Adequacy of the Ultra-Short-Term HRV to Assess Adaptive Processes in Youth Female Basketball Players

The relationship between heart rate variability and glucose clearance in healthy men and women

Heart rate variability (HRV) is a non-invasive indicator of the activity of the autonomic nervous system, which regulates many physiological functions including metabolism. The purpose of this study was to quantify the relationship between resting markers of HRV and oral glucose tolerance test (OGTT) response. Eighteen healthy individuals (10 males, 8 females, (23.8±2.9 years) underwent a 10-minute resting HRV recording. The final five minutes were evaluated via Kubios HRV Standard for: root mean square of successive differences (RMSSD), standard deviation of normal-to-normal sinus beats (SDNN), high frequency (HF), and low frequency (LF). A standard 2-hour OGTT was then administered. Glucose was measured via finger stick before, 30-minutes post, 1-hour post, and 2-hours post OGTT. Pearson correlations demonstrated that RMSSD, SDNN, HF and LF were strongly correlated to fasting blood glucose (FBG) for the group (p<0.05) but not for glucose area under the curve (AUC). When analyzed by sex, only males demonstrated significant correlations between AUC and RMSSD, SDNN, and LF (p<0.05). An independent samples t-test revealed no sex differences for FBG, AUC, RMSSD, SDNN, HF and LF. These findings provide new and interesting insights into the relationship of autonomic activity and glucose uptake, highlighting sex-based relationships.

Autonomic Rebound Following Maximal Exercise in Bodybuilders and Recreationally Active Participants

The off-season for natural bodybuilders (BB) is characterized by increased training loads and fluctuations in caloric intake, which may lead to insufficient recovery. The autonomic nervous system (ANS) plays a pivotal role in recovery. The purpose of this study was to evaluate resting ANS activity and recovery following a maximal exercise bout in off-season BB and compare them to those of recreationally active individuals. Fifteen males participated; 7 recreationally active (RA) (24.6 ± 2.1 years, 81.1 ± 10.8 kg) and 8 BB (21.8 ± 2.9 years, 89.3 ± 13.0 kg). Each performed a graded exercise test. Heart rate variability (HRV) was measured at rest and during a 45 min recovery period. HRV was analyzed as: root mean square of successive differences (lnRMSSD), standard deviation of normal-to-normal sinus beats (lnSDNN), high frequency (lnHF), low frequency (lnLF), and the ratio of low frequency to high frequency (lnLF/lnHF). A one-way ANOVA showed no differences for any resting marker of HRV, HR, and HR recovery. A significant depression in all markers of HRV was observed in the BB group at the 15 min point, and no recovery was observed before 45 min when compared to RA. The results of this study demonstrated depressed HRV recovery following the graded exercise test in BB when compared to the RA group.

Pupillometry as a new window to player fatigue? A glimpse inside the eyes of a Euro Cup Women's Basketball team

A rapidly emerging area of interest in high-pressure environments is that of pupillometry, where handheld quantitative infrared pupillometers (HQIPs) are able to track psycho-physiological fatigue in a fast, objective, valid, reliable, and non-invasive manner. However, the application of HQIPs in the context of athlete monitoring is yet to be determined. Therefore, the main aim of this pilot study was to examine the potential usefulness of a HQIP to monitor game-induced fatigue inside a professional female basketball setting by determining its (1) test-retest repeatability, (2) relationship with other biomarkers of game-induced fatigue, and (3) time-course from rested to fatigued states. A non-ophthalmologic practitioner performed a standardized Pupil Light Reflex (PLR) test using a medically graded HQIP among 9 professional female basketball players (2020-2021 Euro Cup) at baseline, 24-h pre-game (GD-1), 24-h post-game (GD+1) and 48-h post-game (GD+2). This was repeated over four subsequent games, equalling a total of 351 observations per eye. Two out of seven pupillometrics displayed good ICCs (0.95-0.99) (MinD and MaxD). Strong significant relationships were found between MaxD, MinD, and all registered biomarkers of game-induced fatigue (r = 0.69-0.82, p < 0.05), as well as between CV, MCV, and cognitive, lower-extremity muscle, and physiological fatigue markers (r = 0.74-0.76, p < 0.05). Three pupillometrics were able to detect a significant difference between rested and fatigued states. In particular, PC (right) (F = 5.173, η2 = 0.115 p = 0.028) and MCV (right) (F = 3.976, η2 = 0.090 p = 0.049) significantly decreased from baseline to GD+2, and LAT (left) (F = 4.023, η2 = 0.109 p = 0.009) significantly increased from GD-1 to GD+2. HQIPs have opened a new window of opportunity for monitoring game-induced fatigue in professional female basketball players. However, future research initiatives across larger and heterogenous samples, and longer investigation periods, are required to expand upon these preliminary findings.

