The tourniquet is applied, the windlass is turned and secured. From the outside, everything looks correct — yet the bleeding continues, and a distal pulse can still be felt. This situation repeats itself constantly in training and in research, and its cause is usually the same: the mistake was made before the tightening even began.
It is commonly assumed that a failed tourniquet application is caused by too few turns of the windlass. Research shows that the most frequent problem is a strap that was not pulled tight enough when the tourniquet was applied. The remaining slack looks like a minor detail that can be eliminated by turning the windlass — but this is precisely what often determines whether the tourniquet will work properly.
Where the Pressure Goes
The tightening force of the windlass and the inner band is limited. When the strap is snug against the limb before tightening begins, every turn of the windlass increases pressure. When the strap is loose, the first turns of the windlass create no pressure at all — they merely take up the slack.
This is the essential difference. The windlass ends up doing the work that should have been done by hand, and its force may no longer be sufficient for the final pressure. This creates risk: the bleeding is stopped more slowly, more blood is lost, and in the worst case the artery is never occluded — even though, to the user, everything appears to have been done by the book.
What the Studies Found
The study by Polston and colleagues, “No Slackers in Tourniquet Use” (2013), showed that the most common cause of incorrect tourniquet tightening was not an under-rotated windlass, but slack left in the strap before tightening began. Attempts to eliminate it by turning the windlass harder often failed to generate the pressure needed to occlude the artery. A well-tensioned strap, by contrast, allowed bleeding to be stopped faster — the turns of the windlass converted directly into pressure.
Baruch and colleagues (2017), studying tourniquet users without a medical background, described a confidence–competence mismatch: participants were convinced they had applied the tourniquet correctly, even though objectively it was not working. This error is not limited to beginners — experienced users make it too, especially under stress, in darkness, or while wearing gloves.
The work of Kragh and colleagues, including the analysis of tourniquets recovered from Operations Enduring Freedom and New Dawn (2013), supports the same overall conclusion: although the authors used different methods and evaluated different tourniquet models, effectiveness was more often determined not by the number of turns, but by strap tension before turning began.
Practical Takeaways
When teaching tourniquet use, the emphasis should be placed not on the number of windlass turns, but on the sequence of actions and the result. The number of turns naturally varies with limb circumference and strap tension, so there is only one reliable criterion: the bleeding has stopped and the distal pulse has disappeared.
If the windlass requires an unusually high number of turns, or turns with great difficulty, the first thing to check is strap tension — not to apply more force. There is no direct research on this, but it is likely that a loose strap also increases the risk of mechanical failure: when the windlass travel is spent taking up slack, the mechanism is loaded beyond what the design intended.
Practical recommendations:
- Pull the strap as tight as possible and secure it — slack in the strap should never be compensated for at the expense of the windlass.
- Judge the overall result, not the number of windlass turns.
- Windlass turning too hard or for too long? Check the strap tension.
- Train regularly under instructor supervision — this is a mistake users rarely notice on their own.
Conclusion
The success of a tourniquet is decided earlier than most people think — at the moment the strap is wrapped around the limb. A strap pulled to maximum tension allows the full force of the windlass to be used for pressure, rather than wasted on taking up slack.
Tighten first. Only then turn.
References
- Polston RW, Clumpner BR, Kragh JF Jr, Jones JA, Dubick MA, Billings S. No Slackers in Tourniquet Use to Stop Bleeding. J Spec Oper Med. 2013;13(2):12–19. PMID: 23817873.
- Baruch EN, Kragh JF Jr, Berg AL, Aden JK, Benov A, Shina A, et al. Confidence–competence mismatch and reasons for failure of non-medical tourniquet users. Prehosp Emerg Care. 2017;21(1):39–45. doi:10.1080/10903127.2016.1209261
- Altamirano MP, Kragh JF Jr, Aden JK, Dubick MA. Role of the windlass in improvised tourniquet use on a manikin hemorrhage model. J Spec Oper Med. 2015;15(2):42–46.
- Kragh JF Jr, Burrows S, Wasner C, Ritter BA, Mazuchowski EL, Brunstetter T, et al. Analysis of recovered tourniquets from casualties of Operation Enduring Freedom and Operation New Dawn. Mil Med. 2013;178(7):806–810.
- Kragh JF Jr, Walters TJ, Baer DG, Fox CJ, Wade CE, Salinas J, et al. Practical use of emergency tourniquets to stop bleeding in major limb trauma. J Trauma. 2008.