Validity and Efficacy of the Elite HRV Smartphone Application during Slow-Paced Breathing.

Slow-paced breathing is a clinical intervention used to increase heart rate variability (HRV). The practice is made more accessible via cost-free smartphone applications like Elite HRV. We investigated whether Elite HRV can accurately measure and augment HRV via its slow-paced breathing feature. Twenty young adults completed one counterbalanced cross-over protocol involving 10 min each of supine spontaneous (SPONT) and paced (PACED; 6 breaths·min-1) breathing while RR intervals were simultaneously recorded via a Polar H10 paired with Elite HRV and reference electrocardiography (ECG). Individual differences in HRV between devices were predominately skewed, reflecting a tendency for Elite HRV to underestimate ECG-derived values. Skewness was typically driven by a limited number of outliers as median bias values were ≤1.3 ms and relative agreement was ≥very large for time-domain parameters. Despite no significant bias and ≥large relative agreement for frequency-domain parameters, limits of agreement (LOAs) were excessively wide and tended to be wider during PACED for all HRV parameters. PACED significantly increased low-frequency power (LF) for Elite HRV and ECG, and between-condition differences showed very large relative agreement. Elite HRV-guided slow-paced breathing effectively increased LF values, but it demonstrated greater precision during SPONT and in computing time-domain HRV.

Understanding lower limb blood flow occlusion parameters for use in field-based settings.

Reduction of blood flow to the limb using cuffs before or during exercise has become increasingly popular for training and rehabilitation. Our study tested the effects of cuff brand/width on pressures required to reach limb occlusion pressure (LOP) and developed, cross-validated, and compared accuracy of two LOP prediction equations to previously created methods. Supine LOP was determined in the distal popliteal artery using four different cuff brands/widths in 23 adult participants. Participants then had demographic and resting variables assessed, and two LOP prediction equations were developed from these variables and were compared to five previously developed models and a method using posterior tibial artery palpation for LOP assessment in an independent sample (n = 14 adult runners). For cuff comparison, the widest two cuffs had significantly lower LOP (mean ~149 mmHg) than the narrowest cuffs (mean ~176 mmHg), with the narrowest cuff unable to reach LOP. The eight methods used to predict LOP ranged in accuracy (mean absolute percent errors 3.9-23.0%), with highest accuracy in equations using mean arterial pressure (MAP) and BMI. Practitioners using blood flow reduction methods should be consistent with cuff use due to demonstrated differences across brands/widths. Equations using MAP and BMI appear best for prediction of leg LOP.

Acute beetroot juice reduces blood pressure in young Black and White males but not females.

A complex interplay of social, lifestyle, and physiological factors contribute to Black Americans having the highest blood pressure (BP) in America. One potential contributor to Black adult's higher BP may be reduced nitric oxide (NO) bioavailability. Therefore, we sought to determine whether augmenting NO bioavailability with acute beetroot juice (BRJ) supplementation would reduce resting BP and cardiovascular reactivity in Black and White adults, but to a greater extent in Black adults. A total of 18 Black and 20 White (∼equal split by biological sex) young adults completed this randomized, placebo-controlled (nitrate (NO3-)-depleted BRJ), crossover design study. We measured heart rate, brachial and central BP, and arterial stiffness (via pulse wave velocity) at rest, during handgrip exercise, and during post-exercise circulatory occlusion. Compared with White adults, Black adults exhibited higher pre-supplementation resting brachial and central BP (Ps ≤0.035; e.g., brachial systolic BP: 116(11) vs. 121(7) mmHg, P = 0.023). Compared with placebo, BRJ (∼12.8 mmol NO3-) reduced resting brachial systolic BP similarly in Black (Δ-4±10 mmHg) and White (Δ-4±7 mmHg) adults (P = 0.029). However, BRJ supplementation reduced BP in males (Ps ≤ 0.020) but not females (Ps ≥ 0.299). Irrespective of race or sex, increases in plasma NO3- were associated with reduced brachial systolic BP (ρ = -0.237, P = 0.042). No other treatment effects were observed for BP or arterial stiffness at rest or during physical stress (i.e., reactivity); Ps ≥ 0.075. Despite young Black adults having higher resting BP, acute BRJ supplementation reduced systolic BP in young Black and White adults by a similar magnitude, an effect that was driven by males.

Validation of the SmartPlate for detecting food weight and type.

