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EXERCISE FREQUENCY Frequency is prescribed in sessions per day and in days per week. To improve cardiorespiratory fitness for the apparently healthy adult, the range of frequency is between 3 to 5 days per week. For a sedentary individual, the minimum overload is the 3 days per week whereas, for the higher fit individual the overload must be increased to 4 to 5 days per week.
In some chronic disease such as obesity or hypertension the most effective frequency may be a higher frequency per week. In these cases, the initial exercise prescription for a sedentary individual with obesity or hypertension may have higher frequencies than the apparently healthy adult.
Recommendations for exercise progression are essential for injury prevention when high frequency prescriptions are given to sedentary individuals. In the in-patient setting frequency will be prescribed in sessions per day for 3 to 5 days per week. These sessions may be as high as 3 to 5 per day. When programming for physical activity, most, if not all days of the week should be recommended.
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EXERCISE DURATION Exercise durations range from 5 min to 60 min. Rarely will prescribed exercise duration exceed 60 minutes. The law of diminishing returns begins at duration of 60 minutes. That is, the average individual will not receive significantly more benefit by working more than 60 minutes. In fact, the risk of overuse injury increases the risk:benefit ratio of exceeding 60 minutes of cardiorespiratory exercise for the apparently healthy adult.
The lower exercise duration, between 5 to 10 minutes, will be used in the clinical setting for chronic disease and disabilities.
The minimum duration to achieve an improvement in cardiorespiratory fitness is 20 minutes; the range is 20 to 60 minutes.
The minimum duration to maintain fitness is 20 minutes.
The range of prescribed duration, like frequency, is broad. Similar to the principles of prescribing frequency, duration will be prescribed in shorter 10 to 20 minute ranges depending on the fitness and health of the individual.
For apparently healthy individuals who are sedentary, the shorter durations from 20 to 30 or 30 to 40 minutes are adequate to improve cardiorespiratory fitness. For more fit individuals, 40 to 60 minutes may be the required overload to achieve further improvements in cardiorespiratory fitness. When programming for physical activity, duration of at least 30 minutes should be recommended.
The combination of exercise frequency and duration should be viewed with caution. Pollock, in a 1977 classic study, exercised six groups of men within the range frequency and duration for the exercise prescription for apparently healthy adults to improve cardiorespiratory fitness. Intensity was the same for all groups of men. Three groups exercised for 15 min, 30 min and 45 min for three days a week. Three other groups of men exercised 1 per week, 3 per week and 5 per week for 30 minutes.
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| The results of this study are illustrated in the figure to the right. As expected, the improvements in fitness were related to the overload.
However, the higher overloads were also related to higher injury rates. The highest duration and the highest frequency resulted in the highest injury rates.
Therefore, caution should be taken in determining the optimal duration and frequency to improve fitness without causing overuse injuries.
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