The level of effort, rather than muscle exercise intensity determines strength gain following a six-week training

AIM

This study investigated the effect of voluntary motor effort during a low-intensity (30% maximal voluntary contraction [MVC]) muscle exercise training program on increasing muscle strength.

MATERIALS AND METHODS

Eighteen young and healthy individuals were randomly assigned to one of three groups: high mental effort (HME), low mental effort (LME), or a no-training control (CTRL) group. Training lasted for 6weeks (15min/day, 5days/week). The participants' right-elbow flexor muscle strength was measured before and after the training program.

KEY FINDINGS

After training, the HME group gained 20.47±8.33% (P=0.01) strength while the LME and CTRL groups had negligible strength changes (1.89±0.96% and -3.27±2.61%, respectively; P>0.05) despite muscle contraction intensity (30% MVC) sustained during training was the same for the HME and LME groups. These results suggest that the level of effort involved in resistance exercise training plays a critical role in determining the amount of strength augmentation.

SIGNIFICANCE

The finding that high effort combined with low-level physical exercise training can significantly increase muscle strength has rehabilitation applications as many patients and frail older adults have difficulties in participating in high-intensity exercise training such as lifting heavy weights. High effort plus low-level muscle exercise might serve as a safe training regimen for effective muscle strengthening in vulnerable populations.

The effect of motor overflow on bimanual asymmetric force coordination

Motor overflow, typically described in the context of unimanual movements, refers to the natural tendency for a 'resting' limb to move during movement of the opposite limb and is thought to be influenced by inter-hemispheric interactions and intra-cortical networks within the 'resting' hemisphere. It is currently unknown, however, how motor overflow contributes to asymmetric force coordination task accuracy, referred to as bimanual interference, as there is need to generate unequal forces and corticospinal output for each limb. Here, we assessed motor overflow via motor evoked potentials (MEPs) and the regulation of motor overflow via inter-hemispheric inhibition (IHI) and short-intra-cortical inhibition (SICI) using transcranial magnetic stimulation in the presence of unimanual and bimanual isometric force production. All outcomes were measured in the left first dorsal interosseous (test hand) muscle, which maintained 30% maximal voluntary contraction (MVC), while the right hand (conditioning hand) was maintained at rest, 10, 30, or 70% of its MVC. We have found that as higher forces are generated with the conditioning hand, MEP amplitudes at the active test hand decreased and inter-hemispheric inhibition increased, suggesting reduced motor overflow in the presence of bimanual asymmetric forces. Furthermore, we found that subjects with less motor overflow (i.e., reduced MEP amplitudes in the test hemisphere) demonstrated poorer accuracy in maintaining 30% MVC across all conditions. These findings suggest that motor overflow may serve as an adaptive substrate to support bimanual asymmetric force coordination.

Baduanjin Mind-Body Intervention Improves the Executive Control Function

This study aims at comparing the effects of the Baduanjin mind-body (BMB) intervention with a conventional relaxation training program on enhancing the executive function. The study also attempts to explore the neural substrates underlying the cognitive effect of BMB intervention using near-infrared spectroscopy (NIRS) technique. Forty-two healthy college students were randomly allocated into either the Baduanjin intervention group or relaxation training (control) group. Training lasted for 8 weeks (90 min/day, 5 days/week). Each participant was administered the shortened Profile of Mood States to evaluate their mood status and the flanker task to evaluate executive function before and after training. While performing the flanker task, the NIRS data were collected from each participant. After training, individuals who have participated in BMB exercise showed a significant reduction in depressive mood compared with the same measure before the intervention. However, participants in the control group showed no such reduction. The before vs. after measurement difference in the flanker task incongruent trails was significant only for the Baduanjin intervention group. Interestingly, an increase in oxygenated hemoglobin in the left prefrontal cortex was observed during the Incongruent Trails test only after the BMB exercise intervention. These findings implicate that Baduanjin is an effective and easy-to-administering mind-body exercise for improving executive function and perhaps brain self-regulation in a young and healthy population.

