Resistance training (RT) guidelines recommend regularly adjusting training variables to avoid stagnation in adaptations. However, few studies have investigated the combined effects of modulating volume and exercise variation within a single experimental design. This study examined the effects of increased training volume, exercise variation, and their combination on lean tissue mass in young adults of both sexes. Thirty-two participants completed a 14-week upper-body RT program divided into two phases: (1) six weeks of standardized RT for all participants, and (2) eight weeks of unilateral RT. During phase 2, one arm followed a control protocol (CON), while the other arm was randomly assigned to one of three experimental conditions: higher volume (HV), exercise variation (EV), or a combination of both (HV+EV). Changes in muscle upper-limb lean tissue mass were estimated using Dual-Energy X-ray Absorptiometry (DEXA) before training and after each phase. Phase 1 led to an average increase of 4.0% in upper-limb lean tissue mass. In phase 2, all conditions showed an additional increase in upper-limb lean tissue mass (CON: 3.1%, HV: 2.2%, EV: 3.0%, HV+EV: 3.2%), with no significant differences between them. These findings suggest that neither increased volume nor exercise variation, alone or combined, enhanced changes in upper-limb lean tissue mass beyond the control condition, likely because all protocols employed sufficient volume and high effort.
Valério et al. (Wed,) studied this question.