Ski Science #1: How Many Phases Does a Ski Turn Really Have?
Updated: Sep 29
How Many Phases Does a Ski Turn Really Have?
A Cross-Country Comparison — and Why Steepness Changes the Answer
PowerSki Lab | Ski Technique · Biomechanics — By Dr. Sungchul Yang
Introduction
Ask any certified ski instructor how a turn is structured, and you'll likely hear some version of "initiation, control, finish, transition." It's a clean, teachable model — but is it universal? Does a racer on a steep giant slalom pitch experience the same turn structure as a recreational skier cruising a groomer? In this post, we dig into ski instruction manuals from North America and Japan, alongside peer-reviewed alpine ski racing biomechanics research, to answer both questions.
1. Turn-Phase Models Differ by Country — and by Purpose
In the United States (PSIA) and Canada (CSIA), a rough three-part logic — initiation, shaping/control, finish — shows up repeatedly, but there is no single fixed, universally adopted standard. The terminology has actually shifted over time: an older Canadian Ski Coaches Federation (CSCF) model used Unloading-Edging-Loading (three phases), while a revision from around 2015 simplified this to just Transition-Execution (two phases) [1][2]. So even within North America, the number of named phases has moved between two and five depending on the manual and era.
Japan takes a notably different approach for general/recreational instruction. Rather than a functional breakdown, Japanese ski pedagogy most commonly divides a turn geographically, relative to the fall line (the direction of steepest descent): tanimawari (谷回り, the "valley-ward" first half of the turn, entering toward the fall line) and yamamawari (山回り, the "mountain-ward" second half, exiting past the fall line) [3]. Some Japanese technical writers argue this two-part model is functionally ambiguous and propose a three-phase alternative — shido (始動, initiation), kajitori (舵取り, steering), and shiage (仕上げ, completion) — where completion plus the next initiation together form kirikae (切り替え, transition), treated as a duration rather than an instant [4].
The most rigorous phase definitions, however, come from international alpine ski racing biomechanics research, where phase boundaries aren't chosen for coaching cues but defined by measurable kinematic events. A widely cited giant slalom study divides each turn into four phases based on such events: Initiation (edge change to increased edging, ~21% of turn duration), Steering1 (~33%), Steering2 (running from gate passage to
maximum hip/knee flexion, ~32%), and Completion (from the start of leg extension until the skis go flat, ~14%) [5]. Notably, almost none of these racing studies name a separate "transition" phase — the edge change that connects two turns is simply absorbed into the Initiation phase of the new turn.
The takeaway: a fixed four-phase "initiation-control-finish-transition" model is a useful pedagogical framework, but it is not an internationally standardized one. Different traditions slice the same continuous motion differently, depending on whether the goal is teaching cues, terrain-based communication, or biomechanical measurement.
2. Steepness Changes How Much "Finishing the Turn" Actually Matters
Here's a detail that matters a great deal for on-hill coaching: the completion (finishing) phase is not a fixed requirement of every turn — its necessity scales with slope steepness.
Researchers at the Swiss Federal Institute of Sport analyzed giant slalom turn structure across different pitch angles and found that the completion phase was longest on steep terrain and shortest on gentle terrain, while the gliding phase showed the opposite pattern — longest on gentle terrain, shortest on steep terrain [6]. The mechanical logic is straightforward: on steep pitches, the slope-parallel component of gravity accelerates the skier strongly, so a skier needs to redirect the skis fully across and past the fall line — completing the arc — to scrub off speed. On gentler terrain, that deceleration demand largely disappears, so a skier can release into the next turn's initiation earlier without ever fully "finishing" the arc — and doing so may actually be more efficient, since prematurely engaging a full completion phase on flat terrain can bleed off speed unnecessarily.
Pressure data backs this up. A separate French study comparing plantar (under-foot) pressure between a steep (28°) and a gentle (11°) giant slalom pitch found significantly higher overall pressure on the steeper slope, with peak loading occurring during the Steering2 sub-phase — i.e., as the skier moves into the latter half of the turn [7].
A third study adds a tactical dimension. Researchers comparing two giant slalom line strategies — a "Z" strategy (long straight glide followed by a sharp direction change) versus an "S" strategy (a long, continuously curved arc that fully completes the turn) — found that neither strategy was inherently superior. What actually predicted better race times was minimizing energy loss overall, regardless of which line strategy a skier preferred [8]. In other words, whether to fully complete a turn or cut it short isn't a matter of correct versus incorrect technique — it's a tactical decision shaped by slope angle, speed, and the layout of what comes next.
3. What This Means for Coaching
Two practical conclusions follow. First, how many phases a turn "has," and what to call them, depends heavily on which tradition — recreational teaching in North America, Japan's fall-line-based vocabulary, or competitive biomechanics — you're drawing from. Second, and more actionable: the completion/finish phase is not something every turn owes equally. On gentle terrain, forcing a learner to fully "finish" every turn can produce unnatural movement and unnecessary speed loss. Recognizing when a shorter, less-complete arc is appropriate — because the terrain simply doesn't demand more deceleration — is itself a mark of sound, terrain-adapted coaching.
Closing Thoughts
The question of how many phases a turn contains turns out to be less about semantics and more about a very practical one: what does this slope, at this speed, actually require from the skier right now? We'll continue drawing on this kind of cross-national and biomechanics literature to sharpen the technical vocabulary we use in coaching.
Related Videos (PowerSki Channel)
[Video 1] sungchul_Yang 164. Ep.5 — "Is This How You Start Your Turn?" — follows directly from this post's Initiation-phase discussion. https://www.youtube.com/watch?v=482zNY7ljyg
[Video 2] sungchul_Yang 162. Ep.3 — "Downhill Stance?" (Part 1) — how stance adapts to slope and speed. https://www.youtube.com/watch?v=NiUDJ5QhA8s
References
[1] PSIA-AASI. Alpine Skiing Technical Skills Performance Guide. https://thesnowpros.org/wp-content/uploads/2025/01/alpine-ski-performance_guide-jan24.pdf
[2] Canadian Ski Instructors' Alliance (CSIA), The 5 Skills Framework; see also EffectiveSkiing.com, "Phases of the Turn." https://www.effectiveskiing.com/Topic/Phases_of_the_turn
[3] Yuki no Kiseki (雪の軌跡). "Tanimawari and Yamamawari: A Glossary." https://trackonsnow.jp/glossary/what-is-turn-abovebelowfallline/
[4] Yuki no Kiseki (雪の軌跡). "Is It Really Just Tanimawari and Yamamawari? Rethinking Turn Structure." https://trackonsnow.jp/technical_analysis/how-should-we-separate-turning/
[5] Falda-Buscaiot, T., Hintzy, F., Rougier, P., Lacouture, P., & Coulmy, N. (2017). Influence of slope steepness, foot position and turn phase on plantar pressure distribution during giant slalom alpine ski racing. PLOS ONE, 12(5), e0176975. https://doi.org/10.1371/journal.pone.0176975
[6] Bruhin, B., Janssen, R. J. F., Romann, M., et al. (2020). Giant Slalom: Analysis of Course Setting, Steepness and Performance of Different Age Groups — A Pilot Study. Frontiers in Sports and Active Living, 2:107. https://doi.org/10.3389/fspor.2020.00107
[7] Falda-Buscaiot, T., et al. (2017). Same study as reference [5].
[8] Delhaye, C., Cross, M. R., Bowen, M., Samozino, P., & Hintzy, F. (2020). Influence of Line Strategy Between Two Turns on Performance in Giant Slalom. Frontiers in Sports and Active Living, 2:589257. https://doi.org/10.3389/fspor.2020.589257
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