4. Discussion
This investigation compared the effect of two popular techniques used to improve the range of motion. The present results show a statistically significant increase in flexibility in the PNF and FR groups and in both periods of intervention (30 s and 2 min both during and at the end of the intervention). When comparing the two groups, this study obtained better and significant results for the PNF group. These results disagree slightly with two recent meta-analyses that had compared the impact of a single bout of stretching with foam rolling on the range of motion [Other studies observed an increase (practically double) in the gain of flexibility in hamstring muscles when following a six sessions program of static stretching compared to FR [After 2 min of intervention, the present results show a moderate effect in the case of the PNF group and a smaller effect in the case of FR. For this reason, the results suggest that the application of FR for less than two minutes may not be enough in the field of sports to improve the ROM.Although this is purely speculative, both protocols likely result in therapeutic effects via different physiological mechanisms. On one hand, a recent paper suggested that the efficacy of PNF in terms of a gain of flexibility is due to the fact that this type of stretching is focused on the musculotendinous unit and its autogenic inhibition reflex [This study has some important limitations. Firstly, this research only analyzed one parameter of neuromuscular response or function (in this case, the ROM). For future studies, it could be interesting to observe viscoelastic or contractile muscle properties. Secondly, the intervention of FR did not use the vibration information; the use of this mechanical oscillation could produce different effects in the muscle tissue. Thirdly, the present study only analyzed the acute effect of these techniques. Fourthly, the results of the present research could have been different of diverse time domains or different muscle applications had been employed.Finally, our results may also help to provide new insight into athletes’ healthcare and performances by showing how the application of PNF or FR is useful for improving the ROM and how the manipulation of time may promote greater results.