Cardiovascular Training

Cardio, also known as CV training, is a method of physical conditioning that exercises the heart, lungs, muscles and associated blood vessels. Cardio training is essentially any training that elevates your heart rate above resting rates for a prolonged period of time, usually over at least 2 minutes duration. It is often a term used interchangeably with “aerobic” training. Aerobic training forms the basis of cardiovascular training, but it should be recognised that shorter more intense bouts of activity (i.e. anaerobic) can also have beneficial effects on the systems mentioned above.

An enhanced level of cardiovascular conditioning (over sedentary people) is essential for performance in most sports.

Having a well-conditioned CV system can benefit athletes by:

• Aiding continuous moderate to high-intensity efforts (running, cycling, swimming, hiking, etc.)
• Increasing their capacity to perform more volume of training for better training results.
• Increasing their capacity to perform repeated high-intensity efforts (a highly prized attribute for most field or court-based sports).
• Allowing them to recover more efficiently following bouts of exercise and after training and competition.

Key terminology

Let's start off by getting re-acquainted with some essential terms that will play a significant role in this module. Becoming familiar with these will greatly enhance your understanding of the upcoming content. Click on the following terms to re-familiarise yourself with their meaning.

Cardio has received some bad press in recent times. While the internet is a treasure trove of information, not everything is true! If you believe everything you read on the internet about cardio training, you may now believe some of the following statements:

• Cardio makes you fat.
• Cardio is dangerous.
• Cardio is ineffective/wasted training.
• Cardio causes overuse injuries.

The problem with this type of rhetoric is often based on partial truths or information taken out of context. People are all too willing to jump on the anti-cardio bandwagon because that’s what they want to hear. Cardio is uncomfortable, it’s challenging and very hard to get started on (if you are in poor condition). The appeal of lifting weights and group classes motivates many people more.

This highlights the importance of getting your information from reputable sources. The benefits of cardio training for health and fitness are undeniable. Let’s explore some of these statements above and see what the scientific literature has to say about them.

Cardio makes you fat

Dr Jose Antonio is the CEO and co-founder of the International Society of Sports Nutrition. He has written dozens of peer-reviewed articles on the mechanisms of weight/fat loss. Here is what he has to say in response to the "cardio makes you fat crowd".

• Longitudinal training studies of fat kids show that aerobic training results in a loss of body fat.
• Longitudinal training studies of fat adults show that aerobic training results in a loss of body fat.
• Those who do the most cardio over a 15- to 20-year period exhibit the lowest levels of body fat.
• Athletes who are engaged in highly aerobic exercise have single-digit body fat percentages.
• Triathletes with a higher training volume have a lower percentage of fat than those with a lower training volume.
• Cardio does not make you fat, eating too much makes you fat.

This is backed up by every meta-analysis and systematic literature review that I could find. While resistance training has its own outstanding benefits for health and wellness (primarily revolving around maintenance or increases in lean tissue and the metabolic enhancements this leads to), all of the quality scientific literature agrees that balancing time commitments against health benefits, it appears that aerobic training modes (i.e. cardio) are the optimal mode of exercise for reducing fat mass and body mass (Willis et al, 2012). It’s not the only way, it’s not the easiest way, but it is the optimal way.

This is not to say that a multi-faceted approach using a combination of cardio and resistance training methods can’t be equally (or even more) effective, however, this will be a less time-effective approach.

So where does the “cardio makes you fat” idea come from? This is a classic case of information being taken out of context. The key points that people who promote this idea use to back up their theory are:

• Cardio burns muscle: This is true, it can, but only if you haven’t fuelled for the exercise session. In the absence of carbohydrates, the body can turn to protein reserves (muscle) as a fuel source, however, aerobic training promotes both carbohydrate and fat burn during exercise. It is only when carbohydrates run low that the body taps into protein stores. A good pre-exercise meal ensures glycogen stores will last for 60-90 minutes of continuous exercise. It is unlikely that most regular exercisers will be working out for longer than that! But what about fasted cardio? Performing cardio without carbohydrate fuelling can increase the proportion of fat used as a fuel source, but only once the training regime has been well established and the body has made the necessary adaptations. Until then, the body will rely on protein (muscle) as a fuel source, and this will likely result in lean tissue loss. This is why it is recommended to include fuelled resistance training around fasted cardio, to attempt to limit lean tissue losses.
• Cardio makes you hold on to fat: Incorrect. For your average gym goer, cardio training burns significantly more calories than resistance training. Steady-state cardio for a reasonable duration allows the body to burn fat alongside carbohydrates. This is because the body must believe that a constant supply of oxygen is available to metabolise fat for fuel. Higher-intensity cardio modes like intense interval training use the anaerobic system and therefore rely on carbohydrates for fuel. This can have a fat-preserving effect, however total calorie burn for the session is typically higher.
• Cardio raises cortisol levels (which turns on fat storing) - Cortisol is a hormone that can be elevated due to high levels of stress (physical or mental). Provided a person is working at a level that is appropriate to their training age and is ensuring they get enough rest and recovery between sessions this is a nil factor.

