When the aim is to gain muscle mass, the key variables are the training volume (amount of work), intensity (how intense each unit of work is) and training frequency (how often each muscle group is trained), and they were the ones that this research focussed on mainly. Yet the selecting and managing of the exercises are another factor to be taken into consideration if the aim is to maximize the gains.

Outside the scientific community the term “muscle confusion” has been used to argue that muscles should not be allowed to adapt and, therefore, they have to be surprised by being subjected to a range of stimuli. Regarding this aspect the PLOS ONE journal has just published the article entitled ‘The effects of exercise variation in muscle thickness, maximal strength and motivation in resistance trained men’, which is part of the PhD thesis by Eneko Baz-Valle, supervised by Jordan Santos-Concejero of the UPV/EHU’s Department of Physical and Sports Education.

The study aimed to compare two training groups with trained subjects in which one group performed a fixed selection of exercises over an 8-week period and the other had their exercises and repetition ranges varied, while maintaining the same framework in terms of training volume, frequency and intensity.

To obtain the results, measurements were taken of the muscle thickness of the quadriceps (vastus lateralis, vastus intermedium and rectus femoris), the intrinsic motivation of the subjects and the maximal dynamic strength (a maximum repetition on bench-press and squats). The measurements were made in the UPV/EHU’s Department of Physiology and the study was conducted in collaboration with the Autonomous University of Madrid and the City University of New York. “The results of the study revealed significant differences in intrinsic motivation in favour of the group who varied their exercises randomly from one session to the next. Yet we did not observe any differences in the measurements of muscle thickness and maximum dynamic strength between the two groups," said the researchers.

With these data it can be concluded that “muscle confusion” does not offer any more benefits in gaining muscle mass than a regular framework and the gain could even be lower in the medium term. However, those individuals who are less motivated to train may benefit from a more frequent change in exercises. “At the end of the day, with neither adherence nor perseverance it does not make any difference how the remaining variables are managed,” they stressed.

In the research the rotation of exercises was carried out randomly without paying any attention to individual needs or capabilities, so “muscle adaptation could be improved even further through a personalised programme, in which the exercise selection is carefully managed to take biomechanical, physiological and anthropometric factors into consideration," they concluded.