Cerebral blood flow during exercise: mechanisms of regulation

Methods for improving thermal tolerance in military personnel prior to deployment

Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.

Vigorous Aerobic Exercise in the Management of Parkinson Disease: A Systematic Review

OBJECTIVE

To summarize the findings from studies examining the effects of vigorous-intensity aerobic exercise in the management of Parkinson disease. TYPE: Systematic review.

LITERATURE SURVEY

PubMed/MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Library, SPORTDiscus, and ScienceDirect databases were searched up to May 2020. Reference lists of the included articles were also searched for additional studies. Searches were restricted to English language.

METHODOLOGY

Seven papers, including six studies, five randomized controlled trials and one controlled trial, were identified. The studies examined the effects of vigorous-intensity aerobic exercise in participants with Parkinson disease. Studies in which the minimal intensity required was ≥77% of maximum heart rate, 60% of heart rate reserve or 64% of maximal oxygen uptake met the inclusion criteria. Method appraisal showed a mean score of 5.3 in the Physiotherapy Evidence Database (PEDro) scale.

SYNTHESIS

No statistically significant differences were found between vigorous-intensity aerobic exercise and moderate/low-intensity aerobic exercise for the main outcomes (disease severity and motor function). Only one study concluded a significant higher aerobic fitness in favor of the group that exercised at vigorous intensity compared to the moderate intensity group.

CONCLUSIONS

Vigorous-intensity aerobic exercise has not shown statistically significant improvements in motor and nonmotor impairments in individuals with Parkinson disease as compared to moderate/low-intensity aerobic exercise. Hence, the current evidence is too limited to allow recommendations for clinical practice.

Effects of Interval-Training Exercise on People Who Have Had Persistent Post-Concussive Symptoms for Less Than One Year: A Pilot Study

This study is to examine the effects of a 12-session moderate intensity-interval-training program with blood flow restriction (BFR) and body cooling (BC) on people who have had persistent post-concussive symptoms (PPCS) for <1 year. A single-blind randomized controlled trial of interval-training exercise with BFR and BC was conducted. Twenty-five adults with PPCS were assigned to the experimental group (n = 14) or the control group (n = 11). Both groups rode a recumbent elliptical machine for 21 min at moderate intensity (65% predicted maximum heart rate) twice a week for 6 weeks, but only the experimental group received BFR and BC while riding. The variances of overall PPCS scale scores and their sub-domain scores for individuals during the 6-week intervention and 6-week follow-up period were calculated. During the intervention, the fluctuation of overall symptom severity, severity in the cognitive domain and severity in the mood domain were significantly less in the experimental group (p = 0.03; p = 0.02; p = 0.02). During the follow-up period, the number of symptoms remained more stable in the experimental group (p = 0.02), and a trend toward less fluctuation of symptom severity (p = 0.05) was also observed. The reduced number of symptoms in the cognitive and sleep domains remained more stable in the experimental group following the intervention (p = 0.007; p = 0.02). The severity of mood and sleep symptoms also remained more stable during the follow-up period in the experimental group (p = 0.04). More stable recovery was found in individuals who exercised using BFR and BC than in those who underwent exercise without BFR and BC. Moderate intensity-interval-training exercise with BFR and BC alleviated post-concussive symptoms in people who have had PPCS <1 year.

Longitudinal study of cerebral blood flow regulation during exercise in pregnancy

Cerebrovascular adaptation to pregnancy is poorly understood. We sought to assess cerebrovascular regulation in response to visual stimulation, hypercapnia and exercise across the three trimesters of pregnancy. Using transcranial Doppler (TCD) ultrasound, middle and posterior cerebral artery mean blood velocities (MCAv_mean and PCAv_mean) were measured continuously at rest and in response to (1) visual stimulation to assess neurovascular coupling (NVC); (2) a modified Duffin hyperoxic CO₂ rebreathe test, and (3) an incremental cycling exercise test to volitional fatigue in non-pregnant (n = 26; NP) and pregnant women (first trimester [n = 13; TM1], second trimester [n = 21; TM2], and third trimester [n = 20; TM3]) in total 47 women. At rest, MCAv_mean and P_ETCO₂ were lower in TM2 compared to NP. PCAv_mean was lower in TM2 but not TM1 or TM3 compared to NP. Cerebrovascular reactivity in MCAv_mean and PCAv_mean during the hypercapnic rebreathing test was not different between pregnant and non-pregnant women. MCAv_mean continued to increase over the second half of the exercise test in TM2 and TM3, while it decreased in NP due to differences in ΔP_ETCO₂ between groups. Pregnant women experienced a delayed decrease in MCAv_mean in response to maximal exercise compared to non-pregnant controls which was explained by CO₂ reactivity and P_ETCO₂ level.

Effects of high intensity interval exercise on cerebrovascular function: A systematic review

High intensity interval exercise (HIIE) improves aerobic fitness with decreased exercise time compared to moderate continuous exercise. A gap in knowledge exists regarding the effects of HIIE on cerebrovascular function such as cerebral blood velocity and autoregulation. The objective of this systematic review was to ascertain the effect of HIIE on cerebrovascular function in healthy individuals. We searched PubMed and the Cumulative Index to Nursing and Allied Health Literature databases with apriori key words. We followed the Preferred Reporting Items for Systematic Reviews. Twenty articles were screened and thirteen articles were excluded due to not meeting the apriori inclusion criteria. Seven articles were reviewed via the modified Sackett’s quality evaluation. Outcomes included middle cerebral artery blood velocity (MCAv) (n = 4), dynamic cerebral autoregulation (dCA) (n = 2), cerebral de/oxygenated hemoglobin (n = 2), cerebrovascular reactivity to carbon dioxide (CO₂) (n = 2) and cerebrovascular conductance/resistance index (n = 1). Quality review was moderate with 3/7 to 5/7 quality criteria met. HIIE acutely lowered exercise MCAv compared to moderate intensity. HIIE decreased dCA phase following acute and chronic exercise compared to rest. HIIE acutely increased de/oxygenated hemoglobin compared to rest. HIIE acutely decreased cerebrovascular reactivity to higher CO₂ compared to rest and moderate intensity. The acute and chronic effects of HIIE on cerebrovascular function vary depending on the outcomes measured. Therefore, future research is needed to confirm the effects of HIIE on cerebrovascular function in healthy individuals and better understand the effects in individuals with chronic conditions. In order to conduct rigorous systematic reviews in the future, we recommend assessing MCAv, dCA and CO₂ reactivity during and post HIIE.

Immediate effects of a single session of physical exercise on cognition and cerebral blood flow: A randomized controlled study of older adults

BACKGROUND

Regular physical activity is beneficial for cognitive performance in older age. A single bout of aerobic physical exercise can transiently improve cognitive performance. Researchers have advanced improvements in cerebral circulation as a mediator of long-term effects of aerobic physical exercise on cognition, but the immediate effects of exercise on cognition and cerebral perfusion are not well characterized and the effects in older adults are largely unknown.

METHODS

Forty-nine older adults were randomized to a 30-min aerobic exercise at moderate intensity or relaxation. Groups were matched on age and cardiovascular fitness (VO2 max). Average Grey Matter Blood Flow (GMBF), measured by a pulsed arterial-spin labeling (pASL) magnetic resonance imaging (MRI) acquisition, and working memory performance, measured by figurative n-back tasks with increasing loads were assessed before and 7 min after exercising/resting.

RESULTS

Accuracy on the n-back task increased from before to after exercising/resting regardless of the type of activity. GMBF decreased after exercise, relative to the control (resting) group. In the exercise group, higher n-back performance after exercise was associated with lower GMBF in the right hippocampus, left medial frontal cortex and right orbitofrontal cortex, and higher cardiovascular fitness was associated with lower GMBF.

CONCLUSION

The decrease of GMBF reported in younger adults shortly after exercise also occurs in older adults and relates to cardiovascular fitness, potentially supporting the link between cardiovascular fitness and cerebrovascular reactivity in older age.

Cognitive Impairment during High-Intensity Exercise: Influence of Cerebral Blood Flow

PURPOSE

Cognitive performance appears to be impaired during high-intensity exercise, and this occurs concurrently with a reduction in cerebral blood flow (CBF). However, it is unclear whether cognitive impairment during high-intensity exercise is associated with reduced CBF. We tested the hypothesis that a reduction in CBF is responsible for impaired cognitive performance during high-intensity exercise.

