Aerobic exercise: How hard should I work out?

"How hard should I be working out?" This is one of the most common questions people ask me during fitness training. This is a good question and the answer is different for everyone. This is because an individual's exercise intensity level, or how hard they need to be working, is directly related to things like their fitness level, age and health. Everyone should ask themselves this important question before beginning an exercise program and when reassessing a current workout. Knowing your exercise intensity level is important in determining how best to bring about improvements in your health.

You may have heard the expression "in the zone" with regard to exercise intensity. This can be used to describe target heart rate (THR) training levels which are benchmarks that are measured during aerobic exercise. You may have seen this range visually depicted in a chart on your gym's treadmill control panel. Some use the misleading phrase "fat burning zone", more on this later, where others just say training zone. In any case, the theory of training in a target heart rate zone can seem a little perplexing.

Adding to the confusion, especially for women, is the emerging scientific data about a gender specific formula for maximum heart rate, which directly impacts how a woman knows if she's in "the zone." Additional information is available here, but before we get into that let's take a look at several factors that are helpful in determining whether or not you're working hard enough during your aerobic workout.

What is an aerobic workout? When we perform aerobic exercise, or aerobics as coined by Dr. Kenneth Cooper way back in 1968, we are increasing our need for oxygen by performing an activity that engages the larger muscles of the body.  This sustained activity, in turn, causes the heart and lungs to work harder than when the body is at rest in order to provide more oxygenated blood to fuel the working muscles (1). There are many health benefits to aerobic exercise (3), and the Mayo Clinic lists ten of them here.  One reason we are focusing on in this post is heart health. 

Heart rate or pulse is the rate at which blood is squeezed out of the heart per minute (BPM). We can use our heart rate to measure how hard our heart is working at rest or during aerobic exercise. This can be done by taking a pulse or heart rate and determining our BPM number. Pulse points are places where an artery passes close to the skin and makes it easier to feel blood pulsing through it. There are several pulse point locations on the body, but 2 of the more commonly used sites are found on the wrist (radial pulse), or on the neck (carotid pulse).

Once you've found your pulse, count the number of times you feel the blood pulsing under your fingers for 10 seconds. Then multiply that number by 6 and you will have your heart rate for one minute. For a more precise measure, you can also use a blood pressure monitor that counts your pulse for you. To learn more about manually taking your pulse, just follow the link here to the Cleveland Clinic's website.

Resting heart rate (RHR) is another useful indicator of heart health. This is the number of times our heart beats per minute while we aren't engaging in any activity and is best taken in the morning before we get out of bed (3). I suggest measuring it for 3 mornings and then taking the average. According to the National Institutes of Health, a normal RHR range is:
Newborn infants - 100-160 BPM
Children 1 to 10 yrs. - 70-120 BPM
Children over 10 and adults (including seniors): 60-100 BPM
Well-trained athletes - 40-60 BPM (5)

Maximum heart rate (MHR) - Knowing your MHR will help you in calculating your target or training heart rate (THR).  The gold standard for determining your MHR is to take a doctor supervised treadmill test. However, for many of us this may not be practical, so exercise physiologists have developed several formulas to help estimate MHR.  One of these is called the estimated maximum heart rate formula:

MHR = 220 BPM - age

At the beginning of this decade, research conducted on the estimated MHR formula found that it "underestimated MHR in older adults" (7). These scientists proposed a new MHR formula:

MHR = 208 - 0.7 x age

This year, more recent research has found that this formula overestimates the MHR for age in women, especially those over the age of 35. See footnote (8). As a result of this finding a new gender specific MHR formula is being proposed, however it is not yet being used in a clinical setting because the research is considered preliminary. The gender specific formula is:

MHR = 206 - .88(age)

After we have determined our MHR we can calculate our training heart rate.


Training heart rate (THR) and finding the right intensity for you - THR is the desired heart rate range which will provide us with the most benefit from our aerobic workouts. Calculating a THR zone helps us determine the level of sustained exercise intensity that best challenges our heart and lungs safely. When calculating THR, I prefer to use the Karvonen or Heart Rate Reserve Formula.  This formula is more personalized because it factors in the resting heart rate (RHR) to determine heart rate reserve (HRR). The formula for calculating HRR is:

HRR = MHR - RHR

Now we move to the next step in determining THR. We multiply HRR by the desired training intensity range at which we want to workout. The American College of Sports Medicine recommends healthy adults exercise at a range beginning at 55% and up to no higher than 90% of MHR.

