About the Sensorimotor Laboratory



    In addition to causing postural disturbances, space flight has been shown to modify the reflexes of antigravity muscles. In 1971, a form of stretch reflex, referred to as the functional stretch reflex (FSR), was located in the gastrocnemius muscle during application of a dorsiflexion force. This reflex appeared as a burst of activity in the electromyogram (EMG) roughly 120 ms after the force was applied. This response was termed "functional" because, unlike the early (20-30 ms) monosynaptic response (T-reflex) that contributes little to overall muscle tension; it directly corresponded with a sustained rise in force generated by the muscle.
    Measurement of sensorimotor function in 6° head down position. Reflex is evoked with ankle rotation via 100 lb/ft servo controlled DC torque motor Measurement of sensorimotor function in 6° head down position. Reflex is evoked with ankle rotation via 100 lb/ft servo controlled DC torque motor


    Weightlessness affects the amplitude of the FSR, making it a good candidate for proprioceptive assessment testing. The Sensorimotor Laboratory has been established to evaluate the effect of bed rest on the FSR (where muscle unloading is the primary driver for change) and to compare these results with those observed as a function of flight. Namely that the amplitudes of both the FSR and T- reflexes will decrease throughout the bed rest campaign as the reflex serves no functional purpose during this period. This paradigm is essentially one of exclusion (an exclusionary analog) where the unloading of bed rest can be compared to the unloading and sensorimotor changes driven from vestibular/proprioceptive changes as a function of space flight. As an analog to flight the Sensorimotor Laboratory investigates the FSR and related reflex components as a function of centrifugation.

    Close-up of functional stretch testing Close-up of functional stretch testing
    During testing of the FSR, subjects are positioned in a 6o head down supine position with the ankle firmly attached to the dynamometer (or 100 lb/ft torque motor) head in a position of 0 degrees of plantar and dorsiflexion. EMG electrodes with a high impedance probe are placed on the triceps surae and tibialis anterior muscle groups. A dorsiflexion torque is applied at 250o/sec to randomized angular amplitudes of 5, 10, and 15 degrees. For half of these trials EMG data on the FSR is obtained by instructing subjects to resist the force. For the other half of these trials subjects are instructed to provide no resistance to the torque, enabling collection of T-reflex data. EMG data is then analyzed both for latency times and amplitudes.

    Contacts: