Oxygenation in the motor cortex during exhaustive pinching exercise

Intranasal administration of DHED protects against exhaustive exercise-induced brain injury in rats

DHED (10β,17β-dihydroxyestra-1,4-dien-3-one) is a brain-selective prodrug of 17β-estradiol and has been reported to have a strong neuroprotective effect. In this study, the exhaustive swimming rat model was used to investigate the therapeutic effects and mechanisms of intranasal DHED treatment. Male eight-week-old healthy Sprague Dawley rats were randomly divided into three groups: control group (Cont), exhaustive swimming (ES), and DHED + exhaustive swimming (DHED). The open-field test and beam-walking test were performed to measure exploratory behavior and general activity in rats. Immunofluorescence staining, western blotting, ELISA analysis and related assay kits were applied to measure brain damage, inflammatory cytokines, and apoptosis pathways. Behavioral data shows that DHED intranasal administration can prevent neurobehavioral impairment caused by exhaustive swimming. Using a series of bioanalytical assays, we demonstrated that DHED markedly abated neuronal injury compared to the exhaustive swimming group, as evidenced by the reduced expression of apoptosis-regulated proteins, the improvement of neural survival, and the prevention of myelin loss. In addition, mitochondrial fission was attenuated distinctly, and a dynamic equilibrium was restored. Intranasal administration of DHED likewise significantly suppressed reactive gliosis and the release of inflammatory cytokines in the rat cerebral motor cortex. Consistent with previous reports, DHED treatment ameliorated changes of excitatory neurotransmitters. These results provide strong support for the promising therapeutic effects of DHED on neuroprotection during exhaustive swimming. The underlying mechanisms may rely on mitochondrial dynamics, neuroinflammation, and the balance of neurotransmitters.

Effect of muscle fatigue on brain activity in healthy individuals

Fatigue is affected by both peripheral and central factors. However, the interrelationship between muscle fatigue and brain activity has not yet been clarified. This study aimed to clarify the effect of muscle fatigue due to sustained pinch movement on brain activity in healthy individuals using functional near-infrared spectroscopy (fNIRS). Ten healthy adults participated in the study. Pinch movement of isometric contraction was the task to be performed, and electromyogram of the first dorsal interosseous muscle and brain activity by fNIRS were measured in this period. The median power frequency (MdPF) was calculated as an index of muscle fatigue and the oxygen-Hb value in the bilateral premotor and motor areas was calculated as an index of brain activity. As a result, MdPF showed a significant decrease in the middle and later phases compared with that in the early phase (p < 0.05, p < 0.001, respectively) and a significant decrease in the later phase compared with that in the middle phase (p < 0.05). The oxygen-Hb values in the motor cortex were not significantly different between the analysis sections. The oxygen-Hb values in the premotor cortex was significantly increased in the later phase (p < 0.05) compared with that in the early phase. The premotor cortex was found to be specifically activated during muscle fatigue.

Effects of knee extension with different speeds of movement on muscle and cerebral oxygenation

Background

One of the mechanisms responsible for enhancing muscular hypertrophy is the high metabolic stress associated with a reduced muscular oxygenation occurring during exercise, which can be achieved by reducing the speed of movement. Studies have tested that lowered muscle oxygenation artificially induced by an inflatable cuff, could provoke changes in prefrontal cortex oxygenation, hence, to central fatigue. It was hypothesized that (1) exercising with a slow speed of movement would result in greater increase in cerebral and greater decrease in muscle oxygenation compared with exercises of faster speed and (2) the amount of oxygenation increase in the ipsilateral prefrontal cortex would be lower than the contralateral one.

Methods

An ISS Imagent frequency domain near infrared spectroscopy (NIRS) system was used to quantify oxygenation changes in the vastus lateralis muscle and prefrontal cortex (contra- and ipsilateral) during unilateral resistance exercises with different speeds of movement to voluntary fatigue. After one maximal repetition (1RM) test, eight subjects performed three sets of unilateral knee extensions (∼50% of 1RM), separated by 2 min rest periods, following the pace of 1 s, 3 s and 5 s for both concentric and eccentric phases, in a random order, during separate sessions. The amount of change for NIRS parameters for muscle (ΔHb: deoxyhemoglobin, ΔHbO: oxyhemoglobin, ΔHbT: total hemoglobin, ΔStO₂: oxygen saturation) were quantified and compared between conditions and sets by two-way ANOVA RM. Differences in NIRS parameters between contra- and ipsilateral (lobe) prefrontal cortex and conditions were tested.

