Colorectal cancer (CRC) is one of the most common cancers in Western countries and is the second most common cancer for both men and women in Australia. Though 5-year CRC survival has significantly improved in recent years, incidence of the disease has remained relatively stable, therefore increasing the number of people living in CRC survivorship. It is well understood that those living in CRC survivorship are at a heightened risk of again developing the disease.
Though the mechanisms are still not clearly understood, physical activity (PA) levels and intensity are inversely related to the risk of CRC recurrence. A potential factor involved in the relationship between PA and CRC development in CRC survivors is interleukin-8 (IL-8), a recognised molecular driver of cancer growth that can be influenced by exercise. Further justifying the importance of PA to CRC survivors is its ability to improve aerobic fitness and body composition, two health parameters that are often poor in CRC survivors. The primary purpose of the present study was to examine the influence of exercise intensity on IL-8 in a sample of CRC survivors. The secondary purpose was to examine potential changes in peak oxygen consumption (V̇O2peak) and body composition in response to exercise training completed at two different intensities.
Eighteen CRC survivors were randomly assigned to either a high intensity interval training (HIIT) or moderate intensity training (MIT) group. Participants completed three exercise sessions a week for eight weeks on a cycle ergometer. Each HIIT training session required participants to complete four intervals of 4 minutes each at 85-95% peak heart rate (HRpeak) while in each MIT session, participants completed 50 minutes of exercise at 70% HRpeak. Physiological testing was conducted at baseline (0 weeks), midpoint (4 weeks), and endpoint (8 weeks) of the intervention. Physical activity and diet were controlled in the seven and three days preceding testing respectively. Physiological testing sessions included assessment of V̇ O2peak and body composition using dualenergy X-ray absorptiometry (DXA), with blood collected and analysed for plasma IL-8 concentrations.
IL-8 did not significantly change in either training group at any timepoint. However, secondary analysis of participants from both groups who had elevated baseline IL-8 concentrations (n=4) approached significance for the eight weeks of exercise training to reduce IL-8 values (P=0.068). V̇ O2peak significantly improved in both HIIT and MIT groups after 4 weeks (26.6%, P=0.036 and 3.0%, P=0.043 respectively) and 8 weeks (28.1%, P=0.015 and 7.2%, P=0.018 respectively). After 8 weeks, there was also a group-effect favouring HIIT for improvement in V̇ O2peak (P=0.041). Fat mass and body fat percentage were significantly lower in the HIIT group after 4 weeks (-3.7%, ! P<0.01 and (-3.7%, P<0.01) and 8 weeks (-4.9%, P<0.01 and (-3.7%, P<0.01) compared to the MIT group where no changes were observed for either variable. Similarly, lean mass increased in the HIIT group after 4 weeks (+2.2%, P<0.01) and after 8 weeks (+1.9%, P<0.01) but no change in lean mas was found for the MIT group at either timepoint. Changes in lean mass were greater for the HIIT group than the MIT group at 8 weeks (P<0.01). Reductions in fat mass were greater after 4 weeks and 8 weeks for the HIIT group than the MIT group (P=0.046 and P=0.017 respectively).
In summary, exercise failed to elicit significant changes in IL-8 in CRC survivors, likely due to baseline values in IL-8 being within normal ranges. The significant training-induced changes in V̇ O2peak, fat mass, lean mass, and fat percentage found for the HIIT group are potentially clinically meaningful and important, as similar improvements in these markers have previously been associated with reduced cancer specific- and all cause-mortality. The present study has shown that HIIT appears to be a safe and effective mode of exercise for rapidly improving cardiorespiratory fitness and body composition in CRC survivors.