Key points
- A review paper published on the 30th March this year took a closer look at how monitoring lactate levels in the blood may provide a tool to support the management of post exertional malaise.
- The exact reason PEM occurs remains unknown, it is likely to be related to be related to the “transport, delivery, and utilization of oxygen” within the muscles of the body.
- The body produces most of its energy through aerobic respiration a process in which oxygen and glucose are converted into carbon dioxide, water, and 38 molecules of energy.
- When oxygen supply to the cells is decreased for any reason, energy can still be produced without the need for oxygen through anaerobic respiration in which glucose is converted to 2 molecules of energy, and lactate.
- Due to mitochondrial dysfunction, and impaired oxygen delivery to cells, people with ME/CFS, and those with long COVID, may use anaerobic respiration – and produce more lactate, at lower levels of activity compared with healthy controls.
- Monitoring blood lactate levels may provide an indication of abnormally increased anaerobic respiration in those with ME/CFS, and long COVID, but more research is needed.
Post exertional malaise (PEM) is often referred to as the cardinal symptom of ME/CFS – and one of four “symptoms for suspecting ME/CFS” in the 2021 NICE guidelines alongside; fatigue, unrefreshing sleep, and cognitive difficulties.
PEM is also experienced by some people with long COVID – the 2022 NICE guidelines which ask “What are the signs and symptoms?” of long COVID state that the most common generalized symptoms include; “fatigue — some people develop post-exertional malaise, or post-exertional symptom exacerbation; fever, and pain”.
Qualitative research published earlier this year found that the “uncertainty and debility of PEM created despair” amongst participants with ME/CFS. In addition “planning and moderation of energy expenditure were seen as essential to avoiding PEM”.
Therefore, of particular interest is a review paper published on the 30th March this year which takes a closer look at how monitoring lactate levels in the blood may provide a tool to support the management of PEM – although more research is needed.
What is lactate, and how does it relate to ME/CFS?
When there is sufficient supply of oxygen to the cells – in healthy people this is usually at rest or with only gentle exercise, most energy production in the body occurs within mitochondria – sometimes referred to as the “powerhouses” of cells. This type of energy production is known as aerobic respiration, where oxygen and glucose are converted into carbon dioxide, water, and 38 molecules of energy (adenosine triphosphate (ATP)).
If the supply of oxygen to cells decreases for any reason – for example, in more intense exercise, ATP can still be produced in the fluid within cells (cytoplasm) without the need for oxygen. This process is called anaerobic respiration. Here, glucose is converted to two molecules of ATP, and lactate – a substance which builds up in muscles causing pain and tiredness, and can lead to cramp.
The authors of the paper state that anaerobic respiration may also play a role in chronic disease states where there is impaired oxygen delivery to cells, and mitochondrial dysfunction – both thought to be involved in ME/CFS, and long COVID. Here, it is thought that anaerobic respiration may occur at lower levels of activity – resulting in increased levels of the waste product lactate in the blood.
Why might blood lactate level monitoring be useful for people with ME/CFS, and long COVID?
In the paper, the researchers discuss that that while the exact reason PEM occurs remains unknown, it is likely to be related to be related to the “transport, delivery, and utilization of oxygen” within the muscles of the body. In fact it is possible that people with ME/CFS, and those with long COVID, could be using anaerobic respiration for energy production at markedly lower levels of activity compared with healthy controls.
It is possible that the lactate produced during anaerobic respiration may act as a biomarker of these abnormally increased anaerobic respiration levels, and indicate disturbance of normal energy production in the body.
Portable blood lactate monitoring devices have been developed, and are used regularly in sport. These devices help athletes understand responses to exercise training by giving an indication of anerobic threshold – the exercise intensity at which your body starts to produce lactate through anaerobic respiration faster than it can be removed, causing the waste product to accumulate in the blood.
In theory, monitoring blood lactate levels, and knowing how much activity can be done before the anaerobic threshold is reached, may allow people with ME/CFS, and those long COVID, to plan, monitor, and adjust activities of daily living in a more reliable way.
The researchers also suggest that following more research blood lactate monitoring could be used to assess the effectiveness of some pharmacological treatments for ME/CFS by monitoring the impact they have on anaerobic threshold, and levels of lactate in the blood. It was also commented that these blood lactate monitors could even be used alongside pharmacological interventions to help increase functional capacity – the ability to perform activities and tasks necessary to live independently, in a safe and effective way.
Summary
With more research, portable blood lactate level monitoring devices may provide a way to provide people with ME/CFS, and those with long COVID, more information about how their body is producing energy – and when their anaerobic threshold is reached. This could help them to pace more effectively by ensuring that activity is carried out at a level at which the body can maintain aerobic respiration – or being able to plan for activities which may push them into anaerobic respiration, and allocate rest time appropriately.
ME Research UK adds that more rigorous, high-quality biomedical research is needed to assess the safety and efficacy of blood lactate monitoring in people with ME/CFS, and those with long COVID. This research should include investigation on the potential impact on both quality of life, and functional capacity but also the feasibility and cost of this type of blood lactate level monitoring. These investigations should be carried out in different subgroups of people with ME/CFS, and those with long COVID; such as males and females, different ethnic groups, in those with different levels of disease severity, and different length of disease.