Results

Exercising with slow speed of movement was associated to larger muscle deoxygenation than normal speed of movement, as revealed by significant interaction (set × condition) for ΔHb (p = 0.01), and by significant main effects of condition for ΔHbO (p = 0.007) and ΔStO₂ (p = 0.016). With regards to the prefrontal cortex, contralateral lobe showed larger oxygenation increase than the ipsilateral one for ΔHb, ΔHbO, ΔHbT, ΔStO₂ in each set (main effect of lobe: p < 0.05). Main effects of condition were significant only in set1 for all the parameters, and significant interaction lobe × condition was found only for ΔHb in set1 (p < 0.05).

Discussion

These findings provided evidence that speed of movement influences the amount of muscle oxygenation. Since the lack of oxygen in muscle is associated to increased metabolic stress, manipulating the speed of movement may be useful in planning resistance-training programs. Moreover, consistent oxygenation increases in both right and left prefrontal lobes were found, suggesting a complementary interaction between the ipsi- and contralateral prefrontal cortex, which also seems related to fatigue.

Cortical motor output decreases after neuromuscular fatigue induced by electrical stimulation of the plantar flexor muscles

AIM

Neuromuscular electrical stimulation (NMES) causes early onset of neuromuscular fatigue. Peripheral electrophysiological explorations suggest that supra-spinal alterations are involved through sensitive afferent pathways. As sensory input is projected over the primary somatosensory cortex (S1), S1 area involvement in inhibiting the central motor drive can be hypothesized. This study assessed cortical activity under a fatiguing NMES protocol at low frequency.

METHODS

Twenty healthy males performed five NMES sequences of 17 trains over the plantar flexors (30 Hz, 4 s on/6 s off). Before and after each sequence, neuromuscular tests composed of maximal voluntary contractions (MVCs) were carried out. Cortical activity was assessed during MVCs with functional near-infrared spectroscopy over S1 and primary motor (M1) areas, through oxy- [HbO] and deoxy-haemoglobin [HbR] variation. Electrophysiological data (H-reflex during MVC, EMG activity and level of voluntary activation) were also recorded.

RESULTS

MVC torque significantly decreased after the first 17 NMES trains (P < 0.001). The electrophysiological data were consistent with supra-spinal alterations. In addition, [HbO] declined significantly during the protocol over the S1 and M1 areas from the first 17 NMES trains (P < 0.01 and P < 0.001 respectively), while [HbR] increased (P < 0.05 and P < 0.01 respectively), indicating early decline in cortical activity over both primary cortical areas.

CONCLUSIONS

The declining cortical activity over the M1 area is highly consistent with the electrophysiological findings and supports motor cortex involvement in the loss of force after a fatiguing NMES protocol. In addition, the declining cortical activity over the S1 area indicates that the decreased motor output from M1 is not due to increased S1 inhibitory activity.

The activity of the primary motor cortex ipsilateral to the exercising hand decreases during repetitive handgrip exercise

The brain function controlling muscle force production is not yet fully understood. The purpose of this study was to examine bilateral primary motor cortex (M1) oxygenation during static-handgrip exercises performed with the right hand (60% maximal voluntary contraction; 10 s exercise/75 s rest; five sets). Twelve healthy, right-handed male subjects participated in this study. Near-infrared spectroscopy probes were positioned over the bilateral M1 to measure cortical oxygenation during handgrip exercises. The maximum values of the changes in concentrations of oxyhemoglobin (HbO(2)) and deoxyhemoglobin (Hb) across the trials (i) did not change significantly during the contralateral M1 activation (p > 0.05), whereas (ii) in the case of the ipsilateral M1 activation a significant (p < 0.05) decrease in HbO(2) and a significant (p < 0.01) decrease in Hb could be measured. The activation in ipsilateral M1 at the fifth trial was significantly decreased compared with that in the first trial (HbO(2): p < 0.001; Hb: p < 0.001). The present results suggest that the ipsilateral M1 is recruited during the motor task in compensation for the contralateral M1 and the habituation to motor task might alter the efficiency for interaction of the ipsilateral M1 to the contralateral M1. The interhemispheric interaction might change due to habituation to motor task.

Cerebral oxygenation decreases but does not impair performance during self-paced, strenuous exercise

AIM

The reduction in cerebral oxygenation (Cox) is associated with the cessation of exercise during constant work rate and incremental tests to exhaustion. Yet in exercises of this nature, ecological validity is limited due to work rate being either fully or partly dictated by the protocol, and it is unknown whether cerebral deoxygenation also occurs during self-paced exercise. Here, we investigated the cerebral haemodynamics during a 5-km running time trial in trained runners.

