ORIGINAL ARTICLE Resistance training promotes increase in intracellular hydration in men and women ALEX S. RIBEIRO 1 , ADEMAR AVELAR 2 , BRAD J. SCHOENFELD 3 , RAPHAEL M. RITTI DIAS 4 , LEANDRO R. ALTIMARI 5 , & EDILSON S. CYRINO 1 1 Metabolism, Nutrition, and Exercise Research Group, Londrina State University, Londrina, Brazil, 2 Physical Education Department, Maringá State University, Maringá, Brazil, 3 Exercise Science Department, CUNY Lehman College, NY, USA, 4 School of Physical Education, Pernambuco University, Recife, Brazil, 5 Neuromuscular System and Exercise Research Group, Londrina State University, Londrina, Brazil Abstract The main purpose of the present study was to investigate the effect of 16 weeks of resistance training (RT) on body water in men and women. Thirty men (22.7 ± 4.4 years, 68.4 ± 9.0 kg and 174.5 ± 6.6 cm) and 34 women (22.7 ± 4.1 years, 58.8 ± 11.9 kg and 162.6 ± 6.2 cm) underwent progressive RT for 16 weeks (2 phases, 8 weeks each), 3 times per week, that consisted of 10–12 whole body exercises with 3 sets of 8–12 repetitions maximum. Total body water, TBW (intracellular water, ICW and extracellular water, ECW compartments) and skeletal muscle mass (SMM) were assessed using a spectral bioelectrical impedance device (Xitron 4200 Bioimpedance Spectrum Analyzer). TBW, ICW compartment and SMM increased significantly (P < 0.05) over time in men (+7.5%, +8.2% and +4.2%, respectively) and women (+7.6%, +11.0% +3.9%, respectively), with no sex by time interaction (P > 0.05). We conclude that progressive RT promotes an increase in body water, principally by intracellular content; however, the hydration status is not influenced by sex. Keywords: Strength training, skeletal muscle, gender, cellular hydration Introduction Resistance training (RT) is a modality of physical exercise used for performance enhancement and health promotion purposes. Thus, RT has been recommended for a variety of different populations due to its numerous morphological, neuromuscular, physiological and metabolic benefits (American Col- lege of Sports Medicine [ACSM], 2009). Increasing skeletal muscle mass (SMM) is a primary goal of many recreational individuals of both sexes who are engaged in RT programmes. Mechanisms by which RT promotes increases in SMM have been attributed to various factors includ- ing mechanical, metabolic and hormonal processes (ACSM, 2009; Schoenfeld, 2010, 2012, 2013). Among the metabolic factors, one of the potential mechanisms that may contribute to muscle hyper- trophy is via an increase in intracellular water (ICW) compartment (Schoenfeld, 2012, 2013). This phenomenon, termed cell swelling, serves as a physiological regulator of cell function stimulating anabolic processes both by increasing protein syn- theses and decreasing protein breakdown (Grant, Gow, Zammit, & Shennan, 2000; Haussinger, 1996; Haussinger, Roth, Lang, & Gerok, 1993; Millar, Barber, Lomax, Travers, & Shennan, 1997). Fast-twitch fibres play an important role in cellular hydration as they are particularly sensitive to osmotic changes (Frigeri, Nicchia, Verbavatz, Valenti, & Svelto, 1998; Sjogaard, Adams, & Saltin, 1985). In addition, cellular swelling is maximised by exercise that relies heavily on glycolysis (Schoenfeld, 2012, 2013). Considering that percentage of fast-twitch fibres are proportionally higher in men than in women (Sale, MacDougall, Alway, & Sutton, 1987; Schantz, Randall-Fox, Hutchison, Tydén, & Åstrand, 1983), and that men have higher efficiency in glycogen degradation during exercise compared with women (Tarnopolsky, 2008), we cannot rule Correspondence: Alex Silva Ribeiro, Carmela Dutra Street 862, Jataizinho 86210-000, Paraná, Brazil. E-mail: alex-silvaribeiro@hotmail. com European Journal of Sport Science, 2014 Vol. 14, No. 6, 578–585, http://dx.doi.org/10.1080/17461391.2014.880192 © 2014 European College of Sport Science Downloaded by [Tulane University] at 14:57 25 August 2014