Multiple sclerosis (MS) is a chronic neurological condition affecting an estimated 2.8 million people worldwide and is a leading cause of long-term disability in young adults (Brownlee et al., 2017; Walton et al., 2020). In MS pathology, damage to myelinated axons disrupts neural communication within the brain and spinal cord, leading to a variety of symptoms ​(Dobson and Giovannoni, 2019; Horng and Fabian, 2017)​. Among the most impactful of these symptoms is a progressive decline in motor and sensory function (Ghasemi et al., 2017; Green et al., 2017)​. These physical limitations can significantly interfere with daily life, as many people with MS (PwMS) face increasing challenges with movement and balance over time (Cameron and Nilsagard, 2018; Lublin et al., 2022).

One of the most detrimental consequences of MS-related physical impairments is an increased risk of falls (Mazumder et al., 2014). Falls begin early in the disease course, sometimes preceding a clinical MS diagnosis, and increase in frequency as the disease advances (Moen et al., 2011). Falls pose a heightened risk of physical injury (e.g., fractures, head injuries), and they precipitate a cascade of psychological and social effects (Peterson et al., 2007; Tinetti et al., 1995). Falls and the fear of falling impede individual independence by reducing physical activity, limiting comfort and confidence in movement, and decreasing social engagement, ultimately leading to diminished quality of life (Coleman et al., 2013; Peterson et al., 2008, 2007; Sutliff, 2010; Zwibel, 2009).

Many falls occur during transfer movements when an individual changes body positions, such as when rising and lowering from a chair (Robinovitch et al., 2013). As such, clinical assessments of sit-to-stand transfer ability are particularly relevant. The Five Times Sit-to-Stand Test (5XSST) is a reliable measure of transfer ability and functional strength in aging and neurological populations (Lord et al., 2002; Mong et al., 2010; Paul et al., 2012; Wang et al., 2012). Moreover, according to clinical practice guidelines for neurorehabilitation, the 5XSST is the best practice for assessing sit-to-stand transfer ability in PwMS (Moore et al., 2018).

Beyond evaluating functional mobility, metrics derived from force plates during a sit-to-stand transfer, such as peak lower-body power, differentiate fallers from non-fallers in older adults (Cheng et al., 2014). While measuring lower-body power during transfers may help identify fall risk in PwMS, the equipment and time required to measure power is largely inaccessible to clinicians. Accordingly, equations that use readily available metrics such as patient height, weight, and time to complete the transfer assessment have been developed to estimate lower-body power during sit-to-stand transfers (Alcazar et al., 2018). Currently, it is unknown whether these equations accurately estimate lower-body power during transfers in PwMS. Given the high rate of falls among PwMS and the harmful impact falls have on health and well-being, assessing transfer ability and lower-body power with clinically feasible tests like the 5XSST can provide valuable insights for enhancing health monitoring and outcomes within neurological conditions such as MS.

Therefore, the aims of this study were to 1) examine differences in 5XSST vertical ground reaction force (vGRF) profiles and associated kinetic metrics between PwMS and matched controls, 2) establish the relationship between force plate-derived lower-body power with estimated lower-body power during the 5XSST, and 3) compare force plate derived power and estimated power during the 5XSST between fallers and non-fallers with MS. Together, this work aids in developing accessible methods for fall risk monitoring, prevention, and neurorehabilitation for PwMS.