[Best Laid Plans Epub Styloid
Addison Mauldin
We aimed to explore whether different kinematic patterns and strategies occur in the first recovery step in single-step trials in which a single step was required to recover from a fall, and in multiple-step trials in which more than one step was required to recover from a fall. In addition, in the multiple-step trials, we examined kinematic patterns of balance recovery where extra steps were needed to recover balance.
Kinematic patterns and strategies of the first recovery step in the single-step trials were significantly dependent on the perturbation magnitude. It took a small, yet significantly longer time to initiate a recovery step and a significantly longer time to complete the recovery step as the magnitude increased. However, the first recovery step in the multiple-step trials showed no significant differences between different perturbation magnitudes; while, in total balance recovery of these trials, we observed a small, yet significant difference as the magnitude increased.
At relatively low perturbation magnitudes, i.e., single-step trials, older adults selected different first stepping strategies and kinematics as perturbation magnitudes increased, suggesting that this population activated pre-planned programs based on the perturbation magnitude. However, in the first recovery step of the multiple-step trials, i.e., high perturbation magnitudes, similar kinematic movement patterns were used at different magnitudes, suggesting a more rigid, automatic behavior, while the extra-steps were scaled to the perturbation magnitude. This suggest that older adults activate pre-planned programs based on the magnitude of the perturbation, even before the first step is completed..
A sideways fall caused by an unexpected lateral loss of balance is more likely to result in direct ground contact with the greater trochanter, possibly resulting in hip fracture [1,2,3]. Previous studies show more prominent impairments in the balance control system in the frontal plane, i.e., ML-direction [4, 5], and that measuring lateral instability provides better predictors of falls and even injurious falls [6, 7]. The importance of measuring balance in the frontal plane is further increased since many falls involve lateral falls [8, 9], resulting in hip fractures [8]. Avoiding lateral falls is equally essential compared with BMI [10,11,12]. Most research on mediolateral balance reactive control has focused mainly on the first recovery step in mediolateral perturbation, and at a specific perturbation magnitude [2, 13,14,15,16]. Several research studies have been conducted of older participants exposed to increasing magnitudes of mediolateral perturbations [2, 17,18,19,20,21,22,23,24,25]. In these investigations, it was found that in cases in which the perturbation magnitudes were low, a fixed base of support strategies were used to preserve balance. At higher perturbation magnitudes, a change in base-of-support strategies were used, i.e., a single-recovery step response; and in higher perturbation magnitudes extra steps were needed to preserve balance, i.e., a multiple-step response. Recently, Fujimoto et al. [21] investigated if balance stability at first-step initiation (i.e., first step lift-off) differed between multiple- and single-step responses to lateral perturbations in older adults who received lateral waist-pulls at five different magnitudes of perturbations. They found that compared to younger people, older adults had reduced stability at the first foot contact that was associated with taking additional steps. More recently, Batcir et al. [22] found that older adults who reported several falls showed a significant delay in step initiation duration, and had longer step duration and a larger center of mass (CoM) displacement during single-step trials compared with non-fallers and one-time fallers. In their multiple-step threshold trials, when extra steps were needed to recover balance, the participants who had reported several falls exhibited larger CoM displacements and took a longer time to fully recover from balance loss [22]. It is thought that these stepping responses could also be attributed to the CoM motion state as early as the first step lift-off, preceding foot contact [22]. The kinematic characteristics of the first recovery step (e.g., step timing, length, velocity, and acceleration) need to match the requirements for optimal control of stability in different conditions, i.e., perturbation magnitudes [26].
