The in-run crouch explained: why ski jumpers make themselves small, how that becomes around 90 km/h and why the trunk angle matters more than the legs.
The in-run crouch is the deep, compact position ski jumpers hold on the way down the approach — and it has exactly one purpose: speed. Trunk low and forward, knees strongly bent, arms tight to the body — all of it to minimise drag so that around 90 km/h arrive at the take-off table [1]. It looks like "making yourself small out of fear". It is the opposite: a highly precise working position.
How precise, computational flow simulations of the in-run show. The trunk angle of attack — how steeply the upper body sits relative to the direction of travel — dominates every other joint angle, and its optimum lies at 0 to 2 degrees [2]: practically flat over the thighs, not propped up. A posture optimised this way cuts total in-run drag by roughly 5 % [2]. Five percent sounds like nothing — on the hill it is the difference between "solid" and "in the mix".
The honest answer to "why do they make themselves so small?": the in-run is the only part of the jump where speed is still handed to you. After that it is only managed.
This section explains what the in-run crouch does and how it is practised — it is not an instruction to ride a hill on your own.
It is the aerodynamic base position in the approach: knees strongly bent, trunk laid low and forward over the thighs, arms tight to the body, eyes down the track [1]. The in-run drops at roughly 35 degrees, and the take-off table at the end points about 10.5 degrees downward [1]. Your job in those few seconds: do nothing that brakes.
That is the surprise from the flow simulation: it is not the leg position that decides but the trunk angle of attack at 0 to 2 degrees [2]. Tiny corrections at the upper body outweigh anything you change at knee or hip angle [2]. Which is why coaches correct the top first, not the bottom.
Ski jumpers reach 80 to 90 km/h in the approach, about 22 to 25 metres per second [2] — country-road speed, on two boards, in a crouch. That speed is the raw material of the whole jump: without in-run speed the best take-off achieves little. Forearms and hands belong stretched out and guided tight as well [2].
Off the hill the position is drilled in the so-called imitation jump — the take-off movement without a hill. Biomechanical comparisons show that imitation jumps from a rolling platform reproduce the real hill take-off considerably better than jumps from a standing start [4]. And three of four movement criteria are matched best when jumping boots are worn [4].
The in-run crouch is not a trick of its own, it is the loading position. The take-off is the most important phase of the entire jump — it sets flight speed, flight angle, rotation and body attitude [3]. From a crouch that is too high and too loose, that impulse never comes out cleanly. Lose the crouch and you have lost the jump before the table.
Plain talk: this guide explains and motivates — it never replaces supervised training in a club or on the hill. The in-run crouch is the most harmless position in the entire sport and still not a do-it-yourself project: it leads into a take-off at around 90 km/h [1], and that transition belongs exclusively in supervised hands.
Separate understanding from execution. You may feel the position out on the ground, stand in the crouch, sense the trunk angle — that is dry-land practice, and it is exactly how clubs begin too [5]. What you do not do: try it on a hill, a steep slope or a self-built ramp. Ski jumping is learned in stages under supervision — dry-land practice, then the smallest hill, then bigger, every step only once you can.
Get into the crouch at home once and have someone film you from the side. Watch one thing only: does your back lie flat over your thighs or is it propped up at an angle? The simulation says the optimum is a trunk angle of attack of 0 to 2 degrees [2] — nearly horizontal. Almost every newcomer stands far too upright on the first try. Once you have seen that, you understand why ski jumpers polish this position for years even though it is "just sitting while riding".
The in-run crouch is the deep, compact position in the approach: knees strongly bent, trunk forward over the thighs, arms tight to the body [1]. Its only purpose is to minimise drag so the jumper reaches the take-off table at maximum speed. It is pure aerodynamics — and at the same time the loading position for the take-off [3].
Around 90 km/h at take-off [1]; measurements and simulations of the approach phase give 80 to 90 km/h, about 22 to 25 metres per second [2]. That is country-road speed — reached in a few seconds, purely through gradient and posture. Which is exactly why every detail of the crouch counts.
The take-off at the table. It lasts only fractions of a second but sets flight speed, flight angle, angular momentum and body attitude in the air [3]. The in-run crouch is the preparation for it: it delivers the speed and the body position that make this impulse possible in the first place.
Through imitation jumps — the take-off movement without a hill. Comparison with real hill jumps shows that imitation jumps from a rolling platform reproduce the target movement better than jumps from a standing start, and that three of four movement criteria are matched best with jumping boots [4]. For beginners, simple dry-land drills of the crouch are enough [5].
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