Improving access to public physical activity events for disadvantaged communities in Australia.

BACKGROUND: Physical activity has numerous health benefits, but participation is lower in disadvantaged communities. 'parkrun' overcomes one of the main barriers for disadvantaged communities, the cost of activities, by providing a free, regular community-based physical activity event for walkers, runners and volunteers. This study assesses equity of access (in terms of distance to the nearest parkrun) stratified by socioeconomic deprivation, and identifies the optimal location for 100 new events to increase equity of access. METHODS: We combined information about population location and socioeconomic deprivation, with information about the location of 403 existing parkrun events, to assess the current level of access by deprivation quintile. We then used a two-step location-allocation analysis (minimising the sum of deprivation-weighted distances) to identify optimal regions, then optimal towns within those regions, as the ideal locations for 100 new parkrun events. RESULTS: Currently, 63.1% of the Australian population lives within 5 km of an event, and the average distance to an event is 14.5 km. A socioeconomic gradient exists, with the most deprived communities having the largest average distance to an event (27.0 km), and the least deprived communities having the best access (living an average 6.6 km from an event). Access improves considerably after the introduction of new event locations with around 68% of the population residing within 5 km of an event, and the average distance to the nearest event approximately 8 km. Most importantly, the improvement in access will be greatest for the most deprived communities (now an average 11 km from an event). CONCLUSIONS: There is a socioeconomic gradient in access to parkrun events. Strategic selection of new parkrun locations will improve equity of access to community physical activity events, and could contribute to enabling greater participation in physical activity by disadvantaged communities.

Non-contrast MRI can accurately characterize adnexal masses: a retrospective study.

OBJECTIVE: To determine the accuracy of interpretation of a non-contrast MRI protocol in characterizing adnexal masses. METHODS AND MATERIALS: Two hundred ninety-one patients (350 adnexal masses) who underwent gynecological MRI at our institution between the 1st of January 2008 and the 31st of December 2018 were reviewed. A random subset (102 patients with 121 masses) was chosen to evaluate the reproducibility and repeatability of readers' assessments. Readers evaluated non-contrast MRI scans retrospectively, assigned a 5-point score for the risk of malignancy and gave a specific diagnosis. The reference standard for the diagnosis was histopathology or at least one-year imaging follow-up. Diagnostic accuracy of the non-contrast MRI score was calculated. Inter- and intra-reader agreement was analyzed with Cohen's kappa statistics. RESULTS: There were 53/350 (15.1%) malignant lesions in the whole cohort and 20/121 (16.5%) malignant lesions in the random subset. Good agreement between readers was found for the non-contrast MRI score (к = 0.73, 95% confidence interval [CI] 0.58-0.86) whilst the intra-reader agreement was excellent (к = 0.81, 95% CI 0.70-0.88). The non-contrast MRI score value of ≥ 4 was associated with malignancy with a sensitivity of 84.9%, a specificity of 95.9%, an accuracy of 94.2% and a positive likelihood ratio of 21 (area under the receiver operating curve 0.93, 95% CI 0.90-0.96). CONCLUSION: Adnexal mass characterization on MRI without the administration of contrast medium has a high accuracy and excellent inter- and intra-reader agreement. Our results suggest that non-contrast studies may offer a reasonable diagnostic alternative when the administration of intravenous contrast medium is not possible. KEY POINTS: • A non-contrast pelvic MRI protocol may allow the characterization of adnexal masses with high accuracy. • The non-contrast MRI score may be used in clinical practice for differentiating benign from malignant adnexal lesions when the lack of intravenous contrast medium precludes analysis with the O-RADS MRI score.

Temporal assessment of pancreatic blood flow and perfusion following secretin stimulation using noninvasive MRI.

