For years, it was assumed that varying strength training programs had an impact on training results. New research at the University of Copenhagen shows that varied strength training has a positive effect on strength development, but not on muscle growth.

According to the researchers, the answer to why periodized strength training can promote the development of strength, but not muscle mass, likely lies in our nervous system. Photo: Getty Images

For years, the word around gyms has been that to build muscle, a person needs to vary their training in terms of weights, reps, and exercises. But in a new study from the Department of Nutrition, Exercise and Sports at the University of Copenhagen, researchers can find that what is known as “periodized muscle training” – where training is varied according to increasing variables and decreases such as the amount of weight lifted, as well as the number of repetitions – promotes the development of strength.

“The study establishes that periodized strength training is conducive to the development of strength, but not muscle mass. If you want to get stronger, it is important to vary your training”, is the main message from Associate Professor Jesper Lundbye-Jensen, the latest author of the study.


  • Periodic strength training means that the weight load and number of reps go up and down week by week. For example, a person may do fewer reps with more weight one week, before moving on to more reps with fewer pounds the next week.
  • The researchers collected 35 existing studies in the field with more than 1,200 participants from around the world, which they reviewed and reanalyzed.
  • More than 800,000 Danes are active members of a fitness centre.

According to the researchers, the answer to why periodized strength training can promote the development of strength, but not muscle mass, likely lies in our nervous system.

“While people get stronger with periodized training compared to non-periodized training, this is likely because strength training also trains the nervous system, and therefore our ability to coordinate and activate muscles to the maximum. “, explains Jesper Lundbye. -Jensen.

According to Lukas Moesgaard, the first author of the study, increasing muscle mass through strength training requires training until fatigue sets in and spending a sufficient number of hours to the gym to do it.

“Research suggests that strength training especially leads to muscle growth when training muscles to exhaustion. And, as a general rule, more exercise leads to more muscle growth,” he explains. he.

Trained people get stronger through regular variations

In the study, the researchers were also able to find that those who already exercised regularly improved their strength more by varying the intensity of their weekly training and alternating between heavy and light lifting exercises.

Untrained people, on the other hand, received the same benefit from training whether the variation took place on a daily or weekly basis, or whether the training was adjusted in a linear fashion – i.e. by increasing loads as the individual gains strength – over a period of time. extended period of time.

“Overall, the study demonstrates that varying the weight load and number of repetitions of strength training can help if one wishes to get stronger, and that the variation should probably occur more often. when one is trained than if one is not trained. However, our results also demonstrate that varying loads and the number of repetitions do not seem to affect the amount of muscle growth,” says Lukas Moesgaard.

The article is based on a scientific study known as a systematic review with meta-analysis, where researchers collect and review all relevant scientific literature in a given field.

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