Research Review By Dr. Demetry Assimakopoulos©

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Date Posted:

September 2013

Study Title:

The Effects of Isolated and Integrated ‘Core Stability’ Training on Athletic Performance Measures

Authors:

Reed CA, Ford KR, Myer GD & Hewett TE

Author's Affiliations:

Cincinnati Children’s Hospital; Ohio State University, Division of Sports Medicine in the Department of Pediatrics, University of Cincinnati; Department of Physical Therapy, School of Health Science, High Point University, North Carolina; Departments of Orthopedic Surgery, College of Medicine, University of Cincinnati; Departments of Athletic Training, Sports Orthopedics and Pediatric Science, Rocky Mountain University of Health Professionals; Departments of Physiology & Cell Biology, Family Medicine, Orthopedics and Biomedical Engineering, Ohio State University, Columbus Ohio.

Publication Information:

Sports Medicine 2012; 42(8): 697-706.

Background Information:

Most athletes perform strength and conditioning protocols to improve their performance. Typically, these programs include core strengthening in some way. Bearing this in mind, a pertinent question arises: Does improving core strength and stability actually improve performance? While several studies have attempted to draw conclusions on this issue, the current body of evidence has failed to reach consistent results. This systematic review attempted to reveal an association between core stability and sports-related performance measures. Secondarily, the authors sought to identify any potential difficulties encountered while attempting to train the core with the goal of improving athletic performance.

Summary:

Operational Definitions:
  1. The core includes both the passive and active structures, including bone, muscle and ligaments of the lumbar spine, pelvis and hip (1-4).
  2. Core strength: the ability of the core muscles to generate and maintain force.
  3. Core stability: the ability of the active and passive stabilizers in the lumbopelvic spinal regions to maintain trunk and hip posture, balance and control whilst performing either static or dynamic movement.
The average PEDro score for all non-randomized studies was 4.6 ± 1.1. On average, randomized articles scored 6.4 ± 0.7. The average score for all studies (n = 24) was 5.3 ± 1.3.

General Performance:

Seven studies reported significant improvements in maximum lift performance, post-intervention. In many of these studies, core training was not performed in isolation, but as part of a whole training program.

Interventions that targeted the core showed improvements in core stability and endurance. One study showed improvements in isometric back endurance and one-minute sit-up test after 10 weeks of group aerobics, while another showed significant positive changes in Sahrmann core stability testing after training with a Swiss ball. However, it is important to note that improvements were not observed uniformly.

In spite of these positive results, some studies showed insignificant improvement in some core endurance tests. One such study featuring elite baseball players, had a control group who performed a generalized strength and conditioning program and an experimental group who performed additional core stability exercises. This study showed an improvement in flexor muscle endurance, but no difference in the magnitude of increase between groups. The same study also found no increase in back-extension endurance or side-bridge endurance in either group.

Some authors have chosen to examine performance in core stability tests after a core stability training program on labile surfaces. One such study found improvements in the duration spent standing one-legged on a BOSU ball and in the time to complete a shuttle-run. However, the results did not last 2 weeks post-cessation of training. As a result, the researchers concluded that training on a BOSU ball may improve dynamic skills and sway parameters, and that it is uncertain as to whether these skills actually transfer to sporting activity.

Lower Extremity Performance:

The core plays a significant role in creating stability in the lumbopelvic region and in transferring energy dynamically from the lower limb through the rest of the body. Much like the studies above, the articles studying core training and running found mixed results: 3 studies found positive increases in running performance, while another two showed no improvement. This overall conclusion is likely due to the fact that, throughout the literature, the groups included in the studies, training programs and study durations were not homogeneous.

Other studies focused on the effects of core training on lower extremity strength. One study examined the changes elicited by 10 weeks of targeted neuromuscular training (TNMT: the authors offer no definition of what this is) of the trunk and hip in high-school female volleyball players. At the end of the 10 week program, TNMT increased standing hip abduction strength, leading the authors to conclude that this improvement might improve the ability of female athletes to better control their lower extremity and lumbopelvic region. This obviously requires further research!

