The decision to combine cardiovascular exercise and resistance training into the same daily schedule, a practice known as concurrent training, is a frequent question for people seeking efficiency in their fitness routines. While many people find it convenient to complete both modalities in a single day, the potential conflict between the two types of exercise requires careful consideration. Understanding how the body responds to these different demands is the first step in structuring a program that works for your specific goals.
Understanding the Interference Effect
Combining strength and endurance work can sometimes lead to a physiological conflict known as the “interference effect.” This concept suggests that training for one adaptation, such as muscle growth, may lessen the gains you make in the other, like endurance capacity, compared to training them separately. The primary mechanism involves competing signaling pathways within muscle cells.
Resistance training activates a pathway called mTOR (mammalian target of rapamycin), which promotes muscle protein synthesis and leads to increases in muscle size and strength. Endurance exercise, especially high-volume or high-intensity cardio, activates a different pathway called AMPK (AMP-activated protein kinase) in response to high energy demand and metabolic stress. Research indicates that the activation of AMPK can transiently suppress the mTOR pathway.
This suppression means that if a resistance training session is immediately followed by a fatiguing endurance session, the body’s signal to build muscle may be temporarily blunted. Studies demonstrated this effect, showing compromised strength gains in individuals who combined both types of training. However, this interference is generally most pronounced with high-volume and high-intensity concurrent training, and it is less of a concern for general health and fitness goals.
Optimizing the Workout Order
If your schedule requires you to perform cardio and weights on the same day, the order of these sessions becomes a factor in managing fatigue and adaptation. A common recommendation is to prioritize the type of training that aligns with your most important goal by performing it first when your energy reserves are highest.
If your primary focus is maximizing strength and muscle size, you should generally perform resistance training before cardiovascular exercise. Heavy lifting requires peak neuromuscular power and concentration, which can be significantly compromised if the muscles are already fatigued from a demanding cardio session. Starting with weights ensures that the key muscle-building signal (mTOR) is activated before any potential suppression from the endurance work.
If your schedule allows for separation, incorporating a temporal gap between the two workouts is the most effective strategy to mitigate the interference effect. Separating a strength session and an endurance session by at least four to six hours allows the molecular signals from the first workout to subside and the body to replenish some fuel stores. Performing a strength workout in the morning and a low-to-moderate intensity cardio session in the evening can yield better results than doing them back-to-back.
Programming Based on Specific Fitness Goals
The optimal way to structure concurrent training depends heavily on whether you are prioritizing muscular strength and size or cardiovascular endurance. The principle of specificity suggests that your training volume should reflect your main objective.
For those with a primary goal of maximizing strength or hypertrophy, the volume and intensity of endurance exercise on lifting days should be limited. Low-intensity steady-state (LISS) cardio is preferable to high-intensity interval training (HIIT), and sessions should be kept short to limit energy depletion and systemic fatigue. This approach allows for the benefits of cardiovascular health without generating a strong interference signal.
Conversely, if your main focus is on improving endurance, such as training for a distance running event, it is acceptable to perform the cardio session first. On these key endurance days, resistance training should be kept to a lower volume or focused on upper body muscles to avoid pre-fatiguing the leg muscles needed for running or cycling. For individuals training for general health, combining the two modalities is a highly time-efficient way to achieve overall fitness, as the interference effect is minor.
Prioritizing Recovery and Fueling
Combining weights and cardio substantially increases the total training stress on the body, making proper recovery and fueling non-negotiable for sustained progress. The body’s energy demands are significantly higher when performing two taxing workouts in one day, necessitating a focus on adequate caloric intake.
Timely consumption of carbohydrates and protein is particularly important when training concurrently. Carbohydrates replenish muscle glycogen stores, which are heavily depleted by both strength and endurance exercise, while protein provides the amino acids necessary for muscle repair. Consuming a meal or snack containing both macronutrients between separated sessions, or immediately after a combined session, supports the recovery process and ensures readiness for the next workout.
Beyond nutrition, recovery must include sufficient, high-quality sleep and planned rest days to prevent overtraining. Sleep is foundational for recovery, as it regulates hormones and allows for the physical and mental restoration needed to adapt to the high training volume. Incorporating active recovery, such as light walking or easy zone 2 cardio, can aid in reducing muscle soreness and improving blood flow on rest days.