The sternum strap connects the two shoulder straps across the chest, and correct adjustment comes down to two separate settings: height on its webbing track, and tension once buckled.
Setting the height
Most sternum straps slide up or down a short track sewn to each shoulder strap. The right height sits roughly one to two inches below the collarbone, across the upper chest rather than near the throat or down near the ribs. Too high, it can rub the neck or interfere with head turns; too low, it does less work keeping the shoulder straps aligned and can press against the diaphragm during heavy breathing on a climb.
Setting the tension
Buckle the strap and pull it just tight enough that the shoulder straps stop drifting outward with each stride, but not so tight that it compresses the chest. A sternum strap cinched too far is a common, easily overlooked cause of chest tightness on long climbs, since it can restrict the ribcage's normal expansion during deep breathing.
Where it fits in the adjustment order
The sternum strap is adjusted after the hipbelt, shoulder straps, and load-lifter straps, and before hipbelt stabilizer straps. It plays no role in transferring pack weight — that's the hipbelt's job — so setting it earlier in the sequence, before the load-bearing straps, doesn't help and can mask problems with the fit underneath it.
Quick troubleshooting
- Chest feels restricted on climbs: loosen the strap by an inch or two; tension, not height, is usually the cause.
- Shoulder straps still slide outward: tighten slightly, or check that the strap sits at chest height rather than too low.
- Rubbing near the throat: slide the strap down its track to a lower position on the chest.