Let's put all this information into practice. A 30 year old healthy female who has a RHR of 70 and is of average fitness level wants to determine her THR zone.  Here is how she would calculate her THR range:
Begin by calculating MHR. Using the new gender specific MHR formula -
MHR = 206 - .88(age)
179.6 = 206 - 26.4
MHR = 180
Next we determine HRR using the formula HRR = MHR - RHR
HRR = 180 - 70
HRR = 110
Now we plug the HRR number into the rest of the Karvonen equation to determine the THR range.  We begin with the lower end of her training range (light to moderate) or 65%.
THR = 110 x .65 + RHR
THR = 71.5 + 70
THR  lower range = 141
Now we find the THR for our sample female of average fitness level at the top end of her training range (moderate to vigorous) or 85%.
THR = 110 x .85 + 70
THR  higher range = 164

So, this individual would monitor and strive to maintain for the duration of her aerobic activity a target heart rate zone between 141-164 BPM.  These numbers would be adjusted as her fitness level changed.


How much aerobic exercise is enough?   According to the American College of Sports Medicine healthy adults under the age of  65 should shoot for at least 30 minutes of aerobic activity, 5 days a week.  The Center for Disease Control (CDC) suggests healthy adults get at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity aerobic activity per week. This activity should be sustained for bouts of at least 10 minutes. For even greater health benefits the CDC urges us to shoot for 300 minutes of moderate intensity or 150 minutes of vigorous intensity aerobic activity per week, or an equivalent mix of both, again in bouts of at least 10 minutes.

What's light, moderate or vigorous intensity activity?  According to the CDC, "moderate intensity means "you're working hard enough to raise your heart rate and break a sweat." Examples would be:

• walking fast
• doing water aerobics
• riding a bike on level ground or with few hills
• playing doubles tennis
• pushing a lawn mower (CDC)

Vigorous intensity aerobic activity means "you're breathing hard and fast, and your heart rate has gone up quite a bit" (CDC). Examples include:

• jogging or running
• swimming laps
• riding a bike fast or on hills
• playing singles tennis
• playing basketball

So, having plowed through the formulas and worked through the calculations, we now know how to determine our THR zones.  As important and useful as this information is, it should be noted that it is all an estimation.  One research study found that when monitoring aerobic exercise in a group setting, perceived rate of exertion, or how the person exercising is feeling, was as good an indicator of training intensity as THR calculations.  Plus, the exercisers didn't have to stop to take their pulse. Whatever method you choose to monitor your exercise intensity,it is always best to work within your comfort level and not to exceed 90% of your MHR because of increased risk for injury.

The short video below from the American College of Sports Medicine's Exercise is Medicine Library talks more about using Rate of Perceived Exertion as a way to monitor THR. The take away from all of this is to just get moving because exercise really is good medicine.

Don't forget: It is important to check with your physician before beginning any exercise program. Next post will take a look at the misleading concept of the fat burning training zone, and will be much shorter I promise!

Sources
(1) http://en.wikipedia.org/wiki/Aerobics
http://www.google.com/dictionary?aq=f&langpair=en|en&q=aerobic&hl=en
(3) http://www.mayoclinic.com/health/aerobic-exercise/EP00002/NSECTIONGROUP=2
(4) http://www.americanheart.org/presenter.jhtml?identifier=4701
(5) http://www.nlm.nih.gov/medlineplus/ency/article/003399.htm
(6) Physical activity & health: an interactive approach, Thomas, D.Q., Kotecki, J.E.
(7) Tanaka et al., Age predicted maximal heart rate revisited http://content.onlinejacc.org/cgi/content/full/37/1/153
(8) St. James women take heart study http://circ.ahajournals.org/cgi/content/full/108/13/1554 
American College of Sports Medicine
Centers for Disease Control

Women, heart disease and new max heart rate formula

When it comes to women's healthcare, females are typically treated like smaller versions of males.  We women know we aren't "mini-me's" of men, but a patriarchal society hasn't been as quick to recognize this fact. Thankfully, the emerging science of gender based biology is proving what women already knew to be true. We are different. Here's a sampling of the gender differences research is revealing at the system, organ, tissue and even cellular levels:

