Metabolic Heat Production Modulates the Cardiovascular Drift-V̇O2max Relationship Independent of Aerobic Fitness in Women.

INTRODUCTION/PURPOSE: The purpose of this study was to test the hypothesis that cardiovascular (CV) drift and associated decrements in maximal oxygen uptake (V̇O2max) are greater in high-fit compared to low-fit women during exercise at the same %V̇O2max, but comparable at the same rate of metabolic heat production. METHODS: Six high-fit (HI) and 6 low-fit (LO) women cycled in 35 °C for 15 min or 45 min at the same relative intensity (60% V̇O2max; 15REL and 45REL) or fixed rate of heat production (500 W; 15FX and 45FX), immediately followed by a GXT to measure V̇O2max. The separate 15- and 45-min trials permitted measurements of V̇O2max over the same time interval as CV drift. RESULTS: During 45REL, higher heat production in HI (496 ± 51 W vs. 364 ± 44 W in LO) resulted in greater end-exercise core temperature (38.7 ± 0.4 °C vs. 38.2 ± 0.1 °C, P = 0.03); greater increases in HR [15 beats·min-1 (10%) vs. 10 beats·min-1 (6%), P = 0.03] and decreases in SV [11 mL·beat-1 (16%) vs. 5 mL·beat-1 (8%), P = 0.001]; and larger reductions in V̇O2max (16% vs. 5%, P = 0.04) compared to LO. During 45FX, temperature responses, CV drift and decreased V̇O2max were not different between groups (all P > 0.05), despite differences in %V̇O2max (60% vs. 75% for HI and LO, respectively). CONCLUSIONS: We conclude metabolic heat production modulates the CV drift-V̇O2max relationship, independent of fitness level. These results support previous findings showing the magnitude of CV drift is proportional to reductions in V̇O2max.

Acute Effects of Cadence-Controlled Walking on Cognition and Vascular Function in Physically Inactive Older Adults: A Randomized Crossover Study.

BACKGROUND: Cadence-controlled walking may be a desirable approach for older adults to self-monitor exercise intensity and achieve physical activity guidelines. We examined the acute effects of cadence-controlled walking on cognition and vascular function in physically inactive older adults. METHODS: In a randomized crossover design, 26 participants (65% females, 67.8 ± 11.3 years) underwent 30-min acute exercise (walking at 100 steps/min) and control (sitting) conditions. We measured cognition, central blood pressure (BP), and arterial stiffness before, and immediately, after each condition. RESULTS: We observed significant Time × Condition interactions in the Flanker Inhibitory Control and Attention (Flanker) test and Dimensional Change Card Sort (DCCS) test scores, and in central systolic BP, central pulse pressure, and carotid to femoral pulse wave velocity (p < .05). The Flanker and DCCS scores significantly increased after walking (d = 0.4 and 0.5, respectively), but not after sitting. Central systolic BP, central pulse pressure, and carotid to femoral pulse wave velocity significantly increased after sitting but remained unchanged after acute walking (d = 0.4-0.2), with p-values < .05. After walking, significant correlations were observed between DCCS and diastolic BP and central pulse pressure change scores and change scores in central pulse wave velocity, Flanker, and DCCS (rs = -0.45 to -0.52). CONCLUSION: These findings suggest that a single bout of cadence-controlled walking elicited an immediate improvement in cognition and might have mitigated increases in arterial stiffness and central BP observed in the seated control condition. Further research is needed to examine the association between cognition and vascular function following acute exercise compared to control conditions. SIGNIFICANCE: Our findings may have practical implications for developing daily physical activity recommendations for improving the cognitive health for successful aging.

Greater weekly physical activity linked to left resting frontal alpha asymmetry in women: A study on gender differences in highly active young adults.

