Use a towel looped through the handle of a kettlebell to master the swing: if you pull with your arms, the towel slackens and the kettlebell oscillates abnormally, which forces you to propel the weight solely through the dynamic extension of your hips.

noli's read

This technique relies on solid concepts of biomechanics and motor learning. A study by Lake and Lauder (2012, observational, Journal of Strength and Conditioning Research) demonstrates that the power of the swing must come from the extension of the hips and the posterior chain, not the upper limbs. The towel trick creates a highly effective external physical constraint. According to the work of Gabriele Wulf (2013, consensus review on motor learning), the use of immediate sensory feedback and external foci of attention considerably accelerates the integration of a new movement pattern. While the expression 'in a few minutes' is a bit optimistic for guaranteeing perfect long-term technique, this instant fix is an excellent pedagogical tool validated by movement science.

the sources

No named source held this one up — that absence is part of the verdict.