ChestMachineBeginner

How to Use the Pec Deck

By Bryan Alger, Co-Founder of Gravitus

· Updated Sep 30, 2026

A pec deck, also called a butterfly machine, is a seated chest fly. Set the seat so your elbows sit just below your shoulders, keep your elbow angle fixed and bring the pads or handles together in front of your chest. It trains the chest, with the front delts helping. Most lifters do 3 sets of 10 to 15 reps.

Sets x reps 3 x 10-15

Median 10-rep weight 13060 lbkg men 5022.5 lbkg women

Muscles Chest, front delts

Setup Elbows just below shoulders

1Start. Seat set so your elbows sit just below your shoulders. Back on the pad, arms open wide with a slight bend in the elbows.
2Squeeze. Bring the handles together in front of your chest, pause for a second, then let them open under control.

Watch 3 video demonstrations

Video 1 of 3

Find more video demonstrations in the Gravitus app

Technique

How to use the pec deck

Set the seat so that, holding the handles, your elbows sit level with or slightly below your shoulders. On a machine with elbow pads, your upper arms should be level with the floor.
Set the start lever so the handles begin level with your chest or a little behind it, where you feel a stretch while your shoulders stay on the back pad.
Sit with your back on the pad and your feet flat. Take the handles with a slight bend in your elbows, or rest your forearms on the pads, and keep that elbow angle for the whole set.
Bring the handles together in a wide arc until they meet in front of your chest. Squeeze for a second.
Let them open over 2 to 3 seconds back to the stretch, without letting the plates touch.

Setup

Seat height, pads or handles, and the start lever

Seat heightElbows just below shouldersToo low and your arms ride above your shoulders, which gives the front delts more work and pinches some shoulders. Raise the seat until your elbows drop just below.

Elbow padsThe classic pec deckElbows bent to 90 degrees, forearms on the pads. Push with your forearms and elbows; your hands stay relaxed and the biceps have nothing to do.

HandlesCommon on newer machinesArms nearly straight with a small bend, like a cable fly. The biceps hold the bend. Often a combo machine that also does rear delt flys.

Start leverSets your stretchA lever or pin on each arm sets how far back the rep starts. Begin level with your chest and move back a notch at a time.

The Life Fitness instructions for its pec fly set the seat so the elbows sit slightly below the shoulders with the handles held, and set the start position with a range-of-motion adjuster on each arm (Life Fitness manual). Pads and handles train the same muscle. With a bent elbow against a pad, the pad pushes straight back on your forearm, so the elbow muscles have nothing to hold; with handles, the biceps keep the slight bend, as in a cable fly. No study has compared the two for growth. Use whichever your gym has, and set it up the same way every session so your log stays comparable.

Range of motion

How far back to go

Open your arms until your hands or elbows are level with your chest or slightly behind it, as far as you can control without your shoulders rolling off the pad. That is the stretched end of the rep, and it is worth keeping.

The chest responds to load at long lengths. Over 8 weeks, 15 minutes a day of hard pec stretching, 4 days a week, grew the chest as much as 5 sets of pec deck flys 3 days a week (Wohlann 2024). Nobody needs to stretch that long, but it is a reason not to shorten the stretch to lift a heavier pin.

A stretch you feel at the front of the shoulder instead of across the chest means the start lever is set too far back.

Front of the shoulder pinching

Move the start lever forward one notch. Then check the seat: if your elbows sit above your shoulders, raise it.

Gravitus data

How much weight should you pec deck?

On Gravitus, the median man lifts 130 lb (60 kg) for 10 reps on the pec deck, and the median woman 50 lb (22.5 kg).

Men, typical 130 lb for 10 reps

Most lift: 100 to 170 lb
Top 10% lift: 210 lb or more
Starting out: under 100 lb

Women, typical 50 lb for 10 reps

Most lift: 40 to 70 lb
Top 10% lift: 90 lb or more
Starting out: under 40 lb

Men, typical 60 kg for 10 reps

Most lift: 45 to 77.5 kg
Top 10% lift: 95 kg or more
Starting out: under 45 kg

Women, typical 22.5 kg for 10 reps

Most lift: 18 to 32.5 kg
Top 10% lift: 40 kg or more
Starting out: under 18 kg

One-rep max / 10-rep weight, rounded to 5 lb (2.5 under 40). From 6,520 men and 729 women who log the pec deck on Gravitus, computed Oct 4, 2026 (Brzycki). Methodology
Percentile	Men	Women
25th	130 / 100 lb	55 / 40 lb
Median	175 / 130 lb	70 / 50 lb
75th	225 / 170 lb	95 / 70 lb
90th	280 / 210 lb	120 / 90 lb

One-rep max / 10-rep weight, rounded to 2.5 kg (1 under 20). From 6,520 men and 729 women who log the pec deck on Gravitus, computed Oct 4, 2026 (Brzycki). Methodology
Percentile	Men	Women
25th	60 / 45 kg	25 / 18 kg
Median	77.5 / 60 kg	32.5 / 22.5 kg
75th	102.5 / 77.5 kg	42.5 / 32.5 kg
90th	127.5 / 95 kg	55 / 40 kg

Pec deck numbers do not compare between gyms. Each brand gears its stack through different cams and arm lengths, so the same pin can feel much heavier on one machine than on another. On most machines the pin is the load for both arms together, and many pec decks double as a rear delt machine, so log those sets as a reverse pec deck. Compare yourself to your own log on the same machine and start setting.