This study determined accuracy (comparing to criterion), inter-plate reliability (comparing measures between two plates), and intra-plate reliability (comparing successive measures on one plate) of the SmartPlate for food weight and type. Food weight validation included comparing SmartPlate weights to criterion [reference] scale weights (1,980 measures) and weights of 188 foods (2,256 measures). Food type validation included assessing SmartPlate accuracy for 188 foods. For weight, mean absolute percent errors for accuracy, inter-plate reliability, and intra-plate reliability were 6.2, 7.4, and 4.9%, respectively. For food type, foods were correctly identified/listed or searchable 67.0 or 98.9% of the time, respectively, with 76.0% inter-plate reliability and 86.3% intra-plate reliability. The SmartPlate had acceptable accuracy and reliability for assessing food weight and type and may be appealing for monitoring dietary surveillance or intervention. Due to high intra-plate reliability, the SmartPlate may be especially useful for one-on-one interventions and assessing change over time.

Heart Rate Variability and Chronotype in Young Adult Men.

Whether morning heart rate variability (HRV) predicts the magnitude of its circadian variation in the absence of disease or is influenced by chronotype is unclear. We aimed to quantify associations between (1) morning HRV and its diurnal change, and (2) morning HRV and a Morningness−Eveningness Questionnaire (MEQ)-derived chronotype. Resting electrocardiograms were obtained in the morning and evening on separate days in a counterbalanced order to determine the mean RR interval, root mean square of successive differences (RMSSD), and standard deviation of normal-to-normal RR intervals (SDNN) in 23 healthy men (24.6 ± 3.4 yrs; body mass index: 25.3 ± 2.8 kg/m2). The MEQ was completed during the first laboratory visit. Morning RMSSD and SDNN were significantly higher (Ps < 0.05) than evening values. Morning RMSSD and SDNN were associated with their absolute (Ps < 0.0001), and relative diurnal changes (Ps < 0.01). No associations were observed between HRV parameters and the MEQ chronotypes (Ps > 0.09). Morning HRV was a stronger determinant of its evening change than chronotype. Greater diurnal variation in HRV was dependent on higher morning values. Strategies to improve basal HRV may therefore support healthier cardio-autonomic circadian profiles in healthy young men.

Habituation attenuates the sex-specific associations between ischemic pain, blood pressure, and arterial stiffness in young adults.

Cardiovascular reactivity (CVR) during physical stress is prognostic for incident cardiovascular disease. CVR is influenced by perceived pain. However, there is limited data on the effect of sex differences and repeated exposures to painful stimuli on CVR. We measured blood pressure (BP) and carotid-femoral pulse wave velocity (cf-PWV; an index of arterial stiffness) at rest, during isometric handgrip (HG) exercise at 30% of maximum voluntary contraction, and during postexercise circulatory occlusion (PECO) during two identical trials in 39 adults (20M/19F; 18-39 yr). We assessed participants' perceived pain using a visual analog scale after the first minute of each stimulus. We collected BP during minute 2 of each stimulus and cf-PWV during minute 3 of each stimulus. In male participants, we observed moderate associations (Ps ≤ 0.023) between perceived pain and changes in brachial diastolic (ρ = 0.620) and mean BP (ρ = 0.597); central diastolic, mean, and systolic BP (ρs = 0.519-0.654); and cf-PWV (ρ = 0.680) during PECO in trial 1, but not trial 2 (Ps ≥ 0.162). However, in female participants, there were no associations between pain and CVR indices during either trial (Ps ≥ 0.137). Irrespective of sex, reductions in perceived pain during trial 2 relative to trial 1 were weakly to moderately associated (Ps ≤ 0.038) with reductions in brachial diastolic (ρ = 0.346), mean (ρ = 0.379), and systolic BP (ρ = 0.333); central mean (ρ = 0.400) and systolic BP (ρ = 0.369); and cf-PWV (ρ = 0.526). These findings suggest that 1) there are sex differences in pain modulation of CVR in young adults and 2) habituation blunts pain and CVR during PECO, irrespective of sex.NEW & NOTEWORTHY We demonstrate sex differences in the association between pain perception and cardiovascular reactivity (CVR) during ischemic pain. We also demonstrate habituation to pain and reduced CVR during repeated exposure in a sex-independent manner. Accounting for sex differences and habituation may improve the prognostic utility of CVR.

Does Wim Hof Method Improve Breathing Economy during Exercise?

