Thoracic spinal manipulation: exploring force-time profiles and force modulation strategies in French chiropractors

BACKGROUND: Spinal manipulation (SM) involves the application of controlled, high-velocity low-amplitude (HVLA) forces with specific biomechanical properties. While prior research has outlined how these force-time characteristics evolve with practitioner expertise, the strategies used to intentionally adjust such parameters remain insufficiently explored. This study sought to assess the thoracic SM profiles of French chiropractors and to explore how instructions related to a clinical scenario, age, gender and years of practice are associated with SM force-time profiles. METHODS: Forty-six licensed chiropractors participated during a national professional gathering on the 15th and 16th March, 2024. Each performed thoracic HVLA manipulations on a manikin under three sequential conditions: initial familiarization, a simulated clinical case involving a patient with thoracic pain, and a constrained task requiring a 50% reduction in peak force. A force-sensing table captured detailed force-time data, including preload, peak force, peak thrust duration, and rate of force application. Linear mixed models were performed to examine the effects of trial number and experimental condition on each force-time parameter, with subjects included as random effects to account for repeated measures. RESULTS: In the clinical simulation, the average peak force reached 569.1 N, with an average rate of force application of 3093.8 N/s. During the modulation task, chiropractors applied significantly lower forces (mean peak: 379.0 N) and a reduced rate of force application (mean: 2072.8 N/s). Clinical scenarios and gender significantly impacted SM biomechanical parameters (p < 0.05). No effect was observed for age, year of practice, or types of therapy techniques. CONCLUSION: Chiropractors adapted their force during the 50% modulation task by substantially reducing peak force and rate of force application, while minimally decreasing peak thrust duration This pattern could reflect a pulse-height control strategy, where force amplitude is scaled while temporal structure is preserved, suggesting that training consistent timing may enhance precision and adaptability in manual therapy.