METHODS

Using a randomized crossover design 17 healthy males performed spatial delayed response and Go/No-Go tasks in three conditions (exercise [EX], exercise+CO2 [EX+CO2], and a nonexercising control [CON]). In the EX and EX+CO2, they performed cognitive tasks at rest and during 8 min of moderate and high-intensity exercise. Exercise intensity corresponded to ~50% (moderate) and ~80% (high) of peak oxygen uptake. In the EX+CO2, the participants inspired hypercapnic gas (2% CO2) during high-intensity exercise. In the CON, they performed the cognitive tasks without exercise.

RESULTS

Middle cerebral artery mean velocity increased during high-intensity exercise in the EX+CO2 relative to the EX (69.4 [10.6] cm·s, vs 57.2 [7.7] cm·s, P < 0.001). Accuracy of the cognitive tasks was impaired during high-intensity exercise in the EX (84.1% [13.3%], P < 0.05) and the EX+ CO2 (85.7 [11.6%], P < 0.05) relative to rest (EX: 95.1% [5.3%], EX+CO2: 95.1 [5.3%]). However, no differences between the EX and the EX+CO2 were observed (P > 0.10). These results demonstrate that restored CBF did not prevent cognitive impairment during high-intensity exercise.

CONCLUSIONS

We conclude that a reduction in CBF is not responsible for impaired cognitive performance during high-intensity exercise.

Distinct Effects of Acute Aerobic Exercise on Declarative Memory and Procedural Memory Formation

Objective: To investigate the different effects of acute aerobic exercise on the formation of long-term declarative memory (DM) and procedural memory (PM). Methods: Twenty-two young men completed DM and PM tasks under three experimental conditions: pre-acquisition exercise, post-acquisition exercise, and no exercise (control). The DM task encompassed word learning, free recall tests both immediately and 1 h later, and a recognition test conducted 24 h after word learning. A serial reaction time task (SRTT) was utilized to assess exercise effects on PM. The SRTT included a sequence learning phase followed by sequence tests 1 h and 24 h later. The exercise program consisted of 30 min of moderate-intensity aerobic exercise. Results: In the DM task, compared to the control condition, pre-acquisition exercise, but not post-acquisition exercise, enhanced free recall performance significantly 1 h and 24 h later. The target word recognition rate and discriminative index (d') of the recognition test were significantly enhanced in both exercise conditions compared to the control condition. In the PM task, we observed significantly reduced (improved) reaction times at the 24-h test in the post-acquisition exercise condition compared to in the control condition. Conclusion: Acute aerobic exercise may enhance long-term DM and PM via effects on different processing periods. For DM, exercise had a pronounced effect during the encoding period, whereas for PM, exercise was found to have an enhancing effect during the consolidation period.

Vascular control of the CO2/H+-dependent drive to breathe

Respiratory chemoreceptors regulate breathing in response to changes in tissue CO2/H+. Blood flow is a fundamental determinant of tissue CO2/H+, yet little is known regarding how regulation of vascular tone in chemoreceptor regions contributes to respiratory behavior. Previously, we showed in rat that CO2/H+-vasoconstriction in the retrotrapezoid nucleus (RTN) supports chemoreception by a purinergic-dependent mechanism (Hawkins et al., 2017). Here, we show in mice that CO2/H+ dilates arterioles in other chemoreceptor regions, thus demonstrating CO2/H+ vascular reactivity in the RTN is unique. We also identify P2Y2 receptors in RTN smooth muscle cells as the substrate responsible for this response. Specifically, pharmacological blockade or genetic deletion of P2Y2 from smooth muscle cells blunted the ventilatory response to CO2, and re-expression of P2Y2 receptors only in RTN smooth muscle cells fully rescued the CO2/H+ chemoreflex. These results identify P2Y2 receptors in RTN smooth muscle cells as requisite determinants of respiratory chemoreception.

Prevention and Treatment of Alzheimer's Disease: Biological Mechanisms of Exercise

Alzheimer's disease (AD) is the most common form of dementia. With an aging population and no disease modifying treatments available, AD is quickly becoming a global pandemic. A substantial body of research indicates that lifestyle behaviors contribute to the development of AD, and that it may be worthwhile to approach AD like other chronic diseases such as cardiovascular disease, in which prevention is paramount. Exercise is an important lifestyle behavior that may influence the course and pathology of AD, but the biological mechanisms underpinning these effects remain unclear. This review focuses on how exercise can modify four possible mechanisms which are involved with the pathology of AD: oxidative stress, inflammation, peripheral organ and metabolic health, and direct interaction with AD pathology. Exercise is just one of many lifestyle behaviors that may assist in preventing AD, but understanding the systemic and neurobiological mechanisms by which exercise affects AD could help guide the development of novel pharmaceutical agents and non-pharmacological personalized lifestyle interventions for at-risk populations.

Increased cerebral blood flow supports a single-bout postexercise benefit to executive function: evidence from hypercapnia

A single bout of aerobic exercise improves executive function; however, the mechanism for the improvement remains unclear. One proposal asserts that an exercise-mediated increase in cerebral blood flow (CBF) enhances the efficiency of executive-related cortical structures. To examine this, participants completed separate 10-min sessions of moderate- to heavy-intensity aerobic exercise, a hypercapnic environment (i.e., 5% CO₂), and a nonexercise and nonhypercapnic control condition. The hypercapnic condition was included because it produces an increase in CBF independent of metabolic demands. An estimate of CBF was achieved via transcranial Doppler ultrasound and near-infrared spectroscopy that provided measures of middle cerebral artery blood velocity (BV) and deoxygenated hemoglobin (HHb), respectively. Exercise intensity was adjusted to match participant-specific changes in BV and HHb associated with the hypercapnic condition. Executive function was assessed before and after each session via antisaccades (i.e., saccade mirror-symmetrical to a target) because the task is mediated via the same executive networks that demonstrate task-dependent modulation following single and chronic bouts of aerobic exercise. Results showed that hypercapnic and exercise conditions were associated with comparable BV and HHb changes, whereas the control condition did not produce a change in either metric. In terms of antisaccade performance, the exercise and hypercapnic, but not control, conditions demonstrated improved postcondition reaction times (RT), and the magnitude of the hypercapnic and exercise-based increase in estimated CBF was reliably related to the postcondition improvement in RT. Accordingly, results evince that an increase in CBF represents a candidate mechanism for a postexercise improvement in executive function.NEW & NOTEWORTHY Single-bout aerobic exercise "boosts" executive function, and increased cerebral blood flow (CBF) has been proposed as a mechanism for the benefit. In this study, participants completed 10 min of aerobic exercise and 10 min of inhaling a hypercapnic gas, a manipulation known to increase CBF independently of metabolic demands. Both exercise and hypercapnic conditions improved executive function for at least 20 min. Accordingly, an increase in CBF is a candidate mechanism for the postexercise improvement in executive function.

Measurement and Changes in Cerebral Oxygenation and Blood Flow at Rest and During Exercise in Normotensive and Hypertensive Individuals

PURPOSE OF REVIEW

Summarize the methods used for measurement of cerebral blood flow and oxygenation; describe the effects of hypertension on cerebral blood flow and oxygenation.

RECENT FINDINGS

Information regarding the effects of hypertension on cerebrovascular circulation during exercise is very limited, despite a plethora of methods to help with its assessment. In normotensive individuals performing incremental exercise testing, total blood flow to the brain increases. In contrast, the few studies performed in hypertensive patients suggest a smaller increase in cerebral blood flow, despite higher blood pressure levels. Endothelial dysfunction and increased vasoconstrictor concentration, as well as large vessel atherosclerosis and decreased small vessel number, have been proposed as the underlying mechanisms. Hypertension may adversely impact oxygen and blood delivery to the brain, both at rest and during exercise. Future studies should utilize the newer, noninvasive techniques to better characterize the interplay between the brain and exercise in hypertension.

ABBaH: Activity Breaks for Brain Health. A Protocol for a Randomized Crossover Trial

Introduction: Extended periods of sitting may have detrimental effects on brain health. However, the effects of breaking up prolonged sedentary periods with frequent, short physical activity bouts on mechanisms to improve brain health remain unclear. Therefore, this study aims to investigate the immediate effects of uninterrupted sitting and frequent, short bouts of physical activity on cerebral blood flow and cognitive function in the prefrontal cortex in middle-aged adults.

