Changes in Upper-Limb Lean Tissue Mass in the Early Stages of Resistance Training: The Role of Volume Progression and Exercise Variation in Young Women and Men.

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.