Bioimpedance analysis (BIA) provides a simple, non-invasive, and inexpensive approach to identifying biomarkers of cellular damage and cell death, components of body composition, cell volume, and hydration in a geriatric population by determining whole-body cell membrane quality and depicting individual fluid distribution (1). More recently, some studies have opted to use bioelectrical impedance vector analysis (BIVA) and phase angle (PhA) to avoid errors associated with the use of derived BIA equations (2). Briefly, BIVA uses the raw parameters obtained from BIA (i.e., resistance and reactance), normalized for height yielding a vector of specific magnitude (length) and direction (3). Previous studies indicated that BIVA could identify body fluids changes and hydration status (4,5), even using deuterium dilution as the reference method to track water compartment changes (6,7,8). The phase angle is calculated as the arctangent of Xc/R × 180◦/π (3) reflecting changes in fluid shifts between the compartments and, therefore, highly related to the extra to intracellular water ratio (9), whose reductions have also been linked to cell damage, inflammation, aging, and mortality (10,11,12,13). In this regard, aging-associated alterations in body composition, manifested by reduced skeletal muscle mass and increased body fat, may influence BIVA parameters, resulting in decreased PhA (14).
In contrast, resistance training (RT) induces changes in the cellular volume of skeletal muscle tissue, which is a highly hydrated tissue due to variations in metabolic demand, cell membrane potential, and blood supply, and these alterations are associated with muscle hypertrophy and reduced adiposity (15). Consequently, RT can be one of the potential strategies to reverse the adverse effects of aging on cellular integrity and function (16,17,18). However, evidence-based dose-response relationships regarding specific RT variables, such as frequency, intensity, and volume, are unclear in healthy older trained adults.
In this regard, the more appropriate dose-response relationship of RT in healthy older adults is not yet well established (19,20,21) since the benefits of RT are dependent on proper manipulation of training variables, such as the number of exercises, sets, and repetitions; duration (length of a period program); frequency (number of sessions per week), the magnitude of load; the velocity of muscular action; and rest intervals between sets and exercises (22, 23). Among these variables, the number of sets may play an essential role in the RT program since it directly influences training volume. It is considered important for increasing muscular strength and, mainly, for developing muscle hypertrophy (24,25,26).
Though recent studies reported similar results between RT with single and multiple sets for skeletal muscle mass (24,27), intracellular water (16), PhA (28), and muscular strength (24) in untrained older women, it is expected that for trained individuals, the use of multiple-set may be fundamental to avoid a supposed adaptative plateau. Also, little is known about the impact of the set volume reduction on RT programs on different outcomes, particularly whether these changes could affect PhA, given the relation of this indicator with muscular strength and skeletal muscle mass in older women (29). It is worth mentioning that RT volume reduction can be systematically planned to achieve a balance in stimulus/recovery to optimize fitness outcomes over a given training cycle, to avoid the effects of detraining and maintain acquired adaptations, or perhaps even to continue to optimize such adaptations (30,31,32). In this regard, manipulating RT volume over time may be particularly important for older individuals, given that aging seems to slow the recovery process from exercise (33).
Thus, the purpose of the present study was to compare the effects of the RT volume reduction on BIVA and PhA in older women after being engaged in a 20-week RT program. We hypothesized that training with volume reduction can maintain the adaptations acquired with the previous training. In contrast, training without volume reduction can still promote adaptations affecting fluid body distribution as assessed by BIVA and increases in PhA.