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Endurance, Strength and Flexibility

To achieve a level of physical fitness, your plan must include appropriate exercise activities. To better understand some of the dynamics of effective exercise, it will help to break up your fitness prescription into 3 measurable parts: Endurance, Strength and Flexibility. Endurance is defined as "the ability to keep moving for long periods of time." There are 2 categories of endurance, Cardiorespiratory and Muscular.

Cardiorespiratory Endurance

Cardiorespiratory Endurance is the prolonged ability of your heart and lungs to supply muscles with nutrients and oxygen. Aerobic exercise like biking, jogging, and swimming enhance cardiorespiratory endurance, and performance can be measured for speed, duration and distance.

Building endurance promotes higher energy levels. Aerobic exercise also burns calories and fat to keep your weight under control. A fit cardiorespiratory system lowers the risk of death from heart attacks, strokes, and pulmonary disease.

Developing the Aerobic Phase

The following principles should be applied when developing the aerobic phase of a general fitness exercise prescription to enhance cardiorespiratory fitness:

1. Type of Activity...The activity must use large muscle groups and must be maintained for a period of time.

2. Intensity...The average conditioning intensity for healthy adults is 60-70% of their functional capacity, referred to as maximum heart rate. Monitoring a target heart rate training zone during exercise is a good way to measure intensity.

3. Duration...The duration of the exercise will depend on the intensity of the exercise. Usually activities of lower intensity, such as walking, can last longer than a high intensity exercise like running. Aerobic fitness can also be accomplished by alternating high and low level activities as in walking between brief periods of jogging for 15 to 60 minutes of continuous or discontinuous aerobic activity.

4. Frequency of Conditioning... The aerobic activity must be performed from 3 to 5 days a week.

5. Rate of Progression... In the first 6-8 weeks of exercise, significant conditioning effects will occur. The fitness professional will have to adjust the intensity and duration of the activity if progress is to continue.(2)

Progression and the Aerobic Phase

There are 3 stages of progression in the aerobic or endurance phase of the exercise prescription:

1. The Initial Conditioning Stage...During the first 4 to 6 weeks, low level activities of 10-15 minutes, at 60-70% of maximum heart rate, are recommended for the average healthy individual. You should also include some stretching and light calisthenics, such as abdominal work.

2. The Improvement Conditioning Stage...Initially, there is a slight increase in exercise intensity. Thereafter, duration of the activity is increased every 2 to 3 weeks. Older individuals may take longer to adapt to increases in conditioning.

3. The Maintenance Conditioning Stage... Usually after 6 months of aerobic training, the average individual has achieved their goal of general fitness and just wants to maintain. Aerobic Maintenance Conditioning can be accomplished in as few as three 30 minute workouts a week, training at 60-70% of maximum heart rate.(2)

Muscular Endurance

The second type of endurance one must develop to be physically fit is Muscular Endurance. Muscular Endurance is defined as the ability of your muscles to perform contractions for long periods of time. The number of curl ups one can perform, for example, is a measure of abdominal endurance.

Improving Muscular Endurance

Generally, the performance of resistance exercises enhances the endurance of the muscles involved. The muscular endurance phase of a general fitness exercise prescription may include the performance of a circuit routine consisting of multiple exercises targeting different muscle groups.


Muscular Strength is another measure of fitness, and is categorized into 2 types:

1. Static Strength...How much weight you can hold in place.

2. Dynamic Strength...How much weight you can move. It is desirable to be strong in order to perform heavy work with less chance for injury. Maintaining strength is more difficult with age and the increasing loss of lean weight.

Increasing Strength

Strength can be increased through static contractions, as in isometric exercise, or by low repetition isotonic exercises. For a beginner, one set of 12 repititions done with high intensity will work well. For more advanced trainees, three sets of an exercise in a 7-12 rep range, will initiate optimal strength gains, when performed 2-3 times a week.


The final measure of fitness is Flexibility. Flexibility is defined as the ability to move muscles and joints through their full range of motion. One way to measure flexibility is to see how close one comes to touching the toes with legs straight.(1)

Flexibility of muscles and joints will help prevent injury and maintain mobility with aging. Of particular concern, is flexibility in the posterior thigh and low back. Lack of flexibility in these areas increases the risk of chronic low back pain.

Increasing Flexibility

Stretching will increase flexibility. It is important that stretching is done slowly with gradual increases in the range of motion. The stretch should be sustained from 10 to 30 seconds, and should not cause pain. Stretching exercises need to be performed at least 3 times a week. It is safer to stretch muscles that are already warm. Stretching is best performed after the aerobic phase or between sets of resistance exercises performed in both the muscular endurance and strength phases of the general fitness exercise prescription.

Specificity of Exercise

The development of speed, agility and coordination will also enhance overall physical performance. Exercise is "sport specific" to the activity being performed. If you wish to grow stronger, you will have to lift heavier weights. If you wish to be more flexible, you will have to practice stretching, and so on.

The General Fitness Exercise Prescription

The days and times that you schedule for your workouts will dictate the selection of the most appropriate set of exercises to achieve optimum results. If you have decided to dedicate an hour, three times per week to the exercise component of your fitness, this is a list of general guidelines that would apply to you. A well-balanced exercise session aimed at maintaining overall fitness for the average beginning individual could consist of the following:

1. 5 minute warm-up doing a low level aerobic activity, such as walking.

2. 20 minutes of aerobic activity performed at 60-80% of maximum heart rate, such as jogging or walking on a treadmill, or a combination of walking and jogging.

3. 5 minutes of abdominal work to cool-down. Perform about 5 minutes of stretching after the aerobic phase and between sets of resistance exercises, paying particular attention to hamstrings, lower back, calves, and shoulders.

4. 25 minutes of weight training. Performing one or two sets of twelve reps of the following exercises; Squats or Leg Presses; Deadlifts or Back Extensions; Bench Presses; Shoulder Presses; Lat Pulldowns or Bentover Rows. Remember, this is a general guideline. Each individual has a preferred set of exercises that will give the safest, best progress.

As a reminder, upon reaching the Maintenance Conditioning Stage, the above one hour of exercise, performed a minimum of 3 times a week, will maintain an average level of overall fitness for most people.

REFERENCES: President's Council On Physical Fitness and Sports,

Get Fit. How to get in shape to meet The President's Challenge.

American College Of Sports Medicine, Guidelines For Exercise

Testing And Prescription, Third Edition, 1986, Lea & Febiger

NFPT Personal Trainer Magazine

Articles appearing on this website are included as a learning resource for our visitors. While Living Strong does not necessarily endorse or agree with all of the information presented in each article, we feel the content contains worthwhile information and include it as a reference for your study. The information presented is specific in nature and may not be appropriate for your personal situation.



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