Introduction Maximal muscle strength is a strong predictor of functional skills and ability to maintain independent living in elderly. Muscle contraction properties has been shown to decline to a greater extent than muscle strength with aging and it has been considered the main responsible of the observed decline in functional status (Izquierdo et al., 1999). Endurance high intensity interval training (HIT), by involving large muscle groups, and eccentric strength exercise (IRT), by producing high mechanical loads, could be used in elderly to improve muscle function and quality of life (Milanovi et al., 2015). Therefore, the aim of this study was to examine the changes in muscle properties in elderly after 8 wk of HIT and IRT. Methods 12 moderately active older adults (age: 69.4±4.3 yy; BMI: 22.9±2.7 kg/m2; V’O2max: 29.5±4.1 mL/kg/min) have completed 8 wk of: i) HIT, 7 two-minute cycling repetitions at 90% of V’O2max, 3 times/wk, and, after 4 months, ii) IRT performed with an isoinertial leg press (YoYo TechnologyAB) comprised 4×7 maximal concentric-eccentric knee extensions, 3 times/wk. Maximum voluntary contraction (MVC) was measured using a cell load in a custom-made setup (90° knee flexion). Electrically evoked muscle single twitch was superimposed onto MVC: neuromuscular activation (NA) was calculated as the ratio between the amplitudes of the superimposed and resting twitches. Muscle volume of the quadriceps (Qvol) was obtained by MRI scans. Results MVC at 90° knee flexion, increase significantly only after IRT (P < 0.01). Both training modalities affected significantly NA (P < 0.05): +12.4% after HIT and +14.2 after IRT. Similarly, Qvol increase by 5.1% (P < 0.05) after HIT intervention and by 4.9% (P < 0.05) after IRT. Discussion Our results confirm the feasibility and effectiveness of HIT and IRT to improve muscle qualities: 8 wk of specific training are able to modify muscle mass, MVC and neuromuscular activation in elderly subjects. This stresses the importance of using effective approaches such as exercise treatment with high loads and high intensities in the prevention of disuse in elderly individuals who are concurrently exposed to the deleterious effects of aging on muscle contractile function and mass (Behrens et al., 2016). We can therefore speculate that the two proposed training modalities may be helpful in improving functional status and prevent frailty in elderly subjects. References Izquierdo M, Aguado X, Gonzalez R, Lopez JL, Hakkinen K. (1999). Eur J Appl Physiol Occup Physiol, 79, 260-7. Milanovi Z, Sporiš G, Weston M. (2015). Sports Med, 45(10), 1469-81. Behrens M, Brown N, Bollinger R, Bubeck D, Mau-Moeller A, Weippert M, Zschorlich V, Bruhn S, Alt W. (2016). Appl Physiol Nutr Metab, 41(1), 110-3.