Effects of load and type of physical training on resting and postexercise cardiac autonomic control

The effects of acute exercise and a nap on heart rate variability and memory in young sedentary adults

Recent evidence suggests that the autonomic nervous system can contribute to memory consolidation during sleep. Whether fluctuations in cardiac autonomic activity during sleep following physical exercise contribute to the process of memory consolidation has not been studied. We assessed the effects of a non-rapid eye movement (NREM) nap following acute exercise on cardiac autonomic regulation assessed with heart rate variability (HRV) to examine if HRV influences memory processes. Fifty-six (59% female) healthy young adults (23.14 ± 3.74 years) were randomly allocated to either the exercise plus nap (ExNap, n = 27) or nap alone (NoExNap, n = 29) groups. The ExNap group performed a 40-minute moderate-intensity cycling, while the NoExNap group was sedentary prior to learning 45 neutral pictures for a later test. Subsequently, participants underwent a 60-minute NREM nap while measuring EKG, followed by a visual recognition test. Our results indicated that heart rate did not significantly differ between the groups (p = .243), whereas vagally mediated HRV indices were lower in the ExNap group compared to the NoExNap group (p < .05). There were no significant differences in sleep variables between the groups (p > .05). Recognition accuracy was significantly higher in the ExNap group than in the NoExNap group (p = .027). In addition, the recognition accuracy of the ExNap group was negatively associated with vagally mediated HRV (p < .05). Pre-nap acute exercise appears to attenuate parasympathetic activity and to alter the relationship between memory and cardiac autonomic activity.

Validation of a smart shirt for heart rate variability measurements at rest and during exercise

Heart rate variability (HRV) monitoring is a promising option to estimate the autonomic nervous system regulation responding to exercise. Textiles with embedded sensors recording heartbeat intervals are a simple tool for data collection. So-called smart shirts offer comfort for a daily use and are managed easily. Their measurement accuracy for HRV calculation at rest is promising but remains questionable during exercise. Therefore, the present study validated the Ambiotex smart shirt using HRV indices (RMSSD, rel. HF power and rel. LF power) during exercise. Eighty-three healthy participants (31 ± 6 years; 39 females, 44 males) completed an incremental exercise test on a bicycle ergometer wearing the smart shirt and an electrocardiogram simultaneously. We compared HRV indices of segments at rest (5 min), at warm-up (3 min) and twice at the exercise test (each 5 min). At rest and at warm-up, we observed excellent linear relationship (r > 0.96; R² > 0.94), excellent relative reliability (ICC ≥ 0.98; α ≥ 0.98) and acceptable agreement (bias < 10%). During the exercise test, measurement accuracy declined with increasing intensity but remained high (> 0.8), although results for partial HRV indices were insufficient. In addition, percentage bias was unacceptable during exercise test. However, the findings support the validity of the smart shirt for measuring HRV especially at rest and at warm-up. We suggest using the smart shirt for monitoring HRV indices on a daily basis but caution should be taken in the interpretation of HRV indices obtained during moderate to vigorous exercise intensities. This article is protected by copyright. All rights reserved.

Individual Adaptation in Cross-Country Skiing Based on Tracking during Training Conditions

Research on heart rate (HR), mean arterial pressure (MAP) and blood pressure (BP) during specific training stages is less common in endurance athletes, whereas resting BP and HR are less studied in relationship to HR_max. In the current study, the objective was to conduct a medium-term HR, BP and MAP analysis while tracking individual training outcomes. The study was conducted during the 2017–2018 season, over 43 days and 1033 km of training volume, on 12 competitive male cross-country ski athletes. One VO_2max test was performed 10 days before the start of the training program. After the test, training volume and intensity was preset for each subject, according to the general training methodology. Early morning HR, MAP and BP measurements were taken as part of the basic functional analysis. Training volume was correlated to both distance (p = 0.01, r = 0.85, CI95% = 0.80 to 0.88) and training HR%, namely the percentage of HR_max (p = 0.01, r = −0.47, CI95% = −0.58 to −0.34). Both the supine (sHR) and orthostatic HR (oHR) values were significantly correlated with the training intensity. We obtained a significant correlation between sHR and oHR values and the training objective (p = 0.01). An increased oHR was correlated to high intensity training activity (HIT) during the second training session (p = 0.01). Heart rate and blood pressure measurements represent predictive functional adaptation parameters over different training phases. We highlight a link between sHR, oHR, MAP data, and the athletes’ ability to perform in lower effort zones during physical exertion. However, we failed to validate MAP as a cardiovascular stress indicator following high intensity training.

