Core Sits: how, why, and when to do them

Core Sits

What are they?

The core sit is an isometric trunk exercise that adopts the principles of the McGill Curl-Up. The McGill Curl-Up is one of three core exercises designed by spine expert Dr. Stuart McGill to address lower back pain. 

The starting posture is with hands under the arch of the lower back, one leg bent at the knee and the other flat on the floor. First, elbows are raised from the floor. Then, the head and shoulders are elevated a short distance. The tendency for many is to curl up too far: when done correctly, the curl up is a subtle movement- just enough to engage the recuts abdominis- with a short (6-10 second) hold. 

Why Do them? 

The spine is an incredibly unique structure, with some very complex demands. It’s a stack of vertebrae that must bear load, yet be flexible. In order to facilitate this stability through range, we have a kind of muscle guy wire system, with several muscle groups attaching to and surrounding the spine. These muscles co-contract (work together) to brace, support, and offload the spine during movement/loading. 

To be able to fulfil this role, these stabilising muscles must be able to switch on (at relatively low levels of force) for sustained periods of time. Therefore, to be functionally specific, training for this muscle system must emphasise endurance and motor control over strength and hypertrophy.   

This is the foundation of the core sit: it’s an exercise that builds endurance in the muscles that create spinal stability, which is an important pre-requisite for tolerating the loads necessary to build strength through a range of motion. 

What muscles do they work? 

The core sit is one of our favourite exercises for developing spinal stability according to the aforementioned training principles, as it challenges the entire abdominal wall. 

Have you ever observed someone wearing a back belt when lifting heavy objects? Perhaps an Olympic lifter, or a furniture removalist. The idea behind this is for the belt to compress the abdomen and torso. The person breathes out against the belt to increase abdominal pressure, thereby stabilising the spine while lifting heavy loads. 

What many people don’t know is we all have an in-built back belt in the form of the abdominal hoop: a group of muscles at the front (abdominal fascia), back (lumbodorsal fascia), and sides (active abdominal muscles) of the trunk. When these muscles co-contract, they increase abdominal pressure and stabilise the spine. This is what’s known as ‘abdominal bracing’. 

The core sit involves purposeful abdominal wall contraction. By generating an isometric contraction, it engrains motor patterns and develops endurance of the abdominal muscles which contribute to spinal stability through a range of motion, building the foundation for eventual strength and power training. 

When can they be applied in a rehabilitation setting? 

The core sit is an incredibly effective lower back and trunk stability exercise, and is therefore a staple in my long-term rehab plan for patients with lower back pain. 

When treating someone in the acute stages of a lower back pain episode, I’ll often prescribe the core sit in combination with a side plank variation, and a front plank or bird-dog variation. As per the ‘McGill Big 3’, this combination of exercises builds endurance in the muscles at the front, back, and sides of the trunk, creating a solid foundation of core strength and neuromuscular performance to create spinal stability during virtually any task. 

Endurability in these muscles is the precursor for building strength. Therefore, my exercise programs emphasise endurance first, then progress to stability and strength-based exercises. At this stage, I’ll often use the core sit as a warm up, in order to prime the appropriate muscles to optimize spinal stability during subsequent exercises (including compound lifts such as squats, deadlifts, and overhead presses). 

What’s my number one tip for performing the exercise? 

Firstly, don’t come up too far! Remember, this isn’t a strength building exercise- it’s an endurance one. The head and shoulders only need to come up a short distance in order to engage the rectus abdominis, and that’s where you hold. 

Secondly, to progress the exercise, do so by increasing the repetitions of exertions rather than increasing the duration of each hold.