Core Muscle Training

“Training the abs” and “training the core” are not the same thing. The core is a whole system of muscles on which the stability of the trunk, the transfer of force in basic exercises, and, in part, the health of the back depend. The editorial team explains how these muscles work, which exercises are most effective for them, and which myths not to believe.

What the core is and what it consists of

The term “core” (from the English “core,” meaning “center, nucleus”) denotes the group of muscles surrounding the lumbar spine, pelvis, and abdominal cavity. Contrary to the popular notion, the core is not just the “six-pack” of the abs, but a whole complex of muscles that work as a single system.

The core usually includes the rectus abdominis, the external and internal obliques, the transversus abdominis, the back extensors, the multifidus muscles, the quadratus lumborum, and also the diaphragm and the pelvic-floor muscles. Many authors include here the gluteal and hip muscles, since they attach to the pelvis and influence its position.

A convenient model is to imagine the core as a cylinder. The diaphragm is its lid, the pelvic floor is the bottom, the abdominal wall is the front and side walls, and the back muscles are the rear wall. When all these muscles contract in a coordinated way, intra-abdominal pressure rises inside the cylinder, making the trunk stiffer.

A 2006 review by Kibler, Press, and Sciascia describes the role of the core in athletic activity as a link that transfers force between the lower and upper limbs. The effectiveness of this link determines how much of the legs' force “reaches” the arm during a throw, a strike, or a press.

Functions of the core: stability matters more than “six-pack”

The main function of the core is not to flex the trunk, but to control its position: to resist unwanted movements under load. Stuart McGill, one of the most well-known researchers of spinal biomechanics, emphasizes that in most athletic and everyday movements the core works as a rigid rod that transfers effort.

Hence the division of exercises into several categories: resisting extension (the plank, the ab-wheel rollout), resisting lateral flexion (the side plank, a single-arm carry), resisting rotation (the Pallof press), and resisting flexion (the deadlift, squats with a straight back).

• anti-extension — holding a neutral lower back under load from the front;
• anti-lateral flexion — stability under an asymmetric load;
• anti-rotation — control of the trunk under effort to one side;
• dynamic movements — flexion, rotation, throws in sport.

This does not mean that crunches or leg raises are forbidden. They develop the rectus abdominis and have their place in the program. However, for overall stability and transfer to heavy basic exercises, anti-movement exercises are usually more effective.

It is also important that heavy squats, deadlifts, and standing presses in themselves significantly load the core muscles. For many strength athletes, separate core work is a supplement, not the foundation.

The core and back pain

Lower-back pain is one of the most common problems in the world, and core exercises are often offered as a “cure.” A 2021 Cochrane review by Hayden and colleagues confirmed that therapeutic exercise is more effective than no treatment or usual care for reducing pain in chronic nonspecific lower-back pain, though the effect is moderate.

At the same time, studies do not show a clear advantage of special “stabilization” exercises over other kinds of activity: general strength work, Pilates, or aerobic exercise. The main thing is regularity and gradual progression, not the “right” set of core exercises.

The once-popular idea of “activating the transversus abdominis” before every movement has also been revised. Excessive focus on drawing in the belly can even hinder natural movement. For most people it is enough to learn to moderately tense the trunk — so-called “bracing.”

If back pain is accompanied by numbness in the legs, weakness, disturbed urination, fever, or weight loss, these are warning symptoms. In such cases you need a consultation with a doctor, not exercises from the internet.

Example exercises and progressions

You should build a core program on the same principle of progressive overload as for other muscles. First — control of body position in simple exercises, then — increasing the leverage, instability, or weight.

McGill proposes the so-called “big three” for back health: the modified crunch, the side plank, and the “bird dog” (an on-all-fours exercise with the opposite arm and leg). These exercises minimize the load on the lower back and suit as a warm-up or a separate complex.

As for the duration of holds: to develop core endurance it is better to perform several shorter holds of 10–30 seconds with perfect technique than one minute-long plank with a sagging lower back.

A 2010 review by Behm and colleagues on training on unstable surfaces shows that it increases activation of the core muscles but reduces strength and power. For strength athletes, the main exercises should be performed on a stable base.

Common myths

The first myth: ab exercises burn belly fat. There is no spot fat reduction: fat decreases throughout the whole body through an energy deficit. The “six-pack” becomes visible only at a sufficiently low body-fat percentage, and exercises merely develop the muscles beneath it.

The second myth: a weightlifting belt “switches off” the core. The belt increases intra-abdominal pressure and gives the trunk muscles something to push off against. It does not make the core weak if the athlete performs part of the work without a belt. However, at light weights a belt is mostly unnecessary.

The third myth: hundreds of crunches daily are the best way to strengthen the core. The rectus abdominis, like any other muscle, needs recovery and progressive overload. A large number of same-type spinal flexions gives no advantage and can irritate the lower back in people prone to pain.

The fourth myth: a strong core guarantees the absence of back injuries. The core is an important but not the only component. Technique, load management, general strength, sleep, and recovery matter no less.

Editorial conclusions

The core is a system of muscles around the trunk and pelvis that works as a single whole, not just the rectus abdominis. Its main function is to stabilize the trunk and transfer effort between the lower and upper body.

The most useful core exercises are those that resist unwanted movements: planks, the ab-wheel rollout, the Pallof press, and carries. Basic strength exercises with free weights also significantly develop the core.

In back pain, exercise helps, but no substantial advantage of special “stabilization” complexes over other kinds of regular activity has been found. Warning symptoms require examination by a doctor.

We also recommend our articles on functional training, on training with a shoulder injury, and on strength training for women.

References

1. Kibler WB, Press J, Sciascia A. The role of core stability in athletic function. Sports Med. 2006;36(3):189–198.
2. McGill SM. Core training: evidence translating to better performance and injury prevention. Strength Cond J. 2010;32(3):33–46.
3. Hibbs AE, Thompson KG, French D, et al. Optimizing performance by improving core stability and core strength. Sports Med. 2008;38(12):995–1008.
4. Behm DG, Drinkwater EJ, Willardson JM, Cowley PM. The use of instability to train the core musculature. Appl Physiol Nutr Metab. 2010;35(1):91–108.
5. Hayden JA, Ellis J, Ogilvie R, et al. Exercise therapy for chronic low back pain. Cochrane Database Syst Rev. 2021;(9):CD009790.
6. Akuthota V, Nadler SF. Core strengthening. Arch Phys Med Rehabil. 2004;85(3 Suppl 1):S86–S92.
7. McGill S. Low Back Disorders: Evidence-Based Prevention and Rehabilitation. 3rd ed. Champaign (IL): Human Kinetics; 2016.