The present study examined the association between foot and ankle characteristics with fear of falling (assessed using the Falls Efficacy Scale International) and mobility (assessed using the Timed Up and Go Test) in older adults. The findings of this study indicate that foot and ankle characteristics contribute to both fear of falling and impaired mobility in older adults. Our results revealed that decreasing plantar flexor muscle strength and increasing pressure-time integral, foot pain, and tactile sensitivity were significantly and independently associated with increased fear of falling. We also observed independent associations between decreased plantar flexor muscle strength and increased pressure-time integral and decreased centre of pressure velocity with impaired mobility.
Overall functioning of the postural control system is dependant on lower limb muscle strength [13]. The foot and ankle complex, as the only part of the body that contacts the ground during walking and standing, needs to be sufficiently stable to maintain the center of mass within the base of support. Foot and ankle muscles contribute to postural stability [14], so decreased strength and the subsequent perceived loss of balance in daily life situations may induce fear of falling. The results of our study confirm that leg muscles play an important role in balance as ankle plantarflexor muscle strength was independently and significantly associated with FESI and TUGT. This finding is consistent with the available literature showing that those with fear of falling demonstrate less strength of the knee extensor [6, 15, 16] and ankle plantarflexor [6] muscles.
The association between plantar loading patterns during walking with fear of falling and mobility performance is a novel finding. The significant association between increased pressure-time integral with higher FESI and TUGT scores is particularly noteworthy. The underlying mechanism for this is difficult to determine, but the greater duration and magnitude of plantar loading when walking may predispose to foot pain, which has been shown to impair balance and functional ability in older people [17–19]. Although pain has previously been reported to be associated with impaired balance and fear of falling, most studies have investigated general body pain [20–22]. We found foot pain to be independently associated with fear of falling, which is consistent with the only other study in which this association was investigated [8]. Clinicians working with older adults with pain should therefore consider foot pain as an individual risk factor for fear of falling.
Older adults who failed the tactile sensitivity test scored worse in FESI, and the results of the linear regression model showed that it has a strong association with the FESI score. The integration of visual, vestibular, and somatosensory information is necessary to generate appropriate balance responses [23]. Individuals rely primarily on proprioceptive and cutaneous input to maintain standing balance [24], and several studies have shown that age-related peripheral sensory loss is associated with increased postural sway [25, 26] and is an independent predictor of falls [27, 28]. The perceived loss of balance due to impaired tactile sensitivity may therefore induce fear of falling in older people.
The COP on the plantar surface of the foot reflects the progression of the whole body center of mass during gait [29], therefore the forward velocity of the COP may potentially affect walking speed and sit to stand, the two components of TUGT. The negative association we observed between COP velocity and higher TUGT scores (indicative of poorer mobility) suggest that both walking speed and sit to stand, to some extent, require the same strategies in which the goal is to regulate speed and to remain upright during the transfer of bodyweight. This observation is consistent with previous studies which have reported that both walking [30] and sit to stand [31] are skills that involve rapid and coordinated balance transfers.
A number of potential limitations need to be considered. Firstly, the cross-sectional design of this study does not provide evidence of temporal relationships between variables, although it is unlikely that these foot characteristics are the result of either fear of falling or TUGT. Secondly, we used the TUGT as our measure of mobility. Although this is a widely used and useful measure, other tests more specific to balance may have identified stronger associations with foot and ankle characteristics. Finally, although we used a wide range of foot and ankle measures in our model, other factors (such as anxiety and depression scales) may have explained additional variance [32].