has determined the cortical correlates of increasing NMES current intensity at or above MTI (Muthalib et al., 2012). In our previous study (Muthalib et al., 2012), we assessed contralateral PFC activation using 1-channel functional near infrared spectroscopy (fNIRS) during NMES of the elbow flexors by increasing current intensity from motor threshold to greater than MTI and showed a linear relationship between NMES current intensity and the level of PFC activation. However, the relationship between NMES current intensity and activation of the motor cortical network, including SMC and PFC, has not been clarified. Moreover, it is of scientific and clinical relevance to know how NMES affects the central nervous system, especially in comparison to voluntary (VOL) muscle activation. Therefore, the aim of this study was to utilise multi-channel time domain fNIRS to compare SMC and PFC activation between VOL and NMESevoked wrist extension movements

The use of near-infrared spectroscopy in understanding skeletal muscle physiology: recent developments

This article provides a snapshot of muscle near-infrared spectroscopy (NIRS) at the end of 2010 summarizing the recent literature, offering the present status and perspectives of the NIRS instrumentation and methods, describing the main NIRS studies on skeletal muscle physiology, posing open questions and outlining future directions. So far, different NIRS techniques (e.g. continuous-wave (CW) and spatially, time- and frequency-resolved spectroscopy) have been used for measuring muscle oxygenation during exercise. In the last four years, approximately 160 muscle NIRS articles have been published on different physiological aspects (primarily muscle oxygenation and haemodynamics) of several upper- and lower-limb muscle groups investigated by using mainly two-channel CW and spatially resolved spectroscopy commercial instruments. Unfortunately, in only 15 of these studies were the advantages of using multi-channel instruments exploited. There are still several open questions in the application of NIRS in muscle studies: (i) whether NIRS can be used in subjects with a large fat layer; (ii) the contribution of myoglobin desaturation to the NIRS signal during exercise; (iii) the effect of scattering changes during exercise; and (iv) the effect of changes in skin perfusion, particularly during prolonged exercise. Recommendations for instrumentation advancements and future muscle NIRS studies are provided

Reliability of near-infrared spectroscopy for measuring biceps brachii oxygenation during sustained and repeated isometric contractions

We examine the test-retest reliability of biceps brachii tissue oxygenation index (TOI) parameters measured by near-infrared spectroscopy during a 10-s sustained and a 30-repeated (1-s contraction, 1-s relaxation) isometric contraction task at 30% of maximal voluntary contraction (30% MVC) and maximal (100% MVC) intensities. Eight healthy men (23 to 33 yr) were tested on three sessions separated by 3 h and 24 h, and the within-subject reliability of torque and each TOI parameter were determined by Bland-Altman+/-2 SD limits of agreement plots and coefficient of variation (CV). No significant (P>0.05) differences between the three sessions were found for mean values of torque and TOI parameters during the sustained and repeated tasks at both contraction intensities. All TOI parameters were within+/-2 SD limits of agreement. The CVs for torque integral were similar between the sustained and repeated task at both intensities (4 to 7%); however, the CVs for TOI parameters during the sustained and repeated task were lower for 100% MVC (7 to 11%) than for 30% MVC (22 to 36%). It is concluded that the reliability of the biceps brachii NIRS parameters during both sustained and repeated isometric contraction tasks is acceptable

Systemic inflammatory responses to maximal versus submaximal lengthening contractions of the elbow flexors

We compared changes in markers of muscle damage and systemic inflammation after submaximal and maximal lengthening muscle contractions of the elbow flexors. Using a cross-over design, 10 healthy young men not involved in resistance training completed a submaximal trial (10 sets of 60 lengthening contractions at 10% maximum isometric strength, 1 min rest between sets), followed by a maximal trial (10 sets of three lengthening contractions at 100% maximum isometric strength, 3 min rest between sets). Lengthening contractions were performed on an isokinetic dynamometer. Opposite arms were used for the submaximal and maximal trials, and the trials were separated by a minimum of two weeks. Blood was sampled before, immediately after, 1 h, 3 h, and 1-4 d after each trial. Total leukocyte and neutrophil numbers, and the serum concentration of soluble tumor necrosis factor-alpha receptor 1 were elevated after both trials (P < 0.01), but there were no differences between the trials. Serum IL-6 concentration was elevated 3 h after the submaximal contractions (P < 0.01). The concentrations of serum tumor necrosis factor-alpha, IL-1 receptor antagonist, IL-10, granulocyte-colony stimulating factor and plasma C-reactive protein remained unchanged following both trials. Maximum isometric strength and range of motion decreased significantly (P < 0.001) after both trials, and were lower from 1-4 days after the maximal contractions compared to the submaximal contractions. Plasma myoglobin concentration and creatine kinase activity, muscle soreness and upper arm circumference all increased after both trials (P < 0.01), but were not significantly different between the trials. Therefore, there were no differences in markers of systemic inflammation, despite evidence of greater muscle damage following maximal versus submaximal lengthening contractions of the elbow flexors

