Background Sensorimotor exercises (SE) are evident to enhance neuromuscular activity of the trunk muscles (TM). However, it is unclear if an additional unexpected perturbation leads to higher muscular activity and therefore enhances training efficacy.

Objective To analyse effects of additional unexpected perturbations on trunk neuromuscular activation pattern during SE.

Design Cross-sectional design.

Setting University Outpatient Clinic, Sports Medicine Centre.

Participants Ten healthy, normal active participants (5 m/5 f; 29±2 yrs; 177±7 cm, 74±12 kg) were included.

Assessment of Risk Factors All participants were prepared with a bilateral 12-lead trunk EMG (Mm. rectus abdominis (RA), external obliquus (EO), internal obliquus (IO), latissimus dorsi (LD), thoracic (UES) and lumbar erector spinae (LES)). Warm-up on an isokinetic dynamometer (extension/flexion; 30 rep; 60°sec) was followed by maximum voluntary isometric contraction measurements (MVC, 5 sec). Next, a (right-armed) side plank on stable surface (SP; 30 sec) and 2 different instable conditions were randomly assigned (SP plus pad under the elbow (SPP), SPP plus perturbation (SPP+P)).

Main Outcome Measurements Root mean square (RMS) normalized to MVC (%MVC) was calculated during the whole exercise. Muscles were grouped to ventral right/left (VR;VL=mean of RA, IO, EO), and dorsal right/left (DR;DL=mean of LD, UES, LES). Differences between conditions were calculated for muscle groups, Ventral:Dorsal (V:D) and Side-Right/Side-Left ratio (S_R;S_L) (repeated-measures ANOVA; α=0.05).

Results SPP+P showed highest EMG-RMS (e.g,VR: 81±9%; DR: 55±12%) for all muscle groups except DL with significant differences (p<0.05) between conditions SP and SPP+P in VR, VL and DR muscle groups. No differences were found between SPP (e.g.,VR: 71±11%) and SPP+P (e.g.,VR: 81±9%)(p>0.05). Statistically significant higher V:D ratios was found in SPP+P compared to SP (p<0.05). S_R:S_L ratio did not show any differences (p>0.05).

Conclusions The use of additional perturbations during core stability training is superior to enhance trunk neuromuscular activity and should be implemented into sensorimotor exercises addressing the trunk.