PT on the Net Research

How to Integrate Bracing and Hollowing for Superior Trunk Conditioning

“Engage your abs.”

 “Brace your abs for a punch.”

 “Draw your abdominal wall towards your spine.”

 “Press your abs into the (powerlifting) belt.”

Personal trainers are familiar with different ways of teaching engagement of the trunk muscles during resistance training. Logically, personal trainers consequently ask which of the above cues is best: How should personal trainers cue abdominal contraction for their clients?

The discussion about how to cue abdominal contraction often becomes polarized with positions of a “right” way and a “wrong” way. A black or white conclusion is unfortunate because most exercise tactics have both advantages and disadvantages.

  Advantage Disadvantage
Tactic 1  Exploit Avoid
Tactic 2 Exploit Avoid

Table 1: Most exercise tactics have advantages and disadvantages

When personal trainers know how to exploit the advantages and avoid the disadvantages of available exercise tactics, then both tactics—rather than just one—can be added to the tool box and used at the right time.

This article explores the fairly well researched tactics of abdominal drawing in (synonymous with abdominal hollowing) and abdominal bracing. The purpose of the article is to:

What is the purpose of abdominal drawing in and bracing?

Draw the lower abdomen up and in towards the spine without moving the trunk or pelvis is the instruction given to the client when the aim is the abdominal drawing in technique. The purpose of abdominal drawing in is neuromuscular retraining and kinesthetic awareness of the transverse abdominis muscle (1).

Contract your abdominal muscles without any geometric change in the abdominal wall or spine is the instruction given to the client when the aim is the abdominal brace (2). The purpose of bracing is to activate all layers of the abdominal wall and extensor muscles with a task specific, appropriate level of contraction to achieve optimal spinal stability (3).

What are the trunk muscle recruitment patterns associated with abdominal drawing in or bracing?

Abdominal drawing in may result in an emphasis on the transverse abdominis and internal oblique muscles by de-recruitment of the rectus abdominal muscle (1,4). However, a maximal abdominal brace recruits all layers of the abdominal wall and may result in higher activation of the transverse abdominis muscle compared to abdominal drawing in (5).

The biggest difference between abdominal drawing in and abdominal bracing may be that global, superficial trunk muscles are de-recruited during abdominal drawing in.

What is the rationale for integrating abdominal drawing in and bracing?

During simple arm or leg movements, there is an anticipatory activation of the deep trunk muscles. (6) This pattern is absent in individuals with back problems, but can be restored through exercises that focus on the deep trunk muscles. This is the finding behind the focus on preferential recruitment of deep abdominal muscles during rehabilitation from back injury (5).

Abdominal bracing results in increased spinal stability and may be a superior activation strategy during movements that thrive on spinal stiffness (2,3). However, during movements that require suppleness, bracing — even at low levels of maximal voluntary contraction (MVC) — may result in excessive whole body stiffness (7).

The main pattern of integrating abdominal drawing in and bracing is in a long-term cycle that involves a progression from abdominal drawing in (during rehabilitation from injury) to abdominal bracing (during more demanding movements).

Are there any good arguments for integrating abdominal drawing in and abdominal bracing within the same sessions and within the same sets for individuals without back pain?

Many studies have looked at muscle activation patterns during minor variations of the same exercises and found that the muscle activation pattern is highly specific to the specific variation of an exercise (9). This fact is expressed in the concept of functional differentiation:

According to the concept of functional differentiation, the nervous system fine tunes activation of motor units according to the optimal line of pull for a given exercise. Functional differentiation within skeletal muscle refers to the ability of the Central Nervous System (CNS) to control, with a degree of independence, individual subunits of a muscle during a particular muscle contraction. Essentially, the concept of functional differentiation within skeletal muscle suggests an ability of the CNS to selectively activate those segments of a muscle that have the most appropriate line of action for the task as a means of ensuring the muscle’s efficient utilization (10).

A muscle can be divided into neuromuscular compartments, which are distinct regions of the muscle, each of which is innervated (activated) by an individual nerve branch and therefore contains motor unit territories with a unique set of characteristics. In other words, different portions of a muscle may be called into play depending on the task and demands of the situation. It is because each compartment has its own innervations that it is possible that one can selectively recruit a particular region of that muscle (11).

Based on the above, it is hypothesized that abdominal drawing in and abdominal bracing may recruit different portions of the transverse abdominis muscle. Consequently, the regular inclusion of both abdominal drawing in and bracing in a training program may result in a more complete development on the deep abdominal muscles.

