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How to build a core of steel

Wie Du eine Körpermitte aus Stahl aufbaust

You've probably read a lot about how important it is to have a core of steel. And you've probably also come across plenty of differing opinions on what the best way to achieve this is.

Some say that squats and deadlifts will build all the core strength you'll ever need. Others will tell you that the best way to strengthen your core is to spend time on the Swiss Ball, BOSU Ball or other unstable surfaces.

The term 'core' causes a lot of confusion, mainly because everyone seems to have a different opinion on what exactly it means

For most people, the term midsection is simply another name for the abdominal muscles. But in reality, this term refers to a much larger set of muscles that stabilize the spine. These muscles work together to keep the spine as neutral as possible, which corresponds to its natural curved shape.

A neutral spine is not a single position that your spine never moves away from. Rather, think of it as a neutral zone or area where your spine can move while remaining relatively healthy. A lack of spinal stability can lead to movement that is outside of this zone, which in turn increases the risk of pain and/or tissue damage.

When we talk about stability, what we really mean is that we want the lower back - the lumbar spine - to move as little as possible when subjected to stress. This small range of motion is called the neutral zone. The smaller it is, the greater the stability of your core.

When muscles contract, they generate stiffness. Muscle stiffness not only stabilizes the spine and reduces the risk of tissue damage, but is also a necessity when it comes to optimal athletic performance.

A 'stiff' core is particularly important for sports that rely on strength, speed and quickness. When the core is mentioned in this context (i.e. as a pathway for transmitting force), the term usually refers to the muscles of the trunk and hips - basically anything that doesn't fall under the head, arms or legs.

This is much more than just abs and lower back and extends from your shoulders to the biceps femoris - the leg flexor that crosses the hip (2, 9).

Does training on an unstable surface lead to greater activation of the core muscles?

Performing exercises on an unstable surface, such as sitting on a Swiss Ball or standing on a BOSU Ball, is said to place a greater emphasis on activating some of the muscles of your core, which should help to increase core stability, protect against back pain, improve athletic performance, etc.

Such exercises often appear to be much harder than their more stable counterparts. This is mainly because you have to work so hard to maintain balance. And due to the fact that you are not used to these exercises, they often generate the impression that they are superior to the same exercises performed on the floor.

There is scientific research that shows that an exercise performed on an unstable surface leads to greater activity in the muscles of the core compared to the same exercise performed on the floor (2).

Squats with a light weight performed standing on two inflatable discs, for example, lead to greater activation of the muscles of the trunk than squats performed standing directly on the floor (1).

However, a major limitation of many of these studies is that they involve the use of relatively light weights. This is a problem because most people can move a much heavier weight if they are swaying back and forth on the floor rather than on an unstable surface.

What happens when you compare differences in muscle activity that take into account the fact that you can move more weight on a stable surface than on an unstable surface?

This is exactly what scientists at Eastern Illinois University wanted to find out (7). They looked at muscle activation in a group of 12 trained men who performed four different exercises - deadlifts, overhead squats and barbell curls - at two different intensities (50% of 1RM weight and 75% of 1RM weight) while standing on a stable or an unstable surface (BOSU BALL).

Muscle activity in the abdominal muscles and lower back muscles was not significantly different when subjects performed deadlifts, squats, overhead presses and barbell curls with a light weight on a BOSU ball instead of standing on the floor.

There were also no significant differences in muscle activity in the external lateral abdominal muscles and lower back muscles for all four exercises between performing the exercises with 75% of the 1RM weight on a stable surface and performing the exercises with 50% of the 1RM weight on an unstable surface.

However, when overhead presses were performed on a stable surface using heavier weights, the rectus abdominis (the six-pack muscle) worked significantly harder than when performing the same exercise with a lighter weight on a BOSU ball.

Performed on a stable surface, overhead presses and barbell curls also provided useful stimulation (40 to 50% of maximum spontaneous contraction - MVC for maximum voluntary contraction) to the deeper abdominal muscles.

