Debra D'Acquisto

As a fitness professional and physical educator you may be asked some seemingly "out-of- the-blue" questions such as, "What do I do for the best exercise?" "How long do I have to work out?" "How hard do I have to work?" "How do I drop body weight?" These questions may be laced with overzealous misconceptions such as, "I don't have an hour a day to exercise." Or, "I heard you have to do 3 days of cardio and 3 days of lifting weights, and then stretch or do yoga; I don't have that kind of time, so why bother?" And, a question or comment that refers to intensity may sound like, "I can't keep up with the (fill in the blank) _______________ (aerobic class, the joggers, the noontime walkers, the spinning group, etc)."

Many people drop-out or refrain from even trying an activity because their perception of it, or their previous experience with it, leads them to believe it is too hard.

INTENSITY AS A VARIABLE:

Attaining physical fitness follows the FITT principle. FITT is the acronym that represents the variables that can be manipulated and individualized to meet various training needs. The letters in FITT stand for frequency, intensity, time, and type of activity.

Frequency (F) refers to the number of times per week an activity is performed. The original American College of Sports Medicine's (ACSM) position in 1990 suggested we perform some form of cardiovascular-based activity 3-5 times per week. Their position was established after the review of numerous well-documented scientific sources (1). The intensity (I) of activity performed should be between 60% – 90% of maximal heart rate. The suggested time (T) for continuous and sustained physical activity is between 20–60 minutes or more. The type of exercise (T) recommended is aerobic, and one that predominately uses the large muscle groups. Good examples include jogging, swimming, x-c skiing, bicycling, brisk walking, and dancing.

The art of individualized exercise programming, in part, depends on adjusting the 4 variables. This concept of adjusting variables rose in importance when statistics revealed American people's fitness levels had not increased after the guidelines were established. Although the ACSM guidelines were flexible, many thought they were too aggressive, thus resulting in low adherence. Based on numerous observational studies and data from the Center of Disease Control (CDC), an association was observed between reductions in chronic diseases and increases in leisure time physical activity. We typically wouldn't think a leisure time activity would elicit the same health benefits as hard or even moderately hard physical efforts. However, to realize health benefits American adults don't need to play hard 5 times a week. Less will do. Thus, new physical activity recommendations developed by the CDC and ACSM organizations led to the following statement:

"Every US adult should accumulate 30 minutes or more of moderate intensity physical activity on most, preferably all, days of the week. This recommendation emphasizes the benefits of moderate intensity physical activity and activity that can be accumulated in relatively short bouts. Adults who engage in moderate intensity, i.e. enough to expend approximately 200 calories a day can expect many of the health benefits, described herein." (2)

Ways to gauge intensity
Okay, so the old ACSM guidelines refer to intensity as a percentage of maximal heart rate, and the revised guidelines refer to intensity as moderate effort, and even suggest how many calories should be expended relative to a moderate effort. So, let's take a look at several ways to gauge exercise intensity. In addition, let's do a little bit of number crunching to figure out the relationship between calorie expenditure and exercise intensity.

1) Maximal heart rate

Maximal heart rate (MaxHR) is a widely used method to determine exercise intensity. The formula is: 220 minus age in years equals a predicted heart rate maximum in beats per minute. According to ACSM guidelines, exercising at an intensity of between 60-90% is the preferred range. For example, a 40 year old who wants to workout at the low end of the recommended range would follow this formula: 220 - 40 = 180 MaxHR, 180 (MaxHR) x .60 = 108 beats per minute (bpm). Find a pulse at the carotid artery or at the radial artery by counting the number of times the heart pulses or beats in a minute.

There are many reasons why MaxHR is not used universally. However, it is widely used in conjunction with other methods. It is a useful method for generally healthy adults, but has its limitations with deconditioned and highly conditioned individuals, as well as limitations with some modes of activity. Highly conditioned athletes need to know specific heart rates during intense interval training (which incorporates high intensity work cycles with lower range of intensity rest cycles). A deconditioned individual may be on a medication which interferes with heart rate response. Swimming, due to the hydrostatic pressure of the water and the exaggerated arms movements above the head, may elicit lower than accurate heart rate responses. The exaggerated arms movements performed in aerobic dance or step benching may also produce inaccurate heart rate responses.

