The value of measuring isometric strength in firefighter trainees

Maximal strength is often viewed as an essential trait for firefighters, but may be challenging to measure in first responder populations. Dynamic strength tests can be time consuming and may not be appropriate for many trainees due to insufficient training history and increased risk of injury. The isometric midthigh pull (IMTP) could provide a valid strength measure, while also being an efficient test to conduct with first responder trainees who tend to have a wide range of fitness and ability levels. What would further validate the use of the IMTP in first responder populations is comparisons with job-specific tasks.

PURPOSE:
To determine predictive relationships between isometric strength and other general fitness measures with job-specific tasks in firefighter trainees.

METHODS:
Data from 47 firefighter trainees (41 men, 6 women) from one fire department were analyzed. General fitness tests included: two countermovement jump trials; two IMTP trials; 2-minute hand release push-ups; and the Yo-Yo Intermittent Recovery Test Level 1 (YYIRT1). Job-specific tests comprised: two drags with a 131.8-kg manikin over 40 m; two trials of a 10.67-m (35 feet) ladder extension; and a 5-lap tower climb wearing a 12.9-kg self-contained breathing apparatus while carrying a 24.9-kg, 30.5-m long hose pack. The best of the two trials for the countermovement jump, IMTP, manikin drag, and ladder extension were considered. Only one trial was completed for push-ups, the YYIRT1, and stair climb. Stepwise regression, controlling for sex (coded as 1 = male, 2 = female), derived relationships between the general and job-specific fitness tests (p < 0.05), with a focus on the IMTP.

RESULTS: Both the manikin drag and ladder extension were predicted by sex and the IMTP, with approximately 41% and 34% explained variance, respectively (Table 1). The predictive formula for the drag was: manikin drag time (s) = 85.256 + 9.814(Sex) – 0.016(IMTP). For the ladder extension, the predictive formula was: ladder extension time (s) = 21.509 + 3.314(Sex) – 0.004(IMTP). There were no significant predictive relationships for the stair climb.

CONCLUSIONS: Casualty or body drags and ladder extensions are essential, physically demanding tasks performed by firefighters that can ensure the safety of the general population and property. The current results show the need for maximal strength in performing these tasks, with the IMTP being involved in significant predictive relationships for 40-m, 131.8-kg manikin drag and 10.67-m ladder extension times. Greater isometric strength could aid the faster performance of these job tasks in trainees.

PRACTICAL APPLICATIONS:
The IMTP could be used to predict performance in job-specific tasks such as manikin drags and ladder extension in firefighter trainees. This strength test has the added value of being low-fatiguing and relatively easy to perform regardless of individual training background, so the IMTP could have application for many first responders.