Instability has its place and its justification. Some exercises use instability, for example, to emphasize the muscles of the core. Physiotherapists have also been using unstable surfaces for years to support rehabilitation training for knee and ankle injuries (10).

However, for many exercises, training with a lighter weight on an unstable surface will not make the core muscles work harder than performing the same exercises with a heavier weight on a stable surface.

Are squats and deadlifts all you need to train your core?

Squats and deadlifts will make all other direct ab workouts completely redundant, as these two exercises will provide all the stimulation your abs will ever need. At least that's the theory, but the science shows a different picture.

Squats and deadlifts work many muscles of the core, but these are mainly the muscles of your back - and in particular the back extensors that run parallel to the spine on the right and left. In fact, squats and deadlifts train the back extensors better than pelvic lifts, side bridges and back extension exercises performed on a Swiss ball (3, 6).

Especially during deadlifts, the back extensors work very hard to keep your spine in its natural arched position. The main reason why powerlifters have such well-developed back extensors is because these muscles have to do so much work when performing classic powerlifting exercises to prevent flexion of the spine.

Squats and deadlifts are good for developing the posterior muscles of the core. The quadratus lumborum, a small but important muscle in the lower back that helps stabilize the spine, is also intensely worked during deadlifts (4).

However, none of these exercises do much for the muscles of the front of the midsection - the abs.

The illustration below is from Dr. Jeffrey McBride, a professor of biomechanics at Appalachian State University. Dr. McBride studied the activation of the anterior abdominal muscles (rectus abdominis) of trained strength athletes performing a series of different exercises.

As you can see, squats and deadlifts don't work the rectus abdominis very hard - even if you're using a heavy weight in the 80-90% of your 1RNM weight range. In fact, overhead presses activate the rectus abdominis more than both deadlifts and squats (7). However, even this activation is relatively low compared to rollouts or curl-ups (in the region of 10% of maximum spontaneous contraction (MVC)).

Similar results were observed in a study that included a group of elite male rugby players as subjects (11). These were quite strong guys who were in the advanced and very advanced range in terms of squat strength. They were therefore not the typical "untrained beginners" who often serve as test subjects in such studies.

The scientists measured muscle activity in the abdominal muscles during squats, overhead squats and various abdominal exercises. In this study too, the abdominal muscles did not have to work very hard during squats - only 10% of their maximum. The scientists were able to observe greater activation of the abdominal muscles even during planks, sit-ups and jackknives.

A person who can perform standing shoulder presses with their own body weight and deadlifts with twice their body weight will have already developed a very high level of core strength simply by focusing on getting stronger at both exercises. However, for full core development, squats, deadlifts and presses are not enough - you will need additional exercises that train the abdominal muscles directly.

While I'm on the subject of core training, I'd like to briefly mention the topic of spinal rotation

Probably the most popular spinal rotation exercise is the torso twist with a broomstick on the shoulders, which is also undoubtedly the most pointless exercise ever invented.

This is not to say that it is not necessary to train the muscles that rotate the torso, but there are far better ways to do this than rotating the torso from side to side with a broomstick on your back.

Instead of pure rotation, you should use resistance to rotation. And by resistance to rotation, I mean exercises that require you to overcome forces that try to pull your torso in the opposite direction.

Let's take one-arm dumbbell rowing as an example. Although this is primarily an exercise to train the muscles of the back, the lateral abdominal muscles are also involved. This is because these muscles actively prevent your torso from rotating during the rowing movement.

The same principle applies to other one-arm exercises such as the one-arm shoulder press. I recently injured my shoulder, which meant I couldn't do a heavy workout with my left arm. However, I wanted to continue training my right side using the principle of 'cross education' (where training with one side of the body has a small but significant effect on the strength of the other side of the body).

