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The “Anatomy” of Investigating Abdominal Exercises

Olson, Michele Ph.D., FACSM, C.S.C.S.

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ACSM’s Health & Fitness Journal: July/August 2013 - Volume 17 - Issue 4 - p 8-15
doi: 10.1249/FIT.0b013e318296bfa3
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One of the most popular topics in fitness is “abs.” Fitness leaders, exercise scientists, and the general public are presented regularly with volumes of news and information on abdominal (abs) exercise. Many media outlets, including professional journals, magazines, television, and newspapers, are saturated with the latest information about belly fat and abdominal conditioning. In fact, trainers and fitness enthusiasts are virtually pursued by news flashes and bulletins about the most current research findings and advertisements for programs and products publicized to shrink waistlines and create rock-hard abs. The International Health, Racquet & Sportsclub Association reported that abdominal exercise machine use ranked sixth among the top 10 health club activities in its Trend List for 2012 (11). It is essential for trainers and instructors to know whether a particular exercise, exercise style (such as Pilates), product, or abdominal training device is effective. It also is important for practitioners to be able to match a regimen of abdominal training to the needs and limitations of their clients and more so for a client whose needs demand abdominal exercises with a high degree of “friendliness” to the spine (13,23). This article will detail the “anatomy” of how exercise scientists go about determining the validity of abdominal exercise practices and provide a focus on current trends such as yoga, Pilates, and standing abdominal moves, including selected advancements in core and spine stability.


Exercise scientists use a technology labeled electromyography (EMG) to measure and chart the level of muscle activation produced when doing abdominal exercises, such as crunches, sit-ups and curls, and planks on a stability ball. Electromyography more commonly referred to as EMG, is quite similar to electrocardiography (EKG). Like EKG testing, electrodes are placed on the skin over the area of the muscle under investigation. With EKG testing, that muscle is the myocardium (heart muscle). With EMG, the muscle is usually a skeletal muscle, such as a hamstring, gluteal, quad, or abdominal muscle. Both EMG and EKG measure the muscle’s level of contraction. More specifically, the electrical energy that triggers the muscle to contract is captured and recorded for analysis. The greater the intensity of the electrical signal, the higher the degree of muscle activity.


There are actually two types of EMG: surface EMG and fine-wire EMG. Surface EMG also is known as external EMG and fine-wire EMG often is referred to as intramuscular EMG. Surface EMG is used more often and is particularly efficient in measuring the activity of the more extrinsic muscles. Two of the four abdominal muscles most studied with surface EMG are the rectus abdominis, often called the six pack, and the external obliques — commonly targeted with diagonal or oblique movements, such as diagonal crunches or the bicycle exercise (1,25). Both muscles reside close to the skin and are visible to the eye, especially in individuals with low body fat (photo 1, electrodes placed on study participant).

However, the deeper abdominal muscles are difficult, if not impossible, to test using surface EMG because they reside under, and are occluded by, the rectus abdominis and external obliques (Figure). For instance, the transverse abdominis, which both appears and functions much like a corset providing support to the lower trunk and spine, is impossible to access using surface EMG, and very little of the internal obliques can be directly accessed from atop the skin. So, scientists in more specialized settings (e.g., in spine research laboratories) use intramuscular EMG to most accurately capture the activity of the deeper abdominal muscles. Briefly, with intramuscular EMG, electrodes in the form of small fine wires are inserted through the skin and outer abdominal muscles directly into the deep muscles. Because intramuscular/fine-wire EMG is invasive, researchers have validated techniques whereby surface EMG can provide a reasonable estimate of the activity ofthe deep abdominal muscles (15). Therefore, superficial EMG has been used in most scientific studies on abdominal exercise.



