Cardio Exercise Helps Prevent Injury

How many times have we left the scene of a collision wondering why the driver didn’t pay attention, drive slower or find a designated driver?

It reminds me of the adage, “an ounce of prevention is worth a pound of cure.” This directly relates to health and fitness; it’s much easier to become fit than it is to treat disease and illness caused by lack of fitness.

We don’t normally think about whether a victim of chest pain followed an exercise, weight-control or stress-management program. As members of a high-stress profession, we need to consider the effects of being out of shape and make exercise a part of our lifestyle. This article will help by getting you acquainted with cardiorespiratory fitness, one of the three components of physical fitness.

The Basics

Cardiorespiratory fitness refers to the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity. Regular exercise training makes these systems more efficient, enabling more blood to be pumped with each ventricular contraction and increasing the number of small arteries in trained skeletal muscles. This means more blood is supplied to working muscles, and the structures within the muscle become more efficient at utilizing oxygen.

Training requires a working knowledge of the Principle of Overload: When increased demands are made on body systems, the systems respond by becoming stronger when given the appropriate nutrition and recovery time. This is the objective of cardiorespiratory training.

Intensity Guidelines

To improve cardiorespiratory fitness, the American College of Sports Medicine (ACSM) recommends activities that can be sustained for a prolonged period of time, such as walking, jogging, stationary cycling, jump-roping or similar activities. You should participate in these activities three to five days per week for 20-60 minutes per session.

During these exercises, you need to monitor the intensity of your workout to make sure you aren’t under or over working yourself. Exercise intensity is monitored by heart rate, and intensity between 40% and 85% of heart rate reserve (HRR) is necessary to improve cardiorespiratory fitness. HRR is the difference between maximum heart rate (HRmax) and resting heart rate (RHR). A simple and commonly used set of formulas for estimating HRmax is below:

Predicted HRmax = 220 – age

HRR = HRmax – RHR

HRR intensity = HRR x intensity (40-85%)

Target Heart Rate Range = HRR intensities + RHR

An individual who is deconditioned (has not exercised on a regular basis in over a year) or in poor physical condition should start with a lower intensity of 40-60% of HRR.

Let’s take Bob, a 47-year-old EMS professional who has a resting heart rate of 73 beats per minute (bpm) and is beginning an exercise program for the first time in years.

40% HHR 60% HHR

220 – 47 = 173 220 – 47 = 173

173 – 73 = 100 173 – 73 = 100

100 x 0.4 = 40 100 x 0.6 = 40

73 + 40 = 113 73 + 60 = 133

So, a target heart rate range of 113/133 would be ideal for Bob to improve cardiorespiratory fitness and develop some cardioprotective benefits from exercise.

Exertion Guidelines

If monitoring heart rate during exercise is difficult, the rate of perceived exertion (RPE) scale could be used to adjust exercise intensity. The scale is a measure of perceived exertion and is defined as the degree of heaviness and strain according to a specific rating method (see Table 1).

To use the scale, assign a number to how hard you perceive the intensity of your exercise to be. The average range associated with improvements in cardiorespiratory fitness is 12-16.

The goal of exercise is to expose the body to an overload stimulus in a safe manner. The body, given appropriate rest and recovery, will respond by becoming stronger, improving endurance or enhancing efficiency in the activity. As you improve physical fitness, the intensity may be increased to continue improving cardiorespiratory function.

Bob’s target RPE would be about 12, but if we increased the intensity to 60-70% of HRR, the target heart rate range would change to 131-141 bpm, assuming the RHR remained unchanged, and his corresponding RPE would change to about 13 or 14.

The intensity and exertion levels described above are the required intensity ranges for improving overall cardiorespiratory fitness. However, fat loss will occur when more calories are being expended than consumed. Prolonging cardiorespiratory exercise or adding shorter sessions throughout the day for the sake of increasing caloric expenditure may be excellent methods for managing weight. Shape Up America offers more information on this at

Don’t Forget

If you’re a male over 45 or a female over 55 years of age, seek approval from your physician prior to beginning a new exercise program. If you’re younger than this, complete the Physical Activity Readiness Questionnaire (PAR-Q) to determine if there’s any other reason to seek a physician’s approval. This form is on the Shape Up America Web site (

It’s also important to progress at a gradual pace. As fitness improves, the same level of exercise intensity may no longer be enough to meet your target heart rate range goal. This means that you’re adapting to the exercise training through improved cardiorespiratory fitness, which is a good thing! These improvements will be more pronounced in less-fit individuals.

Modifying an exercise program by gently increasing the intensity and/or duration of your exercise will allow continued improvement. When optimum fitness levels have been achieved, a maintenance program should be initiated; however, remember to vary the workout to keep it fresh. You should also incorporate weight training into your routine at least two days per week.

It’s important to warm-up and cool-down to prevent injury. The warm-up increases the body’s temperature and prepares the body for the more intense training to follow. An effective warm-up is to perform the activity, but at a lower intensity. The cool-down eases the body into a resting state by lowering the intensity of exercise for fiveà10 minutes, allowing heart rate to approach resting levels. Stretching during the cool-down will improve flexibility and reduce soreness from exercise.

Try This

If you’ve been exercising on a regular basis for at least four months and would like to increase the intensity of aerobic training, interval training is another way to keep an exercise program fun. It combines higher intensity work segments with lower intensity active recovery/rest segments.

For example, a 2:1 ratio may involve one minute of more intense exercise followed by 30 seconds at a slower pace. Developing an interval training program to suit individual needs allows for greater creativity. The higher intensity segments of interval training increase metabolic demand, which increases energy (kilocalories) expended during and after the training session.

If you can jog comfortably at a 5-mph pace for an extended period of time, then try this 11-minute interval training session: 6 mph for two minutes; 5 mph for one minute; 6.5 mph for two minutes; 4.8 mph for one minute; 6.8 mph for two minutes; 4.8 mph for one minute; 7 mph for one minute; and 4.8 mph for one minute.

The objective of interval training is to increase intensity, so only add it if you’ve been exercising regularly for at least four months. Also, the speeds involved in developing an interval training session would be experimental; it’s best to be conservative.


As educated medical professionals, we know the value of “an ounce of prevention” and should take an active role in our own personal health to prevent the illnesses and injuries common in EMS. JEMS


  1. American College of Sports Medicine: ACSM’s Guidelines for Exercise Testing and Prescription, 7th edition.

    Lippincott, Williams & Wilkins: Maryland, 2006.
  2. Borg G: Borg’s Perceived Exertion and Pain Scales. Human Kinetics: Champaign, Ill., 1998.

John Amtmann,EdD, NREMT-B, is a professor of Applied Health Science at Montana Tech of the University of Montana in Butte. He_s an EMT with A-1 Ambulance in Butte, an ACSM certified preventive”žand rehabilitative exercise specialist and an NSCA certified strength and conditioning specialist. Contact him at

 This article originally appeared in the July 2009 issue of JEMS.

No posts to display