PURPOSE: To dynamically quantify pancreatic perfusion and flow within the arteries supplying the pancreas in response to secretin stimulation. MATERIALS AND METHODS: Twelve healthy male subjects were scanned at 1.5T with arterial spin labeling to measure tissue perfusion and phase contrast magnetic resonance imaging (MRI) to measure vessel flow. Superior mesenteric (SMA), gastroduodenal (GDA), common hepatic (HA), and splenic (SA) arterial flow and pancreatic perfusion were serially measured for 50 minutes following 1 IU/kg intravenous secretin. The significance of differences between timepoints was tested using a repeated measures one-way analysis of variance (ANOVA). RESULTS: Baseline blood flow (mean ± SEM or median [IQR]) for SMA, HA, SA, and GDA was 7.6 ± 1.3, 4.0 ± 0.5, 8.2 ± 0.8, and 0.9 (0.8-1.4) ml/s, respectively. Baseline pancreatic perfusion was 200 ± 25 ml/100g/min. Blood flow increased in the SMA (234%, P < 0.0001) and GDA (155%, P = 0.015) immediately after secretin injection. Reduced HA blood flow was observed after 10 minutes (P = 0.066) with no change in SA flow (P = 0.533). Increased pancreatic perfusion was maintained for 40 minutes after injection with a maximal increase at 5 minutes (16.8%, P = 0.025). CONCLUSION: Intravenous secretin resulted in significant temporal changes in pancreatic perfusion and arterial blood flow.

Sixteen-year trends in multiple lifestyle risk behaviours by socioeconomic status from 2004 to 2019 in New South Wales, Australia.

Few studies have examined trends in inequalities related to lifestyle risk behaviours. This study examined 1) 16-year (2004-2019) trends of individual lifestyle risk factors and a combined lifestyle risk index and 2) trends in socioeconomic inequalities in these risk factors, in New South Wales (NSW; Australia) adults. Data was sourced from the NSW Adult Population Health Survey, an annual telephone survey of NSW residents aged ≥16 years, totalling 191,905 completed surveys. Excessive alcohol consumption, current smoking, insufficient physical activity, insufficient fruit and/or vegetable consumption, sugar-sweetened beverage [SSB] consumption, and a combined lifestyle risk index (overall high-risk lifestyle defined as total number of lifestyle risk behaviours ≥2) were examined. Socioeconomic status was assessed using education attainment, postal area-level disadvantage measured by Index of Relative Socioeconomic Disadvantage (IRSD), and remoteness based on Accessibility-Remoteness Index of Australia Plus (ARIA+). Socioeconomic inequalities were examined as prevalence difference for absolute inequalities and prevalence ratio for relative inequalities. The prevalence of lifestyle behaviours by levels of each socioeconomic status variable were estimated using predicted probabilities from logistic regression models. After adjusting for covariates, there was a decrease in prevalence over time for most lifestyle risk behaviours. Between 2004 and 2019, the prevalence decreased for current smoking from 21.8% to 17.1%, insufficient physical activity from 39.1% to 30.9%, excessive alcohol consumption from 15.4% to 13.7%, daily SSB consumption from 29.9% to 21.2%, and overall high-risk lifestyle from 50.4% to 43.7%. Socioeconomic inequalities, based on one or more of the socioeconomic variables, increased over time for current smoking, insufficient physical activity, daily SSB consumption, and an overall high-risk lifestyle. Overall, the health behaviours of the NSW population improved between 2004 and 2019. However, some socioeconomic inequalities increased during this time, highlighting the need for effective public health strategies that seek to improve health behaviours among the most socioeconomically disadvantaged.

Placental MRI: Identification of radiological features to predict placental attachment disease regardless of reader expertise.

PURPOSE: To compare the accuracy of placental MRI in reporting placental adhesive disease in readers with different expertise and to identify the most reliable MRI features that predict placental pathology regardless of reader expertise. METHODS: Retrospective analysis of 27 placental MRI studies by six radiologists with different expertise levels; specificity, sensitivity, and accuracy were used to quantify the predictive performance of eight radiological features previously described in the literature. Histopathological evaluation was used as a diagnostic gold standard when available and the presence of the radiological features was decided by consensus. Features with higher sensitivity and specificity were identified and the optimal cut-off was calculated to obtain the resulting accuracy. RESULTS: The accuracy for seniors with expertise was non-statistically higher (0.83) compared to senior with no expertise (SWE) (0.65) and juniors (0.74) with SWE having tendency to over-estimate the severity of abnormality (26% vs 17%), whilst junior underestimated the degree of placental infiltration when compared to seniors with expertise (18.5% vs 0%, p = 0.006). Dark bands was the criteria with the highest sensitivity (95%) and high specificity (74%), followed by myometrial thinning (89%-76%) and uterine bulging (86%-81%). These three features demonstrated substantial (K) agreement. Using these features with optimal diagnostic cut-off, the accuracy increased to 0.91 for both the seniors and SWE and to 0.93 for the juniors. CONCLUSION: Placental MRI is most accurately interpreted by experienced radiologists; however, less experienced readers can obtain an accurate diagnosis relying on set criteria that are easier to be identified.