Physical activity, beneficial for physical and psychological health, may facilitate affective mechanisms of positive emotion and approach-motivation. Greater resting frontal alpha asymmetry (FAA), an index of greater relative left than right frontal cortical activity, is a neural correlate of affective mechanisms possibly associated with active lifestyles. This study sought to amplify limited literature on the relationship between physical (in)activity, FAA, and gender differences. College students (n = 70) self-reported physical activity (Total PA) and sedentary activity (Total Sitting) via the International Physical Activity Questionnaire-Short Form (IPAQ-SF), followed by a resting electroencephalography session to record FAA. A Total PA × gender interaction (ß = 0.462, t = 3.163, p = 0.002) identified a positive relationship between Total PA and FAA in women (ß = 0.434, t = 2.221, p = 0.030) and a negative relationship for men (ß = -0.338, t = -2.300, p = 0.025). Total Sitting was positively linked to FAA (ß = 0.288, t = 2.228, p = 0.029; no gender effect). Results suggest affective mechanisms reflected by FAA (e.g., positive emotion, approach-motivation) are associated with physical activity for women, indicating a possible mechanism of the psychological benefits linked with physically active lifestyles. A positive relationship between sedentary behavior and greater left FAA may also reflect motivated mechanisms of behavior that aid in minimizing energy expenditure, particularly within the context of our highly active sample.

Lower limb blood flow occlusion increases systemic pressor response without increasing brachial arterial blood flow redistribution in women.

This study was conducted to investigate the systemic hemodynamic and vascular changes in women during and after two commonly used clinical blood flow restriction (BFR) pressures at rest. There are minimal data regarding the independent effects of BFR on hemodynamic and systemic vascular changes due to pressor response, particularly among women. Therefore, this study investigated BFR-induced alterations in pressor response and systemic flow redistribution at rest during two commonly used pressures (50% and 80% limb occlusion pressure [LOP]). Fifteen women (22.1 ± 4.2 years) completed two randomised sessions involving 8-min of bilateral, lower limb restriction at 50% or 80% LOP followed by 8-min of recovery post-deflation. Changes in vascular (arterial diameter [DIA], time-averaged mean velocity [TAMV], volume flow [VF], and area) and hemodynamic (heart rate [HR] and blood pressure) measures over time (pre-, during, post-occlusion) and by session (50% vs. 80% LOP) were tested using repeated measures analysis of variance. Repeated measures correlations (rrm) quantified common intraindividual associations between BFR-induced hemodynamic and vascular responses. HR increased from baseline during 50% LOP and remained elevated during recovery (p < 0.05). HR increased from baseline during 80% LOP, while tibial VF and TAMV decreased (p < 0.03 for all). HR and TAMV values returned to baseline during recovery, while brachial artery VF decreased (p < 0.05). Changes in HR, brachial VF, and brachial TAMV were similar between 50% and 80% LOP (rrm = 0.32-0.70, p < 0.05 for all). At 80% LOP, changes in HR were positively correlated with brachial VF (rrm = 0.38) and TAMV (rrm = 0.43) and negatively correlated with tibial VF (rrm = -0.36) and TAMV (rrm = -0.30) (p < 0.05 for all). Results suggest that BFR at 80% LOP elicits an acute systemic pressor reflex without concomitant increases in brachial arterial flow, while 50% LOP elicits a subdued response.

Acute work rate adjustments during high-intensity interval training in a hot and temperate environment.

Heart rate drifts upward over time during interval exercise and during exercise in hot conditions. As such, work rate must be lowered to maintain target heart rate. The purpose was to characterize acute work rate adjustments during high-intensity interval training based on target heart rate. Seven humans (three females) completed five study visits: a graded exercise test on a cycle ergometer to measure maximal heart rate (HRmax) in ∼22 °C and four trials performed in ∼22 °C (TEMP) or ∼35 °C (HOT), consisting of an 8 min warm-up at 70% HRmax followed by one (15TEMP and 15HOT) or five (43TEMP and 43HOT) rounds of high-intensity interval training (one round = 4 min work at 90% HRmax and 3 min recovery at 70% HRmax) totaling 15 min or 43 min of exercise, respectively. Work rate was lowered 33 ± 20 W (p = 0.005) in 43TEMP and 56 ± 30 W (p = 0.003) in 43HOT between the first and fifth work intervals. Thermal strain (0.2 °C higher rectal temperature, p = 0.01) and cardiovascular strain (6 beats·min-1 larger increase in heart rate from first to fifth recovery interval, p = 0.01) were greater in 43HOT versus 43TEMP. Using target heart rate during high-intensity interval training may reduce the training stimulus, especially in hot environments, but it may also limit thermal strain and enable participants to complete the prescribed workout despite the heat.

