TRX Body Saw

What the TRX body saw actually trains

A TRX body saw is an anti-extension exercise: you hold a forearm plank with your feet in suspension straps and push your whole body forward and back in a small sawing motion.

The rectus abdominis does the bulk of the work, holding the ribcage down towards the pelvis as gravity tries to pull the middle of your body towards the floor. The external and internal oblique and transversus abdominis stiffen the abdominal wall against any sideways or rotational drift. The lats and shoulders hold the upper body in place, the glutes keep the hips from dropping, and the erector spinae work alongside the abdominal wall to keep the trunk in one line.

The important idea here is lever length. A plank is only as hard as the distance between your support points and your centre of mass. Push your body forward and that distance grows, which increases the torque trying to fold you at the hips. Pull back and it shrinks.

This is what makes the body saw better than a plank. A plank has no progression except time, and once you can hold one for two minutes, extending to three teaches you nothing. The saw gives you a finely adjustable dial: move two centimetres further forward and it is measurably harder.

Marchetti and colleagues examined abdominal activation during an isometric ab wheel rollout at different shoulder angles and found the demand changes substantially with position, which is exactly the mechanism the saw exploits.

The straps add instability you do not especially need. Sliders on a smooth floor give the same lever change with less fuss, and an ab wheel gives you more range for a fraction of the price.

So this is a good exercise, not a uniquely good one. If you do not own straps, you are not missing much.

Setting up and executing

Set the suspension straps so the foot cradles sit just above the floor. Too high and the exercise becomes something else.

Kneel facing away from the anchor and place both feet into the cradles. Come forward onto your forearms with the elbows under the shoulders.

Straighten the legs, squeeze the glutes and brace the abs with the ribs pulled down. Check that the hips sit level, in line between the shoulders and the heels.

Push the body forward by driving through the forearms, not by pushing with the legs. Go only as far as you can hold the line.

Stop before the lower back begins to sag, then pull back to the start using the abdominal muscles rather than the legs.

Repeat smoothly, for reps or for time.

The mistakes that cost you the most

Hips sagging at the far point is the fault that defines the exercise. Once the lower back drops, the abdominal wall has stopped resisting and the lumbar spine is carrying the load in extension. That is the moment the set ended, whether or not you keep moving.

Piking the hips is the opposite cheat and it is subtle. Lifting the hips towards the ceiling shortens the effective lever and makes the movement almost free, while looking identical from the side.

Pushing with the legs moves the straps forward and leaves your trunk where it was. The forearms drive the movement.

Straps set too high raises the feet and turns the exercise into a partial handstand, loading the shoulders instead of the abdominal wall. Cradles just above the floor.

And going too far too soon is the mistake with actual consequences. Range is the load in this exercise, so adding range you cannot control is exactly the same error as adding fifty kilos to a squat. Add a centimetre at a time.

Sets, reps and rest by goal

Low reps, short range, absolute control.

For muscle gain, three sets of eight to twelve slow saws with a minute rest. For strength, three sets of six to ten with the longest range you can hold, resting ninety seconds. In a fat loss phase, three sets of twenty to forty seconds of continuous sawing with forty five seconds rest.

Progress by range first, then tempo, then a pause at the far position. A two second hold at the hardest point is a substantial jump and needs no equipment change.

Once range and pauses are exhausted, a light weight vest is the only real way to add load, which is the ceiling here.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, and anti-extension work does contribute, though it accumulates volume slowly compared with loaded flexion.

Refalo and colleagues found stopping short of failure produces comparable growth to going to failure, which applies neatly here because the failure point is positional. The set ends when the hips sag, not when the muscle gives out.

Two sessions a week is plenty. This is fatiguing work for a muscle group that also has to survive your squats and deadlifts.

Where it fits in your split

At the end of a session, never at the start.

On push, pull and legs it fits at the end of push day. On a bro split it is the anti-extension movement on ab day. On an upper and lower split it belongs in the full body session. On a full body programme it is a strong finisher when straps are available. On a bodyweight programme it goes anywhere, and a long lever plank substitutes when there are no straps.

Keep it away from heavy compound work. Anti-extension exercises fatigue exactly the musculature that holds your spine in position under a heavy bar, and a tired abdominal wall before deadlifts is a bad exchange.

The case for including it is that most people's trunk training is entirely flexion, and anti-extension work is a genuine gap. The case against is that an ab wheel does the same job through a longer range and costs almost nothing.

Pick one anti-extension movement, do it properly for a block, and progress it. Doing three of them badly is the more common approach and the less productive one.

Variations worth knowing

The slider body saw puts the feet on furniture sliders or a folded towel on a smooth floor, which removes the strap swing and is easier to control, while producing the same lever change.

The ab wheel rollout moves the arms rather than the body and gives you a longer range, which makes it the more complete anti-extension exercise for most people.

The long lever plank is a static hold with the elbows further forward than usual, which parks you at the hardest point of the saw without any movement.

The TRX fallout reverses the setup, putting the hands in the straps and reaching forward overhead, which shifts more of the demand onto the lats and shoulders.

The standard plank is the same position with no movement, and is where anyone whose hips sag should be spending their time first.

And the barbell rollout allows real external load to be added, which makes it the natural progression once bodyweight anti-extension work has become easy.

What the evidence says

McGill's review of core training makes the case for training the trunk to resist unwanted motion rather than to produce it, and anti-extension work is the clearest example of that principle in practice.

Marchetti and colleagues measured abdominal activation during isometric ab wheel rollouts at different shoulder angles and found that involvement changes substantially with body position, which is the mechanism behind the body saw and the reason range is the correct progression variable.

Escamilla and colleagues compared commercial and common abdominal exercises and found meaningful differences in muscle involvement, supporting one or two anti-extension movements rather than a collection.

A further study from Escamilla and colleagues on Swiss ball and traditional abdominal work found added instability does not reliably increase abdominal involvement, a fair caution against assuming straps beat sliders.

Vigotsky and colleagues warned that surface electromyography amplitudes do not translate directly into hypertrophy, so a high activation figure for a suspension exercise settles nothing.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, and this exercise accumulates that volume slowly.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to training to failure, so ending the set when the hips drop is correct rather than a compromise.

Common questions

How far forward should I go?

Only as far as you can keep the line from your shoulders to your heels. That distance is your current load, and it will extend over weeks. Pushing past it does not train the abdominal wall harder; it hands the work to your lower back.

Why does my lower back ache during these?

Because you are going further forward than your abdominal wall can hold, so the pelvis tips and the lumbar spine takes the strain. Shorten the range until the line holds, and treat that shorter range as your working weight.

Is this better than an ab wheel rollout?

No. The rollout has a longer range, adds load more easily and costs a fraction of the price. The body saw is a good option if you already have straps in front of you, but it is not worth buying equipment for.

Do the straps make it more effective?

Not especially. The instability adds a little oblique work and a lot of fiddling. Sliders on a smooth floor give you the same lever change with better control, and the evidence on unstable surfaces does not support the assumption that wobblier means better.

How is it different from a plank?

A plank has one difficulty setting and one progression variable, which is time. The saw changes the lever length continuously, so it gets harder in small, controllable steps. That is the whole reason to choose it.