Study involving San Diego firefighters examines back muscle strength, endurance & flexibility
By Joe Verna, Colin Stowell, Richard Parker, Antonio Duran & John Mayer

For information about exercises to help support back strength, check out "Back for More: Exercises that can help prevent low back pain or injury," by Jeff and Martha Ellis, in the November issue of FireRescue magazine.

The National Institute of Standards and Technology (NIST) reported that approximately 81,000 firefighters in the United States were injured during 2002 at a cost of $3–8 billion(1). Most injuries to firefighters occur on the fireground, and many of these injuries are musculoskeletal-related. The musculoskeletal system’s primary functions include supporting the body, allowing motion and protecting vital organs. Sprains and strains, including those of the low back and abdominal regions, account for most of the musculoskeletal injuries in firefighters(2). And back injuries represent the vast majority of these injuries(3). Further, low back injury is the most common injury related to early retirement from the fire service(4).

The high rate of low back injuries can be attributed to the high-risk activities that firefighters are expected to perform, such as operating charged hoselines, climbing ladders, breaking windows, ventilating structures, performing overhaul and lifting objects greater than 40 lbs.(4). These tasks are often accomplished while the body’s posture is ergonomically unsound or on unstable ground.

Involving the Wellness/Fitness Initiative
Considering that firefighters are at high risk for many types of injuries and illnesses, the International Association of Firefighters (IAFF) and the International Association of Fire Chiefs (IAFC) developed the Fire Service Joint Labor Management Wellness/Fitness Initiative (WFI)(5,6). The WFI provides guidance to fire departments on how to implement properly designed health, wellness and fitness programs to help firefighters become more physically able to safely carry out their work duties and common activities of daily living. (For more information about the WFI, visit www.iaff.org/hs/well/index.htm.)

The WFI consists of five major components: 1) medical evaluation, 2) fitness testing and exercise, 3) rehabilitation, 4) behavioral health promotion and 5) data collection. Each of these components is comprehensive in nature, particularly the periodic medical evaluation. Within the fitness testing component, the WFI recommends several assessment procedures for lower trunk and lower extremity function, such as an isometric leg/back lift tested with a static dead lift (this serves to test back strength), a test of hamstring flexibility, and a test of trunk flexion endurance using abdominal crunches (curl-up). In the third edition of the WFI, which was published after the present study was completed, assessment of core stability using the static plank test is also recommended(6).

The WFI does not include a test to assess back extension muscular endurance, which has been shown to be a good predictor of future low back pain and disability following a back injury(7). Because of this, a new WFI-based program has incorporated an isometric back extension endurance test with the standard elements of its WFI-based periodic health evaluations for firefighters being performed at a municipal fire-rescue department in the United States.

In this article, we’ll describe the findings of a recent research study, which assessed the back muscle strength, endurance and flexibility characteristics of firefighters who participated in WFI-based periodic health evaluations.

The Study
The study involved a group of professional firefighters from the San Diego Fire-Rescue Department (SDFRD) who presented for initial WFI-based periodic health evaluations. Exactly 793 (725 male, 68 female) firefighters—94 percent of the department’s firefighter workforce—participated in the voluntary periodic evaluation. The study protocol was reviewed and approved by a licensed institutional review board to ensure adequate protection for the participants.

The comprehensive periodic evaluation consisted of procedures described in the second edition of the WFI(5). These procedures included various health history and health-habit questionnaires, clinical laboratory tests, imaging, comprehensive medical evaluations and fitness tests. All medical evaluations and fitness tests were administered by trained personnel under the direct supervision of appropriately licensed healthcare providers, including one of the investigators, as well as the wellness officer (a captain) from the SDFRD.

In addition to the WFI-based procedures, participants performed an isometric back extension muscle endurance test (Figure 1). Similar versions of this test have been used by various clinicians and researchers for civilian populations(7,8). To complete the isometric back endurance test, the participant is positioned prone on a bench with the anterior superior iliac spine at the edge of the bench. Arms are held against the chest with hands on opposite shoulders, while the examiner secures the participant at the ankles. The participant is instructed to elevate their torso to a horizontal position and the examiner begins timing as soon as the torso is unsupported. The participant is verbally encouraged to hold this position as long as possible. When the torso drops 10 degrees below the starting position, the examiner stops the test and time is recorded in seconds.

