Sungjae Hwang

Biomechanical effect of electromechanical knee–ankle–foot-orthosis on knee joint control in patients with poliomyelitis

In this study, an ideal electromechanical KAFO, satisfying stability in the stance and knee flexion in the swing phase during walking, was developed. Biomechanical evaluations were performed on four polio patients by means of three-dimensional gait analyses and energy consumption studies. From the three-dimensional gait analysis on poliomyelitis patients, a considerable amount of knee flexion during the swing phase was observed in controlled-knee gait, which resulted in approximately 33% less energy consumption than in locked-knee gait. The developed electromechanical KAFO in this study was helpful in poliomyelitis patients having partial or complete paralysis of the lower extremity, providing both stability in the stance and free swinging of the knee. This unit was efficient in the transfer of energy.

Motion analysis based on a multi-segment foot model in normal walking

The foot, an exceedingly complicated system, is essential to move the body forward and to keep dynamic stability during gait. In most previous studies on gait analysis, the foot has been defined as a single rigid segment, which results in many problems to understand the foot motion in detail. The purpose of this study is to develop a multi-segment foot model that can help analyze biomechanics of the foot during gait. A 9-segment foot model with 8 major joints was developed in this study. In addition, it was applied to the 3D motion analysis to determine the kinematics and the kinetics of the foot in the normal walking. Understanding the detailed foot motions by the present multi-segment foot model would be very useful to diagnose patients with various foot diseases.

Development of an active ankle-foot orthosis for hemiplegic patients

In this study, we developed an active ankle-foot orthosis (AAFO) which could control dorsiflexion/plantarflexion of the ankle joint to prevent foot drop and toe drag during walking. To prevent foot slap after initial contact, the ankle joint needs to be actively controlled to minimize forefoot collision with the ground. During late stance, the ankle joint also needs to be controlled to provide toe clearance and to help push-off. 3D gait analyses were performed on a hemiplegic patient under three different gait conditions: gait without AFO(NAFO), gait with the conventional hinged AFO without controlling ankle joint (HAFO), and gait with the developed AFO(AAFO). Results showed that AAFO could prevent not only foot drop by the proper plantarflexion during loading response but also toe drag by sufficient amount of plantarflexion in pre-swing and reasonable dorsiflexion during swing phase, enhancing all temporal gait parameters. The present results indicated that the developed AAFO might have more clinical benefits to treat foot drop and toe drag in hemiplegic patients, comparing with conventional AFOs.

A hybrid static optimisation method to estimate muscle forces during muscle co-activation

The general static optimisation (GSO) process is one of various muscle force estimation methods due to its low computational requirements. However, it can show biased muscle force estimation under muscle co-contraction. In the present study, we introduced a novel hybrid static optimisation (HSO) method to estimate reasonable muscle forces during muscle co-activation movements using more specific equality constraints, i.e. agonist and antagonist muscle moments predicted from a new correlation coefficient approach. The new method was evaluated for heel-rise movements. We found that the proposed method improved the potential of antagonist muscle force estimation in comparison to the GSO solutions. The proposed HSO method could be applied in biomechanics and rehabilitation, for example.

Development of an active ankle foot orthosis to prevent foot drop and toe drag in hemiplegic patients: A preliminary study

We developed an active ankle-foot orthosis AAFO that controls dorsiflexion/plantarflexion of the ankle joint to prevent foot drop and toe drag during hemiplegic walking. To prevent foot slap after initial contact, the ankle joint must remain active to minimize forefoot collision against the ground. During late stance, the ankle joint must also remain active to provide toe clearance and to aid with push-off. We implemented a series elastic actuator in our AAFO to induce ankle dorsiflexion/plantarflexion. The activator was controlled by signals from force sensing register FSR sensors that detected gait events. Three dimensional gait analyses were performed for three hemiplegic patients under three different gait conditions: gait without AFO NAFO, gait with a conventional hinged AFO that did not control the ankle joint HAFO, and gait with the newly-developed AFO AAFO. Our results demonstrate that our newly-developed AAFO not only prevents foot drop by inducing plantarflexion during loading response, but also prevents toe drag by facilitating plantarflexion during pre-swing and dorsiflexion during swing phase, leading to improvement in most temporal-spatial parameters. However, only three hemiplegic patients were included in this gait analysis. Studies including more subjects will be required to evaluate the functionality of our newly developed AAFO.

