Is Core Really Important for Performance? - Part II

In our last article, we talked about what composes the core in general terms and looked at a study by Butcher et al which investigated the impact that core training has on vertical takeoff.   The results of this study showed that core training had a direct impact on vertical jump and hence power output.  This was one of the first studies to highlight the impact that core training can have on performance. 

In 2013, in the Journal of Strength and Conditioning Research, Hoshikawa et al looked at the impact that stabilization training would have on muscularity and physical performance in soccer players.     

Methods:  Twenty eight male youth soccer players 12-13 years of age participated in the study.  Subjects were allocated to either a control group (N=13) or training group “TG” (N=16).  All subjects were players from one of Japan’s most successful soccer clubs and participated in a supervised competitive soccer training program and had daily food intake supervised by clubs nutritionist.  The soccer training program consisted of 5 days per week, 2 hours per day and 1 game on weekends.  The soccer training was same for both groups.  In addition to the soccer training program, the TG also performed a stabilization training program consisting of 5 exercises performed 4 times per week.  The 5 exercises consisted of:

• Elbow-Toe (more commonly known as plank) – this was performed for 30 seconds.
• Elbow-heel (more commonly known as pike position) – this was performed for 30 seconds
• Side-Bridge (also known as side plank) – this was performed for 30 seconds
• Modified 1 legged squat – 10 reps per set
• Bent knee push-up – 20 reps per set.

During the 6 months of the training program, each of the exercises were performed for 1-2 sets per training session.  Prior to initiation of the training and immediately after conclusion of the six months of training, the cross sectional area of the rectus abdominus, obliques, psoas major, quadratus lumborum and erector spinae were determined via MRI.  Both groups also had peak torques during hip extension and flexion @ 1.05 rad/second measured, peak heights of squat and countermovement jumps taken and time taken to sprint 15 m measured for all subjects. 

Results:  At the conclusion of the study, what the investigators found was that both the TG and the control group had significant increases in cross sectional area (13.4% increase TG & 10.9% increase control) of the muscles examined and improved sprint time (1.4% TG & 1.6% control).  However, the results were not significantly different between the two groups.  But the control group had significant increases in peak height of the squat jump, countermovement jump and increased hip extension torque. 

Discussion:  The results of this study are further indication that even low level core training does have a direct impact on performance.  In this example, the most significant impact appears to be to power output or vertical jump.  When reviewing this study, several questions are raised.

1.      Supervision.  The authors made a point to acknowledge that the soccer training program was supervised but did not mention if the core stabilization training was supervised.  If these exercises were not supervised, it is highly suspected that they would be performed incorrectly and hence the full training effect may not have been realized.

2.      Intensity.  The core stabilization protocol was very low level considering the level of athlete.  When reviewing the soccer training schedule in comparison to the core stabilization training, the core stabilization training appears too low to elicit a physiological and neuromuscular training effect.  The duration of the exercises and the limited number of repetitions would be too easy for this level of athlete and hence lead to limited physiological and neuromuscular change.

3.      Progression.  All of the exercises in the core stabilization program remained at the same level of intensity throughout the study.  So, even though the subjects may have been able to progress to a higher level of intensity to facilitate further physiological adaptation and neuromuscular change, the intensity stayed the same throughout.

4.      Muscles tested.  Despite the fact that the Okubo et al, as well as others, have shown the % of maximal volitional contraction is highest in the transverse abdominus and multifidus with plank test, the cross sectional area of these muscles was not assessed.  Willson et al also showed that the % MVC of the gluteus medius was not only high in side plank position and single leg squat but also instrumental in lower extremity function and injury prevention.  However, the cross sectional area of this muscle was also not assessed.

Although the above points to some flaws in the study, this should not detract from the significance of the results.  Core training, no matter how limited, does impact performance.  Can you imagine if this training had been more directed and intense, what the net result to performance could have been?  If you are including core training, make sure it is direct, make sure it is of appropriate intensity to promote physiological and neurological adaptation without promoting poor technique and make sure it is supervised and progressed according to ability.  Train hard, train well and train smart.  Doing so will prevent injuries and improve performance.