Methods: This is a protocol article to describe a randomized crossover study. We will collect data from 13 healthy adults, aged between 40 and 60 years old, with a body mass index <35 kg/m². Participants will be required to come into the laboratory on three occasions, sit for 3 h, and perform a different type of break for 3 min every 30 min at each visit in a random order, being either: (1) a social break; (2) brisk walk on a treadmill; or (3) simple resistance activities. Before and after each experimental condition, cerebral blood flow (primary outcome) will be measured using functional near-infrared spectroscopy (fNIRS), with short-separation channels, and working memory (1-, 2-, and 3-back on the computer) will be assessed. The following additional secondary outcomes will be collected: psychological factors (questionnaires); arterial stiffness; salivary cortisol levels; and blood glucose levels.

Conclusion: The results from this randomized crossover study will determine the effects of uninterrupted sitting and frequent, short bouts of physical activity on cerebral blood flow and cognitive performance. Publication of this study protocol emphasizes the importance of registration and publication of protocols in the field of sedentary behavior research.

Cerebral tissue pO2 response to treadmill exercise in awake mice

We exploited two-photon microscopy and Doppler optical coherence tomography to examine the cerebral blood flow and tissue pO₂ response to forced treadmill exercise in awake mice. To our knowledge, this is the first study performing both direct measure of brain tissue pO₂ during acute forced exercise and underlying microvascular response at capillary and non-capillary levels. We observed that cerebral perfusion and oxygenation are enhanced during running at 5 m/min compared to rest. At faster running speeds (10 and 15 m/min), decreasing trends in arteriolar and capillary flow speed were observed, which could be due to cerebral autoregulation and constriction of arterioles in response to blood pressure increase. However, tissue pO₂ was maintained, likely due to an increase in RBC linear density. Higher cerebral oxygenation at exercise levels 5–15 m/min suggests beneficial effects of exercise in situations where oxygen delivery to the brain is compromised, such as in aging, atherosclerosis and Alzheimer Disease.

Does depth of squat-stand maneuver affect estimates of dynamic cerebral autoregulation?

Repeated squat-stand maneuvers (SSM) are an effective way of measuring dynamic cerebral autoregulation (dCA), but the depth of SSM required to improve dCA estimations has never been studied. We compared beat-to-beat cerebral hemodynamic parameters between maximal depth SSM (SSMD ) and a shallower alternative (SSMS ) in two age groups (younger [20-34 years] vs. older [50-71 years]) at a frequency of 0.05 Hz. Cerebral blood flow velocity, continuous blood pressure (BP) and end-tidal CO2 (EtCO2 ) were measured using transcranial Doppler ultrasound, the Finometer device, and capnography, respectively. Coherence (at 0.05 Hz) was significantly higher in both SSM recordings compared to spontaneous BP oscillations at baseline standing (BS ). Median (IQR) autoregulation index (ARI) was reduced during SSMD (4.46 [4.03-5.22], p < .01) compared to SSMS (5.96 [5.40-6.69]) and BS (6.03 [5.20-6.49], p < .01) with similar relative differences also observed for phase (at 0.05 Hz). End-tidal CO2 was increased in SSMD (38.3 ± 3.7 mmHg, p < .01) compared to both SSMS (36.6 ± 3.6 mmHg) and BS (35.5 ± 3.2 mmHg). The older group demonstrated significantly lower ARI and phase estimates during SSM and found SSMS more effortful than SSMD . In conclusion, both SSMD and SSMS are effective at estimating dCA, and dCA appears to be less efficient during maximal depth SSM compared to baseline rest or a shallower alternative.

Exercise-induced elevations in cerebral blood velocity are greater in running compared to cycling at higher intensities

The optimal exercise intensity and modality for maximizing cerebral blood flow (CBF) and hence potential exposure to positive, hemodynamically derived cerebral adaptations is yet to be fully determined. This study compared CBF velocity responses between running and cycling across a range of exercise intensities. Twenty-six participants (12 females; age: 26 ± 8 years) completed four exercise sessions; two mode-specific maximal oxygen consumption (VO2max ) tests, followed by (order randomized) two incremental exercise protocols (3-min stages at 35%, 50%, 65%, 80%, 95% VO2max ). Continuous measures of middle cerebral artery velocity (MCAv), oxygen consumption, end-tidal CO2 (PET CO2 ), and heart rate were obtained. Modality-specific MCAv changes were observed for the whole group (interaction effect: p = .01). Exercise-induced increases in MCAvmean during cycling followed an inverted-U pattern, peaking at 65% VO2max (Δ12 ± 7 cm/s from rest), whereas MCAvmean during running increased linearly up to 95% VO2max (change from rest: Δ12 ± 13 vs. Δ7 ± 8 cm/s for running vs. cycling at 95% VO2max ; p = .01). In contrast, both modalities had an inverted-U pattern for PET CO2 changes, although peaked at different intensities (running: 50% VO2max , Δ6 ± 2 mmHg; cycling: 65% VO2max , Δ7 ± 2 mmHg; interaction effect: p = .01). Further subgroup analysis revealed that the running-specific linear MCAvmean response was fitness dependent (Fitness*modality*intensity interaction effect: p = .04). Above 65% VO2max , fitter participants (n = 16; male > 45 mL/min/kg and female > 40 mL/min/kg) increased MCAvmean up to 95% VO2max , whereas in unfit participants (n = 7, male < mL/min/kg and female < 35 mL/min/kg) MCAvmean returned toward resting values. Findings demonstrate that modality- and fitness-specific profiles for MCAvmean are seen at exercise intensities exceeding 65% VO2max .

Functional high-intensity exercise is more effective in acutely increasing working memory than aerobic walking: an exploratory randomized, controlled trial

Aerobic and resistance exercise acutely increase cognitive performance (CP). High-intensity functional training (HIFT) combines the characteristics of both regimes but its effect on CP is unclear. Thirty-five healthy individuals (26.7 ± 3.6 years, 18 females) were randomly allocated to three groups. The first (HIFT) performed a functional whole-body workout at maximal effort and in circuit format, while a second walked at 60% of the heart rate reserve (WALK). The third group remained physically inactive reading a book (CON). Before and after the 15-min intervention period, CP was assessed with the Stroop Test, Trail Making Test and Digit Span Test. Repeated-measures ANOVAs and post-hoc 95% confidence intervals (95% CI) were used to detect time/group differences. A significant group*time interaction was found for the backwards condition of the Digit Span Test (p = 0.04) and according to the 95% CI, HIFT was superior to WALK and CON. Analysis of the sum score of the Digit Span Test and the incongruent condition of the Stroop Test, furthermore, revealed main effects for time (p < 0.05) with HIFT being the only intervention improving CP. No differences were found for the Trail Making Test (p > 0.05). In conclusion, HIFT represents an appropriate method to acutely improve working memory, potentially being superior to moderate aerobic-type exercise.

Objectively measured physical activity is associated with dorsolateral prefrontal cortex volume in older adults

BACKGROUND

Epidemiological studies suggest physical activity (PA) can slow or prevent both cognitive decline and age-related atrophy in frontal and hippocampal gray matter volumes. However, much of this evidence is based on self-reported measures of PA.

METHODS

PA was measured objectively with a SenseWear™ Armband to examine the cross-sectional associations between the duration of light, moderate and vigorous intensity PA with gray matter volume in the dorsolateral prefrontal cortex (DLPFC) and hippocampus in 167 (female: 43%) cognitively healthy older adults aged 73 to 78.

RESULTS

The duration of objective moderate to vigorous intensity physical activity (MVPA) was associated with a greater volume of the right DLPFC (β ​= ​0.16; p ​= ​0.04). In addition, objective moderate-intensity PA alone was also associated with greater volume of the left (β ​= ​0.17; p ​= ​0.03) and right (β ​= ​0.19; p ​= ​0.01) DLPFC after controlling for covariates and adjustment for multiple comparisons. In contrast, there were no significant associations between light- or vigorous-intensity PA and gray matter volumes (all p ​> ​0.05). No associations between PA and cognitive performance were detected, and self-reported PA was not associated with any of the outcomes investigated.