Data management, analysis and interpretation procedures were conducted by investigators who were not involved with the assessments and did not have access to private health information. Data was sanitized of private health information and subsequently entered into a database. The database was designed by the investigators specifically for WFI programs in accordance with the requirements set forth in the WFI second edition(5). Descriptive data (means and standard deviations) were calculated for each assessment variable. Isometric back extension endurance times were compared to a target endurance time and subsequently categorized as “normal” or “below normal”(8). Finally, standard statistical tests were conducted to compare firefighters with and without a self-reported history of low back pain.

The Results
The demographic and fitness test data are shown in Table 1. Almost half of the firefighters (45.4 percent; 360 out of 793) reported a history of low back pain. Interestingly, when compared to firefighters without a history of low back pain, firefighters with a history of low back pain had significantly inferior results in most areas, including isometric back extension endurance, trunk flexion endurance, low back/lower extremity lift strength, arm strength, upper body muscle endurance, aerobic capacity and percentage of body fat. However, there was no significant difference in low back/hip flexibility between firefighters with and without a history of low back pain. Most firefighters (83 percent; 658 out of 793) had isometric back extension muscle endurance times below the recommended target time (target time for men = 147 seconds; target time for women = 189 seconds), and 37 percent (293 out of 793) were more than one standard deviation below the target time (one standard deviation below target time for men = 95 seconds; one standard deviation below target time for women = 129 seconds).

Discussion Points
An isometric back extension endurance test was successfully implemented as a component of the WFI-based periodic health evaluation for firefighters at the SDFRD. The addition of this test enhances the current battery of WFI tests for assessing physical fitness, and provides useful information for those designing preventive exercise programs for firefighters.

In agreement with previous studies (3,5,6), this study found that low back pain is highly prevalent in firefighters. This study also demonstrated that firefighters with a history of low back pain are less physically fit compared to their back-pain-free counterparts in many areas of physical fitness, including back extension endurance, abdominal muscle endurance, trunk/leg lift strength, arm strength, aerobic capacity, subcutaneous body fat and resting blood pressure. Interestingly, there was no difference in low back/hip flexion flexibility between firefighters with and without low back pain. Although the clinical meaning of these functional deficits in firefighters with low back pain is unclear, stakeholders are encouraged to address them in well-designed and targeted physical fitness programs.

Perhaps the most important finding of this study is that a large majority of firefighters had isometric back extension endurance times that were below the recommended target times for healthy individuals(8). Although normative data on isometric back extension endurance in firefighters is not available, this finding suggests that firefighters should engage in exercise programs to improve back extension endurance and the functional capacity of related core muscles. Future research should asses the efficacy of these exercise programs in preventing low back injuries.

Although the underlying factors related to low back pain are likely multifaceted, deconditioned core trunk muscles are strongly associated with low back pain. For example, individuals with low back pain exhibit a loss of strength and endurance in trunk extensor muscles(9,10). Unilateral atrophy of the deep postural muscles around the spine (e.g., multifidus) has been reported in those suffering from acute low back pain(11). Atrophy and fatty infiltration of the lumbar muscles have been reported in those with chronic low back pain(10). Moreover, altered activation patterns in various core muscles and spinal functional instability have been reported in those with low back pain(12,13).

Of these relationships, the relationship between back extension endurance and low back pain may be most compelling, particularly for the purpose of formulating effective back injury prevention programs for firefighters. Poor isometric back extension endurance has been linked to an increased risk for future low back pain episodes and a higher incidence of work disability due to chronic back disorders(7,14). These relationships suggest that exercise programs for the prevention and treatment of low back disorders should focus on improving the endurance capacity of the back extensor muscles through long duration, high repetition and low-intensity exercise. It’s important to note, however, that this premise has not been tested in clinical trials for the prevention of low back injury in firefighters or civilian populations(15).

