Background: The foot is a complex body structure that plays an important role in static and dynamic situations. Previous studies have reported that altered foot posture might affect knee joint strength and postural stability, however their relationship still remains unclear. Objects: The purpose of this study was to identify whether pronated foot posture has an influence on knee isokinetic strength and static and dynamic postural stability. Methods: Forty healthy young males aged 18 to 26 years were included. Foot posture was evaluated using the Foot Posture Index-6 (FPI-6), and the subjects were divided into two groups according to their FPI-6 scores: a neutral foot group (n = 20, FPI-6 score 0 to +5) and a pronated foot group (n = 20, FPI-6 score +6 or more). Biodex Systems 3 isokinetic dynamometer was used to evaluate knee isokinetic strength and hamstring to quadriceps ratio at three angular velocities: 60°/sec, 90°/sec, and 180°/sec. The static and dynamic postural stability in a single-leg stance under the eyes-open and eyes-closed conditions were measured with a Biodex Balance System. Results: There were no significant differences between the groups in knee isokinetic strength and static postural stability (p > 0.05), but there was a significant difference in the medial– lateral stability index (MLSI) for dynamic postural stability under the eyes-closed condition (p = 0.022). The FPI-6 scores correlated significantly only with the dynamic overall stability index (OSI) and the MLSI (OSI: R = 0.344, p = 0.030; MLSI: R = 0.409, p = 0.009) under the eyesclosed condition. Conclusion: Participants with pronated foot had poorer medial–lateral dynamic stability under an eyes-closed condition than those without, and FPI-6 scores were moderately positively correlated with dynamic OSI and dynamic MLSI under the eyes-closed condition. These results suggest that pronated foot posture could induce a change in postural stability, but not in knee isokinetic strength.

Postural instability can increase the likelihood of hazardous slip and fall accidents in workplaces. The present study intended to extend understanding of the effect of abnormal neck posture on postural control during quiet standing. The effect of body fatigue on the postural control was also of primary concern. Twelve healthy undergraduate students volunteered to participate in the experiment. Standing on a force platform with the neck neutral, flexed, extended, or rotated, subjects’ center of pressures (COP) were measured under the two levels of body fatigue. For the fatigue condition, Subjects exercised in a treadmill to meet the predetermined level of body fatigue. Analyzing the position coordinates of COPs, the length of postural sway path was assessed in both medio-lateral (ML) axis and anterior-posterior (AP) axis. Results showed that, in AP direction, neck extension or rotation significantly increased the sway length as compared with neck neutral. Neck extension led to greater sway length compared to neck rotation. Neck flexion did not differ from neck neutral. The sway length in the AP direction also became significantly larger as the body fatigue accumulated after treadmill exercise. In ML direction, as compared to neutral posture, the neck extension, flexion, or rotation did not significantly affect the length of postural sway path. However, the sway length seemed to increase marginally with the neck extended during the fatigued condition. This study demonstrates that abnormal neck posture may interfere with postural control during standing. The ability to maintain postural stability decreases significantly with the neck extended or rotated. Body fatigue leads to postural instability further.

이 연구의 목적은 비만한 사람들의 자세 제어 능력의 부족에 관한 경험적 증거를 얻는 것이었다. 이를 위해서 비만 여대생(15명)과 정상체중 여대생(15명)에게 전, 후, 좌, 우 방향으로 기울여서 버티는 과제를 수행시켰다. 그리고 지면 반력기를 이용하여 압력 중심의 y축과 x축의 최대값, 최소값을 산출하여 그 절대값을 전, 후, 좌, 우 방향의 자세 안정성 한계의 측정치로 사용하였다. 비만 여부와 기울이기 방향에 대한 반복측정 이원분산분석을 실시한 결과, 첫째, 좌우 방향의 안정성 한계가 전후 방향의 안정성 한계보다 컸다. 둘째, 비만 집단이 정상체중 집단보다 안정성 한계가 작았다. 특히, 비만 집단과 정상체중 집단간의 차이는 전방 안정성 한계와 오른쪽 안정성 한계에서 나타났다. 즉, 비만 집단은 정상체중 집단과 비교해서 앞으로 기울이기아 오른쪽으로 기울이기 능력에서 결함을 나타냈다. 이러한 연구 결과는 비만한 사람들의 자세 유지 능력의 부족을 의미하며, 비만과 자세 제어에 관한 추후 연구를 제안하였다.