Abstract Background The current recommendations on resistance training involving older adults have reported an improvement of body composition variables. Despite this, there is a lack of knowledge on how elastic resistance training (ERT) affects the muscle mass in older adults population. The purpose of this study was to determine the effects of a short-term ERT on muscle mass of health and untrained older adults. Methods Forty older adults were randomized into two groups of 20 individuals each: Control Group (CG = 66.2 ± 6.6 years) and Training Group (TG = 69.1 ± 6.3 years). TG underwent an ERT twice a week during 8 weeks and control group did not receive any specific intervention. The primary outcome was the upper and lower limbs muscle mass, measured by Dual-energy x-ray absorptiometry. The secondary outcomes were knee isokinetic peak torque (PT) at 60°/s and 120°/s speeds and isometric handgrip strength. A 2×2 mixed model (group [TG and CG] × time [pre and post]) analysis of variance (ANOVA) was applied to determine the effect on primary and secondary outcomes. Results The results of the ANOVA showed no significant effects in group x time interaction for (1) upper limbs fat free mass (F [1.38] = 1.80, p  = 0.19, effect size [ES] = 0.1) and for (2) lower limbs fat free mass (F [1.38] = 0.03, p  = 0.88, ES = 0.02). Regarding muscle strength, the ANOVA showed no significant effects in group x time interaction for (3) PT at 60°/s (F [1.38] = 0.33, p  = 0.56, ES = 3.0), for (4) PT at 120°/s (F [1.38] = 0.80, p  = 0.38, ES = 4.1) and for handgrip strength (F [1.38] = 0.65, p  = 0.42-value, ES = 0.9). Analysis of PT in TG showed a significant change of 4.5 %, but only at 120°/s ( p  = 0.01) when comparing pre and post-training (time interaction). Conclusions Eight weeks of ERT did not show significant changes in muscle mass and strength of untrained older adults. Trial registration NCT02253615 (09/25/14)