On the use of event-related potentials to auditory stimuli in the Go/NoGo task.

The N2 and P3 components of the event-related potential (ERP) are putative markers of inhibition in the Go/NoGo task. If this is the case, they should be unaffected by stimulus presentation modality. Theoretical researchers have suggested that the effect is smaller or absent with auditory stimuli, while others have shown that the effect depends on the perceptual similarity of the stimuli. Meanwhile, clinical researchers appear to be unaware of the debate. This study examined the N2 and P3 NoGo effects elicited by five sets of auditory stimuli varying in perceptual similarity. The N2 NoGo effect was significant for similar and different letters, and for similar tones, but not for different tones or novel sounds. As expected by the perceptual overlap hypothesis, the largest N2 NoGo effect was observed with the similar letters. In contrast, the P3 NoGo effect was significant and of a similar magnitude for all stimulus sets. The differential effect of the stimulus sets suggests separable underlying processes reflected in N2 and P3. Guidelines are provided for clinical researchers wishing to use auditory stimuli in the Go/NoGo task.

Serous borderline ovarian tumours: an extensive review on MR imaging features.

Serous borderline ovarian tumours (SBOTs) are an intermediate group of neoplasms, which have features between benign and malignant ovarian tumours and for which, fertility-sparing surgery can be offered. MRI in imaging of SBOTs is, therefore, crucial in raising the possibility of the diagnosis, in order to present the patient with the most appropriate treatment options. There are characteristic MRI features that SBOTs demonstrate. In addition, recent advanced techniques, and further classification into subtypes within the borderline group have been developed. The aim of this article is to review the MRI features of SBOT and provide the reporter with an awareness of the imaging tips and tricks in the differential diagnosis of SBOT.

Differentiating uterine sarcoma from leiomyoma: BET1T2ER Check!

Although rare, uterine sarcoma is a diagnosis that no one wants to miss. Often benign leiomyomas (fibroids) and uterine sarcomas can be differentiated due to the typical low T2 signal intensity contents and well-defined appearances of benign leiomyomas compared to the suspicious appearances of sarcomas presenting as large uterine masses with irregular outlines and intermediate T2 signal intensity together with possible features of secondary spread. The problem is when these benign lesions are atypical causing suspicious imaging features. This article provides a review of the current literature on imaging features of atypical fibroids and uterine sarcomas with an aide-memoire BET1T2ER Check! to help identify key features more suggestive of a uterine sarcoma.

Diagnostic interpretation of non-contrast qualitative MR imaging features for characterisation of uterine leiomyosarcoma.

OBJECTIVE: To assess the value of non-contrast MRI features for characterisation of uterine leiomyosarcoma (LMS) and differentiation from atypical benign leiomyomas. METHODS: This study included 57 atypical leiomyomas and 16 LMS which were referred pre-operatively for management review to the specialist gynaeoncology multidisciplinary team meeting. Non-contrast MRIs were retrospectively reviewed by five independent readers (three senior, two junior) and a 5-level Likert score (1-low/5-high) was assigned to each mass for likelihood of LMS. Evaluation of qualitative and quantitative MRI features was done using uni- and multivariable regression analysis. Inter-reader reliability for the assessment of MRI features was calculated by using Cohen's κ values. RESULTS: In the univariate analysis, interruption of the endometrial interface and irregular tumour shape had the highest odds ratios (ORs) (64.00, p < 0.001 and 12.00, p = 0.002, respectively) for prediction of LMS. Likert score of the mass was significant in prediction (OR, 3.14; p < 0.001) with excellent reliability between readers (ICC 0.86; 95% CI, 0.76-0.92). The post-menopausal status, interruption of endometrial interface and thickened endometrial stripe were the most predictive independent variables in multivariable estimation of the risk of leiomyosarcoma with an accuracy of 0.88 (95%CI, 0.78-0.94). CONCLUSION: At any level of expertise as a radiologist reader, the loss of the normal endometrial stripe (either thickened or not seen) in a post-menopausal patient with a myometrial mass was highly likely to be LMS. ADVANCES IN KNOWLEDGE: This study demonstrates the potential utility of non-contrast MRI features in characterisation of LMS over atypical leiomyomas, and therefore influence on optimal management of these cases.

