The answer to whether you should alternate cardio and strength training is generally yes, as this approach provides the most effective pathway for balanced physical development. Cardio training, or aerobic exercise, focuses on building endurance and improving cardiovascular efficiency. Strength training, also known as resistance training, involves working against a force to increase muscle mass and physical power. Alternating between these two workout types ensures you develop both heart health and your muscular system without compromising the benefits of either.
Why Alternating Prevents Exercise Interference
The physiological reason for separating these two training types involves conflicting molecular signals within muscle cells. Strength training primarily activates the mammalian target of rapamycin (mTOR) pathway, which signals the body to synthesize protein and promote muscle growth. Intense endurance training activates the 5′ adenosine monophosphate-activated protein kinase (AMPK) pathway.
The AMPK pathway is activated in response to energy depletion. Scientific evidence shows that when highly activated by intense cardio, the AMPK pathway can actively inhibit the mTOR signaling cascade. This conflict is called the “interference effect,” where endurance signals blunt the muscle-building adaptations sought from resistance exercise.
This interference is most pronounced with high-volume or high-intensity endurance training. Separating the workouts, whether by several hours or entire days, allows the molecular signals for each adaptation to be processed without clash.
Scheduling Methods for Different Days
The most straightforward way to alternate is by dedicating entire days to a single training modality, maximizing recovery and adaptation. A common weekly split involves three days of strength training and two to three days of cardio, with at least one full rest day (e.g., Strength, Cardio, Strength, Rest, Strength, Cardio, Rest).
This separation ensures that muscles are not fatigued from a prior endurance workout, and cardio performance is not hindered by residual soreness. The National Academy of Sports Medicine recommends allowing 48 to 72 hours of rest between exercising major muscle groups with resistance training.
Dedicated rest days or active recovery, such as light walking, allows microscopic tears to heal and energy stores to replenish. Neglecting recovery can lead to overtraining, reducing gains and increasing injury risk.
Combining Both Types in One Session
When scheduling constraints make separate-day training impossible, performing both strength and cardio in the same session is necessary (concurrent training). The two critical factors are the order of the exercises and the time separating them. If the goal is to maintain or build muscle, strength training should be performed first.
Starting with strength training ensures maximal energy reserves for resistance work, which requires fresh muscles for proper form and maximal effort. Performing heavy lifts while fatigued increases injury risk and reduces the weight handled, compromising the strength stimulus. Cardio performed afterward carries less injury risk.
The best strategy is to maximize the time between workouts, ideally separating them by at least six to eight hours. This buffer allows conflicting molecular pathways to begin resetting. If a full separation is impossible, a shorter, less intense cardio session immediately after lifting minimizes interference more effectively.
Prioritizing Training Based on Your Fitness Goals
The ideal alternating schedule is determined by your specific fitness objectives, as goals dictate the volume and intensity of each training type.
If your primary goal is muscle growth or strength gain (hypertrophy), prioritize resistance training volume and intensity. Cardio should be kept to lower-intensity sessions, such as brisk walking, and controlled in volume to prevent excessive caloric expenditure that could hinder muscle building.
Conversely, if your main focus is on endurance, such as training for a long-distance race, the schedule should feature longer, more frequent cardio sessions. Strength training acts as a supplementary tool to build resilience, prevent muscle loss, and reduce injury risk. For endurance athletes, strength workouts might focus more on muscle endurance than maximal power.
Manipulating the frequency and intensity of your strength and cardio days personalizes the alternating strategy. The key is to avoid high-volume, high-intensity workouts of both types on consecutive days or in close proximity, which leads to diminished returns.