Should I Perform Cardio or Weights First?

Take to the treadmill before starting your squats? Or deal with deadlifts before rattling the rower? Which is better?

It is a question that I am often presented with and it is a very common area of interest for regular gym goers. Personally I prefer to perform resistance training first and cardio later and I will go on to explain why this is the case. Let’s think about fuelling exercise first…

Glucose and Glycogen

Glucose is the primary energy source used by the body to maintain regular bodily function and generate motion through muscular contraction. Your primary source of glucose comes through your diet – specifically carbohydrates, which are broken down in glucose. The body can store a limited amount of glucose, now known as glycogen, with average human being capable of storing approximately 300-400g of glycogen in muscle and 70-100g stored in the liver. Glycogen acts as an instantaneous fuel stores which will relied upon when required. Strenuous exercise will be such one instance where these fuel stores will be needed. As exercise duration and intensity increases, so glycogen levels begin to deplete…

What happens when Glycogen becomes fully depleted?

As blood glucose levels drop, the individual will begin to feel a distinct lack of energy and extreme fatigue as the body struggles to maintain performance. This is often referred to as “hitting the wall”.

In order to maintain movement and performance, the body will produce catabolic hormones. Catabolic hormones are hormones which cause the break down of certain molecules. In this instance, these hormones will create energy through the breakdown of protein. However, this process will not provide the body with the same amount of energy in comparison to the stored glycogen which explains why it is difficult to maintain a high level of intensity over a prolonged period.

Fatigue Factor and the Lactic Lie

Additionally, as the muscles are exposed to a high load over a prolonged period, muscular fatigue will begin to build. This is where the muscles are no longer able to sustain or create the same amount of force as previously. This is may be partly down to energy depletion as mentioned in the above point but there are other factors that may cause muscular fatigue.

Lactic acid is a by-product of energy production (when oxygen is not present). Lactic Acid ISN’T thought to drive muscular fatigue which goes against the ideas that many have of lactic acid. I’m sure you’ve all experienced that burning sensation within the muscle which eventually causes you to stop exercising. This is often attributed to the build-up of lactic acid within the muscle. However, recent research actually indicates that actually lactic acid helps to reduce that burning sensation! The burning sensation you experience is actually thought to occur due to the site becoming more acidic. When energy (ATP) is burned, protons are released. An accumulation of protons will cause acidosis and it is this state of acidosis which is thought to cause muscular burn and fatigue. If you are exercising at a low intensity, these protons are still being release but only at a very low rate. As you begin to ramp up the intensity and work the muscles hard, you use more energy (ATP) producing protons much more rapidly and therefore increasing the acidity in the muscles.

Another possible reason behind muscular fatigue is down to the nervous system. Muscular control occurs due to the conduction of electrical signals from the brain to the muscles. These signals may experience some interference when the muscle is working at it’s maximal capacity. It appears that the rate of electrical impulse production reduces when under a heavy load and as a result the maximal amount of force the muscle can produce becomes significantly lessened.


“Okay, that’s all fine and well Chris… but what has that got to do with the cardio or weights first argument?”


Resistance Training as the Foundation

Whether it be fat loss, rehabilitation or improving overall health, in the majority of cases, the foundation of your training should be resistance training. Cardio undoubtedly has it’s place however, unless your primary goal is to complete a distance event, it should be used to compliment your strength training and should not form the foundation of your training – focus on resistance.

Taking into account the above points in regards to limited energy stores, muscular fatigue and now the notion that resistance training needs to form the foundation of training, it would make sense to focus our energy on resistance first and complete any cardio after that. If we decide to conduct cardio first we are potentially going into our strength training already in a partially fatigue, partially depleted state which means we may not be able to lift as heavy or maintain as high a level of performance which may hinder progress.

Finally, just a quick note on strength training itself. The same principle applies here. Ensure you perform your biggest lifts first and smaller lifts towards the end. For example, we don’t want to start our session with leg extensions, use up energy, cause fatigue and then finish our workout with heavy squats. Heavy lifts first, smaller lifts second.

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