In the present study, we sought to investigate the kinematic patterns of the recovery step in single-stepping responses and of the first recovery step in multiple-stepping responses when right/left perturbations systematically increased from very low magnitudes to very high magnitudes in standing. This would provide a clearer understanding of the dynamics of recovery step responses in older people, and can deepen insight into the underlying balance control mechanisms of balance recovery. Earlier, Vlutters et al. [25] exposed young people to right/left and forward/backward pelvic perturbations at various magnitudes at two different treadmill walking speeds (i.e., low and high). They found that foot placement after right/left perturbations was adjusted proportionally to the right/left CoM velocity, whereas forward/backward unexpected perturbations did not show a similar response. Nachmani et al. [27] found that as the perturbation magnitudes increased during self-selected treadmill walking, older adults showed a small, yet significant decreases in the timing of the step response, and increased their step length
To truly demonstrate the existence of different control patterns at different perturbation magnitudes, in our experimental set-up, we adjusted the magnitude of perturbations from very low to very high, and set different onset timings and directions of the perturbations, i.e., right/left. We hypothesized that older people would show similar timing for their first recovery step initiation and step duration at different perturbation magnitudes, suggesting that the temporal patterns of the recovery step response are stereotypic and almost automatic in nature. We also hypothesized that spatial parameters of the first recovery step such as step length, step velocity, and CoM displacement would be adjusted proportionally to the magnitude of the right/left perturbation. In regard to multiple-step trials, i.e., higher perturbation magnitudes, we hypothesized that the total time to recover balance would be scaled to the magnitude of right/left perturbations and be more adaptive.
The participants signed the consent form, then they stood with their heels and toes touching on a i.e., a motor-driven perturbation treadmill device (i.e., Balance Measure & Perturbation System) that in the presnt experiment provided right or left unannounced surface translation in standing condition [29]. They were exposed to a total of 26 random right and left unannounced surface translation perturbations that systematically increased from low to high magnitudes (13 perturbation magnitudes). The specific instructions given to the subjects were "unconstrained" by any specific instructions i.e., react naturally. The magnitudes of 13 perturbations were specified in terms of transverse motion in cm of the Balance Measure & Perturbation System, thetiming in ms, the velocity in cm/ms, and the acceleration in cm/ms2 (details in supplementary Table 1). The order of unannounced perturbation times across the experimrnt and the direction were randomized, while the magnitudes were not. We performed this experimental setup since exposing old adults to high perturbation magnitude at an early stage of the experiment induced a stepping response at all perturbation magnitudes, which impairs our ability to identify step thresholds. The participants were instructed to stop the experiment or rest at any point. During the experiment, the participant wore a safety harness that did not influence lower extremity kinematics and prevented falling on the ground.
3D kinematic data were captured in the single- and multiple-step trials with the Ariel Performance Analysis System (APAS, Ariel Dynamics Inc.; CA, USA) using two video cameras that simultaneously recorded the motion of 8 reflective markers that were placed at the anterior midpoint of the ankle joints, anterior superior iliac spines, acromion processes, and radial styloid processes (see a detailed description in [22, 26]). This approach was previously shown to be valid and reliable [30].
The kinematic parameters that were calculated: Step initiation duration (in milliseconds, ms) defined asthe time from perturbation to foot-off the ground initiating the recovery step; the first recovery step duration (ms), defined as the time from perturbation to contacting the ground with the foot completing the recovery step; and the length of the first recovery step defined as the distance that the foot marker moved in cm during the first recovery step. In case several steps were needed to recover balance, we calculated: The total balance recovery duration (ms), defines as the time from perturbation until the participant completed his/her balance recovery, performing several steps; Balnce recovery steps path-length (cm), defined as the distance that the foot marker moved in cm performing several steps to complete full balance recovery; and eCoM total path (cm), the estimated CoM dispalcment in cm to complete balance recovery when several steps were needed. The reliability of the emanination procedure is presented in detlais in Batcir et al. [26].
Age, MMSE [19], height, weight, BMI, number of medications taken per day, number of diagnosed diseases, gender proportion, number of falls in the last year, the Fall Efficacy Scale (FES-I) [31], late life function, and disability [32] were also assessed.
Mosaic plots in Fig. 3 show the frequencies of the strategies performed in the first recovery step in the single-step and multiple-step trials (Fig. 3A, B). In the single-step trials, there was a gradual increase in the incidence of LLSS (blue boxes) and leg abduction (yellow boxes) strategies and a concurrent decrease in the ULSS strategy (red boxes). However, when multiple-steps were needed to recover balance (Fig. 3B), the strategy of the first recovery step appeared to be the same along all perturbation magnitudes.
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