Biomechanical analysis of dynamic balance

Background and Purpose Balance represents one of the most basic aspects in both sports and everyday activities like running, jumping and walking. Several factors such as injuries, anthropometric variables, sex, biofeedbacks and neurodegenerative processes as Parkinson’s disease (PD) might negatively influence balance performances. The evaluation of balance provides essential information about neuromuscular and skeletal systems. In this regard, several postural control assessments have been used to evaluate dynamic balance such as force plates and functional tests due their reliability and validity. However, due the multifaceted features of this ability, new approaches are needed to accurately evaluate and measure dynamic balance performances. During large-scale evaluations, inexpensive, easy, administrable and accurate tools such as computerized Wobble Boards (WBs) have been suggested to be reliable in the evaluation of this ability in several populations. Therefore, the aims of this project were to measure WB performances and to evaluate the effect anthropometrics, sex, visual biofeedback (VBF) and PD process on dynamic balance performances assessed by computerized WB. Methods The project is organized in three phases, as follows: The first part of the present project aimed to measure wobble performance in individuals with unilateral chronic ankle instability (CAI). For the study, 39 healthy and 20 unilateral CAI recreationally active young adults were enrolled. subjects were required to perform a 3-minute familiarization, followed by 1-minute rest in sitting position, standing on the WB in a single leg stance position, finding a comfortable and central position with the knee slightly bent and keeping the hands on the hips. The balance test consisted of three 30-second trials per limb with 1-minute sitting rest in between. During the test each subject was asked to focus on the motion marker (MM) displayed on the monitor placed at eye level 2-meter in front of him or her and to keep it inside the target zone (TZ) as long as possible. Visual markers were also applied to the participants’ base of the fifth metatarsal, lateral malleolus, lateral joint line of the knee, anterior superior iliac spine and acromion process. All WB trials were recorded by a video camera. On each video, a researcher measured joint angles from the beginning to the end of the test trial using the visual markers as references. Hip angular-displacement was measured as the angle between the acromion process and lateral joint line of the knee with the greater trochanter serving as the fulcrum. Knee angular displacement was measured as the angle between the greater trochanter and lateral malleolus with lateral knee joint serving as the fulcrum. Ankle angular-displacement was measured as the angle between a line from the lateral knee joint and the base of the fifth metatarsal with the lateral malleolus being the fulcrum. The influence of anthropometrics, sex, and VBF on human dynamic balance is well documented, however no study has yet investigated on the effect and the interaction of the above-mentioned factors on computerized WB. For this purpose, the second part of this project investigated the effect of anthropometric characteristics, sex, and VBF on the WB balance performances during double leg stance. During this phase, 27 subjects (14 females, 13 males) were required to perform 3-minute of free practice on the WB followed by three 30-second double leg stance trials and 1- minute sitting recovery in between. Subjects were asked to perform WB test during two conditions. For the VBF condition subjects were asked to keep visual focus on the MM showed on the display and try to keep it inside the TZ as long as they could within 30 seconds; and for without Visual Biofeedback (NVBF) one, subjects were instructed to look at a fixed point on a black board, keeping visual focus on a marking in front of them and instructed to maintain the WB as flat and still as possible for as long as possible within the recording period of 30 seconds. Regarding the third part, a protocol study was developed to evaluate dynamic balance and fine motor skills performances assessed by WB and Grooved Pegboard test (GPT) in PD patients. Recruited subjects will be enrolled for the single-blind study and randomly allocated in two groups: PD group and Control group (CON group). PD group will participate in the intervention program; CON group will participate in a stretching program. Before (PRE) and after (POST) the intervention program (combined balance and fine motor skills exercises) both groups will perform the WB and GPT tests in a randomized order. The WB evaluation will be performed for both lower and upper limbs. During lower limb tests, subjects will be required to be in a seated position on a chair with back support with the hands resting on their legs and WB placed in front of the chair. During upper limb tests, subjects will be in a seated position, with the tested limb placed at 90° on the WB and the contralateral one (limb not performing the test) resting on the lower limb of the same side. The WB will be placed on a table and the monitor at eye level. Regarding the GPT, the subjects will familiarize themselves with the task by filling only the first top row. Subsequently, subjects will be instructed to insert pegs one by one into the pegboard, as fast as possible, completing the rows from left to right for the right limb and from right to left for the left limb, from top to bottom (with 1-minute recovery in between). Subjects will be free to perform trials when they prefer. Only the dominant hand will be assessed and all subjects with PD will perform the GPT two times. The recording time will start when subjects take the first peg and will stop when the last peg is inserted. For all tests, the starting limb and the order of conditions will be randomly chosen. Lastly, to avoid any balance and stability provided by shoes, all testing procedures were performed barefoot. Results Results showed that ankle and knee angular-displacement parameters, body height and lower limb length were the major predictors of the WB performance and played major roles on the accuracy of the extrapolated equation models. Additionally, the extrapolated equation may provide different methods to quantify the WB performance and accurately detect the injured limb in individuals with unilateral CAI. VBF improved dynamic balance on the WB with respect to the condition NVBF. When investigating the effect of anthropometrics variables, sex, and their interactions on the conditions, a significant main effect of the lower limb/height ratio (HTR) sex, and their interaction on the condition without visual biofeedback was found. Moreover, significant effects were found for sex and body mass and sex and moment of inertia in the VBF condition. Finally, it was hypothesized that computerized WB would be useful to detect dynamic balance and fine motor skills in PD subjects. Conclusion The computerized WB used in this project is reliable and valid to assess subjects with unilateral CAI. The extrapolated equations quantify the WB performance and accurately detect the injured limb in individuals with unilateral CAI. The WB measures were influenced by anthropometrics, sex and feedbacks, confirming that dynamic balance performances on the WB are affected by other sources of variability. Since WBs are easy to set and to interpret, they have the potential in screening, monitoring and quantifying the progression of balance performances. Moreover, the affordability and transportability of WBs are key factors during filed evaluations, making data collection on balance performances feasible for health specialists and/or coaches looking for inexpensive, portable, reliable, and valid assessment tools. Lastly, results from the present project could have an impact on training and evaluations protocols, especially when several populations such as children, athletes, older adults, people with balance disorders and neurodegenerative disorders are involved.