P5.71 Surface Electromyography of the Equine Splenius Muscle During Neck Exercises in Relation to Ultrasonographic Muscle Appearance

Neck muscles of the horses used in the daily life of the horses, and the splenius muscle undergoes age-related changes associated with postural and phasic muscles. The sonographic documentation of these changes as well as their effect on the muscle activity remains unknown. Investigating muscle activity, size and volume as well as sonographic muscle characteristics and the area changes of the splenius muscle during flexion-extension neck exercises. Surface electromyography activity of the splenius muscle was measured in 6 horses (3-mature horse and 3 aged) without signs of neck pain during flexion and extension of the head/neck unit as well as in a neutral position. Electrodes were placed over both splenius muscles at the level of C2. The measurements were taken by use of an EMG telemetric system with a sample frequency 1.2 kHz. For the ultrasound measurements the 7.5 MHz linear probe without a stand-off pad was used. The probe was positioned transversely and longitudinally over the left and right splenius muscles in the resulting stretched and flexed as well as neutral head/neck positions. In each position, grey-scale analysis as well as fibre alignment was assessed. Additionally, the relationship between the head/neck movement and the sonographic muscle appearance at the resulting head/neck position was assessed. Muscle volume and pattern changes were documented in the splenius muscle of the aged horses. There was a marked difference in longitudinal appearance of the contracted (in head/neck extension) and relaxed (in head/neck flexion) splenius muscles in all horses. While larger muscle volumes were associated with larger EMG activities, sonographic determination of fibrous tissue within the muscle was represented by lower EMG maximum activity during extension only. Increase of connective tissues indicates the aging effect and reduces muscle activity patterns.