“Should I do aerobic training before or after a weights session?” This is a frequently asked question and one over which a wide spectrum of opinion exists even though it may seem like trivia if you’re new to weight training. Yet, as with many issues in the exercise sciences, answers to complex questions can be blurred by qualifications and exceptions and tempered by the exercise goals you have set — weight loss, muscle, strength, sporting prowess, appearance and so on.
The following attempts to clarify the issue and provide some clear direction.
Cardio and Aerobics
Aerobic exercise, often called ‘cardio’ for short, is any exercise at an intensity at which oxygen can be sustainably supplied to large muscle groups over time and which places consistent demands on the heart and lung system, the cardiorespiratory system.
Cardio is something you do at a sustained pace over a longer period of time rather than in short bursts of energy such as in interval running or lifting weights. Cardio is walking, jogging, distance running, swimming and cycling; and using treadmill, stepper, cross trainer and rowing machines in the gym. Blood glucose and stored glucose and fats are the main fuels used in aerobics.
Training with Weights
In contrast, lifting weights is an activity practiced in short bursts of anaerobic (without oxygen) activity. In effect, ‘anaerobic’ doesn’t mean that we stop using oxygen, it just means that the activity is of such an intensity that the muscle’s requirement for oxygen is exceeded, resulting in metabolic products such as lactate and an eventual inability to continue at that intensity. Stored muscle glucose and phosphocreatine are the main fuels used in strength training.
Now that you’re clear on the essential difference between aerobics and weight training, let’s consider this in the context of doing cardio before or after a weights session. I’ll assume that a ‘session’ is one visit to a gym for the purposes of a workout. Let’s examine the scenarios I propose.
Scenario 1 – Cardio after Weights
You walk into the gym and do a warmup on the treadmill for 10 minutes, but you don’t want to do too much cardio because you reckon you need the energy to max out your weights session. Anyway, you heard that you’ll burn more fat if you do it after the weights.
Saves energy for weight lifting. This may seem to be good logic; however, doing 40 minutes of cardio at moderate pace is not going to deplete enough energy to prevent you from lifting well. As long as you’ve replaced your carbohydrate glucose stores after any previous exercise session with proper eating, the body will have stored up to 500 grams, or a pound of glycogen.
A jogging or running treadmill session of 40 minutes may use about 600 kcalories of energy, depending on your size and pace. Of this, some fuel will be fat, some will be stored glucose and some blood glucose. A reasonable estimate is that you would use around 80 to 100 grams (3 or 4 ounces) of stored glucose out of, say, 400 grams that you have available. You can see that you have plenty left in reserve for strength training.
What’s more, if you replace some of this used fuel with a sports drink or energy bar before you start the weights, you’ll only be a little depleted from when you walked in the door.
Burn more fat. Now this one really sounds attractive, the idea being that if you deplete some carbohydrate stores, particularly blood glucose, with an initial weights session, you’ll be in fat burning mode. Theoretically this makes some sense but , the fat burning zone is a mythical construct and what really matters is how much energy you expend overall.
Score for Scenario 1: sounds good, but in reality only 2 points out of 5.
Scenario 2 – Cardio before Weights
You get stuck into the cardio first up for 40 minutes because you think you will be too tired to tackle it at the end of the weights program. You understand you will expend more energy with cardio when you’re fresh, so you can use more energy overall in the session, which is what you’re aiming for.
Fresh legs for better cardio. If you do your cardio before you lift, there’s little doubt you will do this part of your program more efficiently, which probably means at higher intensity and with a higher aerobic fitness outcome. Heavy legs and arms after weights are not conducive to a good cardio session. I’ve tried both sequences many times, and running first is my preference even without the technical considerations.
Cardio of moderate output expends considerably more energy than an equal session of weights, so if you want to maximize energy output for weight loss and aerobic fitness, doing a solid cardio session is essential. Doing cardio first will maximize your output.
On the other hand, with attention to fueling, refueling and fluid intake, you will still be capable of a strong weights session after your aerobic session.
Strong arteries. It’s also important to know that aerobic exercise is important even for specialist weight lifters and bodybuilders from a health perspective. Cardio helps keep the arteries elastic, which is beneficial for cardiovascular health. This is called ‘arterial compliance’ and several studies have shown that this worsens in weight trainers who do little aerobic exercise.
Study Shows Cardio before Weights is Beneficial
A study from the Human Performance Research Center, Brigham Young University, Provo, Utah, examined what happened to ten men who did resistance only, run only, resistance-run, and run-resistance sessions. (‘Resistance-run’ means weights before cardio and vice versa.)
Here’s what they reported:
This was not a large study, so the results should be interpreted with caution. Nevertheless, this is in line with my own experience with this training sequence, and also that of some clients.
Other research found that ‘running economy’ is also impaired after a weights session, another reason why the weights-cardio sequence is less efficient.
Score for Scenario 2: the evidence is not quite in yet, but I’ll score it 4 our of 5 for doing cardio before a weights session.
Cardio Killed My Muscle
Some weight trainers are reluctant to do much cardio training because they believe it produces catabolic hormones like cortisol that break down muscle stores for fuel thus interfering with the anabolic muscle building process.
Although this subject is worthy of a more complete article on weight training nutrition and metabolism, a brief response is that you can protect muscle from this process by ensuring adequate nutrition before, during and after a session and by keeping aerobic training to under one hour if you have muscle building goals.
Forty or so minutes of cardio within an adequate nutritional environment is not going to hurt your muscle. In fact, in view of the discussion above, doing cardio after weights could be more damaging to muscle as ‘beaten up’ muscle strives to deal with the burden of aerobic activity. Your immediate post-weights activity should be dedicated to maximizing the anabolic environment. This is time for building up not breaking down. You achieve this by eating sensibly and adequately and by resting and sleeping — and by not doing cardio after weights.
Here are my recommendations:
Drummond MJ, Vehrs PR, Schaalje GB, Parcell AC. Aerobic and resistance exercise sequence affects excess postexercise oxygen consumption. J Strength Cond Res. 2005 May;19(2):332-7.
Palmer CD, Sleivert GG. Running economy is impaired following a single bout of resistance exercise. J Sci Med Sport. 2001 Dec;4(4):447-59.
Miyachi M, Kawano H, Sugawara J, Takahashi K, Hayashi K, Yamazaki K, Tabata I, Tanaka H. Unfavorable effects of resistance training on central arterial compliance: a randomized intervention study. Circulation. 2004 Nov 2;110(18):2858-63.