Electromyographic analysis of core training exercises using Bosu® and Flyboard® tools

Purpose: Core stability and strength exercises are commonly included in different training programs in order to improve performance, prevent injuries and enhance functional rehabilitation. Previous researches highlighted the importance of these components to increase neuromuscular control and trunk strength in sport, fitness and medical fields, and several tools have been suggested. In particular, unstable surfaces (like Bosu® and Flyboard®) have been investigated in order to analyse core musculature during specific exercises. Even if previous studies suggested how to train those muscles in different conditions, the role of unstable surfaces is still debate. The aim of this study is to investigate the activation of abdominal and lumbar muscles during trunk movements executed with specific tools and body positions. Methods: Ten healthy and trained people volunteered for the study (8 male and 2 female, mean age 27,8 years). They performed 4 exercises using Bosu® and Flyboard® : trunk flexion (supine position on the tools - FLEX), trunk extension (prone position on the tools - EXT), sagittal body sway (vertical position on the tools – SAG) and frontal body sway (vertical position on the tools - FRONT). Each movement was executed by holding static muscles contraction at specific body position in order to highlight muscles activation. Muscle activity was recorded using electromyography (EMG) for rectus abdominis (RA), obliquus externus (OE) and lumbar erector spinae (ES) in right (R) and left (L) side of the body. Data were analysed in order to compare different surfaces (Bosu® and Flyboard®) and to quantify the role of each muscle. Results: Muscle activity changed in relation to specific tool and body position. In particular, FLEX evidenced higher values for RA using Flyboard® and for OE using Bosu® in both sides, even if the differences between two surfaces were not significant (p>0.05). EXT highlighted similar EMG activity for ES R and ES L in both tools (p>0.05). FRONT global muscle activity is significantly superior using Flyboard® compared to Bosu ® (p<0.05). In particular, OE and ES for R and L side showed higher values in relation to sway direction (p<0.05). SAG evidenced increased muscles activity for RA and OE during posterior sway and for ES during anterior sway, (p<0.01) even if no differences were found between two tools (p>0.05). Conclusions: Bosu® and Flyboard® increase muscle activity in a similar way during trunk flexion and extension movements. Although the differences were not significant, Bosu® and Flyboard® seem to mainly improve OE and RA activation, respectively. The level of instability and tool’s shape could determine these results. Body sway movements in frontal plane elicit higher muscle activity using Flyboard®, while no differences between surfaces emerge in sagittal plane. The stabilizing role of core musculature is highlighted during anterior and posterior sway, where front and back muscles are differently involved in lumbo-pelvic control. Consequently, isometric exercises using Bosu® and Flyboard® can effectively challenge the core region. Reference: Imai A., Kaneoka K., Okubo Y., Shiina I., Tatsumura M., Izumi S., Shiraki H., “Trunk Muscle Activity During Lumbar Stabilization Exercises on Both a Stable and Unstable Surface”, J Orthop Sports Phys Ther 2010 Jun ; 40(6):369-75.