The McGill Big 3 are three specific core exercises designed to stabilize the spine without placing harmful load on it: the curl-up, the side bridge, and the bird-dog. They were developed by Stuart McGill, a spine biomechanics researcher who spent 30 years as a professor at the University of Waterloo studying how the lower back gets injured and how it heals. The exercises are isometric, meaning you hold positions rather than moving through repetitions, and they’re built around one central idea: a strong core protects the spine by limiting excess motion, not by creating it.
Why These Three Exercises
Most people think of core training as crunches, sit-ups, or planks. McGill’s research found that true spinal stability comes from balanced stiffness across the entire ring of muscles surrounding your trunk. That includes the front abdominal muscles, the obliques along the sides, the deep back extensors running along the spine, and the muscles connecting the ribs to the pelvis. No single exercise hits all of them equally, so McGill selected three that, performed together, cover the full circuit.
The exercises create what’s essentially a muscular brace around your spine. This stiffness has been shown to persist even after a session ends, which is part of why the routine works well for people dealing with joint instability from overuse or overload. The stiffness also scales to what you’re doing: your body learns to brace harder for heavy lifting and less for everyday movements like standing up from a chair.
The Modified Curl-Up
This is not a crunch. The range of motion is tiny, and your lower back stays in its natural curve the entire time.
Lie face-up on a firm surface. Slide one heel toward your buttock so that knee is bent, and keep the other leg straight. Place both hands underneath the small of your back, filling the natural curve. From there, lift your head and shoulders just barely off the ground. A useful cue: imagine your head is resting on a bathroom scale, and you’re simply lifting enough for it to read zero. Your neck stays straight, your lower back doesn’t flatten, and the movement comes entirely from your upper torso. Hold, then lower back down.
The curl-up primarily targets the rectus abdominis (your “six-pack” muscles), which research shows activate to roughly 30% of their maximum during bridging and stabilization exercises. That moderate level of activation is intentional. The goal is endurance and control, not maximum force.
The Side Bridge
The side bridge loads the obliques and the quadratus lumborum, the deep muscle connecting your lowest rib to your pelvis. These muscles resist lateral bending and rotation, two movements that put the lower back at risk during daily life and sport.
Lie on your side with your forearm flat on the floor and your elbow directly under your shoulder. Place your opposite hand on the shoulder that’s facing up to help lock your torso in position. Pull your feet back so your knees are bent to about 90 degrees. Lift your hips off the floor and hold, keeping a straight line from your head to your knees. That’s the beginner version. The progression is to straighten your legs and support yourself from your feet instead of your knees, which significantly increases the demand on your lateral core.
Hold each side for 8 to 10 seconds. Because this exercise is unilateral, you’ll perform it on both sides in every set.
The Bird-Dog
The bird-dog trains the back extensors and the deep obliques in a cross-body pattern. Electromyography studies show it produces the highest activity in the internal oblique on the side of the raised arm and in the back extensors on the opposite side, which mirrors how your trunk actually stabilizes during walking and running.
Start on your hands and knees with your hands under your shoulders and knees under your hips. Extend one leg straight back while simultaneously raising the opposite arm forward. The key cue that separates McGill’s version from the generic exercise: actively kick your heel backward rather than just floating the leg up, and push forward through your hand as though pressing into the ground from your shoulder. This engages your posterior chain and upper back muscles rather than just waving your limbs around. Hold for 8 to 10 seconds, return to the starting position, then switch sides.
Sets, Reps, and Hold Times
McGill recommends a reverse pyramid structure. You perform three sets of each exercise, starting with the most repetitions and decreasing with each set. A typical starting point looks like this:
- Set 1: 8 reps
- Set 2: 6 reps
- Set 3: 4 reps
Each rep is held for no more than 8 to 10 seconds. The reasoning behind this is that repeated shorter holds build muscular endurance more effectively than a single long hold, while also reducing the fatigue that leads to form breakdown. As your endurance improves, you add reps to each tier (10-8-6, then 12-10-8, and so on) rather than increasing hold duration.
The descending pyramid structure also matters for safety. Your muscles are freshest at the start, so you do the most work then. As they fatigue across sets, the reduced volume helps you maintain clean form through the end of the session.
Who They’re Designed For
The Big 3 were originally developed for people with chronic, non-specific low back pain, meaning back pain without a clear structural cause like a fracture or disc herniation requiring surgery. A study in the Journal of Physical Therapy Science found that McGill’s stabilization approach increased trunk muscle coordination and reduced pain and functional disability in this population. The exercises are specifically designed to strengthen the lumbo-pelvic region without loading the lumbar spine, which is what makes them different from conventional core work.
They’ve since been adopted much more broadly. Powerlifters and kettlebell athletes use them as warm-ups to “turn on” spinal stiffness before heavy sessions. Office workers with stiff, achy backs use them as daily maintenance. Physical therapists program them as a foundation before progressing clients to more demanding movements. The routine takes about 10 to 15 minutes, which makes it easy to add to whatever you’re already doing.
Common Mistakes to Avoid
The most frequent error across all three exercises is making the movements too big. The curl-up should barely lift your shoulders off the ground. The bird-dog should keep your hips level, not rotating toward the ceiling as your leg extends. The side bridge should form a straight line, not a pike at the hips. These exercises are about controlled, small-range holds, and expanding the range defeats the purpose by loading the spine in the positions McGill’s research identifies as risky.
Another common mistake is holding your breath. Bracing your core does not mean holding your breath. You should be able to breathe normally throughout each hold. If you can’t, you’re bracing too hard for the level of demand, which typically means you need an easier progression.
Speed is also a factor. Rushing through reps to finish faster introduces momentum, which reduces muscle activation and increases the chance of sloppy form. Each hold should feel deliberate, and each return to the starting position should be controlled rather than a collapse.