Percentages of 1RM

Strength coaches sometimes write strength training programs calling for specific percentages of 1RM (for example, 3 sets of 10 reps with 75% of 1RM). While this might appear to create a standard stimulus for each lifter, differences in fatigue resistance between people (and as a result of the various ways in which such workouts can be performed) mean that it does not.

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#1. The number of reps that can be done with a given percentage of 1RM differs between exercises

Lifters are able to do more reps to failure when they perform certain exercises compared to when they perform other exercises, even when the percentage of 1RM is exactly the same in each case. So, when a lifter performs a set with a submaximal number of reps and a given percentage of 1RM, the proximity to failure in the later sets of the workout will vary depending on the exercise used.

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#2. The number of reps that can be done with a given percentage of 1RM differs between individuals of different training backgrounds

Endurance-trained people are able to do more reps to failure in a given set than individuals who are strength-trained. Consequently, when a lifter performs a set with a submaximal number of reps and a given percentage of 1RM, the proximity to failure in the later sets of the workout will vary according to their training background.

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#3. The number of reps that can be done with a given percentage of 1RM differs according to the tempo

Lifters are able to do more reps to failure when they use faster tempos compared to when they slower tempos. Consequently, when a lifter performs a set with a submaximal number of reps and a given percentage of 1RM, the proximity to failure in the later sets of the workout will vary depending on the tempo used. In practice, this means that unless a certain tempo is stipulated, the proximity to failure in a set could vary widely. 

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#4. The number of reps that can be done with a given percentage of 1RM differs according to the rest period 

Obviously, lifters are able to perform more reps to failure on the later sets of a workout when they take longer rest periods between sets compared to when they take shorter rest periods between sets. Consequently, when a lifter performs a set with a submaximal number of reps and a given percentage of 1RM, the proximity to failure in the later sets of the workout will vary depending on whether the rest periods are long or short.

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#5. The number of reps that can be done with a given percentage of 1RM differs according to the focus of attention used

When lifters use an external focus of attention while they are lifting, they tend to achieve a greater number of reps to failure compared to when they use either no focus of attention or an internal focus of attention. Consequently, when a lifter performs a set with a submaximal number of reps and a given percentage of 1RM, the proximity to failure will vary depending on whether the set is done with an external focus or an internal focus.

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#6. Why does the number of reps that can be done with a given percentage of 1RM matter?

Proximity to failure matters because only the reps that are close to failure are able to stimulate muscle growth. Therefore, using percentages of 1RM instead of repetition maximums (such as 8RM or 12RM) is likely to lead to an uncertain number of stimulating reps being achieved in a set that is not performed to muscular failure (read more).

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Conclusions

Strength coaches sometimes write strength training programs calling for specific percentages of 1RM (for example, 3 sets of 10 reps with 75% of 1RM). While this way of programming might appear to create a standard stimulus for each lifter, differences in fatigue resistance between people (and as a result of the various ways in which such workouts can be performed) mean that it does not. Indeed, lifters with endurance exercise experience typically are able to perform more repetitions with a given percentage of their 1RM than lifters with only strength training exercise experience. Additionally, the number of repetitions that can be achieved in a set to failure with a given percentage of 1RM varies according to: [1] the tempo used (since far more repetitions are possible to perform when the tempo is faster), [2] the duration of the rest period between sets (since far more repetitions are possible to perform when the rest period is longer), and [3] the focus of attention that they employ (since far more repetitions are possible to perform when an external focus of attention is used instead of an internal focus of attention, which is also called a mind-muscle connection). Hence, percentages of 1RM should not be used in combination with fixed numbers of repetitions. Instead, repetition maximums should be used, such as 10RM or 12RM. In contrast, percentages of 1RM can be used when training to failure, since this does mean that a standardized stimulus is attained.