Six minute walking test

[jnmaciuch]

This discussion has been split from Physical function and psychosocial outcomes after a 6-month self-paced aquatic exercise program for individuals with [ME/CFS], 2025, Broadbent+

I personally don't think the six minute walking test is a good objective measure for people with mild ME/CFS, the people who are likely to choose to participate in a study like this. Unless a person slides down to a lower level of severity where walking becomes difficult, I don't think a person with mild ME/CFS on a good day is hindered when walking for 6 minutes. It therefore becomes more of a subjective outcome - how determined are you to walk fast and keep up that pace? If you come to like your instructors and want to help the research, you will probably try harder at the end pf the trial than at the beginning.

Agreed. You'd need to have a test of how long/far you can go before you reach X threshold, and that threshold would have to be somewhat objectively defined.

Even saying "how far can you walk at a steady pace before you tap out" would be subjective since there might be differences in how much someone is willing to push themselves.

So really, to effectively measure any intervention, we might need to first find a biomarker that occurs during activity and is predictive of PEM at a later timepoint.

That way, you can objectively measure how much activity someone can do before [signal X] is significantly different from baseline (if measured continuously during activity). Of course, easier said than done.

 

[Simon M]

I personally don't think the six minute walking test is a good objective measure for people with mild ME/CFS, the people who are likely to choose to participate in a study like this.

Do you have any indication of how this group’s severity compares with people who took part in the Pace trial? The six minute walking test worked perfectly well there to expose the problems. But yes, a Fitbit test would be more useful. The Pace trial also did a fitness test, which showed that even those in the GET group who showed a small improvement in six minute walking distance after a year of working on their walking had no gain in fitness.

 

[Hutan]

Do you have any indication of how this group’s severity compares with people who took part in the Pace trial? The six minute walking test worked perfectly well there to expose the problems.

Did it though?

Here are the PACE trial results
Group: Baseline distance (m): 52 week distance (m)

Adaptive Pacing: 314: 334
CBT: 333: 354
GET: 312:379
Standard care as usual: 326: 348

The 6 minute walking test in the PACE trial claimed to show that GET increased physical function, although improvements relative to other treatments were trivial. I don't think we can distinguish between 'none of the treatments made much of a difference' and 'this measure does not have sufficient discriminatory power to identify changes in physical fitness'.


Those numbers suggest to me that the following is possible:

1. There's a ceiling. The distances really don't change very much. Individual variation might be more related to stride length or interpretation of the rules than physical fitness. A measure where most of the participants are at their ceiling at baseline is not worth much.

2. There's a learning effect. The distances increase in all the groups in the second test. I think a learning effect is very likely, and that is why it's so bad that the aquatic exercise study concentrated on the change over time in the intervention group and ignored the fact that there was no significant difference between the two groups in post-trial distance.

3. There's scope for small variation according to motivation. I think it's highly likely that participants in the GET group were encouraged to push themselves harder, perhaps even thought to themselves and were encouraged to think 'I am in the GET group, I can do this'. (Also of course, the dropouts in the GET group probably were more likely to be the ones who were struggling physically.)

I'm not sure how translatable distances walked are from one trial to another. There could be differences in implementation.

• distance between turns
• walk around the end markers or just touch and turn?;
• is the end point marked with a cone, or a mark on the ground?;
• ground surface making it easy to pivot or hard?;
• what shoes are people wearing (do they come prepared?);
• a chance to watch others doing it so as to pick up ideas on how to do it better?
• how close to running were participants allowed to get?
• what happened if the person jogged for a few steps, or a lot of steps? Or if they did not quite touch the end point? Was the person required to start again if they did it wrong? Did they get tired if they had to start again? Bias could easily creep into quality control.
• differences in the encouragement given (again subject to bias)

I don't think the 6 minute walk test in mild ME/CFS measures changes in physical disability well. It's not discriminatory enough and it's too easy to bias. The people with a gross deterioration that the test could pick up will mostly have already dropped out. The rest will continue to be able to walk for 6 minutes, and will probably do better on the re-test because they have experience in it.

If there's a walking test, it needs to be for 30 minutes or an hour. Or otherwise, it needs to be a well-defined physical action that is more demanding and will result in quicker tiring.

 

[Hutan]

Do you have any indication of how this group’s severity compares with people who took part in the Pace trial? The six minute walking test worked perfectly well there to expose the problems. But yes, a Fitbit test would be more useful. The Pace trial also did a fitness test, which showed that even those in the GET group who showed a small improvement in six minute walking distance after a year of working on their walking had no gain in fitness.

Simon, I think you added that last bit about the fitness test after I started writing a response.

