## 1 Introduction  
The 21 st century runs its course towards an aged society, with more than 1 billion people aged over 60 years [1].  
The aging process causes systemic changes at functional and structural levels related to a higher prevalence of comorbidities, such as cardiovascular, cognitive, and neurodegenerative diseases [2, 3]. Therefore, older adults often experience multimorbidity associated with polypharmacy [2, 4], which can exacerbate their declines in physiological and biomechanical parameters, such as slowness, reduced flexibility and mobility, decreased proprioception and body stability, sarcopenia, and fatigue [4, 5]. These alterations can be an early sign of their functional worsening and risk of falling [6, 7], being particularly important given that falls are the main cause of injuries in this population [8]. It has been estimated that one third of the community-dwelling population aged over 60 years experiences at least one fall per year [9]. In this context, not only the history of fall (HoF) but also the fear of falling (FoF) has been shown to have a high association with the risk of falling [7, 10]. In older adults, it has been estimated that 20% of falls occur on stairs [8], and from these, 75% occur while descending stairs [11].  
Stair descent imposes a higher neuromuscular and sensorimotor demand [12; 13], and older adults have more difficulty controlling the fast vertical displacements of the center of mass (CoM) [14; 15]. Additionally, they adopt alternative strategies, such as decreased descent velocity and single-support time [16], increased double-support time [17] and foot placement (FP) [16], and reduced foot clearance (FC) [18]. Falls usually happen during the transition to gait [18], when the nervous system must quickly respond to a change in the motor task, with this ability becoming less efficient with aging [19]. Notably, stair descent is related to a higher incidence of falls and worse consequences in older adults [20; 21], and it is an essential task for the independence and quality of life of this population [12; 22]. Therefore, the study of solutions capable of predicting incapacity in older adults is demanded to prevent the occurrence of falls [21].  
Research has shown the influence of age on stair descent in older adults; however, few studies have integrated spatiotemporal parameters and lower-limb kinematics [8; 15; 16; 18; 19; 21]. Few authors have focused on both stair descent and gait transition [8; 11; 14; 19], and the literature lacks analyses of the association between HoF and FoF with respect to these parameters during stair descent and gait transition. Thus, beyond the range of kinematic parameters, during stair descent, the assessment of key events such as the transition to gait could bring relevant data, since, at these transitional moments, older adults exhibited strategies prioritizing stability over the range of motion [23].  
Therefore, the aim of this study is to evaluate the association between HoF and FoF on spatiotemporal parameters and lower-limb kinematic parameters in older adults during stair descent and gait transition. Specifically, spatiotemporal parameters will be assessed through task velocity and time, single- and double-support time, and peak downward CoM velocity, and kinematic data will be assessed through hip, knee, and ankle positions, FC, and FP.