The effectiveness of time domain and nonlinear heart rate variability metrics in ultra-short time series

Ultra short-term (UST) heart rate variability (HRV) has been used to establish normative HRV values. This study aims to investigate whether HRV metrics can capture changes in HRV from external stimuli, and whether these metrics remain effective under various recording length. Participants completed varying stimulating activities including viewing images, arithmetic tasks, and memory recall of viewed images. SDNN, RMSSD, pNN50, SD2, SD1/SD2, and DFA were extracted from the data. Comparing arithmetic calculation and the first minute of memory recall, SDNN, pNN50, SD2, and SD1/SD2 had significant HRV differences; this suggests that these metrics can distinguish the inherently different stimuli participants were exposed to. However, comparing first minute of viewing with that of the second, SDNN, pNN50, and SD2, presented some significant HRV differences during two inherently similar stimuli. Comparing the first 60-120 s during viewing, SDNN, pNN50, and SD2 also presented significant differences. Our results suggest that SDNN, pNN50, and SD2 may not be robust in evaluating UST HRVs in replacement of the standard short-term HRV. It may be beneficial to analyze multiple HRV metrics, particularly SD1/SD2, to achieve a more holistic understanding of the underlying physiology.

Impact of acute moderate-intensity aerobic exercise on circulating extracellular vesicles in pregnant and non-pregnant women

Exercise improves cardiovascular and metabolic health in pregnancy and may represent a non-pharmacological approach to improving pregnancy outcomes. Extracellular vesicles (EVs) are emerging biomarkers of endothelial dysfunction and offer the potential for evaluating vascular health non-invasively during pregnancy. The purpose of this study was to investigate changes in circulating EV levels after an acute bout of moderate-intensity aerobic exercise in healthy pregnant and non-pregnant women. We studied plasma samples from pregnant (N = 13, 13-28 weeks) and non-pregnant (N = 17) women. A pre-exercise blood sample was obtained followed by a 30 min bout of moderate-intensity treadmill-based exercise. Immediately following the exercise, a post-exercise blood draw was collected. Large EVs were isolated from plasma by differential centrifugation and characterized by Western blot and electron microscopy. We quantified circulating EVs by nanoscale flow cytometry. Endothelial EVs were identified as VE-Cadherin+, platelet EVs as CD41+, and leukocyte EVs as CD45+ events. Acute exercise was associated with a significant reduction in levels of circulating endothelial EVs in the non-pregnant group (p = 0.0232) but not in the pregnant group (p = 0.2734). A greater proportion of non-pregnant women (13/17, 76.47%) exhibited a reduction in endothelial EVs compared with their pregnant counterparts (4/13, 30.76%, p < 0.05). We also observed a positive association between measures of fitness (average speed) and baseline levels of platelet (r = 0.5816, p = 0.0159) and total EVs (r = 0.5325, p = 0.0296) in the non-pregnant group but not in pregnant individuals. Collectively, our study highlights that after a matched acute exercise, changes to circulating EV levels differ depending on pregnancy status.

Training, Wellbeing and Recovery Load Monitoring in Female Youth Athletes

Participation in youth sports is ever-increasing, along with training and competition demands placed upon youth athletes. Young athletes may experience high training loads due to playing several sports, as well as participating in school physical education. Therefore, monitoring youth athlete load is an emerging area of research that may help limit non-functional overreaching, injury, or illness and assist with long-term athlete development. This narrative review highlights that multiple measures have been explored to monitor both internal and external load. However, the validity, reliability and practicality of these measures are often not fully understood in female youth populations. The most commonly used external monitoring methods are GPS tracking and TRIMP whereas common internal monitoring tools are questionnaires, perceived exertion rating and heart rate measures. The reporting of injuries and menstrual cycles is also crucial for providing completeness when monitoring an athlete. It has been suggested that the combination of training load, recovery and wellbeing monitoring variables is the optimal way to monitor an athlete's fatigue levels. Whichever monitoring method is applied, in a youth population it is important that the protocol can be individualised, is inexpensive and can be easily implemented and reported so that the monitoring is sustainable.

