Although the negative effects of bed-rest on muscle strength and muscle mass are well established, it still remains a challenge to identify effective methods to restore physical capacity of elderly patients recovering from hospitalization. The present study compared different training regimes with respect to muscle strength, muscle fiber size, muscle architecture and stair walking power in elderly postoperative patients. Methods: Thirty-six patients (60-86 yrs) scheduled for unilateral hip-replacement surgery due to hip-osteoarthritis (OA) were randomized to either; 1) Resistance Training [RT:3/wkx12wks], 2) Electrical Stimulation [ES:1h/dayx12wks] or 3) Standard Rehabilitation [SR:1h/dayx12wks]. All measurements were performed at baseline, 5 and 12 wks post-surgery. Results: After 12 wks of RT maximal dynamic muscle strength increased by 30% at 60°/s and by 29% at 180°/s , muscle fiber area increased for type I (+17%), type IIa (+37%) and type IIx muscle fibers (+51%) while, muscle fiber pennation angle increased by 22% and muscle thickness increased by 15%. Furthermore, stair walking power increased by 35% and was related to the increase in type II fiber area (r=0.729, p<0.05) . In contrast, there was no increase in any measurement outcomes with ES and SR. Discussion: The present study is the first to demonstrate the effectiveness of resistance training to induce beneficial qualitative changes in muscle fiber morphology and muscle architecture in elderly postoperative patients. In contrast, rehabilitation regimes based on functional exercises and neuromuscular electrical stimulation had no effect. The present data emphasizes the importance of resistance training in future rehabilitation programs for elderly individuals.