Cardiorespiratory and neuromuscular deconditioning in fatigued and non-fatigued breast cancer survivors.
OBJECTIVE
Fatigue is one of the most commonly reported side effects during treatment for breast cancer and can persist following treatment completion. Cancer-related fatigue after treatment is multifactorial in nature, and one hypothesized mechanism is cardiorespiratory and neuromuscular deconditioning. The purpose of this study was to compare cardiorespiratory and neuromuscular function in breast cancer survivors who had completed treatment and met the specified criteria for cancer-related fatigue and a control group of breast cancer survivors without fatigue.


METHODS
Participants in the fatigue (n = 16) and control group (n = 11) performed a maximal exercise test on a cycle ergometer for determination of peak power, power at lactate threshold, and VO(2) peak. Neuromuscular fatigue was induced with a sustained submaximal contraction of the right quadriceps. Central fatigue (failure of voluntary activation) was evaluated using twitch interpolation, and peripheral fatigue was measured with an electrically evoked twitch.


RESULTS
Power at lactate threshold was lower in the fatigue group (p = 0.05). There were no differences between groups for power at lactate threshold as percentage of peak power (p = 0.10) or absolute or relative VO(2) peak (p = 0.08 and 0.33, respectively). When adjusted for age, the fatigue group had a lower power at lactate threshold (p = 0.02) and absolute VO(2) peak (p = 0.03). There were no differences between groups in change in any neuromuscular parameters after the muscle-fatiguing protocol.


CONCLUSIONS
Findings support the hypothesis that cardiorespiratory deconditioning may play a role in the development and persistence of cancer-related fatigue following treatment. Future research into the use of exercise training to reduce cardiorespiratory deconditioning as a treatment for cancer-related fatigue is warranted to confirm these preliminary findings.
Department of Physical Therapy, University of British Columbia, Vancouver, BC, Canada.
Sarah E
SE
Neil
Riggs J
RJ
Klika
S Jayne
SJ
Garland
Donald C
DC
McKenzie
Kristin L
KL
Campbell
D000328:Adult; D000368:Aged; D015308:Anaerobic Threshold; D001943:Breast Neoplasms / Q000628:therapy*; D018493:Cardiovascular Deconditioning / Q000502:physiology; D005080:Exercise Test; D005221:Fatigue / Q000209:etiology*; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D052097:Quadriceps Muscle / Q000378:metabolism; D017741:Survivors
D019344:Lactic Acid