For the first time, a team of researchers measured heart rate variability (HRV) in those with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) to understand how the autonomic nervous system (ANS) responded prior to, during, and following exercise. Typically, those with ME/CFS have a low HRV, which means that the sympathetic nervous system is over-responding while the parasympathetic nervous system is under-responding. This can result in a host of health issues. In this study, shares Health Rising, researchers wanted to understand if ME/CFS caused slower exercise recovery due to low HRV. Ultimately, the researchers determined that those with ME/CFS did, in fact, have a tougher time recovering.

To take a deeper look at the findings, check out the Journal of Clinical Medicine.

Measuring Heart Rate Variability (HRV)

The Harvard Health Blog describes heart rate variability (HRV) as:

a measure of the variation in time between each heartbeat. Based on data gathered from many people, if the system is in more of a fight-or-flight mode, the variation between subsequent heartbeats tends to be lower…[whereas] if the system is in more relaxed state, the variation between beats may be higher.

In this study, researchers wanted to evaluate HRV in those with ME/CFS and understand how it related to exercise tolerance and recovery. Altogether, 40 participants enrolled. 50% of these individuals had ME/CFS, while the rest represented healthy controls. During the study, participants had their heart rate and HRV, as well as blood pressure, measured prior to, during, and following exercise during which 75% of age-predicted maximum heart rate was reached.  Findings from the study include:

• HRV, heart rate, and blood pressure – at rest – were normal within both groups, though each was lower in those with ME/CFS than within the control group. Researchers believe this could suggest an underactive ANS.
  • Note: Researchers also felt that the underactive ANS could point to problems with the baroreceptor reflex (baroflex). In studies evaluating fibromyalgia, patients had lowered baroflex responses. This could lead to more pain, bodily stress, and sensitization, potentially linking baroflex issues with ME/CFS.
• Heart rate and blood pressure were also normal in both groups during exercise.
• Within 10 minutes following exercise, the control group’s heart rates had returned to normal. However, those with ME/CFS still had significantly higher heart rates – despite HRV returning to normal – compared to both before and during exercise.
  • Note: This is important as prior studies have shown that heart rates that do not return to normal within the first 60 seconds following exercise signified an increased risk of death.

About Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS)

Doctors are not exactly sure what causes myalgic encephalomyelitis (ME), or chronic fatigue syndrome (ME/CFS). However, researchers surmise that triggers can include genetics, immune system issues, viral infections, and hormone imbalances. ME/CFS is a chronic condition characterized by extreme and debilitating fatigue that fails to improve with rest. The onset of this condition most often occurs between ages 30-50. It is also more common in females than in males. Potential symptoms include:

• Intense fatigue that worsens during activity and does not improve with rest
• Low stamina
• Problems with memory and concentration
• Joint and/or muscle pain
• Dizziness and blurred vision
• Chills and night sweats
• Bowel dysfunction, such as diarrhea
• Excess sleepiness or sleep disturbances
• Headache
• Irregular heartbeat
• Shortness of breath
• Swollen lymph nodes, particularly in the neck or armpits
• Depression