Identification of the contribution of the ankle and hip joints to multi-segmental balance control

Background\ud \ud Human stance involves multiple segments, including the legs and trunk, and requires coordinated actions of both. A novel method was developed that reliably estimates the contribution of the left and right leg (i.e., the ankle and hip joints) to the balance control of individual subjects. \ud \ud Methods\ud \ud The method was evaluated using simulations of a double-inverted pendulum model and the applicability was demonstrated with an experiment with seven healthy and one Parkinsonian participant. Model simulations indicated that two perturbations are required to reliably estimate the dynamics of a double-inverted pendulum balance control system. In the experiment, two multisine perturbation signals were applied simultaneously. The balance control system dynamic behaviour of the participants was estimated by Frequency Response Functions (FRFs), which relate ankle and hip joint angles to joint torques, using a multivariate closed-loop system identification technique. \ud \ud Results\ud \ud In the model simulations, the FRFs were reliably estimated, also in the presence of realistic levels of noise. In the experiment, the participants responded consistently to the perturbations, indicated by low noise-to-signal ratios of the ankle angle (0.24), hip angle (0.28), ankle torque (0.07), and hip torque (0.33). The developed method could detect that the Parkinson patient controlled his balance asymmetrically, that is, the right ankle and hip joints produced more corrective torque. \ud \ud Conclusion\ud \ud The method allows for a reliable estimate of the multisegmental feedback mechanism that stabilizes stance, of individual participants and of separate leg

Glyphosate and neurotoxicity - a call for scientific renewal

Glyphosate, a controversial herbicide, has been approved for use in the European Union for another 10 years despite uncertainty over whether it increases the risk of neurodegenerative disorders such as Parkinson disease. We call for new approaches to assessing the neurotoxicity of glyphosate and other pesticides and improving their regulation

Gait disorders and balance disturbances in Parkinson's disease: Clinical update and pathophsyiology (online?)

Purpose of review: Gait disorders and balance impairments are one of the most incapacitating symptoms of Parkinson's disease. Here, we discuss the latest findings regarding epidemiology, assessment, pathophysiology and treatment of gait and balance impairments in Parkinson's disease. Recent findings: Recent studies have confirmed the high rate and high risk of falls of patients with Parkinson's disease. Therefore, it is crucial to detect patients who are at risk of falling and how to prevent falls. Several studies have shown that multiple balance tests improve the prediction of falls in Parkinson's disease. Difficulty turning may be caused by axial rigidity, affected interlimb coordination and asymmetries. Turning difficulties are easily assessed by timed performance and the number of steps during a turn. Impaired sensorimotor integration, inability of switching between sensory modalities and lack of compensatory stepping may all contribute to the high incidence of falls in patients with Parkinson's disease. Similarly, various studies highlighted that pharmacotherapy, neurosurgery and physiotherapy may adversely affect balance and gait in Parkinson's disease. Summary: Insights into the pathophysiology of Parkinson's disease continue to grow. At the same time, it is becoming clear that some patients may in fact deteriorate with treatment. Future research should focus on the development and evaluation of multifactorial fall prevention strategies

Rotation amplitude dependency of the intrinsic ankle stiffness during standing

BACKGROUND AND AIM: To ensure upright balance the ankle joint stiffness must be sufficient to resist the gravitational pull. This stiffness arises from both intrinsic and reflexive components. Determining their individual contribution might give insight in neuromuscular and balance related disorders. Ankle joint stiffness is often investigated by fitting a parametric model to a torque response, obtained from an applied joint rotation. Direct, non-parametric estimation is often not applicable because the applied rotations cannot rule out reflex activity. Here the rotational amplitude dependency of the intrinsic ankle stiffness was estimated in standing, using fast ramp-and-hold stretches to circumvent reflexive contributions. METHODS: Eight healthy subjects participated in the study. Subjects stood on the Bilateral Ankle Perturbator (BAP, figure top), with which 0.08-0.005 rad plantar- and dorsiflexion rotations were applied to the individual ankle joints. Rotations consisted of 40 ms ramp-and-hold minimum jerk profiles [1]. The intrinsic stiffness was obtained by dividing the difference in torque exerted on the platform before and after rotation onset by the rotational amplitude. These values were normalized to the critical stiffness [2]. EMG data of the triceps surae and tibialis anterior muscles were recorded to investigate reflex activity. RESULTS: The EMG signals of the streched muscles showed short latency reflex activity starting approximately 5 ms after the rotation ended (figure middle). The EMG of the gastrocnemius medialis is shown. The intrinsic ankle stiffness decreased non-linearly with increasing rotation amplitude. There was no significant difference in stiffness between plantar- and dorsiflexions. A fit to all subjects' pooled data in comparison with other values in literature [2-4] is shown (figure bottom). CONCLUSIONS: The intrinsic ankle stiffness is insufficient to ensure balance, hence changes in muscle activation are required to realize upright stance. Reflex activity is not expected to have influenced the stiffness estimates due to the short latency of the perturbations and the electro-mechanical delay of muscle tissue. The decrease in stiffness is attributed to muscle cross-bridge breakage leading to sliding of filaments, decreasing the overall stiffness. References: [1] Burdet e.a.-2000-J.Biomech. [2] Casadio e.a.-2005-Gait Posture [3] Loram e.a.-2002-J.Physiol. [4] Loram e.a.-2007-J.Physiol