The conditioning phase of an exercise session involves participation in aerobic and/or strength training activities at an intensity that challenges the body enough to gain health benefits.  Depending on fitness goals, exercise chosen, and time available this component can be as short as 10 minutes when done three times per day or longer than 30 minutes when performed once.  To develop aerobic fitness (the ability of your heart, lungs, and blood vessels to efficiently provide blood and oxygen to working muscles) you will want to choose activities that use the major muscle groups of your body in a rhythmic and continuous fashion.  Walking, running, swimming, biking, and aerobic dance are some common examples of this type of activity.  It is recommended that you perform these exercises at a moderate-to vigorous-intensity level to improve health.

     An easy way to monitor the intensity of exercise is by the "talk test".  In the 2008 Physical Activity Guidelines for Americans issued by the federal government, it states that if you engage in moderate-intensity exercise, you should still be able to carry on a conversation, but not sing.  If you are exercising at a vigorous-intensity, you are only able to speak a few words before needing to take a breath.

     Another way that you can monitor exercise intensity is by measuring your heart rate.  To gain health benefits you want to keep your heart rate within a certain range.  This range can be determined by using a calculation known as the Karvonen Method.

     This calculation relies on knowledge of both your maximal heart rate and your resting heart rate to determine your target heart rate range.  Although it is best to have your maximal heart rate determined from an exercise stress test performed at a medical facility, you can estimate your maximal heart rate by the following formula:

208 - 0.7 x age = estimated maximum heart rate (EMHR)

To determine your resting heart rate check your pulse for one minute after you have been sitting quietly for about five minutes.  Once you have determined your maximal and resting heart rates you can use the Karvonen Method below to determine your exercise heart rate range.

1.  EMHR - resting heart rate (RHR) = heart rate reserve (HRR)

2.  HRR x 60% + RHR = lower end of training range (moderate-intensity exercise)

3.  HRR x 80% + RHR = upper end of training range (vigorous-intensity exercise)

     De-conditioned individuals just starting an exercise program will want to exercise near the lower end of their heart rate range.  As fitness improves, progression toward the higher end of the range can occur.  Individuals who already regularly exercise will want to exercise near the higher end of their heart rate range.

     The intensity of muscle-strength training exercises is determined differently.  You will want to perform one set of 8-12 repetitions at an intensity that would be challenging to perform another repetition at the end of the set.  For example, if you were doing one set of eight repetitions of the bicep curl exercise, the activity should become increasingly difficult as you progress through the set so that you cannot perform a ninth repetition.

     You will want to perform the "talk test" or check your heart rate periodically throughout your workout to make sure you are maintaining an appropriate exercise level.  Make adjustments in intensity level as needed.  Keep in mind exercising above the recommended range can increase your risk of injury and cardiovascular events.  Exercising below the recommended range may not produce the desired gains in fitness and health.

Note:  Before beginning an exercise program or increasing the intensity level of a current routine a physician's approval should be obtained, especially for older adults and those at risk for or who currently have chronic health conditions.

Resources:

ACSM's Guidelines for Exercise Testing and Prescription/American College of Sports Medicine; 7th edition.

Journal of the American College of Cardiology, 2001 Jan; 37 (1): 153-6.  "Age-predicted Maximal Heart Rate Revisited", Tanaka H, Monahan KD, Seals DR. Dept. Of Kinesiology and Applied Physiology, University of Colorado at Boulder, 80309-0354, USA.

2008 Physical Activity Guidelines for Americans; www.health.gov/paguidelines