Purpose It is not clear whether fat-free mass gains impact negatively on swimming performance in swimmers. Moreover, less is known about the impact of different dry-land resistance training (DLRT) periodization models on body fat changes in swimmers. Hence, this study aimed to test whether block periodization DLRT (DLRT-BP) and daily undulating periodization DLRT (DLRT-DUP) are similar in improving fat-free mass, swimming and physical performance, muscular strength, and body fat in female and male amateur swimmers. Methods The participants were randomized into three groups: DLRT-BP [n = 10, three blocks of training with different intensities (changing each 4 week)], DLRT-DUP [n = 10, three sessions of training per week with different intensities (alternating each session)], and control group (n = 8, swimming training alone). Both intervention groups training three times a week. Muscle mass index (indicator of fat-free mass) and body fat percentage (iDXA), swimming (50-M swim velocity and time) and physical (squat jump) performance, muscular strength (1RM) were analyzed at baseline and after 12-weeks of DLRT. Results There were similar improvements in fat-free mass, swimming performance, and muscular strength from pre-intervention, and when compared to control group (P < 0.05). However, body fat percentage and squat jump did not change (P > 0.05). Fat-free mass changes explained 17% the improvement in 50-M swim velocity (r = 0.41, P = 0.040) in both training groups than control group. Conclusions Thus, although both DLRT periodization models induce fat-free mass gains (independent of sex), it does not seem to affect the responses in swimming performance and muscular strength in amateur swimmers.
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