MRI of the endometrium - from normal appearances to rare pathology.

MRI was recently included as a standard pre-operative diagnostic tool for patients with endometrial cancer. MR findings allow a better risk assessment and ultimately guides the surgical planning. Therefore, it is vital that the radiological interpretation is as accurate as possible. This requires essential knowledge regarding the appropriate MRI protocol, as well as different appearances of the endometrium, ranging from normal peri- and post-menopausal changes, benign findings (e.g. endometrial hyperplasia, polyp, changes due to exogenous hormones) to common and rare endometrium-related malignancies. Furthermore, this review will emphasize the role of MRI in staging endometrial cancer patients and highlight pitfalls that could result in the underestimation or overestimation of the disease extent.

MRI findings in-between leiomyoma and leiomyosarcoma: a Rad-Path correlation of degenerated leiomyomas and variants.

Leiomyomas are the most common benign tumors of the uterus. On the opposite side, leiomyosarcomas are rare malignant uterine tumors that account for a significant proportion of uterine cancer deaths. Especially when large and degenerated, leiomyomas and leiomyoma variants can have overlapping imaging characteristics with those of leiomyosarcomas. Although not always possible, it is paramount to be able to differentiate between leiomyomas and leiomyosarcomas on imaging, as the therapeutic management can differ. This pictorial review aims to familiarize radiologists with imaging features of leiomyomas and various types of leiomyoma degeneration and variants, together with their pathology correlates.

Signals of motor command bias joint position sense in the presence of feedback from proprioceptors.

Joint position sense is believed to be mediated by muscle afferent signals. Because a "phantom" hand produced by a sensory and motor nerve block appears to move in the direction of voluntary effort, signals of "motor command" or "effort" can influence perceived joint position. To determine whether this occurs when sensory signals are available, three studies assessed position sense when motor command and afferent signals were available, but joint movement was prevented. First, the hand was positioned to stop movement at the proximal joint of the middle finger, and movement at the distal joint was impossible because the muscles had been "disengaged". Voluntary efforts produced illusory position changes in the direction of the effort (12.6 +/- 2.0 degrees distal joint; 12.3 +/- 2.3 degrees proximal joint for efforts at 30% maximum; means +/- SD). Second, when subjects attempted to move the index finger under isometric conditions, the index finger appeared to move 7.4 +/- 1.2 degrees in the direction of efforts. These illusions graded with the level of effort (10 or 30% maximum) and far exceeded any real joint movement. Finally, because changes in muscle afferent feedback might have accompanied the voluntary efforts, all forearm and hand muscles were completely paralyzed by locally infused rocuronium. During paralysis, passive wrist position was signaled accurately, but, during attempted efforts (30% maximum), perceived wrist position changed by 9.7 +/- 4.9 degrees . Before paralysis, isometric efforts changed it by 6.7 +/- 3.6 degrees . Thus all studies concur: when joint movement is prevented, signals of motor command contribute to joint position sense.

The combined effect of muscle contraction history and motor commands on human position sense.

Along with afferent information, centrally generated motor command signals may play a role in joint position sense. Isometric muscle contractions can produce a perception of joint displacement in the same direction as the joint would move if unrestrained. Contradictory findings of perceived joint displacement in the opposite direction have been reported. As this only occurs if muscle spindle discharge in the contracting muscle is initially low, it may reflect increased muscle spindle firing from fusimotor activation, rather than central motor command signals. Methodological differences including the muscle contraction task and use of muscle conditioning could underlie the opposing findings. Hence, we tested perceived joint position during two contraction tasks ('hold force' and 'hold position') at the same joint (wrist) and controlled muscle spindle discharge with thixotropic muscle conditioning. We expected that prior conditioning of the contracting muscle would eliminate any effect of increased fusimotor activation, but not of central motor commands. Muscle conditioning altered perceived wrist position as expected. Further, during muscle contractions, subjects reported wrist positions displaced ~12 degrees in the direction of contraction, despite no change in wrist position. This was similar for 'hold force' and 'hold position' tasks and occurred despite prior conditioning of the agonist muscle. However, conditioning of the antagonist muscle did reduce the effect of voluntary contraction on position sense. The errors in position sense cannot be explained by fusimotor activation. We propose that central signals combine with afferent signals to determine limb position and that multiple sources of information are weighted according to their reliability.

Perception of movement extent depends on the extent of previous movements.