In the 1990s, the early trend toward more evidence-based fitness programming resulted in a marked change in abdominal exercise practices. By 2001, The American Council on Exercise reported on a research project titled, “New Study Puts the Crunch on Ineffective Ab Exercises” (1). Driven in large part by this “new” EMG research, health clubs and trainers moderated their approach to abdominal exercise. For instance, “full” (flexion) and “straight leg” sit-ups with the feet anchored (by a partner or sit-up board) were replaced with partial curl-ups and unanchored feet (3). Well known as the “crunch,” the increased use and popularity of this version of the sit-up was further bolstered by research that showed that the crunch was more spine friendly compared with its full-flexion processors. Soon after came the marriage of the crunch to the large (physical therapy) Swiss or stability ball (1,23), which served to increase the intensity of the crunch, particularly the intensity to the rectus abdominis, by close to 40% (21). And as exercise trainers became more sophisticated in prescribing exercise, EMG studies, directed more toward muscle specificity, became increasingly available. For instance, the “bicycle” maneuver was found to be tops at activating the external obliques, and “hip-ups” were shown to be king in firing the more distal areas of the abdominals (8,24).

In sports medicine circles, certified athletic trainers and physical therapists began teaching athletes to “draw in” or “hollow” (out) their abdominals based on EMG and related research — research that pointed to the role that the deep muscles, especially the transverse abdominis, provided in stiffening and stabilizing of the low spine and sacroiliac joints in those with back pain (20).“Drawing in” has been increasingly popularized and advocated in the general fitness setting, particularly by the Pilates method. However, “drawing in” also has become a hotly debated abdominal technique and its validity is questioned in general fitness and athletics (4,10). Also at the forefront remain questions and a sensible level of skepticism about the validity of the Pilates, yoga, and mat-free standing exercise maneuvers prompting our research team at Auburn University Montgomery to provide trainers with information and valid approaches that can be used for long-term use in real-world training and conditioning settings.


Science and Practice Moving Forward

Yoga has been practiced for centuries and Pilates since the mid-1920s. Both have recently surged in popularity because the numerous variations and styles promise a range of benefits fromimproved flexibility, a stronger core, and weight control. Functional movement now also is a common practice in fitness circles and has popularized total-body, weight-bearing movements such as walking lunges and squats often coupled with overhead presses, lateral raises, and biceps curls. Interestingly, many functional movement patterns also have a yogic base. Yoga means “to yoke or join together” and, like the common concepts associated with functional training, involves the use of movement patterns versus muscle isolations such as biceps curls. This particular trend has further evolved the more recent practice of training abs in a standing posture, doing moves such as standing crunches, bicycles, sidebends, and twists.

As noted, our human performance laboratory at Auburn Montgomery became quite interested in these recent trends in abdominal exercise. When searching for quality research studies to see if the purported effects of many current practices had been substantiated with “evidence” from solid science, there were few available.


Pilates and the Deep Abs

Using EMG, we analyzed a series of Pilates abdominal exercises including the “hundred,” “roll-up,” “double-leg stretch,” “criss-cross,” and “teaser” to determine if the Pilates method was superior to a well-studied and often referenced conventional exercise (i.e., the crunch) in activating the muscles of the abdominal wall. We also were interested to see if Pilates was particularly effective in activating the deep transverse abdominis muscle — an effect particularly espoused and punctuated by Pilates practitioners. What we found was that the Pilates maneuvers we tested were significantly more robust than the standard crunch exercise in activating the rectus abdominis and external obliques. In fact, the most notable results showed that the roll-up, criss-cross, and teaser increased the output of the external obliques by 103%, 310%, and 266%, respectively, compared with the crunch (9,19).

However, the claim that Pilates abdominal exercises are highly effective in activating the deep abs with a reduced activation of the superficial abs was only partially supported (18). The hundred and double-leg stretch were the only Pilates exercises that increased the activity of the internal obliques and transverse abdominis to a significantly higher level than the standard crunch while producing lower rectus abdominis activity (Table 1). In contrast, the roll-up and teaser moves elicited significantly greater rectus abdominis activation, producing EMG values that were notably higher than those of the crunch. The reason is directly related to the nature of these different Pilates movements. For instance, the roll-up and teaser require full flexion of the trunk (off of the floor) compared with the hundred and double-leg stretch, which are done with just the head shoulder blades lifted (photo 2 of the hundred vs. photo 3 of the roll-up). In a large-scale cooperative study by international spine researchers (12), full-flexion sit-ups and curl-ups generated higher levels of rectus abdominis activity and lower levels of deep muscle activity, whereas exercises with little to no trunk flexion produced the opposite effect (i.e., a higher deep muscle response and blunted rectus abdominis activity). So, although Pilates abdominal exercises provide an ample challenge to the abdominal muscles, they do not “corner the market” in isolating the deep abdominal muscles. Table 1 also shows other EMG-tested exercises (7,8,12,13) that have been found to produce increased deep muscle activity with lower rectus abdominis activity. It also is noteworthy that these exercises also are low on trunk flexion, with many being bridging or plank-style exercises.

