Above: CORONADO, CALIF. (JULY 10, 2023) U.S. Navy SEAL candidates lift inflatable boats during the “Hell Week” crucible of Basic Underwater Demolition/SEAL (BUD/S) training on Naval Amphibious Base Coronado. (U.S. Navy photo by Mass Communication Specialist 2nd Class Dylan Lavin)
By Rob Shaul, Founder
BLUF
A recent study in the Journal of Strength and Conditioning Research of Naval Academy Midshipmen attempting the grueling 24-hour Naval Special Warfare (NSW) Screener at the U.S. Naval Academy in Annapolis, Maryland identified four key factors that predicted success:
1. Taller stature
2. Greater anaerobic power
3. Superior low-back endurance
Standard psychological tools measuring GRIT and resilience did not correlate with success. Nor did max effort shoulder strength or shoulder strength endurance.
What did matter was how the body responded to stress — particularly cold stress. Candidates who exhibited sharper hormonal adaptation to cold during a pre-screener Cold Pressor Test were more likely to finish the event.
Roughly 95% of Naval Academy graduates who go on to BUD/S graduate. That’s in stark contrast to the typical 70–80% attrition seen in the general candidate pool. This screener at the Naval Academy is one step on the way for academy grads to become Navy SEALs.
Context: The NSW Screener vs. BUD/S Hell Week
Unlike BUD/S Hell Week — which lasts 5.5 days and is designed to simulate continuous combat conditions — the Naval Special Warfare Screener at Annapolis is a 24-hour event, held twice yearly, in late fall and early spring. It is the first significant gate for Naval Academy Midshipmen seeking entry into the SEAL pipeline upon graduation.
The 24 hour screener begins at 1800 one day and concludes at 1800 the next. Candidates don’t sleep, and are contantly moving – push ups, burpees. Rucking, running, log PT, small boat PT. They are wet and sandy – and the water temperature around the Naval Academy averages 56°F in the fall and 48°F in the spring.”
These cold, humid, brackish Chesapeake Bay conditions — coupled with sleep deprivation, prolonged water exposure, load carriage, and intense physical testing — create a condensed selection environment.
Study Overview: Who, What, How
The researchers studied 48 male Midshipmen (age 18–26) preparing for and attempting the NSW Screener. A full battery of physiological, psychological, and physical tests were conducted 4–6 weeks prior to the event.
Of the 48 who started, 37 finished and 11 did not. The goal was to identify what characteristics separated finishers from nonfinishers.
The researchers assessed:
- Physical traits and performance metrics
- Psychological scales (resilience, mood, grit)
- Stress biomarker responses before and after cold exposure
- Blood/hormonal markers before and after the actual screener
Physical Testing
Candidates underwent a structured performance assessment that included:
- Wingate Test — measured peak anaerobic power (short-burst explosiveness)
- Vertical Jump — tested lower-body power
- Shoulder Press 1RM — gauged upper-body strength
- Max Reps Shoulder Press at 30% 1RM — evaluated muscular endurance
- Biering–Sorensen Test — isometric hold for low-back/trunk endurance
What Mattered:
Two clear performance predictors emerged:
(1) Anaerobic Power — Finishers had significantly higher peak power output on the Wingate test. Explosive force mattered more than sustained output.
(2) Low-Back Endurance — Finishers held the Sorensen position ~17 seconds longer than nonfinishers. This is directly relevant to the long-duration carries and overhead tasks required during the screener.
Shoulder strength and endurance, vertical jump, and anaerobic capacity (mean power) were not predictive.
Taller, bigger athletes did better. Another statistically significant finding: taller athletes had a higher likelihood of finishing. Finishers averaged ~5 cm (2 inches) taller than nonfinishers.
This height likely correlates to greater absolute strength, which would aid in boat carries, and log PT, better resistance to cold water exposure, and moving mass across terrain. This finding echoes data from a separate cohort of 333 active NSW Operators, who also trend taller and heavier than average soldiers.
Cold Pressor Test: A Window Into Stress Physiology
One of the most innovative parts of this study was its use of the Cold Pressor Test (CPT). Candidates were asked to immerse both feet in near-freezing (~1°C) and keep their feet in the water as long as possible. The test ended at 5 minutes – but candidates were not told this ahead of time. Blood and saliva were collected before and immediately after.
This simulated — in a controlled way — the cold stress experienced during the screener at at BUD/s in California.
The Key Finding: time didn’t Matter, hormone response did. How long someone kept their feet in the ice water did not predict success. But how their hormones reacted to the cold did.
Finishers showed significant decreases in Serum cortisol (SeCORT) and DHEA. Nonfinishers did not show meaningful changes.
In other words, finishers had a more adaptive, regulated hormonal response to cold stress. They didn’t “overheat” their stress systems. These responses mirrored how their bodies reacted after the actual screener — suggesting a kind of physiological consistency in resilience. This also could mean that cold water resistance could be an innate physiological trait for some athletes.
Post-Screener Biomarker Data: Who’s Holding It Together?
Blood and saliva were also collected immediately before and after the 24-hour screener. The findings echoed the CPT results:
– Finishers had significant drops in DHEA, ACTH, and salivary cortisol — suggesting hormonal downregulation and recovery onset.
– Nonfinishers often showed flat or even rising values — suggesting continued elevation and stress load.
– The DHEA:salivary cortisol ratio dropped 133% more in finishers than in nonfinishers — one of the most dramatic physiological distinctions in the study.
– Testosterone and IGF-1 both dropped in finishers — as expected after high-stress exposure — but this did not correlate with success or failure.
No significant differences were seen in inflammatory cytokines like IL-6 or TNF-a, likely due to timing — blood was collected ~12 hours post-event, likely after cytokine peaks had subsided.
Psychological Assessments Didn’t Predict Success
Despite their popularity in military selection research, the three psychological tools used in this study did not differentiate between finishers and nonfinishers:
GRIT Scale — Measured perseverance and passion
CD-RISC (Resilience) — Assessed stress adaptability
POMS (Mood States) — Gauged current emotional states
Scores were high across the board and showed no statistically significant differences. Finishers and nonfinishers were psychologically indistinguishable by these metrics.
The likely explanation? This was already a highly selected, elite population — motivated Naval Academy Midshipmen. The range of psychological difference was probably too narrow to measure with self-report questionnaires.
Why This Screener Matters
The study authors highlight one of the most important data points in the entire paper:
“Approximately 95% of Midshipmen who complete the NSW Screener and go on to BUD/S graduate.”
That number is staggering. BUD/S is notorious for its 70–80% washout rate. The success rate of those who pass the Annapolis 24-hour screener flips that attrition rate upside down.
This validates the screener’s role as an effective predictive filter, and also positions it as a potential model for other tactical units and institutions.
Takeaways
– Sprint capacity and peak power generation may matter more than steady-state endurance for selection events
– Train the trunk. Low-back and core endurance aren’t just afterthoughts — they’re predictive.
– Don’t ignore cold exposure. It’s not just discomfort — it’s a real stressor. Hormonal adaptation matters. The question is can this be trained, efficiently and effectively?
– Bigger athletes may do better in these events, particularly when leverage and load carriage are constant. As well, bigger athletes may be able to resist the cold better than smaller athletes.
– Don’t rely on GRIT scores or motivational assessments to separate finishers from nonfinishers in elite groups. Psychological assessments were not predictive of success.
– Pushups, Burpees, Log PT and other typical selection fitness demands and exercises demand significant shoulder strength and endurance – so it was counter intuitive that 1RM Shoulder Press Strength and Shoulder Strength Endurance had no impact on screener success.
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