So what exactly is a sway back?
A sway back is where the natural inward curve of the spine at the back waist is exaggerated. It could be due to the backward tilt of the thorax, or the forward tilt of the pelvis, or a bit of both.
It causes the vertical distance between the bustline and the hipline to be shorter than normal at the centre back (CB). The side seam remains of normal vertical length:
How does this affect the fit of garments?
Essentially the centre back length (CBL) of the garment appears too long. The appearance depends on whether the garment is fitted or loose:
- In a fitted garment, horizontal wrinkles will form across the back waistline. With a sway back these wrinkles will be most pronounced at the CB, and they will stop short of the side seam which remains flat.
- Looser garments may balloon above the back waist, or the hipline/hemline falls longer at the centre back while the side seams swing forward.
Other issues easily confused with a sway back:
Browsing online, I saw the following fit issues frequently confused with a sway back problem:
- A short (high) waistline – on a fitted garment this causes horizontal wrinkles that extend into the side seams and front bodice. To fix this the whole bodice needs shortening, not just the CB.
- A large back high hip, or prominent buttocks – tightness in these areas causes the fabric to “ride up”. The garment needs to be made wider in these areas to prevent ride up.
- An erect upper back – excess fabric length in the upper back may drop down to the waist area, and to prevent this the complete upper back requires shortening.
- A prominent front or bust – insufficient fabric length in the upper front may pull up the front waist, causing drag lines towards the back waist. The front needs to be lengthened to solve this, and possibly widened also.
- Looseness at the back waistline due to insufficient waistline reduction. The vertical dart shaping should be increased or sculpted for a closer fit.
- Diagonal wrinkles – these can be caused by strain from another direction, eg a prominent bust, or overshaped side seams. Waist reduction should be relatively evenly spaced around the body, not just at the side seams, to prevent these.
However a sway back can exist in conjunction with these fit issues. I also have a short waist, erect back, and a large back high hip. On my tank top, all these issues were contributing to wrinkles across the back waistline. In fact, a sway back was probably the least of my worries!
I recommend fixing these other problems before determining whether a sway back adjustment is required – it may not be necessary after all!
So – how do we adjust for a sway back if it is necessary?
Simple – we reduce the centre back length! The side seam remains unchanged.
First try the garment on and pin out the excess fabric in a horizontal tuck, beginning at the CB and tapering to zero at the side seams:
Measure the total length that you need to reduce – it is usually about 1 – 1.5cm (1/2″). If you need to reduce much more than this, I would definitely check that some of the fit issues mentioned above are not present.
In this example my folded tuck measures 6mm, so I need to reduce the CBL by 12mm in total.
The pattern alteration undertaken depends on whether the garment has a waistline seam, a CB seam or no seams:
- For skirts or trousers:
At the CB, ensure the waistline and CB seam remain square:
- For garments with a horizontal waistline seam:
Scoop out the bodice panel as well as the skirt, enough on each so the waistline seam remains in the correct anatomical position. Fold the darts closed before cutting and square the waistline at the CB like above:
- For garments with a CB seam and no horizontal waistline seam:
Smooth the lines of the CB and side seams (blue dotted line):
The grainline will need to be redrawn – here I have maintained the grainline of the skirt so that it hangs correctly, for a top I would probably maintain the grainline of the bodice:
- For garments with no back seams:
On the half-pattern, slash and overlap your pattern the width of your horizontal tuck as above.
Redraw the CB fold between the CB neck and CB hem:
Square the hem to the centre back:
Trace around the side seam to the CB neck. The CB neck should be square to your new CB fold if it previously was:
You can see the old outline in pencil, and that the back waistline is now larger. To alter this, match the underarm point and side hem points like so:
And redraw the new side seam shaping (line with a tick):
This method is basically what I use for seamless backs, and is the same as that described in Aldrich. But see how it also increases the back bodice width? To prevent this I usually redraw the side seam shaping from the hem directly to the shoulder point instead.
There is also another method I discovered, documented here. This produces a very similar result to mine, but I find the shoulder angle becomes too square for my liking. You might like to try it out to see what you think though.
More for pattern geeks: