Validity of the ithlete™ Smart Phone Application for Determining Ultra-Short-Term Heart Rate Variability

Validity of Ultra-Short-Term Heart Rate Variability Derived from Femoral Arterial Pulse Waveform in a British Military Cohort

Various non-electrocardiogram (ECG) based methods are considered reliable sources of heart rate variability (HRV) measurement. However, the ultra-short recording of a femoral arterial waveform has never been validated against the gold-standard ECG-based 300s HRV and was the aim of this study.A validity study was conducted using a sample from the first follow-up of the longitudinal ADVANCE study UK. The participants were adult servicemen (n = 100); similar in age, rank, and deployment period (Afghanistan 2003-2014). The femoral arterial waveforms (14s) from the pulse wave velocity (PWV) assessment, and ECG (300s) were recorded at rest in the supine position using the Vicorder™ and Bittium Faros™ devices, respectively, in the same session. HRV analysis was performed using Kubios Premium. Resting heart rate (HR) and root mean square of successive differences (RMSSD) were reported. The Bland-Altman %plots were constructed to explore the PWV-ECG agreement in HRV measurement. A further exploratory analysis was conducted across methods and durations.The participants' mean age was 38.0 ± 5.3 years. Both PWV-derived HR (r = 0.85) and RMSSD (rs=0.84) showed strong correlations with their 300s-ECG counterparts (p < 0.001). Mean HR was significantly higher with ECG than PWV (mean bias: -12.71 ± 7.73%, 95%CI: -14.25%, -11.18%). In contrast, the difference in RMSSD between the two methods was non-significant [mean bias: -2.90 ± 37.82% (95%CI: -10.40%, 4.60%)] indicating good agreement. An exploratory analysis of 14s ECG-vs-300s ECG measurement revealed strong agreement in both RMSSD and HR.The 14s PWV-derived RMSSD strongly agrees with the gold-standard (300s-ECG-based) RMSSD at rest. Conversely, HR appears method sensitive.

Reliability of carotid-femoral arterial waveforms for the derivation of ultra-short term heart rate variability in injured British servicemen: An inter-rater reliability study

In this study, the comparative precision of carotid versus femoral arterial waveforms to measure ultra-short term heart rate variability (HRVUST) following traumatic injury was investigated for the first time. This was an inter-rater reliability study of 50 British servicemen (aged 23-44 years) with non-acute combat-related traumatic injury (CRTI). Paired continuous arterial waveform data for HRVUST analysis, were simultaneously sampled at the carotid and femoral arterial sites (14-16 seconds) during pulse wave velocity (PWV) measurement. HRVUST was reported as the root mean square of the successive differences (RMSSD). Following the determination of the superior sampling site (carotid versus femoral), the blinded inter-rater agreement in RMSSD for the preferred site was quantified using the Intra-class Correlation Coefficient (ICC) and the Bland-Altman plot. The mean age of participants was 34.06±4.88 years. The femoral site was superior to the carotid site with a significantly higher number of reliable signals obtained (Fisher's Exact test; p<0.001). The inter-rater agreement in femoral-derived RMSSD was excellent [ICC 0.99 (95%CI: 0.994-0.997)] with a moderate level of agreement (mean difference [bias]: 0.55; 95% CI: -0.13-1.24 ms). In this study, we demonstrated that the femoral artery is a more reliable site than the carotid artery for HRVUST measurement and post-trauma risk stratification following CRTI.

Heart Rate Variability in Individuals with Down Syndrome: A Scoping Review with Methodological Considerations

Individuals with Down syndrome (DS) present similar heart rate variability (HRV) parameters at rest but different responses to selected movement maneuvers in comparison to individuals without DS, which indicates reduced vagal regulation. The present study undertakes a scoping review of research on HRV in individuals with DS, with special attention paid to the compliance of the studies with standards and methodological paper guidelines for HRV assessment and interpretation. A review was performed using PubMed, Web of Science and CINAHL databases to search for English language publications from 1996 to 2020 with the MESH terms "heart rate variability" and "down syndrome", with the additional inclusion criteria of including only human participants and empirical investigations. From 74 studies, 15 were included in the review. None of the reviewed studies met the recommendations laid out by the standards and guidelines for providing the acquisition of RR intervals and necessary details on HRV analysis. Since authors publishing papers on this research topic do not adhere to the prescribed standards and guidelines when constructing the methodology, results of the research papers on the topic are not directly comparable. Authors need to design the study methodology more robustly by following the aforementioned standards, guidelines and recommendations.

Practices and Applications of Heart Rate Variability Monitoring in Endurance Athletes

Heart rate variability reflects fluctuations in the changes in consecutive heartbeats, providing insight into cardiac autonomic function and overall physiological state. Endurance athletes typically demonstrate better cardiac autonomic function than non-athletes, with lower resting heart rates and greater variability. The availability and use of heart rate variability metrics has increased in the broader population and may be particularly useful to endurance athletes. The purpose of this review is to characterize current practices and applications of heart rate variability analysis in endurance athletes. Important considerations for heart rate variability analysis will be discussed, including analysis techniques, monitoring tools, the importance of stationarity of data, body position, timing and duration of the recording window, average heart rate, and sex and age differences. Key factors affecting resting heart rate variability will be discussed, including exercise intensity, duration, modality, overall training load, and lifestyle factors. Training applications will be explored, including heart rate variability-guided training and the identification and monitoring of maladaptive states such as overtraining. Lastly, we will examine some alternative uses of heart rate variability, including during exercise, post-exercise, and for physiological forecasting and predicting performance.

Validity of a Smartphone Application in Calculating Measures of Heart Rate Variability

The purpose of the current study was to determine the concurrent validity of the Elite HRV smartphone application when calculating heart rate variability (HRV) metrics in reference to an independent software criterion. A total of 5 minutes of R−R interval and natural log of root mean square of the successive differences (lnRMSSD) resting HRV data were simultaneously collected using two Polar H10 heart rate monitors (HRMs) in both the seated and supine positions from 22 participants (14 males, 8 females). One H10 HRM was paired with a Polar V800 watch and one with the Elite HRV application. When no artifact correction was applied, significant, but small, differences in the lnRMSSD data were observed between the software in the seated position (p = 0.022), and trivial and nonstatistically significant differences were observed in the supine position (p = 0.087). However, significant differences (p > 0.05) in the lnRMSSD data were no longer identifiable in either the seated or the supine positions when applying Very Low, Low, or Automatic artifact-correction filters. Additionally, excellent agreements (ICC3,1 = 0.938 − 0.998) and very strong to near-perfect (r = 0.889 − 0.997) relationships were observed throughout all correction levels. The Elite HRV smartphone application is a valid tool for calculating resting lnRMSSD HRV metrics.

Acute Effects of a Single-Session of Full-Body Foam Rolling on Heart Rate Variability

Background

Self-myofascial release has been demonstrated to increase relaxation and improve blood flow, yet it is unknown if it can elicit an acute effect on heart rate variability (HRV).

Purpose

This study aimed to determine if a single-bout of foam rolling could increase parasympathetic activity as measured by HRV.

Methods

Twenty (20) participants volunteered and their baseline HRV was assessed using a finger sensor while lying supine, and then a second measure was recorded with them sitting upright with feet on the ground. This study utilized a practical HRV collection method designed for use in the field settings, and the data is recorded in arbitrary units (A.U.). Participants then oscillated on a closed-cell cylindrical foam roller using their body weight on the triceps surae, hamstrings, quadriceps, lumbar spine, and pectoral muscles each for 60 sec. Participants first massaged the right limb and then repeated on the matching muscle group on the left before continuing to the next region. Follow-up HRV measurements were recorded using the same procedures.

