Cardio Kills Gains? How to Balance Strength Training and Cardio
The sentiment that cardio “kills” muscular gains found footing amongst those in the bodybuilding space as far back as the 1980s and 1990s. The main theoretical backings behind this are that there is an “Interference effect” between your body trying to adapt to the stimulus of resistance and endurance training simultaneously. The bro scientists also believe that your body will go catabolic and will start eating away at its muscle if you do cardio in addition to strength training. While these both sound good on paper, in practice they are both fundamentally wrong.
What is the Interference Effect?
The interference effect refers to the idea that combining endurance (cardio) and resistance (strength) training may impair muscle hypertrophy and strength gains due to conflicting cellular signaling pathways - primarily AMPK activation from endurance exercise inhibiting mTOR signaling, which drives muscle growth. However, recent evidence suggests the interference effect is context-dependent and often overstated. A 2012 meta-analysis by Wilson et al. found that concurrent training may slightly reduce strength and hypertrophy compared to resistance training alone, but only when endurance training volume is high and performed too close to lifting sessions (Wilson et al., J Strength Cond Res, 2012). More recent studies, such as by Fyfe et al. (2016), show that when appropriately programmed using moderate cardio intensity, adequate recovery, and separating modalities - the interference effect is minimal or non-existent (Fyfe et al., Sports Med, 2016). In fact, concurrent training can enhance mitochondrial function and cardiovascular health without compromising muscle gains when intelligently designed.
How do you Effectively Program Both Hypertrophy AND Cardio?
The question then stands: How do we structure training that includes cardiovascular exercise and hypertrophy concurrently? As we’ve seen through research, the main key points are:
- Cardio intensity and frequency matters - try to keep them more moderate and not overdo the cardio
- Prioritize what you want to improve the most at - If you want to maximize hypertrophy and have both weights and cardio planned for the same day, do weights first.
- Keep calorie/protein intake and weight training intensity high - You need adequate fuel and training stimulus to recover and build muscle, so don’t take it easy on your training or nutrition.
How a Sample Weekly Split Would Look:
- Monday: Lower Body Hypertrophy + Low Intensity Cardio
- Tuesday: Upper Body Hypertrophy + Core/stability training
- Wednesday: Rest Day
- Thursday: Conditioning + Mobility (HIIT training)
- Friday: Full Body Hypertrophy + Moderate Intensity Cardio (Zone 2-3)
The Bottom Line
To summarize, the Interference Effect is not as prominent as people have once believed. Cardio does not kill gains, and combining weight training and cardio can be highly effective for building muscle and improving cardiovascular health when programmed intelligently. By focusing resistance training on hypertrophy and strategically placing low to moderate intensity cardio on or around lifting days - while using high-intensity intervals on separate days, you can avoid the interference effect and prevent catabolism. Paired with adequate nutrition, recovery, and intensity management, concurrent training supports both muscle growth and endurance without compromise.