We read “Longitudinal Decline in Cardiorespiratory Fitness With Age Among Male Firefighters in San Diego, California, 2005–2015” by Cameron et al.1 with great interest. This article demonstrated that age is negatively associated with cardiorespiratory function (CRF) among firefighters. Given that cardiovascular disease is the leading cause of death among on-duty firefighters and that CRF impairment is a pronounced risk factor for cardiovascular disease, the findings of this study indicate that (1) the reduced CRF in combination with high physical and mental demands might increase the likelihood of death among older firefighters, and (2) improving CRF may prevent cardiovascular disease and reduce death caused by cardiovascular disease among on-duty aging firefighters.
Some highlighted findings require further clarification. First, the researchers found that body fat does not moderate the association between age and CRF. However, previous studies have documented that increased age is directly associated with CRF reduction,2 that age is positively related to body fat,3 and that elevated body fat is inversely associated with CRF.4 Therefore, body fat may serve as a mediator in the causal pathway between age and CRF, instead of a moderator. Additionally, this could suggest the addition of several different moderators, such as the initial CRF level, which may counterbalance this mediation effect.
Second, Cameron et al. concluded that CRF increased by 0.9 metabolic equivalents over 10 years among those aged 50 years and older. This marked increased in CRF seen in the older group occurred possibly because the authors may not have consider the extremely high rate of dropout (e.g., retirement), resulting in dramatically decreasing the number of participants from 212 at baseline visit to 7 at the 10th visit. This suggests that the remaining older firefighters are fit because of their recorded maximal oxygen uptake (VO2max) compared with national norms. Furthermore, the treadmill test is not equivalent to cycle ergometer testing because the treadmill test might lead to a 14% higher VO2max compared with the VO2max obtained during cycle ergometer testing.5
Third, we believe that it is difficult to claim that this small sample size is representative of all US firefighters. Obviously, this study was conducted in San Diego, California, which indicates a regional sample instead of a representative sample. Fourth, it might not be a strict observational study because the intervention, a wellness program, was included. Finally, the treadmill test might lead to a 14% higher VO2max compared with the VO2max obtained during cycle ergometer testing.5
In summary, we support the need to provide interventions and wellness programs to promote CRF in firefighters, who protect public health and ensure public safety.
ACKNOWLEDGMENTS
The research was previously presented at University of California, San Diego Public Health Research Day, April 4, 2018.
We appreciated contributions made by the members of the San Diego Fire-Rescue Department for their service and the staff at the San Diego Sport Medicine and Family Health Center.
Note. The views expressed are those of the authors and do not necessarily reflect the official policy or position, either expressed or implied, of the US Air Force, Department of Defense, Department of Health and Exercise Science, Colorado State University, or the US government.
CONFLICTS OF INTEREST
The authors have no conflicts of interest to declare.
REFERENCES
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