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.
"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. "
[Show abstract][Hide abstract] 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
"The study of multisegmental movements (head, trunk and hip), and the COM relative to the COP provides information on the strategies used to control dynamic equilibrium   . Moreover, the gap between the COM and the COP trajectories allows to explain the generation of the dynamic forces (e.g., propulsive forces) needed to walk . "
[Show abstract][Hide abstract] ABSTRACT: This study sought to highlight the balance control process during gait in children with Cerebral Palsy (CP) by analyzing the different strategies used in order to generate forward motion whilst maintaining balance. Data were collected using a motion analysis system in order to provide a clinical gait analysis for 16 children with CP and 16 children with Typical Development. Significant differences between the two groups are observed in terms of kinetic data of the propulsive forces of the Center of Mass (COM) and of the Center of Pressure (COP) dynamic trajectory and for locomotor parameters. The imbalance generated by divergent trajectories of COM and COP produce the propulsive forces responsible for human gait initiation. Moreover, we observe in children with CP an “en bloc” postural strategy resulting in increasing divergence between trajectories of COM-COP. This particular strategy of the children with CP is characterized by a greater time duration between the moment of COM-COP trajectory divergence and the moment where the forward propulsive forces became apparent.
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