Pete McCall by Pete McCall

Are you familiar with the movie Groundhog Day? In the movie the main character, played by Bill Murray, has to relive the same day over and over and over until he finally does everything right. If you work in a health club, you might be familiar with that phenomenon. It can often feel like you can walk through your gym floor at a given time on any day and see the same members on the same pieces of equipment doing the same exercises with the same amount of weight. I recently visited a gym where I used to teach a few group fitness classes in the early 2000s. It was early on a weekday evening at about the same time I used to teach. As I walked through the facility it felt like a time warp because I saw a number of the same members on the same pieces of equipment that they had been using years earlier when I worked there regularly.

Insanity can be described as doing the same thing over and over again but expecting different results. The overload principle of exercise program design states that to create physiological changes an exercise stimulus must be applied at an intensity greater than the body is accustomed to receiving. One of the most common challenges faced by the average fitness enthusiast is reaching a plateau, where exercise no longer seems to have an effect and the body stops making any physiological changes. This happens because, just like the Groundhog Day scene described above, doing the same exercises with the same weight for the same number of repetitions will not create a sufficient overload to initiate any physiological changes. To cause an adaptation with resistance training, it is necessary to either perform enough repetitions to cause momentary fatigue of the involved muscles or use a resistance that is heavy enough to induce fatigue after only a few repetitions.

A high-intensity heavy load applies a mechanical stress to muscle, while performing a high number of repetitions creates a significant metabolic stress. Both types of stress can stimulate the physiological reactions related to muscle growth and definition. Whether it is by the amount of weight used or performing reps to fatigue, the demand on the involved muscles should be sufficient to initiate both neurological and structural adaptations.

Therefore, the two variables of program design most closely related with the overload principle are intensity and repetitions. Intensity is the magnitude of resistance used and is commonly expressed as a percentage of the one-repetition maximum (%1-RM) for a particular lift. Another way to describe intensity is by listing the maximum number of repetitions that can be performed for a particular lift. For example, if an individual can bench press 200 pounds for a total of 10 repetitions and is unable to perform another rep, then 200 is his or her 10-RM. Either method of describing intensity can be used by to assign specific intensities for the exercise in an individual’s workout program.

A repetition is a single, individual action of the muscles responsible for creating movement at a joint or series of joints. A repetition involves three phases of muscle action: eccentric lengthening, which is a momentary isometric pause and concentric shortening. The number of repetitions assigned for an exercise indicates the number of times an individual should perform that particular movement. As mentioned above, to create the necessary overload to promote specific adaptations, repetitions should be performed until momentary muscle fatigue occurs.

Repetitions and intensity have an inverse relationship; as intensity increases the number of repetitions that an individual is able to perform decreases. Higher-intensity loads can only be performed for a few repetitions, while lower-intensity loads can be moved for a relatively high number of repetitions before fatigue sets in. It is not necessary to put a client through strenuous strength testing to identify his or her 1-RM. The table below relates the number of repetitions that can be performed at a specific amount of intensity for different training outcomes.

Recommended Training Volumes to Achieve Specific Goals

Training Goal


Intensity (% 1-RM)

Strength Endurance

≥ 12

≤ 67%


6 - 12

67 - 85%

Maximum Strength

≤ 6

≥ 85%


  • Single-repetition event
  • Multiple-repetition event

1 - 2
3 - 5

80 - 90%
75 - 85%

Reference:  NSCA Essentials of Strength Training and Conditioning (3rd ed.) 2008.

  • Strength endurance is the ability to produce and sustain muscle force over an extended period of time.
  • Hypertrophy is the technical term for an increase in muscle size (and definition).
  • Maximum strength is the ability to generate a maximal amount of muscle force for a particular exercise.
  • Power is the ability to generate a significant magnitude of force in the shortest amount of time possible.  

The intensity of an exercise will determine the number of repetitions that can be performed. For example, if a client has a goal to develop hypertrophy (the technical term for muscle definition) then he or she should use enough intensity per exercise to only be able to perform six to 12 repetitions, fatiguing by the final rep. If a client can only execute 12 repetitions with a particular weight for an exercise, then that weight is the 12-RM. As soon as the client can do more than 12 reps the weight should be increased so the rep range stays between six and 12. It should be noted that if the training goal is to improve muscle tone or definition, the exercises MUST be performed to fatigue. This  is the only way to induce the overload to create that response.

Given the popularity of high-intensity fitness programs, it is important to note the recommended rep ranges for power-specific exercises. Training for muscular power places tremendous metabolic and mechanical demands on muscle tissue and can rapidly fatigue the nervous system responsible for maintaining proper joint mechanics. When using heavy weights for technical power-based lifts like the snatch or the clean-and-jerk, the rep range should focus on the maximum force output for one or two reps and, at the most, be limited to no more than four or five. The snatch and clean-and-jerk are technically demanding lifts. If an individual tries to perform too many without sufficient rest or recovery, he or she is at significant risk of injury.  

If a client is interested in improving muscle “tone,” there are two options for intensity and repetitions, either of which can recruit the type II (fast twitch) motor units and muscle fibers responsible for improving definition:

  • Use a moderate-intensity load (approx. 67-85% 1-RM) to fatigue by six to 12 reps; or
  • A low-intensity load where the client performs reps to fatigue (the inability to do another rep)

If an individual is hiring you as a personal trainer or taking the time to participate in your group workouts, he or she is most likely interested in seeing results. Adding repetitions or increasing Intensity can challenge clients or class participants to work harder than they might on their own. Overload doesn't need to be significant, but it does need to be consistent and effective to create results!

Part 1: How to Select the Right Exercises for Your Clients

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