Dissertation Abstract

Muscle function and cancer-related fatigue in cancer survivors

Cancer-related fatigue (CRF) is a common and debilitating complaint among cancer survivors, both during and post treatment. Its cause is unknown but it is likely multifactorial with psycho-social and physiological contributions. Because exercise is a successful intervention in CRF, it was hypothesized that muscle function contributes to CRF. The purpose of this study was to examine the relationship between muscle function and CRF in cancer survivors undergoing radiation therapy.

Sixteen cancer survivors (14 prostate, 2 lung) were tested prior to and following 6 weeks of external beam radiation therapy. A control group of 12 subjects underwent a time control of 6 weeks. At each session CRF (Revised-Piper Fatigue Scale), sleepiness, depression, and cognition were measured. Maximal voluntary contraction (MVC) or strength, and endurance were examined using intermittent isometric exercise of the dorsiflexor muscles contracting at 40% MVC at a 75% duty cycle (6 secs on, 2 secs off) until task failure. Muscle fatigue was quantified as the post/pre exercise MVC. Endurance time (ET) was the time to task failure. To determine the role of central and peripheral mechanisms during the fatigue task, an interpolated force technique was utilized before and after the fatiguing task.

Data analyses were by non-parametric and parametric statistics. Results are mean ± SE. Prior to radiation, cancer survivors reported higher CRF than controls, however sleepiness, depression, cognition, strength, and ET were not different. Following radiation, ET was significantly decreased in the cancer survivors (p=0.027), with a significant difference between groups (p=0.05), despite similar strength and MVC fatigue. In cancer survivors, CRF increased after radiation (pre, 24±6, post, 51±9, p=0.004). Following, but not prior to radiation, depression and CRF were correlated (r=0.675). In addition, the sensory subscale of the R-PFS and ET were correlated (r=-.578, p=0.038) in cancer survivors following radiation. Differences in ET resulting from radiation were not explained by central or peripheral factors, however cancer subjects had a significant, but not clinical, decrease in hemoglobin (p=0.007). It was concluded that 6-wks of radiation causes an increase in already present CRF in cancer survivors. In addition, depression, Hb and ET are associated with CRF.

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