Anatomy

Pec deck muscles worked

Chest (pectoralis major)Brings the arms together across the body. The upper and lower portions both grew with pec deck training (Pinto 2025).

Primary

Front deltsHelp bring the arms forward. They do more when your elbows ride above your shoulders.

Secondary

BicepsHold the slight elbow bend on handle machines. On elbow pads they have almost nothing to do.

Stabilizer

Rotator cuff, shoulder blade muscles, coreKeep the shoulders steady and your back on the pad. The machine does most of the balancing.

Stabilizer

Research

What the research says about the pec deck

"It works the inner chest." The chest has an upper (clavicular) and a lower (sternocostal) portion, not an inner and an outer one. Every fiber shortens as your hands meet. Twelve weeks of pec deck training grew both portions by similar amounts (Pinto 2025).
"It does not work the upper chest." It does. In the same study the upper chest grew 17 to 18%, close to the 21% of the rest of the chest (Pinto 2025).
"Flys hit the chest harder than presses." The pec deck, bent-forward cable crossovers and the barbell bench press drew similar chest activity, with no significant difference between them (Schanke 2012).
"Pre-exhaust makes the chest work harder on the press." Doing pec deck flys right before a chest press did not raise chest activity during the press; the triceps worked harder instead (Gentil 2007). The same happened with a fly before the bench press (Brennecke 2009).
"It trains the pec minor." No pec deck study has measured it, and surface EMG cannot reach it. It pulls the shoulder blade forward, which the "back on the pad" cue works against.

Compare

Pec deck vs cable fly vs dumbbell fly

Attribute	Pec deck	Cable fly	Dumbbell fly
Hardest point	Set by the machine	Set by pulley height and stance	In the stretch, nothing at the top
Balance needed	None, back on a pad	Some, split stance	Some, on a bench
Angles	One fixed path	High, mid or low	Flat, incline or decline
Best for	Taking sets to failure safely	Choosing the angle	Loading the stretch

Verdict

All three train the whole chest. The pec deck, bent-forward cable crossovers and the bench press drew similar chest activity (Schanke 2012). The pec deck is the easiest to set up the same way every week, which makes progress easy to track.

Programming

Pec deck sets, reps and progression

3Sets

10-15Reps

0-2Reps left

Stop each set 0 to 2 reps short of failure. Sets taken close to failure build muscle across a wide range of reps (Schoenfeld 2021), so 10 to 15 is a range, not a rule. In untrained men, one hard set of pec deck flys grew the chest as much as three sets over 12 weeks (Pinto 2025), so 2 to 3 sets is plenty.

Do it after your presses unless the pec deck is your priority that day. With the bench press first, lifters got more bench press reps; with the machine fly first, more fly reps; total reps were about the same (Senna 2019).

Add reps before weight. When every set reaches 15 with the same start setting, move up one plate and drop back to 10.

Form

Common mistakes

Seat too lowYour arms ride above your shoulders and the front delts take over. Raise the seat until your elbows sit just below your shoulders.
Start lever too far backThe arms drag your shoulders forward off the pad and the stretch lands in the front of the shoulder. Move it forward a notch.
Bending and straightening the elbowsOn handle machines the fly turns into a press. Set a slight bend and keep it.
Pushing with the hands on a pad machineYour wrists and biceps get involved. Push through your forearms and elbows with your hands relaxed.
Letting the stack touchResting the plates between reps unloads the stretch. Stop just short and start the next rep.

Variations

Pec deck variations

Reverse pec deckFace the pad and pull the handles back. Trains the rear delts and upper back on the same machine.

Single-arm pec deckOne side at a time, which evens out a weak side. The 12-week pec deck study trained each arm this way (Pinto 2025).

Machine flyA handle-only fly machine. Set the seat and start lever the same way.

Cable FlyTwo pulleys instead of a pad, so you choose the angle.

Dumbbell FlyOn a bench with dumbbells. Heaviest in the stretch, nothing at the top.

FAQ

Questions people ask

What muscle does pec deck work?

The chest (pectoralis major), upper and lower portions, with the front delts helping. On handle machines the biceps hold the elbow bend.

Is pec deck push or pull?

Push. Your chest and front delts move your arms forward and across your body, the same muscles as the bench press, so it belongs on push day.

Is pec deck isolation or compound?

Isolation. Only the shoulder moves; your elbow angle stays fixed. That is why it works best after a compound press.

Does pec deck work upper chest?

Yes. Over 12 weeks of pec deck training, the upper chest grew 17 to 18%, close to the 21% of the rest of the chest (Pinto 2025).

Does pec deck work inner chest?

There is no separate inner chest. The whole pectoralis major shortens as your hands meet, and pec deck training grew its upper and lower portions by similar amounts (Pinto 2025).

Can pec deck replace bench press?

For chest work, largely; the pec deck and the bench press drew similar chest activity (Schanke 2012). It trains no triceps and no pressing strength, so keep a press if you want a bigger bench.

How much weight should I pec deck?

For 10 reps, the median on Gravitus is 130 lb (60 kg) for men and 50 lb (22.5 kg) for women. The strongest quarter lifts 170 lb (77.5 kg) and 70 lb (32.5 kg) or more.

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