Cardio is what we're talking about today.
Your gas tank. Your engine. The thing that either gets you in trouble when you're walking up a hill or saves your ass when you're on your 3rd set of split-squats because your coach is a sadistic a**hole.
At the outset, let's get clear on what we're talking about with cardio since it's such a throwaway term. We all know that we're referring to our cardiovascular system, and for most when we think of cardio we picture someone on the treadmill or cross-trainer slogging away in a puddle of sweat. But that's about as far as it goes.
The uses of cardio can be boiled down to 2 things: improving your overall level of conditioning and enhancing your ability to burn fat.
Let's look at the conditioning side and focus mainly on the aerobic side of things, as even now, it's still misunderstood.
Energy Systems
Our bodies are constantly producing and using energy. For the purposes of training, we use 3 primary energy systems to do this: aerobic, anaerobic lactic, and anaerobic alactic. Each system has a different pathway to produce energy, but all are constantly being used with certain systems getting prioritised depending on the nature and intensity of the physical activity.
Credit. Ultimate MMA Conditioning (Joel Jamieson)
The aerobic system relies on oxygen to produce molecules ATP (ATP is the energy currency of the body), which is the fuel the muscles of the body run on. All the food you eat gets broken down and converted into proteins, carbs, or fats to get stored and turned into ATP later as needed. The aerobic system can produce energy for a long time without fatigue, which makes it the most important system for sports or activities that last anything longer than 2 minutes.
The anaerobic lactic and anaerobic alactic systems are capable of very powerful energy production because they don't rely on oxygen and use relatively few chemical reactions to produce ATP. Both these systems give you the power for high-intensity exertions, but the downside is that they can't sustain that level of energy for very long periods of time and there's a cost associated with using these systems too long that creates huge amounts of fatigue (lactate being one).
Credit. Ultimate MMA Conditioning (Joel Jamieson)
Why does any of this matter?
As already mentioned, all 3 systems work interchangeably while one system is prioritised based on the duration and intensity of the activity. If you're reading this, odds are that you're someone who wants to build muscle and get stronger, maybe you want to get fitter for a half-marathon. Developing your energy systems will have a direct carryover to your ability to get bigger and stronger. That's a fact. The problem is that most people go about their "cardio" in a very haphazard manner and don't get as much from it as they could.
Weight training for instance is a predominantly aerobic activity. Heart rates rarely exceed 150 beats per minute, except when you're pushing hard on sets. There are many limiters for people who are no longer beginners to weight training that prevents them from seeing continued progress. Being unfit is one of them.
You won't be able to train with enough intensity to stimulate growth in muscle or strength if you can't take the target muscle close to failure or recover from your training. If your aerobic system is crap, the limiter is going to be you getting out of breath rather than the muscle failing. If you can't recover from your sessions well enough, you're inhibiting the training intensity, probably going to have to cut down on effective volume, and all that leads to regression. So having better stamina should be a big consideration for anyone wanting to improve their ability to build muscle and strength. Below are some ways that we can do that.
In order to improve our aerobic system, we need to do 3 things:
1) increase oxygen supply to working muscle
2) increase how much oxygen the muscle themselves can actually use
3) increase the supply of the raw materials the body can use to produce energy aerobically
The cardiac output method is one way to improve your aerobic system, in particular your aerobic capacity.
Cardiac output is effective in improving how much blood your heart can pump with each beat. You'll have done it before. It's what we know as steady-state cardio or 'Long Slow Duration' cardio. The reason it's effective in improving the aerobic system is down to what's known as eccentric cardiac hypertrophy. The way this works is that when the heart rate is kept below a certain threshold (roughly below 150 beats per minute), the left ventricle (chamber) of the heart constantly fills up with blood. When this is done for long enough, the chamber walls stretch and expand and what's left is a larger left ventricle. Picture a balloon that's constantly being filled with water. Over time it will stretch and get bigger. A bigger left ventricle means the heart has to work less to pump blood to the body to supply oxygen to the muscles.
Guidelines for cardiac output training:
30-90 minutes long slow duration work
HR kept between 120-150pm (if you're older stay on the lower end and if younger towards the higher end)
1-3 sessions per week
Start low and increase volume and frequency over time
any low intensity and low pressure exercise will work, such as cycling, jogging, jumping rope, pad work, etc.
If your resting heart rate is in the 60s and 70s then including some cardiac output work is a good idea for general health but also to improve your ability to get stronger and build muscle.
Another effective method for improving the aerobic system is the cardiac power interval method. The primary goal here is to improve how forcefully the heart can contract with each beat. To relate it back to resistance training, the reason this is important is that when the intensity of the activity and the heart rate increases, a stronger heart means it's less likely to fatigue and is capable of delivering more oxygen to working muscles. Think of the particularly hard sets, where the heart rate can spike above 150. If your heart can't beat forcefully each time to pump out a lot of oxygenated blood to meet the demand, it will fatigue and your ability to sustain that intensity will drop. This isn't an issue with lower heart rates because oxygen is not the limiting factor.
Guidelines for cardiac power intervals:
maximal heart rate with each "rep"
60-120 seconds of work
rest for 2-5 minutes or bring your heart rate to 120-130 beats per minute
4-12 "reps" per session
1-2 sessions per week
any high intensity drills that elevate the heart rate can be used, such as sprinting, cycling, rowing, etc.
The cardiac intervals complement the eccentric cardiac adaptations achieved through the cardiac output method as outlined previously.
These are just 2 methods at out disposal to develop our aerobic systems, but will go a long way towards improving our stamina. Cardiac output and cardiac power intervals are also the places to start from when looking at improving endurance, and like we've already discussed, these can have benefits for our progress in the weight room.
A final note about including energy systems work into a weight training programme. There will naturally be some trade-offs. This doesn't mean that all qualities can't be improved, but it does mean that at the more extreme levels, the adaptations that these methods create are often in competition. There's a reason the world's strongest man won't be able to run a sub 3-hour marathon, and likewise while an ultra-runner won't squat 300kg. That said, most programmes can accommodate inclusion of aerobic work at any phase of training, and its positive effects will go beyond simply losing fat. You'll see an increase in nutrient partitioning, oxygen supply and utilization, increased movement efficiency, muscle growth, strength improvements, and improved digestion to name a few.
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