Are You Fit for the Challenge? By Steve Vrieze, MS, NREMT-B

Are You Fit for the Challenge?

By Steve Vrieze, MS, NREMT-B

 

Albert Einstein has been quoted as saying “insanity is doing the same thing over and over again and expecting a different result”. To the outside individual, physical fitness may seem like insanity. Day after day training hard, doing the work with the hope of making oneself physically fit. Often one notices improvements, maybe running a little faster or adding another round. However, to objectively know all this effort is effective, one needs to periodically assess their cardiovascular (CV) fitness. Doing so provides a basis for comparison to the physical requirements of firefighting.

 

                  To assess CV fitness is to measure one’s oxygen consumption, oxygen uptake, or VO2. For practical purposes oxygen consumption, oxygen uptake, and VO2 all basically mean the same thing. According to Wasserman it is the amount of oxygen extracted from inspired gas in a given period of time, expressed in milliliters or liters per minute (1). In simple terms VO2 is a rate at which the body consumes and uses oxygen. To be able to evaluate fitness across body type and make comparisons body weight is factored out to give what is known as relative VO2 in millimeters per kilogram per minute. The higher a person’s relative VO2 the better a person’s cardiovascular fitness.

                

                  Measuring VO2 can be accomplished several ways. The gold standard is to complete a cardiopulmonary stress test. This type of testing is typically offered in a clinical setting such as a medical center, at an institution of higher education with an exercise science program, or at a fitness center which offers this service. Cardiopulmonary or VO2 testing typically uses the same procedures and protocols discussed in Overview of a Stress Test, with the addition of measuring the subjects breathing and gas exchange to determine actual VO2 using a metabolic or gas exchange system as pictured while breathing through a mask or mouthpiece.

 

VO2 can also be determined based on workload achieved during a standard stress test. Each stage of a stress test is associated with a previously measured VO2 or metabolic equivalent (MET). MET stands for metabolic equivalent where 1 MET equals a VO2 of 3.5 ml/kg/min. A VO2 of 3.5 ml/kg/min is the average resting VO2 for an adult. Each stage of a stress test using the Bruce protocol, for instance, would increase by approximately by 2-3 METs. Therefore if one achieves 12 minutes on the treadmill that would be associated with a workload approximately 11 times greater that baseline or a VO2 of 38.5 ml/kg/min.

 

Many submaximal options are available to fire departments or individuals looking for a standard measure to assess fitness. Tests such as the Queen’s College Step Test or Rockport walk test require little equipment and could accommodate a number of individuals at a time to test. These tests use prediction equations such as a standard stress test to determine VO2 but are not performed in a clinical setting make them a cost effective option.

 

Armed with the tools and knowledge to assess a firefighter’s fitness it is worth discussing how this information is useful. A high level of CV fitness has been shown to be a necessity in fireground operations. In the late 1970s research was conducted to understand the physical requirements. Performing simulated firefighter tasks showed that firefighters with a VO2 of less than 40 ml/kg/min or able to achieve a workload of 11.5 METs were able to meet the demands more readily than those with a VO2 under 40 ml/kg/min. To achieve this level of fitness is the equivalent of exercise approximately 12 minutes on the Bruce protocol used in standard stress testing. More recently a study conducted in conjunction with the Indianapolis Fire Department used real alarm situations over 6 months. This study found that fire suppression work often required firefighters operating at near 70% to100% of their maximum heart rates (2). Heart rate has a linear relationship with VO2. Therefore higher the heart rate requirement means higher the VO2 needed. Even receiving the alarm type can be associated with elevated heart rates of as much as 76% of the predicted heart rate (2). For the fit firefighter the likelihood of an elevated heart rate at alarms is diminished due to having a higher VO2. Much of fire suppression work, such as fire attack, ventilation, and overhaul, is performed at these high heart rates and is anaerobic in nature. Working anaerobically means the body does not utilize oxygen to generate the energy needed for the task and relies on stored supplies. However, excellent CV fitness allows a firefighter to recover faster from the anaerobic work and reduce the stress placed on the heart.

Any firefighter knows that firefighting is strenuous work placing significant demands on the body. Science has been shown to support this. ReIying on a firefighter’s ability to gauge their own level of fitness has been shown to be inaccurate and in the over confident firefighter could lead to compromising situations (4).   From time the tones drop to end of overhaul, a lot is asked of the body. Have you trained hard to be able to do the work? Don’t perpetuate the insanity, understand your fitness level. Assessing fitness and knowing your VO2 can give you confidence in your ability to get the job done.

 

References:                                                                                                      

  1. Wasserman, K., J.E. Hansen, D.Y. Sue, W.M. Stringer, B.J. Whipp. Principles of Exercise Testing and Interpretation 4th ed. Philadelphia: Lippincott, Williams, and Wilkins, 2005.
  2. Lemon, P.W.R, R.T. Hermiston. The human energy cost of fire fighting. J Occ Med. 19:558-562, 1977.
  3. Brown, J., J. Stickford.       Physiological Stress Associated with Structural Firefighting Observed in Professional Firefighters. Firefighter Health & Safety Research, School of Health, Physical Education and Recreation, Department of Kinesiology, University of Indiana, Bloomington. 2009.
  4. Peate, W.F, L. Lundergan, and J.J. Johnson. Fitness self-perception and VO2max in firefighters. J Occ Environ Med. 44:546-550, 2002.