(31) NORMATIVE PEAK FORCE VALUES FROM IS0METRIC MIDTHIGH ASSESSMENTS AND RELATIONSHIPS WITH MUSCULAR STRENGTH IN FIREFIGTHERS

Background: The isometric midthigh pull (IMTP) is an assessment used to evaluate lower body peak force, with minimal risk of injury and few technical requirements. Limited information is available regarding IMTP normative values for tactical populations and its relationship to muscular strength measures.

Purpose: The purpose was to produce percentile rankings for IMTP assessments in career firefigthers and examine relationships between measures of muscular strength and aerobic performance.

Methods: Eighty-five firefighters (women, n=4; age: 37.0 ± 8.9 yr.; height: 1.80 ± 0.07 cm; body mass: 91.8 ± 14.1 kg; BF%: 20.7 ± 7.3 %) completed an IMTP test to assess lower body peak force. For the IMTP, firefighters pulled upward as forcefully as possible on a stationary bar located at mid-thigh level, standing on bilateral force platforms. Bar height was adjusted to initial knee and hip angles of 125° and 145°, respectively. Three maximal effort attempts (no straps allowed) were competed, with 2-minutes of rest in between attempts. Peak forces for the three attempts were averaged. On a separate day, a sub-cohort of firefighters (n=39) completed a battery of tests including body composition assessment, upper and lower body maximal strength and muscular endurance testing. Five-Repetition Maximum (5RM) determination on the bench press (BP), back squat (BS), and hex bar deadlift (Hex DL) exercises were performed using standard protocols and used to estimate one-repetition maximum (1RM). Repetitions to Failure (RTF) was assessed for BP (45.3 kg), bent-over dumbbell row (20.4 kg) and Hex DL (61.2 kg) and BS (61.2 kg). Relationships between peak force from the IMTP and additional measures of performance were evaluated. Correlation coeficients were defined as: very weak: < 0.20; weak: 0.20–0.39; moderate: 0.40–0.59; strong: 0.60–0.79; and very strong: >0.80.

Results: Percentile rankings for IMTP were 2037 N (Poor), 2721 N (Below Average), 3052 N (Average), 3252 N (Above Average), and 3670 N (Very Good) for the 5^th, 25^th, 50^th, 75^th and 95^th percentiles, respectively. Strong relationships were observed for IMTP peak force and Hex DL 1RM (r=0.662), p< 0.01. Moderate relationships were observed between IMTP peak force and BS 1RM (r=0.501), and Hex DL RTF (r=0.429), p< 0.01. Peak force was positively associated with height (r=0.434), weight (r=0.504), body mass index (r=0.283), and fat-free mass (r=0.588), p< 0.01.

Conclusions: IMTP peak force is strongly associated with Hex bar DL 1RM, and moderately associated with  BS 1RM and Hex DL RTF. Taller, heavier, and individuals with more fat-free mass produced more force. PRACTICAL APPLICATIONS: The current percentile rankings can be used to characterize peak force derived from the IMTP among tactical populations. The IMTP may offer an alternative method of evaluating lower body strength, using a less technical and safer movement compared to other more dynamic measures of lower body strength.

Acknowledgements: None