Bicycle Crunches

What the bicycle crunch actually trains

A bicycle crunch is a floor based abdominal exercise where you alternate drawing one knee towards the chest while rotating the torso towards it, extending the other leg out straight as you go.

The rectus abdominis produces the flexion that holds your shoulders off the floor. The external and internal oblique produce the rotation. The hip flexors, mainly psoas major, iliacus and rectus femoris, drive the cycling action of the legs.

That last part is worth stating plainly rather than treating it as a fault. Any exercise in which the legs move relative to the trunk uses the hip flexors, and trying to cue them out of it just makes the exercise worse.

What makes it more interesting than a plain crunch is the rotation. Most abdominal work is pure flexion, which trains the rectus abdominis properly and the obliques only incidentally. Adding rotation while already holding a flexed position loads the obliques through their actual job, which is turning the trunk and resisting it being turned.

Escamilla and colleagues measured muscle activity across a long list of common and commercial abdominal exercises and found the bicycle manoeuvre near the top for both rectus abdominis and oblique activity. That is the honest basis for its reputation, and it is a reasonably strong one.

What it cannot do is progress. You have your bodyweight, your leverage and your tempo, and that is the entire toolkit. As a starting point, fine. As the only abdominal work you do for two years, it is the reason nothing has changed.

Setting up and executing

Lie on your back with the knees bent and the feet off the floor. Put your fingertips lightly behind your ears, not laced behind your head.

Press your lower back flat into the floor before you start, then lift your shoulder blades clear of it and keep them there for the whole set.

Draw one knee in towards your chest while the other leg extends straight and low, close to the floor but not touching it.

Rotate your ribs towards the bent knee. Think about turning the ribcage, not about where the elbow ends up. Pause for a beat at the end of the rotation.

Reverse the legs smoothly, keep the shoulders lifted, and alternate for the full set at a pace slow enough that each rotation is deliberate.

The mistakes that cost you the most

Touching elbow to knee is the fault that defines this exercise, and it comes from a badly chosen instruction. Aiming for the touch makes you pull the arm across your body while the ribcage stays where it is, which produces a shoulder movement rather than an oblique one. Rotate the torso and allow the elbow to arrive as a consequence, or not at all.

Racing through reps is the second. At speed the legs swing under their own momentum and the abdominals stop doing the work of controlling them. Slow enough to feel each rotation is the right tempo, which usually halves the rep count people are used to.

Pulling on the neck happens once fatigue arrives, particularly with the hands laced behind the head. Fingertips behind the ears and elbows wide removes the temptation.

The lower back arching off the floor as the leg extends means the leg is going lower than your current strength supports. Keep it higher. The extended leg's height is the difficulty dial on this exercise, and there is no shame in using it.

Dropping the shoulders between reps unloads the abdominals completely, turning a continuous set into a series of separate easy ones. Stay up until the set ends.

Sets, reps and rest by goal

Since you cannot add weight, the variables are reps, tempo and leg height.

For muscle gain, three sets of fifteen to twenty five per side with a minute rest. For strength, three sets of twelve to twenty per side with ninety seconds, keeping the extended leg lower and the tempo slower. In a fat loss phase, three sets of twenty to thirty per side with forty five seconds.

Sets of forty fast reps per side are a conditioning drill, not abdominal training. If you can do them, slow down and lower the free leg until twenty is genuinely hard.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, and the abdominals are not exempt from that. Three to six hard sets of direct abdominal work, twice a week, is a sensible target. Fifteen easy sets is not better.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to going all the way, which is useful here because the last few reps of a bicycle crunch are usually the ones where the neck starts pulling and the rotation disappears.

Once the exercise stops being hard at a controlled tempo with the leg low, stop adding reps and move to something you can load. Abdominals respond to progressive tension the same way every other muscle does.

Where it fits in your split

At the end of a session, on any day you like.

On push, pull and legs, legs day is the natural home, since the hip flexor involvement pairs badly with heavy squatting beforehand rather than after. On an upper duo split, tack it onto either session. On a bro split it fills space on arms or legs day. On upper and lower plus full body, put it in the full body session. On a bodyweight programme it fits anywhere, since it needs nothing at all.

Do not put it before heavy squatting or deadlifting. Fatiguing the trunk before a lift that depends on trunk stiffness is a bad trade. Twice a week is enough, since the abdominals recover like other muscles and do not need daily attention.

The realistic role for this exercise is as one of two or three abdominal movements, covering rotation, while something loaded covers flexion. On its own it is incomplete.

Variations worth knowing

The standard crunch is pure flexion with no rotation, which is simpler and much easier to load with a plate or a cable.

Alternating heel taps are a far easier lateral flexion drill, useful if holding the crunch position for a full set is not yet possible.

The cable woodchop is the loadable version of the rotational element, standing, with a stack you can add to week by week.

A hanging knee raise with a twist takes the same rotational idea to a bar and adds substantial hip flexor and lower abdominal demand.

The Russian twist is seated rotation against a held weight, easier to load than a bicycle crunch though through a shorter range.

And the dead bug is the anti-movement counterpart, where you resist rotation and extension rather than producing them, which trains the same muscles in the opposite role.

What the evidence says

Escamilla and colleagues compared commercial and common abdominal exercises and found the bicycle manoeuvre produced high rectus abdominis and oblique activity relative to most alternatives, which is the main empirical case for the exercise.

Escamilla and colleagues also examined traditional and non traditional abdominal exercises, finding that variations differ mainly in how much oblique involvement they add on top of a similar flexion demand, which is exactly what the rotation here does.

Escamilla and colleagues' comparison of Swiss ball and traditional abdominal work reinforces the point, that changing position or stability demand shifts the balance between rectus abdominis and oblique rather than producing a different exercise.

Vigotsky and colleagues cautioned that surface electromyography amplitudes should not be read as a direct ranking of how much a muscle will grow, which is why the strong activity numbers for this exercise are a reason to include it rather than proof it is the best.

McGill's review of core training argues the benefits are real but narrower than the marketing suggests, and that transfer to performance and to injury reduction is far less established than commonly claimed. Treat abdominal work as muscle training, not insurance.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, which supports a small number of genuinely hard abdominal sets over long unloaded circuits.

Refalo and colleagues found training close to failure is not required for growth, so there is no need to grind out reps once the rotation has degraded into a neck pull.

Common questions

Should my elbow touch my knee?

No, and aiming for it actively harms the exercise. The touch encourages you to pull the arm across while the ribcage stays still, which is a shoulder movement. Rotate the ribs towards the knee and let the elbow finish wherever it finishes.

How is this different from a normal crunch?

The rotation. A standard crunch is pure flexion with only incidental oblique work; the bicycle adds trunk rotation, so it covers both. The trade is that a crunch is far easier to load.

Why do I feel it in my hip flexors?

Because they are working, which is the correct outcome for an exercise where your legs move. Psoas major, iliacus and rectus femoris drive the cycling action. It is not a technique error and there is nothing to fix.

Will these give me a flatter stomach?

They will build the abdominal muscles. They will not remove fat from over them, because spot reduction does not work. Visible abdominals are a body fat outcome; abdominal training is what makes them worth seeing when they arrive.

How many should I do?

Enough that the last few reps are genuinely hard at a slow tempo with the free leg held low, usually fifteen to twenty five per side. If you can exceed that comfortably, make the exercise harder rather than longer.