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The proportional recovery rule (PRR) posits that most stroke survivors can expect to reduce a fixed proportion of their motor impairment. As a statistical model, the PRR explicitly relates change scores to baseline values - an approach that arises in many scientific domains but has the potential to introduce artifacts and flawed conclusions. We describe approaches that can assess associations between baseline and changes from baseline while avoiding artifacts due either to mathematical coupling or to regression to the mean. We also describe methods that can compare different biological models of recovery. Across several real datasets in stroke recovery, we find evidence for non-artifactual associations between baseline and change, and support for the PRR compared to alternative models. We also introduce a statistical perspective that can be used to assess future models. We conclude that the PRR remains a biologically relevant model of stroke recovery., Competing Interests: JG, TK, AG, RK, AL, CS, WB, GK, JK No competing interests declared, (© 2022, Goldsmith et al.)

In 2008, it was proposed that the magnitude of recovery from nonsevere upper limb motor impairment over the first 3 to 6 months after stroke, measured with the Fugl-Meyer Assessment (FMA), is approximately 0.7 times the initial impairment ("proportional recovery"). In contrast to patients with nonsevere hemiparesis, about 30% of patients with an initial severe paresis do not show such recovery ("nonrecoverers"). Hence it was suggested that the proportional recovery rule (PRR) was a manifestation of a spontaneous mechanism that is present in all patients with mild-to-moderate paresis but only in some with severe paresis. Since the introduction of the PRR, it has subsequently been applied to other motor and nonmotor impairments. This more general investigation of the PRR has led to inconsistencies in its formulation and application, making it difficult to draw conclusions across studies and precipitating some cogent criticism. Here, we conduct a detailed comparison of the different studies reporting proportional recovery and, where appropriate, critique statistical methodology. On balance, we conclude that existing data in aggregate are largely consistent with the PRR as a population-level model for upper limb motor recovery; recent reports of its demise are exaggerated, as these excessively focus on the less conclusive issue of individual subject-level predictions. Moving forward, we suggest that methodological caution and new analytical approaches will be needed to confirm (or refute) a systematic character to spontaneous recovery from motor and other poststroke impairments, which can be captured by a mathematical rule either at the population or at the subject level.

Recent findings in the field of neurophysiology showed that operant conditioning on the human H-Reflex is possible. This leads to many possible clinical applications as well as possible sophisticated training methods for athletes. Although stretch reflexes have been subject to extensive literature, knowledge about the influence of short latency stretch reflexes on task performance is lacking. Within this study an ankle control task was designed where perturbations in the magnitude of functional relevance were applied. Results analyzing angle over time after perturbation confirm previous findings which used to analyze the EMG and force response to ankle perturbations. Further it was found that after training the response to perturbations shifted from initially containing latencies which indicate conscious support by transcortical pathways to latencies which could only origin from unconscious stretch reflex responses. The trend of the short latency response to shift towards the long latency response and to diminish, while pre-defined performance criteria improved, denote a functional relevance of the short latency stretch reflex to task performance. Whereas short latency reflexes have any importance at all or if improvements emerge only out of enhancements in the long latency response future work making use of operant conditioning on the short latency H-Reflex will have to unravel.