Involvement of Cardiorespiratory Capacity on the Acute Effects of Caffeine on Autonomic Recovery

Background and objectives: As a result of ergogenic properties, caffeine has been increasingly taken prior to physical exercise, yet its effects on post-exercise recovery, considering the differences in the cardiorespiratory capacity of the individuals, has not yet been studied or fully elucidated. Optimizing the post-exercise recovery can convey advantages to physical activity practitioners. We evaluated the acute effects of caffeine on heart rate (HR) autonomic control recovery following moderate aerobic exercise in males with different cardiorespiratory capacities. Materials and Methods: We split young adult men into two groups based on their various oxygen consumption peaks (VO₂ peak): (1) Higher VO₂ (HO): Sixteen volunteers, peak VO₂ > 42.46 mL/kg/min and (2) Low VO₂ (LO): Sixteen individuals, VO₂ < 42.46 mL/kg/min). The volunteers were submitted to placebo and caffeine protocols, which entailed 300 mg of caffeine or placebo (starch) in capsules, followed by 15 min of rest, 30 min of moderate exercise on a treadmill at 60% of the VO₂ peak, followed by 60 min of supine recovery. Heart rate variability (HRV) indexes in the time and frequency domains were examined. Results: Effect of time for RMSSD (square root of the average of the square of the differences between normal adjacent RR intervals) and SDNN (standard deviation of all normal RR intervals recorded in a time interval) was achieved (p < 0.001). Significant adjustments were observed (rest versus recovery) at the 0 to 5th min of recovery from exercise for the LO during the placebo protocol and at the 5th at 10th min of recovery for the caffeine protocol. For the HO in both procedures we found significant alterations only at the 0 to 5th min of recovery. Conclusion: Caffeine delayed parasympathetic recovery from exercise in individuals with lower cardiorespiratory capacity.

Chronotropic Incompetence and Reduced Heart Rate Recovery in Rheumatoid Arthritis

BACKGROUND/OBJECTIVE

Recent studies have indicated that cardiac autonomic dysfunction is an early sign of cardiovascular impairment in rheumatoid arthritis (RA). Previous studies have mainly focused on resting assessments; however, analysis of heart rate (HR) responses to exercise might provide additional information on cardiac autonomic dysfunction in this disease. Thus, we aimed to assess the HR responses during and after a maximal graded exercise test in patients with RA and healthy controls (CONs).

METHODS

This was a cross-sectional study in which 27 female RA patients and 14 female CONs frequency matched by physical activity, age, and body mass index were compared for HR responses during and after a maximal graded exercise test.

RESULTS

Rheumatoid arthritis patients showed reduced chronotropic response (94.3% ± 16.3% vs. 106.1% ± 10.3%, p = 0.02) and lower HR recovery (HRR) at 30 seconds (8.6 ± 6.7 vs. 13.4 ± 5.2 beats/min [bpm], p = 0.02), 60 seconds (16.5 ± 7.8 vs. 24.0 ± 9.9 bpm, p = 0.01), 120 seconds (32.6 ± 9.9 vs. 40.7 ± 12.3 bpm, p = 0.03), and 180 seconds (46.5 ± 12.6 vs. 55.5 ± 13.4 bpm, p = 0.05) post-maximal exercise test when compared with CONs. Moreover, the prevalence of chronotropic incompetence (i.e., failure to reach 80% of the HR-predicted response) and abnormal HRR (i.e., HRR ≤12 bpm) were, respectively, 22.2% and 37.1% in RA patients.

CONCLUSIONS

Patients with RA showed reduced chronotropic response to exercise and slower postexercise HRR. These abnormal autonomic responses to exercise indicate the presence of cardiac autonomic dysfunction and increased cardiovascular risk in this population.

