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A trip to Seattle to see Dr. Ruhoy held up the blogs a bit but they’re back!

exercise study

Wust assessed the effects of exercise on heart rate variability.

Exercise physiologist Rob Wust’s “Wearable heart rate variability monitoring identifies autonomic dysfunction and thresholds for post-exertional malaise in Long COVID” study did something simple but important: it tracked heart rate variability (HRV) while assessing activity levels, and before and after exercise, and during daily activities to get a sense of how the autonomic nervous system in long-COVID patients stood up to exertion.

In general, we want high HRV readings. Note, though, that HRV levels are highly individual: what is considered high or low for one individual might be different for another. The key is observing how HRV levels fluctuate over time and in relation to exertion.

Low HRV levels suggest that sympathetic nervous system dominance is present, aka a “fight or flight” process. That, of course, comports well with the “wired but tired” symptoms found in these diseases.

The HRV test tracks a known pattern: our heart rate speeds up when we inhale and slows down when we exhale. The inhalation triggers SNS activation while the exhalation triggers the parasympathetic nervous system.

Since we both inhale and exhale more when we exercise, an exercise test provides a nice glimpse into how well our autonomic nervous system handles stress. A healthy, flexible cardiovascular system should be characterized by a heart that’s able to speed up and slow down rapidly during the long inhalations/exhalations during exercise.

The GIST

  • Exercise physiologist Rob Wust’s Wearable heart rate variability monitoring identifies autonomic dysfunction and thresholds for post-exertional malaise in Long COVID” study did something simple but important: it tracked heart rate variability (HRV) while assessing activity levels and before and after exercise and during daily activities to get a sense of how the autonomic nervous system in long COVID patients stood up to exertion.
  • In general, we want high HRV readings. Low HRV levels suggest that sympathetic nervous system dominance, aka a “fight or flight” process, is present and that the parasympathetic nervous system arm of the autonomic nervous system has failed to kick in.
  • This nice-sized (127—Long COVID; 21 healthy controls) study tracked HRV during numerous activities, every hour for 24 hours after exercise, and during sleep.
  • The authors also used the exercise study to recommend heart rates for each patient that would keep them below their anaerobic threshold—the point at which the body increasingly relies upon the vastly less efficient and ultimately toxic mode of anaerobic energy production.
  • Heart rate variability (HRV) levels were lower in patients with long COVID compared to healthy controls across all activities and during sleep. While HRV levels recovered after strenuous exercise in the healthy controls within 3-6 hours, they remained lower for a remarkable 24 hours in long COVID patients, indicating that a state of postexertional malaise had been reached. Mild exercise  – exercise done at a heart rate 80-90% of VTI (anaerobic threshold) – was better tolerated with HRV levels recovering (to a still lower level) within 5-6 hours.
  • Over 40 percent of long-term COVID patients recorded heart rates exceeding their anaerobic threshold during their daily activities; i.e., they were exerting too much.
  • Intense exercise didn’t affect nighttime HRV levels in the healthy controls, but dramatically reduced them in the long COVID patients.
  • ME/CFs and fibromyalgia studies have also found that intense exertion impacts the autonomic nervous system negatively. For instance, the parasympathetic nervous system should quickly brake the sympathetic nervous system and return heart rates to normal. While in the healthy controls, they did, ten minutes after exercise, the heart rates of the ME/CFS patients remained significantly elevated.
  • A similar process appears to be present regarding mental exertion.
  • Long COVID patients who engaged in more than 60 minutes of exercise, regardless of intensity, experienced greater reductions in HRV than patients who engaged in 20 minutes of exercise.
  • Even short periods of intense exercise (>100%  of their safe heart rate), though, were associated with “abnormal diurnal adjustments of HRV in patients”. i.e., abnormally reduced low HRV at night.
  • Studies suggest increased sympathetic nervous system activity may be behind ME/CFS patients’ poor sleep. An inability of the parasympathetic nervous system to kick in and cool down the sympathetic nervous system during the deepest sleep stages may keep people with these diseases from experiencing the “recuperation of energy” that sleep normally brings.

 

The Study

This nice-sized (127-long COVID; 21-healthy controls) study went well beyond others in the length of time it tracked HRV (several days) and the detail with which it tracked it. It assessed HRV during numerous activities (sleep, eating, travel, relaxation, work, walking, exercise, household chores, etc.), every hour for 24 hours, after intense exercise, and nighttime after exercise.

The authors also used the exercise study to recommend heart rates for each patient that would keep them below their anaerobic threshold—the point at which the body increasingly relies upon the vastly less efficient and, ultimately, toxic mode of anaerobic energy production.

