Wednesday, November 7, 2012

Endurance Sports and Heart Health (Part II): What are the benefits?

This is the second part in a series of posts on endurance sports and heart health.

2,466,115,200. That's how many times my heart will beat if I live as long as the average American is expected to (78.2 years). (My wife says it better beat for longer.) My resting heart rate is about 60 beats per minute. That's a fascinating number to think about. For almost eight decades my heart will supply my entire body (and itself) with the oxygen it needs to survive, and never stopping. 

When it comes down to it, the heart is a relatively simple organ - essentially a four-chambered pump with some tubing going into it and coming out of it. But of course the devil is in the details. Over the course of more than 2 million beats, there is a lot of opportunity for things to go wrong, and many times these things are the result of accumulated issues over time.

As I discussed in the first part of this series, with endurance exercise, there is a fine line between performance and pathology - something referred to as the "grey area" in the scientific literature. There are risks when it comes to endurance sports. But risks can be managed and risks must also be viewed in the context of benefits (it's all about optimizing). 

In this post I discuss some of the benefits of endurance sports and regular exercise, particularly from a physiology perspective, as well as a public health standpoint. But I close with some cautions about maximizing exercise while neglecting other areas of daily life that contribute to heart disease and heart issues.

Popularity of Endurance Sports is Increasing

Endurance sports, such as half-marathons, marathons and triathlons, are becoming more and more popular. The previous post in this series showed the increasing level of participation in USAT-sanctioned triathlon events. Half-marathons and marathons held in the U.S. show a similar trend. Not only are there more races, but more people are participating. For example, according to Running USA, a non-profit that tracks trends in U.S. distance running events, the number of marathons in the U.S. more than tripled between 1985 and 2011, from 200 events to 720 events., an online community for sports and event registration hub for a variety of activities (including running, cycling, triathlon, and more), revealed similar increases based on race registrations between 2008 and 2010. During these three years, marathon registrations increased 203%; half marathons rose 154%, 10K events rose 155% and 5K events rose 144%.

Why is This a Good Thing from an Individual Health Perspective?

Your heart is a muscle, and like other muscles, it responds to stimuli like exercise. It can grow stronger and increase in size similar to other muscles in our body after periods of exercise. And generally (and up to a point), the more exercise, the stronger, more efficient, and sometimes larger the muscle. Endurance activities markedly improve the efficiency of your heart, increasing stroke volume (or the amount of blood pumped by the heart with each beat) and thereby decreasing the number of overall beats needed.

Other markers of heart health have also been positively linked with endurance exercise, such as lower blood pressure and increased HDL cholesterol.

There is also evidence to suggest that exercise plays a strong role is energy partitioning, or the type of energy (such as carbohydrates or fat) our body preferentially burns for fuel. One study of 55 years old women found a more than 9% increase in energy derived from fat after 12 weeks of endurance exercise training.

The weight-bearing movements of regular exercise and strength training support bone health and improve longevity, particularly as people age. Exercise is also associated with lower stress levels, higher energy levels, and overall positive mental health.

Not a bad list of benefits.

Why is This Essential from a Public Health Standpoint?

Physical inactivity is becoming a new norm and the trends don't look promising. A recent review from researchers from the University of North Carolina looked at trends of metabolic equivalent hours (just a fancy way to show the amount of exertion by your body doing different activities) from 1965 to the present, and also projected trends through 2030. Between 1965 and 2009, MET-hours per week decreased by about half (235 to 160), and they are projected to decrease to roughly 126 by 2030. You can see the trend in the graph below, which traced MET-hours in several different areas, such as physical activity during work, transport, domestic activities, and leisure time. The black line is the average hours per week of being sedentary.

The rising trend from 2010 to 2030 represents one of the major public health challenges we face. 


What These Trends Don't Tell Us  

Even though registration and participation levels in endurance activities, such as triathlon and marathon, are increasing for a range of age groups, a couple things to remember.

First, this is still a relatively small proportion of the overall U.S. population, which is almost 315 million. From a sports, competition, and individual health perspective, increasing participation is a great thing. For people like myself, it provides a great opportunity to continue competing, setting and working towards new individual goals, staying in good overall health (though my third point mentions another counter-argument to this), and traveling to new and interesting places. However, one must keep this all in perspective that we're still talking about a fairly exclusive cohort of people.

Second, inequalities, particularly in regards to access, are major issues. Opportunities to participate in physical activity pay huge dividends with individual physical and mental health, population health, and create millions of dollars of health care cost savings annually. But, not everyone can afford a gym membership; or can safely walk to a park; or can spare the $120 marathon registration or the extra 30 minutes a day to train. The challenge is to celebrate record numbers of people taking on the endurance challenges of running, triathlon, cycling, etc, but to also ensure environments are conducive to regular physical activity for everyone.

Third, all the effort put into exercising everyday could be for naught if you spend hours sitting for the rest of the day. A recent review examining the link between sedentary time and diabetes, cardiovascular disease and cardiovascular and all-cause mortality in adults older than 18 years of age found that "higher levels of sedentary behavior are associated with a 112% increase in the RR of diabetes, 147% increase in the risk of cardiovascular disease, 90% increase in the risk of cardiovascular mortality and 49% increase in the risk of all cause mortality." Even more frightening are the results from a recent National Health and Nutrition Examination Survey. The study looked at almost 5,000 adults 20 years of age or older and found "Independent of potential confounders, including moderate-to-vigorous exercise, detrimental linear associations of sedentary time with waist circumference, HDL-cholesterol, C-reactive protein, triglycerides, insulin, HOMA-%B, and HOMA-%S were observed." (emphasis added) This essentially is saying that even if someone exercises in the morning, and the rest of the day is spent sitting, this could have a detrimental effects on risk factors - high levels of triglycerides, higher inflammation, higher waist circumference (a fairly good measure for dangerous visceral fat), etc - for heart disease and other chronic diseases.

So, I come back to this theme of optimizing. Sure there are a lot of health benefits to exercise and endurance training. But at the same time, if you're trying to maximize in this area of your life, and neglect other things (such as diet, stress, amount of time sitting during the day, etc), are you really optimizing for better overall health?

Let me know your thoughts and post a comment below.

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