Concurrent training involves performing both strength (resistance) and endurance (aerobic) exercise, often within the same training session or day. This combined approach is common for people who want to be both strong and have good cardiovascular fitness. Whether running after lifting is detrimental to muscle growth depends entirely on the exerciser’s primary fitness goal. The body’s response to these two different types of stimuli creates a physiological competition, and poor sequencing can compromise the desired outcome.
The Physiological Conflict of Concurrent Training
Combining strength and endurance work in one session sets up a molecular conflict within the muscle cells, a phenomenon often described as the “interference effect.” Resistance exercise primarily activates the mTOR (mammalian target of rapamycin) signaling pathway, which regulates muscle protein synthesis and growth. Endurance activities like running, especially longer or high-intensity sessions, activate a different pathway called AMPK (adenosine monophosphate-activated protein kinase).
AMPK acts as a cellular energy sensor, turning on when energy stores, specifically muscle glycogen, are low. The activation of AMPK inhibits the mTOR pathway, prioritizing energy conservation and endurance adaptation over muscle building. This molecular “cross-talk” means that the post-lift muscle-building signal is less potent when immediately followed by a fatiguing endurance activity. The strength training stimulus may still occur, but the body’s adaptive response is blunted by the subsequent running session.
How Running After Lifting Affects Muscle Growth
Running immediately following a lifting session can directly inhibit the gains in strength and muscle mass compared to lifting alone. The fatigue from the run, particularly if it is long or intense, extends the recovery time and compromises the crucial post-workout window for activating muscle protein synthesis. Research indicates that this interference effect is more pronounced with running than with non-weight-bearing activities like cycling, likely due to the greater eccentric loading and associated muscle damage from running.
The accumulated fatigue can also reduce the quality of subsequent strength workouts if the recovery period is not sufficient. Furthermore, performing intense running on already fatigued legs from lifting can alter running mechanics and potentially increase the risk of overuse injuries. For individuals whose main objective is to maximize muscle size and strength, this sequence actively works against their goal.
Optimizing Workout Sequence Based on Training Goals
The order of exercises is the primary tool used to manage the interference effect. If the training goal is primarily focused on maximizing muscle size and strength, the lifting session must be performed first. The body’s signaling pathways for hypertrophy are freshest and most responsive when the muscle is not pre-fatigued or energetically depleted.
If the goal is strength or hypertrophy, the most effective strategy is to separate the strength and endurance workouts by at least six to eight hours, or ideally, place them on separate days entirely. For those training for endurance, such as a marathon, the running session should be prioritized and performed first. Running first depletes glycogen stores, reducing the volume or intensity of the subsequent lifting session and compromising the neural stimulus needed for strength gains.
Fueling and Recovery Strategies for Combined Sessions
When concurrent training in a single session is unavoidable, specific nutritional and recovery tactics can help mitigate the negative impact on muscle growth. Immediately after the combined workout, consuming a post-exercise meal containing both protein and carbohydrates is highly recommended. The protein, particularly rich in leucine, helps activate the mTOR pathway to stimulate muscle protein synthesis.
The carbohydrates are necessary to replenish the muscle glycogen stores that were depleted by the running session. Replenishing these stores quickly helps to reduce the signal that activates the AMPK pathway, thereby indirectly supporting the muscle-building process. Beyond immediate nutrition, ensuring adequate sleep and scheduling rest days is crucial, as concurrent training places a significantly higher demand on the body’s overall recovery capacity.