So I continued to do some heavy shoulder presses with my right arm. The next day I could clearly feel the muscles on the left side of my torso. This was due to the fact that they had to work extremely hard to keep me upright during the one-arm shoulder press.

This is a much more efficient use of your training time than a few sets of side bends, which also fall into the "poor use of your time in the gym" category.

Long Lever Plank Shoulder Taps( are another good example of what I mean by this. In the starting position, you resist extension of your spine (flexion of the back), which makes this exercise particularly effective for training the rectus abdominis. Removing one of the contact points (your hand) from the floor introduces an element of instability that requires your body to actively resist rotation. If you find this exercise too difficult, keep your hands in a push-up position under your shoulders instead of in front of your body.

Exercises that involve resistance to rotation are a far better choice than those exercises like Russiuan Twists( that involve actual rotation, which send a shiver down my spine every time I see someone doing them.

If you have a history of back injuries or if you have a healthy and pain-free back and want to keep it that way, then I can only highly recommend that you avoid any exercise that involves this type of movement.

Remember that many muscles of the core can be trained very effectively by preventing a movement rather than performing an actual movement. You can still train the muscles involved in spinal rotation, but you do so in a way that poses less risk to your spine. An exercise does not have to involve actual rotation to train the muscles responsible for rotation.

This doesn't mean you should avoid rotation completely. However, you should make sure that the movement comes from the hips and that the hips and back can move together at the same time as if they were firmly connected.


Building a steel core doesn't have to be complicated, time-consuming or boring. And it doesn't require training on a Swiss Ball, a BOSU Ball or any other surface that isn't the floor.

Many muscles in your core work very hard to prevent movement of the spine during exercises such as squats, deadlifts, one-arm rows, rollouts and standing presses. These exercises not only build core strength, but also full body strength.


  1. Anderson K, Behm DG. (2005). Trunk muscle activity increases with unstable squat movements. Canadian Journal of Applied Physiology, 30, 33-45
  2. Behm DG, Drinkwater EJ, Willardson JM, Cowley PM. (2010). The use of instability to train the core musculature. Applied Physiology Nutrition and Metabolism, 35, 91-108
  3. Hamlyn N, Behm DG, Young WB. (2007). Trunk muscle activation during dynamic weight-training exercises and isometric instability activities. Journal of Strength and Conditioning Research, 21, 1108-1112
  4. McGill SM. (1997). Distribution of tissue loads in the low back during a variety of daily and rehabilitation tasks. Journal of Rehabilitation Research and Development, 34, 448-458
  5. McGill S, Juker D, Kropf P. (1996). Quantitative intramuscular myoelectric activity of quadratus lumborum during a wide variety of tasks. Clinical Biomechanics, 11, 170-172
  6. Nuzzo JL, McCaulley GO, Cormie P, Cavill MJ, McBride JM. (2008). Trunk muscle activity during stability ball and free weight exercises. Journal of Strength and Conditioning Research
  7. Willardson JM, Fontana FE, Bressel E. (2009). Effect of surface stability on core muscle activity for dynamic resistance exercises. International Journal of Sports Physiology and Performance, 4, 97-109
  8. McGill SM, McDermott A, Fenwick CM. (2009). Comparison of different strongman events: trunk muscle activation and lumbar spine motion, load, and stiffness. Journal of Strength and Conditioning Research, 23, 1148-1161
  9. Behm DG, Drinkwater EJ, Willardson JM, Cowley PM. (2010). Canadian Society for Exercise Physiology position stand: The use of instability to train the core in athletic and nonathletic conditioning. Applied Physiology, Nutrition, and Metabolism, 35, 109-112
  10. Behm D, Colado JC. (2012). The effectiveness of resistance training using unstable surfaces and devices for rehabilitation. International Journal of Sports Physical Therapy, 7, 226-241
  11. Aspe RR, Swinton PA. (2014). Electromyographic and kinetic comparison of the back squat and overhead squat. Journal of Strength and Conditioning Research, 28, 2827-2836


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