This study aimed: To analyze the effects of 6-month multicomponent training (MCT) and 4-month detraining on functional capacity and frailty among older adults with/at risk of frailty and to analyze the influence of frailty status on training and detraining adaptations. A total of 106 older adults (80.5 ± 6.0 years) were divided into a control (CON) or training group (TRAIN). The TRAIN performed a 6-month MCT (Eelder-fit), while CON continued their usual lifestyle. Functional capacity was assessed by the Short Physical Performance Battery (SPPB), while frailty was evaluated through Fried (FP) and the short version of the Frailty Trait Scale (FTS-5). Linear mixed models were performed to analyze group effects and to compare differences in changes within and between groups. TRAIN showed improvements in SPPB (3.2 ± 2.4), FP (−0.7 ± 1.3), and FTS-5 (−5.9 ± 5.8), whereas CON improved in SPPB (0.7 ± 2.9) and deteriorated in FTS-5 (2.8 ± 7.6) (all p < 0.05). Group effects favorable to TRAIN were found for all scales during this period (all p < 0.05). After detraining, TRAIN worsened in SPPB (−1.2 ± 2.7) and FTS-5 (4.1 ± 6.1) (both p < 0.05). No relevant differences were observed, accounting for frailty status between TRAIN subgroups. Eelder-fit improved the functional capacity and frailty of this population, whereas 4-months of detraining caused a drop of these variables except in FP.