CONCLUSIONS

These findings suggest that an intensity-dependent relationship may exist, whereby a greater duration of MVPA, perhaps driven by moderate-intensity PA, is associated with preserved gray matter volume in frontal regions of the brain. Future research should investigate the mechanisms of this dose-effect and determine whether greater brain volumes associated with objective PA convey protective effects against cognitive decline.

Towards an understanding of the physical activity-BDNF-cognition triumvirate: A review of associations and dosage

Physical activity has received substantial research attention due to its beneficial impact on cognition in ageing, particularly via the action of brain-derived neurotrophic factor (BDNF). It is well established that physical activity can elevate circulating levels of BDNF, and that BDNF has neurotrophic, neuroprotective and cognitively beneficial properties. Yet, practical implementation of this knowledge is limited by a lack of clarity on context and dose-effect. Against a shifting backdrop of gradually diminishing physical and cognitive capacity in normal ageing, the type, intensity, and duration of physical activity required to elicit elevations in BDNF, and more importantly, the magnitude of BDNF elevation required for detectable neuroprotection remains poorly characterised. The purpose of this review is to provide an overview of the association between physical activity, BDNF, and cognition, with a focus on clarifying the magnitude of these effects in the context of normative ageing. We discuss the implications of the available evidence for the design of physical activity interventions intended to promote healthy cognitive ageing.

Effects of acute cardiovascular exercise on motor memory encoding and consolidation: A systematic review with meta-analysis

Emerging evidence indicates that acute bouts of cardiovascular exercise promote motor memory formation. In this preregistered meta-analysis (CRD42018106288) we synthesize data from 22 studies published until February 2020, including a total of 862 participants. We calculated standardized mean differences (SMDs) with 95 % confidence intervals (CIs) to assess exercise effects on motor memory encoding and consolidation, respectively. The pooled data indicate that exercise mainly benefits the consolidation of memories, with exercise prior to motor practice improving early non-sleep consolidation (SMD, 0.58; 95 % CI, 0.30-0.86; p < 0.001), and post-practice exercise facilitating sleep-dependent consolidation (SMD, 0.62; 95 % CI, 0.34-0.90; p < 0.001). Strongest effects exist for high exercise intensities, and motor task nature appears to be another relevant modulator. We demonstrate that acute cardiovascular exercise particularly promotes the consolidation of acquired motor memories, and exercise timing, and intensity as well as motor task nature seem to critically modulate this relationship. These findings are discussed within currently proposed models of motor memory formation and considering molecular and systemic mechanisms of neural plasticity.

Effect of Acute Exercise on Prefrontal Oxygenation and Inhibitory Control Among Male Children With Autism Spectrum Disorder: An Exploratory Study

Objective: Children with autism spectrum disorder (ASD) experience significant challenges in executive functioning. Emerging evidence suggests exercise may improve executive functioning among children; however, these effects and their mechanisms have not been fully explored among children with ASD. The purpose of this study was to explore the acute effect of exercise on cerebral oxygenation within the prefrontal cortex and inhibitory control among male children with ASD.

Method: Participants (N = 12) were 8–12 years of age with a diagnosis of ASD. A within-subject crossover design was employed. Participants completed three 20-min conditions on separate days: circuit-based workout, treadmill walking, and sedentary control. Pre- and post- each condition participants completed a cancellation task (Leiter-3) as a measure of inhibitory control and cerebral oxygenation was concurrently assessed using functional near-infrared spectroscopy (fNIRS). Heart rate, affect, perceived exertion, motivation, and self-efficacy were measured throughout the experiment as manipulation checks and potential psychological mechanisms. A series of repeated measures ANOVAs were conducted to examine intervention effects.

Results: Results demonstrated medium-to-large interaction effects (time by condition) for cerebral oxygenation (ηp2 = 0.237) and inhibitory control (ηp2 = 0.118). Post hoc analyses revealed that the circuit exercise condition elicited the largest changes in both outcomes. The manipulation checks indicated that the exercises were completed as intended.

Conclusion: These findings suggest that exercise may be a feasible intervention for enhancing executive functioning in children with ASD. More research with larger samples is needed to replicate these findings.

Sedentary behaviours, cognitive function, and possible mechanisms in older adults: a systematic review

BACKGROUND

Physical activity can improve cognitive function of older adults, but the influence of sedentary behaviour on cognition is less clear. This systematic review investigated associations between sedentary behaviour and cognitive function in older adults without dementia, and possible mechanisms involved.

METHODS

Major databases were searched for studies in English between 01/01/1999 and 31/10/2019. The systematic review followed COSMOS-E guideline and a pre-registered protocol (CRD42019122229). Risk of bias was assessed using NICE Quality appraisal checklist. Findings were narratively synthesized and presented.

FINDINGS

Eighteen studies comprised of 13 cross-sectional and five longitudinal analyses (n = 40,228). Evidence suggested varied associations between varied sedentary behaviours and cognitive function in older adults. 50% of study analyses did not control for physical activity. 3/18 studies demonstrated associations between higher sedentary levels and lower levels of brain biomarkers, while 1/18 showed auto-regulatory effect in the left hippocampus. Conducting a meta-analysis was not justifiable due to considerable methodological, participant, outcome and exposure heterogeneity.

CONCLUSION

There is a lack of clarity about the overall and independent association between sedentary behaviour and cognition in older age. Underlying mechanisms are similar to physical activity and probably multi-modal. More studies with robust designs and methodology are needed to confirm effect of sedentary behaviour on cognition.

Comparison of cerebrovascular reactivity recovery following high-intensity interval training and moderate-intensity continuous training

A common inclusion criterion when assessing cerebrovascular (CVR) metrics is for individuals to abstain from exercise for 12-24 hr prior to data collections. While several studies have examined CVR during exercise, the literature describing CVR throughout post-exercise recovery is sparse. The current investigation examined CVR measurements in nine participants (seven male) before and for 8 hr following three conditions: 45-min moderate-continuous exercise (at ~50% heart-rate reserve), 25-min high-intensity intervals (ten, one-minute intervals at ~85% heart-rate reserve), and a control day (30-min quiet rest). The hypercapnic (40-60 mmHg) and hypocapnic (25-40 mmHg) slopes were assessed via a modified rebreathing technique and controlled stepwise hyperventilation, respectively. All testing was initiated at 8:00a.m. with transcranial Doppler ultrasound measurements to index cerebral blood velocity performed prior to the condition (pre) with serial follow-ups at zero, one, two, four, six, and eight hours within the middle and posterior cerebral artery (MCA, PCA). Absolute and relative MCA and PCA hypercapnic slopes were attenuated following high-intensity intervals at hours zero and one (all p < .02). No alterations were observed in either hypocapnic or hypercapnic slopes following the control or moderate-continuous exercise (all p > .13), aside from a reduced relative hypercapnic MCA slope at hours zero and one following moderate-continuous exercise (all p < .005). The current findings indicate the common inclusion criteria of a 12-24 hr time restriction on exercise can be reduced to two hours when performing CVR measures. Furthermore, the consistent nature of the CVR indices throughout the control day indicate reproducible testing sessions can be made between 8:00a.m. and 7:00p.m.

Aerobic exercise improves cognition and cerebrovascular regulation in older adults

OBJECTIVE

To test the hypothesis that aerobic exercise is associated with improvements in cognition and cerebrovascular regulation, we enrolled 206 healthy low-active middle-aged and older adults (mean ± SD age 65.9 ± 6.4 years) in a supervised 6-month aerobic exercise intervention and assessed them before and after the intervention.

METHODS

The study is a quasi-experimental single group pre/postintervention study. Neuropsychological tests were used to assess cognition before and after the intervention. Transcranial Doppler ultrasound was used to measure cerebral blood flow velocity. Cerebrovascular regulation was assessed at rest, during euoxic hypercapnia, and in response to submaximal exercise. Multiple linear regression was used to examine the association between changes in cognition and changes in cerebrovascular function.

RESULTS

The intervention was associated with improvements in some cognitive domains, cardiorespiratory fitness, and cerebrovascular regulation. Changes in executive functions were negatively associated with changes in cerebrovascular resistance index (CVRi) during submaximal exercise (β = -0.205, p = 0.013), while fluency improvements were positively associated with changes in CVRi during hypercapnia (β = 0.106, p = 0.03).

CONCLUSION

The 6-month aerobic exercise intervention was associated with improvements in some cognitive domains and cerebrovascular regulation. Secondary analyses showed a novel association between changes in cognition and changes in cerebrovascular regulation during euoxic hypercapnia and in response to submaximal exercise.