Results

Paired samples t tests assessing pre- and post-foam–rolling HRV measures in supine and seated positions revealed no difference between supine measures (p = .05, d = 0.21), nor the seated measures (p = .27, d = 0.17) among all participants. When sexes were analyzed separately, males showed a significant decrease in HRV in supine positions (p = .03, d = 0.33), but females did not (p = .55, d = 0.09).

Conclusions

The single bout of foam rolling on large muscle groups did not increase parasympathetic activity as hypothesized. Males and females responded differently in supine positions, but no difference was present in seated positions across sexes. The task of self-massage may have prevented the anticipated response from the massage. Further research should investigate if passive massage is more effective on HRV response.

Heart Rate Variability-Guided Training for Improving Mortality Predictors in Patients with Coronary Artery Disease

The objective of this research was to investigate whether heart rate variability (HRV)-guided training improves mortality predictors to a greater extent than predefined training in coronary artery disease patients. Twenty-one patients were randomly allocated to the HRV-guided training group (HRV-G) or the predefined training group (PRED-G). They measured their HRV at home daily and trained three times a week for six weeks. Resting heart rate, isolated vagal-related HRV indices (i.e., RMSSD, HF, and SD₁), weekly averaged RMSSD, heart rate recovery, and maximum oxygen uptake were assessed before and after the training period. There was a statistically significant difference (p = 0.034) in the change in weekly averaged RMSSD in favor of the HRV-G, while no differences were found in the remaining analyzed variables (p > 0.050). Regardless of the training prescription method, exercise training decreased resting heart rate (p = 0.001; -4.10 [95% CI = -6.37--1.82] beats per minute (bpm)), and increased heart rate recovery at 2 min (p = 0.010; 4.33 [95% CI = 1.15-7.52] bpm) and maximum oxygen uptake (p < 0.001; 3.04 [95% CI = 1.70-4.37] mL·kg^-1·min^-1). HRV-guided training is superior to predefined training in improving vagal-related HRV when methodological factors are accounted for.

Validity and reliability of different smartphones applications to measure HRV during short and ultra-short measurements in elite athletes

BACKGROUND AND OBJECTIVE

Heart rate variability (HRV) has been proposed as a useful marker that can show the performance adaptation and optimize the training process in elite athletes. The development of wearable technology permits the measurement of this marker through smartphone applications. The purpose of this study is to assess the validity and reliability of short and ultra-short HRV measurements in elite cyclists using different smartphone applications.

METHOD

Twenty-six professional cyclists were measured at rest in supine and in seated positions through the simultaneous use of an electrocardiogram and two different smartphone applications that implement different technologies to measure HRV: Elite HRV (with a chest strap) and Welltory (photoplethysmography). Level of significance was set at p < 0.05.

RESULTS

Compared to an electrocardiogram, Elite HRV and Welltory showed no differences neither in supine nor in seated positions (p > 0.05) and they showed very strong to almost perfect correlation levels (r = 0.77 to 0.94). Furthermore, no differences were found between short (5 min) and ultra-short (1 min) length measurements. Intraclass correlation coefficient showed good to excellent reliability and the standard error of measurement remained lower than 6%.

CONCLUSION

Both smartphone applications can be implemented to monitor HRV using short- and ultra-short length measurements in elite endurance athletes.

Different acquisition systems for heart rate variability analysis may lead to diverse outcomes

Heart rate variability (HRV) is a relevant physiological variable for the estimation of cardiac autonomic function. Although the gold standard for HRV registration is the electrocardiogram (ECG), several applications (APPs) have been increasingly developed. The evaluation carried out by these devices must be compatible with ECG standards. The aim of this study was to compare the data obtained simultaneously with ECG and APP with chest heart rate transmitters. Fifty-six healthy individuals (28 men and 28 women) were evaluated at rest through a short simultaneous HRV measurement with both devices. Data from both acquisition systems were analyzed separately using their own analysis software and exported and analyzed using a validated software. Signal recordings were compatible between the two acquisition systems (Pearson r=0.99; P<0.0001). Although a high correlation was found for the HRV variables obtained in the time domain (Spearman r=0.99; P<0.0001), the correlation decreased in the frequency domain (Pearson r=0.85; P<0.0001) when two software programs were used. Comparison of the averages of spectral analysis parameters also showed differences when HRV data were analyzed separately in each device for low-frequency (LF) and high-frequency (HF) bands. Although the portability of these mobile devices allows for optimal HRV evaluation, the direct analysis obtained from these devices must be carefully evaluated with respect to frequency domain parameters.

Wrist-Based Photoplethysmography Assessment of Heart Rate and Heart Rate Variability: Validation of WHOOP

Heart rate (HR) and HR variability (HRV) infer readiness to perform exercise in athletic populations. Technological advancements have facilitated HR and HRV quantification via photoplethysmography (PPG). This study evaluated the validity of WHOOP’s PPG-derived HR and HRV against electrocardiogram-derived (ECG) measures. HR and HRV were assessed via HR and HRV were assessed via WHOOP 2.0 and ECG over 15 opportunities during October–December 2018. WHOOP-derived pulse-to-pulse (PP) intervals were edited with WHOOP’s proprietary filter, in addition to various filter strengths via Kubios HRV software. HR and HRV (Ln RMSSD) were quantified for each filter strength. Agreement was assessed via bias and limits of agreement (LOA), and contextualised using smallest worthwhile change (SWC) and coefficient of variation (CV). Regardless of filter strength, bias (≤0.39 ± 0.38%) and LOA (≤1.56%) in HR were lower than the CV (10–11%) and SWC (5–5.5%) for this parameter. For Ln RMSSD, bias (1.66 ± 1.80%) and LOA (±5.93%) were lowest for a 200 ms filter and WHOOP’s proprietary filter, which approached or exceeded the CV (3–13%) and SWC (1.5–6.5%) for this parameter. Acceptable agreement was found between WHOOP- and ECG-derived HR. Bias and LOA in Ln RMSSD approached or exceeded the SWC/CV for this variable and should be interpreted against its own level of bias precision.

Is Ultra-Short-Term Heart Rate Variability Valid in Non-static Conditions?

In mobile healthcare, heart rate variability (HRV) is increasingly being used in dynamic patient states. In this situation, shortening of the measurement time is required. This study aimed to validate ultra-short-term HRV in non-static conditions. We conducted electrocardiogram (ECG) measurements at rest, during exercise, and in the post-exercise recovery period in 30 subjects and analyzed ultra-short-term HRV in time and frequency domains by ECG in 10, 30, 60, 120, 180, and 240-s intervals, and compared the values to the 5-min HRV. For statistical analysis, null hypothesis testing, Cohen’s d statistics, Pearson’s correlation coefficient, and Bland-Altman analysis were used, with a statistical significance level of P < 0.05. The feasibility of ultra-short-term HRV and the minimum time required for analysis showed differences in each condition and for each analysis method. If the strict criteria satisfying all the statistical methods were followed, the ultra-short-term HRV could be derived from a from 30 to 240-s length of ECG. However, at least 120 s was required in the post-exercise recovery or exercise conditions, and even ultra-short-term HRV was not measurable in some variables. In contrast, according to the lenient criteria needed to satisfy only one of the statistical criteria, the minimum time required for ultra-short-term HRV analysis was 10–60 s in the resting condition, 10–180 s in the exercise condition, and 10–120 s in the post-exercise recovery condition. In conclusion, the results of this study showed that a longer measurement time was required for ultra-short-term HRV analysis in dynamic conditions. This suggests that the existing ultra-short-term HRV research results derived from the static condition cannot applied to the non-static conditions of daily life and that a criterion specific to the non-static conditions are necessary.

