Association between cognitive performance, physical fitness, and physical activity level in CFS

[Dolphin]

(note that I shortened the title to fit it in to the character limit)

Free full text: http://www.rehab.research.va.gov/jour/2013/506/ickmans506.html

Association between cognitive performance, physical fitness, and physical activity level in women with chronic fatigue syndrome.

J Rehabil Res Dev. 2013;50(6):795-810. doi: 10.1682/JRRD.2012.08.0156.

Ickmans K1, Clarys P, Nijs J, Meeus M, Aerenhouts D, Zinzen E, Aelbrecht S, Meersdom G, Lambrecht L, Pattyn N.

Author information

Abstract

Limited scientific evidence suggests that physical activity is directly related to cognitive performance in patients with chronic fatigue syndrome (CFS).

To date, no other study has examined the direct relationship between cognitive performance and physical fitness in these patients.

This study examined whether cognitive performance and physical fitness are associated in female patients with CFS and investigated the association between cognitive performance and physical activity level (PAL) in the same study sample.

We hypothesized that patients who performed better on cognitive tasks would show increased PALs and better performance on physical tests.

The study included 31 women with CFS and 13 healthy inactive women.

Participants first completed three cognitive tests.

Afterward, they undertook a test to determine their maximal handgrip strength, performed a bicycle ergometer test, and were provided with an activity monitor. In patients with CFS, lower peak oxygen uptake and peak heart rate were associated with slower psychomotor speed (p < 0.05).

Maximal handgrip strength was correlated with working memory performance (p < 0.05).

Both choice and simple reaction time were lower in patients with CFS relative to healthy controls (p < 0.05 and p < 0.001, respectively).

In conclusion, physical fitness, but not PAL, is associated with cognitive performance in female patients with CFS.

Comment in

Rebuttal to Ickmans et al. association between cognitive performance, physical fitness, and physical activity level in women with chronic fatigue syndrome. J Rehabil Res Dev. 2013;50(6):795-810. www.rehab.research.va.gov/jour/ 2013/506/pdf/ickmans506.pdf. [J Rehabil Res Dev. 2013]

Response. [J Rehabil Res Dev. 2013]

PMID: 24203542 [PubMed - indexed for MEDLINE]

 

[Dolphin]

Another frustrating paper from the Jo Nijs team.

In sum, the healthy controls didn't find a correlation between cognitive scores and exercise test results. This would suggest the results are largely independent (which is sort of what one would expect: there are plenty of unfit people with high IQs (say) and very fit people who still aren't very bright).

So the finding that cognitive scores and exercise test correlate in CFS suggests to me that something unusual happens in CFS: an independent variable, severity, explains both results. Instead, they make out it is to do with deconditioning and similarly the impairments can be alleviated by improving deconditioning.

 

[Dolphin]

I sign of where Nijs and co are at:

In their discussion paper, Wessely et al. suggested that persistent inactivity caused by symptoms like pain and fatigue leads to deterioration of physiological exercise capacity and the subsequent presence of more symptoms, which eventually results in a vicious and self-perpetuating cycle of activity avoidance [23]. This avoidance behavior toward physical activity is in turn likely to influence PAL and exercise performance. A logical consequence would be that the exercise capacity in patients with CFS is significantly lower than in healthy controls. However, a systematic literature review recently conducted by Nijs et al. revealed no definite conclusion in relation to physiological exercise capacity in patients with CFS [20].

 

[Dolphin]

Sounds like a fancy actometer:

Real-time Activity Monitoring
We used the SenseWear(R) Pro3 Armband (SWA) (BodyMedia Inc; Pittsburgh, Pennsylvania) wireless multisensor accelerometer for real-time monitoring of physical activity of all participants during 3 consecutive days. This activity monitor has a two-axis accelerometer, along with several other physiological sensors (heat flux, skin temperature, near-body ambient temperature, body position, movements of the upper arm, and galvanic skin response) from which data are integrated and can subsequently be uploaded and analyzed using computer software. Energy expenditure, which we calculated at 1 min intervals for this study, is estimated based on sex, age, height, and weight, together with the information collected from all sensors. The SWA also registered the time when energy expenditure was >3 metabolic equivalents (METs), the time spent sleeping, and the time spent awake in supine position. The SWA is lightweight and comfortable to wear, worn on the back of the right upper arm over the triceps muscle. Good validity and reliability of the SWA has been shown in healthy adults under laboratory [33] and free-living conditions [34].

 

[Dolphin]

I would have preferred if the actometer had been used at a different time than the three days after the exercise test as it could give untypical results.