Exercise and Academic Performance Among Children With Attention-Deficit Hyperactivity Disorder and Disruptive Behavior Disorders: A Randomized Controlled Trial

PURPOSE

To examine effects of a 10-week after-school physical activity (PA) program on academic performance of 6- to 12-year-old African American children with behavior problems.

METHODS

Participants were randomized to PA (n = 19) or sedentary attention control (n = 16) programs. Academic records, curriculum-based measures, and classroom observations were obtained at baseline, postintervention, and/or follow-up. Mixed models tested group × time interactions on academic records and curriculum-based measures. One-way analysis of variance or Kruskal-Wallis tested for differences in postintervention classroom observations.

RESULTS

Intent-to-treat analyses demonstrated a moderate effect within groups from baseline to postintervention on disciplinary referrals (PA: d = -0.47; attention control: d = -0.36) and a null moderate effect on academic assessments (PA: d = 0.11 to 0.36; attention control: d = 0.05 to 0.40). No significant group × time interactions emerged on direct academic assessments (all Ps ≥ .05, d = -0.23 to 0.26) or academic records (all Ps ≥ .05, d = -0.28 to 0.16). Classroom observations revealed that intervention participants were off-task due to moving at twice the rate of comparative classmates (F = 15.74, P < .001) and were off-task due to talking 33% more often (F = 1.39, P = .257).

CONCLUSION

Academic outcome improvements were small within and between groups and did not sustain at follow-up. Academic benefits of after-school PA programs for children with attention-deficit hyperactivity disorder and/or disruptive behavior disorders were smaller than neurobiological, behavioral, and cognitive outcomes as previously reported.

Psychophysiological Responses During a Cycling Test to Exhaustion While Wearing the Elevation Training Mask

López-Pérez, ME, Romero-Arenas, S, Colomer-Poveda, D, Keller, M, and Márquez, G. Psychophysiological responses during a cycling test to exhaustion while wearing the elevation training mask. J Strength Cond Res XX(X): 000-000, 2020-The aim of this study was to investigate the psychophysiological effects of wearing the elevation training mask (ETM). Twelve men performed time-to-exhaustion (TTE) tests at 75% of peak power output with and without wearing the ETM. Heart rate (HR), rating of perceived exertion (RPE), breathing discomfort (BD), and oxygen saturation (SpO2) were measured during the TTE. Prefrontal cortex (PFC) and vastus lateralis oxygenated, deoxygenated, and total hemoglobin were monitored using near-infrared spectroscopy. At the end of each test, blood lactate values (La-) were collected, and subjects completed the Beck Anxiety Inventory (BAI). The mask caused a reduction in the TTE (-37.7%; p < 0.001) and in the SpO2 (-2%; p < 0.001). Beck Anxiety Inventory scores were negatively correlated with the changes observed in the TTE (r = -0.77; p < 0.01). La-, HR, and muscle oxygenation displayed similar results across conditions. In conjunction with an increased hemodynamic response in the PFC, subjects reported higher RPE and BD values in the ETM condition (p < 0.01). Finally, BAI scores were negatively correlated with the changes observed in the TTE (r = -0.77; p < 0.01). This study suggests that wearing the ETM induces psychophysiological alterations affecting the exercise tolerance and limiting the performance.

Prospective associations between physical activity levels and white matter integrity in older adults: results from the MAPT study

BACKGROUND

Higher levels of physical activity (PA) are known to be associated with better white matter integrity measured by diffusion tensor imaging (DTI) in older adults in cross-sectional studies. However, no studies have investigated the association between PA levels and the evolution of DTI parameters (fractional anisotropy and mean diffusivity).

OBJECTIVES

To examine the cross-sectional associations between PA levels and DTI parameters, then to investigate the association between baseline PA levels and the evolution of DTI parameters in older adults.

METHODS

Data on magnetic resonance imaging with DTI method from the Multidomain Alzheimer's Preventive Trial (MAPT) study were used; 228 participants had data on DTI measured at three time-points over five years. Fractional anisotropy and mean diffusivity were acquired for six different brain regions.

RESULTS

No significant associations were found in the cross-sectional analyses. Only one association was found: compared with active individuals, a faster worsening in the mean diffusivity of the uncinate fasciculus region was found in inactive individuals (-5.0 × 10^-6 (-9.5 × 10^-5, 4.9 × 10^-6)).

CONCLUSIONS

In this study, we found that the condition of the uncinate fasciculus region may be susceptible to changes in PA levels in older adults. Longitudinal studies that assess fitness and PA using objective measurements (e.g. cardiorespiratory fitness and accelerometry) could shed some new light on this topic.

Inter-patient variations in flow boundary conditions at middle cerebral artery from 7T PC-MRI and influence on Computational Fluid Dynamics of intracranial aneurysms

BACKGROUND

Computational fluid dynamics(CFD) of intracranial aneurysms requires flow boundary conditions(BCs) as inputs. Patient-specific BCs are usually unavailable and substituted by literature-derived generic BCs. Therefore, we investigated inter-patient BC variations and their influence on middle cerebral artery aneurysmal hemodynamics.

METHOD

We retrospectively collected CT angiography and 7-T Phase-Contrast(PC)-MRI data from eight middle-cerebral-artery bifurcation aneurysms to reconstruct the geometry and measure the arterial flowrates, respectively. The coefficient of variation(CoV) was calculated for the inlet flowrate and the pulsatility index(PI). The outflow split estimated by Murray's law was compared with PC-MRI measurements. For each aneurysm, we performed seven simulations: "baseline" using PC-MRI-derived BCs and the other six with changing BCs to explore the influence of BC variations on hemodynamics.

RESULTS

From PC-MRI, the inlet flowrate was 1.94 ± 0.71 cm³/s(CoV = 36%) and PI was 0.37 ± 0.13(CoV = 34%). The outflow split estimated by Murray's law deviated by 15.3% compared to PC-MRI. Comparing to "baseline" models, ±36% variations in inlet flowrate caused -61% to +89% changes in time-averaged wall shear stress(WSS), -37% to +32% in normalized WSS(NWSS; by parent-artery), and -42% to +126% in oscillatory shear index(OSI). The ±34% variations in PI caused, -46% to +67% in OSI. Applying ±15% variations in outflow split led to inflow jet deflection and -41% to +52% changes in WSS, -41% to +47% in NWSS, and -44% to +144% in OSI.

CONCLUSION

Inflow rate and outflow split have a drastic impact on hemodynamics of intracranial aneurysms. Inlet waveform has a negligible impact on WSS and NWSS but major impact on OSI. CFD-based models need to consider such sensitivity.

Acute Effects of Resistance Exercise on Cognitive Function in Healthy Adults: A Systematic Review with Multilevel Meta-Analysis

BACKGROUND

Recent research has revealed a beneficial impact of chronic resistance exercise (RE) on brain function. However, it is unclear as to whether RE is also effective in an acute setting.

OBJECTIVE

To investigate the immediate effects of a single RE session on cognitive performance in healthy adults.

METHODS

A multilevel meta-analysis with random effects meta-regression model was used to pool the standardized mean differences (SMD) between RE and no-exercise (NEX) as well as between RE and aerobic exercise (AE). In addition to global cognitive function, effects on reported sub-domains (inhibitory control, cognitive flexibility, working memory, attention) were examined.

RESULTS

Twelve trials with fair methodological quality (PEDro scale) were identified. Compared to NEX, RE had a positive effect on global cognition (SMD: 0.56, 95% CI 0.22-0.90, p = 0.004), but was not superior to AE (SMD: - 0.10, 95% CI 0.01 to - 0.20, p = 0.06). Regarding cognitive sub-domains, RE, compared to NEX, improved inhibitory control (SMD: 0.73, 95% CI 0.21-1.26, p = 0.01) and cognitive flexibility (SMD: 0.36, 95% CI 0.17-0.55, p  = 0.004). In contrast, working memory (SMD: 0.35, 95% CI - 0.05 to 0.75, p  = 0.07) and attention (SMD: 0.79, 95% CI - 0.42 to 2.00, p = 0.16) remained unaffected. No significant differences in sub-domains were found between RE and AE (p > 0.05).

CONCLUSION

RE appears to be an appropriate method to immediately enhance cognitive function in healthy adults. Further studies clearly elucidating the impact of effect modifiers such as age, training intensity, or training duration are warranted.