An additional point to consider on the benefits of cardiovascular training is that it appears to be the only form of training that has a meaningful effect on the reduction of dangerous visceral fat (internal fat deposited around the organs). A systematic review and meta-analysis of the effect of aerobic vs. resistance training on visceral fat found that aerobic exercise modes were the only effective mechanism for reducing visceral fat (Ismail, Baker and Johnson, 2011).

Cardio is dangerous

This is another classic case of taking information out of context. There is evidence that chronic extreme exercise training and competing in ultra-endurance events can lead to heart damage and rhythm disorders, but this is so far removed from your average gym goer and the volume of training they are doing. Yes, people with genetic risk factors (especially those related to the heart) and those who are high on the cardiovascular risk index (high blood pressure, high cholesterol, etc.) are more likely to have complications, but the risk level remains low as long as they follow guidelines for appropriate exercise intensity.

Let’s look at some facts. This statement paper from the American Heart Association written by Franklin et al (2020) looked at cardiovascular exercise-related risk and made the following conclusion statements:

• Cardiovascular risk is reduced by 30-64% in active and fit populations participating in cardio modes of exercise
• Cardio exercise modes can increase the risk of sudden cardiac death or heart attacks, particularly in men unaccustomed to exercise. In absolute terms, acute events like these are extremely rare with an occurrence rate of 0.31-2.1 sudden deaths per 100,000 person-years.
• Most epidemiological studies report a decline in health risk with participation in cardio exercise modes. In fact, there is a sliding scale to this data with elite endurance athletes living on average 3-6 years longer than the general population, with this benefit reducing linearly with reduced cardio participation.
• Franklin et al (2020) concluded that the benefits of participating in long-term cardio training modes overwhelmingly outweigh the risks for the vast majority of the population and that, provided a thorough pre-screening is performed, the risks to those with known cardiovascular related issues remain low if appropriate protocols are followed.

Cardio is ineffective/wasted training

The information detailed above has already effectively countered this argument and we have barely scratched the surface of the benefits associated with participating in cardio exercise modes. We will cover these in greater detail in each of the cardio training modes we will discuss in upcoming topics but here are a few key benefits of cardio reported in a review of mental and physical benefits associated with cardiovascular exercise by Penedo and Dahn (2005).

There are also a number of cardio training adaptations that aid sporting performance. These include:

Increased stroke volume

Endurance or cardio-based training has been shown to increase stroke voulume. This is due to hypertrophy (increase in muscle size) of the myocardium (heart muscle), specifically, the left ventricle. An increase in size and strength of the heart muscle enables the heart to eject more blood per pump, resulting in a higher stroke volume. The following image shows the effect of cardio training on the left ventricle when compared to sedentary or resistance-trained subjects. 

The following image shows the effect of 6 weeks of cardio training (treadmill running) on stroke volume in healthy subjects.

This increase in stroke volume has wide-reaching effects that help to explain many other improvements in exercise performance. Increased stroke volume leads to reductions in both resting heart rate and exercise heart rate during sub-maximal exercise. This essentially means exercise becomes easier. The image below shows the effects of 6 weeks of regular cardio training on exercise heart rate. You can see that heart rate not only starts lower (at the same exercise intensity) but climbs more gradually during increases in intensity meaning exercise is now easier at each running speed.

Increased stroke volume also allows an increased cardiac output (blood pumped to the working systems, e.g. muscle) during intense exercise resulting in an ability to maintain higher levels of exercise output. The image below shows that when exercise intensity (running speed) increases, the heart is able to increase cardiac output to match the demands of working muscles. This increase in blood flow also allows for enhanced removal of exercise waste products ensuring they are not allowed to accumulate.

Increased heart rate recovery

One of the key markers of fitness is the ability to recover from an exercise effort quickly, so you can perform repeated efforts at the same intensity. This effect is likely due to the heart's efficiency in circulating blood (i.e. removal of exercise by-products and delivery of oxygen and replacement nutrients). The graph below illustrates the chronic effect of cardio training on time to recovery. After a period of cardio training, subjects were able to return to baseline heart rates much quicker than before. This has positive benefits for both training (more volume per session) and sporting performance (quicker recovery for more repeated efforts than your opposition).

