Introduction Deteriorations in cardiorespiratory fitness (Vo2peak) and body composition are associated with poor prognosis after colorectal cancer treatment. However, the optimal intensity and frequency of aerobic exercise training to improve these outcomes in colorectal cancer survivors is unknown.

Patients and Methods This trial compared 8 weeks of moderate-intensity continuous exercise (MICE; 50 minutes; 70% peak heart rate [HRpeak]; 24 sessions), with high-intensity interval exercise (HIIE; 4 × 4 minutes; 85%-95% HRpeak) at an equivalent (HIIE; 24 sessions) and tapered frequency (HIIE-T; 16 sessions) on Vo2peak and on lean and fat mass, measured at baseline, 4, 8, and 12 weeks.

Results Increases in Vo2peak were significantly greater after both 4 (+3.0 mL·kg−1·min−1, P = .008) and 8 (+2.3 mL·kg−1·min−1, P = .049) weeks of HIIE compared to MICE. After 8 weeks, there was a significantly greater reduction in fat mass after HIIE compared to MICE (−0.7 kg, P = .038). Four weeks after training, the HIIE group maintained elevated Vo2peak (+3.3 mL·kg−1·min−1, P = .006) and reduced fat mass (−0.7 kg, P = .045) compared to the MICE group, with Vo2peak in the HIIE-T also being superior to the MICE group (+2.8 mL·kg−1·min−1, P = .013).

Conclusion Compared to MICE, HIIE promotes superior improvements and short-term maintenance of Vo2peak and fat mass improvements. HIIE training at a reduced frequency also promotes maintainable cardiorespiratory fitness improvements. In addition to promoting accelerated and superior benefits to the current aerobic exercise guidelines, HIIE promotes clinically relevant improvements even with a substantial reduction in exercise training and for a period after withdrawal.