Ultrashort Versus Criterion Heart Rate Variability Among International-Level Girls' Field Hockey Players

PURPOSE

To assess heart rate (HR) variability responses to various markers of training load, quantify associations between HR variability and fitness, and compare responses and associations between 1-minute ultrashort and 5-minute criterion measures among a girls' field hockey team.

METHODS

A total of 11 players (16.8 [1.1] y) recorded the logarithm of the root mean square of successive differences (LnRMSSD) daily throughout a 4-week training camp. The weekly mean (LnRMSSDM) and coefficient of variation (LnRMSSDCV) were analyzed. The internal training load (ITL) and external training load (ETL) were acquired with session HR and accelerometry, respectively. Speed, agility, repeated sprint ability, and intermittent fitness were assessed precamp and postcamp.

RESULTS

Similar increases in the ultrashort and criterion LnRMSSDM were observed in week 3 versus week 1 (P < .05-.06, effect size [ES] = 0.28 to 0.36). The ultrashort and criterion LnRMSSDCV showed small ES reductions in week 2 (ES = -0.40 to -0.50), moderate reductions in week 3 (ES = -0.61 to -0.72), and small reductions in week 4 (ES = -0.42 to -0.51) versus week 1 (P > .05). Strong agreement was observed between the ultrashort and criterion values (intraclass correlation coefficient = .979). The ITL:ETL ratio peaked in week 1 (P < .05 vs weeks 2-4), displaying a weekly pattern similar to LnRMSSDCV, and inversely similar to LnRMSSDM. Changes in the ultrashort and criterion LnRMSSDCV from week 1 to 4 were associated with ITL (P < .01). The ultrashort and criterion LnRMSSDCV in week 4 were associated (P < .05) with postcamp fitness.

CONCLUSIONS

The ultrashort HR variability parameters paralleled the criterion responses, and the associations with ITL and fitness were similar in magnitude.

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.

Can HRV Biofeedback Improve Short-Term Effort Recovery? Implications for Intermittent Load Sports

As intensity and physical demands continue to rise in sport competition, faster and better recovery becomes essential. The aim of this study was to assess the effects of HRV biofeedback (HRVB) while recovering from a submaximal aerobic exercise. Ten physically-active graduate students participated in the study, which was conducted in four sessions: exercise with free-breathing recovery, first resonance frequency (RF) detection, second RF detection, and exercise applying HRVB during recovery. Measurements included time spent running and recovering, HRV parameters, and recovery/exertion perceptions. The results indicate that using HRVB during recovery improves cardiac variability (RRmean, SDNN, RMSSD and LF; p < 0.01). HRVB also lowers recovery time (p < 0.05) and seems to be improving the perception of recovery (p = 0.087). Moreover, time spent exercising (p < 0.01) and perceived physical exertion (p < 0.05) were higher when applying HRVB. The improvement in the psychophysiological adaptation after intensive aerobic exercise provided by the HRVB is a valuable benefit, not only for competition-driven athletes, but also for the general population.

Suitability of Ultra-Short-Term Heart Rate Variability in Military Trainees

We aimed to (a) evaluate the agreement between ultra-short-term and criterion resting heart rate variability (HRV) measures in military trainees, and (b) compare associations between HRV recording lengths and body composition. HRV recordings were performed for 10 min in 27 military male students. Mean RR interval, the root-mean square of successive differences (RMSSD), RMSSD:RR interval ratio, standard deviation of normal-to-normal RR intervals (SDNN), and SDNN:RR interval ratio were determined from the last 5 min of the 10-min recording and considered the criterion. Parameters were also recorded in successive 1-min epochs from the 5-min stabilization period. No differences were observed between criterion values and any of the 1-min epochs (p > 0.05). Effect sizes ranged from -0.36-0.35. Intra-class correlations ranged from 0.83-0.99. Limits of agreement ranged from 38.3-78.4 ms for RR interval, 18.8-30.0 ms for RMSSD, 1.9-3.1 for RMSSD:RR, 24.1-31.4 ms for SDNN, and 2.5-3.0 for SDNN:RR. Body fat% was associated (p < 0.05) with all HRV parameters at varying time segments. A 1-min HRV recording preceded by a 1-min stabilization period seems to be a suitable alternative to criterion measures. Ultra-short procedures may facilitate routine HRV tracking in tactical populations for status-monitoring purposes.