Deep Abdominal Activity for Selected Exercises Including Pilates

Yoga and Planks

Yoga has been marketed frequently as an exercise discipline that can develop abdominal fitness. There are numerous exercise videos and books such as “Yoga Works for Everybody: Fit Abs” (5) and “Yoga for Flat Abs” (22). Many yoga programs also incorporate large stability balls in the effort to enhance the challenge yoga may provide to the core and abdominal muscles, for example, the exercise video, “On the Ball Yoga Workout for Beginners” (17). Compared with Pilates, yoga has received more scientific study. In 2005, “ACE Fitness Matters” reported significant improvements in flexibility and increased performance on push-ups and curl-ups after 8 weeks of hatha yoga (1). Therefore, it is important to better understand abdominal muscle activity and recruitment patterns for popular yoga movements and poses. Thus, using superficial EMG, our research team at Auburn University Montgomery also tested the yoga boat pose, yoga side plank, and the yoga dolphin plank on a stability ball (photos 4 to 6). The results, although limited to just these three movements, were quite impressive and produced EMG values between 5% and 54% higher than the crunch (17) (Table 2). In fact, the intensity of these yoga poses ranged from 63% to 96% of maximum muscle output. Briefly, maximum muscle output, more scientifically referred to as maximal voluntary contraction, represents the greatest intensity produced by the muscle and is determined by recording the EMG when the muscle is contracting against a maximal force. For instance, when determining the maximal output of the rectus abdominis, a laboratory technician will push against the subject’s shoulders, providing strong resistance while the subject attempts to perform a crunch. The highest, or maximum, EMG values produced while flexing against the external resistance are recorded. Researchers classify intensities more than 60% of maximum muscle output as “very high,” which indicates that the yoga exercises studied here are more than suitable for abdominal muscle conditioning (8).

Rank* of Superficial Abdominal Muscle Activity for Tested Yoga and Standing Abdominal Exercises

As noted previously, the addition of the stability ball to the crunch markedly increases abdominal muscle output (23). The abdominal activity when doing the yoga dolphin plank on stability provided an impressive challenge to the abs. When done conventionally on a mat, the dolphin plank activates the abs to moderate level of intensity (18). The abdominal muscles clearly play an increased role in resisting the destabilizing effect of the ball during yoga plank-style exercises.


Similar moves to the yoga dolphin plank that are “flexion/crunch-free” and done with a ball (e.g., prone rollout and stir the pot) cause the abdominals to act like a “brace” and are preferred particularly for those with known back pain (4,8,12,13). The brace is a reflexive response that is similar to the global stiffening that occurs in the abdominal area when one braces to absorb a punch to the stomach. The entire abdominal wall or without the navel drawing inward.

Yoga-like planking maneuvers may offer another spine-saving benefit. For instance, other studies have found that planking (sometimes called bridging) exercises also place lower forces on the spine’s shock-absorbing discs compared with flexion-oriented sit-ups and trunk curls (3,12,13,14).

Standing Exercises: The Quest for “Crunch-Free” Abs

Like planks, standing exercises such as sidebends and rotational movements also have become a very popular style of “crunch-free” abdominal exercise. However, compared with Pilates and yoga, there is even less scientific evidence that substantiates the use of standing movements for training the abdominal muscles. Once again, EMG revealed the effects of the standing front crunch, bicycle, and sidebend on the abdominals (photos 7,8,9). Through our laboratory testing, we found that these exercises activated the abdominal muscles to a significantly lower degree than the standard crunch and yoga exercises (17), producing an intensity of about 20% of maximum muscle output for the rectus abdominis and external obliques. This is as much as 57% less intense than the crunch (i.e., see standing front crunch compared with the standard crunch for the external obliques in Table 2).


