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Association of Sickle Cell Trait and Hemoglobin S Percentage with Physical Fitness


Medicine & Science in Sports & Exercise: December 2018 - Volume 50 - Issue 12 - p 2488–2493
doi: 10.1249/MSS.0000000000001720

Purpose This study aimed to determine the association between sickle cell trait (SCT) as a binary variable and hemoglobin S percentage as a stratified categorical variable with aerobic and anaerobic fitness.

Methods This retrospective cohort study included all recruits who entered US Air Force Basic Training between January 2009 and December 2014. Fitness parameters among recruits with and without SCT were compared using a standardized fitness assessment of a 1.5-mile timed run, 1 min of push-ups, and 1 min of sit-ups. Performance was further compared by stratifying those with SCT by their hemoglobin S percentage (20%–29.99%, 30%–39.99%, and ≥40%).

Results Of all recruits (N = 210,461) who entered training during the surveillance period, 2161 (1.0%) had SCT. After adjusting for age, sex, race, body mass index, and ambient temperature while conducting the fitness assessment, recruits with SCT were slower on their initial run than their peers without SCT by a mean (standard error) of 9.4 s (2.6 s) (P < 0.001) and completed 0.5 (0.3) fewer push-ups (P < 0.05); sit-up completion was statistically equivalent between the two groups. When retested 6 wk later, recruits with SCT improved their run time by a margin of 4.3 s (2.1 s) over their counterparts without SCT (P < 0.05). Baseline physical fitness was largely consistent across strata of hemoglobin S percentages; increased percentages were modestly correlated with faster run times (R 2 = 0.374) and fewer push-ups (R 2 = 0.339).

Conclusions As compared with their peers, recruits with SCT had slightly inferior aerobic fitness and similar anaerobic fitness at the outset of basic training, and gaps further narrowed over 6 wk of training. Stratifying recruits by their hemoglobin S percentage did not dramatically change the strength or direction of association.

1Epidemiology Consult Service, US Air Force School of Aerospace Medicine, Wright-Patterson Air Force Base, OH;

2Department of Preventive Medicine and Biostatistics, Uniformed Services University of the Health Sciences, Bethesda, MD;

3Trainee Health Squadron, Joint Base San Antonio-Lackland, TX; and

4Consortium for Health and Military Performance, Uniformed Services University of the Health Sciences, Bethesda, MD

Address for correspondence: Nathaniel S. Nye, M.D., 1515 Truemper St, Bldg 6612, Joint Base San Antonio-Lackland, TX 78236; E-mail:

Submitted for publication December 2017.

Accepted for publication July 2018.

© 2018 American College of Sports Medicine