An examination of single day vs. multi-day heart rate variability and its relationship to heart rate recovery following maximal aerobic exercise in females

The purpose of this study was to examine the relationship of a single day measure of heart rate variability (HRV), and the averaged baseline measures of HRV to heart rate recovery (HRR) following maximal exercise. Thirty females (22.9 ± 3.2 years, 64.8 ± 8.4 kg) completed four visits (V1-V4), where a 10-min HRV was recorded. Upon completing the V4 recording, a treadmill graded exercise test (GXT) was performed, followed by a 5-min active cool down. HRV was assessed through time domain measures [natural log of root mean square of successive R-R differences (lnRMSSD) and standard deviation of normal to normal intervals (lnSDNN)] and natural log frequency domain measures [low frequency (lnLF) and high frequency (lnHF)]. Variables collected over V1-V4 were measured as; day of (DO) GXT, 3 day (AV3), and 4 day average (AV4). HRR was calculated as the maximal HR achieved minus the HR at: 30-s (HRR30), 1-min (HRR1), 2-min (HRR2), 3-min (HRR3), 4-min (HRR4) or 5-min (HRR5) of recovery. Pearson's Product correlations revealed significant correlations (P = < 0.05) between all HRV_DO measures to each HRR measure and are presented in ranges: lnSDNN (r = 0.442-0.522), lnRMSSD (r = 0.458-0.514), lnLF (r = 0.368-0.469), lnHF (r = 0.422-0.493). For HRV_AV3, lnRMSSD_AV3 and HRR1 were positively correlated (r = 0.390, P = 0.033). Last, HRV_AV4 showed positive relationships (P = < 0.05) between lnRMSSD_AV4 and HRR30 (r = 0.365, P = 0.048); and for HRR1 and lnSDNN_AV4 (r = 0.400, P = 0.029), lnRMSSD_AV4 (r = 0.442, P = 0.014), and lnHF_{AV4 (}r = 0.368, P = 0.045); and lnRMSSD_AV4 and HRR3 (r = 0.381, P = 0.038). Within the current study HRV_DO displayed the strongest correlations to HRR therefore, averaged resting HRV measures do not strengthen the prediction of cardiovascular recovery following a GXT in this population.

A Novel Smartphone App for the Measurement of Ultra-Short-Term and Short-Term Heart Rate Variability: Validity and Reliability Study

Background

Smartphone apps for heart rate variability (HRV) measurement have been extensively developed in the last decade. However, ultra–short-term HRV recordings taken by wearable devices have not been examined.

Objective

The aims of this study were the following: (1) to compare the validity and reliability of ultra–short-term and short-term HRV time-domain and frequency-domain variables in a novel smartphone app, Pulse Express Pro (PEP), and (2) to determine the agreement of HRV assessments between an electrocardiogram (ECG) and PEP.

Methods

In total, 60 healthy adults were recruited to participate in this study (mean age 22.3 years [SD 3.0 years], mean height 168.4 cm [SD 8.0 cm], mean body weight 64.2 kg [SD 11.5 kg]). A 5-minute resting HRV measurement was recorded via ECG and PEP in a sitting position. Standard deviation of normal R-R interval (SDNN), root mean square of successive R-R interval (RMSSD), proportion of NN50 divided by the total number of RR intervals (pNN50), normalized very-low–frequency power (nVLF), normalized low-frequency power (nLF), and normalized high-frequency power (nHF) were analyzed within 9 time segments of HRV recordings: 0-1 minute, 1-2 minutes, 2-3 minutes, 3-4 minutes, 4-5 minutes, 0-2 minutes, 0-3 minutes, 0-4 minutes, and 0-5 minutes (standard). Standardized differences (ES), intraclass correlation coefficients (ICC), and the Spearman product-moment correlation were used to compare the validity and reliability of each time segment to the standard measurement (0-5 minutes). Limits of agreement were assessed by using Bland-Altman plot analysis.

