Knees-to-elbows pulls the knees up to the elbows in a hang. Learn kip, trunk tension and tempo in five steps, with milestones and a list of typical mistakes.
Knees-to-elbows (K2E) means: hanging from the bar, you pull both knees up to your elbows. It is the stepping stone to toes-to-bar and a movement where the swing from kipping does most of the work. The honest answer: K2E is easier than toes-to-bar, but not "easy" – without a clean kip you tire your abs before your grip gives out.
Measurements of kipping show this. In a study with 11 athletes, the rectus abdominis worked 28.7 percentage points harder in a kipping pull-up, the hip flexor 26.1 – while the biceps worked 26.7 percentage points less [1]. At the same time, the hip angle was almost 49° larger: the legs swing strongly [1]. A second study with 11 athletes found the same trend: more activity in legs and abs, less in the upper body [2].
Realistically you learn K2E after a few weeks of two or three sessions (experience, not study data). Speed comes once the swing is in place.
Hang from the bar with shoulders slightly pulled down and the body stretched. The hanging position is the base for everything after.
Milestone: 3×20 seconds without swinging, shoulders not by your ears.
Swing between hollow (belly forward, ribs down) and arch (chest forward). The swing comes from the shoulders, not the arms. In a study with 11 athletes, kipping and butterfly pull-ups used the leg muscles and abs more than the strict one [2].
Count in your head: hollow – arch – hollow. In the arch you push the chest forward through the arms, in the hollow you roll the ribs toward the pelvis (practice, not study data).
Milestone: 10 even swings.
Pull the knees up to the hips in a controlled way, without swinging. This is harder than it looks: in a hanging leg raise with straight legs, the abdominal muscle and external oblique reached over 130 percent and 88 percent of maximal activity; the spine carried about 3,000 newtons, the weight of roughly 300 kilograms [3]. That was the straight-leg version; with bent knees it is easier (TRANSFER, not a direct value for K2E).
Milestone: 3×8 clean reps.
Come from arch into hollow and pull the knees up until they touch the elbows. The swing gives the start, the abs guide the knees. In a hanging knee-up with straps, the abs were also among the most strongly challenged muscles in a measurement with 21 people [4].
Timing matters: only when your body swings back in the arch and the swing reverses do you pull the knees. If you pull too early, you kill the swing (practice, not study data).
Milestone: 5 reps in a row.
Chain the reps with a continuous swing. The more even the rhythm, the less strength you need.
Milestone: 3×10, later 15 in a row.
In a survey of 308 German CrossFit athletes, the shoulder and knee were injured most often [5]; among 456 Czech athletes, the shoulder came second after the spine [6]. So practice with a clean hang and build sets slowly. Stop if the shoulder stabs (not: if your abs burn).
This guide explains and motivates but does not replace supervised training – have your kip filmed from the side or checked by a coach.
When pulling up, do not think of the knees but of the bar: mentally pull the bar down toward you and the knees come by themselves. This image takes load off the arms and joins arch and hollow into one beat (practice experience, not study data).
It depends on trunk strength and rhythm. Realistically a few weeks of two or three sessions (experience). If you have a clean kip swing, you are faster.
In K2E you pull the knees up to the elbows, in toes-to-bar the feet up to the bar. Toes-to-bar needs more mobility and trunk strength. K2E is the logical stepping stone.
In competition yes, for practice no. With kip the abs work harder and the biceps less [1] – that makes sets longer but the start more complex.
Yes. In a straight-leg hanging leg raise the abdominal muscle reached over 130 percent of maximal activity [3]. K2E is easier but trains the same pattern.
Usually you hang slack or pull too much with the arms. Hang actively, let the swing do the work and use chalk or grips. The kipping measurement shows that with swing the biceps works less [1] – that spares the arms, and you can last longer because the swing takes over part of the work.
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