How to integrate abdominal drawing in and abdominal bracing within one set of the Curl Up.

There are multiple ways to integrate abdominal drawing in and abdominal bracing during trunk training. The following example emphasizes the Curl Up and abdominal drawing in.

  1. Lie supine with one leg bent and the foot flat on the floor. The other leg is straight.
  2. Slide a flat hand— of the side of the straight leg— under the low back and adjust the lumbar curve to match height of the knuckles
  3. Maximize the distance between the crown of the head and the tailbone— you should feel tension throughout the back. Look for the toes.
  4. Put your shoulder blades in imaginary back pockets and feel tension in your lats and abdominal muscles
  5. Perform a curl up:

    Perform a deep inhale, but keep the abdominal wall flat. Notice that the ribcage and the head are resting on the floor with a certain weight: Imagine that there is a scale under the ribcage and head and lift in such a way that you stay in touch with the scale, but the scale shows 0 as you exhale completely and brace the abs. Hold the contraction for the duration of the exhalation.

  6. Relax, switch the position of the legs and repeat.
  7. Perform the abdominal drawing in beginning with one leg bent and the other leg straight and a neutral lumbar curve (see points 1 & 2):

    Lie fairly relaxed on the floor and perform a deep diaphragmatic inhalation through the nose. Allow the abdominal wall to expand. Draw the lower abdomen up and in towards the spine without moving the trunk or pelvis as you exhale. Perform another draw in inhalation/exhalation while keeping the abdominal wall drawn in— during the inhalation you will feel that the downward movement of the diaphragm tends to expand the abdominal wall. Restrict this tendency through muscular effort.

  8. Switch positions of the legs and repeat.

    Perform 8-12 repetitions per set and 1-2 sets per session depending on the client’s training capacity and specific goals.


The purpose of abdominal drawing in is neuromuscular retraining of the transverses abdominal muscle. The purpose of the abdominal brace is to optimize stiffness of the spine by a task-appropriate contraction of the abdominal wall. Traditionally, a client—in the process of rehabilitation from a back injury and returning to normal training— may first use abdominal drawing in followed by abdominal bracing. Concurrent use of abdominal drawing in and abdominal bracing for non-injured clients may enhance control of the abdominal wall and provide a more complete stimulus to the deep abdominal muscles.


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  2. McGill S. Groove motion/motor Patterns and corrective exercise. Ultimate Back Fitness and Performance 4th Ed. Chapter 10, page 185. BackFit Pro Inc 2009
  3. McGill S. Enhancing Lumbar Spine Stability. Ultimate Back Fitness and Performance 4th Ed. Chapter 5, page 121. BackFit Pro Inc 2009
  4. Valclene G, Bersldene K, Slapsinskaite A, Mauriciene V, Racon S. Not only static: Stabilization Maneuvers in dynamic exercises – A pilot Study. https://
  5. Hirayama K, Akagi R, Moniwa Y, Okada J, Takahashi H. Transversus Abdominis Elasticity During Various Exercises: A Shear Wave Ultrasound Elastography Study. International Journal of Sports Physical Therapy 12(4):601-606. 2017
  6. Crommert ME, Halvorsen K, Ekblom MM. Trunk Muscle Activation at the Initiation and Breaking of Bilateral Shoulder Flexion Movements of Different Amplitudes. DOI:10.1371/journal.pone.0141777. 2015
  7. Campbell A, Kemp-Smith K, O’Sullivan P, Straker L. Abdominal Bracing Increases Ground Reaction Forces and Reduces Knee and Hip Flexion During Landing. Journal of Orthopedic and Sports Physical Therapy. 46(4): 286-292. 2016
  8. Schmidt RA, Wrisberg CA. Movement Production and Motor Programs. Motor Learning and Performance. Chapter 5, page 147-149. Human Kinetics. 2004
  9. Sale D. Neural Adaptation to Strength Training. Strength and Power In Sport. Chapter 9B, p. 249-265. Blackwell Science. 1991
  10. Paton ME, Brown JM. Functional differentiation within Latissimus Dorsi.
  11. Antonio, J. Non-uniform Response of Skeletal Muscle to Heavy Resistance Training: Can Bodybuilders Induce Regional Muscle Hypertrophy. J Strength Cond Res. 14(1): 102-113. 2000