Reply to: “Pickleball Tremor”

We thank Dr. Jankovic for his thoughtful letter and for sharing an interesting clinical observation of tremor occurring while holding a pickleball paddle, without any tremor while hitting the pickleball, in a patient with Parkinson's disease (PD). 1 His description highlights how tremor phenomenology may become particularly evident during specific motor contexts and we appreciate the opportunity to further discuss this topic in relation to the “shopping bag tremor” (SBT) described in our recent report. 2 In our study, SBT was characterized as a strictly load-dependent tremor that emerges during sustained weight holding, representing an activation-dependent or isometric tremor phenomenon. Electrophysiological recordings demonstrated rhythmic alternating activation of the flexor and extensor carpi radialis muscles at approximately 5 Hz, which occurred exclusively during the weight-holding condition. Notably, tremor amplitude showed a bell-shaped load–response relationship, with maximal amplitude at intermediate loads and attenuation with both lighter and heavier loads. 2 These findings suggested that both mechanical loading and central sensorimotor feedback mechanisms may interact to shape the expression of this tremor. The phenomenon described by Dr. Jankovic appears phenomenologically similar in that tremor emerges during sustained loading of the upper limb while holding a pickleball paddle. However, the clinical context differs in that the patient had established PD with rest tremor, dopaminergic responsiveness, and imaging evidence of nigrostriatal dysfunction. 1 Contemporary models of Parkinsonian tremor propose that basal ganglia circuits may trigger tremor episodes, while cerebello-thalamo-cortical pathways modulate the ongoing tremor amplitude. 3, 4 Such network dynamics may help to explain why tremor expression can vary across specific motor contexts or mechanical loading conditions. Thus, while both SBT and the described “pickleball tremor” occur during sustained limb loading, they may represent different manifestations of tremor physiology. SBT appears to be a load-specific, activation-dependent tremor that can occur in otherwise neurologically normal individuals or in patients with minimal tremor manifestations. In contrast, the pickleball tremor described in PD may reflect task-contextual modulation of underlying Parkinsonian tremor networks. Importantly, Dr Jankovic's observation underscores a broader and clinically relevant concept: the interaction between task demands, mechanical loading, and central oscillatory circuits can strongly influence tremor expression. 5 Careful characterization of such context-dependent tremor phenomena may provide valuable insights into tremor pathophysiology and its relationship to established tremor syndromes. We agree that further systematic study incorporating electrophysiological characterization and standardized load-response paradigms will determine whether these activity-dependent tremors represent variants within a shared mechanistic spectrum or distinct tremor entities. It would also be interesting to explore whether similar tremor phenomena occur when holding sporting implements of different weights (for example, rackets or bats), which might further clarify the role of mechanical load in modulating tremor expression. The use of wearable inertial sensors or surface EMG during such real-world activities may allow objective characterization of tremor dynamics in naturalistic settings. Such observations could potentially inform individualized exercise strategies in patients with tremor disorders, where selecting activities or equipment with specific mechanical loads might help optimize motor performance while maintaining the benefits of physical activity. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Manuscript Preparation: A. Writing of the first draft, B. Review and Critique. J. G.: 1A, 1B, 1C, 2A R. K.: 1B, 1C S. C.: 1B, 1C D. D.: 1B, 1C H. K.: 1A, 2B Ethical Compliance Statement: The authors confirm that the approval of an institutional review board/ patient consent was not required for this work. We also confirm that the patients have given written informed consent for the publication of their videos. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. Funding Sources and Conflict of Interest: The authors declare that there are no conflicts of interest or funding relevant to this work. Financial Disclosures for the Previous 12 Months: The authors declare that there are no additional disclosures to report. Author disclosures are available in the Supporting Information. Data sharing not applicable to this article as no datasets were generated or analysed during the current study. Data S1. COIdisclosure. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.