Results

Compared to standard measures in both ECG and PEP, pNN50, SDNN, and RMSSD variables showed trivial ES (<0.2) and very large to nearly perfect ICC and Spearman correlation coefficient values in all time segments (>0.8). The nVLF, nLF, and nHF demonstrated a variation of ES (from trivial to small effects, 0.01-0.40), ICC (from moderate to nearly perfect, 0.39-0.96), and Spearman correlation coefficient values (from moderate to nearly perfect, 0.40-0.96). Furthermore, the Bland-Altman plots showed relatively narrow values of mean difference between the ECG and PEP after consecutive 1-minute recordings for SDNN, RMSSD, and pNN50. Acceptable limits of agreement were found after consecutive 3-minute recordings for nLF and nHF.

Conclusions

Using the PEP app to facilitate a 1-minute ultra–short-term recording is suggested for time-domain HRV indices (SDNN, RMSSD, and pNN50) to interpret autonomic functions during stabilization. When using frequency-domain HRV indices (nLF and nHF) via the PEP app, a recording of at least 3 minutes is needed for accurate measurement.

Post-Exercise Recovery of Ultra-Short-Term Heart Rate Variability after Yo-Yo Intermittent Recovery Test and Repeated Sprint Ability Test

This study aimed to examine the agreement and acceptance of ultra-short-term heart rate (HR) variability (HRV_UST) measures during post-exercise recovery in college football players. Twenty-five male college football players (age: 19.80 ± 1.08 years) from the first division of national university championship voluntarily participated in the study. The participants completed both a repeated sprint ability test (RSA) and a Yo-Yo intermittent recovery test level 1 (YYIR1) in a randomized order and separated by 7 days. Electrocardiographic signals (ECG) were recorded in a supine position 10 min before and 30 min after the exercise protocols. The HR and HRV data were analyzed in the time segments of baseline 5~10 min (Baseline), post-exercise 0~5 min (Post 1), post-exercise 5~10 min (Post 2), and post-exercise 25~30 min (Post 3). The natural logarithm of the standard deviation of normal-to-normal intervals (LnSDNN), root mean square of successive normal-to-normal interval differences (LnRMSSD), and LnSDNN:LnRMSSD ratio was compared in the 1st min HRV_UST and 5-min criterion (HRV_criterion) of each time segment. The correlation of time-domain HRV variables to 5-min natural logarithm of low frequency power (LnLF) and high frequency power (LnHF), and LF:HF ratio were calculated. The results showed that the HRV_UST of LnSDNN, LnRMSSD, and LnSDNN:LnRMSSD ratio showed trivial to small effect sizes (ES) (−0.00~0.49), very large and nearly perfect interclass correlation coefficients (ICC) (0.74~0.95), and relatively small values of bias (RSA: 0.01~−0.12; YYIR1: −0.01~−0.16) to the HRV_criterion in both exercise protocols. In addition, the HRV_UST of LnLF, LnHF, and LnLF:LnHF showed trivial to small ES (−0.04~−0.54), small to large ICC (−0.02~0.68), and relatively small values of bias (RSA: −0.02~0.65; YYIR1: 0.03~−0.23) to the HRV_criterion in both exercise protocols. Lastly, the 1-min LnSDNN:LnRMSSD ratio was significantly correlated to the 5-min LnLF:LnHF ratio with moderate~high level (r = 0.43~0.72; p < 0.05) during 30-min post-exercise recovery. The post-exercise 1-min HRV assessment in LnSDNN, LnRMSSD, and LnSDNN:LnRMSSD ratio was acceptable and accurate in the RSA and YYIR1 tests, compared to the 5-min time segment of measurement. The moderate to high correlation coefficient of the HRV_UST LnSDNN:LnRMSSD ratio to the HRV_criterion LnLF:LnHF ratio indicated the capacity to facilitate the post-exercise shortening duration of HRV measurement after maximal anaerobic or aerobic shuttle running. Using ultra-short-term record of LnSDNN:LnRMSSD ratio as a surrogate for standard measure of LnLF:LnHF ratio after short-term bouts of maximal intensity field-based shuttle running is warranted.

