The influence of lower-limb dominance on postural balance

ABSTRACT CONTEXT AND OBJECTIVE: Maintainance of postural balance requires detection of body movements, integration of sensory information in the central nervous system and an appropriate motor response. The purpose of this study was to evaluate whether lower-limb dominance has an influence on postural balance. DESIGN AND SETTING: This was a cross-sectional study conducted at Faculdade de Medicina da Universidade de São Paulo (FMUSP) and at Hospital do Coração (HCor). METHODS: Forty healthy sedentary males aged 20 to 40 years, without any injuries, were evaluated. A single-foot balance test was carried out using the Biodex Balance System equipment, comparing the dominant leg with the nondominant leg of the same individual. The instability protocols used were level 8 (more stable) and level 2 (less stable), and three instability indices were calculated: anteroposterior, mediolateral and general. RESULTS: The volunteers’ mean age was 26 ± 5 years (range: 20-38), mean weight 72.3 ± 11 kg (range: 46-107) and mean height 176 ± 6 cm (range: 169-186). Thirty-four of them (85%) presented right-leg dominance (defined according to which leg they used for kicking) and six (15%) had left-leg dominance. There were no significant differences between the dominant and nondominant legs at the two levels of stability (eight and two), for any of the instability indices (general, anteroposterior and mediolateral). CONCLUSION: The lower-limb dominance did not influence single-foot balance among sedentary males.


intrODUctiOn
Balance is defined as the process of maintaining the body's center of gravity within the weight support base.[3][4] Maintenance of postural balance requires detection of body movements, integration of sensory information in the central nervous system and an appropriate motor response.The body's position in space is determined by visual, vestibular and somatosensory functions.[6] The dominant limb can be defined on the basis of muscle strength, functional use and personal preference and these parameters may interfere with balance.Limb dominance should be determined according to which leg the individual chooses and relies on to carry out a variety of functional activities, including maintaining balance. 7However, there is a lack of consensus regarding the definition and determinants of lower-limb dominance.The methods most used have been evaluations of kicking and hopping on a single leg.
Comparisons between the limbs are used in orthopedic evaluations and balance tests in order to diagnose functional instabilities, make therapeutic decisions, evaluate results and determine whether patients are in a condition to return to locomotion and/ or to sports activities. 8,9ilateral tests are routinely incorporated into clinical practice in order to compare an injured limb with the intact contralateral limb (long jump and high jump tests and single-foot balance test, among others).The contralateral limb serves as a control for the evaluation that is carried out.Postural balance evaluations are one of the ways of measuring proprioceptive loss and they help to determinate the efficiency of habilitation after injury or surgery. 1,8,9ere has been little investigation relating to variation between the lower limbs and balance, including in relation to dominance. 7The body weight support and functional activi-

OBJectiVeS
The aim of the present study was to evaluate whether low-limb dominance has an influence on postural balance.This was a cross-sectional study without intervention, in which 40 male volunteers were evaluated.For the sample size calculation, we assumed the following for the two-tailed hypothesis: alpha value (type 1 error probability) of 5%; beta value (type 2 error probability) of 20%; and thus, a test power of 80% and a difference between the groups regarding the main outcome of 10%

MetHODS
To meet these conditions, at least 40 subjects were needed (taking one limb as the unit of analysis, 40 nondominant limbs and another 40 dominant limbs would be needed). 10e inclusion criteria were that the volunteers should: a) sign the free and informed consent statement; b) be male; c) be between 20 and 40 years old; d) not have done any physical activity for a minimum of six months; e) not present any neurological, cardiovascular, metabolic, rheumatic or vestibular diseases; f) not have any injuries or previous surgery on the legs; and g) not present any clinical instability in the knees or ankles.
The balance test was carried out using the Biodex Balance System (Biodex, from Biodex Medical Systems, Inc., 2009).The protocols followed the instructions of the equipment manual and previous studies.The instability protocols used were level 8 (more stable) and level 2 (less stable).Level 2 allowed an inclination of up to 20º in the horizontal plane in all directions.Stability varies according to the level of resistance (such that level 8 is the most stable and level 1 is the least stable).[13][14][15]

Positioning
The patients were each positioned barefoot on the platform, with their weight supported on one foot and with the corresponding knee semi-flexed at 10º.The contralateral knee remained flexed at 90º.The patients crossed their arms over their chests, looking at the screen in front of them (Figure 1).The platform was indices: general P = 0.27, anteroposterior P = 0.16 and mediolateral P = 0.85 (Table 1).

