Concurrent training, which combines resistance training and aerobic exercise, requires optimizing the order of the two modalities. For those incorporating lower-body resistance work, or “leg day,” alongside cardiovascular exercise, the sequence significantly influences the results achieved. The decision of whether to do cardio before or after your leg workout depends on which physiological adaptation you intend to prioritize. Understanding how each sequence affects muscle energy stores and fatigue is key to structuring an effective workout.
The Impact of Performing Cardio First
Starting your session with cardio, especially high-intensity or long-duration exercise, immediately taps into the body’s primary energy sources. This initial activity depletes muscle glycogen stores in the leg muscles, which fuel high-force contractions. By the time you transition to heavy resistance training, these lowered stores compromise your ability to generate maximal power and strength.
This pre-exhaustion causes significant fatigue in the muscles and the central nervous system. Reduced strength capacity means you cannot lift the same heavy weight or complete the required repetitions with the same intensity. Furthermore, performing complex, heavy lifts like squats or deadlifts with fatigued muscles increases the likelihood of compromised form. This breakdown in technique diminishes the training stimulus needed for muscle growth and elevates the potential for injury.
The Impact of Performing Cardio Last
Performing leg resistance training first ensures that your muscles and energy systems are fresh for the effort requiring the highest power output. Resistance training utilizes immediate energy stores and causes localized glycogen depletion in the working muscles. This strategic depletion primes the body for subsequent aerobic work by forcing a metabolic shift.
When cardio follows the resistance session, the body is already in a state of lower glycogen availability. This encourages a greater reliance on fat as a fuel source during the aerobic activity, enhancing fat oxidation and supporting body composition goals. Additionally, light to moderate-intensity cardio can serve as active recovery. Increased blood flow helps deliver oxygen and nutrients to fatigued muscles, which may assist in removing metabolic byproducts and potentially reduce muscle soreness. However, an intense, long-duration cardio session immediately afterward may be compromised due to systemic fatigue from heavy lifting.
Choosing the Optimal Sequence Based on Your Goal
The optimal order for combining leg training and cardio is determined by your primary fitness objective, as the sequence dictates which adaptation is prioritized. If your goal is to increase lower-body strength or muscle size (hypertrophy), you should perform resistance training first. Studies show that sequencing strength training before endurance leads to significantly better improvements in lower-body maximal strength compared to the reverse order.
Conversely, if your primary focus is improving cardiovascular endurance, such as training for a race, the cardio session should be performed first. This ensures that your muscles are not fatigued, allowing you to maintain the required pace and intensity for the endurance stimulus.
For those focused on weight loss and improving body composition, performing resistance training before cardio is generally the preferred method. Lifting first preserves the intensity needed for muscle maintenance while the subsequent cardio session capitalizes on the glycogen-depleted state to promote maximum fat burn.