Physical demands and physiological strain of American football referees while officiating.

OBJECTIVES: Certain occupations are associated with greater risk of triggering a sudden cardiac event because of high levels of physical exertion and extreme thermal environments in which they occur. The extent to which sports officials--particularly high school (HS) American football referees--experience these conditions is unknown. Forty-six male HS officials (72% White/Caucasian; age = 48 ± 12 years, body mass index = 31.7 ± 6.6 kg·m-2) were studied to quantify the physiological strain and physical demands of officiating. METHODS: Referee demographics (e.g., experience, habitual exercise), pre-game urine specific gravity (USG), thermal (peak core temperature [Tcore]) and cardiovascular (average heart rate [HR]) strain, kinematic activity (e.g., total distance, speed, mechanical intensity), and environmental conditions were measured during 10 regular season varsity HS football games (≈2.5 h each) in the Southeastern United States (average wet bulb globe temperature and relative humidity: 18.9 ± 6.0 °C and 78.2% ± 12.1%). Analyses included descriptive statistics, bivariate correlations, and linear regression. RESULTS: Referees covered 5.2 ± 1.2 km per game, eliciting average HR and peak Tcore of 71.5% ± 8.0% HRmax and 38.3 ± 0.5 °C, respectively; 38% began games dehydrated (USG = 1.026 ± 0.004). Multiple regression analyses revealed that obesity (ß = 0.34), not participating in regular exercise (ß = -0.36), and officiating at lower mechanical intensity (ß = -0.33) predicted greater cardiovascular strain (all p ≤ 0.03). White/Caucasian race/ethnicity (ß = 0.59), younger age (ß = -0.46), and obesity (ß = 0.28) predicted greater thermal strain (all p ≤ 0.01). CONCLUSION: HS football referees experienced elevated levels of physiological strain while officiating, with individual factors modulating the magnitude of strain. Strategies aimed at reducing obesity, increasing exercise participation, and improving cardiovascular health should be emphasized to mitigate strain and prevent cardiac events.

Vagally Derived Heart Rate Variability and Training Perturbations With Menses in Female Collegiate Rowers.

INTRODUCTION: The parasympathetically derived marker of heart rate variability, root mean square of successive R-R differences (RMSSD), and the daily fluctuations as measured by the coefficient of variation (RMSSDCV) may be useful for tracking training adaptations in athletic populations. These vagally derived markers of heart rate variability may be especially pertinent when simultaneously considering a female athlete's menstrual cycle. PURPOSE: The purpose of this study was to observe the perturbations in RMSSDCV, while considering RMSSD, across a season in the presence and absence of menses with training load in female collegiate rowers. METHODS: Thirty-six (20 [1] y, 25.6 [3.4] kg·m-2) National Collegiate Athletic Association Division I female rowers were monitored for 18 consecutive weeks across a full season. Seated, ultrashortened RMSSD measurements were obtained by the rowers on at least 3 mornings per week using a smartphone photoplethysmography device. Following the RMSSD measurement, athletes indicated the presence or absence of menstruation within the application. Individual meters rowed that week and sessions rate of perceived exertion were obtained to quantify training load. RESULTS: Longitudinal mixed-effects modeling demonstrated a significant effect of menses and time, while also considering RMSSD, such that those who were on their period had a significantly greater RMSSDCV than those who were not (11.2% vs 7.5%, respectively; P < .001). These changes were independent of meters rowed, sessions rate of perceived exertion, body mass index, birth-control use, and years of rowing experience, which were all nonsignificant predictors of RMSSDCgV (P > .05). CONCLUSION: The presence of menses appears to significantly impact RMSSDCV when also considering RMSSD, which may allow coaches to consider individualized training plans accordingly.