Increased lactate threshold

The lactate threshold indicates the work rate at which the cardiovascular system can no longer keep up with muscular demands for delivery of oxygen and removal of waste products (i.e. a shift from aerobic to anaerobic energy system reliance). A more efficient heart leads to an enhanced ability to remove exercise by-products before they accumulate. If lactate is allowed to accumulate within the muscle, it can lead to reduced muscle output. Essentially, a fitter heart can keep up with muscular demands at higher intensities which means higher levels of effort can be maintained without succumbing to fatigue. This is represented in the graph below where a period of cardio training has led to a shift in the lactate threshold to the right indicating the ability to work at higher intensity (faster running speed) while still using the aerobic energy system.

Blood volume and haematocrit levels

A chronic effect of cardio training is an increase in the oxygen-carrying capacity of blood. This occurs due to progressive oxygen demand stress placed on the system as progressive overload is applied to cardio training. While the image below depicting the changes to blood composition following a period of cardio training appears to show reduced amounts of red blood cells (percentage), the reality is that total blood volume has increased along with the number of red blood cells. More red blood cells mean enhanced oxygen delivery.

Increased fat utilisation

The graph below shows the contribution of fat and carbohydrate (as fuels) to aerobic exercise. You can see that as exercise intensity rises fat is used less and carbohydrate more.

There are two limiting factors associated with fat use as a fuel during higher-intensity exercise. These are 1) The ability to deliver a constant supply of oxygen (O2 is needed to metabolise fat) and 2) The speed at which fat can be converted to energy in the muscle. As you get fitter by performing cardio exercise, the muscles become more equipped to process fat as a fuel source during aerobic exercise at higher levels of intensity. There are two key adaptations involved in this improvement. The first is the enhancement of blood flow to working muscles which ensures oxygen is supplied at a rate the muscles require to burn fat (even at higher intensities). This essentially means a fitter athlete has improved their ability to work aerobically at higher intensities. The second contributing factor involves changes within the muscle fibres that include increased mitochondrial density (enhancing the ability to produce ATP for continued muscle contraction) and an increase of the enzymes involved in the metabolism of fat for energy (B-oxidation).

Cardio causes overuse injuries

This one is not a myth, but it is often blown out of proportion. Any exercise performed repeatedly for long durations can lead to overuse injuries over time. This is especially true if the mechanics of the movement are sub-optimal. Most research in this area is focused on running. Mechelen (1992) performed a review of the literature on running injuries and found that running injuries occurred at a rate of between 2.5-12 injuries per 1000 running hours and that around 50% of running injuries were categorised as overuse injuries. That translates to a prevalence of 1.25-6 overuse injuries per 1000 hours of running. The most common causes were a lack of warm-up, previous injury, a lack of running experience, an inappropriate volume increase and improper footwear. So, provided a client performs a warm-up, follows appropriate progression protocols, does not run while injured and wears supportive running shoes, the likelihood of overuse injury is very low. The rate and prevalence of overuse injuries while running compare favourably with other forms of training. Serefim et al (2023) conducted a systematic review on injuries with resistance training modes and reported that injury rates in cross-fit, powerlifting and strength training were between 4-12.6% per 1000 hours of exercise. This shows that the prevalence of injury is no more than in other common training modes.

To improve cardiovascular fitness, you must challenge the organ systems involved (heart, lungs, muscles). By progressively adding stress to these systems (whilst allowing adequate rest and recovery), they will adapt to accommodate the increased stress placed upon them (General Adaptation Syndrome).

Programming for cardiovascular training approaches is actually a very similar approach to programming for resistance training. The key variables that we manipulate to achieve progressive overload are the volume and intensity of exercise.

Volume	Volume is a simple measure when it comes to CV training. Cardio training volume is typically measured in distance (metres or kilometres) or duration (i.e. time spent exercising). Volume can be adjusted in the training schedule by adding or subtracting movement distances.
Intensity	The intensity of cardio training is best measured using a percentage of heart rate maximum (in the same way that we used percentage of 1RM for resistance training). In order to do this, you need to know how to calculate a client’s HR Max and percentage of HR max to determine the intensity they should work at. You can do this using the Karnoven Formula.

The Karnoven formula is considered by many as the most accurate way to determine appropriate target heart rate intensity zones for exercise sessions because it takes into account a client’s age, resting heart rate and maximum heart rate. There are 4 steps to using the Karnoven formula. See the following table that explains each step.