Analysis of Joint movements and muscle length during sit-to-stand at various sitting heights in the Korean elderly daily life

In this study, we analyzed the elderly joint movements and changes in muscle length during STS at various sitting heights through the motion analysis and the musculoskeletal modeling. Five elderly and five young were participated in this experiment. Three heights of sitting posture which could represent typical sitting in Korean daily life were chosen as table seat (42cm), bath seat (21cm) and bottom (0cm). As the results, the elderly showed both smaller knee/hip flexion and larger trunk flexion relatively in comparison to the young during table seat STS. The elderly also showed larger dorsi flexion and smaller ROM of knee, hip, trunk compared to the young during bath seat STS. Additionally, the elderly showed larger plantarflexion, hip flexion, smaller knee flexion and trunk flexion during the first half of bottom STS and larger knee flexion, hip flexion and trunk flexion during the second half of bottom STS. In addition, we could know contraction and relaxation characters of major muscles in lower limb during various STS through the analysis of changes in muscle length by musculoskeltal modeling.

Analysis of Activation and Contribution of Muscles of the Elderly During Arm Flexion and Extension Resistance Exercise with Increased Load

The purpose of this study was to assess activation and contribution of muscles of the elderly according to increased loading during the arm flexion extension resistance exercise. Surface electromyographic signals were acquired from biceps brachii, triceps brachii, deltoid posterior, pectoralis major and latissimmus dorsi to determine the difference of the activation of specific muscles between the elderly and young. Five elderly and five young males with no musculoskeletal disease volunteered for the study. Electromyographic activities in the muscles were measured during resistance exercise and normalized to the maximum EMG activity recorded in the maximal voluntary static contraction (MVC). Against the increased loading during arm flexion/extension resistance exercises, the young uses muscles evenly but the elderly uses one specific muscle frequently. Contribution of triceps brachii during extension and deltoid posterior during flexion was principal in the elderly.

Multi-Segment Foot Motion Analysis on Hallux Valgus Patients

In this study, a multi-segment foot motion analysis on hallux valgus patients were performed using the 9-segment foot model and then compared with the results from normal subjects. Results showed that there were no significant differences in hindfoot motions between normal subjects and HV patients. However, noted in HV patients were hyper-external rotation in the talocrural joint, an excessive eversion of the subtalar joint during early stance and lack of dynamic motion in hallux MP and medial MP joints especially during terminal stance. In spite of limitation in this study due to the small number of HV patients, the current multi-segment foot model would be feasible to diagnose and treat patients with various foot diseases, combined with further studies in the future

Development of Hybrid Robotic-Assisted Gait Training System with Personalized Adaptive Training Program

Gait, a method of locomotion, is a process that an animal moves itself from one position to another. The human gait serves an individual’s basic need to move from place to place. As such, the gait is the most common in all human movements. It also can provide independence and in the many activities of daily life. The importance of gait as an ability of humans has been emphasized for a long time by many researchers. The rapid-onset gait disorder represents the combined effects of more than one coexisting condition. Therefore, many kinds of gait training methods have been applied to recover or improve the walking abilities of patients with gait disorders. However, various conventional gait training methods have some limitations due to the inappropriateness and the ineffectiveness in the rehabilitation training.

THE BALANCE RECOVERY MECHANISMS AGAINST THE FORWARD PERTURBATION

In this paper, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles, linear accelerations, EMG activations, CoP movements and ground reaction forces(GRF). The sequence of joint motions due to the forward perturabation was in the order of ankle dorsiflexion, knee flexion and then hip flexion during the second half of the acceleration phase. Forward accerlerations were found both at the heel and the sacrum during the second half of the acceleration phase and the early, constant speed phase. Tibialis anterior(TA) for ankle dorsiflexion and biceps femoris(BF) for knee flexion, the primary muscle to recover balances against the forward perturbation, was activated during the half of acceleration phase. Ankle strategy was used for slow-speed perturbation, but mixed strategy of both ankle and hip used for the fast-speed perturbation. In addition, speed and magnitude of the perturbation influenced the postural response.