In the first post, we learned that blood pressure (BP) is the product of cardiac output (amount of blood pumped per minute) and pulse rate. Our last post discussed the many positive benefits that exercise for our heart and blood vessels, including the ability to maintain a high cardiac output to provide active muscles oxygen during exercise. Fit individuals can maintain a high cardiac output and BP. But, high BP during exercise is a negative marker of health. Let’s untangle these ideas.
Below, we hope to answer 2 primary questions:
1) Why is high blood pressure during exercise a BAD thing?
2) Why high blood pressure during exercise could be a GOOD thing?
Before we get into the good and bad, let’s describe what an exercise test is. First, an exercise physiologist would fit a strap around your chest to measure pulse rate. Sometimes 10 sticky-pad electrodes would be placed on your torso and rib cage to closely monitor heart function (an electrocardiogram; EKG). Then, a BP cuff would be fitted around your upper arm.
Your resting pulse rate and BP are recorded then it’s time to hop on the treadmill (or stationary bike). After a brief warm-up, each 2-3 minute stage includes an increase in speed and/or an incline (or resistance). At the end of each stage your BP is measured. This continues until physical exhaustion at your maximal exercise capacity. After a brief cool-down, your BP is monitored until it returns to resting levels.
After the test, you can look at your peak BP and fitness level (each stage completed represents a higher level of cardiorespiratory fitness).
Let’s look at the evidence supporting high exercise BP as a “bad” thing.
The bad: high blood pressure during exercise.
As early as 1981, scientists were beginning to understand the value of exercise BP in predicting future development of high BP, a major risk factor for heart disease. Finding that those with the highest exercise BP’s were most likely to develop high BP later in life.
Fast forward to 2011, a report published in the Journal of Human Hypertension, followed-up with 294 women and men 10-12 years after a maximal cycling exercise test. They found that high peak systolic BP during exercise was predictive of future high BP. A limitation of this study was that it may not have been representative of the population, as most of the participants were referred for exercise testing based on “unexplained chest pain or [for] investigation of suspected coronary heart disease.” But, are exercise BP values useful for predicting future risk of high BP in healthy individuals?
The short answer is yes. Eighteen research studies measuring BP during exercise, including over 35,000 individuals with normal resting BP, were reviewed by a group of German scientists. They concluded that high exercise BP is linked to increased future risk for high BP and adverse cardiovascular events (i.e., heart attacks, strokes).
It looks like there is plenty of evidence that high exercise BP is a bad thing. Let’s look at the other side of the coin.
The good: high blood pressure during exercise.
A 2017 study compared the relation between cardiorespiratory fitness and health care costs. Not surprisingly, they found that the fittest individuals had the lowest health care costs. However, upon closer examination something interesting appeared.
The change in systolic BP during exercise in the least fit group (<60% age predicted fitness) was 34mmHg, whereas the fittest group (>100% age predicted fitness) had a change of 52mmHg.
Since statistical analysis were not carried out for this variable, I used the reported group means and standard deviations for statistical analysis, using a one-way ANOVA. As expected, the results demonstrated a statistically and, more importantly, a clinically significant, higher peak systolic BP in the fittest individuals compared to those with the lowest fitness (p<0.01)*.
In the previous section, we learned that higher BP responses during exercise is associated with greater future risk of high BP and adverse cardiovascular events. However, these results suggest that greater fitness is associated with lower healthcare costs, which is not a stretch to represent the (lack of) disease presence.
Let’s look at two reasons that might explain this discrepancy (least fit vs. most fit):
1- Peak metabolic workload (4.4 vs. 10.8 metabolic equivalents (MET))
2- Use of beta-blockers (39% vs 22% individuals)
The oxygen demand during peak exercise in each group was vastly different. The 4.4 peak MET level in the least fit group can be attained by “walking at 3.5mph or playing Ping-Pong” whereas the 10.8 MET level in the fittest group can be attained by “vigorous cycling or ice hockey” (Exercise Physiology textbook). With this new context, we can see that while the RELATIVE workload (peak for all groups) was matched, the ABSOLUTE workload (walking vs. vigorous cycling) vastly differed. Further, the least fit group had a much higher prevalence of heart disease, which would limit individuals’ peak workload.
High heart disease ---> High beta-blocker usage
Beta-blockers are prescribed to reduce blood pressure, specifically during physical activity. They work by reducing your pulse rate and the force of heart contraction.
While peak BP was higher in the fittest group, we now see the difference can be at least partly to the higher cardiorespiratory fitness and lower prevalence of disease/BP medications. This study included almost all men (>97%), however we would expect to find a similar relation between high fitness and low health care costs.
Let’s review what we learned here:
Low workload ---> small BP increase
High workload ---> large BP increase
Low workload ---> large BP increase
We must remember that science is a process, and when new reports are published, we must remember the larger picture to keep things in context. Each new finding brings about new research questions. This is good as it acts a positive feedback loop to keep moving science moving forward.
While each finding on its own may not be massively impactful, it becomes part of a larger network of what we have come to understand. One of my favorite quotes that captures this idea was shared by Robert Collier, “Success is the sum of small efforts – repeated day in and day out.”
Let’s keep moving forward. We will continue to learn about how the body works in future posts. Until then feel free to leave your thoughts, comments, and questions.
Thanks for reading. Stay curious.
Editor(s): Austin Robinson, PhD
Curious to learn more? Check out these related resources.
*There were also significantly higher peak BP in group 1 (fittest group) vs. groups 2, 3, & 4 (the least fit group); in group 2 vs. groups 3 & 4; and in group 3 vs. group 4. Tukey HSD post-hoc analyses (p<0.02 for all comparisons).
It is usually convenient to store new information that conforms with our current beliefs, but the magic happens when we stop to consider the ideas that challenge our thinking. To quote F. Scott Fitzgerald, “The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.”
Curious where you would fall based on your BP response during a maximal exercise test. This 2017 study provides percentile ranks using reference values for each age group.