Why Horses Get Muscle Soreness After Exercise: DOMS Explained

Is It Lactic Acid or Delayed Onset Muscle Soreness?

Muscle soreness after exercise is common in equine athletes, yet the underlying cause is often misunderstood. Riders frequently attribute soreness to “lactic acid buildup,” but research shows that this explanation is incorrect.

The condition most commonly responsible for delayed post-exercise muscle soreness is Delayed Onset Muscle Soreness (DOMS). DOMS refers to muscle pain and stiffness that develops 24 to 72 hours after intense or unfamiliar exercise due to microscopic damage within muscle fibers.

Understanding why DOMS occurs helps riders manage recovery more effectively and reduce the risk of compensatory movement patterns that may contribute to injury.

What Is Delayed Onset Muscle Soreness in Horses

Delayed Onset Muscle Soreness occurs when microscopic tears develop within muscle fibers during exercise. This type of damage most commonly occurs when muscles experience unfamiliar or high mechanical stress.

DOMS is particularly associated with:

• eccentric muscle loading
• unfamiliar exercise intensity
• sudden increases in training volume
• new movement patterns or training demands

These microscopic tears trigger a localized inflammatory response as the body begins repairing the damaged tissue. The inflammatory process contributes to soreness, stiffness, and temporary reductions in muscle performance.

Exercise physiology research demonstrates that DOMS results from structural muscle damage and inflammatory repair processes, rather than metabolic waste accumulation (Cheung et al., 2003).

The Myth of Lactic Acid Buildup

A persistent myth in both human and equine sports is that muscle soreness is caused by lactic acid buildup.

In reality, lactate produced during exercise is cleared from muscle tissue relatively quickly, often within 30 to 60 minutes after exercise.

Lactate is not a harmful waste product. It plays a beneficial role in metabolism by acting as a temporary energy substrate for working muscles and can be recycled by the liver through the Cori cycle.

Research has shown that lactate does not inhibit muscle contraction and is not responsible for delayed muscle soreness (Robergs et al., 2004).

The soreness associated with DOMS occurs long after lactate levels have returned to baseline, further confirming that lactate accumulation is not the cause.

Why DOMS Matters in Performance Horses

Although DOMS represents a normal adaptive response to exercise, unmanaged muscle soreness can influence movement patterns and performance.

When muscles are sore, horses may alter their biomechanics to reduce discomfort. These compensations can change how forces are distributed throughout the body.

Potential consequences include:

• reduced joint range of motion
• decreased shock absorption
• altered muscle sequencing and recruitment patterns
• compensatory loading of surrounding structures

Over time, these compensatory movement patterns may contribute to muscular imbalance or increase the risk of injury if underlying soreness is not addressed (Proske and Morgan, 2001).

Signs Your Horse May Be Experiencing DOMS

Recognizing the signs of post-exercise muscle soreness allows riders to adjust training and recovery strategies appropriately.

Common indicators include:

• sensitivity to muscle palpation
• stiffness during movement
• reluctance to move forward
• shortened stride
• reduced performance in collected movements

These signs often appear one to three days after intense exercise, rather than immediately following work.

Because DOMS develops gradually, riders may notice subtle changes in movement quality or willingness before obvious stiffness becomes apparent.

DOMS vs Tying Up in Horses

How to Tell the Difference

One reason muscle soreness is frequently misunderstood in horses is that Delayed Onset Muscle Soreness (DOMS) is sometimes confused with exertional rhabdomyolysis, commonly called tying up.

Although both conditions involve muscle discomfort after exercise, they are very different physiologically and clinically.

Delayed Onset Muscle Soreness (DOMS)

DOMS is a normal response to unfamiliar or intense exercise. It occurs when microscopic muscle fiber damage triggers an inflammatory repair response.

Key characteristics include:

• soreness appearing 24 to 72 hours after exercise
• mild to moderate muscle stiffness
• sensitivity to palpation of affected muscle groups
• slight reduction in performance or range of motion
• gradual improvement over several days

DOMS is part of the normal adaptation process that occurs when muscles are exposed to new workloads (Proske and Morgan, 2001).