Heart rate recovery fast-to-slow phase transition: Influence of physical fitness and exercise intensity

BACKGROUND

Postexercise heart rate (HR) recovery presents an exponential decay, with two distinct phases: a fast phase, characterized by abrupt decay of HR, and determined by parasympathetic reactivation; and a slow phase, characterized by gradual decay of HR, and predominantly determined by sympathetic withdrawal. Although several methods have been proposed to assess postexercise HR recovery, none of those methods selectively assesses the time of transition from the fast to the slow phase of the HR recovery curve (HRR_PT ), and the magnitude of decay prior to (HRR_FP ) and after this point (HRR_SP ). Therefore, the aim of the present study was to propose a method to identify HRR_PT , HRR_FP , and HRR_SP and to verify the effects of exercise intensity and physical fitness on such parameters.

METHODS

Ten healthy young participants (24 ± 3 years; 23.6 ± 1.7 kg/m² ) randomly underwent two exercise sessions (30 min of cycling), at moderate (MI) and high intensity (HI); followed by 5 min of inactive recovery. HR was continuously recorded during the sessions. The algorithm for HRR_PT analysis was written in Python and is freely available online.

RESULTS

HRR_PT and HRR_SP were increased in HI session compared with MI (81 ± 24 vs. 60 ± 20 s; 8 ± 10 vs. 1 ± 5 bpm; p = .04), and there was no difference in HRR_FP between sessions (49 ± 15 vs. 46 ± 10 bpm; p = .17). In addition, HRR_PT for MI exercise session was significantly and negatively associated with VO_2max (r = -0.85, p < .05).

CONCLUSION

The method herein presented was sensitive to exercise intensity, and partially responsive to aerobic fitness. Next studies should perform the pharmacological and clinical validations of the method.

Different times of day do not change heart rate variability recovery after light exercise in sedentary subjects: 24 hours Holter monitoring

Incidence of cardiovascular events follows a circadian rhythm with peak occurrence during morning. Disturbance of autonomic control caused by exercise had raised the question of the safety in morning exercise and its recovery. Furthermore, we sought to investigate whether light aerobic exercise performed at night would increase HR and decrease HRV during sleep. Therefore, the aim of this study was to test the hypothesis that morning exercise would delay HR and HRV recovery after light aerobic exercise, additionally, we tested the impact of late night light aerobic exercise on HR and HRV during sleep in sedentary subjects. Nine sedentary healthy men (age 24 ± 3 yr; height 180 ± 5 cm; weight 79 ± 8 kg; fat 12 ± 3%; mean±SD) performed 35 min of cycling exercise, at an intensity of first anaerobic threshold, at three times of day (7 a.m., 2 p.m. and 11 p.m.). R-R intervals were recorded during exercise and during short-time (60 min) and long-time recovery (24 hours) after cycling exercise. Exercise evoked increase in HR and decrease in HRV, and different times of day did not change the magnitude (p < 0.05 for time). Morning exercise did not delay exercise recovery, HR was similar to rest after 15 minutes recovery and HRV was similar to rest after 30 minutes recovery at morning, afternoon, and night. Low frequency power (LF) in normalized unites (n.u.) decreased during recovery when compared to exercise, but was still above resting values after 60 minutes of recovery. High frequency power (HF-n.u.) increased after exercise cessation (p < 0.05 for time) and was still below resting values after 60 minutes of recovery. The LF/HF ratio decreased after exercise cessation (p < 0.05 for time), but was still different to baseline levels after 60 minutes of recovery. In conclusion, morning exercise did not delay HR and HRV recovery after light aerobic cycling exercise in sedentary subjects. Additionally, exercise performed in the night did change autonomic control during the sleep. So, it seems that sedentary subjects can engage physical activity at any time of day without higher risk.

The short-term impact of the catheter ablation on noninvasive autonomic nervous system parameters in patients with paroxysmal atrial fibrillation

BACKGROUND

The autonomic nervous system (ANS) is a potentially potent modulator of the initiation and perpetuation of atrial fibrillation (AF), whereas the presence of AF can activate and alter the ANS. The catheter ablation of AF (AFCA) may cause the cardiac ANS dysfunction, whereas restoration of sinus rhythm or sympathovagal imbalance by AFCA can reverse this process. Our principal goal was to investigate the short-term effect of AFCA on ANS functions evaluated by noninvasive chronotropic (CI), resting heart rate (RHR), and heart rate recovery (HRR) indices.

