If your goal is building muscle, cardio isn’t the enemy—but too much of the wrong kind, done too often, or placed too close to your lifting can slow hypertrophy. This is called the concurrent training “interference effect”: when endurance training and resistance training compete for recovery and adaptation.
Below is what the research suggests about how much cardio is “safe,” what types are most likely to interfere, and how to structure it so you can stay fit and keep building muscle.
What the “interference effect” actually means
Interference doesn’t mean “no gains.” It usually means:
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slower lower-body strength gains
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less muscle growth (especially legs/glutes)
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more fatigue that reduces your lifting quality (less load, fewer hard sets, weaker performance)
A classic early study showed that adding a high volume of endurance work to strength training reduced strength development compared with strength training alone (Hickson, 1980). Later meta-analyses and reviews support that the risk of interference rises as endurance volume, frequency, and impact increase (Wilson et al., 2012; Baar, 2014; Fyfe et al., 2014).
The 3 cardio variables most likely to interfere with hypertrophy
1) Too much total volume
Cardio becomes more “interfering” when it meaningfully increases weekly fatigue and recovery demands—especially when you’re already training hard for hypertrophy.
The biggest red flags:
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Long sessions (45–60+ minutes) done frequently
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High weekly frequency (4–6 cardio days/week) on top of serious lifting
Meta-analytic data suggests endurance frequency and duration are key drivers of interference (Wilson et al., 2012).
2) High-impact modalities (running > cycling)
Running tends to be more problematic than cycling for hypertrophy and strength outcomes in concurrent training research—likely due to greater eccentric muscle damage and higher recovery cost (Wilson et al., 2012).
If legs/glutes are a priority: running is the first thing I’d reduce, swap, or re-schedule.
3) Poor timing (too close to lifting)
When cardio and lifting are crammed together (or cardio is done right before leg training), it can reduce:
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training performance (loads/reps)
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quality “hard sets”
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recovery between sessions
Spacing sessions improves your odds of getting the best of both worlds (Fyfe et al., 2014).
How much cardio can start to slow muscle gains?
There isn’t one magic number, but the pattern across research is:
“Low interference” range (for most lifters prioritizing muscle)
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2–3 cardio sessions per week
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20–30 minutes each
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low to moderate intensity (you can still talk in short sentences)
This is often enough for heart health, work capacity, and keeping body composition moving without stealing recovery from lifting.
“Higher interference risk” range (especially for legs/glutes)
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4+ sessions/week and/or
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30–60+ minutes/session and/or
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lots of running, hills, long intervals, or frequent HIIT
The more you push endurance volume and intensity, the more carefully you must manage recovery and training order (Wilson et al., 2012; Baar, 2014).
What type of cardio is best if you want hypertrophy?
Best choices (hypertrophy-friendly)
Low-impact, easy-to-control modalities:
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incline walking
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cycling
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rowing (moderate)
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elliptical / stair mill (moderate)
These tend to deliver conditioning with a lower “recovery tax,” especially compared with running (Wilson et al., 2012).
HIIT: helpful, but dose matters
HIIT can build fitness efficiently, but it’s still a high stress stimulus. If you use it, keep it low volume:
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1–2 HIIT sessions/week
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short total work time (example: 6–10 hard minutes total inside the session)
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avoid stacking HIIT right before heavy leg days
If hypertrophy is your priority, HIIT is best treated like a “workout,” not a casual add-on (Fyfe et al., 2014; Baar, 2014).
The simplest rules to do cardio without sacrificing muscle
Rule 1: Lift first (if done the same day)
If you must do both in one session:
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weights first
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cardio after (or keep it very easy before as a warm-up)
Rule 2: Separate cardio and lifting by ~6+ hours when possible
AM cardio / PM lift (or different days) is usually better for performance and recovery than back-to-back sessions (Fyfe et al., 2014).
Rule 3: Put the hardest cardio away from leg day
If you care about legs/glutes growth:
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keep leg days “fresh”
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do harder cardio on upper-body days or separate days
Rule 4: Choose low-impact cardio when muscle gain is the goal
If you love running, you don’t have to quit—just understand it’s more likely to interfere at higher volumes than cycling/walking (Wilson et al., 2012).
Rule 5: Fuel like someone who’s trying to grow
If your calories and carbs are too low, cardio becomes even more costly because recovery is underfunded. Muscle gain requires:
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enough total calories
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plenty of protein
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adequate carbs to support training quality
Quick cardio templates for muscle gain goals
If your main goal is hypertrophy (especially lower body)
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2x/week: 20–30 min incline walk or bike (easy/moderate)
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Optional: 1x/week short HIIT only if recovery is solid
If you want hypertrophy + noticeable conditioning improvements
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2x/week: 25–35 min moderate cycling/elliptical
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1x/week: brief HIIT (low total volume)
If fat loss is also a goal (but you still want muscle)
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Add cardio gradually, but protect lifting performance first
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Increase steps, add short low-intensity sessions before piling on HIIT or long runs
Bottom line
Cardio won’t “ruin” muscle gains—but interference becomes more likely when you combine high frequency + long duration + high impact (running) + poor timing while also trying to train hard for hypertrophy.
If you want the simplest hypertrophy-friendly approach:
2–3 low-impact sessions/week, 20–30 minutes, moderate intensity, separated from lifting when possible.
References
Baar, K. (2014). Using molecular biology to maximize concurrent training. Sports Science Exchange, 27(136), 1–6.
Fyfe, J. J., Bishop, D. J., & Stepto, N. K. (2014). Interference between concurrent resistance and endurance exercise: Molecular bases and the role of individual training variables. Sports Medicine, 44(6), 743–762.
Hickson, R. C. (1980). Interference of strength development by simultaneously training for strength and endurance. European Journal of Applied Physiology and Occupational Physiology, 45(2–3), 255–263.
Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M. C., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: A meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293–2307.
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