Comparison of Heart Rate Variability Responses to Varying Resistance Exercise Volume-Loads.

Purpose: The aim of this study was to compare the effects of low ([LV]; 4 total sets), moderate ([MV]; 8 total sets), and high set volumes ([HV]; 12 total sets) in acute full-body resistance exercise sessions on post-exercise parasympathetic reactivation measured using RMSSD. Methods: Ten resistance-trained participants (25.8 ± 6.8 yr., 173.4 ± 10.6 cm, 75.4 ± 9.9 kg) performed three resistance exercise sessions. During each session, heart rate variability (HRV) was measured pre- and for 30 min post-exercise, divided into 5-min segments stabilization, Post5-10, Post10-15, Post15-20, Post20-25, and Post25-30. Repeated-measures ANOVA was used to assess differences within and between pre-post exercise natural logarithm RMSSD (LnRMSSD) values. To assess the initial change in LnRMSSD, the delta percent change (ΔLnRMSSD) from pre-exercise to Post5-10 (ΔLnRMSSDpre-post) was calculated for each session. The ΔLnRMSSD was also calculated between Post5-10 and Post25-30 (ΔLnRMSSDpost5-30) to assess recovery. Results: Significant differences were observed between sessions and when comparing pre-exercise values to all post-exercise times across sessions (p ≤ .05). The LV session resulted in significantly higher mean LnRMSSD value (3.62) post-exercise compared to both the MV (3.11, effect size [ES] =  3.77) and HV (3.02, ES =  3.92) sessions while the MV and HV sessions produced similar responses. Across sessions no return to baseline occurred and when comparing sessions, no significant differences were found in ΔLnRMSSDpre-post or ΔLnRMSSDpost5-30. Conclusion: Acute bouts of full-body resistance exercise can cause similar reductions in LnRMSSD from pre-exercise levels and can delay parasympathetic reactivation back to baseline values during the same 30-min recovery period despite differences in set volume.

Heart-Rate Variability Recording Time and Performance in Collegiate Female Rowers.

PURPOSE: To assess the agreement of the root mean square of successive R-R interval (RMSSD) values when recorded immediately upon waking to values recorded later in the morning prior to practice, and to determine the associations of the RMSSD recordings with performance outcomes in female rowers. METHODS: A total of 31 National Collegiate Athletic Association Division I rowers were monitored for 6 consecutive days. Two seated RMSSD measurements were obtained on at least 3 mornings using a smartphone-based photoplethysmography application. Each 1-minute RMSSD measure was recorded following a 1-minute stabilization period. The first (T1) measurement occurred at the athlete's home following waking, while the second (T2) transpired upon arrival at the team's boathouse immediately before practice. From the measures, the RMSSD mean and coefficient of variation were calculated. Two objective performance assessments were conducted on an indoor rowing ergometer on separate days: 2000-m time trial and distance covered in 30 minutes. Interteam rank was determined by the coaches, based on subjective and objective performance markers. RESULTS: The RMSSD mean (intraclass correlation coefficient = .82; 95% CI, .63 to .92) and RMSSD coefficient of variation (intraclass correlation coefficient = .75; 95% CI, .48 to .88) were strongly correlated at T1 and T2, P < .001. The RMSSD mean at T1 and T2 was moderately associated with athlete rank (r = -.55 and r = -.46, respectively), 30-minute distance (r = .40 and r = .41, respectively), and 2000 m at T1 (r = -.37), P < .05. No significant correlations were observed for the RMSSD coefficient of variation. CONCLUSION: Ultrashort RMSSD measurements taken immediately upon waking show very strong agreement with those taken later in the morning, at the practice facility. Future research should more thoroughly investigate the relationship between specific performance indices and the RMSSD mean and coefficient of variation for female collegiate rowers.

