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Cardiovascular Drift: How it Affects Runners and their Training

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For most people working out and training boils down to reading the digits of their training gadgets or deriving issues and solutions from the data derived from these gizmos designed to help your training efforts. For runners, be it a novice or a seasoned runner, understanding the concept is of utmost importance instead of just blindly taking in records and timings. The theory behind every concept will help you to optimize your performance and can be put to its full potential instead of just running up subjective digits. Such is the case with cardiovascular drift. This concept is a direct correlation between the effort being put in and the heart rate because of it and understanding the ins and outs of it will help you to train more constructively and raise your potential as a runner. We will be discussing how cardiovascular drift or cardiac drift affects runners and what the best way to harness it is.

What is Cardiovascular Drift?

Before we define cardiovascular, keep in mind a simple concept – ‘Consistent pace doesn’t always equal consistent heart rate.’

The term cardiovascular drift, also known as cardiac drift, refers to the physiological changes in the functioning of the heart whilst exercising over a prolonged time period. In the case of running, this points towards the increase in the heart rate which takes place over time even when you run with (little or) no change in the pace. 

Cardiovascular drift is generally caused due to the natural increase in the core body temperature whilst running. The increase in the core body temperature will lead to an elevation in the heart rate much in the same way as running in hot conditions would. In the course of the extended exercise, the stroke volume drops steadily while the heart rate increases. 

Stroke volume refers to the amount of blood that the heart pumps out with every beat. While there is an increase in the heart rate, the cardiac output and oxygen intake would still remain constant during prolonged exercise, since it gets balanced out by the drop in stroke volume. Generally one would note that despite the increase in heart rate the decrease in stroke volume leads to a drop in cardiac output. Cardiac output is a function of stroke volume times the heart rate.  

You will see that whilst completing harder training runs and you enter an anaerobic stage, the heart rate naturally increases over time, especially with the increase in the level of exertion. 

cardiovascular  drift
Know your pace and cardiac drift (source)

The Significance of Comprehending Cardiac Drift 

If you are someone who uses a device to measure your heart rate while running, you could be very easily misled if you do not understand the theory behind cardiac drift. While monitoring your intensity by the heart rate, the device could lead you to believe that you are working harder than you actually are. A long run at constant effort can cause a drift up after around ten to fifteen minutes, by as much as 20% despite the fact that you’re performing at the same pace and consuming the same amount of oxygen. Noticing an increase in the heart rate would be a convincing factor to ease up on your workload and in doing so would make your training session counterproductive, i.e. your training effectiveness would be lost. 

Also, remember that an increase in your heart rate does not automatically point towards burning calories the same way as it doesn’t automatically point towards oxygen uptake or increase in effort. What we’re saying here is that do not believe any data which states that an increase in your heart rate has led to losing ‘X’ number of calories since that data would be futile. 

What is actually happening?

Cardiac drift means that your heart is working harder and then some, at technically the same work rate. Ideally, you would want the exact opposite – that the heart rate remains the same when maintaining the same amount of pace or power or effort. 

Why does this happen? 

The major reason is fatigue being backed up dehydration. The blood comprises of a lot of water, dehydration means less water means that your blood is not only thicker but there’s also less of it. 

Because of the less amount of blood your heart is pumping harder so as to distribute the same amount of oxygen and nutrients to the working muscles. So when there’s less blood, it means there’s less oxygen reaching your muscles, which means there’ll definitely be a decrease in your performance. 

An Interesting Twist: 

So we’ve established that the heart rate tends to drift upwards steadily over a certain period of time. But in the case of endurance events like ultra races etc. the story takes a bit of a turn. 

Over extensive time, the intensity decreases by six to seven percent due to a result of substrate shifts and neuromuscular fatigue. Substrate shifts mean the relative use of carbohydrate to the use of fats. All of this means that the heart rate will decrease and a downward cardiac drift will take place. Similar to an upward cardiovascular drift, a decreasing cardiovascular drift can be corrected by proper hydration, re-fuelling and electrolyte homeostasis

How is Cardiac Drift affecting your Training /Workout?