Brain Functional Connectivity Is Different during Voluntary Concentric and Eccentric Muscle Contraction

Previous studies report greater activation in the cortical motor network in controlling eccentric contraction (EC) than concentric contraction (CC) of human skeletal muscles despite lower activation level of the muscle associated with EC. It is unknown, however, whether the strength of functional coupling between the primary motor cortex (M1) and other involved areas in the brain differs as voluntary movements are controlled by a network of regions in the primary, secondary and association cortices. Examining fMRI-based functional connectivity (FC) offers an opportunity to measure strength of such coupling. To address the question, we examined functional MRI (fMRI) data acquired during EC and CC (20 contractions each with similar movement distance and speed) of the right first dorsal interosseous (FDI) muscle in 11 young (20-32 years) and healthy individuals and estimated FC between the M1 and a number of cortical regions in the motor control network. The major findings from the mechanical and fMRI-based FC analysis were that (1) no significant differences were seen in movement distance, speed and stability between the EC and CC; (2) significantly stronger mean FC was found for CC than EC. Our finding provides novel insights for a better understanding of the control mechanisms underlying voluntary movements produced by EC and CC. The finding is potentially helpful for guiding the development of targeted sport training and/or therapeutic programs for performance enhancement and injury prevention.

Motor effort training with low exercise intensity improves muscle strength and descending command in aging

This study explored the effect of high mental effort training (MET) and conventional strength training (CST) on increasing voluntary muscle strength and brain signal associated with producing maximal muscle force in healthy aging. Twenty-seven older adults (age: 75 ± 7.9 yr, 8 women) were assigned into 1 of 3 groups: MET group-trained with low-intensity (30% maximal voluntary contraction [MVC]) physical exercise combined with MET, CST group-trained with high-intensity muscle contractions, or control (CTRL) group-no training of any kind. MET and CST lasted for 12 weeks (5 sessions/week). The participants' elbow flexion strength of the right arm, electromyography (EMG), and motor activity-related cortical potential (MRCP) directly related to the strength production were measured before and after training. The CST group had the highest strength gain (17.6%, P <0.001), the MET group also had significant strength gain (13.8%, P <0.001), which was not statistically different from that of the CST group even though the exercise intensity for the MET group was only at 30% MVC level. The CTRL group did not have significant strength changes. Surprisingly, only the MET group demonstrated a significant augmentation in the MRCP (29.3%, P <0.001); the MRCP increase in CST group was at boarder-line significance level (12.11%, P = 0.061) and that for CTRL group was only 4.9% (P = 0.539). These results suggest that high mental effort training combined with low-intensity physical exercise is an effective method for voluntary muscle strengthening and this approach is especially beneficial for those who are physically weak and have difficulty undergoing conventional strength training.

Post-exercise depression following submaximal and maximal isometric voluntary contraction

It is well known that corticomotor excitability is altered during the post-exercise depression following fatigue within the primary motor cortex (M1). However, it is currently unknown whether corticomotor reorganization following muscle fatigue differs between magnitudes of force and whether corticomotor reorganization occurs measured with transcranial magnetic stimulation (TMS). Fifteen young healthy adults (age 23.8±1.4, 8 females) participated in a within-subjects, repeated measures design study, where they underwent three testing sessions separated by one-week each. Subjects performed separate sessions of each: low-force isometric contraction (30% maximal voluntary contraction [MVC]), high-force isometric contraction (95% MVC) of the first dorsal interosseous (FDI) muscle until self-perceived exhaustion, as well as one session of a 30-min rest as a control. We examined changes in corticomotor map area, excitability and location of the FDI representation in and around M1 using TMS. The main finding was that following low-force, but not high-force fatigue (HFF) corticomotor map area and excitability reduced [by 3cm(2) (t(14)=-2.94, p=0.01) and 56% respectively t(14)=-4.01, p<0.001)]. Additionally, the region of corticomotor excitability shifted posteriorly (6.4±2.5mm) (t(14)=-6.33, p=.019). Corticomotor output became less excitable particularly in regions adjoining M1. Overall, post-exercise depression is present in low-force, but not for HFF. Further, low-force fatigue (LFF) results in a posterior shift in corticomotor output. These changes may be indicative of increased sensory feedback from the somatosensory cortex during the recovery phase of fatigue.

Reproducibility of transcranial magnetic stimulation metrics in the study of proximal upper limb muscles

OBJECTIVE

Reproducibility of transcranial magnetic stimulation (TMS) metrics is essential in accurately tracking recovery and disease. However, majority of evidence pertains to reproducibility of metrics for distal upper limb muscles. We investigate for the first time, reliability of corticospinal physiology for a large proximal muscle - the biceps brachii and relate how varying statistical analyses can influence interpretations.