Aging reduces cerebral blood flow regulation following an acute hypertensive stimulus

Aging increases arterial stiffness, which has a negative impact on cerebral blood flow (CBF) regulation (decreases CBF and increases CBF pulsatility). The association between arterial stiffness and CBF pulsatility may, in part, explain the relationship between elevated blood pressure (BP) fluctuations and end-organ disease with aging. To understand the mechanisms by which large BP alterations influence cerebral blood flow regulation in both young and old, we examined the effects of age on central and cerebral blood flow regulation following an acute hypertensive stimulus [resistance-exercise (RE)]. Measurements were obtained pre and immediately, 5, and 30 min post-RE in young (n = 35) and older (n = 26) adults. Measurements included cerebral blood velocity (CBv), CBv pulsatility, central pulse-wave velocity (PWV), beta-stiffness index (β), and carotid blood flow pulsatility. Central hemodynamics and BP were continuously recorded. Mean CBv increased immediately post-RE only in the young and decreased below baseline at 5 min post-RE in both groups (interaction, P < 0.05). Older adults had a greater increase in CBv pulsatility immediately post-RE compared with the young (interaction, P < 0.05). Mean BP was higher and carotid pulsatility was lower in the older group and increased immediately post-RE in both groups (P < 0.05). PWV increased immediately post-RE (P < 0.05). There were no changes in β. In conclusion, with aging, greater central arterial stiffness leads to a greater transmission of pulsatile blood velocity from the systemic circulation to the cerebral circulation following an acute hypertensive stress.NEW & NOTEWORTHY Reductions in cerebral blood flow and increases in flow pulsatility with aging are associated to cerebrovascular disease; however, little is known about how an acute hypertensive stimulus effects cerebral blood flow regulation in an aged population. Following the hypertensive stimulus, older adults elicit an attenuated increase in cerebral blood velocity and greater transmission of pulsatile velocity to the brain compared with young adults, demonstrating reduced cerebral blood flow regulation to elevated blood pressure responses with aging.

Benefits of physical exercise on cognition and glial white matter pathology in a mouse model of vascular cognitive impairment and dementia

White matter (WM) pathology is a clinically predictive feature of vascular cognitive impairment and dementia (VCID). Mice overexpressing transforming growth factor-β1 (TGF) with an underlying cerebrovascular pathology when fed a high cholesterol diet (HCD) develop cognitive deficits (VCID mice) that we recently found could be prevented by physical exercise (EX). Here, we further investigated cognitive and WM pathology in VCID mice and examined the cellular substrates of the protective effects of moderate aerobic EX focusing on WM alterations. Six groups were studied: Wild-type (WT) and TGF mice (n = 20-24/group) fed standard lab chow or a 2% HCD, with two HCD-fed groups given concurrent access to running wheels. HCD had a significant negative effect in TGF mice that was prevented by EX on working and object recognition memory, the latter also altered in WT HCD mice. Whisker-evoked increases in cerebral blood flow (CBF) were reduced in HCD-fed mice, deficits that were countered by EX, and baseline WM CBF was similarly affected. VCID mice displayed WM functional deficits characterized by lower compound action potential amplitude not found in EX groups. Moreover, there was an increased number of collapsing capillaries, galectin-3-expressing microglial cells, as well as a reduced number of oligodendrocytes in the WM of VCID mice; all of which were prevented by EX. Our findings indicate that a compromised cerebral circulation precedes reduced WM vascularization, enhanced WM inflammation and impaired oligodendrogenesis that all likely account for the increased susceptibility to memory impairments in VCID mice, which can be prevented by EX. MAIN POINTS: A compromised cerebral circulation increases susceptibility to anatomical and functional white matter changes that develop alongside cognitive deficits when challenged with a high cholesterol diet; preventable by a translational regimen of exercise.

Continuous reduction in cerebral oxygenation during endurance exercise in patients with pulmonary arterial hypertension

BACKGROUND

Patients with pulmonary arterial hypertension (PAH) have lower cerebral blood flow (CBF) and oxygenation compared to healthy sedentary subjects, the latter negatively correlating with exercise capacity during incremental cycling exercise. We hypothesized that patients would also exhibit altered CBF and oxygenation during endurance exercise, which would correlate with endurance time.

METHODS

Resting and exercise cardiorespiratory parameters, blood velocity in the middle cerebral artery (MCAv; transcranial doppler) and cerebral oxygenation (relative changes in cerebral tissue oxygenation index (ΔcTOI) and cerebral deoxyhemoglobin (ΔcHHb); near-infrared spectroscopy) were continuously monitored in nine PAH patients and 10 healthy-matched controls throughout endurance exercise. Cardiac output (CO), systemic blood pressure (BP) and oxygen saturation (SpO2 ), ventilatory metrics and end-tidal CO2 pressure (PET CO2 ) were also assessed noninvasively.

RESULTS

Despite a lower workload and endurance oxygen consumption, similar CO and systemic BP, ΔcTOI was lower in PAH patients compared to controls (p < .01 for interaction). As expected during exercise, patients were characterized by an altered MCAv response to exercise, a lower PET CO2 and SpO2 , as wells as a higher minute-ventilation/CO2 production ratio ( V ˙ E / V ˙ CO 2 ratio). An uncoupling between changes in MCAv and PET CO2 during the cycling endurance exercise was also progressively apparent in PAH patients, but absent in healthy controls. Both cHHb and ΔcTOI correlated with V ˙ E / V ˙ CO 2 ratio (r = 0.50 and r = -0.52; both p < .05 respectively), but not with endurance time.

CONCLUSION

PAH patients present an abnormal cerebrovascular profile during endurance exercise with a lower cerebral oxygenation that correlate with hyperventilation but not endurance exercise time. These findings complement the physiological characterization of the cerebral vascular responses to exercise in PAH patients.

Association of Exercise and Swimming Goggles With Modulation of Cerebro-ocular Hemodynamics and Pressures in a Model of Spaceflight-Associated Neuro-ocular Syndrome

Importance

Astronauts on International Space Station missions demonstrate adverse neuro-ocular changes. Reversing a negative translaminar pressure gradient (TLPG) by modulating cerebral blood flow, decreasing intracranial pressure, or increasing intraocular pressure (IOP) has been proposed as potential intervention for spaceflight-associated neuro-ocular syndrome (SANS).

Objective

To examine whether exercise (resistance, moderate-intensity aerobic, and high-intensity aerobic) or artificially increasing IOP is associated with modulated cerebro-ocular hemodynamic and pressure changes during head-down tilt (HDT), an analogue of spaceflight, in healthy adults.

Design, Setting, and Participants

A single-center investigation was conducted at Johnson Space Center, Houston, Texas, from January 1, 2014, to December 31, 2016, in 20 healthy men.

Exposure

On 3 separate days, participants rested supine, were tilted to -15° HDT, and then completed 1 of 3 experimental exercise conditions (moderate-intensity aerobic, resistance, or high-intensity interval aerobic). A subset of 10 participants wore swimming goggles on all days.

Main Outcomes and Measures

Applanation rebound tonometry was used to noninvasively assess IOP, and compression sonography was used to assess internal jugular venous pressure (IJVP). Estimated TLPG was calculated as the difference between IOP and IJVP. Cerebral inflow and outflow were measured in extracranial arteries using color-coded duplex ultrasonography.

Results

Twenty men participated in the study (mean [SD] age, 36 [9] years). Compared with supine IOP (mean [SD], 19.3 [3.7] mm Hg), IJVP (mean [SD], 21.4 [6.0] mm Hg), and estimated TLPG (mean [SD], -2.1 [7.0] mm Hg), -15° HDT was associated with increased IOP (mean difference, 2.3 mm Hg; 95% CI, 1.4-3.3 mm Hg; P < .001) and IJVP (mean difference, 10.5 mm Hg; 95% CI, 8.9-12.2 mm Hg; P < .001) and with decreased TLPG (mean difference, -8.2 mm Hg; 95% CI, -10.1 to -6.3 mm Hg; P < .001). Exercise (regardless of modality) at -15° HDT was associated with decreased IOP (mean difference, -1.6 mm Hg; 95% CI, -2.6 to -0.6 mm Hg; P = .002) and TLPG (mean difference, -3.5 mm Hg; 95% CI, -6.2 to -0.7 mm Hg; P = .01) compared with rest. Both IOP (mean difference, 2.9 mm Hg; 95% CI, 0.7-5.1 mm Hg; P = .01) and TLPG (mean difference, 5.1 mm Hg; 95% CI, 0.8-9.4 mm Hg; P = .02) were higher in participants who wore swimming goggles compared with those not wearing goggles.