(1) Background: Breathing economy during endurance sports plays a major role in performance. Poor breathing economy is mainly characterized by excessive breathing frequency (BF) and low tidal volume (VT) due to shallow breathing. The purpose of this study was to evaluate whether a 4 week intervention based on the Wim Hof breathing method (WHBM) would improve breathing economy during exercise in adolescent runners. (2) Methods: 19 adolescent (16.6 ± 1.53 years) middle- and long-distance runners (11 boys and 8 girls) participated in the study. Participants were randomly divided into experimental (n = 11) and control groups (n = 8). The study was set in the transition period between competitive race seasons and both groups had a similar training program in terms of running volume and intensity over the course of the study. The experimental group performed breathing exercises every day (~20 min/day) for 4 weeks. The control group did not perform any kind of breathing exercise. The breathing exercises consisted of three sets of controlled hyperventilation and consecutive maximum breath holds. Before and after the intervention, participants performed incremental cycle ergometer testing sessions consisting of two minute stages at 1, 2, 3, and 4 W·kg−1 with breath-by-breath metabolic analysis. During the testing sessions, BF, VT, and minute ventilation (VE) were assessed and compared. (3) Results: There were no statistically significant differences (p > 0.05) in BF, VT, or VE between experimental and control groups before or after the intervention. A nonsignificant small-to-large effect for an increase in VE and BF in both groups following the 4 week intervention period was observed, possibly due to a reduction in training volume and intensity owing to the down period between competitive seasons. (4) Conclusions: The 4 week intervention of WHBM did not appear to alter parameters of breathing economy during a maximal graded exercise test in adolescent runners.

Individual versus Group Calibration of Machine Learning Models for Physical Activity Assessment Using Body-Worn Accelerometers.

PURPOSE: We sought to determine if individually calibrated machine learning models yielded higher accuracy than a group calibration approach for physical activity intensity assessment. METHODS: Participants (n = 48) wore accelerometers on the right hip and nondominant wrist while performing activities of daily living in a semistructured laboratory and/or free-living setting. Criterion measures of activity intensity (sedentary, light, moderate, vigorous) were determined using direct observation. Data were reintegrated into 30-s epochs, and eight random forest models were created to determine physical activity intensity by using all possible conditions of training data (individual vs group), protocol (laboratory vs free-living), and placement (hip vs wrist). A 2 × 2 × 2 repeated-measures analysis of variance was used to compare epoch-level accuracy statistics (% accuracy, kappa [κ]) of the models when used to determine activity intensity in an independent sample of free-living participants. RESULTS: Main effects were significant for the type of training data (group: accuracy = 80%, κ = 0.59; individual: accuracy = 74% [P = 0.02], κ = 0.50 [P = 0.01]) and protocol (free-living: accuracy = 81%, κ = 0.63; laboratory: accuracy = 74% [P = 0.04], κ = 0.47 [P < 0.01]). Main effects were not significant for placement (hip: accuracy = 79%, κ = 0.58; wrist: accuracy = 75% [P = 0.18]; κ = 0.52 [P = 0.18]). Point estimates for mean absolute error were generally lowest for the group training, free-living protocol, and hip placement. CONCLUSIONS: Contrary to expectations, individually calibrated machine learning models yielded poorer accuracy than a traditional group approach. In addition, models should be developed in free-living settings when possible to optimize predictive accuracy.

Validity and Reliability of the VO2 Master Pro for Oxygen Consumption and Ventilation Assessment.

This study assessed validity and reliability of the VO2 Master Pro portable metabolic analyzer for assessment of oxygen consumption (VO2) and minute ventilation (VE). In Protocol 1, eight male participants (height: 182.6 ± 5.8 cm, weight: 79.6 ± 8.3 kg, age: 41.0 ± 12.3 years) with previous competitive cycling experience completed an hour-long stationary cycling protocol twice, progressing from 100-300 Watts every 10 minutes while wearing the VO2 Master and a criterion measure (Parvomedics) for five minutes each, at each stage. In Protocol 2, 16 recreationally active male participants (height: 168.2 ± 8.4 cm, weight: 76.5 ± 13.3 kg, age: 23.0 ± 9.4 years) completed three incremental, maximal stationary cycling tests wearing one of three analyzers for each test (VO2 Master version 1.1.1, VO2 Master version 1.2.1, Parvomedics). For Protocol 1 and convergent validity, the VO2 Master had mean absolute differences from the Parvomedics of <0.3 L/min for absolute VO2 and <5 L/min for VE overall and at each exercise stage. Mean absolute percent differences (MAPD) for VO2 and VE were <9% overall and <12% at each stage. Test-retest reliability of the VO2 Master (MAPD: 8.9-10.9%) was somewhat poorer than the Parvomedics (MAPD: 5.3-7.6%). For Protocol 2, validity was similar for both VO2 Master models (MAPD ~12% overall) compared to the Parvomedics for VO2 and VE. The VO2 Master had an acceptable validity and test-retest reliability for most intensities tested and may be an appealing option for field-based VO2 and VE analysis.