DISCUSSION
The study by Freeman et al. 11 advocated that activities performed on a single leg should be used in order to decrease the effects of functional instability.Since then, functional activities with the body weight supported on a single foot have been greatly used for evaluating and rehabilitating balance impairments relating to musculoskeletal injuries.However, the difference in performance between the dominant and nondominant limbs needs to be known.
Hoffman et al. 7 carried out a series of functional tests that they called "functional determination of the dominant limb" and established that the dominant limb was the one that performed the movement with more precision and skill.They confirmed that the dominant leg was the one used for kicking a ball.We used the criterion of the kicking leg to determine dominance in the present study.
As expected, the validity and reliability of balance tests using the Biodex Body System has been considered satisfactory in published studies.[14] There was no difference between the dominant and nondominant limb at both levels of instability, but at the level of greater instability of the equipment (level 2), the range of motion was greater because of the need for greater postural adjustments in order to maintain balance. 6,17,18However, these findings are similar to those of Alonso et al., 6 who found that in groups of sedentary individuals and recreational football players, there was no difference between the limbs.In another study by Alonso et al. 16 using the same equipment and making the same comparison, but this time on the stability limits among sedentary individuals and judo practitioners, there were no differences between the limbs or in relation to the time taken to achieve effective action in the tests.This was also shown by Tookuni et al., 2 who used the Fscan Mat equipment, Hoffman et al. 7 with a force platform and McCurdy and Langford, 17 who correlated force and balance by means of squat tests with weights on a platform using single-foot support.These findings are very important because they could be used to evaluate rehabilitation results and postural balance deficit.
Hoffman et al. 7 stated that asymmetry between the lower limbs was due to acute or chronic lesions and was unrelated to limb dominance.However, McCurdy and Langford 17 stated that there was no knowledge about the effect of dominance on athletes who used their legs in repetitive asymmetrical activities that would have the potential to generate distinct balance patterns in single-foot evaluations and therefore to interfere with the training and rehabilitation of these athletes.

Statistical analysis
The statistical analysis was performed using SPSS 13.0 for Windows.Differences were taken to be significant when the p value was less than 0.05 (P < 0.05).
The statistical analysis for comparing the dominant leg with the nondominant leg was performed using the paired Student t test for parametric samples.
Comparing the data through the paired Student t test, there were no significant differences between the dominant and nondominant legs at stability level 8, for any of the instability indices: general P = 0.30, anteroposterior P = 0.73 and mediolateral P = 0.13.
There were no significant differences between the dominant and nondominant legs at stability level 2, for any of the instability Our results demonstrate that dominance does not interfere in the evaluation of single-foot balance among healthy sedentary individuals who use their legs for their daily activities and for walking.These findings are particularly important for clinicians and researchers who use comparative evaluations between the limbs, for the purposes of either enabling progression in functional exercises or identifying balance deficits in injured individuals.Further studies are needed with different populations, including elderly people and athletes, in order to confirm these results.

CONCLUSIONS
In this cross-sectional study, the lower-limb dominance did not influence single-foot postural balance among young sedentary males.
ties of the lower limbs are more important on the dominant side, and thus, dominance might influence postural balance.Unilateral body weight support tests can be used, in order to correlate dominance and postural balance.Our hypothesis was that different lower-limb activities such as body weight support and functional activities with the dominant limb could modify postural balance.
This study was conducted at the Institute of Orthopedics and Traumatology, Hospital das Clínicas (HC), Faculdade de Medicina da Universidade de São Paulo (FMUSP) and at Hospital do Coração (HCor) after approval granted by the Ethics Committee of Universidade de São Paulo (USP) (number 013/02).

Figure 1 .
Figure 1.Patient's position in the Biodex Balance System.
released and the patients were instructed to keep themselves in balance with the indicator kept at the center of the target on the screen.When the patient was capable of doing this (i.e.achieving a balance position) without hand support, the foot position was recorded using the platform rail.test Once the subjects had been positioned, they were instructed not to move their feet until the end of each measurement.The changes were recorded in relation to the center of the platform.Three measurements of 20-second duration separated by one-minute intervals were made on each leg.The result was the arithmetic mean of the three measurements, and this was supplied automatically by the equipment.All the tests started with the dominant leg.

Table 1 .
Comparison of postural balance between individuals' dominant and nondominant sides, at stability levels eight and two SD = standard deviation.