The question of whether combining running with resistance training compromises the ability to build muscle and strength, commonly referred to as “gains,” is a long-standing concern among athletes. Gains primarily refer to muscle hypertrophy, which is the increase in muscle size, and maximal strength development. The practice of performing both endurance and resistance exercises within a single training program is known as concurrent training. Research confirms that this combination can sometimes lead to a biological conflict called the “interference effect,” where the adaptations sought from one mode of exercise are diminished by the other. Understanding the underlying physiological mechanisms and programming variables is necessary to mitigate this effect and successfully pursue both goals simultaneously.
The Physiological Mechanism of Interference
The potential for running to interfere with muscle gains stems from a conflict at the cellular level within the muscle tissue. Resistance exercise stimulates a signaling pathway known as the mammalian target of rapamycin (mTOR), which acts as the primary switch for initiating muscle protein synthesis and subsequent muscle growth. This anabolic signal is what drives the desired adaptations of strength and hypertrophy. Simultaneously, high-volume or high-intensity endurance exercise, such as running, activates a different pathway called adenosine monophosphate-activated protein kinase (AMPK).
AMPK functions as the cell’s energy sensor, promoting the conservation of energy and adaptations related to endurance, like mitochondrial biogenesis. The conflict arises because the activation of AMPK can suppress the mTOR signaling pathway. This molecular crosstalk means the muscle receives conflicting signals—one to build and one to save—which limits the full potential for hypertrophy. The eccentric nature of running, which involves muscle lengthening under tension, may also contribute to a greater interference effect compared to other endurance activities like cycling.
Programming for Concurrent Training
Minimizing the interference effect requires manipulation of training variables: volume, intensity, and timing. Interference is observed most clearly when high frequency and high volume of endurance training are included alongside resistance work. While the threshold varies, studies suggest that weekly running mileage exceeding a moderate amount can negatively impact lower-body hypertrophy and strength development. Managing the total weekly load is an important first step in protecting muscle gains.
The timing and order of workouts on the same day also significantly influence the degree of interference. Researchers generally recommend separating resistance and endurance sessions by at least six to eight hours to allow the molecular signaling pathways to reset. If a long separation is not possible, a minimum gap of three hours may still be sufficient to mitigate some of the negative effects. For individuals prioritizing strength gains, performing the resistance training session before the running session is generally the more favorable order.
The intensity of the running session plays a role in the magnitude of the interference effect. Low-Intensity Steady State (LISS) running is less detrimental to strength and size goals than high-intensity, high-volume running. High-Intensity Interval Training (HIIT) may be less inhibitory than continuous moderate-intensity training, though this depends on the overall volume and proximity to the lifting session. When strength is the main goal, keeping running sessions lower in intensity and volume helps prevent excessive cumulative fatigue and minimize conflicting cellular signals.
Fueling the Dual Goal: Nutritional Considerations
Successfully combining resistance training and running requires a nutritional strategy to support the dual demands placed on the body. A primary consideration is maintaining an adequate caloric intake, as concurrent training in a substantial caloric deficit will compromise muscle gains. The body needs sufficient energy to fuel both the running sessions and the recovery and repair processes following resistance training, favoring an anabolic environment for growth.
The elevated training volume increases the need for specific macronutrients. Protein intake must be sufficient to support muscle repair and synthesis, with recommendations for athletes often falling in the range of 1.6 to 1.8 grams per kilogram of body weight daily. In periods of intense training, requirements can reach up to 2.0 grams per kilogram of body weight.
Adequate intake of carbohydrates is equally important, as they serve as the primary fuel source for running and high-intensity exercise. Running rapidly depletes muscle glycogen stores, and if these are not replenished, the body may break down muscle tissue for energy. Athletes engaged in high-volume concurrent training may require a carbohydrate intake of six to ten grams per kilogram of body weight daily to maintain performance and promote recovery.
The Bottom Line on Concurrent Training
Running does not automatically eliminate the potential for muscle and strength gains, but the combination introduces a challenge that must be actively managed. The negative impact, or interference effect, is not an inevitability but a consequence of unmanaged training stress. Progress in both domains is achievable by implementing a few simple rules. Managing the volume of running, separating the lifting and running sessions by several hours, and prioritizing the goal-specific workout are the most effective programming strategies. Paired with a diet that supports the energetic and structural demands of both training types, the potential for interference is minimized.