The validity and reliability of ultra-short-term heart rate variability parameters and the influence of physiological covariates

Ultra-short-term (UST) heart rate variability (HRV) metrics have increasingly been proposed as surrogates for short-term HRV metrics. However, the concurrent validity, within-day reliability, and between-day reliability of UST HRV have yet to be comprehensively documented. Thirty-six adults (18 males, age: 26 ± 5 yr, BMI: 24 ± 3 kg/m²) were recruited. Measures of HRV were quantified in a quiet-stance upright orthostatic position via three-lead electrocardiogram (ADInstruments, FE232 BioAmp). All short-term data recordings were 300 s in length and five UST time points (i.e., 30 s, 60 s, 120 s, 180 s, and 240 s) were extracted from the original 300-s recording. Bland-Altman plots with 95% limits of agreement, repeated measures ANOVA and two-tailed paired t tests demarcated differences between UST and short-term recordings. Linear regressions, coefficient of variation, intraclass correlation coefficients, and other tests examined the validity and reliability in both time- and frequency domains. No group differences were noted between all short-term and UST measures, for either time- (all P > 0.202) or frequency-domain metrics (all P > 0.086). A longer recording duration was associated with augmented validity and reliability, which was less impacted by confounding influences from physiological variables (e.g., respiration rate, carbon dioxide end-tidals, and blood pressure). Conclusively, heart rate, time-domain, and relative frequency-domain HRV metrics were acceptable with recordings greater or equal to 60 s, 240 s, and 300 s, respectively. Future studies employing UST HRV metrics should thoroughly understand the methodological requirements to obtain accurate results. Moreover, a conservative approach should be utilized regarding the minimum acceptable recording duration, which ensures valid/reliable HRV estimates are obtained.NEW & NOTEWORTHY A one size fits all methodological approach to quantify HRV metrics appears to be inappropriate, where study design considerations need to be conducted upon a variable-by-variable basis. The present results found 60 s (heart rate), 240 s (time-domain parameters), and 300 s (relative frequency-domain parameters) were required to obtain accurate and reproducible metrics. The lower validity/reliability of the ultra-short-term metrics was attributable to measurement error and/or confounding from extraneous physiological influences (i.e., respiratory and hemodynamic variables).

Evaluating the Clinical Utility of Daily Heart Rate Variability Assessment for Classifying Meaningful Change in Testosterone-to-Cortisol Ratio: A Preliminary Study

The study purpose was to determine the relationship of resting heart rate variability (HRV) and testosterone to cortisol (T:C) ratio, along with the diagnostic ability of HRV to assess changes in T:C ratio during a 9-week high-intensity functional training intervention. Eight recreationally-active men (n = 4, age 24.25 ± 1.75 yrs, height 181.25 ± 3.86 cm, weight 79.68 ± 11.66 kg) and women (n = 4, age 26 ± 3.6 yrs, height 164.25 ± 3.3, weight 73.4 ± 8.42) completed daily HRV measurements (HRVdaily) using photoplethysmography via a commercially-available smartphone application along with weekly saliva samples. Saliva samples were analyzed for concentrations of testosterone (T) and cortisol (C) via enzyme-linked immunosorbent assays. Upon study completion 72 data points were available, due to participant compliance and inadequate saliva sample, 67 matched pairs of HRV and T:C ratio were analyzed. A statistically significant negative relationship (n = 67, r = -.315, p < 0.05) was found between HRVdaily and saliva T:C ratio concentrations within aggregate data. Individual participant relationships showed considerable variability (r = -0.101 - 0.665, p = 0.103 to 0.829 The model which best explained the data resulted in AIC = 130.247 with factors HRVdaily (β = -0.218, 95%CI = -0.391, -0.044, t = -2.46, p < 0.05), Sex (β = 0.450, 95%CI = -0.214, 1.114, t = 1.113, p = 0.242), and Group (β = -0.394, 95%CI = -1.089, 0.302, t = -1.11, p = 0.311). Diagnostically, HRVdaily demonstrates excellent sensitivity (95%), but poor specificity (5%) for detecting meaningful changes in T:C ratio. Assessment of HRVdaily may be a clinically valid proxy measure for monitoring hormonal changes throughout a training intervention.

Eligibility Classification as a Factor in Understanding Student-Athlete Responses to Collegiate Volleyball Competition

The current study examined differences in heart rate variability (HRV) across student-athletes of different eligibility classifications and analyzed differences in HRV when competing at home or away. Fourteen female collegiate volleyball players volunteered for the study. Data collection encompassed an entire collegiate season, with comparisons in HRV made between home and away games, as well as pre-gameday, gameday, and post-gameday recordings for the whole squad. Comparisons were also made between student-athlete eligibility classification, with self-reported measures of sleep quality, fatigue, muscle soreness, stress, and mood recorded at the time of HRV measurement. Freshman athletes reported a significantly (p < 0.05, η² = 0.17) lower HRV (80.3 ± 9.7) compared to sophomore (85.7 ± 7.2), junior (91.2 ± 8.3), and senior (86.5 ± 7.2) athletes, while junior athletes had a significantly higher HRV when compared to sophomore and senior athletes. All athlete classifications reported similar HRV for home and away games, and there was no difference in HRV for any athlete classification group when comparing pre-gameday, gameday, and post-gameday measures. Freshman athletes reported significantly (p < 0.05, η² = 0.23) worse mood states compared to the other eligibility classifications, while self-reported stress was significantly (p < 0.05) worse in junior and senior athletes. Results suggest that monitoring the workload of student-athletes based on their eligibility classification holds merit. Collegiate coaching and support staff should be aware of the academic and competitive demands placed on their student-athletes. In particular, freshman athletes adjusting to the increased demands placed on them as collegiate student-athlete may warrant additional support.

Inter- and Intra-Day Comparisons of Smartphone-Derived Heart Rate Variability across Resistance Training Overload and Taper Microcycles

The purposes of this study were: (1) to determine if smartphone-derived heart rate variability (HRV) could detect changes in training load during an overload microcycle and taper, and (2) to determine the reliability of HRV measured in the morning and measured immediately prior to the testing session. Twelve powerlifters (male = 10, female = 2) completed a 3-week resistance training program consisting of an introduction microcycle, overload microcycle, and taper. Using a validated smartphone application, daily measures of resting, ultra-short natural logarithm of root mean square of successive differences were recorded in the morning (LnRMSSD_M) and immediately before the test session (LnRMSSD_T) following baseline, post-overload, and post-taper testing. LnRMSSD_M decreased from baseline (82.9 ± 13.0) to post-overload (75.0 ± 9.9, p = 0.019), while post-taper LnRMSSD_M (81.9 ± 7.1) was not different from post-overload (p = 0.056) or baseline (p = 0.998). No differences in LnRMSSD_T (p < 0.05) were observed between baseline (78.3 ± 9.0), post-overload (74.4 ± 10.2), and post-taper (78.3 ± 8.0). LnRMSSD_M and LnRMSSD_T were strongly correlated at baseline (ICC = 0.71, p < 0.001) and post-overload (ICC = 0.65, p = 0.010), whereas there was no relationship at post-taper (ICC = 0.44, p = 0.054). Bland–Altman analyses suggest extremely wide limits of agreement (Bias ± 1.96 SD) between LnRMSSD_M and LnRMSSD_T at baseline (4.7 ± 15.2), post-overload (0.5 ± 16.9), and post-taper (3.7 ± 15.3). Smartphone-derived HRV, recorded upon waking, was sensitive to resistance training loads across an overload and taper microcycles in competitive strength athletes, whereas the HRV was taken immediately prior to the testing session was not.

