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Mechanisms of Fatigue in Cancer Survivors: 9298:00 AM – 8:15 AM

Ng, Alexander V. FACSM; Alt, Carlynn; Gore, Elizabeth; Jablonski, Kristen; Montagnini, Marcos; Stern, Jean; Dufek, Shelly

Medicine & Science in Sports & Exercise: May 2006 - Volume 38 - Issue 5 - p S82
Presidential Closing Remarks 12:05 PM – 12:15 PM: Immediately Following President's Lectures ROOM: Ballroom 2/3 and Ballroom 1: E-16 Free Communication/Slide – Clinical Exercise Physiology – Cancer: FRIDAY, JUNE 2, 2006 8:00 AM – 9:30 AM ROOM: 612

1Marquette University, Milwaukee, WI.

2Medical College of Wisconsin, Milwaukee, WI.

3Veterans Affairs Medical Center, Milwaukee, WI


Funded by the Lance Armstrong Foundation

Cancer-related fatigue (CRF) is a common complaint in cancer survivors (CS). It can be present before, during, or some time after therapy and can be debilitating. The cause of CRF is unknown but it is likely multi-factorial and it has been suggested that CRF may have a neuromuscular component.

PURPOSE: To determine if muscle fatigue and endurance becomes worse during radiation therapy and contribute to CRF in CS.

METHODS: 16 men with cancer (14 prostate, 2 lung) were tested pre and post 6 weeks of curative external beam radiation therapy. 12 age-matched control subjects (C) were tested 6 weeks apart with no intervention. At each session we assessed CRF with the Modified Piper Fatigue Scale (PFS) which consists of 4 subscales, sleepiness (Epworth scale), and depression (CES-D). Strength or maximal voluntary contraction (MVC) and endurance were examined using intermittent isometric ankle dorsiflexor exercise at 40% MVC (6 s contract, 2 s relax) until task failure. Muscle fatigue was quantified by the post/pre exercise MVC. Endurance time (ET) was the time to task failure. The degree of central motor activation was assessed with the central activation ratio (CAR), an interpolated force technique where CAR = MVC/ (MVC+ superimposed force). Data were analyzed using rmANOVA, paired comparisons, and Pearson correlations.

RESULTS: Results are mean ± SE. Cancer survivors tended to report higher CRF than C prior to radiation (CS = 24±7, C = 9±3, p=0.06) but neither sleepiness, depression, strength, muscle fatigue, nor ET, were different (p>0.5). Following radiation, CRF increased only in the CS group (p <0.001) and was greater than C (CS = 51 ±12, C = 12±4, p <0.001). No changes were noted in depression or sleep for either group post radiation. ET decreased in the cancer survivor group (pre= 556 ± 98s, post= 391 ± 51s, p=0.03), with no change in strength. In contrast, ET in the C group increased (pre= 616 ± 112s, post= 753 ±160s, p=0.03) with no change in strength. The change in ET differed between CS and C groups (p=0.002). All participants fatigued to a similar end point in both the pre- and post-radiation therapy and time control sessions (∼58%, p>0.7). Changes in CAR could not explain the decreased ET in CS after radiation. Following but not prior to radiation, depression and CRF were correlated (r=0.64, p=0.01) as was the sensory subscale of the PFS and ET (r =−0.60, p = 0.03).

CONCLUSIONS: A 6-week course of radiation therapy in cancer survivors results in decreased muscle endurance consistent with decreased oxidative capacity. This change in muscle function contributes to CRF as does depression.

© 2006 American College of Sports Medicine