2) Heart rate reserve or Karvonan formula

A more reliable method of determining an exercise intensity range, and one which accommodates various fitness level differences among participants, is the Karvonan formula, also called the heart rate reserve method. You’ll need to know your resting heart rate (RHR) for this calculation. RHR reflects your heart rate during a rested and quiet state. RHR would ideally be taken immediately after waking in the morning. Resting heart rate decreases as the heart becomes a more fit muscle. The Karvonan formula uses heart rate reserve (HRR) to find target heart rate (THR). Below is an example:

The calculated value of 146 bpm represents 70% of this individual's HRR, which is considered moderate exercise intensity.

3) Talk Test

The talk test is an easy gauge of exercise intensity that uses just what it says - talk. The premise is that if one can carry on a conversation while working out, the intensity is not high enough to be heart challenging. On the other hand, gasping for air and not being able to speak a word is too vigorous an intensity and really isn't a fun way to exercise. You should be able to breathe comfortably and string a couple of words together throughout the aerobic exercise. Ask your friends, even those who love to exercise, if piecing together a conversation is a more pleasurable way to exercise than gasping for air.

4) Borg's RPE Scale

The Rating of Perception of Effort (RPE) is another easy way to gauge intensity of aerobic activity. Swedish psychologist Gunnar Borg, in a rigorous scientific manner, developed a measurement tool in the form of a category scale. Ratings on the scale depend on the interaction of sensory, cognitive, emotional, and cardiopulmonary cues, as well as musculoskeletal functions and psychosocial factors. Two of the most common RPE scales used by exercise professionals are Borg's 1 – 10 Perceived Exertion Rating Scale and Borg's 6 – 20 Perceived Exertion Scale.

Example: An individual canoeing at 5 METS would expend about 6 kcals per minute (1.2kcals x 5 METS x 1 min). For general purposes, consider a reference individual weighing 70 kg (154lbs). So, if you weigh quite a bit more or less than 70kg, the caloric expenditure should be slightly adjusted. Knowing the exercisers body weight in kg will yield a more accurate estimation of energy expenditure. Use the following MET equivalent, 1kcal/kg body weight/hour, to determine energy expenditure during a 30 minute canoeing activity for the given values:

Given: Body weight 60 kg
Canoeing at 5 METS (see compendium)
30 minutes
(5 METS x 60 kg) x (30min/60min) = 150 kcal for 30 min

The following are various activities, chosen from the compendium, determined to be at a 5 MET intensity level:

Low impact aerobic dance Operating a punch press Walking downstairs or standing carrying a 25-49 lb object Playing cricket or bowling Playing golf and pulling the clubs Skateboarding Snorkeling Canoeing Skiing downhill with a light effort Fishing from the river bank Hunting small game such as rabbit, raccoon, squirrel

That was a lot of information on exercise intensity! Hopefully it has refreshed your understanding of the "I" in FITT. Refer back to the questions posed at the beginning of this article. I imagine it will now be easier for you to find out enough about the individual asking the "exercise" question to be able to construct an appropriate response. "How hard do you have to work out?" Educate the exerciser about the moderate training zone according to one of the intensity gauges presented above. To the individual that perceives exercise as too hard, educate them about leisure activities or occupational activities that yield the same MET value as a sport!

How many calories does a brisk walk for 15 minutes around the local school yard playground burn? Now you have the tools to figure that out! Also, what do the numbers on the new heart rate monitor mean? What does MET mean on the treadmill? You've got the basics now!

Thanks for spending time with me. I'd be happy to answer any questions you have via e-mail.

References:

1) The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Med Sci Sports Exerc 22:265-274, 1990.

2) Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC. Physical Activity and public health: a recommendation from the Centers of Disease Control and Prevention and the American College of Sports Medicine. JAMA 273:402-407, 1995.

3) Noble, B and Robertson, R. 1996. Perceived Exertion. Human Kinetics, Champaign, Ill.

4) Ainsworth BE, Haskell WL, Leo AS, et al. Compendium of Physical Activities: classification of energy costs of human physical activities. Med Sci Sports Exerc 1:71-80, 1993.

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