Physiological explicit of delayed psychological stress response induced by extra neural regulation

BACKGROUND AND OBJECTIVE

Acute psychological stress is conducted along a different neural pathway from acute physical stress and causes a conduction delay. This conduction delay reflected on the central nervous system (CNS) as an evaluation process, which allows the human body to make the best response to a stressor based on preceding experiences. However, how this conduction delay reflected on physiological explicit, remains to be studied.

METHODS

In this work, the variation of nine traditional heart rate variability (HRV) features are studied from twenty-six healthy subjects during acute physical (Cold pressor test (CPT)) and psychological (Stroop color word test (SCWT)) stress on separate occasions. Besides, we discussed ultra-short and short-term HRV analysis and their relationship with acute stress.

RESULTS

The experimental results suggest that there was a delayed response of HRV features under acute psychological stress compared with acute physical stress. In addition, during the later stage of stress, four features could differentiate between baseline and acute psychological stress (p < 0.05): SDNN, LFpower, HFpower, LF/HF, but these features do not have significant difference during acute physical stress (p > 0.05).

CONCLUSIONS

Due to the delayed psychological stress response induced by extra neural regulation, a significant change of HRV features was found at the third minute of psychological stress stage. And the variation of these features have linear correlation with time during the remaining three to five minutes stress stage (r = -0.987, 0.996, -0.952, 0.938 for SDNN, LFpower, HFpower, LF/HF).

Tai Chi training for attention deficit hyperactivity disorder: A feasibility trial in college students

OBJECTIVE

Many young adults are affected by attention deficit hyperactivity disorder (ADHD) and often desire non-pharmacological treatment options. Mind-body techniques might serve as complementary therapies to first-line stimulant medications, but studies are limited. Tai Chi is an increasingly popular practice that integrates movement with cognitive skills relevant to ADHD. We performed a feasibility trial of Tai Chi training in undergraduates to inform the design of a fully powered randomized controlled trial (RCT).

METHOD

Undergraduates with ADHD were recruited, screened, enrolled, and assessed at baseline. They were assigned to three parallel seven-week intervention arms, Tai Chi, Active Control (cardio-aerobic fitness), and Inactive Control (no contact), with follow-up assessments. Feasibility of a larger clinical trial was evaluated, especially with respect to enrollment and retention. Additionally, potential clinical outcome measures were examined for practicality and reliability.

RESULTS

21 participants were assessed at baseline and 19 at follow-up (90 % retention). The primary clinical outcome measure, self-reported inattention symptoms (Conners' CAARS-S:L DSM-IV Inattentive Symptoms subscale), exhibited good test-retest reliability in controls (r = 0.87, n = 10) and correlated with reduced mindfulness (FFMQ acting with awareness subscale) at baseline (r = -0.74, n = 20). Class attendance and self-reported daily practice time were variable. Randomization to group classes was hindered by the college students' restricted schedules.

CONCLUSION

The high retention rate and good data quality suggest that an RCT of Tai Chi for ADHD is feasible. Further measures are identified to improve enrollment rates, adherence, and randomization procedures. Future work might extend to other young adult populations and high school students.

A Pilot Study of the Reliability and Agreement of Heart Rate, Respiratory Rate and Short-Term Heart Rate Variability in Elite Modern Pentathlon Athletes

Research on reliability of heart rate variability (HRV) parameters in athletes has received increasing attention. The aims of this study were to examine the inter-day reliability of short-term (5 min) and ultra-short-term (1 min) heart rate (HR), respiratory rate (RespRate) and HRV parameters, agreement between short-term and ultra-short-term parameters, and association between differences in HR, RespRate and HRV parameters in elite modern pentathletes. Electrocardiographic recordings were performed in stable measurement conditions with a week interval between tests. Relative reliability was evaluated by intra-class correlation coefficients, absolute reliability was evaluated by within-subject coefficient of variation, and agreement was evaluated using Bland-Altman (BA) plot with limits of agreement and defined a priori maximum acceptable difference. Short-term HR, RespRate, log transformed (ln) root mean square of successive normal-to-normal interval differences (lnRMSSD), ln high frequency (lnHF) and SD2/SD1 HRV indices and ultra-short-term HR, RespRate and lnRMSSD presented acceptable, satisfactory inter-day reliability. Although there were no significant differences between short-term and ultra-short-term HR, RespRate and lnRMSSD, no parameter showed acceptable differences with BA plots. Differences in time-domain and non-linear HRV parameters were more correlated with differences in HR than with differences in RespRate. Inverse results were observed for frequency-domain parameters. Short-term HR, RespRate, lnRMSSD, lnHF, and SD2/SD1 and ultra-short-term HR, RespRate and lnRMSSD could be used as reliable parameters in endurance athletes. However, practitioners should interpret changes in HRV parameters with regard to concomitant differences in HR and RespRate and caution should be taken before considering 5 min and 1 min parameters as interchangeable.

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: Base_Pre1 (ES = 0.42), Base_Pre2 (0.30), RE_Pre1 (0.26), RE_Pre2 (0.36), and RE_Post (1.14). The correlations ranged from moderate to very large: Base_Pre1 (r = 0.59), Base_Pre2 (r = 0.63), RE_Pre1 (r = 0.63), RE_Pre2 (r = 0.76), and RE_Post (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.

Comparison of Omegawave Device and an Ambulatory ECG for RR Interval Measurement at rest

The aim of this study was to validate the measurements of the beat intervals taken at rest by the Omegawave^® device by comparing them to an ambulatory electrocardiogram system. For this purpose, the electrocardiogram was digitally processed, time-aligned, and scrutinized for its suitable use as gold-standard. Rest measurements were made for 10 minutes on 5 different days to 10 men and 3 women (24.8±5.05 years; 71.82±11.02 kg; 174.35±9.13 cm). RR intervals were simultaneously recorded using the Omegawave device and a Holter electrocardiogram. The processing of Holter electrocardiogram signals included the detrending of baseline noise and a high-pass filtering for emphasizing the QRS complexes and attenuating the T waves. After obtaining the RR intervals from the electrocardiogram, those from the Omegawave device were automatically aligned to them with cross-correlation digital processing techniques and compared to check whether both measurements could be considered superimposable. A Bland-Altman analysis was applied to the 5 measurements made for all subjects. The Omegawave device exhibited very strong agreement with a quality-controlled Holter electrocardiogram. Deviations not exceeding 25 ms could be expected in 95% of the cases, which is within manageable ranges both for clinical practice and for sports.

A validation study of a smartphone application for heart rate variability assessment in asymptomatic adults

BACKGROUND

Assessment of heart rate variability (HRV) is an effective non-invasive tool to obtain data on cardiac autonomic modulation and may be assessed by a range of devices, including mobile applications. Objective: This study aimed to validate a smartphone application by comparing the R-R intervals (RRi) obtained by the app with a classic electrocardiogram (ECG)-derived reference condition Methods: Fifteen asymptomatic adults (24.9±3.4 years) underwent an orthostatic challenge during which RRi were simultaneously recorded by a freeware smartphone application and by an ECG recorder. Pearson correlation coefficients (r) and coefficients of determination (r ²) were calculated to determine the degree of association between the two electronic devices. Two-way repeated measures analysis of variance and Bland-Altman analysis were used to calculate the measurement consistency and agreement, respectively, between the two methods. Effect size was also used to estimate the magnitude of the differences.

