We assessed the convergent validity of commonly applied metrics of cerebral autoregulation (CA) to determine the extent to which the metrics can be used interchangeably. To examine between-subject relationships among low-frequency (LF; 0.07-0.2 Hz) and very-low-frequency (VLF; 0.02-0.07 Hz) transfer function coherence, phase, gain, and normalized gain, we performed retrospective transfer function analysis on spontaneous blood pressure and middle cerebral artery blood velocity recordings from 105 individuals. We characterized the relationships (n ϭ 29) among spontaneous transfer function metrics and the rate of regulation index and autoregulatory index derived from bilateral thigh-cuff deflation tests. In addition, we analyzed data from subjects (n ϭ 29) who underwent a repeated squat-to-stand protocol to determine the relationships between transfer function metrics during forced blood pressure fluctuations. Finally, data from subjects (n ϭ 16) who underwent step changes in end-tidal PCO 2 (PETCO 2 ) were analyzed to determine whether transfer function metrics could reliably track the modulation of CA within individuals. CA metrics were generally unrelated or showed only weak to moderate correlations. Changes in PET CO 2 were positively related to coherence [LF: ␤ ϭ 0.0065 arbitrary units (AU)/mmHg and VLF: ␤ ϭ 0.011 AU/mmHg, both P Ͻ 0.01] and inversely related to phase (LF: ␤ ϭ Ϫ0.026 rad/mmHg and VLF: ␤ ϭ Ϫ0.018 rad/mmHg, both P Ͻ 0.01) and normalized gain (LF: ␤ ϭ Ϫ0.042%/mmHg 2 and VLF: ␤ ϭ Ϫ0.013%/mmHg 2 , both P Ͻ 0.01). However, PETCO 2 was positively associated with gain (LF: ␤ ϭ 0.0070 cm·s

Compression garments (CGs) provide a means of applying mechanical pressure at the body surface, thereby compressing and perhaps stabilizing/supporting underlying tissue. The body segments compressed and applied pressures ostensibly reflect the purpose of the garment, which is to mitigate exercise-induced discomfort or aid aspects of current or subsequent exercise performance. Potential benefits may be mediated via physical, physiological or psychological effects, although underlying mechanisms are typically not well elucidated. Despite widespread acceptance of CGs by competitive and recreational athletes, convincing scientific evidence supporting ergogenic effects remains somewhat elusive. The literature is fragmented due to great heterogeneity among studies, with variability including the type, duration and intensity of exercise, the measures used as indicators of exercise or recovery performance/physiological function, training status of participants, when the garments were worn and for what duration, the type of garment/body area covered and the applied pressures. Little is known about the adequacy of current sizing systems, pressure variability within and among individuals, maintenance of applied pressures during one wear session or over the life of the garment and, perhaps most importantly, whether any of these actually influence potential compression-associated benefits. During exercise, relatively few ergogenic effects have been demonstrated when wearing CGs. While CGs appear to aid aspects of jump performance in some situations, only limited data are available to indicate positive effects on performance for other forms of exercise. There is some indication for physical and physiological effects, including attenuation of muscle oscillation, improved joint awareness, perfusion augmentation and altered oxygen usage at sub-maximal intensities, but such findings are relatively isolated. Sub-maximal (at matched work loads) and maximal heart rate appears unaffected by CGs. Positive influences on perceptual responses during exercise are limited. During recovery, CGs have had mixed effects on recovery kinetics or subsequent performance. Various power and torque measurements have, on occasions, benefitted from the use of CGs in recovery, but subsequent sprint and agility performance appears no better. Results are inconsistent for post-exercise swelling of limb segments and for clearance of myocellular proteins and metabolites, while effects on plasma concentrations are difficult to interpret. However, there is some evidence for local blood flow augmentation with compression. Ratings of post-exercise muscle soreness are commonly more favourable when CGs are worn, although this is not always so. In general, the effects of CGs on indicators of recovery performance remain inconclusive. More work is needed to form a consensus or mechanistically-insightful interpretation of any demonstrated effects of CGs during exercise, recovery or - perhaps most importantly - fitness development. Limited practical recommendations for ...