Validity of Smartphone Heart Rate Variability Pre- and Post-Resistance Exercise.

The aim was to examine the validity of heart rate variability (HRV) measurements from photoplethysmography (PPG) via a smartphone application pre- and post-resistance exercise (RE) and to examine the intraday and interday reliability of the smartphone PPG method. Thirty-one adults underwent two simultaneous ultrashort-term electrocardiograph (ECG) and PPG measurements followed by 1-repetition maximum testing for back squats, bench presses, and bent-over rows. The participants then performed RE, where simultaneous ultrashort-term ECG and PPG measurements were taken: two pre- and one post-exercise. The natural logarithm of the root mean square of successive normal-to-normal (R-R) differences (LnRMSSD) values were compared with paired-sample t-tests, Pearson product correlations, Cohen's d effect sizes (ESs), and Bland-Altman analysis. Intra-class correlations (ICC) were determined between PPG LnRMSSDs. Significant, small-moderate differences were found for all measurements between ECG and PPG: BasePre1 (ES = 0.42), BasePre2 (0.30), REPre1 (0.26), REPre2 (0.36), and REPost (1.14). The correlations ranged from moderate to very large: BasePre1 (r = 0.59), BasePre2 (r = 0.63), REPre1 (r = 0.63), REPre2 (r = 0.76), and REPost (r = 0.41)-all p < 0.05. The agreement for all the measurements was "moderate" (0.10-0.16). The PPG LnRMSSD exhibited "nearly-perfect" intraday reliability (ICC = 0.91) and "very large" interday reliability (0.88). The smartphone PPG was comparable to the ECG for measuring HRV at rest, but with larger error after resistance exercise.

Frontal asymmetry: A novel biomarker for physical activity and sedentary behavior.

Past research has demonstrated that regular physical activity provides a myriad of physical, mental, and emotional benefits. The decision of whether to partake in physical activity (PA) or remain sedentary appears to be partially influenced by motivational and emotional systems. Research suggests left frontal alpha asymmetry is a neural marker of approach motivation. However, studies have not explored whether habitual levels of PA and sedentary behavior relate to this neurophysiological signal. Across two studies, individuals completed measures of habitual PA and sedentary behavior using the International Physical Activity Questionnaire-Short Form. Then, resting electroencephalography activity was recorded. Results of Study 1 (N = 32, 72% women) indicated that more time spent sitting on both weekdays and weekend days were associated with less left frontal asymmetry (r = -.45, p = .027, and r = -.55, p = .005, respectively). Study 2 recruited a larger sample (N = 96, 31% women) and investigated moderators. Greater levels of moderate (r = .27) and total (r = .29) PA were associated with greater left frontal asymmetry (ps < .05), and the relationship between sedentary behavior and less left frontal asymmetry was moderated by sex (weekday: ß = .62, p = .011; weekend day: ß = .41, p = .034). Our results suggest that left frontal asymmetry may be a novel neurophysiological marker for PA and sedentary behavior.

Profiles of Heart Rate Variability and Bar Velocity after Resistance Exercise.

INTRODUCTION: The aim of this investigation was to observe the association in the time course in recovery between multiple heart rate variability (HRV) metrics and neuromuscular performance, as assessed by mean bar velocity (BVM) in the back squat, over a 72-h period after an exhaustive back squat protocol. METHODS: Eight resistance-trained males completed five laboratory visits within a 7-d period. The first visit involved short-term HRV recordings followed by a familiarization of BVM procedures and a one-repetition maximum test of the back squat. Forty-eight hours later, participants returned to the laboratory for prestimulus measurements, immediately followed by a back squat protocol (8 sets of 10 repetitions at 70% of one-repetition maximum with a 2-min rest). The HRV and the BVM measurements were replicated at 0.5, 24, 48, and 72 h after squat protocol. A multivariate profile analysis and repeated-measures correlation between recovery scores [(new/prestimulus) × 100] for each HRV metric and BVM was computed. RESULTS: All log-transformed (ln) HRV metrics, except low frequency (lnLF) (P = 0.051), had a significant interaction with BVM over time (P < 0.05), indicating that recovery scores in BVM and HRV were not parallel. In addition, recovery scores in all HRV metrics significantly differed from BVM (P < 0.05) in at least one time point across the 72-h period. Furthermore, repeated-measures correlation analysis indicated a lack of intraindividual association (P > 0.05) between the change in BVM and all HRV measurements over time. CONCLUSION: The time course in recovery in HRV measurements after an exhaustive bout of lower-body resistance exercise was not associated with neuromuscular performance recovery.