In Conclusion
An isometric back extension endurance test can be efficiently incorporated into WFI-based fitness test batteries, and can provide useful information about the physical performance characteristics of firefighters’ back muscles. Fire departments should consider adding this simple test to their wellness-fitness programs and periodic health evaluations. It’s also reasonable to recommend that future editions of the WFI incorporate an isometric back extension endurance test as a standard component of fitness testing. In order to improve the validity of this test for firefighters, normative data on firefighters from a wide variety of fire service departments are needed. Additionally, targeted exercise approaches are needed to address the functional deficits of firefighters’ back muscles. Finally, more research is needed to assess the clinical effectiveness and cost-effectiveness of exercise programs and other approaches in preventing low back injury, and to determine which specific exercises and approaches are most appropriate for firefighters.

Joe Verna, DC, is a board member and clinical researcher with the Spine & Sport Foundation in San Diego; Colin Stowell is a battalion chief with the SDFRD; Richard Parker, DO, is the medical director with the San Diego Firefighter Regional Wellness Center; Antonio Duran is a Los Angeles County Fire Department fire captain and safety officer for the Risk Management Division; and John Mayer, DC, PhD, is the Lincoln Endowed Research Chair and an associate professor with the College of Medicine and the School of Physical Therapy & Rehabilitation Sciences at the University of South Florida in Tampa.

Note: This study was supported by 1) a grant from the U.S. Department of Homeland Security, Federal Emergency Management Agency, Assistance to Firefighters Grant awarded to the City of San Diego, and 2) the Spine & Sport Foundation (aka, The Vert Mooney Research Foundation).

References
1. National Institute of Standards and Technology. Billions in cost estimated for firefighter injuries. ScienceDaily. 2005. http://www.sciencedaily.com/releases/2005/04/050411203847.htm.

2. Karter M, Molis J. U.S. Firefighter Injuries - 2007: National Fire Protection Association: Washington, D.C., 2008.

3. National Institute of Standards and Technology: The Economic Consequences of Firefighter Injuries and Their Prevention. Final Report. U.S. Department of Commerce: Arlington, VA, 2005. (Report number NIST GCR 05-874)

4. Nuwayhid I, Stewart W, Johnson J. Work activities and the onset of first-time low back pain among New York City fire fighters. Am J Epidemiol. 137(5):539–548, 1993.

5. International Association of Fire Fighters, International Association of Fire Chiefs: The Fire Service Joint Labor Management Wellness-Fitness Initiative, 2nd edition. IAFF: Washington, D.C., 1999.

6. International Association of Fire Fighters, International Association of Fire Chiefs. The Fire Service Joint Labor Management Wellness-Fitness Initiative, 3rd edition. IAFF: Washington, D.C., 2008.

7. Biering-Sorensen F. Physical measurements as risk indicators for low back trouble over a one-year period. Spine. 9(2):106–119, 1984.

8. McGill S, Childs A, Liebenson C. Endurance times for low back stabilization exercises: Clinical targets for testing and training from a normal database. Arch Phys Med Rehabil. 80(8):941–944, 1999.

9. Latimer J, Maher C, Refshauge K, et al. The reliability and validity of the Biering-Sorensen test in asymptomatic subjects and subjects reporting current or previous nonspecific low back pain. Spine. 24(20):2085–2090, 1999.

10. Mooney V, Gulick J, Perlman M, et al. Relationships between myoelectric activity, strength, and MRI of the lumbar extensor muscles in back pain patients and normal subjects. J Spinal Disord. 10(4):348–356, 1997.

11. Hides J, Stokes M, Saide M, et al. Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain. Spine. 19(2):165–172, 1994.

12. Standaert C, Weinstein S, Rumpeltes J. Evidence-informed management of chronic low back pain with lumbar stabilization exercises. Spine J. 8(1):114–120, 2008.

13. Soderberg G, Barr J. Muscular function in chronic low back dysfunction. Spine. 8:79–85, 1983.

14. Rissanen A, Helivaara M, Alaranta H, et al. Does good trunk extensor performance protect against back-related work disability? J Rehabil Med. 34(2):62–66, 2002.

15. Bigos S, Holland J, Holland C, Webster J, Battie M, Malmgren J. High-quality controlled trials on preventing episodes of back problems: systematic literature review in working-age adults. Spine J. 9:147–168, 2009.