METHODS

14 young right-handed healthy participants completed two sessions assessing resting motor threshold (RMT), motor evoked potentials (MEPs), motor map and intra-cortical inhibition (ICI) from the left biceps brachii. Analyses included paired t-tests, Pearson's, intra-class (ICC) and concordance correlation coefficients (CCC) and Bland-Altman plots.

RESULTS

Unlike paired t-tests, ICC, CCC and Pearson's were >0.6 indicating good reliability for RMTs, MEP intensities and locations of map; however values were <0.3 for MEP responses and ICI.

CONCLUSIONS

Corticospinal physiology, defining excitability and output in terms of intensity of the TMS device, and spatial loci are the most reliable metrics for the biceps. MEPs and variables based on MEPs are less reliable since biceps receives fewer cortico-motor-neuronal projections. Statistical tests of agreement and associations are more powerful reliability indices than inferential tests.

SIGNIFICANCE

Reliable metrics of proximal muscles when translated to a larger number of participants would serve to sensitively track and prognosticate function in neurological disorders such as stroke where proximal recovery precedes distal.

Weakening of Corticomuscular Signal Coupling During Voluntary Motor Action in Aging

BACKGROUND

Aging is associated with muscle weakness and impairment in performing skilled motor tasks. Still, little is known about whether the link or functional coupling or connection between the central and peripheral systems during voluntary motor performance is compromised in the elderly subjects. The purposes of this study were to estimate functional corticomuscular connection (CMC) strength in the elderly subjects by calculating EEG-EMG coherence during voluntary motor performance, determine the relationship between the CMC and voluntary muscle force, and compare these between the old and the young subjects.

METHODS

Maximal voluntary contraction (MVC) of elbow flexion (EF) and EFs at three submaximal (20%, 50%, and 80% MVC) levels were performed in 28 healthy older (74.96±1.32 years) and 20 young (22.60±0.90 years) individuals, while EEG and EMG from biceps brachii, brachioradialis, and triceps brachii muscles were recorded simultaneously.

RESULTS

Compared with the young, older individuals exhibited significantly weakened CMC at all force levels tested. There was a proportional relationship between the CMC and EF force and high-positive correlation between the CMC and EF strength in both groups.

CONCLUSIONS

Weakened CMC in aging may be a major factor contributing to age-related muscle weakness, and the linear relationship between the CMC and voluntary muscle force suggests dependence of force output on translation of the descending command to muscle electrical signal.

Hemispheric activation during planning and execution phases in reaching post stroke: a consort study

Enhanced activation in the non-lesion hemisphere in stroke patients was widely observed during movement of the affected upper limb, but its functional role related to motor planning and execution is still unknown.This study was to characterize the activation in the non-lesion hemisphere during movement planning and execution by localizing sources of high-density electroencephalography (EEG) signal and estimating the source strength (current density [A/m]).Ten individuals with chronic stroke and shoulder/elbow coordination deficits and 5 healthy controls participated in the study.EEG (64 channels) was recorded from scalp electrodes while the subjects performed a reach task involving shoulder flexion and elbow extension of the affected (patients) or dominant (controls) upper extremity. Sources of the EEG were obtained and analyzed at 17 time points across movement preparation and execution phases. A 3-layer boundary element model was overlaid and used to identify the brain activation sources. A distributed current density model, low-resolution electromagnetic tomography (LORETA) L1 norm method, was applied to the data pre-processed by independent component analysis.Subjects with stroke had stronger source strength in the sensorimotor cortices during the movement compared with the controls. Their contralesional/lesional activation ratio (CTLR) for the primary motor cortices was significantly higher than that of the controls during the movement-planning phase, but not during the execution phase. The CTLR was higher in planning than in the execution phase in the stroke group.Excessive contralesional motor cortical activation appears to be more related to movement preparation rather than execution in chronic stroke.

Evidence of significant central fatigue in patients with cancer-related fatigue during repetitive elbow flexions till perceived exhaustion

OBJECTIVE

To investigate whether fatigue induced by an intermittent motor task in patients with cancer-related fatigue (CRF) is more central or peripheral.

METHODS

Ten patients with CRF who were off chemo and radiation therapies and 14 age-matched healthy controls were enrolled. Participants completed a Brief Fatigue Inventory (BFI) and performed a fatigue task consisting of intermittent elbow-flexion contractions at submaximal (40% maximal voluntary contraction) intensity till self-perceived exhaustion. Twitch force was elicited by an electrical stimulation applied to the biceps brachii muscle. The relative degree of peripheral (muscle) vs. central contribution to fatigue induced by the intermittent motor task (IMT) was assessed using twitch force ratio (TF ratio) defined as post IMT twitch force to pre IMT twitch force. The total number of trials (intermittent contractions) and total duration of all trials performed by each subject were also quantified.

