Key Takeaways
- Doing cardio and strength training in the same program can be effective when sessions are structured thoughtfully.
- High volumes of endurance exercise can limit some strength and muscle-building adaptations.
- Separating cardio and strength sessions by several hours, or placing them on different days, reduces interference.
- The type and intensity of cardio matters: cycling tends to interfere less with leg strength gains than running does.
- Most adults benefit from both exercise types and do not need to choose one over the other.
Concurrent training
Concurrent training refers to combining both aerobic exercise (cardio) and resistance training (strength work) within the same program. Most people who want to get fit, lose weight, or improve overall health end up doing both. How you arrange those two types of training determines whether they work together or against each other.
Exercise scientists use the term 'interference effect' to describe the potential blunting of strength and muscle adaptations that can occur when high-volume endurance work is layered on top of resistance training.
The interference effect: what the research actually shows
In 1980, researcher Robert Hickson published what became one of the most cited papers in exercise science. He found that subjects who trained for both strength and endurance simultaneously showed smaller strength gains over ten weeks than those who only lifted weights. This became the foundation for what scientists now call the interference effect.
The mechanism involves competing cellular signals. Endurance exercise activates a pathway involving an enzyme called AMPK, which promotes aerobic adaptations. Resistance training activates a separate pathway, mTOR, which drives muscle protein synthesis. When both signals fire frequently and close together, AMPK can suppress mTOR activity, potentially limiting muscle and strength gains.
However, Hickson's subjects trained six days a week at high intensity for both modalities. That volume is far beyond what most adults do. Subsequent research in more realistic training contexts has shown the interference effect is real but considerably smaller than the original study implied, and manageable with sensible programming.
The interference effect is context-dependent
Most studies showing strong interference used high training volumes performed close together, often in untrained or highly trained subjects. For recreational exercisers training at moderate volumes, the effect is generally small. Individual response also varies based on genetics, recovery habits, and overall training history.
Cardio type and volume make a large difference
Not all cardio creates equal interference. Running, which involves repeated eccentric loading of the legs and generates significant muscle damage, tends to interfere more with lower-body strength adaptations than cycling does. A person who runs 30 miles a week and squats heavy three times a week will likely experience more interference than someone who cycles the equivalent aerobic volume.
Volume matters just as much as modality. Low-to-moderate cardio volume (two or three sessions per week at moderate intensity) produces minimal interference for most strength training goals. Problems tend to appear when weekly cardio volume climbs steeply, particularly if sessions are long and frequent.
For people who want general fitness rather than peak performance in either discipline, the overlap is rarely a problem worth worrying about. Short, focused lifting sessions preserve more of their benefit when cardio is kept moderate and recovery is adequate.
31%
Average reduction in strength gains with concurrent training
A meta-analysis published in the Journal of Strength and Conditioning Research found concurrent training reduced strength gains by roughly 31% compared with resistance training alone, with the effect amplified by higher cardio frequencies.
6+ hours
Separation needed to reduce same-day interference
Research cited in Sports Medicine indicates that spacing concurrent sessions by at least six hours on the same day substantially reduces the molecular interference between endurance and resistance training signals.
How to structure concurrent training to reduce interference
Session order and spacing are the two most practical levers available. When both types of training must happen on the same day, placing strength work first generally produces better strength and hypertrophy outcomes. Aerobic work performed afterward still provides cardiovascular benefit without degrading the quality of the resistance training stimulus.
When scheduling allows, training the two modalities on separate days removes most of the interference concern. If same-day training is unavoidable, at least six hours between sessions is a reasonable target based on available evidence.
Exercise selection within the strength session also matters. Building sessions around fundamental movement patterns rather than high-fatigue isolation exercises helps preserve training quality even when cardio volume is moderate. Compound movements done with good mechanics produce a stronger training signal per unit of fatigue.
Recovery quality, sleep, and adequate protein intake all influence how well the body handles the combined load. These factors do not override programming decisions, but they significantly affect outcomes.
When combining both types of exercise is the right choice
For the majority of adults, combining cardio and strength training is not just acceptable; it is practical and well-supported for overall health. Cardiovascular exercise improves heart health, metabolic function, and aerobic capacity. Resistance training preserves muscle mass, supports bone density, and improves functional strength. Neither modality fully replaces the other.
Athletes chasing maximum strength or maximum endurance performance may face meaningful trade-offs. A competitive powerlifter adding substantial running volume will likely see some impact on peak strength. A competitive marathon runner adding heavy lifting will need to manage fatigue carefully. For everyone else, the benefits of both modalities outweigh the modest interference that modest concurrent training produces.
The practical priority is consistency over perfection of order and timing. A program that gets done regularly, even if imperfectly structured, produces better results than an optimally designed one that a person abandons because it is too complicated to schedule.
This article is for general informational purposes only and is not a substitute for advice from a qualified fitness or healthcare professional. Consult a professional before starting a new exercise program, particularly if you have any health conditions or injuries.