Research: Potential abnormalities found in home-based testing of everyday activities in ME/CFS

The following research was funded by the ME Association Ramsay Research Fund

Study authors: Nicola Clague-Baker, Sarah Tyson, Karen Leslie, Helen Dawes, Michelle Bull, and Natalie Hilliard.

Study Title: Home-based testing protocol to measure physiological responses to everyday activities in ME: a feasibility study.

“Our home-based physiological testing conducted during everyday activity revealed potential abnormalities that varied between individuals that have previously not been reported. The protocol was found to be feasible and acceptable for people with mild to severe ME.”


Background and objectives

Individuals with Myalgic Encephalomyelitis (ME) have shown altered physiological responses during maximum cardiopulmonary exercise testing (CPET). However, maximal testing is not representative of the everyday activities reported to cause or increase symptoms in ME and is not accessible for those with severe or very severe illness. The aim of this study was to assess the feasibility and acceptability of a home-based testing protocol to measure physiological responses in ME to everyday activity.


Researchers attended participants’ homes to collect data and provide equipment for independent testing. Adults with ME who met the International Consensus Criteria wore a portable metabolic assessment system and a physiological stress monitor. Blood pressure, heart rate, oxygen saturation and lactic acid were assessed during a range of everyday positions and activities in their own homes.


Online recruitment yielded 70 volunteers in 24 h. 17 eligible individuals reflecting a range of illness severities were enrolled. All participants found the procedures acceptable with 12 (70%) subjects completing every listed activity. Apparent physiological abnormalities were identified in all participants.


Physiological measurement during everyday activities was feasible for our participants who represented a range of ME severities. Activities must be adapted for different levels of severity to avoid significant symptom exacerbation. Further research is needed to develop home-based assessment protocols to advance the biobehavioural understanding of ME.

Extracts from Full Paper



Portable cardiopulmonary-monitoring system.

While maximal exercise testing has revealed abnormal physiology in ME, the method has several limitations. The collected data reflects the person’s capacity during the specific testing conditions and cannot be generalised to performance in daily life. Maximal testing is also not representative of the conditions which lead to Post-Exertional Malaise (PEM) in everyday life, such as routine daily physical activities, postural changes, and cognitive or sensory exertion.

Notably the physiological effects of non-physical activities on PEM have received only limited attention. Furthermore, CPET may exclude people with severe or very severe illness who are unable or unwilling to undergo the procedure, e.g., the severity of symptoms precludes travel to a testing site. Finally, CPET is not an appropriate assessment for PEM in relation to everyday tasks as it lacks ecological validity nor is it a feasible clinical outcome measure.

The aim of this study was to assess the feasibility and acceptability of a testing protocol to measure physiological responses of individuals with ME in association with everyday activities in their own homes. Our long-term goal is to identify potential biobehavioural mechanisms in real time that can potentially inform diagnostic assessments and outcome measure(s).

Our testing protocol assessed cardio-pulmonary function in individuals with ME including rate of oxygen consumption, heart rate, heart rate variability, blood pressure, oxygen saturation, and lactic acid levels. Feasibility was assessed by: (1) Ability to recruit subjects; (2) Acceptability of our methods and adherence to our protocol by participants; (3) Usability of outcome measures; and (4) Measure sensitivity to physiological parameters.