Results

Notice the higher heart rates during the day (red – top graph) and lower heart rate variability (red – bottom graph).

As expected, patients with long COVID had lower power output and oxygen uptake consumption at VT1 than controls.

Heart rate variability (HRV) levels were lower in patients with long COVID than in healthy controls across all activities and during sleep. While HRV levels recovered after strenuous exercise in the healthy controls within 3-6 hours, they remained lower for a remarkable 24 hours in long-COVID patients, indicating that a state of post-exertional malaise had been reached. Mild exercise (done at a heart rate 80-90% of VTI (anaerobic threshold) was better tolerated with HRV levels recovering (to a still lower level) within 5-6 hours.

Over 40 percent of long-term COVID patients recorded heart rates exceeding their anaerobic threshold during their daily activities, indicating that they were exerting too much.

Interestingly, HRV dropped the most in mildly affected patients but not as much in “moderately affected” patients, presumably because the HRV levels in the moderately affected patients had already bottomed out and simply could not go lower. It took 10-13 hours for the HRV levels in moderately affected patients to increase after exercise intensities above 80% (80% is considered mild).

Exercise and the Autonomic Nervous System in Chronic Fatigue Syndrome (ME/CFS) and Fibromyalgia (FM)

Several studies demonstrate that too much exertion produces an autonomic nervous system hit in ME/CFS and FM.

A 40-person 2022 study, “Reduced Parasympathetic Reactivation during Recovery from Exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome,” found normal HRV ratios during rest and exercise but reduced values overall, suggesting that both the sympathetic and parasympathetic nervous systems had taken a hit. Perhaps in a sign of chronotropic incompetence, ME/CFS patients failed to attain normal heart rates during exercise.

It was what happened after the exercise, however, that produced the most interest. Once exercise stops, the parasympathetic nervous system should quickly brake the sympathetic nervous system and return heart rates to normal. While in the healthy controls, they did, ten minutes after exercise, the heart rates of the ME/CFS patients remained significantly elevated. The authors concluded that the results “demonstrate(d) a reduced functional capacity for exercise.”

Delayed Recovery After Exercise Found in ME/CFS and Fibromyalgia

Likewise, a recent fibromyalgia study also found the same strange pattern of decreased heart rates during exercise and increased heart rates 30, 120, 180, 300, and 600 seconds after exercise.

While it may not seem inconsequential that heart rates don’t quickly return to normal, this finding appears to uncover a fundamental weakness. A 1999 study that followed almost 2,500 people found that a delayed decrease in the heart rate during the first minute after exercise was “a powerful predictor of overall mortality”.

The relative risk of dying in the participants (average age 57) doubled over the next six years in those with delayed heart rate recoveries. This did NOT mean they were likely to die, but their risk of dying had increased. Since then, several studies have shown that quick heart rate recovery after exercise is a function of a healthy and responsive parasympathetic nervous system.

A similar process appears to be playing out with mental exertion. Japanese researchers have shown that sympathetic nervous system activity spikes during a cognitive test. Once the test is over, though, the parasympathetic nervous system should step in to shut the sympathetic nervous system down, and return the brain and body to a rested state. The failure of the parasympathetic nervous system to activate after the cognitive test was done was highly correlated with fatigue.

Fatigue – the Japanese Way: A Chronic Fatigue Syndrome Perspective

Nighttime Heart Rate Variability

Intense exercise didn’t affect nighttime HRV levels in the healthy controls but dramatically reduced them in the long-term COVID patients. The decrease in the long-term COVID patients’ HRV during sleep may help explain why it’s so difficult to get a good night’s sleep after too much physical exertion.

Tracking activity levels over time enabled the researchers to determine how different activities affected HRV levels at night. People who engaged in “intense exercise” ( >100% of their “safe heart rate”) for less than 60 minutes experienced significantly reduced HRV levels compared to people who engaged in mild exercise (80-90% of “safe heart rate”). In a further warning not to engage in longer periods of exertion, long-COVID patients who engaged in more than 60 minutes of exercise, regardless of intensity, experienced greater reductions in HRV than patients who engaged in 20 minutes of exercise.

Even short periods of intense exercise (>100% of their safe heart rate), though, were associated with “abnormal diurnal adjustments of HRV in patients”; i.e., abnormally reduced low HRV at night.

The takeaway: short periods of intense exertion and long periods of exertion at varying intensity hit HRV levels at night particularly hard.