Upper Extremity Performance:

The studies incorporated into this part of the review analyzed both males and females competing in baseball, handball and golf. In one 12-week study of high-school baseball athletes, forty-nine players were randomized to a generalized training program for baseball plus 100 bat swings per day, or a second group who performed additional full-body medicine ball exercises. The performance measures used were squat and bench press 1RMs and torso rotational strength. Sport specific measures included throw and linear bat velocity. While both groups improved substantially, the group performing the medicine ball exercises demonstrated significantly greater rotational strength gain, swing velocity, angular hip and shoulder velocity, compared to the other group.

Another recent study involved 24 female handball players, who were stratified by team and assigned to either an experimental or a control group. After six-weeks of core and rotational exercises, the experimental group showed a statistically significant 4.9% increase in maximal throwing velocity over the control group, who did not change at all. Similar results to this last study were found in golfers after an 8-week golf-specific training program consisting of abdominal and hip strengthening, and balance exercises.

Clinical Application & Conclusions:

Overall, it remains uncertain whether core training, in and of itself, improves athletic performance. While many studies showed that a strong and stable core provided a necessary foundation for the performance of athletic tasks, there were a number of studies that concluded there was either no effect, or no difference when compared to a control/comparison group. The general trend of the 24 studies included in this analysis that studied athletes in particular, suggests that improving sport-specific measures improves performance. On the whole, athletes respond better to targeted, or sport-specific training (I think we can all agree on this). What remains to be determined is the specific role core training has in athletic performance.

While athletes respond to targeted training with little improvement in general measures, the reverse holds true for non-athletic populations. Some of the studies also featuring non-athletes included in this review reported a significant improvement in general performance measures in this population.

Core stability and endurance training is commonly used in strength and conditioning programs, in spite of the fact that there is little evidence to prove a direct positive contribution to athletic performance above and beyond a well thought out strength and conditioning program. While this is true, core training appears to be effective in improving the overall performance of non-athletic adults.

Study Methods:

The MEDLINE, CINAHL and SPORTDiscus electronic databases were accessed and screened for studies published between 1982 – (June) 2011. Unpublished studies, and studies published in any language other than English were excluded. Articles were included if the intervention was targeted to the core musculature and featured outcome measures pertaining to athletic performance.

Each of the 24 studies included were given a score using the Physical Therapy Evidence Database (PEDro) scale. This scale involves assigning a score based on the fulfillment of 11 criteria, designed to assess internal and external validity of a trial. At the end, each study is given a score out of 11, with 11/11 representing a perfect score.

Study Strengths / Weaknesses:

Strengths:
  • While intending to study the effects of core training on athletic performance, the authors also commented on the effect of this type of training on the general population. This is clinically important, as many manual therapists and trainers do not exclusively treat or train athletes.
Weaknesses:
  • The study did not account for the fact that generalized strength and conditioning exercises such as squats, deadlifts and push-ups have a large core musculature challenge. Could this be why some studies featuring athletic populations did not see a difference between control groups who performed a generalized strength and conditioning protocol and an experimental group who performed the same general program with additional exercises targeting the core?
  • When examining lower extremity tasks, it is largely incomplete to measure strength and recruitment of muscles. While this is an important factor for identifying the capacity of the individual, it is impossible to draw a conclusion on whether or not the increased capacity will transfer to having greater control of the lumbopelvic region, and thus the lower extremity. Many times, control needs to be engrained into an individual’s motor task programming. While it is presumably important to increase the capacity of the individual, remember that capacity isn’t everything – it needs to be controlled throughout the functional range of motion.
  • Performing an RCT is very difficult in populations such as these, thus identifying a cause and effect relationship between variables is extremely difficult.

Additional References:

  1. Wilson JD, Dougherty CP, Ireland ML, et al. Core stability and its relationship to lower extremity function and injury. J Am Acad Orthop Surg 2005; 13(5): 316-25.
  2. Zazulak BT, Hewett TE, Reeves NP, et al. The effects of core proprioception on knee injury: a prospective biomechanical-epidemiological study. Am J Sports Med 2007; 35(3): 368-73.
  3. Mendiguchia J, Ford KR, Quatman CE, et al. Sex differences in proximal control of the knee joint. Sports Med 2011; 41(7): 541-57.
  4. Willardson JM. Core stability training: applications to sports conditioning programs. J Strength Cond Res 2007; 21(3): 979-85.