So, if a fitness test showed no improvement, but the PACE trial 6 minute walking test showed small improvements in all the treatment arms, with the improvement being a bit bigger in the GET group, then doesn't that suggest that the 6 minute walking test is not a useful test of change in fitness in mild ME/CFS? And suggest that it is too open to bias?

 

[Trish]

The 6 minute walk test in is uniterpretable in PACE because too many didn't do it at the 12 month stage.

 

[Utsikt]

I’ve done a 6 minute walk test twice. IMO, all of @Hutan ’s remarks are relevant.

 

[Simon M]

Simon, I think you added that last bit about the fitness test after I started writing a response.

I don't remember doing so, but as this was yesterday morning there is no chance I would recall

So, if a fitness test showed no improvement, but the PACE trial 6 minute walking test showed small improvements in all the treatment arms, with the improvement being a bit bigger in the GET group, then doesn't that suggest that the 6 minute walking test is not a useful test of change in fitness in mild ME/CFS? And suggest that it is too open to bias?

Possibly - but a small difference vs none isn't much of an effect.

Someone on PR, who I think is here too, did a brilliant analysis of 6MWT results of clinical trials of modest exercise interventions for a number of chronic illnesses. This revealed that many of these showed substantial gains in 6MWT as a result of exercise interventions that were relatively short - and contrasted sharply with the small/trivial gain in 6MWT after a year of exercise in Pace, where walking was the most common exercise chosen by patient.

So, 6MWT generally appears to be useful for measuring useful gains in a range of illnesses. I don't see any good reason to dismiss the 6MWT, as opposed to saying it is far from perfect. It was very helpful in revealing Pace's failure.

One of the most impressive things about the analysis was that the person who did it only included 6MWT studies with a similar walking-test corridor length, as it turns out shorter corridors boost walking distance.

Can anyone remind me who did that work? It may even have been in the Wilshire recovery paper (of which I was a co-author, but it was a long time ago).

 

[Chestnut tree]

Did it though?

Here are the PACE trial results
Group: Baseline distance (m): 52 week distance (m)

Adaptive Pacing: 314: 334
CBT: 333: 354
GET: 312:379
Standard care as usual: 326: 348

The 6 minute walking test in the PACE trial claimed to show that GET increased physical function, although improvements relative to other treatments were trivial. I don't think we can distinguish between 'none of the treatments made much of a difference' and 'this measure does not have sufficient discriminatory power to identify changes in physical fitness'.


Those numbers suggest to me that the following is possible:

1. There's a ceiling. The distances really don't change very much. Individual variation might be more related to stride length or interpretation of the rules than physical fitness. A measure where most of the participants are at their ceiling at baseline is not worth much.

2. There's a learning effect. The distances increase in all the groups in the second test. I think a learning effect is very likely, and that is why it's so bad that the aquatic exercise study concentrated on the change over time in the intervention group and ignored the fact that there was no significant difference between the two groups in post-trial distance.

3. There's scope for small variation according to motivation. I think it's highly likely that participants in the GET group were encouraged to push themselves harder, perhaps even thought to themselves and were encouraged to think 'I am in the GET group, I can do this'. (Also of course, the dropouts in the GET group probably were more likely to be the ones who were struggling physically.)

I'm not sure how translatable distances walked are from one trial to another. There could be differences in implementation.

• distance between turns
• walk around the end markers or just touch and turn?;
• is the end point marked with a cone, or a mark on the ground?;
• ground surface making it easy to pivot or hard?;
• what shoes are people wearing (do they come prepared?);
• a chance to watch others doing it so as to pick up ideas on how to do it better?
• how close to running were participants allowed to get?
• what happened if the person jogged for a few steps, or a lot of steps? Or if they did not quite touch the end point? Was the person required to start again if they did it wrong? Did they get tired if they had to start again? Bias could easily creep into quality control.
• differences in the encouragement given (again subject to bias)

I don't think the 6 minute walk test in mild ME/CFS measures changes in physical disability well. It's not discriminatory enough and it's too easy to bias. The people with a gross deterioration that the test could pick up will mostly have already dropped out. The rest will continue to be able to walk for 6 minutes, and will probably do better on the re-test because they have experience in it.

If there's a walking test, it needs to be for 30 minutes or an hour. Or otherwise, it needs to be a well-defined physical action that is more demanding and will result in quicker tiring.

Agree with all of you points and adding this; there were no actometers right or were not used?

So the distance was self-reported and participants were influenced to do better.

Maybe in reality they didn’t but to satisfy their PACE mentors they reported to be able to walk more.

If my assumptions are incorrect, I will remove my comment.

 

[rvallee]

Agree with all of you points and adding this; there were no actometers right or were not used?

