Are there non-responders to hiit in cancer survivors? changes in cardiorespiratory fitness, body composition and systemic inflammation

INTRODUCTION High intensity interval training (HIIT) has been shown to elicit significant improvements in VO2peak in cancer survivors. Only 46-60% of healthy individuals are reported to respond to exercise interventions, though this rate has not been investigated in cancer survivors. AIMS: To determine the response rate in cancer survivors over 28-weeks of HIIT as measured by changes in cardiorespiratory fitness. Secondarily, the study aimed to observe associations between changes in cardiorespiratory fitness, body composition and inflammatory markers. METHODS 131 survivors of breast, prostate or colorectal cancer were observed over 28-weeks of HIIT (4x4 minutes; 85-95% HRpeak). VO2peak, body composition and markers of systemic inflammation were assessed at baseline, four-, 16- and 28-weeks. An improvement in VO2peak of 3.5 ml.kg-1.min-1 was used as a standard of minimal clinically important difference (MCID). Body composition was measured using DEXA, and inflammatory markers were assessed for each timepoint. RESULTS 59.6% of participants improved their VO2peak greater than MCID (+3.5 ml.kg-1.min-1) and these individuals were retrospectively classified as responders. Responders showed improvements in VO2peak at four- and 16-weeks and maintained this change through to 28-weeks (0-4 weeks: +2.92 ml.kg-1.min-1, p<0.001; 0-16 weeks: +5.70 ml.kg-1.min-1, p<0.001; and 0-28 weeks: +5.30 ml.kg-1.min-1, p<0.001). No significant change in VO2peak was seen in non-responders (40.4%). Time since treatment, cancer type, and cancer treatment were all found to contribute to a model predicting VO2peak change (R=0.464, R2 = 21.5%., adj R2=16.1%, p<0.001). Body composition and inflammatory markers improved in response to training however were not associated with VO2peak change. CONCLUSIONS HIIT elicited a MCID in VO2peak in almost 60% of cancer survivors. Independent to VO2peak change and cancer type, survivors showed significant favourable changes in inflammation and body composition in response to training.