1. "3 out of 4 people who suffer from an autoimmune disease (such as rheumatoid arthritis, lupus and multiple sclerosis) are women" (1);
2. women are 2 times more likely than men to be diagnosed with thyroid diseases (1);
3. 2-3 times more likely than men to suffer depression (1);
4. 2 times more likely than men to contract gallstones (1);
5. more likely than men to suffer a second heart attack within the year after their first heart attack (1);
6. women who smoke are up to 70% more likely to develop lung cancer than men who smoke (1);
7. 80% of  people affected by osteoporosis are women (1);
8. women are more like to suffer migraines than men (1)
9. a woman's liver metabolizes alcohol and drugs less efficiently than a man's liver (1);
10. a woman's heart is one third the size of a man's heart and beats faster (1);
11. woman wake up faster from anesthesia after surgery (1);
12. a woman's brain is neurologically different from a man's brain (1);
13. a woman's heart responds to high blood pressure by developing thicker walls which puts them at greater risk for heart failure than men (4).

Clearly, the contrasts between the sexes go way beyond the basic XX and XY chromosomes and our reproductive capabilities. Unfortunately for women's health, prior to the 1990's men were the model on which medical research was conducted. An example of this is the practice of pharmaceutical companies testing their new drugs only on men. The exclusion of women and minorities from medical research continued until Congress mandated that they be included. As a result of this change in practice, researchers in gender based biology are starting to reexamine drugs that were tested only on men. They are checking for their potential effectiveness because women metabolize drugs differently than men. 

Women and heart disease-

Heart disease is another area where gender based biology has identified differences between men and women. In 1991 the National Institutes of Health (NIH) implemented a landmark observational study concluded in 2006 called the Women's Health Initiative (WIN). WIN provided a great deal of data on women's health. Noteworthy is the finding that women aged 65 and older were more likely to die from heart disease than men. Also, under age 50 a woman's heart attack is twice as likely to be fatal as a man's (5). Experts suggest there are several reasons for this, one of them being that the symptoms of heart attack that men experience aren't necessarily the same for a woman (3). They can be more subtle than the severe chest pain that is the hallmark symptom for men. As a matter of fact, 71% of women reported feeling flu like symptoms in the weeks prior to having a heart attack (5). You can find more information on the topic of heart attack symptoms on The Mayo Clinic website here. A simple, noninvasive way to test for heart disease is the exercise stress test and recent research has provided more insight into the uniqueness of a woman's heart and the use of this diagnostic test.

Women Take Heart Study-

The Women Take Heart Study, conducted by researchers at Northwestern University, focused on determining the normal response of a woman's heart to exercise stress testing. An exercise stress test or treadmill test is used to check a variety of heart functions including: "heart rate, breathing, blood pressure ECG, and how tired you become when exercising" (7). A stress test can also help diagnose or predict safe levels of exercise, coronary artery disease, possible causes of chest pain,  and risk for heart attack (7). During a stress test doctors monitor a patient to determine if they are unable to reach at least 85% of their maximum heart rate. Failure to reach this benchmark means a greater risk of death from heart disease. How a woman's heart rate (HR), or the number of times a heart beats per minute (BPM), responded to the stress of an exercise stress test wasn't understood very well until the Women Take Heart Study. This is because up until this point most of the research in this area had been conducted on men.

Maximum heart rate formula based on male data-

Scientists have known that maximal heart rate (MHR) decreases with aging (9). As a result, the formula that doctors typically use to calculate a normal response to exercise stress includes a person's age. However, the formula doesn't take into account gender differences. The simplest form of the maximal heart rate calculation based on data gathered from research using men is: Average maximal HR (MHR) = 220 - age in years (9).

New maximum heart rate formula for women-

Now to the Women Take Heart study's exciting findings! This year Northwestern University researchers published results of their study that found "the traditional male-based calculation [of  MHR = 220 - age] overestimates the maximum heart rate for age in women" (8) especially in women over age 35 (10). The new gender specific formula for MHR is:

MHR = 206 -  88 percent of your age

Aerobic physical activity and heart rate-

Women whose stress tests were measured using the old formula tended to show a poorer prognosis, so this gender specific formula reflects a more accurate prediction of a woman's risk for heart disease.  The new formula is also important because heart rate is the standard method for monitoring aerobic exercise intensity. Using this new formula for MHR while calculating an aerobic training heart rate will more accurately reflect how hard a woman is exercising during aerobic physical activity. For example, a 50 year old woman's MHR using the old formula would be: 220 - 50 = 170. If she were shooting to work at a moderate to vigorous intensity range her training heart rate (THR) using the old MHR formula and the simple THR formula would be: 111 (170 x 65%) at the range's lower end and 145 (170 x 85%) at the range's higher end (see the Heart Rate Training Zones Chart below).

