There have been numerous studies that have investigated balance stability for various standing postures. However, to date, there does not appear to be any research in existence that focuses on bilateral support standing with toe-extension. In this current study, the differences in postural stability between NS and SWT, and the impact of gender on postural control, were explored.
The results of this study substantiate the hypothesis and show that there was no difference in postural sway in NS and SWT conditions in the OSI, MLSI and APSI. The balance performance as represented by the OSI, MLSI and APSI stability scores was slightly lower during NS, but this was not significant when compared with the score achieved during SWT. Slight differences in the NS and SWT scores may be due to the fact that SWT requires more sway from the CoP as the body regains balance. According to the windlass mechanism, when the toes are extended to their limit, the plantar aponeurosis that wraps around the metatarsal bone tightens and therefore causes the arch to rise, further lifting the metatarsal head 
. Hicks 
claimed that the metatarso-phalangeal (MTP) head will increase the pressure of the toe against the ground and the height of the rising arch is related to the distance of the metatarsal head to the calcaneus. The current study demonstrated that the arch of the foot did rise and that the sway in both ML and AP directions insignificantly increased during as the MTP head extended. Hence, this is inconsistent with the previous findings of Hicks 
which stated that toe-extension of the forefoot increases the postural sway due to the foot pressure that is applied at the MTP joints. As such, the toe extension may result in a reduction of the base of support and this subsequently deteriorates the stability of the body 
In spite of being closely matched for age (p
0.892), the current study showed that gender does not influence human balance in the NS and SWT conditions, since no differences in the stability scores were found between the male and female participants. This is in contrast with previous studies, which reported that males had a greater postural sway than females during quiet standing 
. Lee and Lin 
suggested that the difference in body weight of males will result in greater CoP execution during the single-leg standing task. However, the findings of Mickle 
claimed that males executed greater postural sway, even though the body weight for both genders are nearly similar.
According to the findings, the ML sway among females was slightly higher, but this was not significant when compared with that of the male control group during both the NS and SWT conditions (). Meanwhile, the current findings show that an increased complexity of standing posture leads to an increase in the ML sway. The ML sway was different than the AP sway during NS. There was a significant increase in the ML sway that was required to achieve balance, as the ML sway was similar with the AP sway in SWT. This finding may relate to the Q-angle. Studies have shown that females have a greater Q-angle than males due to the length of their femur and their bigger pelvis area 
. A larger Q-angle for females may result in an increase of rotation in hip movement, since the CoM needs to be maintained within the base of support to achieve body balance 
. As such, greater sway will be generated in the ML direction and sideways sway will increase in response to this in order to regain body equilibrium. Maki et al. 
also demonstrated that an increase in body sway in the ML direction might lead to an increased risk of falling. Interestingly, the findings also revealed that the value of APSI was slightly higher than MLSI across all conditions, although it showed differences in NS and no statistically significant difference in SWT. This is in agreement with previous studies which revealed that the MLSI has a low value compared to APSI 
. Meanwhile, the current findings show that there is an increase in the ML sway in accordance with the increasing complexity of standing posture. The ML sway was found to be different with the AP sway during NS. There is a significant increase in the ML sway that was required to achieve balance, as the ML sway was similar to the AP sway in SWT. As such, the tendency of the ML sway was considered to be an important component for balance equilibrium when a more complex posture was applied during quiet standing.
The investigation of static balance control provides normative stability data for clinicians who are concerned with this specific toe condition. It is important to identify the changes of balance performance during SWT, since it is altered by the base of support and CoM. Some authors reported that the CoP and CoM are approximately equal only in the static or quasi-static conditions 
. Likewise, Murray et al. 
presented the idea that motion in the CoP is greater than that in the CoM in order to keep the CoM within the base of support, since the CoP changes in response to the CoM. From the anatomical point of view, the height of the CoM is normally lower in females than males 
. There are also studies that investigate the effect of the type of female’s footwear on balance 
. High heel shoes tend to affect postural control by raising and shifting the CoM forward 
. Csapo et al. 
highlighted that the long-term use of high heels might diminish the gastrocnemius muscle fascicles and reduce the range of motion in an individual’s ankle, resulting in a feeling of discomfort even when they are wearing in flat shoes.
Although the current study was restricted to an investigation of static postural control during toe-extension standing activities, it would be interesting to compare the postural control between active toe-extension in healthy individuals and the passive toe-extension that can be caused by burn injuries. Nevertheless, the investigation of static postural control has provided a normative stability data in SWT. Besides, the sample size in this study only involved young adults (aged between 19 and 25 years old) from one specific geographical area and, as such, the data is limited.
In conclusion, this study has demonstrated that differences between the NS and SWT conditions do not lead to differences in postural control. However, a small alteration in postural control during SWT shows a trend of greater amount of postural sway than NS, although this is not significantly different. The findings also revealed the interactive effect of postural control in term of the OSI, MLSI and APSI. Gender does not appear to effect static postural stability.