Introduction

Myofascial pain syndrome is a common condition marked by the presence of trigger points. A trigger point is a sensitive spot within a tight band of skeletal muscle fibers. Pressing or stretching this area may provoke local pain, referred pain, weakness, stiffness, or even changes in the autonomic nervous system such as sweating or changes in heart rate.

Trigger points are often detected in patients with musculoskeletal pain, with some studies suggesting that up to 85 percent of people experience them during their lifetime. In animals, including horses, awareness of trigger points is increasing, and they are now recognized as a frequent source of musculoskeletal dysfunction.

The exact cause of trigger points is not fully agreed upon, but current evidence points to muscle overload, repetitive strain, or fatigue. These conditions can lead to abnormal release of neurotransmitters at the neuromuscular junction, elevated calcium levels in muscle cells, and persistent electrical activity in the muscle fibers. Together, these changes contribute to the formation of a tight, palpable band and increased sensitivity.

In horses, trigger points are often associated with conditions such as back pain, girth aversion, or impaired performance. Because horses cannot verbally report their pain, therapists must rely on clinical signs such as changes in posture, altered gait, skin twitching, sudden withdrawal reactions, or characteristic pain-related facial expressions.

One therapeutic approach for trigger points is dry needling. This technique involves inserting thin sterile needles directly into the sensitive spot, aiming to reduce pain and restore normal muscle function. A common side effect in humans is temporary soreness after treatment, which may reflect the intensity of the muscle’s twitch response during needling.

This study examined whether dry needling could reduce pain associated with trigger points in the brachiocephalic muscle of horses. It also investigated whether the number of local twitch responses observed during treatment influenced short-term pain relief, functional improvement, or post-treatment soreness.

Materials and Methods

The study included ninety-eight horses aged between five and fifteen years. All were clinically healthy but presented with at least one trigger point in the lower portion of the brachiocephalic muscle, identified through palpation, observation of pain-related behaviors, and gait assessment. Horses showing aggressive behavior or intolerance to handling were excluded.

Horses were randomly assigned to two groups: a treatment group, which received dry needling, and a control group, which did not. Interventions were carried out once a week for three weeks by an experienced equine physiotherapist. All sessions followed strict protocols to ensure consistency, including standardized grooming, controlled environments, and post-treatment activity restrictions to prevent overuse of the treated muscle.

Pain and function were measured using several methods:

• Pressure pain threshold testing with an algometer to quantify sensitivity.
• Observation of facial expressions associated with equine pain.
• Jump sign responses, such as sudden withdrawal during palpation.
• Owner-reported outcomes, including a numerical pain rating and a functional test score that assessed movement and performance.

Dry needling was performed using the “fast-in, fast-out” technique, with the number of local twitch responses counted during each one-minute treatment session.

Results

The results showed a clear effect of dry needling on pain reduction.

• Pressure pain thresholds: Horses in the treatment group showed progressively higher tolerance to pressure over the three-week period, while the control group showed little change. The greatest improvements were seen after the third session.
• Functional scores: Owners reported progressive improvement in performance-related behaviors, such as ease of rein contact and forelimb engagement.
• Pain ratings: Owners also reported significant reductions in perceived pain, especially after the third week.
• Local twitch responses: The number of twitch responses decreased week by week, corresponding with improved pain tolerance.
• Facial expressions and jump sign: No consistent changes were found, suggesting that these measures may be less sensitive to the subtle changes associated with trigger point pain.

A temporary increase in sensitivity was noted within 24 hours of treatment, which resolved by 72 hours, suggesting that horses may experience a form of post-needling soreness similar to humans.

Discussion

This is the first large-scale study to show that dry needling reduces myofascial pain in horses, as measured both by objective tools and by owners’ observations of performance. The results align with human research showing that dry needling reduces pain and improves muscle function, even if short-term soreness is sometimes observed.

The role of local twitch responses remains debated. In this study, a reduction in twitch responses over time correlated with less pain, suggesting they may indicate successful treatment. However, it remains unclear whether eliciting twitch responses is essential for long-term improvement.

Interestingly, measures such as facial expression scoring and jump sign presence did not capture changes, raising questions about their sensitivity to myofascial pain specifically. Owner-reported scores, in contrast, closely mirrored the objective improvements, highlighting the value of including owner perspectives in equine rehabilitation studies.

Clinical Implications for Therapists

• Dry needling can be an effective tool for reducing myofascial trigger point pain in horses, with measurable benefits in both pain sensitivity and functional performance.
• Post-treatment soreness is likely, but usually resolves within two to three days. This should be explained to owners to set realistic expectations.
• Local twitch responses may serve as a useful guide during treatment, but their necessity remains under discussion.
• Owner-reported outcomes are a valuable complement to clinical and instrumental measures in equine physiotherapy.
• Careful palpation skills and standardized assessment protocols remain essential for accurate identification and monitoring of trigger points.

Conclusion

Dry needling of trigger points in the brachiocephalic muscle significantly reduced pain and improved function in horses over a three-week period. While temporary soreness may occur, the overall benefits support dry needling as a safe and effective therapy for equine myofascial pain. For therapists, this study underscores the importance of integrating manual palpation, objective pain measurement, and owner feedback to optimize treatment outcomes.