Quantitative motor unit action potential analysis in 2 paraspinal neck muscles in adult Royal Dutch Sport horses

Background: Reference values for quantitative electromyography (QEMG) in neck muscles of Royal Dutch Sport horses are lacking. Objective: Determine normative data on quantitative motor unit action potential (QMUP) analysis of serratus ventralis cervicis (SV) and brachiocephalicus (BC) muscle. Animals: Seven adult normal horses (mean age 9.5 standard deviation [SD] ± 2.3 years, mean height 1.64 SD ± 4.5 cm, and mean rectal temperature 37.6 SD ± 0.3°C). Methods: An observational study on QMUP analysis in 6 segments of each muscle was performed with commercial electromyography equipment. Measurements were made according to formerly published methods. Natural logarithm transformed data were tested with ANOVA and posthoc testing according to Bonferroni. Results: Mean duration, amplitude, phases, turns, area, and size index (SI) did not differ significantly among the 6 segments in each muscle. Mean amplitude, number of phases, and SI were significantly (P < .002) higher in SV than BC, 520 versus 448 μV, 3.0 versus 2.8 μV, and 0.48 versus 0.30 μV, respectively. In SV 95% confidence intervals (CI) for amplitude, duration, number of phases, turns, polyphasia area, and SI were 488–551 μV, 4.3–4.6 ms, 2.9–3.0, 2.4–2.6, 7–12%, 382–448, and 0.26–0.70, respectively; in BC this was 412–483 μV, 4.3–4.7 ms, 2.7–2.8, 2.4–2.6, 4–7%, 393–469, and 0.27–0.34, respectively. Maximal voluntary activity expressed by turns/second did not differ significantly between SV and BC with a 95% CI of 132–173 and 137–198, respectively. Conclusions and Clinical Importance: The establishment of normative data makes objective QEMG of paraspinal muscles in horses suspected of cervical neurogenic disorders possible. Differences between muscles should be taken into account.