METHOD

A total of 45 patients were enrolled with symptomatic, drug refractory paroxysmal AF undergoing first cryoballoon (CB) pulmonary vein antrum isolation (PVAI) with one 28-mm CB using single 3-minute freeze techniques without bonus applications. All patients underwent symptom-limited exercise treadmill testing to evaluate noninvasive parameters of ANS before PVAI. For those patients who remained in sinus rhythm, an additional exercise test was repeated after 1 and 3 months after discharge.

RESULTS

The autonomic CI and RHR/HRR indices were impaired after PVAI and persisted post-PVAI 3 months. However, these parameters were not different in patients with and without recurrence.

CONCLUSION

This study demonstrated that the successful AFCA might concurrently impair the ANS parameters. The autonomic imbalance between the sympathetic and parasympathetic activity after AFCA could either become antiarrhythmic and/or proarrhythmic based on which of the two components was going to prevail after successful AFCA. The impaired ANS balance after PVAI might also be another hypothetical mechanism for AF recurrence particularly in the absence of PV reconnection.

Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices

PURPOSE

This study investigated non-invasive indices of post-exercise parasympathetic reactivation (using heart rate variability, HRV) and sympathetic withdrawal (using systolic time intervals, STI) following different exercise durations.

METHODS

13 healthy males (age 26.4 ± 4.7 years) cycled at 70% heart rate (HR) reserve for two durations-8 min (SHORT) and 32 min (LONG)-on separate occasions: HRV (including natural logarithm of root mean square of successive differences, Ln-RMSSD) and STI (including pre-ejection period, PEP) were assessed throughout 10 min seated recovery.

RESULTS

Exercise HR was similar between SHORT and LONG (146 ± 7 and 147 ± 6 b min^-1, respectively; p = 0.173), as was HR deceleration during 10 min recovery (p = 0.199). HR remained elevated above baseline (p < 0.001) throughout recovery for both trials (SHORT 82 ± 13 b min^-1; LONG 86 ± 10 b min^-1, at 10 min post-exercise). Ln-RMSSD was similar at end-exercise between trials (SHORT 1.10 ± 0.30 ms; LONG 1.05 ± 0.73 ms; p = 0.656), though it recovered more rapidly following SHORT (p = 0.010), with differences apparent from 1 min (SHORT 2.29 ± 1.08 ms; LONG 1.85 ± 0.82 ms; p = 0.005) to 10 min post-exercise (SHORT 2.89 ± 0.80 ms; LONG 2.46 ± 0.70 ms; p = 0.007). Ln-RMSSD remained suppressed below baseline throughout recovery following both trials (p < 0.001). PEP was the same at end exercise for both trials (70 ± 6 ms), with exercise duration having no effect on recovery (p = 0.659). By 10 min post-exercise, PEP increased to 130 ± 21 ms (SHORT) and 131 ± 20 ms (LONG), which was similar to baseline (p ≥ 0.143).

CONCLUSIONS

Prolonged exercise duration attenuated the recovery of HRV indices of parasympathetic reactivation, but did not influence STI indices of sympathetic withdrawal. Therefore, duration must be considered when investigating post-exercise HRV. Monitoring these measures simultaneously can provide insights not revealed by underlying HR or either measure alone.

Obesity and Prader-Willi Syndrome Affect Heart Rate Recovery from Dynamic Resistance Exercise in Youth

Following exercise, heart rate decline is initially driven by parasympathetic reactivation and later by sympathetic withdrawal. Obesity delays endurance exercise heart rate recovery (HRR) in both children and adults. Young people with Prader-Willi Syndrome (PWS), a congenital cause for obesity, have shown a slower 60-s endurance exercise HRR compared to lean and obese children, suggesting compromised regulation. This study further evaluated effects of obesity and PWS on resistance exercise HRR at 30 and 60 s in children. PWS (8–18 years) and lean and obese controls (8–11 years) completed a weighted step-up protocol (six sets x 10 reps per leg, separated by one-minute rest), standardized using participant stature and lean body mass. HRR was evaluated by calculated HRR value (HRRV = difference between HR at test termination and 30 (HRRV30) and 60 (HRRV60) s post-exercise). PWS and obese had a smaller HRRV30 than lean (p < 0.01 for both). Additionally, PWS had a smaller HRRV60 than lean and obese (p = 0.01 for both). Obesity appears to delay early parasympathetic reactivation, which occurs within 30 s following resistance exercise. However, the continued HRR delay at 60 s in PWS may be explained by either blunted parasympathetic nervous system reactivation, delayed sympathetic withdrawal and/or poor cardiovascular fitness.