Determination of minimal recording period to assess resting heart rate variability during pregnancy

Traditionally, resting heart rate variability (rHRV) is measured for 10 min using the last 5 min for analyses (e.g., criterion period). It is unknown whether the measurement period can be shortened in pregnant women as there are currently no established standards. We aimed to compare shorter time segments (e.g., from the 1st to 10th minutes) of the parasympathetic index natural logarithm transformation of root mean square of successive R–R differences (Ln rMSSD) with the criterion period in pregnant and nonpregnant women. Twelve pregnant (age: 30.8 ± 3.4 years; gestational age: 20.1 ± 5.0 weeks) and 15 nonpregnant women (age: 29.8 ± 4.0 years) were included. rHRV was measured using a portable heart rate monitor for 10 min while sitting. Ln rMSSD difference/agreement between shorter time segments and criterion period was analyzed. The result observed between the 4th–5th minutes was the shortest time segment not different from/highly agreed with the criterion period in pregnant women (difference [95% confidence interval (CI)]: −0.10 [−0.22 to 0.02]/bias ± 1.96 × SD: −0.06 [−0.38 to 0.25]). In nonpregnant women, the 2nd–3rd-minute segment was the shortest with similar results (difference [95% CI]: −0.04 [−0.15 to 0.07]/bias ± 1.96 × SD: −0.03 [−0.39 to 0.32]). The Ln rMSSD was found to be stable from the 5th–10th minutes and the 3rd–10th minutes in pregnant and nonpregnant women, respectively. A shortened rHRV assessment can increase its applicability in clinical/exercise-training settings.

Novelty Ln rMSSD can be measured for 5 min in pregnant women, with the last 1-min segment analyzed. The last 1-min segment from 3 min can be used for rHRV measurement in nonpregnant women. The shortened rHRV assessment can facilitate its applicability in clinical/exercise-training settings.

Ultra-short-term and Short-term Heart Rate Variability Recording during Training Camps and an International Tournament in U-20 National Futsal Players

The aim of this study was to examine ultra-short-term and short-term heart rate variability (HRV) in under-20 (U-20) national futsal players during pre-tournament training camps and an official tournament. Fourteen male U-20 national futsal players (age = 18.07 ± 0.73 yrs; height = 169.57 ± 8.40 cm; body weight = 64.51 ± 12.19 kg; body fat = 12.42% ± 3.18%) were recruited to participate in this study. Early morning 10 min resting HRV, Borg CR-10 scale session rating of perceived exertion (sRPE), and general wellness questionnaire were used to evaluate autonomic function, training load, and recovery status, respectively. Log-transformed root mean square of successive normal-to-normal interval differences (LnRMSSD) was used to compare the first 30 s, first 1 min, first 2 min, first 3 min, and first 4 min with standard 5 min LnRMSSD. Mean (LnRMSSD_mean) and coefficient of variation (LnRMSSD_cv) of LnRMSSD were used to compare the different time segments of HRV analysis. The result of LnRMSSD_mean showed nearly perfect reliability and relatively small bias in all comparisons. In contrast, LnRMSSD_cv showed nearly perfect reliability and relatively small bias from 2-4 min time segments in all study periods. In conclusion, for accuracy of HRV measures, 30 s or 1 min ultra-short-term record of LnRMSSD_mean and short-term record of LnRMSSD_cv of at least 2 min during the training camps are recommended in U-20 national futsal players.

Relationship Between Resting Heart Rate Variability and Intermittent Endurance Performance in Novice Soccer Players

Purpose: This study examined the relationships between the Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1) and resting heart rate variability (HRV) and submaximal 5'-5' test derived measures in novice male soccer players. Methods: Forty players (11.54 ± 0.58 years) from a soccer academy participated in this study, performing physical tests on two different days, separated by 48 h, as follows: (day 1) resting HRV and Yo-Yo IR1 test, and (day 2) anthropometric assessments (for peak height velocity assessment [PHV]) and the 5'-5' test. The Pearson product-moment correlation coefficient was used to determine the correlations between Yo-Yo IR1 performance and the remaining variables. A partial correlation analysis was further performed using age, stature, body mass, distance to PHV, and age at PHV as "confounders." Results: The highest correlation score was observed between Yo-Yo IR1 performance and resting HRV, when the absolute age was used as confounder (r = 0.72; p < .05). Conclusions: We observed that a practical measure of parasympathetic activity at rest is largely associated with performance obtained during a traditional intermittent endurance performance test.

