Ageing is associated with a loss of muscle mass (muscle atrophy), and a decline in strength measured at the level of the whole joint system (joint torque). In relative terms, the decline in strength is much greater than the loss of muscle mass, as other factors such as muscle architecture, the level of neural activation and antagonist muscle coactivation all play a role in contributing to this strength decline with ageing. Declines in strength and muscle mass with ageing have important consequences for daily functional tasks, which can impinge upon independent living and quality of life. The ageing-related decline in muscle mass and strength can be at least partially mitigated by interventions that increase the level of loading on skeletal muscle above that to which it is habitually accustomed. Typically these interventions have used resistance training, which involves lifting and lowering known loads (concentric and eccentric muscle contractions, respectively) in a single plane to load specific major muscle groups. The extensor muscle groups at the knee and ankle appear to be most severely affected by ageing-related declines in strength and size and therefore, have typically been the focus of resistance training programmes for older adults. Most resistance training programmes utilise relatively high loads, based upon the premise of activating as high a proportion of the muscle’s motor unit pool as possible. Typically training loads are prescribed as a percentage of a ‘repetition maximum’, defined as the maximum load that can be lifted and lowered under control and repeated a given number of times. Typically training loads are recommended between 60 and 100% of the one-repetition maximum, however, effective muscular adaptations have also been seen in older adults with slightly lower training loads (e.g., Vincent et al., 2002). Increases in strength (measured as isometric torque) following resistance training programmes in older people can vary considerably depending upon a number of factors, but for the knee extensors for example, have ranged between 7 and 57% (Tracy et al., 1999; Hakkinen). Concomitant increases in muscle size in response to resistance training have ranged between 2 and 12% (Tracy et al., 1999; Roth et al., 2001). The large variation in the reported muscle size and strength adaptations to training interventions is due to many factors. For example, aspects such as the resistance training load, frequency and total duration of training all vary between studies. An important point in relation to the degree of strength adaptation reported between studies is the mode of testing. ‘True’ strength gains will be overestimated if expressed as the repetition maximum on the training device, due to learning and coordination effects. A more objective measure of training-induced strength gains can be gained by measuring isometric torque. The plasticity of the muscular system in older adults is highlighted by the fact that strength gains in older adults can be comparable to those reported in younger adults following similar resistance training durations (Reeves et al., 2006). Muscle mass is typically assessed by measuring a muscle’s cross-sectional area or total volume. Although these measures are a useful indication of muscle size and any changes with training interventions, they fail to take into account information on the internal muscle architecture and any subsequent modifications with training. Architectural parameters within a muscle include the length of muscle fascicles and the angle of fascicular insertion into the tendon aponeurosis, known as the pennation angle. These parameters affect factors such as the transmission of force through to the tendon and both fascicle lengths and pennation angles have been modified positively after resistance training interventions in older adults (e.g., Reeves et al., 2004). Recently, we have shown how eccentric-only training can cause specific adaptations in muscle architecture, different to those changes seen with ‘conventional’ resistance training in older adults (Reeves et al., 2009). This type of training (eccentric-only) also enabled older adults to train using much higher loads, but with far lower ratings of perceived exertion, which may be an important factor for adherence to training programmes. In summary, resistance training interventions have been shown to be effective for increasing muscle size and strength in older adults, which can at least partially reverse some of the detrimental consequences on skeletal muscle observed with ageing.