Evaluation of the learning effect on the six-minute walk distance in adults with long COVID, 2024, Volckaerts et al.

Evaluation of the learning effect on the six-minute walk distance in adults with long COVID
Tess Volckaerts; Kirsten Quadflieg; Chris Burtin; Kevin de Soomer; Ellie Oostveen; Ella Roelant; Iris Verhaegen; David Ruttens; Thérèse S. Lapperre; Dirk Vissers

No Abstract

Guidelines in chronic respiratory disease report a significant learning effect and therefore advice to perform a practice test. More specific, patients with COPD showed a pooled mean improvement on the second 6MWT of 26.3 m, and patients with asthma had a learning effect of 18 m (95% CI 11 - 24). It is not yet known whether a similar learning effect exists in patients with long COVID. As overexertion can lead to a worsening of symptoms in this population, it is important to carefully consider whether a practice walk is needed. With this research we aimed to investigate whether a learning effect on the 6MWD is present in patients with long COVID.

Two 6MWTs were performed on the same day, according to American Thoracic Society/European Respiratory Society standards, in a straight hospital corridor of 50 meters with a minimum of 30 minutes between both tests. All tests were undertaken by a trained investigator. A standard operating procedure was used with standardized phrases for explaining the goal of the test (walk as far as possible) and for encouragements, which were given each minute. Rating of perceived exertion (RPE) and dyspnea (RPD), using the modified Borg scale (range 0 - 10), was captured before and immediately at the end of the test.

Only 26 patients (51%) performed better during their second 6MWD, while 25 patients (49%) performed less. Four patients (8%) showed more than 30.5 meter increase (the suggested minimal clinical important difference for 6MWD for patients with cardiopulmonary diseases 16), while six patients (12%) showed more than 30.5 meter decrease.

It is not clear yet why almost half of the patients with long COVID decreased their second 6MWD. A possible explanation could be that some patients suffer from post-exertional malaise (PEM), which is an important and debilitating symptom in this population. PEM is the worsening of symptoms following even minor physical or mental exertion, with symptoms typically worsening 12 to 48 hours after activity, but may be immediate, and lasting for days or even weeks. It might be that the effect of overexertion overrules a possible learning effect. We could assume that if patients suffer from fatigue, that their RPE would be higher at the start of their second 6MWD. While in the whole group the baseline RPE did not differ between the two tests (1.8 ± 1.9 vs 2.0 ± 2.0 respectively, p = 0.57), in the group of patients who decreased their second 6MWD (n = 25) baseline RPE was statistically significant higher at the start of the second test (1.8 ± 1.1 vs 2.4 ± 1.6, p = 0.04).


Link | PDF (ERJ Open Research)

 

Learning effect? For a walking test?

Good grief.

 

I can see that that would be a valid finding for something like chronic lung disease or heart failure. You complete the 6 mins at speed X and find that you're a little better than you had thought you would be: pre-judged based on your daily life experiences. You go again and try say 110% of X and that's your true capability with your cardiorespiratory system being the rate-limiter.

Perhaps for us though, as the studies are indicating, cardiorespiratory performance has minimal or nil effect, but the peripheral oxygen extraction / muscle impairment is the limiter. So in that scenario we may judge "I can do 110% of my real capacity", but then find that your (actual 100% effort) walking capability limits before the speed you might otherwise have set for yourself. So you don't and in fact can't do better on #2.

In fact half of them do worse. This is around 30 minutes after #1 so not really in PEM territory as we would think of it. Instead, as per Wüst et al, if your leg muscles are made of fast-twitch highly fatiguable, glycolytic, lactate-inducing, type II fibres, then it's no surprise many haven't recovered to baseline performance for #2.

It would be like expecting Usain Bolt to run a WR 100m and then get the same time or better 30 minutes later. Not gonna happen.