The kick contributes ~10% of forward propulsion in sprint swimming but the kick pattern meaningfully affects how the body enters the bike leg
Interpretation
Deschodt et al. (1999) measured legs contributing ~10% of velocity in maximal 25 m sprint front crawl — establishing that the kick is a minor direct propulsive force and its primary role is indirectly improving stroke mechanics. Ambrosini et al. (2024) then showed in 15 triathletes that 8 weeks of 6-beat kick training reduced heart rate, VO2 and energy expenditure in subsequent cycling — the kick's benefit for triathletes may be primarily in T1/early-bike economy rather than swim speed itself. Ambrosini's groups were very small (~5 each); treat as preliminary.
Practical implication
Frame kick training for triathletes as a cycling-transition investment, not a swim-speed investment. The propulsive contribution data from Deschodt is in sprint conditions; tri swim paces differ — apply directionally, not as a precise percentage.
Sources
2 sources, independently verified.
Eur J Appl Physiol 80(3):192–199. Legs added ~10% velocity in maximal 25 m sprint; kick appeared to improve wrist trajectory indirectly rather than providing direct propulsion. Establishes the quantitative case that kick contributes a minority of forward propulsion, underpinning the article's argument that kick training benefits are primarily about wrist/stroke mechanics and subsequent cycling rather than raw swim speed. Note: co-authors cited 'from memory' of the journal record — cited as 'Deschodt et al.' only.
J Strength Cond Res 2024. 6-beat kick group showed lower stroke frequency and longer stroke length after 8 weeks; lower heart rate, VO2 and energy expenditure in subsequent cycling. Provides the triathlon-specific rationale for kick training: the benefit is not more swim speed, it's a lower physiological cost in the bike leg that follows — a non-obvious mechanism worth naming explicitly. Very small groups (~5 each); treat as preliminary.