Physical fitness seems to play a relevant role in general health [1], and physical fitness in childhood and adolescence profoundly impact future, adult health. In this vein, RT has emerged as powerful modulator of physical fitness [3]. However, it has not been properly studied whether different programmed approaches to RT with adolescents produce different physical and psychosocial outcomes. The goal of the current study was therefore to compare the effects of 8 weeks’ resistance training with linear and undulating programming on physical fitness and mental health of adolescent boys.
Based on the findings, both experimental groups produced significantly greater improvements than the control group in terms of maximal muscle strength. The change percent of upper- and lower extremities strength for LPRT and UPRT groups was + 40.19, + 42.16 and + 102.89, + 126.04, respectively. There were no significant differences between the two programs. These findings are consistent with evidence provided by Niazi, Parnow [30].
Similarly, both experimental groups generated significant improvements in muscle endurance in comparison with controls, but without statistically significant differences between LPRT and UPRT. The change percent for upper- and lower- extremities in LPRT and UPRT groups was + 87.81, + 82.08 and + 86.90, + 379.29, respectively. The findings are in line with previous investigations [30, 31]. In the study performed by Niazi, Parnow [30], reported that both upper- and lower- extremities endurance increased following two LPRT and UPRT trainings in untrained female adolescents. Another research showed that two programmed modes of resistance training with equated intensity and volume could significantly change muscle endurance in adolescent athletes [31].
As for balance, there were no significant differences among the three groups considering right leg, although there were meaningful differences were present after evaluating for left leg balance. Again, it was shown that the two programs similarly improved dynamic balance in male adolescents. Previous studies have shown that combined training modalities are superior to balance-specific and plyometric training in terms of balance gains, while all three are superior to RT [32, 33].
Explosive power improved in both experimental groups, being statistically significant in comparison with controls, but not between themselves. Our findings are in inconsistent with the results of Niazi, Parnow [30], that have revealed that an 8-week LPRT and UPRT did not change the explosive-power in untrained female adolescents.
None of the programs changed speed levels significantly, in alignment with the research by de Villarreal, Requena [34], and in contradiction with other research [35, 36] that has showed the improvement of speed by various interventions including plyometric, resistance training and combined intervention trainings. Perhaps the differences may rely in type, intensity and duration of training protocol, as well as in age and baseline level of physical fitness.
Base on the FFMI findings, there were no statistically significant differences between training groups. Consistent with our results, Rhea, Ball [37] compared 12-week resistance training with LPRT and DUP in changing body composition, and reported no significant differences in both groups. In this regard, another research group also did not find any significant differences between linear and non-linear groups after 12-week training [22].
As for the psychosocial factors, there were no significant differences within and between groups in terms of general health and physical self-concept factors. Therefore, both training programs were ineffective in promoting improvements in the analyzed psychosocial factors. Perhaps 8 weeks were not enough for producing significant changes in such complex constructs. Although the change in physical fitness is considered to be a factor capable of modulating self-esteem, initial levels of physical fitness and self-esteem can influence the magnitude of gains [38].