RESULTS

BFI scores were higher (p < 0.001) in CRF than controls, indicating greater feeling of fatigue in CRF patients than controls. A significantly smaller number of trials and shorter total duration of the trials (p < 0.05) were observed in CRF than control participants. The TF ratio (0.81 ± 0.05) in CRF was higher (p < 0.05) compared with that of controls (0.62 ± 0.05), suggesting CRF patients experienced a significantly lower degree of muscle (peripheral) fatigue at the time of perceived exhaustion.

CONCLUSION

Consistent with prior findings for fatigue under submaximal sustained contraction, our results indicate that motor fatigue in CRF is more of central than peripheral origin during IMT. Significant central fatigue in CRF patients limits their ability to prolong motor performance.

Aging interferes central control mechanism for eccentric muscle contraction

Previous studies report greater activation in the cortical motor network in controlling eccentric contraction (EC) than concentric contraction (CC) despite lower muscle activation level associated with EC vs. CC in healthy, young individuals. It is unknown, however, whether elderly people exhibiting increased difficulties in performing EC than CC possess this unique cortical control mechanism for EC movements. To address this question, we examined functional magnetic resonance imaging (fMRI) data acquired during EC and CC of the first dorsal interosseous (FDI) muscle in 11 young (20–32 years) and 9 old (67–73 years) individuals. During the fMRI experiment, all subjects performed 20 CC and 20 EC of the right FDI with the same angular distance and velocity. The major findings from the behavioral and fMRI data analysis were that (1) movement stability was poorer in EC than CC in the old but not the young group; (2) similar to previous electrophysiological and fMRI reports, the EC resulted in significantly stronger activation in the motor control network consisting of primary, secondary and association motor cortices than CC in the young and old groups; (3) the biased stronger activation towards EC was significantly greater in the old than the young group especially in the secondary and association cortices such as supplementary and premotor motor areas and anterior cingulate cortex; and (4) in the primary motor and sensory cortices, the biased activation towards EC was significantly greater in the young than the old group. Greater activation in higher-order cortical fields for controlling EC movement by elderly adults may reflect activities in these regions to compensate for aging-related impairments in the ability to control complex EC movements. Our finding is useful for potentially guiding the development of targeted therapies to counteract age-related movement deficits and to prevent injury.

Myoelectrical manifestation of fatigue less prominent in patients with cancer related fatigue

PURPOSE

A lack of fatigue-related muscle contractile property changes at time of perceived physical exhaustion and greater central than peripheral fatigue detected by twitch interpolation technique have recently been reported in cancer survivors with fatigue symptoms. Based on these observations, it was hypothesized that compared to healthy people, myoelectrical manifestation of fatigue in the performing muscles would be less significant in these individuals while sustaining a prolonged motor task to self-perceived exhaustion (SPE) since their central fatigue was more prominent. The purpose of this study was to test this hypothesis by examining electromyographic (EMG) signal changes during fatiguing muscle performance.

METHODS

Twelve individuals who had advanced solid cancer and cancer-related fatigue (CRF), and 12 age- and gender-matched healthy controls performed a sustained elbow flexion at 30% maximal voluntary contraction till SPE. Amplitude and mean power frequency (MPF) of EMG signals of the biceps brachii, brachioradialis, and triceps brachii muscles were evaluated when the individuals experienced minimal, moderate, and severe fatigue.

RESULTS

CRF patients perceived physical "exhaustion" significantly sooner than the controls. The myoelectrical manifestation of muscular fatigue assessed by EMG amplitude and MPF was less significant in CRF than controls. The lower MPF even at minimal fatigue stage in CRF may indicate pathophysiologic condition of the muscle.

CONCLUSIONS

CRF patients experience less myoelectrical manifestation of muscle fatigue than healthy individuals near the time of SPE. The data suggest that central nervous system fatigue plays a more important role in limiting endurance-type of motor performance in patients with CRF.