RESULTS

The number of RRi from asymptomatic adults recorded by the ECG and by the free smartphone application was similar at rest in supine position (13,149 vs. 13,157; P = 0.432) and during orthostatic challenge (10,666 vs. 10,664 P = 0.532). RRi in milliseconds from both devices presented a near perfect correlation in the supine position (r = 0.999; Confidence Interval [CI] at 95%: 0.999-0.999; P < 0.0001) and during orthostatic challenge (r = 0.988; 95% CI: 0.988-0.989; P < 0.0001). A negative bias of -0.526 milliseconds (95% limits of agreement [LoA] from -4.319 to 3.266 milliseconds) was observed in supine position between ECG and the smartphone application. On the other hand, a positive bias of 0.077 milliseconds (95% LoA from -10.090 to 10.240 milliseconds) during the orthostatic challenge was observed.

CONCLUSIONS

Our results cross-validated a freeware smartphone application with the ECG-derived reference condition for asymptomatic adults at rest in the supine position and during orthostatic challenge.

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.

Validity of a Smartphone Application and Chest Strap for Recording RR Intervals at Rest in Athletes

OBJECTIVE

To evaluate the accuracy of the smartphone application (app) HRV Expert (CardioMood) and a chest strap (H10 Polar) for recording R-R intervals compared with electrocardiogram (ECG).

METHODS

A total of 31 male recreational runners (age 36.1 [6.3] y) volunteered for this study. R-R intervals were recorded simultaneously by the smartphone app and ECG for 5 minutes to analyze heart-rate variability in both the supine and sitting positions. Time-domain indexes (heart rate, mean R-R, SD of RR intervals, count of successive normal R-R intervals differing by more than 50 ms, percentage of successive normal R-R intervals differing by more than 50 ms, and root mean square of successive differences between normal R-R intervals), frequency-domain indexes (low frequency, normalized low frequency, high frequency, normalized high frequency, low-frequency to high-frequency ratio, and very low frequency), and nonlinear indexes (SD of instantaneous beat-to-beat variability and long-term SD of continuous R-R intervals) were compared by unpaired t test, Pearson correlation, simple linear regression, and Bland-Altman plot to evaluate the agreement between the devices.

RESULTS

High similarity with P value varying between .97 and 1.0 in both positions was found. The correlation coefficient of the heart-rate-variability indexes was perfect (r = 1.0; P = .00) for all variables. The constant error, standard error of estimation, and limits of agreement between ECG and the smartphone app were considered small.

CONCLUSION

The smartphone app and chest strap provide excellent ECG compliance for all variables in the time domain, frequency domain, and nonlinear indexes, regardless of the assessed position. Therefore, the smartphone app replaces ECG for any heart-rate-variability analysis in runners.

Exposure to Contact Sports Results in Maintained Performance During Experimental Pain

During pain, motor performance tends to decline. However, athletes who engage in contact sports are able to maintain performance despite the inherent pain that accompanies participation. This may be the result of being challenged rather than threatened by pain; adaptive coping strategies; habituation to pain; or finding pain less bothersome. This study aimed to measure performance of a novel motor task both in pain and not in pain within experienced contact athletes (n = 40), novice contact athletes (n = 40), and noncontact athletes (n = 40). Challenge and threat perceptions were manipulated during the pain condition and measures of pain tolerance, perception, coping styles, and bothersomeness were taken. Results indicated that contact athletes, regardless of experience, were able to maintain their performance during painful stimulation. Noncontact athletes, conversely, performed significantly worse during pain stimulation. In addition, contact athletes tended to be more challenged and the noncontact athletes more threatened within the pain condition. Experienced contact athletes demonstrated higher levels of pain tolerance and direct coping, and reported lower levels of pain bothersomeness and intensity than the other groups. The results suggest that even relatively brief exposure to contact sports may be enough to help maintain performance in pain. Being in a challenged state appears to be an important factor during performance in pain. Moreover, pain tolerance, intensity, and bothersomeness may differentiate novice and experienced athletes. PERSPECTIVE: Exposure to voluntary pain and challenge states are associated with adaptive responses to pain. Motor task performance may be maintained in individuals with more experience of sports-related pain.

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.

FOAM ROLLING AND INDICES OF AUTONOMIC RECOVERY FOLLOWING EXERCISE-INDUCED MUSCLE DAMAGE

BACKGROUND

With the increased popularity of foam rolling as a recovery tool, it is important to explore possible mechanisms of action toward mitigating soreness and restoring athletic performance.

PURPOSE

The purpose of the present experiment was to assess the influence of foam rolling on gross measures of physical performance and indices of autonomic function following exercise-induced muscle damage (EIMD).

METHOD

In a between-group design, 40 participants performed a session of 40x15 meter sprints, inducing muscle damage. Immediately following sprinting and in the four days following, heart rate variability and pulse wave velocity were recorded, in addition to perceived muscle soreness, vertical jump, and agility. Nineteen subjects (mean±sd; age 23.1±5.0 yrs; BMI 25.6±3.3 kg.m-2) foam rolled their quadricep, gluteal, and gastrocnemius areas prior to testing each day, while 21 (mean±sd; age 24.2±3.4 yrs; BMI 26.3±4.0 kg.m-2) served as a control. Mean values from three days of baseline testing were compared to the area under the curve during five days of recovery after the performance of the repeated sprint protocol. The area under the curve was calculated by summing all five values recorded the recovery days, then these data were compared by condition using a two-tailed Mann-Whitney U test (alpha level = 0.05).

RESULTS

Following EIMD, neither heart rate variability, pulse wave velocity, agility, nor vertical jumping performance versus previously measured baseline differed significantly between groups (p>0.05). Perceived muscle soreness was significantly diminished in the foam rolling condition (p<0.05). Mean Day 1 to Day 5 values for perceived muscle soreness in controls were 16.52, 30.24, 24.48, 17.19, and 11.10. Mean Day 1 to Day 5 values in foam rolling subjects were 12.63, 24.63, 21.79, 15.05, and 10.16.

CONCLUSION

Foam rolling may be useful for reducing soreness following damaging exercise, but according to the outcomes measured in the present experiment, the effect does not appear to be mediated by the autonomic nervous system.

LEVEL OF EVIDENCE

2c.

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 (β = 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.

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.

Heart Rate Variability, Neuromuscular and Perceptual Recovery Following Resistance Training

We quantified associations between changes in heart rate variability (HRV), neuromuscular and perceptual recovery following intense resistance training (RT). Adult males (n = 10) with >1 year RT experience performed six sets to failure with 90% of 10 repetition maximum in the squat, bench press, and pull-down. Changes (∆) from pre- to immediately (IP), 24 and 48 h post-RT were calculated for neuromuscular performance markers (counter-movement jump peak power and mean concentric bench press and squat velocity with load corresponding to 1.0 m∙s⁻¹) and perceived recovery and soreness scales. Post-waking natural logarithm of the root-mean square of successive differences (LnRMSSD) in supine and standing positions were recorded pre-RT (5 day baseline), IP and two mornings post-RT. All parameters worsened at IP (p < 0.05). LnRMSSD measures were not different from baseline by 24 h. Neuromuscular markers were not different from pre-RT by 48 h. Perceptual measures remained suppressed at 48 h. No significant associations among ∆ variables were observed (p = 0.052–0.978). These data show varying timeframes of recovery for HRV, neuromuscular and perceptual markers at the group and individual level. Thus, post-RT recovery testing should be specific and the status of one metric should not be used to infer that of another.