We report an aftereffect in perception of the extent (or degree or range) of joint movement, showing for the first time that a prolonged exposure to a passive back-and-forth movement of a certain extent results in a change in judgment of the extent of a subsequently presented movement. The adapting stimulus, movement about the wrist, had an extent of either 30 degrees or 75 degrees , while the test stimulus was a 50 degrees movement. Following a 4-min adaptation period, the estimated magnitudes of the test stimuli were 61 degrees and 36 degrees in the 30 degrees and 75 degrees condition, respectively (t test(6) = 9.6; p < 0.001). The observed effect is an instance of repulsion or contrast commonly described in perception literature, with perceived value of the test stimulus pushed away from the adapting stimulus.

Can Inhibitory Training Produce Reductions in Drinking? Evaluating the Influence of the Control Condition.

OBJECTIVE: Training in an inhibitory control task has produced reductions in alcohol use among heavy drinkers. However, the longevity of effects remains unknown, and much research has used suboptimal control conditions. Here, we assess the effectiveness of "Beer-NoGo" inhibitory training to reduce consumption up to 4 weeks after training compared with a "Beer-Go" control task, an online version of the Brief Alcohol Intervention (BAI), and an Oddball control condition. METHOD: Eighty-one regular drinkers were randomized into one of four training conditions. In the Beer-NoGo condition, participants responded to a letter superimposed on water-related images and refrained from responding to another letter superimposed on beer-related images. The mapping was reversed for the Beer-Go condition, whereas the Oddball control condition was presented with letters only and inhibition was not required. The last condition was an online BAI. Alcohol use was assessed using a bogus taste test and weekly alcohol consumption. RESULTS: Taste-test consumption was greater in the Beer-Go condition than in the Beer-NoGo, which did not differ from the Oddball and BAI conditions. All groups reduced alcohol intake during the study; however, in the first week the Beer-Go group reduced their drinking while the Beer-NoGo group increased. No group differences were apparent at the fourth week. CONCLUSIONS: The Beer-NoGo task did not produce effects beyond simple assessment on reducing alcohol use among regular drinkers. Previously reported training effects may be artifacts of the Beer-Go task as a suboptimal control. More robust forms of inhibitory training are necessary if a useful clinical adjunct for managing alcohol abuse is to be developed.

Extensive transmission of Mycobacterium tuberculosis among children on a school bus.

We report a tuberculosis outbreak in school children caused by exposure to a sputum-smear positive school bus driver. Exposed children were assessed using 2 versions of interferon-gamma release assays. Fifty-five percent (18/34) had a positive interferon-gamma release assays and 4 children developed tuberculosis. This suggests that transmission may be very efficient in this setting and highlights the need for early diagnosis.

Increased ventilation does not impair maximal voluntary contractions of the elbow flexors.

Exercise performance is impaired by increased respiratory work, yet the mechanism for this is unclear. This experiment assessed whether neural drive to an exercising muscle was affected by cortically driven increases in ventilation. On each of 5 days, eight subjects completed a 2-min maximal voluntary contraction (MVC) of the elbow flexor muscles, followed by 4 min of recovery, while transcranial magnetic stimulation tested for suboptimal neural drive to the muscle. On 1 day, subjects breathed without instructions under normocapnia. During the 2-min MVC, ventilation was approximately 3.5 times that at rest. On another day, subjects breathed without instruction under hypercapnia. During the 2-min MVC, ventilation was approximately 1.5 times that on the normocapnic day. On another 2 days under normocapnia, subjects voluntarily matched their breathing to the uninstructed breathing under normocapnia and hypercapnia using target feedback of the rate and inspiratory volume. On a fifth day under normocapnia, the volume feedback was set to each subject's vital capacity. On this day, ventilation during the 2-min MVC was approximately twice that on the uninstructed normocapnic day (or approximately 7 times rest). The experimental manipulations succeeded in producing voluntary and involuntary hyperpnea. However, maximal voluntary force, fatigue and voluntary activation of the elbow flexor muscles were unaffected by cortically or chemically driven increases in ventilation. Results suggest that any effects of increased respiratory work on limb exercise performance are not due to a failure to drive both muscle groups optimally.

Movement-related potentials in the Go/NoGo task: the P3 reflects both cognitive and motor inhibition.

