Chronic fatigue syndrome (CFS) represents a significant public health concern, possibly affecting as many as 800,000 individuals (primarily adolescents and adults) within the United States 1, 2
. It is a debilitating disorder, characterized by persistent fatigue lasting for more than 6 months. The symptoms are not improved by bed rest and are typically exacerbated by physical and mental activity 3, 4
In adolescents, CFS accounts for marked functional impairment and educational disruption 5
. Research suggests that infectious mononucleosis may be one disease process that leads to symptom complexes involving severe fatigue and associated physical and cognitive symptoms6, 7, 8
. In some cases, these symptom complexes endure for six or more months and cohere with international case criteria for CFS 4, 7, 8
Studies indicate that many individuals with CFS recall a sudden, infectious onset characterized by fever, pharyngitis, and lymphadenopathy9, 10,11,12,13
. This observation appears particularly frequent in adolescent samples14, 15
. In retrospective studies, rates of acute, mononucleosis-like illness preceding chronic fatigue have been documented in 73-78% of adolescents, with 46.7% recalling an active mononucleosis infection at onset 12, 13, 16
. A recent, prospective investigation by our team found that 13% of adolescents presenting with acute mononucleosis infection failed to recover and met criteria for CFS 6 months later 17
. Seven percent continued to meet CFS criteria 12 months later and four percent still met criteria 24 months later. Most individuals recovered with time, but those whose symptoms were consistent with CFS remained quite disabled. Questions remain as to what, in addition to the original mononucleosis infection, led to recovery failure in this subgroup of adolescents.
In addition to the role of infectious disease, evidence also points to the role of activity levels18
as risk or perpetuating factors for CFS. Some studies suggest that high “action-proneness’” or over activity prior to CFS onset may serve as a risk factor for CFS18,19,20,21
MacDonald and associates found that a great number of individuals with CFS exercised more regularly, and for a longer period of time, in the year before illness onset compared with controls.
On the other hand, underactivity, deconditioning, activity avoidance, and poor physical fitness have all been cited as potential perpetuating factors once a patient is ill with CFS22, 23
. Bed rest has also been implicated once a patient has contracted mononucleosis and has subsequently developed CFS24
. Van der Werf and associates measured and classified the actual physical activity levels over a 12-day period and found that the CFS sample had less intense and shorter activity peaks, while the average rest periods that followed these peaks were longer than those of the control group.
White and associates25
found that number of days in bed and low physical fitness predicted CFS 6 months after mononucleosis onset. They argued that characteristics of the infection and its consequent immune reaction may play a more significant role earlier in the post–infectious process, but physical deconditioning may lead to delayed recovery over time. Meanwhile, Fulcher and colleagues reported that patients with CFS were physically weaker, had a significantly reduced exercise capacity, and perceived greater effort during exercise, when compared with sedentary controls. Low exercise capacity in patients with CFS that was related to quadriceps muscle weakness, low physical fitness, and a high body mass index, implied that physical deconditioning helped to maintain physical disability in CFS 23
Similarly, Bazelmans et al. did not find any significant differences in physical fitness between CFS patients and controls, but found that more CFS patients failed to achieve a physiological limitation at maximal exercise. Physical fitness levels were highly correlated with participants’ reports of daily physical activity26
With few exceptions findings from adult studies are largely retrospective and mixed regarding the role of physical activity in the development and perpetuation of CFS25
. Moreover, little is known about the role of physical activity in the development of CFS in an adolescent sample. This study focused on a narrowly-defined subgroup of adolescents with CFS and a group of matched controls, all of whom shared a common infectious onset. We tracked physical activity levels before, during, and after infection to shed more light on the role of activity in the onset and course of CFS over time. Our central objective was to compare adolescents who did and did not recover from acute infectious mononucleosis in terms of fatigue severity and activity levels before, during, and in the two years following infection. We therefore sought to determine whether:
- Adolescents with CFS would report higher fatigue severity compared with controls at all time points.
- In the year before mononucleosis onset, adolescents who later developed CFS would have been more physically active than controls that experienced a normal recovery from infection.
- During mononucleosis, adolescents who later developed CFS would have been less physically active than controls that experienced a normal recovery from infection.
- Adolescents with CFS would demonstrate decreased activity levels and increased sleep as compared with controls at all follow-up time points (6-, 12-, and 24-months after infection).