Muscle Function in the Elderly After Hip-Replacement Surgery - Effects of Long Term Disuse and Physical Training

During the last decades there has been an increase in the relative proportion and life expectancy of elderly people in the industrialised countries. Consequently the amount of elderly with diseases and disabilities related to aging has increased. It therefore appears paramount to gain a better understanding of how disuse and immobilisation affects neuromuscular properties in the elderly, as well as to identify training regimes that ensures an effective rehabilitation.The population of interest in the present study was elderly individuals with long term hip-osteoarthritis undergoing a hip-replacement operation. The study was divided in two parts, a cross-sectional study and an intervention study. The cross-sectional study investigated muscle size, maximal muscle strength, specific force, neural drive and explosive muscle force characteristics in elderly individuals who were affected by unilateral prolonged disuse due to hip-osteoarthritis. The data clearly indicated that the side with hip-osteoarthritis was affected by a marked decrease in muscle mass, maximal muscle strength, neural drive and explosive muscle force characteristics compared to the unaffected side. The intervention study investigated if elderly patients that undergo hip-replacement surgery could benefit from additional training in the early postoperative phase. The data clearly demonstrated that resistance training was an effective and safe way to increase muscle mass, maximal muscle strength, neuromuscular activity, functional performance and decrease the hospitalisation period compared to regimes of conventional rehabilitation regimen or electrical muscle stimulation. Additionally the intervention study demonstrated that resistance training effectively induced marked increases in explosive muscle force characteristics in elderly subjects compared to rehabilitation regimes using electrical muscle stimulation or conventional rehabilitation. Furthermore, the gains in maximal muscle strength and explosive muscle force characteristics were accompanied by significant increases in EMG amplitudes. Furthermore, the demonstration that explosive muscle force capacity of the neuromuscular system remains trainable in elderly recovering from prolonged limb disuse and major surgery may have important implications for future rehabilitation programs, especially when considering the importance of rapid muscle force capacity on postural balance, maximal walking speed and other tasks of daily life actions.