Background <p>Severe falls in older individuals are a leading cause of emergency department (ED) visits and often result in long-term impairments that reduce physical activity (PA). Limited information exists on the characteristics of individuals who suffer from physical inactivity after such falls and the factors that influence it. This study investigates the association between potential moderators and changes in PA in older adults six months after a severe fall.</p> Methods <p>Participants were recruited from the SeFallED study (German Clinical Trials Register ID: 00025949). Moderators were evaluated through a home-based geriatric assessment conducted within four weeks of a severe fall with presentation to the ED. PA was quantified using both sensor-based (<i>n</i> = 72 men (75 years), <i>n</i> = 106 women (74 years) and self-reported (<i>n</i> = 105 men (74 years), <i>n</i> = 174 women (73 years) assessments. A Linear Mixed Model was used for analysis.</p> Results <p>Sensor-based PA revealed a significant time effect for step count (<i>p</i> = 0.006), indicating an increase in PA six months after a severe fall. Fall history (95% CI: -1,009.5 – (-207.4), <i>p</i> = 0.003) and age (95% CI: -315.8 – (-82.5), <i>p</i> &lt; 0.01) were significant negative moderators for changes in PA, only in women. No significant changes in self-reported PA were observed after six months (<i>p</i> = 0.109).</p> Conclusion <p>Participants showed an increase in sensor-based PA six months after a severe fall, though this was negatively associated with age and fall history. Early identification of factors that affect PA recovery may help stratify individuals by risk and target those in need of secondary prevention.</p> Trial registration <p>DRKS (Deutsches Register für klinische Studien, DRKS0 00259 49). Prospectively registered on 4th November, 2021.</p>