Celiac Disease and Bone Health in Children and Adolescents: A Systematic Review and Meta-Analysis.

CONTEXT: Celiac disease is characterized by deficits in bone mineral accrual and longitudinal growth. OBJECTIVE: The purpose of this study was to determine the differences in bone health and stature among children and adolescents with celiac disease versus healthy controls. DATA SOURCES: Articles published before February 27, 2018 were located using searches of the Physical Education Index (n = 186), PubMed (n = 180), Scopus (n = 3), SPORTDiscus (n = 3), and Web of Science (n = 4). STUDY SELECTION: Bone mineral content (BMC) and areal bone mineral density (aBMD) were assessed via dual-energy X-ray absorptiometry, and height was measured using a stadiometer. DATA EXTRACTION: Effect sizes (ES) were calculated as follows: the mean difference of the celiac disease group and healthy control group, divided by the pooled standard deviation. The inverse variance weight was used to calculate the overall mean ES. Random-effects models were used to aggregate a mean ES, 95% confidence intervals (CIs) and to identify potential moderators. RESULTS: The results of 30 effects gathered from 12 studies published between 1996 and 2017 indicated BMC (ES = -0.54, 95% CI: -0.69 to -0.40; p < 0.0001) and aBMD (ES = 0.72, 95% CI: -0.96 to -0.47; p < 0.0001) were lower in youth with celiac disease. LIMITATIONS: These results were limited to only cross-sectional and baseline data from longitudinal studies reporting BMC and BMD, however did not assess changes in bone health over time. CONCLUSION: Children and adolescents with celiac disease have suboptimal bone health and shorter stature.

Changes in Heart Rate Variability and Fatigue Measures Following Moderate Load Resistance Exercise.

The purpose of this study was to determine the relationship between changes in heart rate variability (HRV), neuromuscular performance, and fatigue biomarkers in response to a resistance exercise bout. The root mean square of successive RR interval differences (RMSSD), neuromuscular performance - isometric handgrip (IHG), countermovement jump (CMJ), mean propulsive velocity (MPV) - metabolic stress (lactate [Lac]) and inflammation (interleukin-6 [IL-6]) were measured in 30 subjects who performed 6×10 back squat (BS), 3×10 bench press (BP), and 3×10 bent-over rows (BR) at 70% of 1-repetition maximum (1RM). The RMSSD, neuromuscular performance, and biomarkers were measured 10 min pre-exercise and 30 min post-exercise (Post30); HRV and Lac were also measured immediately post-exercise (Post0). Pre- versus post-exercise differences were evaluated using paired-samples t-tests. Pearson's correlations were used to determine the association between changes. With the exception of IL-6 (P=0.296) and MPVBP (P=0.678), LnRMSSD, neuromuscular performance, and metabolic stress were different post- compared to pre-exercise. We observed moderate associations between ΔLnRMSSD Post0 and ΔLac Post0 (r = -0.44) and ΔLac Post30 (r = -0.55), respectively. Practitioners should use multiple training load indicators to gain an accurate depiction of recovery.

Age-Based Prediction of Maximal Heart Rate in Children and Adolescents: A Systematic Review and Meta-Analysis.