Frontal cortex activation during electrical muscle stimulation as revealed by functional near-infrared spectroscopy

This study compared electrical muscle stimulation (EMS) and voluntary (VOL) contractions of the elbow flexors for changes in frontal cortex (FC) oxygenated hemoglobin (∆O2Hb) and deoxygenated Hb (∆HHb) determined by functional near-infrared spectroscopy (fNIRS). Nine healthy men underwent an EMS session with one arm and 24 h later performed VOL exercise with the other arm. For the EMS session, ∆O2Hb increased (P \u3c 0.05) during the exercise performed at 30% of the maximal voluntary contraction (MVC), and thereafter progressively increased (P \u3c 0.05) with increasing the current amplitude, and both variables were correlated (r = 0.68, P \u3c 0.001). In the VOL session, ∆O2Hb did not change from baseline during 30% MVC contractions; however, ∆O2Hb progressively increased (P \u3c 0.05) during 100% MVC contractions, and ∆O2Hb was greater (P \u3c 0.05) during 100% MVC than 30% MVC. ∆O2Hb was greater (P \u3c 0.05) for EMS than VOL at 30% MVC, but no difference in ∆O2Hb was evident between EMS and VOL at the respective maximum intensity. In conclusion, intensity-related increases in FC activation during EMS can be determined using fNIRS

Comparison in muscle damage between maximal voluntary and electrically evoked isometric contractions of the elbow flexors

This study compared between maximal voluntary (VOL) and electrically stimulated (ES) isometric contractions of the elbow flexors for changes in indirect markers of muscle damage to investigate whether ES would induce greater muscle damage than VOL. Twelve non-resistance-trained men (23-39 years) performed VOL with one arm and ES with the contralateral arm separated by 2 weeks in a randomised, counterbalanced order. Both VOL and ES (frequency 75 Hz, pulse duration 250 &mu;s, maximally tolerated intensity) exercises consisted of 50 maximal isometric contractions (4-s on, 15-s off) of the elbow flexors at a long muscle length (160&deg;). Changes in maximal voluntary isometric contraction torque (MVC), range of motion, muscle soreness, pressure pain threshold and serum creatine kinase (CK) activity were measured before, immediately after and 1, 24, 48, 72 and 96 h following exercise. The average peak torque over the 50 isometric contractions was greater (P &lt; 0.05) for VOL (32.9 &plusmn; 9.8 N m) than ES (16.9 &plusmn; 6.3 N m). MVC decreased greater and recovered slower (P &lt; 0.05) after ES (15% lower than baseline at 96 h) than VOL (full recovery). Serum CK activity increased (P &lt; 0.05) only after ES, and the muscles became more sore and tender after ES than VOL (P &lt; 0.05). These results showed that ES induced greater muscle damage than VOL despite the lower torque output during ES. It seems likely that higher mechanical stress imposed on the activated muscle fibres, due to the specificity of motor unit recruitment in ES, resulted in greater muscle damage

Muscle oxygenation of vastus lateralis and medialis muscles during alternating and pulsed current electrical stimulation

