An Investigation Into the Short-Term Effects of Photobiomodulation on the Mechanical Nociceptive Thresholds of M. Longissimus and M. Gluteus Medius, in Relation to Muscle Firing Rate in Horses at Three Different Gaits.
Authors: Ahmed Waqas, Elbrønd Vibeke S, Harrison Adrian P, Hart Jane O, Williams Rhian E
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Back pain remains prevalent in equine practice, yet objective measures of treatment efficacy are limited. Waqas and colleagues used mechanical nociceptive threshold (MNT) testing via algometry and acoustic myography (AMG) to assess muscle response in eight riding horses (mean age 17 years) before and after class 1 laser therapy applied to the thoracolumbar longissimus and gluteus medius muscles. Whilst MNT readings showed no significant change at 1 and 24 hours post-treatment, AMG analysis revealed statistically significant improvements in temporal summation (T-scores) across all three gaits at 24 hours, indicating altered motor unit firing patterns consistent with those observed in pain relief scenarios. These findings suggest that photobiomodulation may modulate neuromuscular function through mechanisms affecting muscle activation rather than nociceptive sensation alone. For practitioners using laser therapy, this research provides quantitative evidence of physiological change at the muscular level, though the clinical relevance of improved firing patterns without corresponding pressure pain threshold elevation warrants further investigation in horses with diagnosed back pain rather than healthy animals.
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Practical Takeaways
- •Cold laser therapy may improve muscle firing patterns and coordination in the back and hip muscles, even if it does not directly increase pain thresholds measured by algometry
- •Any benefits from laser therapy on muscle function appear to develop within 24 hours rather than immediately, so expect delayed rather than acute effects
- •The dissociation between unchanged pain thresholds and improved muscle firing suggests laser therapy may work through mechanisms other than simple pain relief in healthy horses
Key Findings
- •No significant effect of class 1 laser therapy on mechanical nociceptive thresholds at 1 hour or 24 hours post-treatment
- •Statistically significant improvements in acoustic myography T-scores for M. longissimus and M. gluteus medius across walk, trot, and canter gaits at 24 hours post-treatment
- •Changes in muscle firing frequency observed post-laser therapy were consistent with patterns seen during analgesia in pain-experiencing subjects