Rear Delt Fly: Benefits for Posture and How to Start
The rear delt fly is an exercise where you open your arms out wide against light resistance to work the back of your shoulders, and it is a must because it strengthens the muscles that most desk workers have neglected for years. It is one of my go-to exercises for clients who spend their days hunched over a laptop.
Why the rear delt fly is a must
The rear delt fly mainly works the rear deltoids (the back of your shoulders), along with the rhomboids and middle trapezius, the muscles between your shoulder blades. These muscles pull your arms and shoulders backwards and help hold your shoulder blades in a good position.
The movement pattern is horizontal abduction: moving your arms out to the side and back while your body stays still. Most of us spend our days doing the opposite, with arms forward, typing, driving and scrolling. Many gym routines add to that with lots of chest pressing. The rear delt fly helps balance things out.
It needs only light weights to be effective, which makes it safe and easy to add to the end of a session or do at home with a band. For more back-friendly ideas, see my list of back strengthening exercises.
How it helps in everyday life
Desk posture: stronger upper back muscles can make it easier to sit and stand tall without your shoulders rolling forward.
Reaching behind you: putting on a coat, reaching into the back seat of the car or fastening a seatbelt.
Carrying bags: a strong upper back helps keep your shoulders set when carrying shopping or a laptop bag.
Sport: swimming, tennis, golf and climbing all need strong, balanced shoulders.
Other lifts: a stable upper back makes rows, presses and deadlifts feel more secure.
What it can help prevent
Rounded shoulders: strengthening the back of the shoulders, alongside moving more during the day, may help reduce that forward-slumped posture.
Shoulder niggles: muscle imbalance around the shoulder is commonly linked with discomfort, and balanced strength may help the joint stay healthier.
Neck and upper back tension: some people find that a stronger upper back reduces the achy, tight feeling after long days at a desk, although this varies.
Loss of upper-body muscle with age: regular resistance training helps preserve it.
Who it suits (and who should be careful)
The rear delt fly suits almost everyone, especially office workers, people who already do a lot of pressing, and beginners who want better posture. Because it uses light weights, it is a good choice for older adults too.
Be careful if you have a current shoulder injury, shoulder pain when lifting your arms out to the side, or lower back pain that is aggravated by bending forward. In that case, use a chest-supported or machine version, and check with your GP or physio if pain persists.
How to start safely
Hold light dumbbells (or a band) and hinge forward from the hips with a flat back, or lie face down on an incline bench for support.
Let your arms hang with a soft bend in the elbows and palms facing each other.
Lift your arms out to the sides in a wide arc until they are roughly in line with your body. Think about reaching wide, not squeezing up towards your ears.
Lower slowly over two to three seconds. Keep your neck relaxed and your chin slightly tucked.
Start with 2-3 sets of 12-15 reps with very light weights, two or three times a week.
Easier version: the band pull-apart, done standing with a light resistance band.
Harder version: the reverse pec deck machine or cable rear delt fly for constant tension, or add the face pull for extra upper back work.
FAQs
Does the rear delt fly help posture?
It can help by strengthening the muscles that pull the shoulders back, but posture also depends on how you sit, move and take breaks. Combine it with regular movement for the best effect.
What weight should I use for rear delt flyes?
Lighter than you think. Most beginners do well with 1-4 kg dumbbells, as heavy weights tend to make the upper traps and lower back take over.
Can I do rear delt flyes at home?
Yes. Light dumbbells, water bottles or a resistance band all work well, and a band pull-apart is an easy home alternative.
If you want this coached 1-to-1, my 12-week body transformation in Archway builds exercises like the rear delt fly into a plan around your body and goals, or see my personal training prices.