Pre-performance Physiological State: Heart Rate Variability as a Predictor of Shooting Performance

Heart rate variability (HRV) is commonly used in sport science for monitoring the physiology of athletes but not as an indicator of physiological state from a psychological perspective. Since HRV is established to be an indicator of emotional responding, it could be an objective means of quantifying an athlete's subjective physiological state before competition. A total of 61 sport shooters participated in this study, of which 21 were novice shooters, 19 were intermediate shooters, and 21 were advanced level shooters. HRV, self-efficacy, and use of mental skills were assessed before they completed a standard shooting performance task of 40 shots, as in a competition qualifying round. The results showed that HRV was significantly positively correlated with self-efficacy and performance and was a significant predictor of shooting performance. In addition, advanced shooters were found to have significantly lower average heart rate before shooting and used more self-talk, relaxation, imagery, and automaticity compared to novice and intermediate shooters. HRV was found to be useful in identifying the physiological state of an athlete before competing, and as such, coaches and athletes can adopt practical strategies to improve the pre-performance physiological state as a means to optimize performance.

Resting Cardiac Vagal Tone is Associated with Long-Term Frustration Level of Mental Workload: Ultra-short Term Recording Reliability

Excessive mental workload represent a critical risk factor for workplace accidents. Heart rate variability (HRV) is a non-invasive low cost electrophysiological autonomic biomarker related to emotional and cognitive regulation. Several studies report that mental overload impairs parasympathetic-mediated HRV indices (e.g. rMSSD). However, the influence of resting state HRV as a predictor of long-term mental workload impairments remains unknown. Thirty participants (22 males; 8 females) had their HRV measured (5-min period) before performing the number search task. After the task, the mental load was accessed by the NASA-TLX questionnaire. A simple linear regression model between HRV and NASA-TLX dimensions showed that resting state rMSSD is associated to physical demand (ND-2, R² = 0.143, p = 0.03) and frustration level (ND-6, R² = 0.175, p = 0.02) dimensions of mental workload. The comparison between 1 and 5-min epochs suggests that regression models remain reliable even using the ultra-short term HRV (< 1 min) recording values (R² values from 0.11 to 0.15 for ND-2 and R² values from 0.16 to 0.19 for ND-6). These results suggest that resting state HRV is associated to long-term effects of mental workload on physical and emotional demands. In addition, the ultra-short term HRV indices remains reliable to assess ND-2 and ND-6 dimensions of mental workload when compared to gold-standard time interval (> 5 min). The resting state cardiac autonomic tone assessment optimizes the physiological approach with a quick, non-invasive and low-cost assessment that can provide insights about mental load adjustments to prevent work-related accidents.

Heart Rate Variability Monitoring During Strength and High-Intensity Interval Training Overload Microcycles

Objective: In two independent study arms, we determine the effects of strength training (ST) and high-intensity interval training (HIIT) overload on cardiac autonomic modulation by measuring heart rate (HR) and vagal heart rate variability (HRV). Methods: In the study, 37 well-trained athletes (ST: 7 female, 12 male; HIIT: 9 female, 9 male) were subjected to orthostatic tests (HR and HRV recordings) each day during a 4-day baseline period, a 6-day overload microcycle, and a 4-day recovery period. Discipline-specific performance was assessed before and 1 and 4 days after training. Results: Following ST overload, supine HR, and vagal HRV (Ln RMSSD) were clearly increased and decreased (small effects), respectively, and the standing recordings remained unchanged. In contrast, HIIT overload resulted in decreased HR and increased Ln RMSSD in the standing position (small effects), whereas supine recordings remained unaltered. During the recovery period, these responses were reversed (ST: small effects, HIIT: trivial to small effects). The correlations between changes in HR, vagal HRV measures, and performance were weak or inconsistent. At the group and individual levels, moderate to strong negative correlations were found between HR and Ln RMSSD when analyzing changes between testing days (ST: supine and standing position, HIIT: standing position) and individual time series, respectively. Use of rolling 2-4-day averages enabled more precise estimation of mean changes with smaller confidence intervals compared to single-day values of HR or Ln RMSSD. However, the use of averaged values displayed unclear effects for evaluating associations between HR, vagal HRV measures, and performance changes, and have the potential to be detrimental for classification of individual short-term responses. Conclusion: Measures of HR and Ln RMSSD during an orthostatic test could reveal different autonomic responses following ST or HIIT which may not be discovered by supine or standing measures alone. However, these autonomic changes were not consistently related to short-term changes in performance and the use of rolling averages may alter these relationships differently on group and individual level.

Use of Mobile Applications to Collect Data in Sport, Health, and Exercise Science: A Narrative Review

Peart, DJ, Balsalobre-Fernández, C, and Shaw, MP. Use of mobile applications to collect data in sport, health, and exercise science: A narrative review. J Strength Cond Res 33(4): 1167-1177, 2019-Mobile devices are ubiquitous in the population, and most have the capacity to download applications (apps). Some apps have been developed to collect physiological, kinanthropometric, and performance data; however, the validity and reliability of such data is often unknown. An appraisal of such apps is warranted, as mobile apps may offer an alternative method of data collection for practitioners and athletes with money, time, and space constraints. This article identifies and critically reviews the commercially available apps that have been tested in the scientific literature, finding evidence to support the measurement of the resting heart through photoplethysmography, heart rate variability, range of motion, barbell velocity, vertical jump, mechanical variables during running, and distances covered during walking, jogging, and running. The specific apps with evidence, along with reported measurement errors are summarized in the review. Although mobile apps may have the potential to collect data in the field, athletes and practitioners should exercise caution when implementing them into practice as not all apps have support from the literature, and the performance of a number of apps have only been tested on 1 device.

Monitoring Training Load, Well-Being, Heart Rate Variability, and Competitive Performance of a Functional-Fitness Female Athlete: A Case Study

The aim of this case study was to quantify the magnitude of internal load, acute/chronic workload ratio (ACWR), well-being perception, and heart rate variability (HRV) following 38 weeks of functional-fitness training in a female elite athlete. The internal load was obtained with session rating perceived exertion (session-RPE) while the ACWR was calculated by dividing the acute workload by the chronic workload (four-week average). Furthermore, HRV measurements were analyzed via a commercially available smartphone (HRV4training) each morning upon waking whilst in a supine position. The magnitude of internal load was: the weekly mean total during the 38 weeks was 2092 ± 861 arbitrary units (AU); during the preparation for the Open 2018 was 1973 ± 711 AU; during the Open 2018 it was 1686 ± 412 AU; and during the preparation for the Regionals was 3174 ± 595 AU. The mean ACWR was 1.1 ± 0.5 and 50% of the weeks were outside of the 'safe zone'. The well-being during the 38 weeks of training was 19.4 ± 2.3 points. There were no correlations between training load variables (weekly training load, monotony, ACWR, and HRV), and recuperation subjective variables (well-being, fatigue, sleep, pain, stress, and mood). This case study showed that the training load can be varied in accordance with preparation for a specific competition and ACWR revealed that 50% of the training weeks were outside of the 'safe zone', however, no injuries were reported by the athlete. The effectiveness and cost of these methods are very practical during real world functional-fitness.