Sporting compression garments (CG) are used widely during exercise despite little evidence of benefits. The purpose of this study was to investigate coverage and pressure effects of full-body CG on cardiovascular and thermoregulatory function at rest and during prolonged exercise, and on exercise performance. Twelve recreationally trained male cyclists [mean (SD) age, 26 (7) years; VO(2 max), 53 (8) mL kg(-1) min(-1)] completed three sessions (counterbalanced order), wearing either correctly-sized CG (CSG; 11-15 mmHg), over-sized CG (OSG; 8-13 mmHg), or gym shorts (CONT). Test sessions were conducted in temperate conditions [24 (1)°C, 60 (4)% relative humidity; ~2 m s(-1) air velocity during exercise], consisting of resting on a chair then on a cycle ergometer, before 60-min fixed-load cycling at ~65% VO(2 max) and a 6-km time trial. Wearing CG (CSG or OSG) did not mitigate cardiovascular strain during mild orthostatic stress at rest (p = 0.20-0.93 for garment effects). During exercise, cardiac output was ~5% higher in the CG conditions (p < 0.05), which appears to be accounted for via non-significant higher end-exercise heart rate (~4-7%, p = 0.30; p = 0.06 for greater heart rate drift in CSG); other cardiovascular variables, including stroke volume, were similar among conditions (p = 0.23-0.91). Covered-skin temperature was higher in CG conditions (p < 0.001) but core (oesophageal) temperature was not (p = 0.79). Time-trial performance (mean power, time taken) was similar with or without CG (p = 0.24-0.44). In conclusion, any demonstrable physiological or psychophysical effects of full-body CG were mild and seemingly reflective more of surface coverage than pressure. No benefit was evident for exercise performance.

Although the cerebrovasculature is known to be exquisitely sensitive to CO(2), there is no consensus on whether the sympathetic nervous system plays a role in regulating cerebrovascular responses to changes in arterial CO(2). To address this question, we investigated human cerebrovascular CO(2) reactivity in healthy participants randomly assigned to the α(1)-adrenoreceptor blockade group (9 participants; oral prazosin, 0.05 mg/kg) or the placebo control (9 participants) group. We recorded mean arterial blood pressure (MAP), heart rate (HR), mean middle cerebral artery flow velocity (MCA(V mean)), and partial pressure of end-tidal CO(2) (Pet(CO(2))) during 5% CO(2) inhalation and voluntary hyperventilation. CO(2) reactivity was quantified as the slope of the linear relationship between breath-to-breath Pet(CO(2)) and the average MCAv(mean) within successive breathes after accounting for MAP as a covariate. Prazosin did not alter resting HR, Pet(CO(2)), MAP, or MCA(V mean). The reduction in hypocapnic CO(2) reactivity following prazosin (-0.48 ± 0.093 cm·s(-1) · mmHg(-1)) was greater compared with placebo (-0.19 ± 0.087 cm · s(-1) · mmHg(-1); P < 0.05 for interaction). In contrast, the change in hypercapnic CO(2) reactivity following prazosin (-0.23 cm · s(-1) · mmHg(-1)) was similar to placebo (-0.31 cm · s(-1) · mmHg(-1); P = 0.50 for interaction). These data indicate that the sympathetic nervous system contributes to CO(2) reactivity via α(1)-adrenoreceptors; blocking this pathway with prazosin reduces CO(2) reactivity to hypocapnia but not hypercapnia.

Background: Skin temperature (Tskin) is commonly measured using Tskin sensors affixed directly to the skin surface, although the influence of setup variables on the measured outcome requires clarification.Objectives: The two distinct objectives of this systematic review were (1) to examine measurements from contact Tskin sensors considering equilibrium temperature and temperature disturbance, sensor attachments, pressure, environmental temperature, and sensor type, and (2) to characterise the contact Tskin sensors used, conditions of use, and subsequent reporting in studies investigating sports, exercise, and other physical activity.Data sources and study selection: For the measurement comparison objective, Ovid Medline and Scopus were used (1960 to July 2016) and studies comparing contact Tskin sensor measurements in vivo or using appropriate physical models were included. For the survey of use, Ovid Medline was used (2011 to July 2016) and studies using contact temperature sensors for the measurement of human Tskin in vivo during sport, exercise, and other physical activity were included.Study appraisal and synthesis methods: For measurement comparisons, assessments of risk of bias were made according to an adapted version of the Cochrane Collaboration's risk of bias tool. Comparisons of temperature measurements were expressed, where possible, as mean difference and 95% limits of agreement (LoA). Meta-analyses were not performed due to the lack of a common reference condition. For the survey of use, extracted information was summarised in text and tabular form.Results: For measurement comparisons, 21 studies were included. Results from these studies indicated minor (<0.5°C) to practically meaningful (>0.5°C) measurement bias within the subgroups of attachment type, applied pressure, environmental conditions, and sensor type. The 95% LoA were often within 1.0°C for in vivo studies and 0.5°C for physical models. For the survey of use, 172 studies were included. Details about Tskin sensor setup were often poorly reported and, from those reporting setup information, it was evident that setups widely varied in terms of type of sensors, attachments, and locations used.Conclusions: Setup variables and conditions of use can influence the measured temperature from contact Tskin sensors and thus key setup variables need to be appropriately considered and consistently reported.

