Swiss Ball Exercises and Core Muscle EMG Activity

Introduction

Physiotherapists working in the field of musculoskeletal rehabilitation, which definitely includes sports physiotherapists (and physical therapists), will regularly utilise exercises to both strengthen and improve the neuromuscular coordination of the “core” musculature. This is seen as an important part of both injury rehabilitation and prevention. This article will discuss new EMG research into core muscle activation during a number of swiss ball exercises, and the clinical implications for therapists.

What Is The Importance of Lumbopelvic Control?

There is an ever-growing body of evidence to suggest the importance of “normal” stability and neuromuscular control of the lumbopelvic region to many facets of sports physiotherapy practice. Recruitment of the appropriate core muscles is required to enhance proximal stability, which serves as a cornerstone for the movement of distal segments.

It has been suggested for optimal core stability, both the smaller, deeper core muscles and the larger, superficial core muscles must contract in sequence with appropriate timing and tension (McGill et al., 2003). This has obvious implications for injury rehabilitation. Additionally, core control has been shown to be important for injury prevention. As an example, Myer et al (2008) showed that enhanced stability and neuromuscular control of the lumbopelvic complex decreased knee injury risk.

Thus, the importance of ensuring “normal” core or lumbopelvic control in your athletes is clear. So the pertinent question becomes: what exercises are most effective at eliciting muscle activity in these core muscles? To the research…

Core Muscle Activation During Swiss Ball Exercises

Escamilla and colleagues (2010) performed a sEMG study in an attempt to establish which exercises (both Swiss Ball and traditional) elicited the greatest activity in a number of “core” muscles. 18 healthy subjects (9 women) were recruited and underwent evaluation, which included assessment of maximum voluntary isometric contraction (MVIC) of each muscle to be used for later normalisation of results.

The core muscles evaluated were:

• Upper Rectus Abdominis
• Lower Rectus Abdominis
• External Oblique
• Internal Oblique (which has been shown to exhibit similar activation to Transversus Abdominis (within 15%) (McGill et al., 1996)
• Lumbar Paraspinals
• Latissimus Dorsi
• Rectus Femoris

Which Exercises Elicit The Greatest Core Muscle Activation?

I would suggest that sports physiotherapists are most interested in eliciting muscle activation in the deep abdominal musculature and potentially lower fibres of rectus abdominis. Thus, the exercises are presented in order (from highest to lowest) of the averages of these 2 scores. And the winner is:

1. Pike
MVIC% for Upper Rectus = 47, Lower Rectus = 55, Internal Oblique = 56.

2. Roll-out
MVIC% for Upper Rectus = 63, Lower Rectus = 53, Internal Oblique = 46.

3. Prone Hip Extension
MVIC% for Upper Rectus = 42, Lower Rectus = 41.5, Internal Oblique = 42.5.

4. Skier
MVIC% for Upper Rectus = 38, Lower Rectus = 33, Internal Oblique = 47.

5. Knee-Up
MVIC% for Upper Rectus = 32, Lower Rectus = 35, Internal Oblique = 41.

6. Crunch
MVIC% for Upper Rectus = 53, Lower Rectus = 39, Internal Oblique = 33.

7. Decline Push-up
MVIC% for Upper Rectus = 38, Lower Rectus = 36, Internal Oblique = 33.

8. Bent-knee Sit-up
MVIC% for Upper Rectus = 40, Lower Rectus = 35, Internal Oblique = 31.

9. Sitting March
MVIC% for Upper Rectus = 7, Lower Rectus = 7, Internal Oblique = 16.

So, What Does This Mean For Your Practice?

This research does show a few things that could impact your clinical practice. Firstly, it identifies obvious progressions of your “core training” for your athletes. I would suggest many physiotherapists would commence with isolated transversus abdominis contractions and spinal segment stabilisation exercises as a first line of “core” training. This should then progress to more functional and sports-specific training, which could include some of the above exercises. This research will show you which exercises can be used in early stages and obvious progressions through to more advanced and challenging exercises (e.g. Pike and Roll-Out).

Additionally, it does demonstrate the limitations of some “traditional” core exercises; the crunch and bent knee sit up. These exercises showed lower EMG activity than many of the other exercises. Furthermore, exercises such as the bent knee set up have been shown increase intradiscal pressure secondary to lumbar flexion and compression forces (Nachemson, 1976). This may suggest that exercises such as the “Prone hip extension” and “Decline Push-Up”, in which the athlete maintains a neutral spinal position, may be safer and more effective method to elicit core muscle activity.

Limitations of This Research

There are a number of limitations in this research. The first and most obvious is the use of surface EMG which may be affected by “cross-talk”, particularly when assessing the deep musculature (internal obliques). There is also the challenge of correlating EMG data with force production because eccentric muscle actions can result in lower EMG activity but higher force and with concentric muscle the converse is true (Juker et al, 1998).

Another problem I see is the generalisability of this research to this research to a clinical setting. The subjects who underwent evaluation where “normal” or pain-free athletes with no history of lumbar/pelvic pathology. Thus, we are unable to know if our injured or “rehabilitating” athletes’ core muscles will fire in the same way.

Clinical Implications of This Research

• The Pike and Roll-out elicited the higher core muscle activity
• Traditional abdominal exercises performed poorly compared to some Swiss Ball exercises
• Swiss Ball exercises such as decline push-up and prone extension can elicit more core activity than some traditional abdominal exercises, whilst maintaining a neutral spinal position