Conclusions and Relevance

In this study, exercise was associated with decreased IOP and estimated translaminar pressure gradient in a spaceflight analogue of HDT. The addition of swimming goggles was associated with increased IOP and TLPG in HDT. Further evaluation in spaceflight may be warranted to determine whether modestly increasing IOP is an effective SANS countermeasure.

Acute kick-boxing exercise alters effective connectivity in the brain of females with methamphetamine dependencies

OBJECTIVE

Methamphetamine (METH) dependence, especially among women, is a serious global health problem. Kick-boxing exercise can be used to reduce cue-induced craving and develop a healthy lifestyle for female with METH dependencies. This study aimed to assess acute kick-boxing related changes in effective connectivity (EC) in the brain of females with METH dependencies by using functional near-infrared spectroscopy (fNIRS) signals.

METHODS

The fNIRS signals were continuously recorded from the left and right prefrontal cortices (LPFC/RPFC) and left and right motor cortices (LMC/RMC) of 30 female subjects with methamphetamine dependencies (METH group) and 30 age-matched controls (control group) during resting and kick-boxing exercise (training) periods. EC was calculated in the frequency range of 0.01-0.08 Hz.

RESULTS

In both resting and training state, the EC levels of METH group were significantly lower than the control group (p <  0.05). The EC levels of control group showed more significantly increased connection types than that of the METH group.

CONCLUSION

Acute kick-boxing exercise altered EC in the brain of females with METH dependencies. Furthermore, the efficiency of the information flow between different brain regions in the control group was significantly higher than that in the METH group. This study provides a novel and portable assessment technique for METH rehabilitation in females on the basis of fNIRS signals.

TCD Cerebral Hemodynamic Changes during Moderate-Intensity Exercise in Older Adults

BACKGROUND AND PURPOSE

Exercise plays an important role in supporting overall brain health. However, the mechanisms by which exercise supports brain health are imprecisely defined. Further, brain hemodynamic changes during exercise are not clearly understood, especially in older adults. The primary aim of this study was to compare cerebral blood flow velocity and pulsatility index (PI) during moderate-intensity exercise between older adults with normal pulsatile flow (normal PI) and older adults with elevated pulsatile flow (elevated PI). Secondary aims were to compare cardiovascular disease risk and cognitive function between individuals with elevated and nonelevated PI.

METHODS

Using transcranial Doppler ultrasound (TCD), middle cerebral artery blood velocity (MCAv) and PI were recorded during the rest and moderate-intensity exercise. End tidal carbon dioxide (PET CO2 ) and beat-to-beat mean arterial blood pressure were also recorded.

RESULTS

We enrolled 104 older adults into the study. The change in PI was greater in normal PI group (35.5% vs. 21.3%, P = .005). The change in MCAv was similar in both groups (11.6% for normal PI vs. 10.6% for elevated PI; P = .22). There was no significant difference in cardiovascular disease risk between the two groups (P = .77). Individuals with elevated PI performed significantly worse in WAIS-R Digit Symbol and Trail Making Test A (P = .04 and = .01, respectively).

CONCLUSIONS

The percent increase in PI from rest to moderate-intensity exercise was attenuated in the older adults with elevated resting PI. Higher resting PI may negatively affect brain health as evidenced by the slower processing speed scores.

Blood flow rate and wall shear stress in seven major cephalic arteries of humans

Blood flow rate ( Q ˙ ) in relation to arterial lumen radius (r_i ) is commonly modelled according to theoretical equations and paradigms, including Murray's Law ( Q ˙ ∝ r i 3 ) and da Vinci's Rule ( Q ˙ ∝ r i 2 ). Wall shear stress (τ) is independent of r_i with Murray's Law (τ ∝  r i 0 ) and decreases with da Vinci's Rule (τ ∝  r i - 1 ). These paradigms are tested empirically with a meta-analysis of the relationships between Q ˙ and r_i in seven major arteries of the human cephalic circulation from 19 imaging studies in which both variables were presented. The analysis shows that Q ˙ ∝ r i 2.16 and τ ∝  r i - 1.02 , more consistent with da Vinci's Rule than Murray's Law. This meta-analysis provides standard values for Q ˙ , r_i and τ in the human cephalic arteries that may be a useful baseline in future investigations. On average, the paired internal carotid arteries supply 75%, and the vertebral arteries supply 25%, of total brain blood flow. The internal carotid arteries contribute blood entirely to the anterior and middle cerebral arteries and also partly to the posterior cerebral arteries via the posterior communicating arteries of the circle of Willis. On average, the internal carotid arteries provide 88% of the blood flow to the cerebrum and the vertebral arteries only 12%.

Middle cerebral artery velocity dynamic response profile during exercise is attenuated following multiple ischemic strokes: a case report

Blood flow regulation is impaired in people with stroke. However, the time course of change in middle cerebral artery velocity (MCAv) following repeated stroke at rest and during exercise remains unknown. In this case study, we provide novel characterization of the dynamic kinetic MCAv response profile to moderate-intensity exercise before and after repeated ischemic MCA stroke. The initial stroke occurred in the left MCA. At 3 months poststroke, left MCAv amplitude (Amp) was ~50% lower than the right. At the 6-month follow-up visit, MCAv Amp declined in both MCA with the left MCAv Amp ~50% lower than the right MCAv Amp. Following a second right MCA stroke, we report further decline in Amp for the left MCA. At the 3- and 6-month visit following the second stroke, the left MCAv Amp declined further (~10%). The right MCAv Amp dramatically decreased by 81.3% when compared to the initial study visit. The MCAv kinetic analysis revealed a marked impairment in the cerebrovascular response to exercise following stroke. We discuss potential pathophysiological mechanisms contributing to poststroke cerebrovascular dysfunction and the need to test therapeutic interventions (such as exercise) that might attenuate cerebrovascular decline in people following stroke.

The interactive effects of acute exercise and hypoxia on cognitive performance: A narrative review

Acute moderate intensity exercise has been shown to improve cognitive performance. In contrast, hypoxia is believed to impair cognitive performance. The detrimental effects of hypoxia on cognitive performance are primarily dependent on the severity and duration of exposure. In this review, we describe how acute exercise under hypoxia alters cognitive performance, and propose that the combined effects of acute exercise and hypoxia on cognitive performance are mainly determined by interaction among exercise intensity and duration, the severity of hypoxia, and duration of exposure to hypoxia. We discuss the physiological mechanism(s) of the interaction and suggest that alterations in neurotransmitter function, cerebral blood flow, and possibly cerebral metabolism are the primary candidates that determine cognitive performance when acute exercise is combined with hypoxia. Furthermore, acclimatization appears to counteract impaired cognitive performance during prolonged exposure to hypoxia although the precise physiological mechanism(s) responsible for this amelioration remain to be elucidated. This review has implications for sporting, occupational, and recreational activities at terrestrial high altitude where cognitive performance is essential. Further studies are required to understand physiological mechanisms that determine cognitive performance when acute exercise is performed in hypoxia.

Exercise intensity-dependent effects of arm and leg-cycling on cognitive performance

Physiological responses to arm and leg-cycling are different, which may influence psychological and biological mechanisms that influence post-exercise cognitive performance. The aim of this study was to determine the effects of maximal and submaximal (absolute and relative intensity matched) arm and leg-cycling on executive function. Thirteen males (age, 24.7 ± 5.0 years) initially undertook two incremental exercise tests to volitional exhaustion for arm-cycling (82 ± 18 W) and leg-cycling (243 ± 52 W) for the determination of maximal power output. Participants subsequently performed three 20-min constant load exercise trials: (1) arm-cycling at 50% of the ergometer-specific maximal power output (41 ± 9 W), (2) leg-cycling at 50% of the ergometer-specific maximal power output (122 ± 26 W), and (3) leg-cycling at the same absolute power output as the submaximal arm-cycling trial (41 ± 9 W). An executive function task was completed before, immediately after and 15-min after each exercise test. Exhaustive leg-cycling increased reaction time (p < 0.05, d = 1.17), while reaction time reduced following exhaustive arm-cycling (p < 0.05, d = -0.62). Improvements in reaction time were found after acute relative intensity arm (p < 0.05, d = -0.76) and leg-cycling (p < 0.05, d = -0.73), but not following leg-cycling at the same absolute intensity as arm-cycling (p > 0.05). Improvements in reaction time following arm-cycling were maintained for at least 15-min post exercise (p = 0.008, d = -0.73). Arm and leg-cycling performed at the same relative intensity elicit comparable improvements in cognitive performance. These findings suggest that individuals restricted to arm exercise possess a similar capacity to elicit an exercise-induced cognitive performance benefit.