Non-invasive, multi-parameter methods to estimate core body temperature offer several advantages for monitoring thermal strain, although further work is required to identify the most relevant predictor measures. This study aimed to compare the validity of an existing and two novel multi-parameter rectal temperature prediction models. Thirteen healthy male participants (age 30.9 ± 5.4 years) performed two experimental sessions. The experimental procedure comprised 15 min baseline seated rest (23.2 ± 0.3°C, 24.5 ± 1.6% relative humidity), followed by 15 min seated rest and cycling in a climatic chamber (35.4 ± 0.2°C, 56.5 ± 3.9% relative humidity; to +1.5°C or maximally 38.5°C rectal temperature, duration 20–60 min), with a final 30 min seated rest outside the chamber. In session 1, participants exercised at 75% of their heart rate maximum (HR max) and wore light athletic clothing (t-shirt and shorts), while in session 2, participants exercised at 50% HR max, wearing protective firefighter clothing (jacket and trousers). The first new prediction model, comprising the input of 18 non-invasive measures, i.e., insulated and non-insulated skin temperature, heat flux, and heart rate (“Max-Input Model”, standard error of the estimate [SEE] = 0.28°C, R2 = 0.70), did not exceed the predictive power of a previously reported model which included six measures and no insulated skin temperatures (SEE = 0.28°C, R2 = 0.71). Moreover, a second new prediction model that contained only the two most relevant parameters (heart rate and insulated skin temperature at the scapula) performed similarly (“Min-Input Model”, SEE = 0.29, R2 = 0.68). In conclusion, the “Min-Input Model” provided comparable validity and superior practicality (only two measurement parameters) for estimating rectal temperature versus two other models requiring six or more input measures.

Cerebral blood flow responses to transient blood pressure challenges are frequently attributed to cerebral autoregulation (CA), yet accumulating evidence indicates vascular properties like compliance are also influential. We hypothesized that middle cerebral blood velocity (MCAv) dynamics during or following a transient blood pressure perturbation can be accurately explained by the windkessel mechanism. Eighteen volunteers underwent blood pressure manipulations, including bilateral thigh-cuff deflation and sit-to-stand maneuvers under normocapnic and hypercapnic (5% CO2) conditions. Pressure-flow recordings were analyzed using a windkessel analysis approach that partitions the frequency-dependent resistance and compliance contributions to MCAv dynamics. The windkessel was typically able to explain more than 50% of the MCAv variance, as indicated by R(2) values for both the flow recovery and postrecovery phase. The most consistent predictors of MCAv dynamics under the control condition were the windkessel capacitive gain and high-frequency resistive gain. However, there were significant interindividual variations in the composition of windkessel predictors. Hypercapnia consistently reduced the capacitive gain and enhanced the low-frequency (0.04-0.20 Hz) resistive gain for both thigh-cuff deflation and sit-to-stand trials. These findings indicate that 1) MCAv dynamics during acute transient hypotension challenges are dominated by cerebrovascular windkessel properties independent of CA; 2) there is significant heterogeneity in windkessel properties between individuals; and 3) hemodynamic effects of hypercapnia during transient blood pressure challenges primarily reflect changes in windkessel properties rather than pure CA impairment.

The objective was to examine the effects of layering fabrics on selected properties known to be critical in the outdoor recreational activity market (permeability to air and to water vapor, and thermal-related measures including ’dry’ and ’wet’ thermal resistance). With laboratory-based testing used by manufacturers to aid fabric selection, information on the way in which fabrics behave as layered arrangements is pertinent.Comparisons of effects on fabric properties were based on fibers (merino wool, polyester), knit structures (single jersey, interlock, eyelet), and whether differences were apparent with multiple-layer arrangements typical of end use, including outer layers. Standard methods and modifications to these were applied. Some properties differed according to the spacing (distance) between layers and/or between a first layer and a hypothetical ’skin’ surface. Differences among the different fabrics/fibers were more apparent with one layer than with multiple layers. Layering of fabrics which are likely to be used as garments worn together has major effects on properties such as permeability to air and water vapor, thermal resistance, and nominal thermal conductance. Effects of adding a second layer typically exceeded those of adding a third.