From the last post, we learned that at least 30-min/day (or 150-min/wk) moderate-to-vigorous physical activity is the minimum needed to promote general health benefits. For additional health benefits, engaging in physical activity beyond the Federal Guidelines is encouraged – more is better!
So, how do we gauge intensity? How do we know if what we are doing for physical activity is considered moderate-to-vigorous? For starters, what is the difference between physical activity and exercise? Physical activity can be defined as any activity that causes muscle contractions and results in an increase in energy expenditure. Exercise is a type of planned physical activity that is structured and intentional. For example, playing with your kids for 30-min outside is considered physical activity whereas going to the gym to do cardiovascular and resistance training is considered exercise – it’s planned and intentional.
There are several ways to estimate intensity (absolute and relative). Some field-based methods to estimate intensity include: percent of heart rate reserve (%HRR), percent of HRMAX (%HRMAX), metabolic equivalents (METs), rating of perceived exertion (RPE) and even step rate using pedometers.
Using the Karvonen Formula
To estimate intensity using %HRR (using Karvonen formula):
- 220 –age = maximum heart rate
- Maximum heart rate – resting heart rate = heart rate reserve
- (Heart rate reserve x training % ) + resting heart rate
*Example: A 55yr old with a resting heart rate if 62bpm who wants to train at 60% maximum.
- 220 – 55 = 165bpm
- 165 – 62 = 103bpm (heart rate reserve)
- (103 x 0.6) + 62 = 124bpm
Often times, it’s useful to establish a target heart rate range to keep exercising heart rate within, for example between 60 and 70% HRR. You would simply perform the same calculation with 0.7, which would give an upper %HRR range.
Using the 220 – Age Formula
If you were to use the traditional %HRMAX formula, this same person would have a target heart rate of 99bpm (220 – 62) x 0.6)) = 95bpm. The Karvonen formula almost always calculates a higher target heart rate than the 220 – age method and uses two individual characteristics (i.e., age and resting heart rate). To work at moderate or vigorous intensity, you can see in the below table which percentage values you can reference when trying to establish relative intensity for either method.
| Methods to Estimate Relative Intensity | |||
| Intensity | %HRR | %HRMAX | RPE |
| Very light | <30 | <57 | <Very light (RPE <9) |
| Light | 30-39 | 57-63 | Very light-fairly light (RPE 9-11) |
| Moderate | 40-59 | 64-76 | Fairly light to somewhat hard (RPE 12-13) |
| Vigorous | 60-89 | 77-95 | Somewhat hard to very hard (RPE 14-17) |
| Near-maximal to maximal | >90 | >96 | > Very hard (RPE > 18) |
NOTE: Table adapted from Garber et al., 2011.
Using the Borg Rating of Perceived Exertion (RPE) Scale
Rating of perceived exertion is a subjective score that represents an individual’s evaluation of fatigue based on a scale from 6 to 20 or 0 to 10. Individuals who take medications that influence heart rate can use this scale to easily monitor exercise intensity (exrx.net). Below is the Borg RPE scale (6 to 20). At any point during exercise, you can self-evaluate where you feel your exercise intensity is based on a number from 6 to 20. That number corresponds to a descriptive term (see below).
| The Borg Scale Rating of Perceived Exertion | |
| Rating | Perception of Effort |
| 6 | |
| 7 | Very, very light |
| 8 | |
| 9 | Very light |
| 10 | |
| 11 | Fairly light |
| 12 | |
| 13 | Somewhat hard |
| 14 | |
| 15 | Hard |
| 16 | |
| 17 | Very hard |
| 18 | |
| 19 | Very, very hard |
| 20 | |
Using Metabolic Equivalents (METs)
Just about all the cardio equipment at our facility displays METs. One MET is equal to 3.5ml O2/kg/min, which is the amount of oxygen we consume at rest. As we engage in physical activity, our heart rate elevates and we start to breathe faster and harder. As a result, the amount of oxygen we consume goes up to meet the demands of the body. Likewise, our working MET level also goes up. In other words, a MET is simply another tool we use to gauge intensity. See below for an example table of METs and associated activities. Notice the light, moderate, and vigorous intensity thresholds.
Using absolute methods, such as METs can lead to greater error in estimating intensity when compared to relative methods. For example, an older person working at 6 METs may be exercising at a vigorous to maximal intensity, while a younger individual working at the same absolute intensity may be working at a moderate intensity (Garber et al., 2011). Thus, using a relative method to estimate intensity may be more appropriate, particularly for older and de-conditioned people (Garber et al., 2011).
| Physical activity | MET |
| Light intensity activities | < 3 |
| sleeping | 0.9 |
| watching television | 1.0 |
| writing, desk work, typing | 1.8 |
| walking, 1.7 mph (2.7 km/h), level ground, strolling, very slow | 2.3 |
| walking, 2.5 mph (4 km/h) | 2.9 |
| Moderate intensity activities | 3 to 6 |
| bicycling, stationary, 50 watts, very light effort | 3.0 |
| walking 3.0 mph (4.8 km/h) | 3.3 |
| calisthenics, home exercise, light or moderate effort, general | 3.5 |
| walking 3.4 mph (5.5 km/h) | 3.6 |
| bicycling, <10 mph (16 km/h), leisure, to work or for pleasure | 4.0 |
| bicycling, stationary, 100 watts, light effort | 5.5 |
| Vigorous intensity activities | > 6 |
| jogging, general | 7.0 |
| calisthenics (e.g. push ups, sit-ups, pull-ups, jumping jacks), heavy, vigorous effort | 8.0 |
| running jogging, in place | 8.0 |
| rope jumping | 10.0 |
Using Step Rate from Pedometers
The available evidence suggests that 100 steps/min is a rough approximation of moderate intensity physical activity. However, because of the errors associated with using step counts or prediction algorithms to estimate energy expenditure, researchers recommend using steps/min combined with duration of activity (e.g., 100 steps/min for 30 min/session).
Establishing intensity is an extremely important component of fitness and often times is one of the most challenging. Furthermore, it’s only one piece of the pie. To ensure you set an intensity level that is appropriate for you and that is safe and effective, please see one of our Fitness Professionals.
Happy Exercising,
Ed Davila
About the Author: Ed Davila is the Director of Fitness at the Ridge Athletic Clubs. He is a Registered Clinical Exercise Physiologist & Certified Exercise Physiologist through the American College of Sports Medicine. He is also a Certified Ergonomics Assessment Specialist through the Back School of Atlanta.
References:
- Garber C.E., Blissmer B., Deschenes M.R., Franklin B.A., Lamonte M.J., Lee I-Min., Nieman D.C., Swain D.P. Quantity and quality of exercise for developing and maintain cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 2011. 43(7): 1334-1359.
- exrx.net