The Sleep HRV (Autonomic Nervous System) Connection

Sleep

Intense or long-duration exercise at milder intensities particularly affected HRV levels at night.

The sleep problems in ME/CFS have been a mystery for a while. Despite the problems with unrefreshing sleep, a 2011 sleep study reported that ME/CFS studies have not revealed any substantive evidence indicative of a primary sleep disorder…”. Ditto, a 2011 review concluded “there is no demonstrable neurophysiological correlate to substantiate a basic deficit in sleep function in CFS.”, Then a 2012 review concluded that “polysomnographic and other objective measures of sleep” have observed few differences in sleep parameters. Once again, ME/CFS seemed to evade the researchers’ grasp.

Natelson, however, pointed out that non-EEG studies might be more effective in assessing sleep quality as far back as 1998. By 1997, researchers had shown that ‘autonomic activation’ could induce sleepiness during the daytime. Still, it wasn’t until 2007 that researchers explored how the autonomic nervous system might impact sleep in ME/CFS.

Boneva started it off with a 2007 CDC study, which found higher heart rates, reduced HRV, and high norepinephrine levels during sleep, suggesting that a “state of sympathetic ANS predominance prevailed”. Next, a 2011 Australian study, which found no differences in ‘classical’ sleep tests, found evidence of reduced nighttime heart rate variability. That same year, Wyller’s 2011 pediatric study found evidence of sympathetic nervous system (fight or flight) activation (increased blood pressure, heart rate) precisely when the body should relax and recover during sleep.

The study oted that “the low HRV strongly predicted sleep quality, suggesting a pervasive state of nocturnal sympathetic hypervigilance in CFS Vollmer-Conna,

Natelson’s 2013 study found no significant changes in sleep architecture (time spent in various stages of sleep), but significant changes in all heart rate variability measures between the two groups during sleep. When they looked deeper, they found that patients who felt sleepier had a ‘higher fractal scaling index’, suggesting that ‘micro-arousals’ during non-REM or deep sleep were being undetected in traditional sleep studies.

Looking deeper, a small 2018 Finnish study found that the expected gradual increase in parasympathetic activity as the participants entered slow-wave sleep was missing in people with ME/CFS. They concluded that “parasympathetic functioning during deep restorative sleep seems to be impaired in… CFS.”

The parasympathetic nervous system’s inability to “de-arouse” the autonomic nervous system during the deepest sleep stage may prevent energy recuperation.

An even deeper dive into parasympathetic nervous system activity by Australians in a 2020 at-home sleep study found no reductions in sleep time or sleep stages. However, it revealed reduced parasympathetic nervous system activity during the deeper stages of sleep (NREM2 and slow wave sleep), which was correlated with self-reported sleep quality and well-being.

The authors proposed that a missing “autonomic de-arousal” during slow-wave sleep in the ME/CFS patients prevented them from experiencing the “recuperation of energy” that normally occurs during slow-wave sleep, in particular. Perhaps in an attempt to compensate, people with ME/CFS actually experienced more slow-wave sleep than the healthy controls in the study, but the crucial element—the quality of their slow-wave sleep—was lacking.

During slow-wave sleep – the deepest stage of non-REM sleep – brain glucose consumption (energy consumption) drops significantly, the brain experiences greatly reduced neuronal activity, and goes into repair mode.

Using HRV to Improve Your Health

Your Crash in a Graph? How Heart Rate Variability Testing Could Help You Improve Your Health

 

Heart Rate Variability (HRV) An Underused ME/CFS/FM Management Tool: PT II – Surveying the Landscape

Conclusion

All signs point to the fact that too much exertion – particularly intense and longer duration physical (as well as mental exertion) – disrupts autonomic nervous system (ANS) functioning – in people with long COVID and ME/CFS/FM by putting them into a fight or flight (enhanced sympathetic nervous system) state.  Milder exercise is better tolerated but it can take the ANS 24 hours to recover after intense exercise.

ANS dysfunction, then takes its place alongside the remarkable series of dysfunctions (reduced gene expression, metabolite and protein production, extracellular vesicles, reduced energy production) associated with exercise.

“A Failure to Respond”: the ME/CFS Extracellular Vesicle Exercise Study

Interestingly, a similar type of parasympathetic withdrawal that fails to “de-arouse” the sympathetic nervous system during the deepest states of sleep may hold the key to the unrefreshing sleep that people with these diseases experience. Problems with the stress response, then, may impact many areas on these diseases.

  • Coming up – Improving parasympathetic nervous system activity during slow-wave sleep.

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