Abstract
The toe clearance strategy during leg swinging while walking is closely associated with the risk of tripping and/or falling and is influenced by aging and a fall history. However, it remains unclear how the toe clearance strategy is regulated by the neuromuscular system. The present study investigated the effect of aging and fall/tripping history in the older adults on the toe clearance strategy and neuromuscular regulation of the rectus femoris (RF) muscle, which plays an important role in leg swinging, during prolonged walking. Thirteen older adults (age: 71.3 ± 5.7 years) and nine young adults (age: 20.9 ± 0.8 years) men volunteered for the present study. The older adults were divided into those with (n = 6) and without (n = 7) a fall/tripping history. Subjects walked on a treadmill at their preferred gait speed for 20 min, and lower extremity kinematics and multi-channel surface electromyography along the RF muscle were recorded. Variability of the minimum toe clearance (MTC) and central locus activation (CLA) of the RF muscle in older adults was significantly greater than in the young adults (p < 0.05). MTC significantly decreased with time in the older adults (p < 0.05), but not in the young adults (p > 0.05). There were no significant correlations between any parameters of MTC and CLA in the older adults or young adults (p > 0.05). MTC and variability of CLA significantly decreased with time in the older adults without a fall/tripping history (p < 0.05), but not in the older adults with such a history (p > 0.05). These results suggest that aging and a fall/tripping history in the older adults alter the toe clearance strategy and regional neural regulation of the RF muscle during prolonged walking.
Highlights
The risk of trip-related falls is maximal when the distance between the foot of the swing leg and the surface being walked on, i.e., minimum foot clearance (MFC), is reduced to zero or very small (Winter, 1992; Barrett et al, 2010)
The present study investigated the effect of aging and a fall/tripping history in the older adults on the toe clearance strategy and neuromuscular regulation of the rectus femoris (RF) muscle during prolonged walking
The main findings of the present study were (1) variability of minimum toe clearance (MTC) in the older adults was significantly greater than in the young adults (Figure 2B), (2) MTC significantly decreased with time in the older adults, but not the in young adults (Figure 2A), (3) there were no significant correlations between parameters of MTC and central locus activation (CLA) in the young or older adults (Table 2), and (4) the effects of time on the mean MTC and variability of CLA were not uniform between the older adults with and without a fall/tripping history (Figures 3A,D)
Summary
The risk of trip-related falls is maximal when the distance between the foot of the swing leg and the surface being walked on, i.e., minimum foot clearance (MFC), is reduced to zero or very small (Winter, 1992; Barrett et al, 2010). Variability of MFC during repeated gait cycles increases with aging and the presence of a fall history, and is known as a risk indicator for trips and related falls in the older adults Additional activation at distal region of the RF muscle was observed with activation at proximal regions during the swing phase (Watanabe et al, 2016). This may lead to unexpected knee extension joint moment during the swing phase and alteration in the toe clearance strategy
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