Kinesthetic imagery training of forceful muscle contractions increases brain signal and muscle strength

The purpose of this study was to compare the effect of training using internal imagery (IMI; also known as kinesthetic imagery or first person imagery) with that of external imagery (EMI; also known as third-person visual imagery) of strong muscle contractions on voluntary muscle strengthening. Eighteen young, healthy subjects were randomly assigned to one of three groups (6 in each group): internal motor imagery (IMI), external motor imagery (EMI), or a no-practice control (CTRL) group. Training lasted for 6 weeks (~15 min/day, 5 days/week). The participants' right arm elbow-flexion strength, muscle electrical activity, and movement-related cortical potential (MRCP) were evaluated before and after training. Only the IMI group showed significant strength gained (10.8%) while the EMI (4.8%) and CTRL (-3.3%) groups did not. Only the IMI group showed a significant elevation in MRCP on scalp locations over both the primary motor (M1) and supplementary motor cortices (EMI group over M1 only) and this increase was significantly greater than that of EMI and CTRL groups. These results suggest that training by IMI of forceful muscle contractions was effective in improving voluntary muscle strength without physical exercise. We suggest that the IMI training likely strengthened brain-to-muscle (BTM) command that may have improved motor unit recruitment and activation, and led to greater muscle output. Training by IMI of forceful muscle contractions may change the activity level of cortical motor control network, which may translate into greater descending command to the target muscle and increase its strength.

Neurophysiological correlates of aging-related muscle weakness

Muscle weakness associated with aging implicates central neural degeneration. However, role of the primary motor cortex (M1) is poorly understood, despite evidence that gains in strength in younger adults are associated with its adaptations. We investigated whether weakness of biceps brachii in aging analogously relates to processes in M1. We enrolled 20 young (22.6 ± 0.87 yr) and 28 old (74.79 ± 1.37 yr) right-handed participants. Using transcranial magnetic stimulation, representation of biceps in M1 was identified. We examined the effect of age and sex on strength of left elbow flexion, voluntary activation of biceps, corticospinal excitability and output, and short-interval intracortical and interhemispheric inhibition. Interhemispheric inhibition was significantly exaggerated in the old (P = 0.047), while strength tended to be lower (P = 0.075). Overall, women were weaker (P < 0.001). Processes of M1 related to strength or voluntary activation of biceps, but only in older adults. Corticospinal excitability was lower in weaker individuals (r = 0.38), and corticospinal output, intracortical inhibition and interhemispheric inhibition were reduced too in individuals who poorly activated biceps (r = 0.43, 0.54 and 0.38). Lower intracortical inhibition may reflect compensation for reduced corticospinal excitability, allowing weaker older adults to spread activity in M1 to recruit synergists and attempt to sustain motor output. Exaggerated interhemispheric inhibition, however, conflicts with previous evidence, potentially related to greater callosal damage in our older sample, our choice of proximal vs. distal muscle and differing influence of measurement of inhibition in rest vs. active states of muscle. Overall, age-specific relation of M1 to strength and muscle activation emphasizes that its adaptations only emerge when necessitated, as in a weakening neuromuscular system in aging.

Brain white matter shape changes in amyotrophic lateral sclerosis (ALS): a fractal dimension study

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder. Current diagnosis time is about 12-months due to lack of objective methods. Previous brain white matter voxel based morphometry (VBM) studies in ALS reported inconsistent results. Fractal dimension (FD) has successfully been used to quantify brain WM shape complexity in various neurological disorders and aging, but not yet studied in ALS. Therefore, we investigated WM morphometric changes using FD analyses in ALS patients with different clinical phenotypes. We hypothesized that FD would better capture clinical features of the WM morphometry in different ALS phenotypes than VBM analysis. High resolution MRI T1-weighted images were acquired in controls (n = 11), and ALS patients (n = 89). ALS patients were assigned into four subgroups based on their clinical phenotypes.VBM analysis was carried out using SPM8. FD values were estimated for brain WM skeleton, surface and general structure in both controls and ALS patients using our previously published algorithm. No significant VBM WM changes were observed between controls and ALS patients and among the ALS subgroups. In contrast, significant (p<0.05) FD reductions in skeleton and general structure were observed between ALS with dementia and other ALS subgroups. No significant differences in any of the FD measures were observed between control and ALS patients. FD correlated significantly with revised ALS functional rating scale (ALSFRS-R) score a clinical measure of function. Results suggest that brain WM shape complexity is more sensitive to ALS disease process when compared to volumetric VBM analysis and FD changes are dependent on the ALS phenotype. Correlation between FD and clinical measures suggests that FD could potentially serve as a biomarker of ALS pathophysiology, especially after confirmation by longitudinal studies.

