A Konev | PubMed Health

PubMed1994

Arm tremor and precision of hand force control in a short and long term flight on the MIR-Space-Station.

To determine whether long and short time exposure of man in 0g alters normal physiological tremor patterns we recorded arm tremor using an accelerometer as well as hand forces and tremor during constant isometric contraction using a load cell. Arm tremor was decreased during both flights in amplitude and frequency. Shortly after the long term flight arm tremor amplitude was increased, indicating adaptive changes in the tonic reflex loop. Isometric hand tremor remained unchanged during the long and short time flight demonstrating that the contractile properties of hand muscles remained constant. Precision of hand force was decreased until the half duration of the long term flight.

Arm↗

PubMed1994

Physiological tremor and control of limb position in 1 and 0 G.

Muscle and skeletal mechanoreceptors play an important role for the regulation of muscular tone and the genesis of normal Physiological Tremor (PT). For example if a big limb as the arm or leg is kept against the gravity vector, the la afferent spindle discharges continuously control the load bearing flexor in a negative feedback manner in order to compensate the gravity vector and to the stabilize arm position. This servo-like action, denoted as 'stretch reflex', not only increases static postural stability (tonic stretch reflex) but also counteracts against external disturbances by dynamically increasing the muscle tone. Muscle spindles are very sophisticated sensory organs. They have an own innervation and the endings of the nuclear bag fibres are highly sensitive for small microstretches. EMG and microneurografic studies showed their importance in the mechanism of the 8-12 Hz component for PT. In a 0 G a limb becomes position controlled. In contrast to 1g, where control of limb position is a subordinated function of force compensation in the load bearing muscle, an antagonistic control scheme is necessary in 0 G to compensate the arm against positional drifts. As a consequence there is a shift from load dependent (muscular) to position dependent (skeletal) mechanoreceptors that become involved in the neural control process. As the control process is reflected in the tremor pattern, we investigated arm tremor in a constant limb position in 1 and 0 G.

Arm↗

PubMed1993

[Microvib--a test battery for studies of physiological tremor].

4 simple tests to investigate physiological tremors in different load conditions on the musculo-skeletal system have been developed with regard to the Austromir space missions. Some new results on normal tremors from the space experiments as well as from ground studies using these tests are discussed. It is proposed to introduce these experimental methods in the area of clinics to evaluate precision of motor control.

Adult↗

PubMed1978

[Not Available].

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