Challenges in Upright Limb Occlusion Pressure Determination with the Delfi PTS: Pilot Data from Two Independent Cohorts

Nicholas Rolnick^1,2,3Victor S. de Queiros⁴Luke Hughes⁵Campbell Ruffhead⁶Sean Richard Zupnik⁶Michael Sergio⁶Lucas Kuriawa⁶Tim Werner^6*

• ¹The Human Performance Mechanic, New York, United States
• ²The BFR PROS, New York, United States
• ³Lehman College, New York, United States
• ⁴Universidade Estadual da Paraiba, Campina Grande, Brazil
• ⁵Northumbria University, Newcastle upon Tyne, United Kingdom
• ⁶Salisbury University, Salisbury, United States

Purpose: Blood flow restriction (BFR) exercise prescription relies on accurate determination of limb occlusion pressure (LOP), which is known to vary by body position. While recent guidelines suggest assessing LOP in the same position as the intended exercise, the feasibility of upright LOP assessment remains uncertain. Methods: This pilot study evaluated the feasibility of seated and standing LOP assessment using the Delfi Personalized Tourniquet System (PTS) under multiple postural and cueing conditions. Two separate and independent cohorts (n = 11 each; 18-35 years old) completed three experimental conditions involving either equal weightbearing (with/without visual cueing), seated, or wall-supported standing, with force plates used to monitor weight distribution. LOP was measured on two separate days using manufacturer guidelines. In each condition, three assessments were performed (n = 66 measurements per experimental condition). Results: LOP was unable to be determined in enough participants within and between cohorts to be able to compare reliability of LOP measured between conditions. Therefore, Cochran's Q test revealed no significant differences in successful LOP detection across conditions in cohort 1 (p = 0.234) but did reveal differences in conditions 1 and 3 (p < 0.001) and between 2 and 3 (p = 0.001) in cohort 2. Overall, we were successful in measuring LOP in 28.7% of the total attempts (57/198) in Cohort 1 and 34.8% (69/198) of the total attempts in Cohort 2. Seated LOP assessment was most successfully measured (34/66 attempts, 51%). Conclusion: Seated and standing LOP assessment using the Delfi PTS appears largely unfeasible, regardless of cueing or postural modifications. These findings question the feasibility of implementing seated or standing LOP measurements using the Delfi PTS in research and practice and suggest that future BFR research and application may benefit from supine LOP determination, or from developing dynamic calibration protocols suited for upright exercise.