Upregulation of spinal stretch reflexes during upper-limb posture control task
Bibliographic record
Abstract
Background: Sensory feedback from receptors in the eyes, skin, vestibular organs and muscles allows us to build accurate representations of the position and motion of our body within the environment. In unpredictable situations, such as when holding an umbrella in gusting winds, studies have suggested the nervous system upregulates the sensitivity of sensory organs to counter disturbances and increase the probability of success. To date, studies have focused exclusively on the upregulation of feedback mechanisms in the lower-limbs during standing balance. We know comparatively little about whether and how sensory upregulation contributes to the control of upper limb motor actions. Objectives: Examine the upregulation and adaptation of upper limb muscle activity and spinal stretch reflexes when interacting with unpredictable mechanical environments. Methods: Ten healthy, right-handed adults (age range: 20 – 27 years) performed a postural control task where the goal was to maintain their hand within a fixed target. Participants performed the task while seated with their arm supported in an exoskeleton robot that can sense and disturb arm motion. They received real-time feedback of their movements on a virtual reality system. The protocol was delivered in three phases. The baseline phase consisted of 50 trials where subjects maintained their hand in the target in the absence of mechanical disturbances. Subjects then performed a peri-exposure phase that consisted of 100 null trials (no forces applied), 100 step-torque perturbations that produced rapid elbow flexion (+2Nm), and 100 perturbations that caused rapid elbow extension (-2Nm). We then unexpectedly removed the perturbations and subjects performed 75 trials to determine whether muscle activity returned to baseline levels. Kinematics and muscle activity were recorded throughout the experiment. Results: Preliminary results show that background muscle activity and spinal stretch reflexes were the largest when first exposed to unpredictable mechanical perturbations and adapted systematically with repeated exposure. Conclusions: Similar to results observed in the lower-limbs during standing balance experiments, we observed upregulation of background muscle activity and spinal stretch reflexes when interacting with unpredictable mechanical environments with the upper-limb. The amplitude of spinal stretch responses and background muscle activity decayed systematically with repeated exposure to unpredictable mechanical perturbations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".