Introduction 
Colorectal cancer (CRC) although potentially fatal, can be successfully treated with surgery alone. However, the physiological burden of both cancer and surgery has detrimental impacts on physical function, and as a result quality of life. UK cancer treatment guidelines dictate a maximum of 31 days between decision to treat and surgery, leaving a short time window in which to optimise physical condition through prehabilitation. High-intensity interval training (HIIT) prehabilitation has been shown to improve the physical function of other cancer cohorts [2], but not those with CRC [3]. It may be that HIIT combined with resistance exercise training (ReHIIT) can overcome the adaptive blunting   observed in CRC patients, potentially improving two key aspects of physical function: cardiorespiratory function and muscle strength [4]. The aim of this study was to determine the effects of HIIT versus ReHIIT prehabilitation on commonly used clinical measures of physical function in individuals with CRC.

Methods 
18 CRC patients due to undergo intended curative surgery (5 females; 66 ± 8 years) completed assessments of physical function before and after a period of HIIT (n=9, 1 female, 65 ± 8 years) or ReHIIT (n=9, 4 females, 66 ± 7 years) prehabilitation (randomised). The maximum intervention period was 4-weeks. All participants completed a minimum of 8 prehabilitation sessions, with HIIT performed on a cycle ergometer (5 x 1-minute maximal efforts) and RET performed on cabled machines (3 upper- and 3 lower-body). Distance achieved in the six-minute walk test (6MWT), distance of centre-of-pressure movement during a 30 s right leg balance, and handgrip strength of the right hand were assessed. Data was analysed using 2-way repeated measures ANOVAs with significance assumed as p<0.05. 

Results
No significant difference was observed in 6MWT performance in either group following training (HIIT: 504.6 ± 38.1 vs. 510.8 ± 49.4 m, ReHIIT: 511.1 ± 78.1 vs. 536.9 ± 99.0 m; p=0.51). Similarly, no significant difference was observed in handgrip strength in either exercise modality group (HIIT: 41.1 ± 8.8 vs. 41.4 ± 8.0kg, ReHIIT: 32.8 ± 8.6 vs. 33.4 ± 8.1 kg; p=0.90). Although there was no significant difference in balance performance in either exercise modality group following training, there was a signal of effect (HIIT: 1374 ± 799 vs. 1987 ± 1471 mm, ReHIIT: 1819 ± 792 vs. 1413 ± 833 mm; p=0.06). 

Conclusion 
Neither HIIT nor ReHIIT prehabilitation led to changes in physical function in the short training period before surgery in CRC patients as measured by commonly used clinical tools. It may be that the mandated time frame for intervention is too short to elicit change in this population, or that these tools are not sensitive enough to detect significant change. With known benefits of improving muscle mass and strength, and cardiorespiratory fitness in the pre-operative period, future work should implement assessments specific to these physiological endpoints. In addition, achieving mechanistic understanding of the blunted adaptive capacity seen in CRC patients should be a focus of future work.