  • Fatigue Severity Scale (FSS):
    • This is a nine-item self-report questionnaire that measures the effect of fatigue on function. Each item is rated on a Likert-scale ranging from 1 (no impairment) to 7(severe impairment).
  • Portable cardiopulmonary monitoring system:
    • VO2 (rate of oxygen consumed in L/min)
    • VCO2 (rate of carbon dioxide produced in L/min)
    • VE (minute ventilation measured as respiratory rate x tidal volume)
    • VE/VCO2 (increase in ventilation due to VCO2)
    • Respiratory exchange ratio (CO2 production/O2 uptake.
  • Physiological stress:
    • The FirstBeat bodyguard 2, uses heart rate, breathing frequency, heart rate variability, and oxygen uptake to identify periods of ‘physiological stress’ (suggesting sympathetic nervous system dominance), ‘recovery’ (parasympathetic nervous system) and physical activity.
  • Lactic Acid:
    • Lactic acid was measured with a handheld device (Cosmed Lactate Pro 2) to analyse a finger prick blood sample. Lactic acid is an indication of anaerobic metabolism, where energy is produced in the absence of oxygen. High lactic acid levels increase the acidity of muscle cells, causing a burning sensation in the working muscle.
  • Blood Pressure (BP):
    • BP was measured with a handheld automatic sphygmomanometer cuff on the arm (OMRON M2 Basic).
  • Oxygenation levels and heart rate:
    • Heart rate and oxygenation level was measured with a finger pulse oximeter (OxiPro 2).

Testing procedure

On the day of testing, participants were seen in their homes on waking with the time previously arranged during the screening telephone call. Some participants preferred an early morning hour and others with sleep reversal patterns agreed to an afternoon visit.

The activities were:

  • Lying for 5 min.
  • Sitting for 5 min.
  • Standing for up to 5 min.
  • Typical bathroom activities (e.g., washing, grooming, toileting) for up to 5 min.
  • Walking downstairs.
  • Typical kitchen activities (e.g., preparing breakfast, hot drinks) for up to 5 min.
  • Walking upstairs.
  • A formal cognitive activity (serial sevens test) and other standardised mental arithmetic problems were performed while sitting for up to 5 min.


  • All participants completed the lying and sitting tasks and all but one participant (who had moderate ME) completed the cognitive task.
  • Standing was attempted by all participants, with 13 (76%) able to do so for the full 5 min. The remainder (n = 4) stopped before 5 min due to symptom exacerbations including heart rate increases from 10 to 21 bpm, dizziness, nausea, feeling weak, legs and arms shaking and self-reported cognitive difficulties.
  • Three subjects who could not complete the standing task had severe ME and a co-morbid diagnosis of orthostatic intolerance, and one was moderately affected without a formal diagnosis. Orthostatic intolerance was a co-morbidity for 7 (41%) participants, 4 of whom were able to stand for the full 5 min but experienced symptoms during testing.
  • Data from the Portable Cardiopulmonary-Monitoring System indicated that participants often exceeded their anaerobic threshold during these activities (defined as a respiratory exchange ratio (RER) exceeding 1.0). For two subjects (11%), this occurred while lying down.
  • The activity which caused most participants to exceed their anaerobic thresholds was the cognitive task (n = 10, 62%). One third of participants exceeded this threshold during the more physically demanding tasks (bathroom activities and walking upstairs, Table 3). Healthy participants did not exceed their RER during any activities. 
  • Physiological data collected with Firstbeat Bodyguard for up to six days after the testing day indicated that all participants spent some time (29–95%) in cardiorespiratory ‘physiological stress’ (suggesting sympathetic nervous system dominance).
  • The time in ‘physiological stress’ was not balanced by the time ‘in recovery’ (suggesting parasympathetic nervous system activity) which ranged from 0% to 67% of the time monitored. The proportion of time in ‘physiological stress’ tended to increase with the severity of ME. By comparison, healthy participants exhibited less time in physiological stress on average (30% Healthy: 63% ME) and more time in recovery (55% Healthy: 16% ME). 
  • Lactic acid levels for four participants (2 mild, 1 moderate and 1 severe) were greater than 4 mmol/L at the start of the day of testing, suggesting lactic acidosis.
  • The 1-hour testing procedure increased lactic acid in 5 people (1 moderate and 4 severe), and reduced lactic acid in 11 participants, reflecting the majority of participants with ME. The procedure did not cause excessive anaerobic metabolic changes.
  • Over the follow-up days, high levels of lactic acid (>4 mmol/L) were associated with participant-reported high levels of leg/muscle pain (22 occasions), fatigue (15), cognitive difficulties/brain fog (8), headache (8), dizziness (5), tinnitus (3) and nausea (2).
  • One person with mild ME had consistently high levels of lactic acid rising to 17.6 mmol/L on one occasion. This participant always had significant leg pain and stated that they struggled to pace their activities due to childcare commitments. Normal lactate levels range from 0.5 to 2.2 mmol/L.

