HIFT Boosts VO2max by Up to 15% and Strength by 20% for Hybrid Sport Athletes

Hybrid competitions—events demanding both sustained cardiovascular endurance and repeated bouts of functional strength—are surging in popularity. Formats like CrossFit and HYROX ask athletes to seamlessly integrate running, rowing, weightlifting, and gymnastics under fatigue. Yet the science underpinning optimal preparation for these events has lagged behind their growth. This scoping review set out to map what is actually known about the physiological and psychobiological demands of HIFT and hybrid competition.

Following the Arksey and O'Malley framework and PRISMA-ScR guidelines, the authors searched Web of Science, Scopus, and PubMed between December 2024 and May 2025. From 331 initial records, 39 peer-reviewed studies published between 2015 and 2025 were included after screening. Populations ranged from recreational practitioners to elite CrossFit Games competitors. Quality was appraised using the AXIS cross-sectional study tool.

The most consistent finding was that HIFT produces meaningful aerobic adaptation: VO2max improvements of 8–15% were commonly reported. Strength gains of 10–20% in major compound lifts (e.g., power clean, squat) were also documented. HYROX-specific data from a simulated competition study found athletes spent roughly 80% of race time in the very high heart rate zone, with VO2max, low body fat percentage, and resistance training volume correlating most strongly with finish time. Wall balls emerged as the single most physiologically demanding station. For CrossFit athletes, a composite Total Athleticism Score (TSA) correlated strongly (r = 0.91) with CrossFit Open performance, underscoring that no single capacity dominates—versatility is key.

Psychobiological dimensions were a notable secondary theme. HIFT elicited significantly higher perceived exertion, blood lactate, and peak heart rate compared to traditional high-intensity circuit training (HICT) matched for average HR. More experienced athletes demonstrated superior fatigue tolerance and maintained performance more consistently under metabolic stress. Sex differences emerged in anaerobic performance, with men showing higher absolute peak and mean power, though gaps narrowed substantially when normalised to lean mass.

The review reinforces that HIFT's concurrent training stimulus—combining strength and endurance in the same session—need not produce the classical 'interference effect' when programming is appropriately structured. Recovery windows of 48–72 hours appear necessary after maximal HIFT sessions. Critically, the physiological benefits were more pronounced in already-trained individuals, suggesting that baseline fitness amplifies adaptation. Coaches and athletes can use these findings to justify HIFT as a foundational training method for hybrid sport preparation, while recognising that event-specific demands (e.g., HYROX's fixed sequence vs. CrossFit's variable WODs) call for targeted supplementary work.