Original Research Effects of Static and Dynamic Stretching Performed Before Resistance Training on Muscle Adaptations in Untrained Men Joa ˜ o B. Ferreira-J ´ unior, 1 Ricardo P.C. Benine, 1 Suene F.N. Chaves, 1 Diego A. Borba, 2 Hugo C. Martins-Costa, 3 Eduardo D.S. Freitas, 4 Michael G. Bemben, 4 Carlos A. Vieira, 5 and Martim Bottaro 6 1 Federal Institute of Sudeste of Minas Gerais, Campus Rio Pomba, MG, Brazil; 2 Department of Human Movement Science, State University of Minas Gerais, Campus Ibirit ´ e, MG, Brazil; 3 Pontifical Catholic University of Minas Gerais, Belo Horizonte, MG, Brazil; 4 Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma; 5 Federal University of Goi ´ as, Goiania, GO, Brazil; and 6 University of Bras´ ılia, Bras´ ılia, DF, Brazil Abstract Ferreira-J ´ unior, JB, Benine, RPC, Chaves, SFN, Borba, DA, Martins-Costa, HC, Freitas, EDS, Bemben, MG, Vieira, CA, and Bottaro, M. Effects of static and dynamic stretching performed before resistance training on muscle adaptations in untrained men. J Strength Cond Res XX(X): 000–000, 2019—This study evaluated the effects of dynamic and static stretching (SS) performed before resistance training on biceps femoris hypertrophy and knee flexor strength gains in untrained young men. Forty-five untrained young men (age, 21.2 6 0.5 years; mass, 72.2 6 5.6 kg; height, 178 6 1 cm) were randomly assigned to 1 of the 3 groups: (a) 80 seconds of SS (n 5 14); (b) 80 seconds of dynamic stretching (DS, n 5 13); or (c) control group (CON, n 5 18) in which subjects performed no stretching before exercise. Both SS and DS were performed before resistance exercise. Resistance training consisted of 4 sets of 8–12 repetition maximum of seated leg curl exercise 2 days per week for 8 weeks, with a period of at least 48 hours between sessions. Unilateral biceps femoris muscle thickness (MT) and maximal isometric strength (MIS) of the knee flexors were measured 1 week before training and 1 week after the last training session. There were significant increases in MIS (SS 5 13.9 6 10.3 kgf; DS 5 10.2 6 13.1 kgf; CON 5 12.7 6 7.6 kgf; p , 0.05) and MT (SS 5 6.0 6 3.5 mm; DS 5 6.7 6 4.1 mm; CON 5 5.7 6 3.0 mm; p , 0.05) with no significant differences across groups (p . 0.05). Additionally, all groups demonstrated moderate effect sizes for MIS (1.27–1.4), and DS was the only group that had a large effect size for MT increases (DS 5 2.18; SS 5 1.35; CON 5 0.92). In conclusion, 80 seconds of SS and DS did not induce any additional muscular adaptations to resistance training in untrained young men. Key Words: strength, hypertrophy, exercise, flexibility Introduction Stretching and resistance exercises have been considered as impor- tant components of training programs (23,25). Long-term re- sistance exercise increases strength and muscle mass, and also enhances many health parameters such as body composition, bone mineral density, and physical activity levels (25,39). Stretching exercises, in turn, are considered effective methods for improving joint range of motion (2,8,14,17), muscle strength (14,17,40), and gait speed (27). Additionally, both static stretching (SS) and dy- namic stretching (DS) are generally incorporated into warm-up routines or even performed within or immediately after resistance exercise training (5,7,18,23). The SS exercises consist of holding at stretch position by actively contracting the muscles in opposition to the muscle being stretched, whereas the DS is performed by moving their limb continuously through a challenging range of motion (23). There is a paucity of literature regarding the effects of stretching exercises performed before bouts of resistance exercise. One previous study reported that SS flexibility training combined with resistance training did not compromise strength gains in untrained women (34). Interestingly, it was also recently reported that 50 seconds of SS performed before resistance training ses- sions diminished muscle hypertrophy, whereas muscle strength gains did not seem to be affected in untrained young men (16). On the other hand, 60 minutes of DS for upper and lower limbs did not impair leg press and bench press strength gains in trained women (19). The strength gains induced by resistance training depend on the neuromuscular adaptations (i.e., neural factors and muscle hypertrophy) (25). Thus, these results suggest that re- gardless of the technique used, stretching exercise before re- sistance training does not seem to negatively impact muscular strength adaptations following resistance training, whereas muscle hypertrophy may be diminished by SS. However, not much attention has been given to the effects of DS on muscle hypertrophy. Furthermore, because no study to our knowledge has compared the effects of different stretching techniques on muscle hypertrophy and strength gains before resistance training, using matched training loads, research that evaluates the chronic effects of both SS and DS before resistance exercise is needed. A large number of studies have indicated a deleterious effect of SS performed before exercise on muscle strength (1,5,9,24,33,38) and a positive effect of DS (5,15,33,37,41), suggesting that SS results in a reduced amount of weight lifted during resistance exercise session, whereas DS may allow for greater loads to be lifted. Resistance training adaptations depend on training load Address correspondence to Dr. Joa ˜o B. Ferreira-J ´ unior, jbfjunior@gmail.com. Journal of Strength and Conditioning Research 00(00)/1–6 ª 2019 National Strength and Conditioning Association 1 Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.