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The Dunedin Fatigue Study

Spring has sprung and you’re thinking about doing a physical and mental stocktake? A New Zealand study shows how the two are related for people with rheumatoid arthritis (RA) and osteoarthritis (OA).

Called the Dunedin Fatigue Study, it showed how more physical activity might improve mood. It also showed how overcoming fatigue with exercise might have a positive effect.

In a cohort of 70 patients with rheumatoid arthritis (RA) and 72 patients with osteoarthritis (OA), investigators confirmed that an increase in daily fatigue was associated with reductions in positive mood and an increase in negative mood when controlling for pain and physical activity.

But physical activity moderated the relationship between daily fatigue and positive mood, although not negative mood.

On low physical activity days, there was a significantly stronger relationship between fatigue and positive mood (P<0.01) and this relationship, though weaker, remained significant on high physical activity days (P<0.01) -- suggesting that physical activity had a buffering effect on the fatigue and positive mood relationship.

"We investigated whether physical activity moderated the within-person relationship between daily fatigue and positive and negative mood," Gareth J. Treharne, PhD, of the University of Otago in Dunedin, New Zealand, and colleagues wrote in Arthritis Care & Research.

"And this is the first study to show that higher physical activity may alleviate the detrimental effect of fatigue on daily well-being."

The Dunedin Fatigue Study is a cohort study investigating predictors of fatigue among patients with arthritis.

Fatigue, pain, and mood were each measured on a regular schedule in the morning, mid-morning, mid-afternoon, and evening for 7 days.

"This schedule allowed us to aggregate fatigue (and pain and mood) across the entire day rather than relying on a single end-of-day report which can introduce memory bias," the study authors explained.

Each parameter was measured using a numerical rating scale while physical activity was tracked by having participants wear a pedometer to objectively estimate daily physical activity at the end of each day.

For the average participant, low physical activity days equated to 1,775 steps fewer than average, while high physical activity days equated to 1,775 more steps than average.

"There are several possible reasons why physical activity may act as a fatigue-mood buffer," the researchers wrote.

Physical activity is associated with positive physiologic effects, including the release of endorphins that may in part explain the elevation in positive mood and the reduction in negative mood following a period of physical activity.

Being physically active may also provide patients with a sense of achievement and engagement with valued or meaningful activities while being less physically active may represent disengagement from valued activities.

The behavioural literature also suggests that engaging in a higher level of activity is associated with improved mood, particularly when the activity is meaningful or done in a pleasant environment.

"People with arthritis may avoid being physically active on high-fatigue days in an attempt to control their fatigue," study authors note.

"However, the fatigue associated with arthritis is often pervasive and unresponsive to rest and avoidance of activity may be harmful in the long term due to deconditioning, less exposure to positive mood-induced events, and loss of social contact."

The authors caution that the study's correlational design limits causal interpretation of the data.

"Results of qualitative research support the idea that fatigue is driving changes in mood; however, an alternative possibility is that mood may drive changes in fatigue and positive mood," investigators speculated.

Regardless of the causal direction, physical activity still moderated the link between fatigue and positive mood observed in the study, they added.

The authors also noted that the effect size for the exercise effect on positive mood was relatively small.

Positive and negative mood were also measured only with a single term: "happy" and "frustrated," both of which represented moderately activated mood states.

"Therefore, the observed effects may not extend to high activation (excited, angry) or low activation (calm, sad) mood states," they stated.

Lastly, it was not clear from the data whether subjects were engaged in purposeful physical activity or whether they were simply more active in their family life completing chores, caring for family, or working.

"The current study suggests that increased physical activity on high-fatigue days may be beneficial to arthritis patients' mood in everyday life," investigators concluded.

"Further research is needed to determine whether this buffering effect is due to physiological processes relating to exercise per se or due to increases in meaningful activity."