Reduced Parasympathetic Reactivation during Recovery from Exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Although autonomic nervous system (ANS) dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) has been proposed, conflicting evidence makes it difficult to draw firm conclusions regarding ANS activity at rest in ME/CFS patients. Although severe exercise intolerance is one of the core features of ME/CFS, little attempts have been made to study ANS responses to physical exercise. Therefore, impairments in ANS activation at rest and following exercise were examined using a case-control study in 20 ME/CFS patients and 20 healthy people. Different autonomous variables, including cardiac, respiratory, and electrodermal responses were assessed at rest and following an acute exercise bout. At rest, parameters in the time-domain represented normal autonomic function in ME/CFS, while frequency-domain parameters indicated the possible presence of diminished (para)sympathetic activation. Reduced parasympathetic reactivation during recovery from exercise was observed in ME/CFS. This is the first study showing reduced parasympathetic reactivation during recovery from physical exercise in ME/CFS. Delayed HR recovery and/or a reduced HRV as seen in ME/CFS have been associated with poor disease prognosis, high risk for adverse cardiac events, and morbidity in other pathologies, implying that future studies should examine whether this is also the case in ME/CFS and how to safely improve HR recovery in this population.

The Impact of Functional Overreaching on Post-exercise Parasympathetic Reactivation in Runners

While post-exercise heart rate (HR) variability (HRV) has been shown to increase in response to training leading to improvements in performance, the effect of training leading to decrements in performance (i.e., overreaching) on this parameter has been largely ignored. This study evaluated the effect of heavy training leading to performance decrements on sub-maximal post-exercise HRV. Running performance [5 km treadmill time-trial (5TTT)], post-exercise HRV [root-mean-square difference of successive normal R-R intervals (RMSSD)] and measures of subjective training tolerance (Daily Analysis of Life Demands for Athletes “worse than normal” scores) were assessed in 11 male runners following 1 week of light training (LT), 2 weeks of heavy training (HT) and a 10 day taper (T). Post-exercise RMSSD was assessed following 5 min of running exercise at an individualised speed eliciting 85% of peak HR. Time to complete 5TTT likely increased following HT (ES = 0.14 ± 0.03; p < 0.001), and then almost certainly decreased following T (ES = −0.30 ± 0.07; p < 0.001). Subjective training tolerance worsened after HT (ES = −2.54 ± 0.62; p = 0.001) and improved after T (ES = 2.16 ± 0.64; p = 0.004). In comparison to LT, post-exercise RMSSD likely increased at HT (ES = 0.65 ± 0.55; p = 0.06), and likely decreased at T (ES = −0.69 ± 0.45; p = 0.02). A moderate within-subject correlation was found between 5TTT and post-exercise RMSSD (r = 0.47 ± 0.36; p = 0.03). Increased post-exercise RMSSD following HT demonstrated heightened post-exercise parasympathetic modulation in functionally overreached athletes. Heightened post-exercise RMSSD in this context appears paradoxical given this parameter also increases in response to improvements in performance. Thus, additional measures such as subjective training tolerance are required to interpret changes in post-exercise RMSSD.

Influence of Body Composition on Post-Exercise Parasympathetic Reactivation of Firefighter Recruits

Firefighters have a sustained risk for experiencing a sudden cardiac event after completing a fire call. Heart rate recovery (HRR) can be utilized to characterize autonomic nervous system (ANS) recovery and has been linked to cardiac events. Research suggests that body composition influences post-exercise HRR responses in non-firefighter populations. The purpose of this study was to examine the influence of body mass index (BMI), waist circumference (WC), and percent body fat (BF) on the HRR response of firefighter recruits. BMI (kg·m−2), WC (cm), and BF (%) data from 57 firefighter recruits were collected. HRR (b·min−1) data were collected at completion (HR0), as well as 15 (HR15), 30 (HR30), 45 (HR45), 60 (HR60), 120 (HR120), and 180 (HR180) seconds following a submaximal step test, and commonly utilized clinical HRR indices were calculated (ΔHRR30, ΔHRR60, ΔHRR120, and ΔHRR180). After controlling for sex, linear mixed regression models did not identify significant interactions between body composition (ps > 0.05) and HRR response across time. However, significant (ps < 0.05) indirect semi-partial correlations were identified between BF and ΔHRR30 (rsp = −0.31) and ΔHRR60 (rsp = −0.27), respectively. Reducing overall BF (vs. BMI or WC) should be prioritized to improve the post-exercise ANS recovery of firefighter recruits.

