When planning a workout that combines strength training and High-Intensity Interval Training (HIIT), the sequence of exercises is a frequent point of discussion. Resistance training involves structured, controlled movements using external loads, while HIIT alternates short bursts of all-out effort with brief recovery periods. Both methods offer distinct benefits, but performing them back-to-back can create a conflict known as the “interference effect.” The optimal workout order depends entirely on the physical outcome you wish to prioritize, such as building muscle, improving cardiovascular fitness, or enhancing body composition.
Maximizing Strength: Why Lift First
For individuals whose main objective is to maximize muscle gain or strength, performing resistance training first is the recommended strategy. Lifting heavy weights requires the highest level of neural and physical readiness to ensure proper form and maximal power output. The central nervous system (CNS) must be fresh to effectively recruit high-threshold motor units, which are the fibers with the greatest growth potential.
Pre-fatiguing the body with HIIT first can reduce the electrical signals from the CNS to the muscles, leading to a weaker contraction and compromised lifting performance. High-intensity lifting relies heavily on readily available muscle glycogen stores for energy. HIIT rapidly depletes these reserves, which limits the volume and intensity of subsequent weight training, hindering the stimulus needed for muscle hypertrophy and strength adaptation. Starting with lifting preserves your freshest state for the activity that requires the most explosive effort.
Maximizing Endurance: Why Do HIIT First
If cardiovascular fitness and endurance are the primary goals, beginning the session with HIIT allows for the highest possible effort during the intense intervals. The nature of HIIT demands an all-out effort that is difficult to sustain if the muscles are already fatigued from heavy lifting. Performing the high-intensity bursts first ensures the cardiovascular system is pushed to its maximum capacity, which is necessary for driving cardiorespiratory adaptations.
This sequence can also create a metabolic environment by activating the AMP-activated protein kinase (AMPK) pathway. AMPK is a cellular energy sensor activated by energy depletion, promoting mitochondrial biogenesis for improved endurance. While this pathway is sometimes thought to inhibit the muscle-building mTOR pathway, performing HIIT first ensures the maximal signaling for endurance while you are still fresh. The subsequent resistance training is then completed in a glycogen-depleted state, which may enhance fat utilization and maximize the metabolic challenge.
Aligning Workout Order with Primary Goals
The decision of which activity to perform first serves as a mechanism to prioritize your body’s resources and adaptational signals. If the goal is strength and muscle gain, lift weights first to ensure you handle the heaviest loads and maintain the necessary training volume. The slight interference this causes to the subsequent HIIT session is an acceptable trade-off for preserving the anabolic stimulus.
Conversely, if the focus is on maximizing aerobic capacity or training for a hybrid event, the order should be HIIT first, followed by resistance work. Placing HIIT first sacrifices some potential strength gains but guarantees the quality of the endurance stimulus. For individuals focused on general fitness or fat loss, where neither is significantly prioritized, a balanced approach is best. Start with the activity that is mentally or physically more challenging, or the one you are most likely to skip, ensuring it receives sufficient attention before fatigue sets in.
Alternative Strategies for Combined Training
To minimize the performance interference caused by back-to-back sessions, the most effective solution is to separate the training modalities. Scheduling weight training in the morning and HIIT in the evening, or vice-versa, allows the body several hours to recover and for competing molecular signals to subside. This time separation reduces the acute fatigue that compromises performance in the subsequent session.
Another strategy involves performing the two types of exercise on separate days entirely. If splitting sessions is not feasible, consider replacing traditional HIIT with Low-Intensity Steady-State (LISS) cardio on lifting days. LISS, such as a brisk walk or light cycle, provides cardiovascular benefits with significantly less neurological and muscular fatigue, minimizing impact on strength training adaptations.