It is unclear which parameters of physical activity and sedentary behaviour are important for healthy ageing, and to what extent. This Review aimed to synthesise, quantify, and compare the strength of the associations between physical activity and sedentary behaviour with clinically relevant outcomes. Systematic reviews describing community-dwelling adults older than 60 years and reporting standardised associations of objectively measured physical activity and sedentary behaviour with mortality, activities of daily living, frailty, falls and fear of falling, muscle strength and power, and global cognition, were included. Standardised associations were expressed as standardised regression coefficients (βs) and compared within and across outcome domains. Six systematic reviews were included with sample sizes ranging from 7696 to 43 796 (mean or median age 60–92 years). Higher physical activity and lower sedentary behaviour were most strongly associated with better chair stand test performance and lower body muscle strength, and least with falls and hand grip strength. Number of steps was the most strongly and most consistently associated with clinical outcomes. Conferring to a wide array of positive outcomes, steps provide a clinically relevant target that shows practical ease. Future recommendations should promote steps regardless of ability, encouraging that some physical activity is better than none, or, as the present findings show, that every step counts.