Pre-Anticipatory Anxiety and Autonomic Nervous System Response to Two Unique Fitness Competition Workouts

To evaluate the feasibility of on-site collection of subjective anxiety, autonomic nervous system activity, and salivary catecholamines surrounding high-intensity functional training (HIFT) competition, ten experienced HIFT competitors completed baseline assessments of anxiety and heart rate variability (HRV). Then, in two consecutive weeks (Workout 1 and 2) within the competition, HRV was recorded and examined in 5-min segments prior to exercise (PRE) and across a 30-min period after competitors completed their choice of the prescribed or scaled each workout. Subjective anxiety ratings and saliva samples were collected at PRE and immediately-(IP), 30-min (30P), and 60-min post-exercise (60P). Saliva samples were analyzed for concentrations of epinephrine and norepinephrine. Generalized linear mixed models with repeated measures revealed significant (p < 0.05) differences between workouts for all measures. Compared to Workout 1, anxiety (~50%), epinephrine (173-340%), norepinephrine (29-234%) were greater in Workout 2 and various HRV-derived indices were more depressed. Additionally, some HRV-derived indices appeared to be modulated (p < 0.05) by competitive level and sex at PRE and throughout the 30-min recovery period. These data suggest that autonomic activity may differ between the competitive and laboratory settings, and that the response may be further modulated by the workout's design, the athlete's sex, and competitive level.

The influence of citrus aurantium and caffeine complex versus placebo on the cardiac autonomic response: a double blind crossover design

Background

The purpose of this study was to examine the resting cardiac autonomic nervous system’s response to the ingestion of a complex containing Citrus aurantium + Caffeine (CA + C) and its influence on recovery following a high-intensity anaerobic exercise bout in habitual caffeine users.

Methods

Ten physically active males (25.1 ± 3.9 years; weight 78.71 ± 9.53 kg; height 177.2 ± 4.6 cm; body fat 15.5 ± 3.13%) participated in this study, which consisted of two exhaustive exercise protocols in a randomized crossover design. On each visit the participants consumed either a CA + C (100 mg of CA and 100 mg of C) or placebo (dextrose) capsule. After consumption, participants were monitored throughout a 45-min ingestion period, then completed a repeated Wingate protocol, and were then monitored throughout a 45-min recovery period. Cardiac autonomic function (Heart Rate (HR) and Heart Rate Variability (HRV)) and plasma epinephrine (E) and norepinephrine (NE) were taken at four different time points; Ingestion period: baseline (I1), post-ingestion period (I2); Recovery period: immediately post-exercise (R1), post-recovery period (R2). Heart rate variability was assessed in 5-min increments.

Results

A repeated measures ANOVA revealed significant time-dependent increases in HR, sympathetic related markers of HRV, and plasma E and NE at I2 only in the CA + C trial (p < 0.05); however, no meaningful changes in parasympathetic markers of HRV were observed. Participants recovered in a similar time-dependent manner in all markers of HRV and catecholamines following the PLA and CA + C trials.

Conclusion

The consumption of CA + C results in an increase of sympathetic activity during resting conditions without influencing parasympathetic activity. CA + C provides no influence over cardiac autonomic recovery.

Autonomic response to a short and long bout of high-intensity functional training

The evaluation of Autonomic Nervous System (ANS) recovery following exercise provides insight into the transient stress placed on the cardiovascular system. High-Intensity Functional Training (HIFT) is a form of intense exercise that is prescribed in various modalities and durations; however, little is known about the influence of HIFT duration on ANS recovery. Ten apparently healthy males (28.1 ± 5.4 yrs) performed two HIFT sessions (<5-minute and 15-minute) in a crossover fashion. ANS activity was measured using plasma Epinephrine (E) and Norepineprine (NE); Heart Rate Variability markers of the log transformed Root Mean Square of Successive Differences (lnRMSSD) and High-Frequency power (lnHF). No trial dependent differences were observed in lnRMSSD (p = 0.822), lnHF (p = 0.886), E (p = 0.078), or NE (p = 0.194). A significant main time effect was observed in both trials with a depression in lnRMSSD and lnHF following the trials (p < 0.05) and recovering by 2-hours post (p = 0.141, p > 0.999) respectively. A trial dependent increase in E and NE occurred immediately post (p < 0.05) and recovered by 1-hour post (p > 0.999, p > 0.999) respectively. The HIFT bouts examined within this study demonstrated similar transient strain of the ANS.

