## 4 Discussion
The main practical application of this research is that a new line of OFE that has a series of adaptations to be able to adjust the intensity of the exercise achieves similar EMG activations to conventional gym machinery. This information is valuable for both users and trainers, as it demonstrates that this line of machines could be just as effective as conventional machinery to train lower limbs in trained young men. Most of these machines are located in free, open-access facilities, providing an opportunity for the population to do strength work in an economical way and outdoors. The present research also shows that when this type of OFE does not have a system to adjust the intensity of the exercise, a lower EMG intensity is generated, so that the use of OFE that only allows training with one's own body weight could be less effective for strength training than machines that allow an adjustment of the intensity of the exercise in trained young men. Therefore, it would be advisable for public agencies that are investing in the installation of this OFE in public spaces to consider this in order to choose models that have an adjustment of the intensity of the exercise, thus maximizing the population that will be able to train effectively in these facilities. Regarding possible future lines of research, it would be advisable to analyze other prototypes of OFE to study the effect of different design changes on the EMG presented during their use in the different muscle groups. On the other hand, in the current study, the effect of fatigue was mitigated by allowing a minute of rest between each repetition [51]. Even so, future studies should use one of the various methods of analysis of neuromuscular fatigue [52] as well as zero-crossing of EMG signal [53]. In addition, it would be recommended to replicate the study in a female population or in other age populations to analyze whether the results are replicable in other populations. Despite the novelty of the present study with respect to previous research on the analysis of the effectiveness of OFE, the present investigation is not without limitations. First, the EMG analysis of the gluteus as a hip extensor was not included due to the location of the electrodes being incompatible with the execution of the exercise on the machines, which is performed from sedentation (SLP and BIOFIT-LP). As a second limitation, the three machines exhibited small variations in the biomechanics of execution, which are conditioned by the mechanism of each of the structures, which makes the comparison between the exercises not exact. As a third limitation, the present study did not include the maximum voluntary contraction test as a variable in the EMG analysis, nor did it record the EMG during the 1 RM test, variables that could have helped to differentiate the percentage of activation of each muscle group with respect to its maximum for each of the exercises involved. However, the EMG activation tests on the different machines were performed on the same day, following a randomized order, to eliminate the effect of daily variation on this variable. As a final limitation, although an in situ goniometric analysis was used to differentiate the concentric and eccentric phase, the present study did not include a goniometric analysis of the ankle, knee, and hip joints in the data analysis, which could have helped to discern the origin of the difference in EMG activation between some of the machines.