The results weren't that exciting for the comparisons between physical activity and cognitive performance:

Relationship Between Cognitive Performance and Physical Activity Level in Patients with Chronic Fatigue Syndrome

Only two variables measured with the SWA were significantly correlated with cognitive performance. The amount of time that patients slept per day (sleep time) was inversely related* to Stroop accuracy for neutral (neutral and no word conditions) and inverse negative priming stimuli (r = –0.47, r = –0.60, and r = –0.49, respectively; p < 0.05). A negative** correlation was found between the number of steps taken per day (steps) and the Stroop accuracy score for incongruent stimuli (r = –0.53, p = 0.01). The latter correlation was marginally significant in the control group (r = –0.63, p = 0.05). None of the other significant and nonsignificant relationships observed in the patients with CFS were significant in the control group (p > 0.05).

*This means that more sleep was associated with worse cognitive results in CFS

**This means that more steps was associated with worse cognitive results in CFS (and marginally significant in the control group).

 

[Dolphin]

I'm not going to try to list all the results but here are the Stroop results:

Although we found that overall choice reaction time was lower in patients with CFS relative to controls, as evidenced by slower color naming on all conditions of the Stroop task, Stroop (semantic) interference effect in patients with CFS was not increased relative to controls. Because Stroop interference reflects selective attending ability or the ability to inhibit irrelevant information, this finding demonstrates normal semantic processing in these patients. These findings were not unexpected in that they replicate previous findings [7–9,37–38].

If one looks at Figure 2 (a), (b) and (c) one can see that for each of them, the CFS were quite significantly slower.

 

[Dolphin]

(Not important I think)
This talk about the controls seems speculative

A marginally significant lower score was found in the controls for the sleep-related words condition than the category condition. Furthermore, patients with CFS were even more accurate than controls in color-naming sleep-related words. These results could suggest that sleep-related words had an emotional load on the controls but not on the patients with CFS. Interestingly, all recruited controls were related in one way or another to the patients with CFS because every patient was asked to bring a healthy and inactive relative, friend, or acquaintance to participate in the control group. Indeed, it has been previously shown that the emotional burden of CFS is felt by carers and relatives as well [40].

 

[Dolphin]

Very annoying comment (I thought) in the discussion:

In a previous study of patients with CFS, Van Oosterwijck et al. demonstrated that postexertional malaise, which is a term used to describe symptom exacerbation as a result of excessive exercise, is triggered by submaximal exercise and self-paced, physiologically limited exercise [41]. Consequently, it is possible to explain the reduced exercise capacity in individuals with CFS by an underlying fear of postexertional malaise.

Underlined bit is annoying.

In addition, it is evidenced that patients with CFS report higher ratings of perceived exertion during exercise relative to healthy controls [42–45]. Wallman et al. therefore suggest that the reduced exercise capacity seen in some patients with CFS might be explained by an abnormal sense of effort in these individuals and/or a reluctance to push toward full capacity [45]. On the other hand, we registered a mean RERp value of 1.07 in the patients with CFS, which demonstrates that these patients have cycled to the top of their potential.

More annoying speculation

Likewise, it is well documented that patients with CFS exhibit reduced daily PALs [20–21], and (part of) the cause of this deteriorated physical exercise capacity can possibly be found in the entailed downward spiral of physical inactivity and avoidance behavior toward physical activity.

(replying to them) Or it may not

 

[Dolphin]

(from Discussion)

In contrast with our hypothesis, increased PALs* were not associated with better cognitive performance in patients with CFS. We only observed negative relationships between sleep time, steps taken per day, and some Stroop accuracy scores. Our findings are not in line with those of Christodoulou et al. [25], who evidenced a positive relationship between cognitive impairment and functional daily activity disability, and Vercoulen et al. [24], who reported an association between low PALs and slowed motor and information processing speed in persons with CFS.

*Physical Activity Levels

 

[Dolphin]

A posteriori analysis of correlations between physical exercise capacity and PALs showed a positive relationship between these domains in both groups (higher VO2p values were related to higher physical activity time [>3 METs], physical activity energy expenditure [>3 METs], and mean energy expenditure). The fact that lower physical fitness but not lower PALs were associated with poorer cognitive performance, while we also found a significant positive relationship between PAL and VO2p, is interesting. As a result of these findings, it can be hypothesized that PAL is a potential mediator of the relationship between VO2p and cognitive function in patients with CFS.

The hypothesis in the last sentence seems questionable to me when PAL wasn't related to cognitive function.

 

[Dolphin]

Frank Twisk wrote a reply. It's here along with the authors' reply:
http://www.rehab.research.va.gov/jour/2013/509/pdf/letterstotheeditor509.pdf

 

[Esther12]

They're pretty happy to chuck ideas about us around without much concern about whether it's reasonable, or what harm it may do. What bold and pioneering thinkers they are.

A more moral approach might be less good for their careers: "Oops - another hypothesis shown to be flawed. We should probably keep any further speculations about these patients to ourselves until we have some more evidence to either support or refute our theories."