Obliques

The obliques are two layers of flat muscle at the sides of the abdomen: the external oblique on the outside and the internal oblique beneath it. With the transversus abdominis underneath them, they form the three flat muscles of the abdominal wall. Their fibres run in different directions and cross each other, which strengthens the wall (TeachMeAnatomy). They turn the trunk and squeeze the abdomen, and they are the muscles you feel working when you twist round in your chair.

Where are the obliques?

• External oblique. The largest and most superficial of the flat muscles. It starts on ribs 5 to 12 and runs down and inwards to the top of the pelvis and the pubic bone. It is supplied by nerves from the lower chest, T7 to T12 (TeachMeAnatomy).
• Internal oblique. Smaller and thinner, with fibres running up and inwards, at right angles to the external oblique. It starts from the groin ligament, the top of the pelvis and the fascia over the lower back, and attaches to ribs 10 to 12 (TeachMeAnatomy).

Towards the front, both turn into broad flat tendons that wrap around the “six-pack” muscle, the rectus abdominis, and meet in the midline (TeachMeAnatomy).

What do the obliques do?

• Turn the trunk. The external oblique rotates the trunk to the opposite side, and the internal oblique to the same side (TeachMeAnatomy). Turning to the right therefore uses the left external and the right internal oblique together.
• Squeeze the abdomen. Working on both sides, the internal oblique compresses the abdomen. The abdominal wall muscles also help with forceful breathing out and with coughing (TeachMeAnatomy).
• Help hold upright postures. In 20 healthy adults, the internal oblique, together with the lumbar multifidus, was less active in slumped sitting and in “sway” standing than in upright postures (O’Sullivan et al., 2002). How you sit up matters too: sitting tall by lifting the chest used less internal oblique and more external oblique than sitting tall by rolling the pelvis forward (O’Sullivan et al., 2006).

Do strong obliques protect your back?

This idea grew out of research on “core stability”. In a 1996 study of 15 people with low back pain and 15 without, the deepest abdominal muscle, the transversus abdominis, switched on later in the people with pain when they moved an arm quickly. The other trunk muscles measured showed only isolated differences (Hodges & Richardson, 1996). Stabilisation, or core stability, exercise went on to become the most commonly used form of physiotherapy treatment for this kind of back pain in the UK (Smith et al., 2014).

Trials have since tested core stability programmes. A review of 29 studies found stabilisation exercises slightly better than any alternative treatment or no treatment for long-term pain and disability, but by amounts too small to matter clinically, and no better than other forms of active exercise. The authors described the evidence as strong (Smith et al., 2014). For non-specific low back pain, no single type of exercise has been shown to beat the others.

Of nine exercises tested with muscle sensors in 30 healthy people, the side-bridge activated the external oblique strongly enough for the authors to suggest it for strengthening (Ekstrom et al., 2007). Related pages: bird dog exercise and Does Pilates help back pain?

The obliques at a desk

Turning in your chair to reach a drawer or talk to a colleague is oblique work. Seated twists are part of Bavelu’s desk sessions, designed and filmed by physiotherapists; one of them, a twist using the chair back, is on upper back stretches. More on the lower back in lower back pain from sitting and on the lumbar spine.

When to see a doctor

Pain at the side of the trunk is not always muscular. Back pain can be referred from other organs, such as the kidneys, or from an aortic aneurysm (WHO). Ask for an urgent GP appointment or contact NHS 111 if back pain comes with feeling hot, cold, shivery or generally unwell, or is severe and getting worse quickly, and call 999 if it comes with chest pain (NHS). These are among the red flags for back pain.