In addition, the physiological responses to assigned tasks revealed:

  • Changes in blood pressure during activity. One person showed a large increase on standing (from 109/75 while sitting to 144/77 after 5 min standing and continued to rise to 161/85 for a further 15 min in lying with head propped) while four others showed a reduction in blood pressure (mean 13.75 mmHg (range 10–17) in systolic BP). The remaining participants and activities did not show marked changes in blood pressure.
  • A normal range of VE/VCO2 (minute ventilation/carbon dioxide production) during CPET tests in healthy individuals for this age group is up to 29.9. Mean levels of VE/VCO2 were consistently higher in our participants compared to controls for the following activities:
    • Standing; mean 32; SD 10.8, (controls: mean 30.3; SD 2.84).
    • Bathroom activities; mean 31, SD 6.2(controls: mean 29.9; SD 3.2).
    • Walking downstairs: mean 31.4; SD 8.0 (controls: mean 29.7; SD 3.1).
    • Kitchen work: mean 31.8; SD 12.6 (controls: mean 30.6; SD 1.1).
    • Cognitive activities: mean 31.3; SD 8.9 (controls: mean 26.8, SD 5.2).
  • This suggests that participants had a greater ventilatory requirement for eliminating the CO2 produced by aerobic metabolism and could indicate reduced ventilatory efficiency.


An important challenge in developing a feasible testing protocol was to minimise potential harms to participants from triggering PEM while they performed sufficient activity to detect abnormalities, if present. As expected, the severity of participants’ illness influenced the activities completed, with the more severely affected completing fewer and less demanding activities.

All participants demonstrated some physiological abnormalities during testing, which supports preliminary success to further develop this home-based assessment approach. However, there was no single activity that all participants could complete that caused roughly similar abnormal response(s) in all participants. Thus, future work to produce a standardised testing protocol that yields broadly informative findings on ME pathophysiology is likely to require additional study with larger samples.

Perhaps surprisingly, the activity that caused most participants to exceed their anaerobic threshold was the cognitive task, which all but one participant was able to complete. Thus, cognitive as well as physical activities may show promise for further exploration of potential markers.

All participants were positive about the testing process and would recommend it to others. Although we strove to avoid asking participants to do anything that may trigger more than minimal PEM, some wanted to challenge themselves to see its impact on their objective measurements. This raises several important issues.

Firstly, the challenge of fully standardising any testing protocol, and secondly the importance of careful discussion and shared decision-making with study participants regarding testing.

Finally, we recommend that research projects with ME patients should offer feedback about individualised results, a tangible benefit to participation that may empower subjects to better understand and manage their condition. For example, during the standing task, 11 participants experienced short-lived symptom exacerbation indicative of orthostatic intolerance, three of whom had no pre-existing diagnosis. Their results were forwarded to their GP with recommendations for further investigation and treatment.

This indicates how physiological assessment may have a role in the diagnosis and management of ME and related co-morbidities. Furthermore, our finding that people with ME may exceed their anaerobic thresholds during everyday activity supports the potential for heart rate monitoring to be used as part of an energy management strategy which warrants further investigation.


Our home-based physiological testing conducted during everyday activity revealed potential abnormalities that varied between individuals that have previously not been reported.

The protocol was found to be feasible and acceptable for people with mild to severe ME. This supports the need for further work to develop a reliable, valid and accurate testing protocol to assess, diagnose and monitor ME.

Given the variability in participants’ responses to activities, the testing protocols will need to be individualised to participants’ level of ability and preferences. All subjects demonstrated altered metabolic responses during a number of activities and exceeded their anaerobic threshold during at least one of the everyday activities tested.

Our findings suggest the need to further explore metabolism during everyday tasks in larger samples and more specifically to explore the potential for using heart rate as a surrogate marker to monitor metabolic effort.

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