So the distance was self-reported and participants were influenced to do better.

Maybe in reality they didn’t but to satisfy their PACE mentors they reported to be able to walk more.

If my assumptions are incorrect, I will remove my comment.

6 minute-test is supervised and is a one-and-done thing. But of course a one-and-done test in a highly fluctuating condition is in itself very unreliable, thus requiring extended periods of real-time monitoring with a tracker.

Hence why the PACE gang pretended that it was too hard to do. Of course devices were more primitive at the time that PACE was running, but they had huge budgets and could have made it work, commercial devices already existed. They just didn't because, ah let's turn to the cartoon because it works too well here:

 

[Kitty]

I don't think the 6 minute walk test in mild ME/CFS measures changes in physical disability well. It's not discriminatory enough and it's too easy to bias. The people with a gross deterioration that the test could pick up will mostly have already dropped out. The rest will continue to be able to walk for 6 minutes, and will probably do better on the re-test because they have experience in it.

The other thing about this is that in mild or mild-moderate ME/CFS there may be a warm-up effect, a momentum effect, or both. I've found this throughout my illness.

Over the weekend I did a two-day training towards my licence to survey a protected species. It involved classroom based work and practical training in several survey methods. I had to get up earlier, go without rest for much longer, and do more standing, bending, and walking than I'd ever normally do in a short period.

As always, the second day of pushing myself through it was a lot easier than the first. Muscles forced into action will sometimes not only carry on working, they'll get better at it and give you less pain. For a while, anyway.

Unsurprisingly they're not working now!

 

[Hutan]

Someone on PR, who I think is here too, did a brilliant analysis of 6MWT results of clinical trials of modest exercise interventions for a number of chronic illnesses. This revealed that many of these showed substantial gains in 6MWT as a result of exercise interventions that were relatively short - and contrasted sharply with the small/trivial gain in 6MWT after a year of exercise in Pace, where walking was the most common exercise chosen by patient.

My question would be, what diseases were the subject of those clinical trials? People who aren't constrained when walking for 6 minutes won't be able to increase their walking distance much. People who are constrained may be able to increase their distance after treatment. I think that most people with mild ME/CFS walk enough that they can produce distances in the normal range for a 6 minute walk test.

So, 6MWT generally appears to be useful for measuring useful gains in a range of illnesses. I don't see any good reason to dismiss the 6MWT, as opposed to saying it is far from perfect. It was very helpful in revealing Pace's failure.

I think it may be useful in cohorts of people whose ability to walk for 6 minutes is substantially impaired. For example, serious COPD. I don't think this would have been true for most of the PACE trial participants, provided they weren't in PEM.

And, I don't think the results are very helpful in revealing PACE's failure. As I said, without knowing the details we can't know if many of the participants were close to their healthy distance (and/or none of the interventions improved capacity) . I recall there were concerns expressed by the researchers that the corridor used for the PACE 6 minute walk was too short. In that case, we would expect the distances walked to be shorter than in other tests that use a 30 m track. It's possible that if you took relatively sedentary people matched on age and sex, they might not have recorded better distances under the PACE testing conditions.

One of the most impressive things about the analysis was that the person who did it only included 6MWT studies with a similar walking-test corridor length, as it turns out shorter corridors boost walking distance.

I think the opposite is true, longer shuttle distances boost walking distance. You have time to get into rhythm and build up speed. With short distances before turns, there is a lot of acceleration and deceleration. There do seem to be differences in distances used in various tests (and probably in those other bullet pointed factors I mentioned) so I don't think we can compare distances reported in different trials without knowing a lot about the test protocol.

I think too much about the 6 minute walk test remains subjective for it to be much use except in identifying gross impairment (e.g. as in the frail elderly or in rehabilitating amputees).

 

[poetinsf]

PACE also reported improvement with 6MWT after 6mo. Apart from various issues that experts raised with the data, 6 mo was just not long enough because it could only mean that the patients improved conditioning within their limit imposed by ME/CFS. Your PEM threshold remains the same, in other words. It takes a month for a healthy sedentary people to get back in shape, and I wouldn't be surprised if it took 6 mo or longer for people handicapped by PEM. I think it's likely that the improvement plateaued if the trial continued.

 

[poetinsf]

As always, the second day of pushing myself through it was a lot easier than the first. Muscles forced into action will sometimes not only carry on working, they'll get better at it and give you less pain. For a while, anyway.

Yep, there is that conditioning effect. The problem, of course, is that it doesn't improve PEM threshold. For most of us anyway. You keep pushing thinking that you'll continue to improve, you'll inevitably hit the wall and drop like a fly, possibly making your condition worse.