Functional somatotopy revealed across multiple cortical regions using a model of complex motor task

The primary motor cortex (M1) possesses a functional somatotopic structure-representations of adjacent within-limb joints overlap to facilitate coordination while maintaining discrete centers for individuated movement. We examined whether similar organization exists across other sensorimotor cortices. Twenty-four right-handed healthy subjects underwent functional magnetic resonance imaging (fMRI) while tracking complex targets with flexion/extension at right finger, elbow and ankle separately. Activation related to each joint at false discovery rate of 0.005 served as its representation across multiple regions. Within each region, we identified the center of mass (COM) for each representation, and the overlap between the representations of within-limb (finger and elbow) and between-limb joints (finger and ankle). Somatosensory (S1) and premotor cortices (PMC) demonstrated greater distinction of COM and minimal overlap for within- and between-limb representations. In contrast, M1 and supplementary motor area (SMA) showed more integrative somatotopy with higher sharing for within-limb representations. Superior and inferior parietal lobule (SPL and IPL) possessed both types of structure. Some clusters exhibited extensive overlap of within- and between-limb representations, while others showed discrete COMs for within-limb representations. Our results help to infer hierarchy in motor control. Areas such as S1 may be associated with individuated movements, while M1 may be more integrative for coordinated motion; parietal associative regions may allow switch between both modes of control. Such hierarchy creates redundant opportunities to exploit in stroke rehabilitation. The use of complex rather than traditionally used simple movements was integral to illustrating comprehensive somatotopic structure; complex tasks can potentially help to understand cortical representation of skill and learning-related plasticity.

Influence of nerve supply on hand electromyography coherence during a three-digit task

Intermuscular coupling has been investigated to understand neural inputs to coordinate muscles in a motor performance. However, little is known on the role of nerve innervation on intermuscular coupling. The purpose of this study was to investigate how the anatomy of nerve distribution affected intermuscular coupling in the hand during static grip. Electromyographic (EMG) signals were recorded from intrinsic and extrinsic muscles while subjects performed a static grip. Coherence was computed for muscle pairs innervated by either the same or different nerves. The results did not support the hypothesis that muscles sharing the same nerve exhibit greater coupling than muscles innervated by different nerves. In general, extrinsic muscle pairs displayed higher coherence than intrinsic pairs. The results suggest that intermuscular coupling in a voluntary motor task is likely modulated in a functional manner and that different nerves might transport common neural inputs to functionally coupled muscles.

T2 relaxometry measurements in low spatial frequency brain regions differ between fast spin-echo and multiple-echo spin-echo sequences

OBJECT

Dual-echo fast spin-echo (FSE) sequences are used in T2 relaxometry studies of neurological disorders because of shorter clinical scanning times and protocol simplicity. However, FSE sequences have possible spatial frequency-dependent effects, and derived T2 values may include errors that depend on the spatial frequency characteristics of the brain region of interest.

MATERIALS AND METHODS

Dual-echo FSE and multi-echo spin-echo (MESE) sequences were acquired in nine subjects. The T2 decay curves for FSE and MESE sequences were estimated and percent error maps were generated. T2 error values were obtained along each patient's corticospinal tract (CST). Whole-brain white matter (WM) and gray matter (GM) T2 error values were also obtained. The paired t test was performed to evaluate differences in T2 values in the CST between FSE and MESE sequences.

RESULTS

Histograms of error values in CST and in whole-brain WM and GM structures revealed systematic errors in FSE sequences. Significant differences (P < 0.001) in CST T2 values were also observed between FSE and MESE sequences.

CONCLUSION

Our findings indicate that T2 values derived from FSE sequences are prone to large errors, even in low spatial frequency regions such as the CST, when compared to MESE sequences. Future studies should be aware of this limitation of FSE sequences.

Lack of muscle contractile property changes at the time of perceived physical exhaustion suggests central mechanisms contributing to early motor task failure in patients with cancer-related fatigue

CONTEXT

Fatigue is one of the most common symptoms reported by cancer survivors, and fatigue worsens when patients are engaged in muscle exertion, which results in early motor task failure. Central fatigue plays a significant role, more than muscle (peripheral) fatigue, in contributing to early task failure in cancer-related fatigue (CRF).

OBJECTIVES

The purpose of this study was to determine if muscle contractile property alterations (reflecting muscle fatigue) occurred at the end of a low-intensity muscle contraction to exhaustion and if these properties differed between those with CRF and healthy controls.