Correlates of Heart Rate Measures with Incidental Physical Activity and Cardiorespiratory Fitness in Overweight Female Workers

Previous studies have suggested that physical activity (PA) levels and cardiorespiratory fitness (CRF) impact on the autonomic control of heart rate (HR). However, previous studies evaluating PA levels did not discriminate between incidental PA and regular exercise. We hypothesized that incidental PA “per se” would influence cardiac autonomic indices as assessed via HR variability (HRV) and HR recovery (HRR) in non-exercisers. Thus, the objective of this study was to investigate the relationships between objective PA levels, CRF, and cardiac autonomic indices in adult, regular non-exercising female workers. After familiarization with procedures and evaluation of body composition, 21 women completed a submaximal cycling test and evaluation of HRR on four different days. Resting (2-min seated and standing) and ambulatory (4-h) HRV were also recorded. Levels of PA were assessed by accelerometry over five consecutive days (i.e., Wednesday to Sunday). Maximum oxygen consumption (VO₂max) was measured as an index of CRF. As reliability was low to moderate for most HR measures, relationships between these and PA and CRF were examined using the 4-day average measures. Significant correlations were identified between post-exercise HRR in the first min with various PA indices (daily moderate PA, daily vigorous PA, and the sum of vigorous and very vigorous daily PA). Additionally, VO₂max was significantly correlated to HRV but not to HRR. The current results indicated that CRF was influential in enhancing HRV while incidental or non-exercise based PA was associated with greater autonomic reactivation in adult overweight women. Therefore, both CRF and non-exercise based PA contribute significant but diverse effects on cardiac health. The use of 4-day averages instead of single measures for evaluation of autonomic control of HR may provide a better indication of regular cardiac autonomic function that remains to be refined.

Heart rate recovery and aerobic endurance capacity in cancer survivors: interdependence and exercise-induced improvements

PURPOSE

Whilst evidence supports beneficial effects of exercise on heart rate variability in cancer patients, its impact on heart rate recovery (HRR) and possible associations of exercise capacity and HRR have not yet been investigated. We aimed to evaluate the effects of an exercise intervention on HRR in relation to the baseline aerobic capacity.

METHODS

Cancer patients (n = 309, 178 females) performed a cardiopulmonary exercise test at baseline and at a 4-month interval follow-up with home-based and supervised exercise programs in-between. VO2 and heart rate were assessed during and HRR at 60 and 120 s after test termination. Based on a median split of the VO2 peak baseline values, participants were dichotomized into two groups: below median (47 female; 57.5 ± 10 years) and above median (48 female; 54.3 ± 12 years).

RESULTS

In the baseline sample (n = 309), VO2 peak correlated significantly with HRR60 (r = .327, p < .01) and HRR120 (r = .524, p < .01). For the compliers who completed intervention and assessments (n = 158), group comparisons demonstrated differences between below median versus above median group in absolute changes of HRR60 (3.1 ± 10.5 bpm (95% CI +0.6; +5.4) vs -1.8 ± 8.7 bpm (95% CI -3.7; +0.5)) and VO2 peak (2.9 ± 3.5 ml/kg/min (95% CI +2.1; +3.7) vs 0.66 ± 4 ml/kg/min (95% CI -0.6; +1.5)) (p < .01), but not in HRR120 (3.9 ± 11.8 bpm (95% CI +1.2; +6.6) vs 0.8 ± 10.8 bpm (95% CI -1.7; +3.5); p > .05).

CONCLUSIONS

These findings point toward a positive linear relationship between aerobic capacity and vagal reactivation in cancer patients. Patients with initial VO2 peak values below median showed improved VO2 peak, HRR60 and HRR120 following the moderate aerobic exercise intervention and differences to patients above median in all outcomes compared.