The Old Interference Dilemma
The central worry for those who love both lifting and running is the 'interference effect'. The theory, which dates back to a 1980 study, suggests that the physiological signals sent by endurance exercise can interfere with the signals for muscle growth
from strength training. In simple terms, the body gets conflicting messages. One pathway (AMPK) is activated by cardio to restore cellular energy, which can be a catabolic (breaking down) process. The other, for muscle building (mTOR), is an anabolic (building up) process. The fear was that you couldn't effectively do both at once, and your cardio would 'kill your gains'. While this effect is real, decades of follow-up research show the reality is far more nuanced and less dramatic than many believe.
What New Research Reveals
Recent large-scale studies have provided a clearer picture, shifting the focus from interference to synergy. A major study published in the British Journal of Sports Medicine tracked nearly 150,000 adults over three decades. The findings were compelling: combining both aerobic exercise and resistance training delivered the strongest overall survival benefits and a lower risk of dying from any cause. Specifically, people who did about 90 to 120 minutes of strength training per week saw a 13% lower risk of early death. When this was paired with regular aerobic activity, the protective benefits were even greater, reinforcing that the two types of exercise work better together. The consensus is clear: for general health and longevity, a combined approach is the undisputed winner.
Does the Order of Exercise Matter?
If you're going to do both in the same session, the order can make a difference depending on your primary goal. A 2025 study found that participants who lifted weights before their cardio session experienced greater reductions in overall body fat. The logic is that resistance training depletes your muscles' quick-access energy stores (glycogen), prompting your body to tap more into fat for fuel during the subsequent cardio workout. However, for pure performance, the advice is simpler: do the exercise that is most important to your goals first, when you are freshest. If you're training for a race, start with your run. If your main goal is building strength, hit the weights first.
Smart Ways to Structure Your Week
For most people who aren't elite athletes, the interference effect is small and can be managed with smart programming. Modern analyses show that the biggest negative impact is on explosive power, and primarily only when strength and cardio are performed back-to-back in the same session. To get the best of both worlds, consider these strategies. First, separate your sessions. If possible, do your strength workout in the morning and cardio in the evening, or on alternate days. A gap of at least three hours is recommended to allow your body's signalling pathways to reset. Second, manage your volume. The sweet spot for strength training's longevity benefits appears to be around 90-120 minutes per week. More than that didn't show additional mortality reduction in a recent major study. Finally, consider the type of cardio. Some research suggests lower-impact options like cycling interfere less with lower-body strength gains than high-impact running.