Tying Up (Exertional Rhabdomyolysis)

Tying up is a pathological muscle injury involving significant muscle cell damage.

Unlike DOMS, tying up usually develops during exercise or immediately afterward.

Common signs include:

• severe muscle stiffness, particularly in the hindquarters
• reluctance or refusal to move
• sweating and increased heart rate
• firm, painful muscles
• shortened stride or inability to continue exercise

In some cases, muscle breakdown products such as myoglobin may be released into the bloodstream and appear in the urine, which can cause dark or coffee-colored urine.

Exertional rhabdomyolysis involves disruption of normal muscle cell metabolism and calcium regulation within the muscle fiber (Valberg, 2018).

Why This Distinction Matters

Confusing DOMS with tying up can lead to inappropriate management decisions.

DOMS is generally managed with active recovery, reduced workload, and supportive care.

Tying up, however, may require immediate cessation of exercise and veterinary evaluation, especially if severe muscle pain or abnormal urine color is observed.

Recognizing the difference between these conditions helps riders respond appropriately and protect the horse’s long-term musculoskeletal health.

Best Strategies to Minimize DOMS in Horses

Effective management of delayed muscle soreness focuses on supporting recovery while maintaining appropriate movement.

Active Recovery

Gentle exercise is one of the most effective ways to reduce post-exercise muscle soreness.

Light activity helps:

• increase circulation through fatigued muscles
• facilitate removal of metabolic byproducts
• restore normal muscle function
• maintain joint mobility

Horses in regular training often benefit more from reduced intensity exercise for one to two days following strenuous work rather than complete inactivity (Cheung et al., 2003).

Targeted Workouts

During recovery periods, riders can adjust training programs to work less affected muscle groups while allowing fatigued tissues time to recover.

For example:

• focusing on flatwork instead of jumping
• reducing collection demands
• incorporating light stretching work

This approach helps maintain conditioning while avoiding excessive stress on sore muscles.

Nutrition and Recovery Support

Nutritional strategies may also support muscle recovery and reduce exercise-related muscle damage.

Branched-Chain Amino Acids (BCAAs)

BCAAs support muscle protein synthesis and may reduce markers of muscle damage such as creatine kinase when consumed before exercise (Shimomura et al., 2006).

Magnesium Glycinate

Magnesium plays an important role in neuromuscular signaling and muscle relaxation. Adequate magnesium intake may help reduce muscle tension and support recovery (Volpe, 2015).

L-Theanine

L-theanine has been studied for its potential effects on stress reduction and neurological recovery following exercise (Nathan et al., 2006).

N-Acetylcysteine (NAC)

NAC supports antioxidant activity and may help reduce oxidative stress associated with muscle damage while supporting tissue recovery (Kerksick et al., 2018).

Biomechanics and Muscle Fatigue

Muscle soreness is influenced not only by training intensity but also by biomechanical efficiency.

When joints move inefficiently or asymmetrically, certain muscle groups may compensate by increasing workload and fatigue. Over time, these patterns can contribute to repeated soreness following exercise.

Chiropractic care focuses on restoring normal joint motion and neuromuscular coordination. By improving segmental mobility and proprioceptive input, chiropractic adjustments may help reduce compensatory muscle loading patterns during training.

Improved biomechanics can allow muscles to work more efficiently, potentially reducing excessive fatigue and improving recovery between training sessions (Haussler, 2009).

Key Takeaways

Delayed Onset Muscle Soreness results from microscopic muscle damage and inflammatory repair processes, not lactic acid accumulation.

Recognizing and managing DOMS helps maintain optimal movement, performance, and injury prevention in equine athletes.

Active recovery, thoughtful training progression, nutritional support, and biomechanical management all play important roles in helping horses recover effectively after intense work.

Frequently Asked Questions About Muscle Soreness in Horses

Can horses develop delayed onset muscle soreness?