Heart Rate Variability and Training Load Among National Collegiate Athletic Association Division 1 College Football Players Throughout Spring Camp

Flatt, AA, Esco, MR, Allen, JR, Robinson, JB, Earley, RL, Fedewa, MV, Bragg, A, Keith, CM, and Wingo, JE. Heart rate variability and training load among National Collegiate Athletic Association Division 1 college football players throughout spring camp. J Strength Cond Res 32(11): 3127-3134, 2018-The purpose of this study was to determine whether recovery of cardiac-autonomic activity to baseline occurs between consecutive-day training sessions among positional groups of a collegiate football team during Spring camp. A secondary aim was to evaluate relationships between chronic (i.e., 4-week) heart rate variability (HRV) and training load parameters. Baseline HRV (lnRMSSD_BL) was compared with HRV after ∼20 hours of recovery before next-day training (lnRMSSDpost20) among positional groups composed of SKILL (n = 11), MID-SKILL (n = 9), and LINEMEN (n = 5) with a linear mixed model and effect sizes (ES). Pearson and partial correlations were used to quantify relationships between chronic mean and coefficient of variation (CV) of lnRMSSD (lnRMSSD_chronic and lnRMSSDcv, respectively) with the mean and CV of PlayerLoad (PL_chronic and PL_cv, respectively). A position × time interaction was observed for lnRMSSD (p = 0.01). lnRMSSD_BL was higher than lnRMSSDpost20 for LINEMEN (p < 0.01; ES = large), whereas differences for SKILL and MID-SKILL were not statistically different (p > 0.05). Players with greater body mass experienced larger reductions in lnRMSSD (r = -0.62, p < 0.01). Longitudinally, lnRMSSDcv was significantly related to body mass (r = 0.48) and PL_chronic (r = -0.60). After adjusting for body mass, lnRMSSDcv and PL_chronic remained significantly related (r = -0.43). The ∼20-hour recovery time between training sessions on consecutive days may not be adequate for restoration of cardiac-parasympathetic activity to baseline among LINEMEN. Players with a lower chronic training load throughout camp experienced greater fluctuation in lnRMSSD (i.e., lnRMSSDcv) and vice versa. Thus, a capacity for greater chronic workloads may be protective against perturbations in cardiac-autonomic homeostasis among American college football players.

Motor performance during experimental pain: The influence of exposure to contact sports

BACKGROUND

Athletes who play contact sports are regularly exposed to pain, yet manage to perform complex tasks without significant decrement. Limited research has suggested that superior pain tolerance in contact athletes may be important in this context and this may be altered via experience of pain. Other psychological variables such as challenge states, pain bothersomeness and coping style may also influence skill execution during pain.

METHODS

Forty experienced contact athletes (>3 years experience), 40 novice contact athletes (<6 months experience) and 40 non-contact athletes performed a motor task both in pain and without pain. During the pain condition, pressure pain was induced and half of each group were given challenge instructions and the other half threat based instructions. Measures of cognitive appraisal, heart rate variability, pain bothersomeness, tolerance and intensity and coping styles were taken.

RESULTS

Contact athletes, regardless of experience, performed better during pain compared to the non-contact athletes, this relationship was mediated by pain tolerance and physical bothersomeness. During the threat condition, experience of contact sports moderated performance. Contact athletes were challenged by the pain, regardless of the instructions given, had higher direct coping and found pain less psychologically bothersome. Experienced contact athletes had higher pain tolerance and reported pain as less intense than the other groups.

CONCLUSIONS

Athletes who play contact sports may have better coping and adjustment to experimental pain, especially during threatening conditions. Performance during experimental pain is mediated by pain tolerance and physical pain bothersomeness.

SIGNIFICANCE

Athletes with even relatively small amounts of contact sport experience perform better during experimental pain than athletes who play non-contact sports. Experienced contact athletes had higher levels of direct coping and were more challenged and less threatened by pain than non-contact athletes.

A New Algorithm to Reduce and Individualize HRV Recording Time

The aim of the present work was to propose a Smartphone algorithm to analyze, in real time, the evolution of Heart Rate Variability (HRV) in order to individualize and reduce the recording time according to the specificities of each user. During HRV recording, a new RMSSD value is calculated each time a new RR is captured. The recording process stops once an acceptable stability of HRV is reached. This new method was tested on 3 groups of 15 subjects (cardiac patients, sedentary employees and national-level athletes) and compared with the gold standard method (5 min HRV recording time). The RMSSD indices provided by the short method and by the gold standard method (respectively 62.1 ± 43.7 ms vs. 62.7 ± 44.1 ms) showed no significant differences. In addition, a very strong correlation was observed between RMSSD values obtained by the 2 methods (n = 45; R = 0.998; p < 0.001). Routine duration of the new method was significantly shorter with a time-savings of 2 min (178 ± 51 s vs. 300 s; p < 0.05). This new algorithm seems to adapt perfectly to each subject, and it can detect the stability phase for HRV measurements during the recording process. Algorithm provides an adapted and personal routine duration that can evolve each day depending on parameters such as fatigue or stress level that are known to influence HRV. This solution can be easily implemented in a smartphone application and seems particularly suitable for performing daily HRV monitoring in field conditions.

Ultra-short term HRV features as surrogates of short term HRV: a case study on mental stress detection in real life

Background

This paper suggests a method to assess the extent to which ultra-short Heart Rate Variability (HRV) features (less than 5 min) can be considered as valid surrogates of short HRV features (nominally 5 min). Short term HRV analysis has been widely investigated for mental stress assessment, whereas the validity of ultra-short HRV features remains unclear. Therefore, this study proposes a method to explore the extent to which HRV excerpts can be shortened without losing their ability to automatically detect mental stress.

Methods

ECGs were acquired from 42 healthy subjects during a university examination and resting condition. 23 features were extracted from HRV excerpts of different lengths (i.e., 30 s, 1 min, 2 min, 3 min, and 5 min). Significant differences between rest and stress phases were investigated using non-parametric statistical tests at different time-scales. Features extracted from each ultra-short length were compared with the standard short HRV features, assumed as the benchmark, via Spearman’s rank correlation analysis and Bland-Altman plots during rest and stress phases. Using data-driven machine learning approaches, a model aiming to detect mental stress was trained, validated and tested using short HRV features, and assessed on the ultra-short HRV features.

Results

Six out of 23 ultra-short HRV features (MeanNN, StdNN, MeanHR, StdHR, HF, and SD2) displayed consistency across all of the excerpt lengths (i.e., from 5 to 1 min) and 3 out of those 6 ultra-short HRV features (MeanNN, StdHR, and HF) achieved good performance (accuracy above 88%) when employed in a well-dimensioned automatic classifier.

Conclusion

This study concluded that 6 ultra-short HRV features are valid surrogates of short HRV features for mental stress investigation.

Electronic supplementary material

The online version of this article (10.1186/s12911-019-0742-y) contains supplementary material, which is available to authorized users.

Training Prescription Guided by Heart-Rate Variability in Cycling

PURPOSE

Road cycling is a sport with extreme physiological demands. Therefore, there is a need to find new strategies to improve performance. Heart-rate variability (HRV) has been suggested as an effective alternative for prescribing training load against predefined training programs. The purpose of this study was to examine the effect of training prescription based on HRV in road cycling performance.

METHODS

Seventeen well-trained cyclists participated in this study. After an initial evaluation week, cyclists performed 4 baseline weeks of standardized training to establish their resting HRV. Then, cyclists were divided into 2 groups, an HRV-guided group and a traditional periodization group, and they carried out 8 training weeks. Cyclists performed 2 evaluation weeks, after and before a training week. During the evaluation weeks, cyclists performed a graded exercise test to assess maximal oxygen uptake, peak power output, and ventilatory thresholds with their corresponding power output (VT1, VT2, WVT1, and WVT2, respectively) and a 40-min simulated time trial.

