Posture, dynamic stability, and voluntary movement
This paper addresses the question of why voluntary movement, which induces a perturbation to balance, is possible without falling down. It proceeds from a joint biomechanical and physiological approach, and consists of three parts. The first one introduces some basic concepts that constitute a theoretical framework for experimental studies. The second part considers the various categories of "postural adjustments" (PAs) and presents major data on "anticipatory postural adjustments" (APA). The last part explores the concept of "posturokinetic capacity" (PKC) and its possible applications.
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Available from: Bart Dingenen
- "The results of our study show that control subjects initiated muscle activity before the time point where the upcoming supporting leg is suggested to be loaded (Mx onset) (Dingenen et al., 2015b, 2015c) for all muscles except gluteus maximus in the eyes closed condition. This anticipatory muscle activity prepares the lower extremity for the upcoming postural perturbation created by the voluntary movement (shifting the weight from DLS to SLS) and is believed to be beneficial to develop efficient joint stabilization strategies (Aruin & Latash, 1995; Bouisset & Do, 2008; Hodges & Richardson, 1997; Wikstrom et al., 2006; Williams et al., 2001). In contrast, the ACLI group initiated muscle activity typically after the Mx onset, except for tensor fascia latae in both vision conditions and gluteus medius in the eyes open condition. "
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ABSTRACT: The goal of this study was to evaluate muscle activation onset times (MAOT) of both legs during a transition task from double-leg stance (DLS) to single-leg stance (SLS) in anterior cruciate ligament injured (ACLI) (n = 15) and non-injured control subjects (n = 15) with eyes open and eyes closed. Significantly delayed MAOT were found in the ACLI group compared to the control group for vastus lateralis, vastus medialis obliquus, hamstrings medial, hamstrings lateral, tibialis anterior, peroneus longus and gastrocnemius in both vision conditions, for gluteus maximus and gluteus medius with eyes open and for tensor fascia latae with eyes closed. Within the ACLI group, delayed MAOT of tibialis anterior with eyes open and gastrocnemius with eyes closed were found in the injured leg compared to the non-injured leg. All other muscles were not significantly different between legs. In conclusion, the ACLI group showed delayed MAOT not only around the knee, but also at the hip and ankle muscles compared to the non-injured control group. No differences between both legs of the ACLI group were found, except for tibialis anterior and gastrocnemius. These findings indirectly support including central nervous system re-education training to target the underlying mechanisms of these altered MAOT after ACL injury.
Human Movement Science 12/2015; 44:234–245. DOI:10.1016/j.humov.2015.09.007 · 1.60 Impact Factor
- "Gait initiation involves the correct sequencing of movement preparation and movement execution. Specifically, anticipatory postural adjustments (APAs) precede the onset of voluntary movements such as gait initiation  . The function of APAs is to reduce the effect of the forthcoming body perturbation with anticipatory corrections  . "
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ABSTRACT: Anticipatory postural adjustments (APAs) prior to gait initiation have been largely studied in traditional, laboratory settings using force plates under the feet to characterize the displacement of the center of pressure. However clinical trials and clinical practice would benefit from a portable, inexpensive method for characterizing APAs. Therefore, the main objectives of this study were (1) to develop a novel, automatic IMU-based method to detect and characterize APAs during gait initiation and (2) to measure its test-retest reliability. Experiment I was carried out in the laboratory to determine the validity of the IMU-based method in 10 subjects with PD (OFF medication) and 12 control subjects. Experiment II was carried out in the clinic, to determine test-retest reliability of the IMU-based method in a different set of 17 early-to-moderate, treated subjects with PD (tested ON medication) and 17 age-matched control subjects. Results showed that gait initiation characteristics (both APAs and 1st step) detected with our novel method were significantly correlated to the characteristics calculated with a force plate and motion analysis system. The size of APAs measured with either inertial sensors or force plate was significantly smaller in subjects with PD than in control subjects (p<0.05). Test-retest reliability for the gait initiation characteristics measured with inertial sensors was moderate-to-excellent (0.56<ICC<0.82) for both groups. Our findings support the feasibility of automatically characterizing postural preparation and gait initiation with body-worn inertial sensors that would be practical for unsupervised clinical and home settings.
Gait & posture 09/2015; DOI:10.1016/j.gaitpost.2015.08.015 · 2.75 Impact Factor
Available from: Paolo Cavallari
- "Although the mass involved in this movement is tiny, these intralimb APAs behave similarly [1–3] to the well-known inter-limb APAs of movements involving large masses (for a review see ). "
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ABSTRACT: Recent works provide evidences that anticipatory postural adjustments (APAs) are programmed with the prime mover recruitment as a shared posturo-focal command. However the ability of the CNS to adjust APAs to changes in the postural context implies that the postural and voluntary components should take different pathways before reaching the representation of single muscles in the primary motor cortex. Here we test if such bifurcation takes place at the level of the supplementary motor area (SMA). TDCS was applied over the SMA in 14 subjects, who produced a brisk index-finger flexion. This activity is preceded by inhibitory APAs, carved in the tonic activity of Biceps Brachii and Anterior Deltoid, and by an excitatory APA in Triceps Brachii. Subjects performed a series of 30 flexions before, during and after 20min of tDCS in CATHODAL, ANODAL or SHAM configuration. The inhibitory APA in Biceps and the excitatory APA in Triceps were both greater in ANODAL than in SHAM and CATHODAL configurations, while no difference was found among the latter two (ANODAL vs. SHAM: biceps +26.5%, triceps +66%; ANODAL vs. CATHODAL: biceps +20.5%, triceps: +63.4%; for both muscles, ANOVA p<0.02, Tukey p<0.05). Instead, the APA in anterior deltoid was unchanged in all configurations. No changes were observed in prime mover recruitment and index-finger kinematics. Results show that the SMA is involved in modulating APAs amplitude. Moreover, the differential effect of tDCS observed on postural and voluntary commands suggests that these two components of the motor program are already separated before entering SMA.
Copyright © 2015. Published by Elsevier B.V.
Behavioural brain research 06/2015; 291. DOI:10.1016/j.bbr.2015.05.044 · 3.03 Impact Factor
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