Yes. Horses can develop delayed onset muscle soreness (DOMS) after intense or unfamiliar exercise, just as humans can. DOMS occurs when microscopic muscle fiber damage triggers an inflammatory repair response. This soreness typically appears 24 to 72 hours after exercise and resolves gradually as muscle tissue repairs itself (Cheung et al., 2003).

How long does muscle soreness last in horses?

Mild muscle soreness associated with DOMS usually lasts two to four days. During this period, horses may show stiffness, sensitivity to palpation, or reduced range of motion.

Gradual improvement should occur as the muscle repair process progresses. Persistent soreness beyond several days may indicate excessive training stress or another underlying musculoskeletal issue.

Should a sore horse be rested completely?

Complete rest is not always necessary for mild post-exercise muscle soreness.

In many cases, active recovery is more beneficial. Light exercise such as hand walking or low-intensity riding can improve circulation and help restore normal muscle function.

However, if a horse shows severe pain, reluctance to move, or signs of tying up, exercise should stop and veterinary evaluation may be necessary.

Can poor biomechanics contribute to muscle soreness?

Yes. Inefficient movement patterns can increase stress on specific muscle groups. When joints move asymmetrically or with restricted motion, certain muscles must compensate by working harder.

Over time, this increased workload can contribute to fatigue and soreness after exercise. Addressing biomechanical contributors such as joint mobility, muscle balance, and rider symmetry may help reduce recurrent muscle soreness (Haussler, 2009).

Does lactic acid cause muscle soreness?

No. Research has demonstrated that lactic acid is not responsible for delayed muscle soreness.

Lactate produced during exercise is cleared from muscle tissue relatively quickly and can even serve as an energy source for muscles. DOMS occurs hours to days later and is associated with microscopic muscle fiber damage and inflammation, not lactate accumulation (Robergs et al., 2004).

How can riders reduce the risk of DOMS in horses?

Riders can reduce the risk of delayed muscle soreness by:

• increasing training intensity gradually
• incorporating structured cool-down periods
• allowing appropriate recovery between demanding workouts
• supporting hydration and electrolyte balance
• maintaining proper biomechanics during training

Consistent training management is one of the most important factors in preventing excessive muscle soreness.

References

Cheung K, Hume P, Maxwell L. 2003. Delayed onset muscle soreness: treatment strategies and performance factors. Sports Medicine. 33(2):145 to 164.

Kerksick C, et al. 2018. International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition. 15:38.

Nathan PJ, Lu K, Gray M, Oliver C. 2006. The neuropharmacology of L-theanine. Biological Psychology. 73(1):39 to 46.

Proske U, Morgan DL. 2001. Muscle damage from eccentric exercise: mechanism, mechanical signs, adaptation and clinical applications. Physiological Reviews. 81(4):1725 to 1772.

Robergs RA, Ghiasvand F, Parker D. 2004. Biochemistry of exercise induced metabolic acidosis. American Journal of Physiology. 287:R502 to R516.

Shimomura Y, et al. 2006. Nutraceutical effects of branched-chain amino acids on skeletal muscle. Journal of Nutrition. 136(2):529S to 532S.

Valberg SJ. 2018. Skeletal muscle disorders in horses. Veterinary Clinics of North America: Equine Practice. 34(2):329 to 350.

Volpe SL. 2015. Magnesium in disease prevention and overall health. Nutrients. 7(9): 8199 to 8226.

Haussler KK. 2009. Chiropractic evaluation and management of musculoskeletal disorders in horses. Journal of Equine Veterinary Science. 29(5):346 to 350.

Author

Dr. Arianna Aaron, DC, IVCA
Founder, Peak Performance International
Equine and Rider Chiropractic Care

Dr. Arianna Aaron is a chiropractor specializing in horse and rider biomechanics and performance optimization. Through Peak Performance International, she works with equine athletes and their riders to improve movement efficiency, address biomechanical restrictions, and support long term soundness and athletic performance.