Strength training seems to be an interesting approach to counteract decreases that affect knee extensor strength, muscle mass and muscle quality (force per unit of muscle mass) associated with ageing. However, there is no consensus regarding the changes in muscle mass and their contribution to strength during periods of training and detraining in the elderly. Therefore, this study aimed at verifying the behaviour of knee extensor muscle strength, muscle volume and muscle quality in elderly women in response to a 12-week strength training programme followed by a similar period of detraining. Statistical analysis showed no effect of time on muscle quality. However, strength and muscle volume increased from baseline to post-training (33 and 26 %, respectively). After detraining, the knee extensor strength remained 12 % superior to the baseline values, while the gains in muscle mass were almost completely lost. In conclusion, strength gains and losses due to strength training and detraining, respectively, could not be exclusively associated with muscle mass increases. Training-induced strength gains were partially maintained after 3 months of detraining in elderly subjects.