An Initial Passive Phase That Limits the Time to Recover and Emphasizes the Role of Proprioceptive Information

Abstract

In the present experiments, multiple balance perturbations were provided by unpredictable support-surface translations in various directions and velocities. The aim of this study was to distinguish the passive and the active phases during the pre-impact period of a fall. It was hypothesized that it should be feasible if one uses a specific quantitative kinematic analysis to evaluate the dispersion of the body segments trajectories across trials. Moreover, a multi-joint kinematical model was created for each subject, based on a new 3-D minimally invasive stereoradiographic X-ray images to assess subject-specific geometry and inertial parameters. The simulations allowed discriminating between the contributions of the passive (inertia-induced properties) and the active (neuromuscular response) components during falls. Our data show that there is limited time to adjust the way one fall from a standing position. We showed that the pre-impact period is truncated of 200 ms. During the initial part of a fall, the observed trajectory results from the interaction between the destabilizing external force and the body: inertial properties intrinsic to joints, ligaments and musculotendinous system have then a major contribution, as suggested for the regulation of static upright stance. This passive phase is later followed by an active phase, which consists of a corrective response to the postural perturbation. We believe that during a fall from standing height, it takes about 300 ms for postural responses to start correcting the body trajectory, while the impact is expected to occur around 700 ms. It has been argued that this time is sufficient to change the way one falls and that this makes it possible to apply safer ways of falling, for example by using martial arts fall techniques. Also, our results imply visual and vestibular information are not congruent with the beginning of the on-going fall. This consequence is to be noted as subjects prepare to the impact on the basis of sensory information, which would be uniquely mainly of proprioceptive origin at the fall onset. One limitation of the present analysis is that no EMG was included so far but these data are the subject of a future study.

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Commentary: An Initial Passive Phase That Limits the Time to Recover and Emphasizes the Role of Proprioceptive Information

“…Le Goic et al (1) did not observe these early head accelerations for support surface translations of 35 cm/s [used by Allum et al (8) and Runge et al (14)] and higher velocities. Differences in recording techniques may provide the reason why early head accelerations were not observed.…”

“…A recent article by Le Goic et al (1) raises the very same issues concerning the participation of vestibular-spinal reflexes in balance corrections to support surface movement that existed in the 90's—see Peterson, 1989 (2). Then, Nashner et al assumed (3, 4), as have now Le Goic et al (1), that the apparently delayed onset of head movement following a support surface translations of 35 cm/s or greater suggested little or no direct vestibular contribution to balance corrections.…”

“…However, one could well imagine that using position information sampled at 200 Hz, then filtering these recordings with a filter having a bandwidth of <10 Hz, would leave considerably reduced recorded amplitudes of signals at 10 Hz from which to derive low-noise head acceleration information. Indeed the conclusion would probably be reached that no early head movement had occurred (1). Regardless of how the head accelerations are measured, the most logical conclusion concerning the differences between amplitude of balance correcting muscle responses to support surface perturbations following bilateral peripheral vestibular loss (5, 6, 8, 11) when compared to those of healthy controls (see Figure 1) is that the lack of responses of the vestibular sensory system in the vestibular loss subjects to supra-threshold head accelerations (for healthy controls) must underlie the difference in response modulation seen in the 6 muscles shown in Figure 1.…”