From American Council on Exercise

Using the new Women Take Heart MHR formula a 50 year old woman's MHR would be: 206 - .88(50) = 162. So, now the lower end of her THR range would be: 105 (162 x 65%) and at the higher end of her THR: 138 (162 x 85%).

Most charts will reflect training heart rate zones calculated with the old "men only" formula so keep this in mind when you're at the gym monitoring your exercise intensity. Also, exercise equipment and heart rate monitors have usually calculated THR using the old formula. However, some companies are already updating their equipment, but ask to be sure. There's also talk of an I phone app that can do the calculations for us.

It's important to note that some medications, like beta blockers taken for blood pressure control for example, can give false pulse readings. In this case, it is more accurate to measure your level of aerobic exercise intensity using Rate of Perceived Exertion or the Talk Test. You can read more about the rate of perceived exertion here, and the talk test here. Next week's post will go into a little more detail about the aerobic training zones, discuss the myth of the fat burning zone and also look at how doctors are using heart rate response to exercise as a predictor of disease and even death.

There were some limitations to the Women Take Heart study. Nevertheless, the researchers at Northwestern state that their findings "should be incorporated into clinical practice" (12). This research also underscores the importance of conducting more studies that take into consideration the fact that women are biologically unique and not just mini-men. Thanks to gender based biology research, health care might begin to treat the sexes differently.  

Sources

(1) Gender Biology: Men and Women Really Are Different. Films Media Group, 1998. Films On Demand. Web. 20 November 2010. <http://digital.films.com/PortalPlaylists.aspx?aid=10103&xtid=11115>.

(2) http://www.nature.com/nm/journal/v2/n11/abs/nm1196-1248.html 

(3) http://www.mayoclinic.com/health/heart-disease/HB00040 

(4) http://www.washingtonlifescience.com/readlist/ceo_bianco.htm

(5) http://www.womensheart.org/content/HeartDisease/heart_disease_facts.asp, http://www.womensheart.org/content/HeartAttack/heart_attack_symptoms_risks.asp

(6) http://www.nhlbi.nih.gov/whi/  

(7) http://www.heart.org/HEARTORG/Conditions/HeartAttack/SymptomsDiagnosisofHeartAttack/Non-Invasive-Tests-and-Procedures_UCM_303930_Article.jsp
(8) http://www.medpagetoday.com/PrimaryCare/ExerciseFitness/20954

(9) American College of Sports Medicine, Resource Manual for Guidelines for Exercise Testing and Prescription, 2nd ed.

(10) http://seattletimes.nwsource.com/html/health/2012244688_heart05.html 

(11) http://www.cdc.gov/physicalactivity/everyone/measuring/index.html
(12) http://www.medpagetoday.com/PrimaryCare/ExerciseFitness/20954

Make sleep a priority for good health.

Ahhhhh, the luxury of an extra hour of sleep. This happy event occurred because US Daylight Savings Time ended yesterday and we woke to turn our clocks back. It is such a great feeling to gain this extra hour. Unfortunately, it can't make up for months of lack of sleep.  Evidently, we're not the only sleep deprived nation. According to findings from a 2005 around the world survey of 35,327 people in Austria, Belgium, Brazil, China, Germany, Japan, Portugal, Slovakia, Spain and South Africa, the Japanese slept the least and the Portuguese slept the most. However, the study revealed that although people in Portugal spent more time sleeping, they reported the most sleep disturbances (1).  It turns out that when it comes to sleep, quality and quantity are equally important. Since most of us are lacking in one or both, it's probably safe to say that we are globally sleep deficient.

It seems sleep has become a victim of the current 24/7 mindset, and we are only just beginning to understand the health consequences. Scientific evidence suggests that erratic sleep or lack of sleep increases our risk for a number of diseases, including cancer, heart disease, diabetes and obesity. In addition, although scientists are only just beginning to understand the interactions between sleep and the immune system, they have found that decreased sleep affects our bodies ability to fight infection (3).  Even more startling is the link between lack of sleep and a shortened life expectancy (2). According to researchers at Standford University, "sleep is the most important predictor of how long you will live, perhaps even more important than whether you smoke, exercise or have high blood pressure" (3). That's a pretty strong statement.

