University of Copenhagen: Varied strength-training programmes increase strength, but not muscle mass

For years, it has been assumed that variation in strength-training programmes impacts training outcomes. New research at the University of Copenhagen demonstrates that varied strength training has a positive effect on developing strength, but not on muscle growth.

For years, the word around gyms has been that to put on muscle, a person needs to vary their training with regards to weight, repetitions and exercises. But in a new study from the University of Copenhagen’s Department of Nutrition, Exercise and Sports, researchers can see that so-called ‘periodized strength-training’ – where training is varied by increasing and decreasing variables such as the amount of weight lifted, as well as the number of repetitions – benefits strength development.

“The study establishes that periodized strength training is conducive to the development of strength, but not muscle mass. If one wants to get stronger, it is important to vary their training,” is the main message from Associate Professor Jesper Lundbye-Jensen, the study’s last author.


Periodized strength training means that both the weight load and number of repetitions are increased and decreased from week to week. For example, a person can do fewer repetitions with more weight one week, before transitioning to more repetitions with fewer kilos the next.

The researchers gathered 35 existing studies in the field with over 1200 participants from around the world, which they reviewed and analyzed anew.

More than 800,000 Danes are active members of a fitness center.
According to the researchers, the answer as to why periodized strength training can promote the development of strength, but not muscle mass, is likely found in our nervous system.

“As people become stronger from periodized workouts compared to non-periodized workouts, it is most likely due to the fact that strength training trains the nervous system as well, and thereby our ability to coordinate and activate muscles to a maximum,” explains Jesper Lundbye-Jensen.

According to Lukas Moesgaard, the study’s first author, increasing muscle mass through strength training requires working out until fatigue sets in and putting in a sufficient number of hours at the gym to do so.

“The research suggests that strength training particularly results in muscle growth when training muscles to exhaustion. And, as a rule of thumb, more exercise leads to more muscle growth,” he explains.

Trained people get strongest through regular variation
In the study, the researchers could also see that those who already train regularly achieved more progress in strength by varying the intensity of their weekly training and alternating between heavy- and light-lifting exercises.

The untrained, on the other hand, received the same benefit from training, regardless of whether the variation took place on a daily or weekly basis, or whether the training was adjusted linearly – i.e., by increasing loads as an individual gains strength – over an extended period of time.

“All in all, the study demonstrates that variation in weight load and the number of repetitions in strength training can help if one is keen on getting stronger, and that the variation should probably occur more often when one is trained than if one is untrained. However, our results also demonstrate that varying loads and the number of repetitions doesn’t seem to affect the amount of muscle growth,” says Lukas Moesgaard.

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