reckonerMachine pec fly
The pec deck: a seated machine whose arms swing in to meet in front of your chest. It is a fly with the path built in, so the machine holds the arc and your job is to move through it under control. It is also one of the few chest exercises tested on its own for growth, and in that trial both the upper and the lower chest grew1.
Handles at chest height, soft elbows.
- Pattern
- Horizontal push
- Trains
- Chest, front delts
- Kit
- Machine pec deck
- Loading
- A weight you choose
- Reckoner prescribes
- 3 sets of 8 to 12 reps at RPE 8
- Progression step
- 5 kg once the top of the range is clean
- Skill
- Simple to learn
- Recovery cost
- Low
- Not prescribed if you have declared
- Shoulder
Muscles worked
How to do it
Set the seat so the handles sit at chest height
Sit back against the pad and move the seat until the handles, or the elbow pads if your machine has them, line up with the middle of your chest. Too high and your shoulders shrug into the set. Too low and your arms sweep up instead of across.
Set where the arms start
Many machines have a lever or a pin that sets how far back the arms begin. Start with the handles roughly in line with your chest seen from the side, not behind you, and go wider only as far as your shoulders are comfortable.
Sweep the handles together
Keep a soft, fixed bend at each elbow and bring your arms around until the handles meet in front of your chest. Moving the arm straight across the body is the action that leans on the middle of the chest2.
Open slowly to where you started
Let the handles travel back under control rather than letting the stack pull them. Stop at the width you set, then begin the next rep.
What goes wrong
Starting with the arms too far back
The open end is where the front of the shoulder is stretched with the stack pulling on it. If the handles start behind the line of your chest, set the start narrower. Range is something you own, not something the machine pulls you into.
Pressing instead of sweeping
The elbows bend on the way in and straighten on the way out, and your triceps join the set. It feels stronger because it is a different exercise. Fix the elbow angle and let the shoulder be the only joint that moves.
Letting the stack slam
Losing control on the way back drops the plates and yanks the shoulder at its widest point. If you cannot open slowly, the pin is too heavy for this set.
How Reckoner progresses this lift
Six weeks of this lift, from 30 kg, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 3 x 8 at 30 kg | More reps 8 → 9 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 2 | 3 x 9 at 30 kg | More reps 9 → 10 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 3 | 3 x 10 at 30 kg | More reps 10 → 11 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 4 | 3 x 11 at 30 kg | More reps 11 → 12 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 5 | 3 x 12 at 30 kg | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 2 x 12 at 30 kg | Load up 30 kg → 35 kgYou hit the top of the range with three reps left in the tank (RPE 7), so the weight on the machine goes up 5 kg to 35 kg. The weight went up, so the reps come down to eight. You are now working 8 to 12. The lighter week is over, so this is back to three sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Is the pec deck the same as a machine pectoral fly?
Yes. Pec deck and machine pectoral fly are two names for the same machine, and Reckoner keeps it as one movement. The rear delt fly some of these machines also do, sitting the other way round, is a different exercise.
Do I need a fly if I already press?
Not necessarily. A review of the trials comparing single joint exercises like this one with presses found no difference in upper body growth, and no extra effect from adding them to a pressing program3. Use the pec deck because you like it or because the bench is taken, rather than because a press is missing something.
How much does it take?
In the one trial of this machine on its own, untrained men trained it for 12 weeks and grew the upper and lower chest by 17 to 21 per cent on ultrasound, and one set to failure did as well as three1. They were untrained men in their twenties, so do not read it as the dose for a trained lifter.
Similar movements
Reckoner eases the load first when this lift stalls, and offers one of these only if it stalls again after that. A lift already as light as your kit goes has no load left to ease, so the offer comes straight away. Three of the five have pages so far.
Sources
- Pinto and colleagues, Journal of Strength and Conditioning Research, 2025. Pectoralis clavicular and sternocostal thicknesses increase similarly in response to one and three sets of pec deck resistance training in untrained young men fifteen untrained young men training the pec deck alone for 12 weeks, with clavicular and sternocostal pectoralis thickness rising 17 to 21 per cent and no difference between one set and three
- Paton and Brown, Journal of Electromyography and Kinesiology, 1994. An electromyographic analysis of functional differentiation in human pectoralis major muscle horizontal flexion of the shoulder drawing on the middle segments of the pectoralis major whatever the degree of shoulder flexion; a small, older study of isometric efforts in eight men, cited from its abstract
- Gentil, Fisher and Steele, Sports Medicine, 2017. A review of the acute effects and long-term adaptations of single- and multi-joint exercises during resistance training 23 studies reviewed, with long term upper limb trials finding no difference in size or strength between single and multi joint exercises and no added effect from including single joint exercises in a multi joint program