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INTRODUCTION
What’s the first thing that comes to mind when you hear the term core training? Late-night infomercials featuring incredibly lean fitness models promising the secret to six-pack abs? Endless amounts of crunches, side bends, and back extensions? Planking and bridging exercises held until seismic earth-shaking exhaustion? It is safe to say that core training has an ubiquitous presence across multiple health and fitness disciplines, ranging from rehab protocols for low back pain to protocols for individuals who are pursuing aesthetic or physique-based goals to specific exercises designed to promote physical fitness and enhance athletic performance. According to ACSM’s annual worldwide survey of health and fitness trends, core training has occupied a spot in the top 20 fitness trends for the past 10 years (15), firmly cementing core training into the lexicon of the health and fitness professional. Despite the omnipresent nature of core training, much misinformation continues to exist (9,16), therefore the purpose of this column is to separate the fact from fiction when it comes to the world of core training.
WHAT EXACTLY IS THE CORE?
One of the major challenges of defining core training is the inconsistent and imprecise definition of what actually constitutes the core in both lay and scientific publications (7,16). For many in the lay public, the core is synonymous with the rectus abdominus, the much revered “six-pack,” with the mistaken belief that the core and subsequent core training only encompasses classic bodybuilding isolation exercises such as sit-ups or weighted crunches (9,16). However, a much more nuanced definition of the core addresses the entire trunk region, with the skeleton and connective tissues providing a structural framework, while the muscles of the trunk cause, control, or prevent movement (16). Therefore, for the purposes of this article, the core is operationally defined as the area of the torso between the ball and socket joints of the shoulders and hips (13). Table 1 provides an overview of the kinesiology of the core.
Kinesiology of the Core (Adapted from (6))
CORE CONCEPTS
The terms core strength and core stability often are used interchangeably when describing various core training exercises (7,11). Leading to further confusion is that definitions of core stability and core strength often differ between practitioners in rehabilitation versus those of fitness professionals (7). Nonetheless, core stability is generally agreed to be the ability to control the position and motion of the trunk, whereas core strength is the ability of the core musculature to exert or withstand force (4,7). The concept of core stiffness may provide the best of both worlds, in which proximal stiffness of the core enhances distal segment limb speed. In lay terms, this means core stability in the trunk musculature allows for an efficient transfer of forces (speed, strength, and/or power) in the shoulders and hips (9,13).
CORE TRAINING 101
The four primary movements of the trunk that comprise core training are flexion, extension, lateral flexion, and rotation (6). Thus, when considering specific exercises to address the musculature of the core, the health and fitness professional may select exercises that 1) isolate the core through a dynamic range of motion, 2) isolate the core by preventing motion, often referred to as antiexercises, or 3) integrate the core via exercises that require stability of the core while moving from the hips or shoulders (see Table 2 for sample exercises via movement pattern). In addition, the core demands of many classic resistance training exercises can be manipulated by performing exercises bilaterally or unilaterally (barbell row vs. one-arm dumbbell row; barbell bench press vs. alternating dumbbell bench press). It should become quite evident that nearly every exercise imaginable is fundamentally a core exercise! Therefore, based on the specific goals and needs of the client, program design for the core may address endurance, hypertrophy, strength, power, or specific sport actions, particularly when following ACSM FITT-VP guidelines for exercise prescription: F — Frequency (how often core exercises are performed), I — Intensity (magnitude of loading/difficulty of core exercises), T — Time (duration of core training), T — Type (mode of core exercise selection), V — Volume (total amount of core exercises), and P — Progression (rate of advancement) (2).
Sample Core Exercises
CORE TRAINING MYTHS AND MISPERCEPTIONS
Spot Reduction
Despite the claims of nefarious infomercials, large numbers of crunches and planks will not magically result in selective fat loss from the abdominal region because the claims of spot reduction simply are not supported by research (10). Any type of exercise can contribute to creating a negative energy balance needed to ultimately reduce body fat, but body part–specific exercise does not create preferential fat loss in one region of the body over another (10).
Trunk Muscle Strength Is the Key to Athletic Performance
A recent systematic review and meta-analysis quantified the associations between measures of trunk muscle strength, physical fitness, and athletic performance (12). Not surprisingly, training the core had a large effect on measures of trunk muscle strength. However, core training had only small effects on measures of physical fitness and athletic performance (12). One possible explanation provided by the study authors hypothesizes that the role of specificity of training often is not captured in classic core assessments, in which tests performed in an isometric or prone position do not adequately mimic upright explosive muscle actions observed in sport (12).
Motor Control Exercise and Low Back Pain
Low back pain is the leading cause of activity limitation and work absence throughout much of the world (3) and its prevalence has led some to refer to it as the common cold of the musculoskeletal system (8). Especially among clinicians, motor control exercise (MCE) is a popular intervention that aims to restore coordinated and efficient use of the muscles that control and support the spine, such as the transversus abdominus and multifidus muscles (14). MCE is based on the theory that stability and control of the core is altered in individuals with low back pain (14). Therefore, MCE interventions focus on the activation of the deep trunk muscles in a specific and sequential manner, and may include the use of ultrasound imaging, biofeedback, and palpitation (14). Patients are guided initially by a therapist to selectively recruit and practice normal use of these muscles during simple tasks, and as the patient’s skill increases, the exercises are progressed to more complex and functional tasks involving additional muscles of the trunk and limbs (14). However, MCE has not been shown to be superior to other forms of core training exercises that address either muscle endurance or strength (3). Aerobic exercise, particularly walking, actually has the best evidence of efficacy for low back pain among all exercise regimens (2). Therefore, the choice of exercise for chronic low back pain should be determined by patient and therapist preferences, costs, and safety (14). Despite the frustration that can accompany low back pain, it is not a life sentence (8). In fact, there is clear evidence that individuals who seek therapy early on, and adhere to the exercise therapy, will feel better faster (5)! Whereas the prescription of exercise can play an integral role in helping a client manage acute or chronic low back pain, the health/fitness/exercise professional needs to understand clearly that his or her scope of practice does not ever include a medical evaluation or the diagnosis of low back pain because this rests solely within the scope of practice of a licensed health care professional (1).
Sidebar:
For videos of core exercises, see below:
DB Side Bend (https://links.lww.com/FIT/A43)
Deadbug (https://links.lww.com/FIT/A44)
Farmers Walk (https://links.lww.com/FIT/A45)
Forearm Plank (https://links.lww.com/FIT/A46)
McGill Modified Curl-up (https://links.lww.com/FIT/A47)
Medicine Ball Chop (https://links.lww.com/FIT/A48)
Palloff Press (https://links.lww.com/FIT/A49)
Russian Twist (https://links.lww.com/FIT/A50)
SideBridge (https://links.lww.com/FIT/A51)
Stability Ball Crunch (https://links.lww.com/FIT/A52)
CONCLUSIONS
The popularity and widespread use of core training exercises throughout the health and fitness landscape present a myriad of opportunities for the health and fitness professional to educate his or her clients as to the facts and fictions associated with core training. Given the plethora of information that exists — both good and bad — the health and fitness professional is encouraged to incorporate an evidence-based approach to provide clients the best exercise prescription for their specific goals and needs.
References
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