This study compared between alternating and pulsed current electrical muscle stimulation (EMS) for muscle oxygenation and blood volume during isometric contractions. Nine healthy men (23–48 years) received alternating current EMS (2500 Hz) modulated at 75 Hz on the knee extensors of one leg, and pulsed current EMS (75 Hz) for the other leg separated by 2 weeks in a randomised, counter-balanced order. Pulse duration (400 μs), on–off ratio (5–15 s) and other stimulation parameters were matched between conditions and 30 isometric contractions were induced at the knee joint angle of 100° (0° full extension). Changes in tissue oxygenation index (∆TOI) and total hemoglobin volume (∆tHb) of vastus lateralis and medialis muscles over 30 contractions were assessed by a near-infrared spectroscopy, and were compared between conditions by a two-way repeated measures ANOVA. Peak torque produced during EMS increased over 30 contractions in response to the increase in the stimulation intensity for pulsed current, but not for the alternating current EMS. The torque during each isometric contraction was less stable in alternating than pulsed current EMS. The changes in ∆TOI amplitude during relaxation phases and ∆tHb amplitude were not significantly different between conditions. However, the decreases in ∆TOI amplitude during contraction phases from baseline were significantly (P \u3c 0.05) greater for the pulsed current than alternating current from the 18th contraction (−15.6 ± 2.3 vs. −8.9 ± 1.8%) to 30th contraction (−10.7 ± 1.8 vs. −4.8 ± 1.5%). These results suggest that the muscles were less activated in the alternating current EMS when compared with the pulsed current EMS

Music improves verbal memory encoding while decreasing prefrontal cortex activity: a fNIRS study

cote interne IRCAM: Ferreri13aNone / NoneNational audienceListening to music engages the whole brain, thus stimulating cognitive performance in a range of non-purely musical activities such as language and memory tasks. This article addresses an ongoing debate on the link between music and memory for words. While evidence on healthy and clinical populations suggests that music listening can improve verbal memory in a variety of situations, it is still unclear what specific memory process is affected and how. This study was designed to explore the hypothesis that music specifically benefits the encoding part of verbal memory tasks, by providing a richer context for encoding and therefore less demand on the dorsolateral prefrontal cortex (DLPFC). Twenty-two healthy young adults were subjected to functional near-infrared spectroscopy (fNIRS) imaging of their bilateral DLPFC while encoding words in the presence of either a music or a silent background. Behavioral data confirmed the facilitating effect of music background during encoding on subsequent item recognition. fNIRS results revealed significantly greater activation of the left hemisphere during encoding (in line with the HERA model of memory lateralization) and a sustained, bilateral decrease of activity in the DLPFC in the music condition compared to silence. These findings suggest that music modulates the role played by the DLPFC during verbal encoding, and open perspectives for applications to clinical populations with prefrontal impairments, such as elderly adults or Alzheimer’s patients

Neuromuscular electrical stimulation and voluntary wrist extension movements elicit similar sensorimotor cortex activation: A continuous-wave fNIRS study

Our previous study [1] using a high-cost time-domain (TD) functional near-infrared spectroscopy (fNIRS) prototype instrument showed that unilateral neuromuscular electrical stimulation (NMES) evoked wrist extension movements (50% of maximal tolerated current intensity-50%MTI) activated (increase in oxy-hemoglobin-O2Hb and concomitant decrease in deoxy-hemoglobin-HHb) a similar region of the contralateral sensorimotor cortex (SMC) as that of voluntary (VOL) movements. The aim of this study was to use a continuous-wave (CW) relatively low-cost commercial fNIRS instrument to measure contralateral (left) and ipsilateral (right) SMC activation (O2Hb and HHb time course, integral [O2HbINT and HHbINT] and peak levels [O2Hbmax and HHbmin]) during NMES (50%MTI) and VOL wrist extension movements of the right arm in 7 healthy male volunteers. Both NMES and VOL wrist extension movements activated the contralateral (left) and ipsilateral (right) SMC, however, the level of contralateral SMC activation was significantly greater than the ipsilateral SMC. Although the HHb parameters (HHbINT, HHbmin) indicated that there was no significant difference between conditions, the O2Hb parameters (O2HbINT and O2Hbmax) indicated a significantly greater contralateral SMC activation during VOL than NMES. Since HHb is less influenced by skin blood flow changes than O2Hb, we consider that HHb parameters provide a more accurate estimation of task-related cortical activation. In conclusion, these CW-fNIRS findings using HHb parameters indicate that NMES at moderate current intensity (50%MTI) and VOL wrist extension movements elicit a similar contralateral SMC activation, which confirms our previous study using a TD-fNIRS instrument

Severe hypoxia affects exercise performance independently of afferent feedback and peripheral fatigue

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