Navy SEALs: Inactivity & Deconditioning

Navy SEALS (Photo credit: Rennett Stowe)

Research Paper Title

Aerobic Performance of Special Operations Forces Personnel after a Prolonged Submarine Deployment.


The US Navy’s Sea, Air and Land Special Operations Forces personnel (SEALs) perform a physically demanding job that requires them to maintain fitness levels equivalent to elite athletes. As some missions require SEALs to be deployed aboard submarines for extended periods of time, the prolonged confinement could lead to deconditioning and impaired mission-related performance.


The objective of this field study was to quantify changes in aerobic performance of SEAL personnel following a 33-day submarine deployment. Two age-matched groups of SEALs, a non-deployed SEAL team (NDST, n=9) and a deployed SEAL team (DST, n=10), performed two 12-min runs for distance (Cooper tests) 5 days apart pre-deployment and one Cooper test post-deployment. Subjects wore a Polar Vantage NVTM heart rate (HR) monitor during the tests to record exercise and recovery HR. Variables calculated from the HR profiles included mean exercise heart rate (HRmean), maximum exercise heart rate (HRmax), the initial slope of the HR recovery curve (HRrecslope) and HR recovery time (HRrectime).


The second pre-deployment test (which was used in the comparison with the post-deployment test) showed a 2% mean increase in the distance achieved compared with the first (n=18, p<005) with no difference in HRmean, HRmax, HRrecslope and HRrectime. The test-retest correlation coefficient and 95% limits of agreement for the Cooper tests were 0.79 (p<0.001) and -68.6 +/- 267.5 m, respectively.

For the NDST there were no changes in any of the HR measures or the distance run between the pre- and post-deployment tests. When individual running performances were expressed as a percentage change in the distance run between the pre- and post-deployment tests, the DST performed significantly worse than the NDST (p<0.01). The DST showed a 7% mean decrement in the distance run following deployment (p<0.01). The decrement in performance of the DST was not associated with any changes in HRmean or HRmax; however; there was a 17% decrease in the HRrecslope, (p<0.05) and a 47% increase in HRrectime following the deployment (p<0.05).


In conclusion, prolonged confinement aboard a submarine compromises the aerobic performance of SEAL personnel. The resulting deconditioning could influence mission success.

Source: Fothergill, D.M. & Sims, J.R. (2000) Aerobic Performance of Special Operations Forces Personnel after a Prolonged Submarine Deployment. Ergonomics. 43(10), pp.1489-1500.


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