Functional differences between lower limbs during gait in relation to fall risk

Introduction: During certain motor tasks such as normal walking, the lower limbs exhibit similar movement patterns only with a temporal phase shift, resulting in an almost symmetrical pattern of movement. However, many authors reported asymmetrical behavior of the lower limbs during able-bodied walking and thus it is necessary to consider some range of functional differences between the lower limbs as natural sign of human gait (Gao et al., 2023; Lathrop-Lambach et al., 2014; Riskowski et al., 2012). One of the hypotheses, which could explain gait asymmetry is that one limb (dominant) has a leading role and the second one supporting function (Zverev, 2006). It is expected that leading limb contributes more to forward propulsion of the body while the supporting limb provides more stability. Although these studies suggest functional difference between limbs as leading and supporting limb, the relationship between their roles and maintaining of dynamic balance during gait is not well documented. It is very important especially in relation to fall risk, because understanding of these principles could have some potential for modification of fall prevention programs in elderly. Some authors suggested that asymmetry analyses during gait may provide additional insights into what specific deficits in balance control mechanisms are producing increased gait variability (Peterka et al., 2023).Methods: The observed sample consisted of 131 elderly subjects (108 females, 23 males) with age 71.0 ± 6.8 years. Local dynamic stability was assessed during 5 minutes of indoor walking (over ground) in a 25-metre-long well-lit corridor. The participants were instructed to walk by their self-selected speed straight forward, turn after crossing the marker on the floor and continue by the same walking speed to the next turn. Before walking 3D accelerometers (sampling rate 296.3 Hz, Trigno wireless system, Delsys Inc., Natick, MA, USA) were attached on both shanks approximately 15 cm above the lateral malleolus. Acceleration was recorded in the vertical (V), medial-lateral (ML) and anterior-posterior (AP), directions (sampling rate 296.3 Hz). Local dynamic stability was evaluated using short-term and long-term Lyapunov exponents (LE) computed from 150 strides (Riva et al., 2014) for each direction independently. Fall occurrence was recorded prospectively for one year by phone interviews performed every two weeks. After one year the subjects were divided into groups of fallers (at least one fall) and (non-fallers).Results: The result showed significant effect of limb (better stability on non-dominant limb) for long-term LE in medial-lateral direction (p < 0.001; η2 = 0.121) and for both long-term (p < 0.001; η2 = 0.161) and short-term (p = 0.005; η2 = 0.059) LE in anterior-posterior direction (better stability on dominant limb). There was no effect of group. Group*limb Interaction was significant for long-term LE in medial-lateral direction (p = 0.011; η2 = 0.049) suggesting better stability of non-dominant limb and worse on dominant limb in fallers compared to non-fallers.Conclusions: In conclusion, our study confirmed existence of functional asymmetry between limbs during gait in local dynamic stability measures, however it seems that the roles of the limbs are not associated with acute but rather with long-term response on perturbations.