Cardiovascular Conditioning: adaptations to aerobic training

This piece is written for those with little background in exercise physiology, breaking concepts down as much as possible without losing the integrity of the general concept, adaptations our body makes to aerobic training. For health, safety and performance sake, however, I feel it needs to be made clear from the outset that aerobic training is not the “be all and end all” in taking care of our bodies. Other types of training are necessary for a variety of health and safety reasons. Emphasizing only aerobic training can compromise our ability to respond to emergency situations with the speed and power necessary to protect ourselves and can prevent us from maintaining tissues that have the type of mass, flexibility and elasticity needed to respond with quick movements and absorb minor fall. Please feel free to ask me or your trainer more about this.

Cardiovascular Adaptations

Aerobic training, as the adjective implies, develops our ability to utilize oxygen in processing energy. The aerobic response in the body involves the nervous, endocrine (hormonal), cardiopulmonary and muscular systems most directly. The ability of the heart to transport oxidized blood to the muscle tissue is the dominant and easiest response to measure. With the appropriate stimulus, the primal part of our brains triggers a neural and hormonal response that dilates the arteries that supply the skeletal muscles and constricts those that supply less essential structures. Neural and hormonal responses also trigger the heart to expand as fully as possible and contact as forcefully as possible to bring in as much blood as possible and push out as much blood as possible. The complete filling of the heart causes this muscle to stretch to its fullest capacity, therefore enhancing the expulsion blood by way of an added elastic release to the powerful muscular contraction. This allows more blood to be ejected with fewer contractions. This characteristic is maintained and developed in the cardiovascular system with training, so that at rest the heart will continue to need fewer contractions to provide the body with the oxygen it needs to process energy. This, over time, presents itself as a lower resting heart rate in aerobic athletes.

Energetic Adaptations

The advantage behind supplying so much oxygen so quickly to the muscles is that it allows for a very efficient energy processing system called the oxidative system. This system can produce a lot more energy than the other two major energy systems in our body and better utilizes more fuel sources. Aerobic training encourages the production of those enzymes that aid in the oxidative process, allowing the breakdown of carbohydrates and fats to produce energy.

Neuromuscular Adaptations

Processing energy using large quantities of oxygen happens in the muscle cell within an organelle called a mitochondria. This is a complex structure and in itself requires considerable resources. Some muscle tissues are better adapted to utilizing mitochondria. These are the type I muscle fibers. Aerobic training emphasizes the development of type I muscle tissue. As training continues, muscle filaments and neural connections that are deemed as unnecessary in the type I muscle fibers are replaced with mitochondria to process oxygen. Collagen (a light, tough element in the connective tissue) is added to support the muscle cell in the absence of contractile filaments.

The Overall Result

With continued aerobic training, the athlete develops a cardiovascular system that can transport great quantities of oxygen to an oxidative system that supplies the enzymes that produce energy within very light, efficient muscles that are able to produce movement over and over again for long period of time without rest.
This is perfect for the distance runner and has health benefits for us all but, as stated above, it should never be the only form of exercise one gets. It can diminish flexibility, strength, balance and power (the ability to respond quickly with strength) and by itself is not the best way to lose weight or maintain a healthy weight or body mass.

For the complete story…

The above explanation has gaps big enough to drive a truck through. The full story covers a couple of hundred pages in an exercise physiology book and it’s probably best if you’ve had your biology and chemistry before reading it. If you have any questions about this or the body’s adaptation to different types of training stimuli, feel free to book an appointment with me.

Cardiovascular Conditioning: Maximum Heart Rate

Most people and most athletes don’t fully understand the relationship of cardiovascular to their training goals. We’ve had a string of over-training injuries and conditions during August. Cross country runners pumping out 100 mile weeks and soccer players determined to toughen up quickly with excessive road work, to name just a few. This is no surprise – aerobic training is addictive, easy to do and it is not a simple subject to understand. Even the rationale for the standard formula currently accepted for maximum heart rate is questionable for training purposes. Since the gyms seem to be full of people wearing fashionable heart rate monitors, maximum heart rate seems like a good starting point,  for athlete and non-athlete alike, to better understand the cardiovascular response to training in their bodies.

MHR = 220 – age

The standard formula for maximum heart rate (MHR) and its derivatives is MHR = 220 – age. It’s so commonly used in the training world one would think the scientific foundation for the statement was solid and profound and absolutely the last word. It’s none of the above. The equation was derived in the 1960’s from an observation of data Dr. William Haskell had collected and graphed from a study about heart disease. The subjects were male, under fifty, not in particularly good shape, and many smoked. The original goal of his study was to determine just how hard heart disease patients could push themselves and was not designed at all to evaluate healthy individuals or conditioned athletes. So, how did it become "law"? It wasn’t the study, but the timing of its release. Cardiovascular training was just becoming popular in gyms and on the streets (I can still remember neighbors teasing me, yelling “Hey, what are you running from?” when running in 1968!). Doctors and trainers were hungry for an answer to the question “How hard should I run?”. The formula stuck. Not very scientific when it comes to training perhaps, but whole industries grew up around it so it’s probably going to be in people’s repertoire for a while.

For training purposes we like to manipulate different physiological responses within the body which we know are related to how oxygen is exchanged, which can be roughly related to percentages of the maximum heart rate. Therefore, a Target Maximum Heart Rate formula (TMHR - a percentage of the MHR) is used to target these changes.

For example:

A 40 year old woman is instructed to run at an intensity of 75 to 80% of her maximum heart rate.

TMHR(lower limit) = (220 – 40).75 = (180).75 = 135bpm (or about 23b/10sec)
TMHR(upper limit) = (220 – 40).80 = (180).80 = 144bpm (or about 24b/10sec)

Now for my money, if we are going to use a set formula like this, we need to be looking for the percent of change between the minimum heart rate (resting heart rate, RHR) and maximum heart rate. We can then add in the resting heart rate at the end to provide us with a real countable beats per minute number.

Therefore, that same 40 year old female athlete with a resting heart rate of 60 beats per minute would be:

TMHR(lower limit) = (180 – 60).75 + 60 = 150bpm (or 25b/10sec)
TMHR(upper limit) = (180 – 60).80 + 60 = 156bpm (or 26b/10sec)

One of the reasons this formula has stuck around is that it is relatively safe for the average person. For general conditioning purposes, however, it has been suggested that rate of decrease in heart rate from maximum heart rate to resting heart rate after exercise might be a better indicator of when to increase the intensity of an aerobic workout. That is, in general, how long does it take your system to recover is a better indicator of your health and conditioning. In training athletes, perceived exertion levels are often used instead of specific heart rates, which really does make sense, especially with elite athletes whose heart rates often don’t fit the MHR format at all.

One final note – don’t trust the built-in heart rate monitors in the cardio equipment at the gym. The accuracy varies wildly – depends on the machine and the gym maintaining them. Check it yourself. Yes, your calculations are correct – the machine is wrong.

In future blogs, we will examine the specific changes cardiovascular training promotes in the body.

References Utilized:

1. Ultimate Fitness
     Kolata, Gina Farrar, Straus and Giroux 2003 NY, NY

2. Essentials of Strength and Conditioning, 2nd Edition
    Baechle, Thomas R., Earl, Roger W. Human Kinetics 2000 Champaign, IL