I was surprised to learn that a lack of sleep could impact our health so profoundly. How could skipping a few zzz's cause this to happen? Well, in the case of heart health, it seems that researchers found sleep deprivation elevated levels of an inflammatory marker for heart disease called C-reactive protein (5, 6). One study conducted at Harvard University over a ten year span found that "sleeping six hours a night was associated with an 18% greater risk of heart attack," whereas, sleeping 5 hours a night upped the risk to 40% (4). Elevated C-reactive protein levels have also been linked to other health concerns like high blood pressure, diabetes and even cancer (5). If you're interested in discovering more about the emerging science on inflammation and its link to cancer you can read more here. 

If you've been dieting and exercising and are still frustrated with stubborn weight loss you might consider your sleep. There's a wealth of scientific evidence showing that the two most common risk factors for obesity are overeating and inactivity, but experts are now including lack of sleep as well. Interestingly, recent research has revealed that people "who habitually sleep less than 6 hours per night are much more likely to have higher than average body mass index (BMI)" compared with people who sleep 8 hours (4). It seems that a lack of sleep causes changes in the levels of a few hormones that regulate corresponding body functions like appetite and metabolism. When we sleep less the body produces less leptin, an appetite suppressant and more cortisol, a stress hormone that effects the metabolism of proteins, carbohydrates and fats (8). In addition, levels of  insulin, a glucose regulating hormone, and grehlin, an appetite stimulant hormone, are also raised (8). These effects all combine to create a pro weight gain state.

Not only is lack of sleep a health concern, but poor quality of sleep is as well. The around the world study mentioned in the first paragraph found that 1 in 4 people felt they did not sleep well (1). Experts suspect that the numbers of people sleeping poorly are even higher because most people don't recognize what makes up a night of good, quality sleep. Perhaps adding to the issue of quality sleep is the effect aging may have on  changing sleep patterns. You can find more information about that here. For now, let's take a look at some steps to make quality sleep more possible. Here are the top 10 tips from the Mayo Clinic:

1. Stick to a sleep schedule, even on weekends.
2. Don't eat or drink large amounts before bedtime.
3. Avoid nicotine, caffeine and alcohol in the evening (caffeine limited as much as 8 hours before bedtime).
4. Regular aerobic exercise can help you fall asleep, but don't exercise right before bed.
5. Make your bedroom environment perfect for sleep. Keep it cool, quiet and dark. If it can't be quiet try white noise.
6. Get your primary sleep at night. If you work nights keep your windows darkened.This helps set your body clock and establish sleeping patterns.
7. Choose a comfortable mattress and pillow.
8. Start a relaxing bedtime routine.
9. If you can't fall asleep within 15-20 minutes try getting up and doing something calming. Then return to bed, but try not to stress about falling asleep as this will only keep you from doing so.
10. Use sleeping pills as a last resort (10).

You can find a helpful video, along with other information ranging from adopting healthy sleep habits to when to seek treatment to improve your sleep on the Harvard Medical School's Division of Sleep Medicine Site.

Although it's no guarantee, clearly the quality and quantity of sleep we get is important to our health. Why not try to schedule a little extra sleep time for yourself? Our 24/7 world may seem to suggest that sleep is a guilty luxury, but there's absolutely nothing wrong with giving yourself the gift of being well-rested. Sweet dreams. 

PS - This week is National Drowsy Driving Prevention Week.  Check out the National Sleep Foundation's videos and FAQ sheets found here.   

Sources
1) Soldatos, C.R., Allaert, F.A., Ohta, T. and Dikeos, D.G. How do individuals sleep around the world? Results from a single-day survey in ten countries. Sleep Medicine, 6:5-13, 2005.
2) http://www.sciencedaily.com/releases/2009/04/090421181032.htm
3) http://healthysleep.med.harvard.edu/need-sleep/whats-in-it-for-you/health
4) http://healthysleep.med.harvard.edu/healthy/matters/consequences/sleep-and-disease-risk
5) http://www.ncbi.nlm.nih.gov/pubmed/14975482 
6) http://en.wikipedia.org/wiki/C-reactive_protein


7) http://en.wikipedia.org/wiki/Leptin
8) http://www.nlm.nih.gov/medlineplus/ency/article/003693.htm
9) http://en.wikipedia.org/wiki/Insulin
10) http://www.mayoclinic.com/health/sleep/HQ01387
11) http://www.nlm.nih.gov/medlineplus/ency/article/004018.htm