METHODS

Rating of perceived exertion (RPE) and surface electromyogram (EMG) of lower limb muscles were recorded every 0.5 km. Changes in Cox (prefrontal lobe) were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhaemoglobin (Delta[O(2)Hb], Delta[HHb]). Changes in total Hb were calculated (Delta[THb] = Delta[O(2)Hb] + Delta[HHb]) and used as an index of change in regional blood volume.

RESULTS

During the trial, RPE increased from 6.6 +/- 0.6 to 19.1 +/- 0.7 indicating maximal exertion. Cox rose from baseline to 2.5 km ( upward arrowDelta[O(2)Hb], upward arrowDelta[HHb], upward arrowDelta[THb]), remained constant between 2.5 and 4.5 km, and fell from 4.5 to 5 km ( downward arrowDelta[O(2)Hb], upward arrowDelta[HHb], <-->Delta[THb]). Interestingly, the drop in Cox at the end of the trial coincided with a final end spurt in treadmill speed and concomitant increase in skeletal muscle recruitment (as revealed by higher lower limb EMG).

CONCLUSION

Results confirm the large tolerance for change in Cox during exercise at sea level, yet further indicate that, in conditions of self-selected work rate, cerebral deoxygenation remains within a range that does not hinder strenuous exercise performance.

Effect of severe hypoxia on prefrontal cortex and muscle oxygenation responses at rest and during exhaustive exercise

Near infrared spectroscopy (NIRS) may provide valuable insight into the determinants of exercise performance. We examined the effects of severe hypoxia on cerebral (prefrontal lobe) and muscle (gastrocnemius) oxygenation at rest and during a fatiguing task. After a 15-min rest, 15 healthy subjects (age 25.3 +/- 0.9 yr) performed a sustained contraction of the ankle extensors at 40% of maximal voluntary force until exhaustion. The contraction was performed at two different fractions of inspired O2 fraction (F(IO2) = 0.21/0.11) in randomized and single-blind fashion. Cerebral and muscle oxy-(HbO2) deoxy-(HHb) total-hemoglobin (HbTot) and tissue oxygenation index (TOI) were monitored continuously by NIRS. Arterial O2 saturation (SpO2) was estimated by pulse oximetry throughout the protocol. Muscle TOI did not differ between normoxia and hypoxia after the 15-min rest, whereas SpO2 and cerebral TOI significantly dropped (-6.5 +/- 0.9% and -3.9 +/- 1.0%, respectively, P<0.05) in hypoxia. The muscle NIRS changes during exercise were similar in normoxia and hypoxia, whereas the increased cerebral HbTot and HbO2 near exhaustion were markedly reduced in hypoxia. In conclusion, although F(IO2) had no significant effect on endurance time, NIRS patterns near exhaustion in hypoxia differed from normoxia.

Prefrontal cortex oxygenation and neuromuscular responses to exhaustive exercise

Near-infrared spectroscopy (NIRS) allows non-invasive monitoring of central and peripheral changes in oxygenation during exercise and may provide valuable insight into the factors affecting fatigue. This study aimed to explore the changes in oxygenation of prefrontal cortex and active muscle tissue as limiting factors of incremental exercise performance in trained cyclists. Thirteen trained healthy subjects (mean +/- SE: age 24.9 +/- 1.5 years, body mass 70.1 +/- 1.2 kg, training 6.1 +/- 0.9 h week(-1)) performed a progressive maximal exercise to exhaustion on a cycling ergometer. Prefrontal cortex (Cox) and vastus lateralis muscle (Mox) oxygenation were measured simultaneously by NIRS throughout the exercise. Maximal voluntary isometric knee torques and quadriceps neuromuscular fatigue (M-wave properties and voluntary activation ratio) were evaluated before and after exercise. Maximal power output and oxygen consumption were 380.8 +/- 7.9 W and 75.0 +/- 2.2 ml min(-1) kg(-1), respectively. Mox decreased significantly throughout exercise while Cox increased in the first minutes of exercise but decreased markedly from the workload corresponding to the second ventilatory threshold up to exhaustion (P < 0.05). No significant difference was noted 6 min after maximal exercise in either the voluntary activation ratio or the M-wave properties. These findings are compatible with the notion that supraspinal modulation of motor output precedes exhaustion.