Karvonen Formula Process
1	Calculate your resting HR - the easiest way to do this is to count your pulse for 15 sec and multiply by 4. Ensure you have been sitting quietly for some time before doing this.
2	Calculate your predicted HR max: 220-age = HRmax
3	Next work out how many heart beats you have available for exercise (your resting heart beats are already being used). This is called your HR Reserve. You do this using the following equation: HRmax – Resting HR = HR Reserve (HRR)
4	Once you have your HRR you can calculate your training zone heart rates. You do this by taking your HRR and multiplying it by the decimal representation of the training intensity you want to train at, e.g. 50% is 0.5, 60% is 0.6, 70% is 0.7 etc). Take this figure, then add your resting heart rate to it and you have your training zone heart rate.

In reality, it is very hard to work out and stay at a specific heart rate, so the best advice is to allow a 5-beat heart rate range for clients to try and stay within during their sessions. For example, if you calculated a client's 70% training intensity heart rate as 156bpm, you would set them a target HR training zone of 153-158bpm.

Use the Karnoven formula to work out the training zone heart rates for the following two clients.

Then flip each to reveal the solution and compare it with your calculations. Check the results. Were your calculations accurate?

Rate of perceived exertion

In the absence of HR tracking technology, the perceived rate of exertion can also be used as a means of estimating exercise intensity. This involves using a scale to rate the intensity of exercise (e.g. 1-10). This is a far less accurate measure of intensity as it is a completely subjective measure. Everyone perceives their effort in completing exercise differently. To be accurate in using RPE usually takes considerable experience and often requires the use of HR tracking technology at intervals to confirm RPE selections are within an acceptable range.

RPE SCALE	RATE OF PERCEIVED EXERTION
10	MAX EFFORT ACTIVITY Feels almost impossible to keep going. Completely out of breath, and unable to talk. Cannot maintain for more than a very short time.
9	VERY HARD ACTIVITY Very difficult to maintain exercise intensity. Can barely breathe and speak only a few words.
7-8	VIGOROUS ACTIVITY Borderline uncomfortable. Short of breath, can speak a sentence.
4-6	MODERATE ACTIVITY Breathing heavily, can hold a short conversation. Still somewhat comfortable, but becoming noticeably more challenging.
2-3	LIGHT ACTIVITY Feels like you can maintain for hours. Easy to breathe and carry a conversation.
1	VERY LIGHT ACTIVITY Hardly any exertion, but more than sleeping, slow walk, etc.

Heart rate training zones

Heart rate training zones can be applied in programming in the same way as percentage of 1RM is used to denote load/intensity in resistance training. In the same way that %1RM is aligned with certain resistance training modes (e.g. 85+% for strength training). While there are a few different versions of cardio training zones to be found online, most literature states the heart rate training zones as follows:

Zone	Intensity of Zone
Zone 1	Easy: 50-60% HRmax
Zone 2	Moderate: 60-70% HRmax
Zone 3	Hard: 70-80% HRmax
Zone 4	Very Hard: 80-90% HRmax
Zone 5	Maximal Effort: 90-100% HRmax

How each of these HR training zones relates to the different cardio training modes will be covered in detail within each of the topics you cover this week.

Improving cardiovascular condition (fitness)

There are three key adaptations that need to occur to improve cardiovascular condition. It is important that you have an understanding of these concepts as you begin your journey into cardiovascular training approaches. Cardiovascular condition enhancements are typically encompassed within three key improvement areas:

1. Increase in VO2 Max
2. Improvement in Lactate Threshold
3. Improvement in Movement Economy

Once you understand these concepts in greater detail, you can then better understand how each CV training mode we cover in this module contributes to improved cardiovascular condition. This section will briefly introduce you to these concepts. You will learn about these in greater detail in upcoming topics (under the cardio training modes they most relate to).

Increasing VO2 Max

VO2 Max essentially reflects the size of the cardio “engine”. Those who perform more CV training volume exhibit the highest VO2 Max results. The graph below shows the difference in VO2 Max between untrained subjects, recreational joggers and elite marathoners.

Your VO2 Max is dependent on a number of key variables including your efficiency in getting oxygen into your lungs (influenced by lung capacity), getting oxygen into your bloodstream (the result of increased pulmonary capillaries and more red blood cells), enhanced delivery of oxygenated blood to working muscles (due to improvements to the heart muscle increasing stroke volume and cardiac output) and the ability of your muscles to store and utilise oxygen along with their efficiency in producing ATP (related to an increase in mitochondria within muscle cells). All of these variables allow greater efficiency of oxygen delivery, use and production of energy using aerobic mechanisms resulting in a greater aerobic capacity. More on the science behind these training improvements coming up in later topics.

