From time to time you hear about the ‘kettlebell WTF’ phenomenon coming up. Typically it’s used as an explanation why kettlebell training might transfer to other activities such as deadlifting. This lacks detail and as such, this blog post will explore a couple of potential mechanisms behind this.
I would say that kettlebell training is commonly a novel stimulus for many different lifters (not all), if we take the kettlebell swing as an example it has 1) fast eccentric muscle action, 2) stretch-shortening cycle, 3) a wider grip and 4) involves centripetal force.
The fast eccentric muscle action will preferentially recruit fast-twitch fibres, some studies suggest this leads to greater hypertrophy and advantageous changes in muscle architecture.
In contrast, isometric and concentric muscle actions follow the size principle which just means that they recruit slow-twitch muscle fibres before fast-twitch. Therefore, if someone is inexperienced with this type of training you could allow them to break through plateaus or maintain their current level of performance with minimal training.
Given that kettlebell swing benefits from the stretch-shortening cycle as it has fast negative and positive phases. This causes the tendons to store and utilise elastic energy for the positive portion of a lift. This acutely increases force production and triggers a stretch-shortening cycle. Further, having an eccentric or negative phase before a positive or concentric will mean that more muscles (cross-bridges) will be attached at the start of the positive or concentric contraction, which will offer additional force production. It takes roughly 0.6 seconds to hit peak force, so having more muscle attached may allow greater force production in the concentric muscle actions. The stretch-shortening cycle will acutely increase force output which is likely to lead to greater chronic adaptations.
Kettlebells typically have a wider grip compared to most barbells and dumbbells. Again this may be a novel stimulus. Given that grip strength is a limiting factor for many exercises it may transfer quite well.
The kettlebell swing involves centripetal force which has been shown to change the internal forces within the body. For example, the direction of the force in the spinal segment is in opposite direction during the swing vs a deadlift. Also, the centripetal force may allow greater time to apply force to the kettlebell for a longer period of time, which would allow them to generate greater force.
Whether or not this plays an important role in improving performance is unknown, however, I thought it would be worth mentioning as it is something that is a bit different.
In summary, for many people, training using kettlebells is a new or novel stimulus that may lead to greater gains.