Introduction: Does Cardio Really Kill Strength Gains?
The interference effect suggests that doing cardio and strength training together could compromise muscle gains. But what does science say about whether cardio really kills strength gains? This debate is especially relevant for hybrid athletes preparing for events like Hyrox and Deka, where strength and endurance are equally important.
The so-called interference effect suggests that doing both types of training can compromise progress. But is this backed by science — or is it just an old myth?
What Is the Interference Effect?
The Origin of the Concept
The discussion started with a landmark study by Hickson (1980), where subjects who combined endurance and resistance training gained less strength and muscle compared to those who only lifted weights. This became the foundation for the phrase “cardio kills gains.”
Modern Understanding
More recent studies suggest the effect isn’t so black and white. Interference happens under certain conditions — like very high endurance volume or poor recovery — but with smart planning, strength and endurance can coexist and even complement each other.
Strength and Endurance – Different Adaptations
How Strength Training Works
- Increases muscle fiber size (hypertrophy).
- Improves nervous system efficiency (motor unit recruitment).
- Enhances maximal strength and power output.
How Endurance Training Works
- Improves VO₂ max and aerobic capacity.
- Increases mitochondrial density and capillarization.
- Enhances energy efficiency and fatigue resistance.
The Cellular “Conflict”
At the molecular level, two pathways are often mentioned:
- mTOR → stimulates muscle growth.
- AMPK → triggered by endurance, can suppress mTOR.
This “competition” partly explains the interference effect, but in practice, it depends on training design.
The Science Behind the Interference Effect
Key Research Findings
- Hickson (1980): concurrent training reduced strength and hypertrophy.
- Wilson et al. (2012, meta-analysis): running had more interference than cycling; frequency and volume matter.
- Fyfe et al. (2014): separating endurance and strength sessions by several hours reduces interference.
- Schoenfeld et al. (2016): when programmed well, strength and endurance can coexist without major compromise.
Balancing Cardio and Strength for Optimal Results
- Long-duration endurance (like marathon training) interferes more than short HIIT.
- Cycling/rowing cause less interference than running.
- Separation of sessions (e.g. morning run, evening lift) improves adaptations.
- Training priority matters: if strength is the goal, lift first.
Practical Strategies to Minimize the Interference Effect
For Hyrox and Deka athletes, avoiding cardio is impossible — running is half the event. The challenge is balancing endurance and strength so one doesn’t hold back the other.
Example weekly split:
1 hybrid session (simulate race with stations).
3 strength sessions (lower body, upper push, upper pull).
2 endurance sessions (interval running + steady run).
How to Minimize the Interference Effect
- Separate sessions by at least 6 hours when possible.
- Prioritize your main goal — lift first if strength is the focus.
- Don’t overload endurance volume — keep it race-specific.
- Focus on recovery — sleep, protein intake, hydration.
- Choose smart cardio — cycling, rowing, and intervals are less “destructive” to strength than long-distance running.
Conclusion
The myth that “cardio kills gains” is oversimplified. While interference can occur, it is largely preventable through smart programming. For hybrid athletes, the combination of strength and endurance is not only possible — it’s essential.
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Disclaimer: This training guide is an independent resource and is not officially affiliated with or endorsed by HYROX or DEKA FIT. All trademarks belong to their respective owners.