Purpose: Maximal heart rate (MHR) is an important physiologic tool for prescribing and monitoring exercise in both clinical and athletic settings. However, prediction equations developed in adults may have limited accuracy in youth. The purpose of this study was to systematically review and analyze the available evidence regarding the validity of commonly used age-based MHR prediction equations among children and adolescents. Methods: Included articles were peer-reviewed, published in English, and compared measured to predicted MHR in male and female participants <18 years old. The standardized mean difference effect size (ES) was used to quantify the accuracy of age-predicted MHR values and a priori moderators were examined to identify potential sources of variability. Results: The cumulative results of 20 effects obtained from seven articles revealed that prediction equations did not accurately estimate MHR (ES= 0.44, p < .05) by 6.3 bpm (bpm). Subgroup analyses indicated that the Fox equation (MHR = 220-age) overestimated MHR by 12.4 bpm (ES = 0.95, p < .05), whereas the Tanaka equation (MHR = 208-0.7*age) underestimated MHR by 2.7 bpm (ES = -0.34, p < .05). Conclusions: Age-based MHR equations derived from adult populations are not applicable to children. However, if the use of age-based equations cannot be avoided, we recommend using the Tanaka equation, keeping in mind the range of error reported in this study. Future research should control for potential pubertal influences on sympathetic modulation during exercise to facilitate the development of more age-appropriate methods for prescribing exercise intensity.

The Accuracy of Acquiring Heart Rate Variability from Portable Devices: A Systematic Review and Meta-Analysis.

BACKGROUND: Advancements in wearable technology have provided practitioners and researchers with the ability to conveniently measure various health and/or fitness indices. Specifically, portable devices have been devised for convenient recordings of heart rate variability (HRV). Yet, their accuracies remain questionable. OBJECTIVE: The aim was to quantify the accuracy of portable devices compared to electrocardiography (ECG) for measuring a multitude of HRV metrics and to identify potential moderators of this effect. METHODS: This meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Articles published before July 29, 2017 were located via four electronic databases using a combination of the terms related to HRV and validity. Separate effect sizes (ESs), defined as the absolute standardized difference between the HRV value recorded using the portable device compared to ECG, were generated for each HRV metric (ten metrics analyzed in total). A multivariate, multi-level model, incorporating random-effects assumptions, was utilized to quantify the mean ES and 95% confidence interval (CI) and explore potential moderators. RESULTS: Twenty-three studies yielded 301 effects and revealed that HRV measurements acquired from portable devices differed from those obtained from ECG (ES = 0.23, 95% CI 0.05-0.42), although this effect was small and highly heterogeneous (I2 = 78.6%, 95% CI 76.2-80.7). Moderator analysis revealed that HRV metric (p <0.001), position (p = 0.033), and biological sex (ß = 0.45, 95% CI 0.30-0.61; p <0.001), but not portable device, modulated the degree of absolute error. Within metric, absolute error was significantly higher when expressed as standard deviation of all normal-normal (R-R) intervals (SDNN) (ES = 0.44) compared to any other metric, but was no longer significantly different after a sensitivity analysis removed outliers. Likewise, the error associated with the tilt/recovery position was significantly higher than any other position and remained significantly different without outliers in the model. CONCLUSIONS: Our results suggest that HRV measurements acquired using portable devices demonstrate a small amount of absolute error when compared to ECG. However, this small error is acceptable when considering the improved practicality and compliance of HRV measurements acquired through portable devices in the field setting. Practitioners and researchers should consider the cost-benefit along with the simplicity of the measurement when attempting to increase compliance in acquiring HRV measurements.

Can Exercise Improve Cognitive Symptoms of Alzheimer's Disease?

