5 Reasons to Lift Weights Before Cardio

Whether you're a newbie or have been going to the gym for some time, you might have asked yourself, "Should I do cardio before lifting or lift before doing cardio?" In theory, experts say cardio and weight training should be done in different sessions and preferably on different days. If you're trying to maximize your time and do both in the same session here are 5 reasons why you should lift weights first and finish with some cardio instead of the other way round.

1. Cardio Depletes Energy for Weight Training

Without getting to complicated into the biology of cellular metabolism, the cells of the body use 3 separate energy systems to produce energy to do different tasks. There is the immediate energy system, the fast-glycolytic, and slow-glycolytic all of which produce ATP (the fuel for movement). Think of them as gears in a car, first gear, second gear and third gear. The body shifts into different gears depending on the intensity and time length of each exercise.

The 3 Energy Systems

a) Immediate, ATP-PCr

i) Fuel: Stored ATP (energy)

ii) Activity duration: 6-10s

b) Fast-Glycolytic, Anaerobic

i) Fuel: Carbohydrates

ii) Activity duration: 10-30s

c) Slow-Glycolytic, Aerobic

i) Fuel: Fats

ii) Activity duration: 30s+

*Note: All the energy systems are in use all the time, but at different rates depending on the activity that is happening.

When lifting weights you mainly use the immediate energy system and depending on the circuits you have set up you can tap into the fast-glycolytic energy system. If you do cardio before lifting weights, you have to shift into 1st and 2nd gear before getting to 3rd. In other words, you exhaust the first two energy systems when running and then when you go to lift weights the energy systems are pre-fatigued.

2. Muscle Fatigue Leads to Less Weight Lifted

Cardio before weight training leads to a decent amount of energy loss and will most likely have a negative effect on the amount of weight you lift. Since the main energy systems needed for weight training are already fatigued perceived difficulty will be higher than if cardio had not been done. The higher perceived difficulty will likely cause you do choose a lower weight in order to complete the workout you have planned. So by lowering the weight and keeping the sets and reps the same, the total volume of work you are doing is less. Volume in weight training is calculated: sets X reps X weight.

Example of the effect of fatigue on total volume

a) Volume = sets x reps x weight

b) Volume = 3 x 10 x 100 kg = 3,000 kg

c) If fatigued, 3 x 10 x 90kg = 2,700 kg

3. Fatigue Increases Risk of Injury by Decreasing Sport-Specific Psychomotor Performance

As a coach and personal trainer I consider safety of exercise to be very important since injuries are difficult to train through and recover from both physically and mentally. Weight training is more technical and requires attention and intention in order to move the weight safely through the range of motion. Pre-fatigued muscles may not "fire" or recruit as efficiently as fresh and well-rested muscles. This can become an issue later in the workouts and sets as you try to complete your workout. As you tire you are more likely to sacrifice technique to finish your set which is where injuries are more likely to occur.

As seen in a recent systematic review of the literature (past research),

"MF negatively impacts a myriad of SSPP outcomes, including decision-making, reaction time and accuracy outcomes." Habay et al., 2021.

1) Habay, J., Van Cutsem, J., Verschueren, J., De Bock, S., Proost, M., De Wachter, J., Tassignon, B., Meeusen, R., & Roelands, B. (2021). Mental fatigue and sport-specific psychomotor performance: A systematic review. Sports Medicine, 51(7), 1527–1548. https://doi.org/10.1007/s40279-021-01429-6

4. Weight Training is More Complex than Cardio

Cardio is the same motion or movement repeated again and again for a given time, making it easier to go into "autopilot" and disconnect. You can zone out to a song, watch TV or even read a book while your body works. On the other hand, weight training as stated before requires you to be focused on what you're doing in order to move the weight safely. It is recommended that during a training session exercises be done in order of most complex to less complex. There are many reasons for this, for example, decreased risk of injury, increased results, increased learning or memorization of the exercise and movements, increased efficiency of the energy systems to meet demands and recover, increased work overall in the same amount of time, etc. Do the more challenging items like lifting weights earlier in the workout, and disconnect a little more towards the end.

5. Cardio Metabolic Pathway Trumps Strength Pathway

De Souza, E. O. (2018). Molecular adaptations to concurrent strength and endurance training. Concurrent Aerobic and Strength Training, 99–123. https://doi.org/10.1007/978-3-319-75547-2_8

This final reason can be very complicated and in another series of articles I'll go over it. However, for this article just know that when your body works out and recovers it recognizes the stress it went through and adapts to meet the demands. If you do cardio, over time your body becomes more efficient at consuming, transporting, and absorbing oxygen to produce energy which makes the cardio you do feel easier. When you lift weights your body also makes adaptations to the immediate energy system and with the muscle cells to grow bigger and stronger. There are many different adaptations that happen when either lifting weights or doing cardio, but one thing is for certain and that is that the adaptations for cardio trump or reduce the adaptations of weight training. The AMPK pathway leads to both greater aerobic adaptations and decreased muscle protein synthesis. Doing cardio and weight training is known as concurrent training, and it is a complicated balancing act to get right. Regardless, in order to maximize your valuable time spent in the gym lift weights first and finish with cardio to reduce this overlap effect.

Summary

First off if you're going to the gym great! If you plan to do both weights and cardio and you want to be as efficient as possible then I recommend the following structure to your session:

1. Dynamic warm-up

2. Weight training

3. Cardio

4. Cool-down stretch