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Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability
The authors' measurements suggest that the triceps surae muscles maintain balance via a spring‐like element which is itself too compliant to guarantee stability, suggesting that the brain cannot set ankle stiffness and then ignore the control task because additional modulation of torque is required to maintain balance.
Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius
It is suggested that standing is a skilled, trial and error activity that improves with experience and is automated (possibly by the cerebellum), complement and extend the recent demonstration that paradoxical muscle movements are the norm in human standing.
Human balancing of an inverted pendulum: position control by small, ballistic‐like, throw and catch movements
An artificial task to illuminate the mechanisms underlying the sways and to account for changes in their size using the ankle musculature showed that balance was achieved by the constant repetition of a neurally generated ballistic‐like biphasic pattern of torque which can control both position and sway size.
Active, non‐spring‐like muscle movements in human postural sway: how might paradoxical changes in muscle length be produced?
For the first time, an ultrasound scanner and automated image analysis are used to record the tiny muscular movements occurring in normal standing and contradict the long‐established mechano‐reflex, muscle spring hypothesis that muscle length changes in a spring‐like way during sway of the body.
A cross‐bridge mechanism can explain the thixotropic short‐range elastic component of relaxed frog skeletal muscle
A theoretical model was developed in which the SREC and FRT arise as manifestations of a small number of slowly cycling cross‐bridges linking the actin and myosin filaments of a relaxed skeletal muscle and suggests that the cross‐bridge attachment rate must increase during interfilamentary movement.
Intermittent control: a computational theory of human control
It is shown that event-driven intermittent control provides a framework to explain the behaviour of the human operator under a wider range of conditions than continuous control, and explains why the intermittent control hypothesis is consistent with the continuous control hypothesis for certain experimental conditions.
The passive, human calf muscles in relation to standing: the non‐linear decrease from short range to long range stiffness
During human standing, tonic ankle extensor torque is required to support the centre of mass (CoM) forward of the ankles, and dynamic torque modulation is required to maintain unstable balance.…
Use of ultrasound to make noninvasive in vivo measurement of continuous changes in human muscle contractile length.
The ultrasound tracking procedure had near 100% accuracy at all amplitudes for frequencies up to 3 Hz and showed attenuation at higher frequencies consistent with an effective sampling frequency of 12 Hz and sampling time of 80 ms.
Paradoxical muscle movement in human standing
It is confirmed that intrinsic ankle stiffness is too low to stabilize human standing, and the increase in active tension is associated with muscle shortening, which cannot be produced by muscle stretch reflexes and can only arise from the anticipatory neural control of muscle length that is necessary for balance.
Human balancing of an inverted pendulum: is sway size controlled by ankle impedance?
Results showed that subjects could significantly reduce the mean sway size of the pendulum by giving full attention to that goal and ankle impedance and muscle co‐contraction were not significantly changed when the sway size was decreased.