An increase in heart rate can be noticed approximately ten minutes into a moderately intensive workout, say, for instance, jogging or brisk walking. The heart rate could jump up as much as ten to twenty beats despite maintaining the same amount of effort and pace, placing you at a higher heart rate zone than at the beginning of the workout at the same level of effort. 

Various Reasons for an increase in heart rate:

  • Loss of sleep will raise the heart rate from five to ten beats per minute. 
  • Caffeine will boost the heart rate for up to 24 hours after consumption and ingestion. 
  • Workplace stress will elevate the heart rate by four to six beats per minute.
  • Dehydration could lead the heart to beat five to seven percent faster than normal. 
  • Humid and hot climatic conditions will also cause the heart to beat faster. 

With this fluctuation in your heart rate, you could be training out of the zone that you’re aiming to be in. Since your resting heart rate is changing during the day (could be due to any of the reasons stated above), it means that your training zone is being affected as well. If you do not perceive that your heart rate is higher than normal, and do not recalculate your training zone to match it, you could end up believing you are in an aerobic zone while all while you are already hitting the anaerobic approach in the higher zone. A mistake as such would tire you out faster and you might end up overexerting yourself by pushing too hard thus you can train yourself with anaerobic and aerobic exercises and stay fit.

stressed out
Keep stress at bay

How to Reduce your Cardiovascular Drift?

In order to lower the effects of cardiac drift, limit or decrease the amount of stress being placed on your system during the action of running – both, the event as well as during training sessions.  
Two of the easiest and fastest ways to fight this issue is proper rehydration and attempting to keep the body as cool as possible. 

Proper hydration would include an intake of 24 – 32 ounces of liquids for every one hour at the least. In the case of hot or humid climates, the intake could even be doubled. While the amount may seem like a lot as long as it isn’t causing any gastric distress, then you’re doing alright. A good way to cool down is to slowly pour water over your head. This would aid in restricting the increase of your core body temperature by causing a mentally pleasing effect. 

Few tips on hydration that runners need to keep in mind:

  • The body has a tendency to absorb cool liquids a lot better than warm liquids so chill your bottles or add some ice cubes. 
  • Women’s hydration needs are different from men’s. Since women tend to sweat less their intake of water too would be less comparatively. 
  • Another thing that plays a part in dehydration is your weight. The lighter weighted would deal with heat much better. The key is to know how much you sweat and to replace the same. 
  • Dehydration isn’t a one-day thing. The effects of it are easily carried over and could affect your performance levels, so don’t ignore the signs. 
stay hydrated
Stay hydrated to be on tracks

What to do about Cardiovascular Drift?

Don’t go by what your monitors display as fancy and ‘goal-oriented’ digits. Instead, use your heart rate as an advantage and as a guide to help you get onto the right path. An easy way to get there is to begin using breathing rhythm as a way to determine your intensity. This might pose some difficulty at first, so begin by using your heart rate monitor for the ten to fifteen minutes to get the basic gist, then repeat the same by running by feel and keeping the monitor covered. Glance at your data once you’re done running to compare the breathing rhythm and effort. Similarly, with the other underlying concepts of gizmos and gadgets, you can grasp better application techniques to your training. 

cardiac drift
Don't be slave of heart rate monitors (source)

Summing Up 

Don’t let Cardiac drift lead to a drift in your performance levels. It will occur, but you need to be aware of it and limit it. Your heart rate affects your performance because of oxygen uptake. But realizing how your heart rate is affecting your running will help you to become a better runner. Remember to limit the levels of stress you place on your body by following proper refueling and rehydrating patterns and keeping the body temperatures down. Your body is already stressed giving the different types of training and races you subject it to, put some thought into it, and be kind to your body…. 

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