RESULTS

The HRV-guided group improved peak power output (5.1% [4.5%]; P = .024), WVT2 (13.9% [8.8%]; P = .004), and 40-min all-out time trial (7.3% [4.5%]; P = .005). Maximal oxygen uptake and WVT1 remained similar. The traditional periodization group did not improve significantly after the training week. There were no differences between groups. However, magnitude-based inference analysis showed likely beneficial and possibly beneficial effects for the HRV-guided group instead of the traditional periodization group in 40-min all-out time trial and peak power output, respectively.

CONCLUSION

Daily training prescription based on HRV could result in a better performance enhancement than a traditional periodization in well-trained cyclists.

Classic electrocardiogram-based and mobile technology derived approaches to heart rate variability are not equivalent

We compared classic ECG-derived versus a mobile approach to heart rate variability (HRV) measurement.

METHODS & RESULTS

29 young adult healthy volunteers underwent a simultaneous recording of heart rate using an ECG and a chest heart rate monitor at supine rest, during mental stress and active standing. Mean RR interval, Standard Deviation of Normal-to-Normal (SDNN) of RR intervals, and Root Mean Square of the Successive Differences (RMSSD) between RR intervals were computed in 168 pairs of 5-minute epochs by in-house software on a PC (only sinus beats) and by mobile application "ELITEHRV" on a smartphone (no beat type identification). ECG analysis showed that 33.9% of the recordings contained at least one non-sinus beat or artefact, the mobile app did not report this. The mean RR intervals were significantly longer (p = 0.0378), while SDNN (p = 0.0001) and RMSSD (p = 0.0199) were smaller for the mobile approach.

CONCLUSIONS

Measures of identical HRV parameters by ECG-based and mobile approaches are not equivalent.

Heart Rate Variability Responses to an Undulating Resistance Training Program in Free-Living Conditions: A Case Study in a Collegiate Athlete

The purpose of this case study was to evaluate the response in heart rate variability via the parasympathetically-mediated metric of the log-transformed root mean square of successive R-R interval differences (lnRMSSD) to weekly variations in total volume-load (TVL) during an 18-week periodized strength training program in a competitive collegiate hockey athlete. The program consisted of three 60–90 min full-body exercise sessions per week with at least 24-h of rest between each session. Daily lnRMSSD measurements were taken immediately after waking using a validated smartphone application and the pulse-wave finger sensor. The weekly lnRMSSD values were calculated as the mean (lnRMSSD_MEAN) and the coefficient of variation (lnRMSSD_CV). A Pearson’s bivariate correlation of lnRMSSD_MEAN and TVL revealed no statistically significant correlation between the two variables; TVL (r = −0.105, p = 0.678). However, significant correlations were found between lnRMSSD_CV and both total load (TL) (r = −0.591, p = 0.013) and total volume (TV) (r = 0.765, p < 0.001). Additionally, weekly ratings of perceived exertion (RPE) mean values were statistically significantly correlated to TVL, r = 0.853, p < 0.001. It was concluded that lnRMSSD_CV increased or decreased proportionally to an increase or decrease in TVL during the periodized resistance training program with TV being the strongest, independent indicator of these changes.

Enhancing cardiac vagal activity: Factors of interest for sport psychology

Self-regulation plays a critical role in sport performance. An objective, psychophysiological marker of self-regulation is cardiac vagal activity, the activity of the vagus nerve regulating cardiac functioning. The aim of this paper is to provide an overview of factors influencing cardiac vagal activity, which can be useful for athletes. Specifically, we organize this overview in two main domains: personal factors and environmental factors. Among the personal factors, we discuss the behavioral strategies that can be used by athletes: nutrition, non-ingestive oral habits, water immersion, body temperature reduction, sleeping habits, relaxation methods, cognitive techniques, praying, music, and exercise. Among environmental factors, we discuss those linked to the social (i.e., contact with humans and animals) and physical (i.e., aromas, lights, sounds, temperature, outdoor, altitude) environment. Future research directions are given, as well as practical implications for athletes and coaches.

Stress Detection Using Low Cost Heart Rate Sensors

The automated detection of stress is a central problem for ambient assisted living solutions. The paper presents the concepts and results of two studies targeted at stress detection with a low cost heart rate sensor, a chest belt. In the device validation study (n = 5), we compared heart rate data and other features from the belt to those measured by a gold standard device to assess the reliability of the sensor. With simple synchronization and data cleaning algorithm, we were able to select highly (>97%) correlated, low average error (2.2%) data segments of considerable length from the chest data for further processing. The protocol for the clinical study (n = 46) included a relax phase followed by a phase with provoked mental stress, 10 minutes each. We developed a simple method for the detection of the stress using only three time-domain features of the heart rate signal. The method produced accuracy of 74.6%, sensitivity of 75.0%, and specificity of 74.2%, which is impressive compared to the performance of two state-of-the-art methods run on the same data. Since the proposed method uses only time-domain features, it can be efficiently implemented on mobile devices.

The effects of warm water immersion on blood pressure, heart rate and heart rate variability in people with chronic fatigue syndrome

BACKGROUND

Chronic fatigue syndrome (CFS) is a central sensitisation syndrome with abnormalities in autonomic regulation of blood pressure (BP), heart rate (HR) and heart rate variability (HRV). Prior to exploring the effects of hydrotherapy as a treatment for this population, changes in BP, HR and HRV during warm water immersion need to be established.

OBJECTIVES

The study aimed to determine the effects of warm water immersion on BP, HR and HRV in adults with CFS compared to matched-pair healthy adults.

METHOD

A quasi-experimental, single-blinded study design was used with nine CFS participants and nine matched controls. Participants' BP, HR and HRV were measured before, after 5 minutes and post warm water immersion at the depth of the fourth intercostal space, using the Ithlete® System and Dräger BP monitor.

RESULTS

There was a significant difference between groups in HRV prior to immersion (control group: 73 [55-74] vs. chronic fatigue syndrome group: 63 [50-70]; p = 0.04). There was no difference in HRV post-immersion. A significant difference in HR after immersion was recorded with the control group having a lower HR than those with CFS (78 [60-86] vs. 86 [65-112]; p = 0.03). The low HRV present in the CFS group prior to immersion suggests autonomic dysregulation. Individuals with CFS may have reduced vagal nerve activation post-immersion. During immersion, HRV of the CFS participants improved similar to that of the healthy controls.

CONCLUSION

Prior to immersion, differences were present in the HRV of the participants with CFS compared to healthy controls. These differences were no longer present post-immersion.

CLINICAL IMPLICATIONS

Warm water immersion appears safe and may be beneficial in the management of individuals with CFS.

Vagal Tank Theory: The Three Rs of Cardiac Vagal Control Functioning - Resting, Reactivity, and Recovery

The aim of this paper is to set the stage for the vagal tank theory, showcasing a functional resource account for self-regulation. The vagal tank theory, building on neurophysiological, cognitive and social psychology approaches, will introduce a physiological indicator for self-regulation that has mainly been ignored from cognitive and social psychology, cardiac vagal control (also referred to as cardiac vagal activity). Cardiac vagal control reflects the contribution of the vagus nerve, the main nerve of the parasympathetic nervous system, to cardiac regulation. We propose cardiac vagal control to be an indicator of how efficiently self-regulatory resources are mobilized and used. Three systematic levels of cardiac vagal control analysis are suggested: resting, reactivity, and recovery. Based on this physiological indicator we derive the metaphor of the vagal tank, which can get depleted and replenished. Overall, the vagal tank theory will enable to integrate previous findings from different disciplines and to stimulate new research questions, predictions, and designs regarding self-regulation.