Magnusson SP, Kjaer M. Resistance training induces qualitative changes in muscle morphology, muscle architecture, and muscle function in elderly postoperative patients. J Appl Physiol 105: 180 -186, 2008. First published April 17, 2008 doi:10.1152/japplphysiol.01354.2007.-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. Thirty-six patients (60 -86 yr) scheduled for unilateral hip replacement surgery due to hip osteoarthritis were randomized to either 1) resistance training (RT: 3/wk ϫ 12 wk), 2) electrical stimulation (ES: 1 h/day ϫ 12 wk), or 3) standard rehabilitation (SR: 1 h/day ϫ 12 wk). All measurements were performed at baseline, at 5 wk and 12 wk postsurgery. After 12 wk of resistance training, maximal dynamic muscle strength increased by 30% at 60°/s (P Ͻ 0.05) and by 29% at 180°/s (P Ͻ 0.05); muscle fiber area increased for type I (ϩ17%, P Ͻ 0.05), type IIa (ϩ37%, P Ͻ 0.05), and type IIx muscle fibers (ϩ51%, P Ͻ 0.05); and muscle fiber pennation angle increased by 22% and muscle thickness increased by 15% (P Ͻ 0.05). Furthermore, stair walking power increased by 35% (P Ͻ 0.05) and was related to the increase in type II fiber area (r ϭ 0.729, P Ͻ 0.05). In contrast, there was no increase in any measurement outcomes with electrical stimulation and standard rehabilitation. 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 emphasize the importance of resistance training in future rehabilitation programs for elderly individuals.aging; muscle power; exercise SARCOPENIA HAS LONG BEEN RECOGNIZED as a major cause of loss in muscle strength with old age. In fact, aging and disuse are two of the main conditions leading to skeletal muscle atrophy in humans. In both conditions, the loss of muscle mass leads to a decrease in muscle force production, and recent evidence suggests that a significant additional contribution might come from changes in muscle architecture (38,39). However, only a few studies have examined changes in muscle architecture and muscle fiber morphology in response to aging and physical training, and although the results suggest that a significant plasticity exists, there is generally a lack of data as to what extent different conditioning stimuli may affect muscle architecture in elderly individuals recovering from hospitalization.The loss of muscle mass with aging accelerates from the sixth decade onword, partly owing to a de...