Age-Related Differences in Arm and Trunk Responses to First and Repeated Exposure to Laterally Induced Imbalances

Shoe sole impedes leg muscle activation and impairs dynamic balance responding to a standing-slip

The shoe sole is identified as a fall risk factor since it may impede the afferent information about the outside world collected by the plantar sensory units. However, no study has directly quantified how the shoe sole compromises body balance and increases fall risk. This study aimed to inspect how the sole affects human balance after an unexpected standing-slip. It was hypothesized that individuals wearing the sole, relative to their barefoot counterparts, would exhibit 1) more impaired stability and 2) disrupted lower limb muscle activation following a standing-slip. Twenty young adults were evenly randomized into two groups: soled and barefoot. The soled group wore a pair of customized 10-mm thick soles, while the other group was bare-footed. Full-body kinematics and leg muscle electromyography (EMG) were collected during a standardized and unexpected standing-slip. The EMG electrodes were placed on the tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris bilaterally. Dynamic stability, spatiotemporal gait parameters, and the EMG latency of the leg muscles were compared between groups. The sole impeded the initiation of the recovery step possibly because it interfered with the accurate detection of the external perturbation and subsequently activated the leg muscles later in the soled group than in the barefoot group. As a result, individuals in the soled group experienced a longer slip distance and were more unstable than the barefoot group at the recovery foot liftoff. The findings of this study could augment our understanding of how the shoe sole impairs body balance and increases the fall risk.

Development of an Elliptical Perturbation System that provides unexpected perturbations during elliptical walking (the EPES system)

BACKGROUND

'Perturbation-based balance training' (PBBT) is a training method that was developed to improve balance reactive responses to unexpected balance loss. This training method is more effective in reducing fall rates than traditional balance training methods. Many PBBTs are performed during standing or treadmill walking which targeted specifically step reactive responses, we however, aimed to develop and build a mechatronic system that can provide unexpected perturbation during elliptical walking the Elliptical Perturbation System (the EPES system), with the aim of improving specifically the trunk and upper limbs balance reactive control.

METHODS

This paper describes the development, and building of the EPES system, using a stationary Elliptical Exercise device, which allows training of trunk and upper limbs balance reactive responses in older adults.

RESULTS

The EPES system provides 3-dimensional small, controlled, and unpredictable sudden perturbations during stationary elliptical walking. We developed software that can identify a trainee's trunk and arms reactive balance responses using a stereo camera. After identifying an effective trunk and arms reactive balance response, the software controls the EPES system motors to return the system to its horizontal baseline position after the perturbation. The system thus provides closed-loop feedback for a person's counterbalancing trunk and arm responses, helping to implement implicit motor learning for the trainee. The pilot results show that the EPES software can successfully identify balance reactive responses among participants who are exposed to a sudden unexpected perturbation during elliptical walking on the EPES system.

CONCLUSIONS

EPES trigger reactive balance responses involving counter-rotation action of body segments and simultaneously evoke arms, and trunk reactive response, thus reactive training effects should be expected.

Judokas Show Increased Resilience to Unpredictable Stance Perturbations

Combat sports are characterized by frequent large-scale stance perturbations that may lead to falls. In the present investigation, we compared compensatory arm and leg movements in response to unpredictable stance perturbations between judokas and other athletes whose sports present reduced balance demand, relative to combat sports. Specifically, we tested judokas (n = 9), and a group of swimmers and runners (n = 11, controls) in sudden support base displacements in the mediolateral direction, generated by a movable electronic platform, in the following modes: (a) rotation, (b) translation, and (c) combined rotation-translation. The platform was displaced to either side, in three peak velocities (cm/second or ^o/second) of 20 (low), 30 (moderate), or 40 (high), resulting in 18 distinct perturbations. We evaluated postural responses with a scale for analyzing the stability of compensatory arm and leg movements (CALM). Results showed that, in the most challenging perturbations, judokas had higher stability scores (arm, leg, and global) than did the comparison group. Higher scores for judokas reflected their increased rate of motionless arm and leg responses and absence of near-falls, compared to 30% falls in the most challenging perturbations for the swimmers and runners. As a practical application, judo training may help achieve stable compensatory limb movements in a way that parallels the benefits obtained from perturbation-based balance training in laboratory settings.

Vigor of reactive postural responses is set from feedback and feedforward processes

I explore a distinct perspective from that brought in the book by arguing that in postural control our organism selects the vigor of reactive responses guided by an optimization rule considering first the required postural response for balance recovery as indicated by afferent information from a myriad of sensory receptors, and second the history of previous responses to similar perturbations.