OBJECTIVES: To examine the effects of exercise training on cognitive function in individuals at risk of or diagnosed with Alzheimer's disease (AD). DESIGN: Meta-analysis. SETTING: PubMed, Scopus, ClinicalTrials.gov, and ProQuest were searched from inception until August 1, 2017. PARTICIPANTS: Nineteen studies with 23 interventions including 1,145 subjects with a mean age of 77.0 ± 7.5 were included. Most subjects were at risk of AD because they had mild cognitive impairment (64%) or a parent diagnosed with AD (1%), and 35% presented with AD. INTERVENTION: Controlled studies that included an exercise-only intervention and a nondiet, nonexercise control group and reported pre- and post-intervention cognitive function measurements. MEASUREMENTS: Cognitive function before and after the intervention and features of the exercise intervention. RESULTS: Exercise interventions were performed 3.4 ± 1.4 days per week at moderate intensity (3.7 ± 0.6 metabolic equivalents) for 45.2 ± 17.0 minutes per session for 18.6 ± 10.0 weeks and consisted primarily of aerobic exercise (65%). Overall, there was a modest favorable effect of exercise on cognitive function (d+  = 0.47, 95% confidence interval (CI) = 0.26-0.68). Within-group analyses revealed that exercise improved cognitive function (d+w  = 0.20, 95% CI  = 0.11-0.28), whereas cognitive function declined in the control group (d+w  = -0.18, 95% CI  = -0.36 to 0.00). Aerobic exercise had a moderate favorable effect on cognitive function (d+w  = 0.65, 95% CI = 0.35-0.95), but other exercise types did not (d+w  = 0.19, 95% CI = -0.06-0.43). CONCLUSION: Our findings suggest that exercise training may delay the decline in cognitive function that occurs in individuals who are at risk of or have AD, with aerobic exercise possibly having the most favorable effect. Additional randomized controlled clinical trials that include objective measurements of cognitive function are needed to confirm our findings.

Small Sample Sizes Confound Understanding of Cardiometabolic Responses to Exercise.

Considerable variability exists in the cardiometabolic disease biomarker response to exercise. We propose that a major contributor to this heterogeneity is underpowered studies due to small sample sizes. To test our hypothesis, we conducted a systematic review to identify meta-analyses/reviews of randomized controlled trials (RCT) and RCT that examined the cardiometabolic disease biomarker response to aerobic and resistance exercise.

The antihypertensive effects of aerobic versus isometric handgrip resistance exercise.

BACKGROUND: Aerobic exercise reduces blood pressure (BP) on average 5-7 mmHg among those with hypertension; limited evidence suggests similar or even greater BP benefits may result from isometric handgrip (IHG) resistance exercise. METHOD: We conducted a randomized controlled trial investigating the antihypertensive effects of an acute bout of aerobic compared with IHG exercise in the same individuals. Middle-aged adults (n = 27) with prehypertension and obesity randomly completed three experiments: aerobic (60% peak oxygen uptake, 30 min); IHG (30% maximum voluntary contraction, 4 × 2 min bilateral); and nonexercise control. Study participants were assessed for carotid-femoral pulse wave velocity pre and post exercise, and left the laboratory wearing an ambulatory BP monitor. RESULTS: SBP and DBP were lower after aerobic versus IHG (4.8 ±â€Š1.8/3.1 ±â€Š1.3 mmHg, P = 0.01/0.04) and control (5.6 ±â€Š1.8/3.6 ±â€Š1.3 mmHg, P = 0.02/0.04) over the awake hours, with no difference between IHG versus control (P = 0.80/0.83). Pulse wave velocity changes following acute exercise did not differ by modality (aerobic increased 0.01 ±â€Š0.21 ms, IHG decreased 0.06 ±â€Š0.15 ms, control increased 0.25 ±â€Š0.17 ms, P > 0.05). A subset of participants then completed either 8 weeks of aerobic or IHG training. Awake SBP was lower after versus before aerobic training (7.6 ±â€Š3.1 mmHg, P = 0.02), whereas sleep DBP was higher after IHG training (7.7 ±â€Š2.3 mmHg, P = 0.02). CONCLUSION: Our findings did not support IHG as antihypertensive therapy but that aerobic exercise should continue to be recommended as the primary exercise modality for its immediate and sustained BP benefits.