Swimming-related effects on cerebrovascular and cognitive function

Both acute and regular exercise influence vascular and cognitive function. Upright aquatic exercise increases mean middle cerebral artery blood velocity (MCAvmean ) and has been suggested as favorable for cerebrovascular adaptations. However, MCAvmean has not been reported during swimming. Thus, we examined the cerebrovascular and cognitive effects of swimming. Ten land-based athletes (22 ± 5 years) and eight swimmers (19 ± 1 years) completed three cognitive tasks and four conditions that were used to independently and collectively delineate the swimming-related factors (i.e., posture, immersion, CO2 retention [end-tidal CO2 ; PETCO2 ], and motor involvement). Measurements of MCAvmean and PETCO2 were taken throughout each condition. Prone posture increased MCAvmean by 11% (P < 0.01 vs. upright land). Water immersion independently increased MCAvmean when upright (12%; P < 0.01) but not prone (P = 0.76). The consequent rise in PETCO2 during head-out, breast-stroke swimming (50% heart rate range) independently increased MCAvmean by 14% (P < 0.01), while the motor involvement of swimming per se did not significantly change MCAvmean (P = 0.32). While accounting for sex, swimmers had ~17% lower MCAvmean during all rest conditions (P ≤ 0.05). However, in a subset of participants, both groups had similar internal carotid artery diameters (P = 0.99) and velocities (P = 0.97). Water immersion per se did not alter cognition (P ≥ 0.15), but 20 min of moderate-intensity swimming improved visuomotor performance by 4% (P = 0.03), regardless of athlete group (P = 0.12). In conclusion, breast-stroke swimming increased MCAvmean mostly due to postural and PETCO2 effects, with minimal contributions from water immersion or motor activity. Lastly, swimming improved cognitive functioning acutely, regardless of athlete group. Future research should explore the chronic effects of swimming on cerebrovascular function and cognition, particularly in aging.

Dose-dependent association of accelerometer-measured physical activity and sedentary time with brain perfusion in aging

INTRODUCTION

Age-related decreases in cerebral blood flow (CBF) may lead to cognitive decline, while physical activity (PA) can maintain CBF and cognition in aging. The intensity of PA needed to affect CBF in aging, and the independent effects of sedentary time on CBF are currently unknown. Moreover, research conducted in free-living environments with objective measures of PA (e.g., accelerometry) is lacking.

METHODS

This cross-sectional study used accelerometry to objectively measure sedentary time, all light PA [AllLightPA], moderate-to-vigorous PA [MVPA], and total activity counts [TAC] in 52 cognitively healthy older adults. Robust linear regressions investigated the association of CBF (using arterial spin labeling magnetic resonance imaging) in frontal and medial temporal regions, with each PA intensity and sedentary time.

RESULTS

Greater sedentary time was significantly associated with lower CBF in lateral and medial frontal regions after adjusting for MVPA, while higher AllLightPA (adjusted for MVPA), MVPA (adjusted for AllLightPA), and TAC were associated with greater CBF in lateral and medial frontal regions.

DISCUSSION

Lighter activities, as well as MVPA, are beneficial to CBF in brain regions typically affected by the aging process and malleable to exercise interventions (i.e., the frontal lobes), whereas sedentary time is an independent risk factor for neurovascular dysregulation in normal aging.

Modulation of cortical and subcortical brain areas at low and high exercise intensities

INTRODUCTION

The brain plays a key role in the perceptual regulation of exercise, yet neuroimaging techniques have only demonstrated superficial brain areas responses during exercise, and little is known about the modulation of the deeper brain areas at different intensities.

OBJECTIVES/METHODS

Using a specially designed functional MRI (fMRI) cycling ergometer, we have determined the sequence in which the cortical and subcortical brain regions are modulated at low and high ratings perceived exertion (RPE) during an incremental exercise protocol.

RESULTS

Additional to the activation of the classical motor control regions (motor, somatosensory, premotor and supplementary motor cortices and cerebellum), we found the activation of the regions associated with autonomic regulation (ie, insular cortex) (ie, positive blood-oxygen-level-dependent (BOLD) signal) during exercise. Also, we showed reduced activation (negative BOLD signal) of cognitive-related areas (prefrontal cortex), an effect that increased during exercise at a higher perceived intensity (RPE 13-17 on Borg Scale). The motor cortex remained active throughout the exercise protocol whereas the cerebellum was activated only at low intensity (RPE 6-12), not at high intensity (RPE 13-17).

CONCLUSIONS

These findings describe the sequence in which different brain areas become activated or deactivated during exercise of increasing intensity, including subcortical areas measured with fMRI analysis.

Taking neurogenesis out of the lab and into the world with MAP Train My Brain™

Neurogenesis in the adult hippocampus was rediscovered in the 1990's after being reported in the 1960's. Since then, thousands upon thousands of laboratories have reported on the characteristics and presumed functional significance of new neurons in the adult brain. In 1999, we reported that mental training with effortful learning could extend the survival of these new cells and in the same year, others reported that physical training with exercise could increase their proliferation. Based on these studies and others, we developed MAP Train My Brain™, which is a brain fitness program for humans. The program combines mental and physical (MAP) training through 30-min of effortful meditation followed by 30-min of aerobic exercise. This program, when practiced twice a week for eight weeks reduced depressive symptoms and ruminative thoughts in men and women with major depressive disorder (MDD) while increasing synchronized brain activity during cognitive control. It also reduced anxiety and depression and increased oxygen consumption in young mothers who had been homeless. Moreover, engaging in the program reduced trauma-related cognitions and ruminative thoughts while increasing self-worth in adult women with a history of sexual trauma. And finally, the combination of mental and physical training together was more effective than either activity alone. Albeit effortful, this program does not require inordinate amounts of time or money to practice and can be easily adopted into everyday life. MAP Training exemplifies how we as neuroscientists can take discoveries made in the laboratory out into the world for the benefit of others.

Progressive dry to humid hyperthermia alters exercise cerebral blood flow

INTRODUCTION

Exercising in hot conditions may increase the risk for exertional heat-related illness due to reduction in cerebral blood flow (CBF); however, the acute effect of exercise-induced changes on CBF during compensable and uncompensable heat stress remain unclear. We tested the hypothesis that exercising in hot dry and humid conditions would have different CBF responses.

METHODS

Nine healthy active males completed a 30 min baseline rest then 60 min of low intensity self-paced exercise (12 rating of perceived exertion) in a 1) control compensable neutral dry (CN; 23.7 ± 0.7 °C; 10.7 ± 0.8%Rh) and 2) compensable hot dry (CH; 42.3 ± 0.3 °C; 10.7 ± 1.8%Rh) that progressively increased to an uncompensable hot humid (UCH; 42.3 ± 0.3 °C; 55.2 ± 7.7%Rh) environment in random order separated by at least 4 days.

RESULTS

We observed that during CN environments from rest through 60 min of exercise, middle cerebral velocity (MCAv_mean) and conductance (MCAv_mean CVC) remained unchanged. In contrast, during CH, MCAv_mean, MCAv_mean CVC, and cardiac output (Q) increased and systemic vascular resistance (SVR) decreased. However, under UCH, MCAv_mean, MCAv_mean CVC, and Q was reduced. No difference in mean arterial pressure or ventilation was observed during any condition. Only during UCH, end-tidal PO₂ increased and PCO₂ decreased. The redistribution of blood to the skin for thermoregulation (heart rate, skin blood flow and sweat rate) remained higher during exercise in UCH environments.

CONCLUSIONS

Collectively, exercise cerebral blood flow is altered by an integrative physiological manner that differs in CN, CH, and UCH environments. The control of CBF may be secondary to thermoregulatory control which may provide an explanation for the cause of exertional heat illness.