METHODS

Ten patients (aged 59.9±10.6 years, seven women) with advanced solid cancer and CRF and 12 age- and gender-matched healthy controls (aged 46.6±12.8 years, nine women) performed a sustained contraction of the right arm elbow flexion at 30% maximal level until exhaustion. Peak twitch force, time to peak twitch force, rate of peak twitch force development, and half relaxation time derived from electrical stimulation-evoked twitches were analyzed pre- and post-sustained contraction.

RESULTS

CRF patients reported significantly greater fatigue as measured by the Brief Fatigue Inventory and failed the motor task earlier, 340±140 vs. 503±155 seconds in controls. All contractile property parameters did not change significantly in CRF but did change significantly in controls.

CONCLUSION

CRF patients perceive physical exhaustion sooner during a motor fatigue task with minimal muscular fatigue. The observation supports that central fatigue is a more significant factor than peripheral fatigue in causing fatigue feelings and limits motor function in cancer survivors with fatigue symptoms.

EEG for evaluation of “chemobrain.”

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Background: Cognitive impairment is a poorly understood and worrisome potential complication of adjuvant chemotherapy (CT). We sought to evaluate electroencephalography (EEG) as a means to measure neurophysiologic function in women receiving CT for early breast cancer. Methods: Women planning to undergo CT for operable breast cancer and age-similar controls were evaluated at baseline, during CT and at 1 year with neurophysiologic assessments. Testing included a brief fatigue inventory (BFI), brief mental fatigue assessment (BMF), Processing Speed Index (PSI) derived from Digit Symbol Coding and Symbol Search subtests of the Wechsler Adult Intelligence Scale, and a sustained elbow flexion physical task (PT). EEG recordings were obtained at rest and after the cognitive and physical tasks. Data were analyzed using repeated measures of analysis of variance. Results: Eight patient/control pairs completed baseline and on-treatment evaluations; 7 pairs also completed the 1 year assessment (1 pair withdrawn due to a second malignancy). Subjective mental fatigue measured by BMF is similar for patients and controls at baseline but BMF scores increase significantly during CT for patients relative to controls (p=0.033), recovering to no difference at one year. Differences in PSI are not observed between patients and controls or at the different time points. BFI scores are greater in patients at all 3 time points but endurance on the PT is no different from controls. During chemotherapy EEG total spectrum amplitudes in patients are greater than in controls at rest (p=0.05) and following both the cognitive (p<0.001) and physical (p<0.001) tasks. EEG activity prior to chemotherapy and at one year is not different between patients and controls. For patients but not controls EEG readings after the cognitive task demonstrate greater amplitude than pre-task readings during the time of CT treatment only (p=0.012) with a similar trend seen for the physical task (p=0.06). Conclusions: Patient-perceived mental and physical fatigue during chemotherapy correspond to significant changes in EEG brain activity patterns but not to cognitive testing or physical endurance testing. EEG may offer a sensitive means to measure alterations in brain function associated with CT.

Time-dependent cortical activation in voluntary muscle contraction

This study was to characterize dynamic source strength changes estimated from high-density scalp electroencephalogram (EEG) at different phases of a submaximal voluntary muscle contraction. Eight healthy volunteers performed isometric handgrip contractions of the right arm at 20% maximal intensity. Signals of the handgrip force, electromyography (EMG) from the finger flexor and extensor muscles and 64-channel EEG were acquired simultaneously. Sources of the EEG were analyzed at 19 time points across preparation, execution and sustaining phases of the handgrip. A 3-layer boundary element model (BEM) based on the MNI (Montréal Neurological Institute) brain MRI was used to overlay the sources. A distributed current density model, LORETA L1 norm method was applied to the data that had been processed by independent component analysis (ICA). Statistical analysis based on a mixed-effects polynomial regression model showed a significant and consistent time-dependent non-linear source strength change pattern in different phases of the handgrip. The source strength increased at the preparation phase, peaked at the force onset time and decreased in the sustaining phase. There was no significant difference in the changing pattern of the source strength among Brodmann’s areas 1, 2, 3, 4, and 6. These results show, for the first time, a high time resolution increasing-and-decreasing pattern of activation among the sensorimotor regions with the highest activity occurs at the muscle activity onset. The similarity in the source strength time courses among the cortical centers examined suggests a synchronized parallel function in controlling the motor activity.