OBJECTIVE: The contribution of movement-related potentials (MRPs) to the Go/NoGo N2 and P3 'inhibitory' effects is controversial. This study examined these components in overt and covert response inhibition tasks. METHODS: Twenty adult participants counted or button-pressed in response to frequent (60%) and rare (20%) Go stimuli in a Go/NoGo task with equiprobable rare (20%) NoGo stimuli. RESULTS: The N2 NoGo effect did not differ between Count and Press responses, but the P3 NoGo effect was amplified during the Press task. Additionally, subtraction of the ERP waveform for Count NoGo from Press NoGo trials revealed a positivity between 200 and 400ms, occurring maximally over the central region, contralateral to the responding hand. This difference wave became significant at 210-260ms, close to the estimated time taken to stop an overt response. CONCLUSIONS: The N2 NoGo effect may reflect a non-motoric stage of inhibition, or recognition of the need for inhibition, while the NoGo P3 may overlap with a positive MRP occurring specifically on trials where overt motor responses must be inhibited. SIGNIFICANCE: The study confirms that the N2 and P3 NoGo effects are not solely due to movement-related potentials, and posits the NoGo P3 as a marker of motor inhibition.

Fatigue-sensitive afferents inhibit extensor but not flexor motoneurons in humans.

The role of group III and IV muscle afferents in controlling the output from human muscles is poorly understood. We investigated the effects of these afferents from homonymous or antagonist muscles on motoneuron pools innervating extensor and flexor muscles of the elbow. In study 1, subjects (n = 8) performed brief maximal voluntary contractions (MVCs) of elbow extensors before and after a 2 min MVC of the extensors. During MVCs, electromyographic responses from triceps were evoked by stimulation of the corticospinal tracts [cervicomedullary motor evoked potentials (CMEPs)]. The same subjects repeated the protocol, but input from fatigue-sensitive afferents was prolonged after the fatiguing contraction by maintained muscle ischemia. In study 2, CMEPs were evoked in triceps during brief extensor MVCs before and after a 2 min sustained flexor MVC (n = 7) or in biceps during brief flexor MVCs before and after a sustained extensor MVC (n = 7). Again, ischemia was maintained after the sustained contractions. During sustained MVCs of the extensors, CMEPs in triceps decreased by approximately 35%. Without muscle ischemia, CMEPs recovered within 15 s, but with maintained ischemia, they remained depressed (by approximately 28%; p < 0.001). CMEPs in triceps were also depressed (by approximately 20%; p < 0.001) after fatiguing flexor contractions, whereas CMEPs in biceps were facilitated (by approximately 25%; p < 0.001) after fatiguing extensor contractions. During fatigue, inputs from group III and IV muscle afferents from homonymous or antagonist muscles depress extensor motoneurons but facilitate flexor motoneurons. The more pronounced inhibitory influence of these afferents on extensors suggests that these muscles may require greater cortical drive to generate force during fatigue.

Sustained contraction at very low forces produces prominent supraspinal fatigue in human elbow flexor muscles.

During sustained maximal voluntary contractions (MVCs), most fatigue occurs within the muscle, but some occurs because voluntary activation of the muscle declines (central fatigue), and some of this reflects suboptimal output from the motor cortex (supraspinal fatigue). This study examines whether supraspinal fatigue occurs during a sustained submaximal contraction of 5% MVC. Eight subjects sustained an isometric elbow flexion of 5% MVC for 70 min. Brief MVCs were performed every 3 min, with stimulation of the motor point, motor cortex, and brachial plexus. Perceived effort and pain, elbow flexion torque, and surface EMGs from biceps and brachioradialis were recorded. During the sustained 5% contraction, perceived effort increased from 0.5 to 3.9 (out of 10), and elbow flexor EMG increased steadily by approximately 60-80%. Torque during brief MVCs fell to 72% of control values, while both the resting twitch and EMG declined progressively. Thus the sustained weak contraction caused fatigue, some of which was due to peripheral mechanisms. Voluntary activation measured by motor point and motor cortex stimulation methods fell to 90% and 80%, respectively. Thus some of the fatigue was central. Calculations based on the fall in voluntary activation measured with cortical stimulation indicate that about two-thirds of the fatigue was due to supraspinal mechanisms. Therefore, sustained performance of a very low-force contraction produces a progressive inability to drive the motor cortex optimally during brief MVCs. The effect of central fatigue on performance of the weak contraction is less clear, but it may contribute to the increase in perceived effort.