Although crunch-free, the level of muscle activation for these exercises is clearly not comparable to the robust (63% to 96% of maximum) activation we found for the crunch-free yoga side plank and dolphin plank on the ball shown in Table 2.

During crunch-free maneuvers, clinical researchers have noted other factors where the spine is concerned. For example, a moderate ongoing activation of auxiliary muscles such as the latissimus dorsi may be important in stabilizing the trunk and spine during both abdominal exercise and physical activity in general (7,8). The standing exercises we tested actually produced moderate to moderately high levels of latissimus dorsi activity ranging from about 30% to 45% of maximum output. So, although many standing exercises may not be optimal for improving abdominal strength per se, they may be effective for developing moderate strength and muscular endurance in muscles (i.e., such as the latissimus dorsi) that play a significant role in stabilizing the trunk and spine during movement and exercise. Many exercise experts are directing their efforts toward studying both abdominal and auxiliary muscle activation in the effort to fully clarify the benefits and how-tos for conditioning the entire trunk and core.


Table 3 provides three abdominal exercise supersets grounded in evidenced-based EMG data with respect to significant abdominal exercise trends as follows: Activation of the deep abdominal and core auxiliary muscles and use of more spine-friendly low-flexion movements. Each superset also includes multiple trunk orientations such as supine (face-up), prone (face-down), standing, and/or side-lying orientations. These three superset protocols should serve clients well in overcoming the possible repetitive stress that can occur when doing abdominal exercises primarily in one orientation that results in virtually the same pattern of muscle activation, such as performing a high number of supine trunk flexion variations (i.e., crunch-style maneuvers). Last, many of the exercises in Table 3 also elicit the more functional bracing pattern of abdominal muscle activation.

Three Abdominal Exercise Supersets Based on EMG Results

In summary, external or superficial EMG is the method used by exercise scientists to determine muscle activity during exercise. In testing currently popular styles of abdominal training, EMG research shows that Pilates and yoga produce ample levels of abdominal muscle activation. Lower flexion Pilates moves such as the hundred and double-leg stretch can effectively activate the deep muscles and yoga plank-style moves such as side and dolphin plank on the ball are “crunch-free,” making them spine-friendly techniques. Standing abs exercises provide a more modest challenge to the abdominal muscles, and many of the movements require side bending as well as twisting, which place several loads and forces such as compression, shear, and torsion on the shock-absorbing spinal discs. These loading patterns can be concerning in terms of promoting overuse and “wear and tear” to the spinal discs when the movement patterns occur vigorously and repeatedly such as doing a high number of repetitions on a frequent basis (2). However, coupled with adequate stability and done at a moderate volume, a variety of standing abs exercises may contribute to overall spine and core fitness by activating other muscles that play a role in trunk stabilization. Based on this information, trainers can select and incorporate various Pilates, yoga, and standing abs exercises in ways that are most appropriate to their exercise participants’ goals, fitness levels, and needs.



Based on EMG research, Pilates and yoga-style exercises can be used effectively for abdominal training and conditioning. Many of the planking exercises used in Pilates and yoga also seem to provide a spine-friendly alternative to traditional crunches and sit-ups. Standing “abs” exercises activate the abdominal muscles to a moderately low level and may be not be effective in markedly improving the strength of the abdominal wall. However, standing abdominal exercises activate other “core” muscles,z such as the latissimus dorsi and may contribute to overall strength and stability in the core and trunk.


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      Recommended Readings

      McGill S. Ultimate Back Fitness and Performance. Ontario, Canada: Wabuno Publishers; 2004.
        Willardson JM. A periodized approach for core training. ACSM’s Health Fitness J. 2008;12(10):7–13.

        Electromyography; EMG; Rectus Abdominis; Obliques; Transverse Abdominis; Spine

        © 2013 American College of Sports Medicine.