Cycling before and after Exhaustion Differently Affects Cardiac Autonomic Control during Heart Rate Matched Exercise

During cycling before (PRE) and after exhaustion (POST) different modes of autonomic cardiac control might occur due to different interoceptive input and altered influences from higher brain centers. We hypothesized that heart rate variability (HRV) is significantly affected by an interaction of the experimental period (PRE vs. POST) and exercise intensity (HIGH vs. LOW; HIGH = HR > HR at the lactate threshold (HR_LT), LOW = HR ≤ HR_LT) despite identical average HR.

Methods: Fifty healthy volunteers completed an incremental cycling test until exhaustion. Workload started with 30 W at a constant pedaling rate (60 revolutions · min⁻¹) and was gradually increased by 30 W · 5 min⁻¹. Five adjacent 60 s inter-beat (R-R) interval segments from the immediate recovery period (POST 1–5 at 30 W and 60 rpm) were each matched with their HR-corresponding 60 s-segments during the cycle test (PRE 1–5). An analysis of covariance was carried out with one repeated-measures factor (PRE vs. POST exhaustion), one between-subject factor (HIGH vs. LOW intensity) and respiration rate as covariate to test for significant effects (p < 0.050) on the natural log-transformed root mean square of successive differences between adjacent R-R intervals (lnRMSSD_60s).

Results: LnRMSSD_60s was significantly affected by the interaction of experimental period × intensity [F_{(1, 242)} = 30.233, p < 0.001, η_p² = 0.111]. LnRMSSD_60s was higher during PRE compared to POST at LOW intensity (1.6 ± 0.6 vs. 1.4 ± 0.6 ms; p < 0.001). In contrast, at HIGH intensity lnRMSSD_60s was lower during PRE compared to POST (1.0 ± 0.4 vs. 1.2 ± 0.4 ms; p < 0.001).

Conclusion: Identical net HR during cycling can result from distinct autonomic modulation patterns. Results suggest a pronounced sympathetic-parasympathetic coactivation immediately after the cessation of peak workload compared to HR-matched cycling before exhaustion at HIGH intensity. On the opposite, at LOW intensity cycling, a stronger coactivational cardiac autonomic modulation pattern occurs during PRE-exhaustion if compared to POST-exhaustion cycling. The different autonomic modes during these phases might be the result of different afferent and/or central inputs to the cardiovascular control centers in the brainstem.

Venipuncture procedure affects heart rate variability and chronotropic response

BACKGROUND

Heart rate variability (HRV) has been shown to be influenced by several factors such as noise, sleep status, light, and emotional arousal; however, little evidence is available concerning autonomic responses to a venipuncture. The purpose of this study was to investigate changes of HRV indexes and heart rate (HR) during and following a venipuncture procedure among healthy individuals.

METHODS

33 healthy individuals (22.8 ± 0.56 years, 167 ± 1.56 cm, 69.5 ± 2.61 kg) participated. Testing included 10-minute HRV analysis prior to the venipuncture, a 1-minute venipuncture procedure followed by a 10-minute analysis of HRV, and a total recording of 21 minutes. The first 5 minutes of the 21-minute recordings were discarded, and the remaining 5 minutes of the resting segment was analyzed (PRE), and the last 5 minutes of the 21-minute recording (POST). The log transformation of the time domain root mean squared of successive differences (lnRMSSD) and the frequency domains of high frequency (lnHF) and low frequency (lnLF) and LF/HF ratio (lnLF/HF) were used to quantify autonomic activity. HR was measured in 1-minute segments at 2 minutes prior (PRE), venipuncture (STICK), and post (P1-5).

RESULTS

HR significantly increased at STICK (P = 0.002), and fell below resting at P-5 (P < 0.001). lnRMSSD and lnHF increased significantly by POST (P < 0.001, P = 0.005). lnLF/HF ratio significantly decreased at POST (P = 0.047), while no significant changes occurred for lnLF (P = 0.590).

CONCLUSIONS

HRV and HR are influenced for 10 minutes following the venipuncture procedure. Practitioners and researchers who are interested in collecting blood and measuring HRV need to account for the influence of the venipuncture.