This cross-sectional study examined the differences in toe flexor strength and foot morphology between older individuals who use a wheelchair and those who walk when moving about in everyday life. We found that older people who used a wheelchair were more likely to have a history of fracture or heart disease and weaker toe flexor strength. A wheelchair is often used when it is difficult to walk. However, these study participants did not have motor paralysis and were capable of standing with or without assistance, but they could not walk safely. A history of bone fracture or heart disease had a significant negative effect on the likelihood of walking. However, it is unclear whether the participants who used a wheelchair did so because of joint contracture subsequent to a fracture or because of disuse atrophy associated with heart disease, or whether the turning point for using a wheelchair was disuse as a result of other diseases.
In this study, no significant between-group difference was found in the foot morphology, including for hallux valgus; even in the multiple logistic regression analysis, foot morphology was not among the significant factors. The prevalence of hallux valgus detected on radiographs in older Japanese men and women living in the community was 28.4% (3) and that in day care service users was > 50% (4). In this study, hallux valgus was found in about half of the older participants who needed some assistance with activities of daily living and are undergoing or had received ambulatory rehabilitation in a long-term care health facility. This percentage was higher than that in community-dwelling older people and tended to be similar to that in day care users.
Toe flexor strength was significantly greater in the walking group than in the wheelchair group. The strength of the toe flexors is related to walking parameters such as walking speed (8) and the timed up and go test (16). In particular, a positive correlation between toe flexor strength and the average number of steps taken per day was reported in women aged > 80 years (13). Hallux valgus and lesser toe deformity reduce the strength of plantar flexion (5, 17, 18). In our study, no significant difference was found in the foot morphology between the two groups; however, toe flexor strength was significantly greater in the walking group and was attributed to a difference in the amount of activity performed when standing, including walking. Since there is no difference in foot morphology even when muscle strength is significantly reduced, muscle weakness is unlikely to cause changes in foot morphology.
With regard to the proportion of each muscle strength of the wheelchair group to the mean values of toe flexor strength and hand grip strength in the walking group, the proportion of toe flexor strength was significantly lower than the proportion of hand grip strength. With age, the skeletal muscle mass in the lower limbs is significantly less on magnetic resonance images than that in the upper limbs (19). Furthermore, the ratio of muscle thickness in older people to that in young people was significantly lower in the plantar flexors than in the elbow flexors (20) and there was a significant decrease in the ratio of reduction in toe flexor strength to hand grip strength (21, 22). The results of this study suggest that the standing and walking frequencies had some influence on the values because no difference was found in age between the walking group and the wheelchair group.
A study has reported that the toe flexor muscles and ankle range of motion are important for balance while standing and for functional ability (6). Wheelchair users have significantly less toe flexor strength, which may affect balance when standing. Even when using a wheelchair as a means of mobility in daily living, in order to stand, turn, and sit safely when transferring from a wheelchair, if there is no severe motor paralysis of the lower limbs, joint contracture, or load limitation, the person must be able to stand and may need to maintain toe flexor strength.
This study has several limitations, First, the foot morphology was measured from the contour of the foot; therefore, the influence of edema due to heart disease and involvement of pronation or supination of the ankle joint due to loading on the sole of the foot in the sitting position could not be determined. Second, the reason for using a wheelchair to mobilize in daily living and the duration of wheelchair use are unknown, so it is impossible to exclude factors of functional deterioration other than the foot and toes. Third, the proportion of male participants was lower than that of female participants, so the effect of gender differences was unknown.