BOX 6.5 Percentage of Body Weight as an Initial Exercise Load
•Universal bench press: 30% body weight
•Universal leg extension: 20% body weight
•Universal leg curl: 10% to 15% body weight
sity exercises should be performed before lower intensity exercises.9
Frequency
Frequency in a resistance exercise program refers to the
number of exercise sessions per day or per week.236As
with other aspects of dosage, frequency is dependent on other determinants, such as intensity and volume as well as the patient’s goals, general health status, previous partici- pation in a resistance exercise program, and response to training. The greater the intensity and volume of exercise, the more time is needed between exercise sessions to recover from the temporarily fatiguing effects of exercise. A common cause of a decline in performance from over- training (see discussion later in the chapter) is excessive frequency, inadequate rest, and progressive fatigue. Some forms of exercise should be performed less frequently than others because they require greater recovery time. High- intensity eccentric exercise, for example, is associated with greater microtrauma to soft tissues and a higher incidence of delayed-onset muscle soreness than other modes of exercise.13,108,212Therefore, rest intervals between exercise
sessions are longer and the frequency of exercise is less than with other forms of exercise.
Although an optimal frequency per week has not been determined, a few generalizations can be made. Initially in an exercise program, so long as the intensity and number of repetitions are low, short sessions of exercises some- times can be performed on a daily basis several times per day. This frequency is often indicated for early postsurgical patients when the operated limb is immobilized and the extent of exercise is limited to low-intensity isometric (set- ting) exercises to prevent or minimize atrophy. As the intensity and volume of exercise increases, every other day or up to five exercise sessions per week is common.8,103,168
Frequency is again reduced for a maintenance program, usually to two times per week. With prepubescent chil- dren314and the very elderly,8frequency is usually limited
to two to three sessions per week. Highly trained athletes involved in body building, power lifting, and weight lifting who know their own response to exercise often train at a high intensity and volume up to 6 days per week.170
Duration
Exercise duration is the total number of weeks or months during which a resistance exercise program is carried out. Depending on the cause of an impairment in muscle per- formance, some patients require only a month or two of training to return to the desired level of function or activity, whereas others need to continue the exercise program for a lifetime to maintain optimal function.
As noted earlier in the chapter, strength gains, observed early in a resistance training program (after 2 to 3 weeks) are the result of neural adaptation. For signifi- As with repetitions, there is no optimal number of sets
per exercise session. As few as one set and as many as six sets have yielded positive training effects.9Single-set exer-
cises at low intensities are most common in the very early phases of a resistance exercise program or in a mainte- nance program. Multiple-set exercises are used to progress the program and have been shown to be superior to single- set regimens in advanced training.170
Training to Improve Strength or Endurance: Impact of Exercise Load and Repetitions
Overall, because many variations of intensity and volume cause positive training-induced adaptations in muscle per- formance, there is a substantial amount of latitude for selecting an exercise load/repetition and set scheme for each exercise. The question is: Is the goal to improve strength, muscular endurance, or both?
To Improve Muscle Strength
In DeLorme’s early studies63-65three sets of a 10 RM per-
formed for 10 repetitions over the training period led to gains in strength. Current recommendations are to use an exercise load that causes fatigue after 6 to 12 repetitions for two to three sets (6 to 12 RM).103When fatigue no
longer occurs after the target number of repetitions has been completed, the level of resistance is increased to once again overload the muscle.
To Improve Muscle Endurance
Training to improve local endurance involves performing many repetitions of an exercise against a submaximal load.32,264For example, as many as three to five sets of 40
to 50 or more repetitions against a low amount of weight or a light grade of elastic resistance might be used. When increasing the number of repetitions or sets becomes ineffi- cient, the load can be increased slightly.
Endurance training can also be accomplished by main- taining an isometric muscle contraction for incrementally longer periods of time. Because endurance training is per- formed against very low levels of resistance, it can and should be initiated very early in a rehabilitation program without risk of injury to healing tissues. Remember, when injured muscles are immobilized, type I (slow twitch) fibers atrophy at a faster rate than type II (fast twitch) fibers.207,231This underscores the need for early initiation
of endurance training.
Exercise Order
The sequence in which exercises are performed during an exercise session has an impact on muscle fatigue and the adaptive training effects. When multiple muscle groups are exercised in a single session, as is often the case in rehabilitation or conditioning programs, large muscle groups should be exercised before small muscle groups and multijoint muscles before single-joint muscles.9,103,168
cant changes to occur in muscle, such as hypertrophy or increased vascularization, at least 6 to 12 weeks of resist- ance training is required.1,8,193