The Science of Sequencing
The debate over cardio versus weights first revolves around a concept in exercise science known as "concurrent training," which is simply performing both endurance and resistance exercise in the same training program. For decades, researchers have studied
how these two forms of exercise interact. The general consensus is that the order in which you perform them can create what’s known as an “interference effect.” This means that the fatigue from one type of exercise can slightly reduce your performance and the resulting adaptations from the other. Your body has a limited supply of energy for each session, so which activity you prioritise will determine where that fresh energy goes.
For Maximum Muscle and Strength
If your primary goal is to build muscle (hypertrophy) or increase your maximum strength, the science is quite clear: hit the weights first. Resistance training requires significant focus, energy, and power to lift heavy loads with proper form. When you lift, your muscles rely on stored glycogen for fuel. Starting your session with weights ensures these energy stores are full, allowing you to lift heavier and complete more repetitions, which is the primary stimulus for muscle growth. Performing intense cardio beforehand can deplete this energy and pre-fatigue your muscles, leading to a less effective lifting session and potentially increasing your risk of injury due to compromised form. Research has shown that strength training before cardio allows you to lift heavier and does not negatively affect the gains from the subsequent cardio session.
Prioritising Bone Health
Strong bones are built through stress, and weight-bearing or resistance exercises are the best way to apply that productive stress. Activities like lifting weights, jumping, and even brisk walking cause muscles and tendons to pull on the bones, which signals your body to deposit more bone mineral and strengthen the skeletal structure. Just as with building muscle, to effectively load the bones, you need to be able to apply sufficient force. This is best achieved when you are fresh and not fatigued from a long cardio workout. Therefore, if strengthening your skeleton to ward off conditions like osteopenia and osteoporosis is a key objective, performing your resistance training early in your workout is the most effective strategy.
When Cardio Should Come First
There are, of course, exceptions to the 'weights first' rule. If your main goal is to improve your cardiovascular endurance—for instance, if you're training for a 10k race or a marathon—it makes sense to do your cardio first. Your body can dedicate its prime energy resources to improving your aerobic performance. Performing a strenuous lifting session before a long run could leave your legs feeling heavy and may reduce your running capacity for that session. On days you plan a lower-body strength workout, doing cardio afterward is particularly recommended to avoid tiring out the leg muscles needed for lifting.
The 'General Fitness' Approach
What if you’re not an aspiring powerlifter or marathon runner, but simply want to improve your overall health and fitness? In this case, the order matters far less than consistency. The most important thing is that you show up and complete both cardio and strength components. Some people prefer a light 5-10 minute cardio session as a warm-up before lifting, which is perfectly fine. Others find that doing weights first gives them the energy to push through the rest of their workout. A highly effective strategy for general fitness is to dedicate different days to different priorities. You could have upper-body strength and cardio days, and lower-body strength and rest days, for example, which minimizes the interference effect and allows for better recovery.