VO2 Max and Athletic Success

Having a high VO2 max does not guarantee success, but it certainly helps! Keynan marathon runner Eliud Kipchoge holds the record for the fastest completed marathon (42km) race at 2 hours, 1 minute and 9 seconds. While Kipchoge’s exact VO2 max isn’t definitively known it is estimated to be in the region of 80 ml.kg-1.min-1. Most elite marathon runners in the world (that have been tested) typically return VO2 Max results in the high 70s and a few in the 80s (ml.kg-1.min-1).

The following video explains VO2 Max in a little more detail.

It is possible to be an elite endurance competitor without having a ridiculous VO2 Max. This means there must be other key variables involved in athletic endurance success. One of these other key variables is your “Lactate Threshold”.

Increasing lactate threshold

If your VO2 Max indicates the size of your aerobic engine, lactate threshold indicates what percentage of that engine you are able to use effectively for aerobic exercise. Your lactate threshold is the maximal effort (or intensity) that you can maintain for an extended period of time with little to no increase in lactate in the blood. The lactate threshold refers to a working intensity and not a specific blood lactate level. The level of lactate in the blood begins to increase as you move from using the aerobic to anaerobic energy systems (essentially when your muscles start to use glucose without oxygen to generate energy). If you can increase your lactate threshold, you can work at higher intensity levels without succumbing to the effects of fatigue. More on this under topic three – Lactate threshold training.

Improving economy of movement

The final of the three main contributing factors to cardiovascular conditioning is economy of movement. The effectiveness of this factor cannot be underestimated. In fact, many analysts attribute a large portion of Kipchoge’s outstanding running ability to his exceptional running economy. Movement economy is essentially a term that references the efficiency of an athlete’s technique when performing repetitive CV training modes. Santisteban et al (2022) suggest that running economy can vary by as much as 30-30% among elite runners.

The more economical an athlete’s movement, the less energy (and oxygen) they consume, meaning an individual with efficient movement economy can travel at speeds using less fuel and oxygen than their inefficient opponents (McIlroy, 2016). While movement economy is largely influenced by force summation resulting from an individual’s technique, it is actually a complex, multi-factorial concept that represents the sum of various metabolic, cardiorespiratory, biomechanical and neuromuscular characteristics (Barnes and Kilding, 2015).

Every CV training mode has technical aspects that can be refined from stride length and upper body posture in running, angle of pull in rowing, to kick depth in swimming. Refining technique requires an in-depth knowledge of the CV training mode in question.

Luckily, the neuromuscular system appears to be very good at refining technique through repetition of the action. Essentially, the more you do the activity, the more efficient your neuromuscular system becomes in refining the movement. The literature appears to indicate that economy of movement can be (and should be) enhanced at a range of training intensities. It appears that the workout speeds that are recommended for improving VO2 Max and lactate threshold are also the best for improving movement economy (i.e. LSD and lactate threshold training methods), however, more recent research has also indicated that sprint work, strength and plyometric exercises can also contribute to improved movement economy. From a running perspective, the faster you run, the more you utilise stride length, muscular power and stretch reflex of muscles, all of which improve running economy at slower speeds (Barnes and Kilding, 2015).

So, what have we learned so far?

Cardiovascular conditioning has three main factors we need to target to optimise CV fitness. These are:

1. increasing VO2 Max
2. Increasing the lactate threshold, and
3. Improving movement economy.

In order to target all of these factors, a CV training programme would need to include various approaches including:

• Long distance steady state efforts to build stamina and cause changes in the muscle including increased mitochondria and capillaries. This form of training also helps to refine movement economy.
• Prolonged efforts of up to 20-30 mins that maintain an intensity just below lactate threshold to stress the system enough to cause adaptation and shift the lactate threshold curve to the right.
• Mixed sessions that combine harder efforts with easier efforts to allow the system to become more efficient at clearing exercise by-products during exercise.
• Shorter more intense intervals (above lactate threshold) to further stress the system and increase the lactate threshold (and allow more refinements in running economy).

Bouchard et al (1998) suggest that while the cardiovascular conditioning factors are critical to overall CV condition improvement, there are additional factors that will influence an athlete’s ability to improve CV fitness (and that will determine the amount of improvement possible). These authors suggest that up to 50% of aerobic performance (and therefore improvement) is dictated by genetics (heavily influenced by muscle fibre allocation, anthropometrics (body shape and size) and heart and lung function). They also suggest that a further 15% of aerobic performance/improvement comes down to mental toughness. This demonstrates that there is ample room for improvement for everyone!

Watch the following video which analyses Eliud Kipchoge's groundbreaking unofficial sub-two-hour marathon run. It delves into the strategies he used to enhance his movement efficiency during the race, pushing the boundaries of human potential in cardiovascular performance.