Isometric Floor Press: A Valid, Reliable, and Practical Field-Based Assessment of Upper-Body Strength

ABSTRACT: Kirk, BJC, Wills, JA, Glen, B, and Doyle, TLA. Isometric floor press: A valid, reliable, and practical field-based assessment of upper-body strength. J Strength Cond Res XX(X): 000-000, 2026-There is currently no standardized method for assessing upper-body isometric strength using portable field-based equipment, limiting practitioners' ability to monitor upper-body strength in applied environments. This study evaluated the validity and reliability of 4 novel tests performed using only a force plate system and isometric midthigh pull rack: the isometric push-up (IPU) on knees and feet, and the isometric floor press at 90° (IFP90) and 135° (IFP135) elbow angles. Twenty recreationally trained adults (16 men, 4 women) completed a 1 repetition maximum bench press and familiarization session, followed by 2 isometric testing sessions, each separated by 7 days. Validity was assessed using Pearson correlation with 1 repetition maximum bench press. Within-day and between-day reliability were evaluated using intraclass correlation coefficients (ICC) and coefficient of variation (CV%). IFP90 showed the strongest validity (r = 0.887), followed by IFP135 (r = 0.724), IPU on knees (r = 0.711), and IPU on feet (r = 0.692). All tests demonstrated excellent within-day reliability (ICC = 0.923-0.983; CV% = 5.3-7.7%) and between-day reliability (ICC = 0.912-0.955; CV% = 6.4-12.3%). Supine configurations (IFP) generally showed greater measurement stability than prone push-up variations (IPU), with lower variability and higher ICCs. Results were consistent across a broad strength range (bench press = 65-140 kg), supporting their applicability to both athletic and general populations. These findings suggest that IFP90 offers a valid, reliable, and practical field-based alternative to traditional upper-body strength testing. These tests may be especially useful in settings where safety, measurement sensitivity, and fatigue minimization are priorities.