Effect of differential music tempo on post-exercise cardiovascular recovery parameters in hypertensive individuals: a randomised control trial

Hypertensive individuals tend to have autonomic dysfunction indicated by sympathetic dominance or delayed parasympathetic reactivation. A complimentary therapy such as music following exercise is considered to be beneficial in improving autonomic recovery. The purpose of this study was to assess the effect of differential music tempo on post-exercise cardiovascular recovery parameters in hypertensive individuals. Thirty hypertensive individuals were recruited for the present study which were randomly allocated to no music (n=10), slow music (n=10) and fast music (n=10) group. Participants in all three groups were subjected to submaximal exercise bout by Harvard step test. The cardiovascular recovery parameters i.e. heart rate recovery (HRR), blood pressure recovery (BPR) and rating of perceived exertion recovery (RPER) were assessed in all three groups after 1 min, 2 min and 3 min following termination of exercise. A significant decline was observed in HRR (P=0.002) and RPER (P=0.008) following exercise in slow music group as compared to fast and no music while no significant differences were observed in BPR between the three groups. The study concluded that music accelerates post-exercise recovery and slow music has greater effect as compared to fast or no music. These findings may have potential implications in the cardiovascular recovery dynamics in hypertensive individuals participating in submaximal exercise.

The effects of varying doses of caffeine on cardiac parasympathetic reactivation following an acute bout of anaerobic exercise in recreational athletes

Background: To examine the effects of varying doses of caffeine on autonomic reactivation following anaerobic exercise. Methods: Recreationally active males (N=20; 24±2y) participated in a randomized, double-blind, placebo-controlled, crossover study where participants ingested: (1) Control (CON; no supplement), (2) a non-caffeinated placebo (PLA), (3) 3-mg∙kg-1 of caffeine (CAF3) or (4) 6-mg∙kg-1 of caffeine (CAF6) prior to Wingate testing. Parasympathetic (lnRMSSD, primary outcome) and global HRV (lnSDNN, secondary outcome) were assessed at rest (i.e., pre-ingestion), 45-min post-ingestion, and 5-min and 35-min post-exercise recovery. We used a GLM to assess mean (95% CI) changes from pre-ingestion baseline.Results: Overall, we observed a significant trend for lnRMSSD and lnSDNN (both, p=0.001, ηp2=0.745). Forty-five minutes after treatment ingestion, we observed a significant increase in lnRMSSD for CAF3 (0.15ms, 95%CI, 0.07,0.24) and CAF6 (0.16ms, 95%CI, 0.06,0.25), both being significant (both, p<0.004) vs. CON (-0.02ms, 95%CI, -0.09,0.04). Five-minutes after exercise, all treatments demonstrated significant declines in lnRMSSD vs. baseline (all, p<0.001). After 35-min of recovery, lnRMSSD returned to a levels not significantly different than baseline for CAF3 (0.03ms, 95%CI, -0.05, 0.12) and CAF6 (-0.03ms, 95%CI, -0.17, 0.10), while PLA (-0.16ms, 95%CI, -0.25, -0.06) and CON (-0.17ms, 95%CI, -0.28, -0.07) treatments remained significantly depressed. A similar pattern was also observed for SDNN.Conclusion: Caffeine ingestion increases resting cardiac autonomic modulation and accelerates post-exercise autonomic recovery after a bout of an anaerobic exercise test in recreationally active young men. However, no differences between caffeine doses on cardiac autonomic reactivity were observed.

Dose Effect of Caffeine Ingestion on Cardiac Parasympathetic Reactivation Following an Acute Bout of Anaerobic Performance Exercise in Recreational Athletes

Background: To examine the dose effects of caffeine ingestion on autonomic reactivation following anaerobic exercise. Methods: Recreationally active males (N=20; 24±2y) participated in a randomized, double-blind, placebo-controlled, crossover study where participants ingested: (1) Control (CON; no supplement), (2) a non-caffeinated placebo (PLA), (3) 3-mg∙kg-1 of caffeine (CAF3) or (4) 6-mg∙kg-1 of caffeine (CAF6) prior to a Wingate testing. Parasympathetic (lnRMSSD, primary outcome) and global HRV (lnSDNN, secondary outcome) were assessed at rest (i.e., pre-ingestion), 45-min post-ingestion, and 5-min and 35-min post-exercise recovery. We used a GLM to assess mean (95% CI) changes from pre-ingestion baseline.Results: Overall, we observed a significant trend for lnRMSSD and lnSDNN (both, p=0.001, ηp2=0.745). Forty-five minutes after treatment ingestion, we observed a significant increase in lnRMSSD for CAF3 (0.15ms, 95%CI, 0.07,0.24) and CAF6 (0.16ms, 95%CI, 0.06,0.25), both being significant (both, p<0.004) vs. CON (-0.02ms, 95%CI, -0.09,0.04). Five-minutes after exercise, all treatments demonstrated significant declines in lnRMSSD vs. baseline (all, p<0.001). After 35-min of recovery, lnRMSSD returned to a levels not significantly different than baseline for CAF3 (0.03ms, 95%CI, -0.05, 0.12) and CAF6 (-0.03ms, 95%CI, -0.17, 0.10), while PLA (-0.16ms, 95%CI, -0.25, -0.06) and CON (-0.17ms, 95%CI, -0.28, -0.07) treatments remained significantly depressed. A similar pattern was also observed for SDNNConclusion: Caffeine ingestion increases resting cardiac autonomic modulation and accelerates post-exercise autonomic recovery after a bout of anaerobic exercise test in recreationally active young men. However, no differences between caffeine doses on cardiac autonomic reactivity were observed.