Equine Body Muscle Score: A Professional Guide to Assessing Muscle Mass and Muscle Loss

Muscle Atrophy Scoring System, or MASS

Introduction

A horse’s muscle development is one of the most important indicators of strength, athletic readiness, soundness, recovery, and overall health. Muscle supports the skeleton, stabilizes joints, powers movement, protects soft tissues, and helps the horse perform ordinary activities such as rising, walking, turning, carrying a rider, and maintaining balance.

Equine Body Muscle Scoring is a practical system used to evaluate visible and palpable muscle over key regions of the horse. The goal is not simply to decide whether a horse “looks fit,” but to identify whether muscle is normal, reduced, uneven, or progressively wasting.

Don't confuse Equine Body Muscle Score with Body Condition Scoring. Body Condition Scoring (BCS) evaluates fat, while Body Muscle Scoring evaluates muscle. A horse can have an ideal body weight but still show muscle loss, especially along the neck, back, or hindquarters. Using both systems gives a clearer picture of the horse’s overall health, nutrition, strength, and physical condition. Read our article Body Condition Scoring: What It Is And How To Score Your Horse to learn more.

A research-based framework commonly used for this purpose is the Muscle Atrophy Scoring System, or MASS, which assigns a score from 1 to 4 to specific regions of the horse.

In this system 1 indicates no muscle atrophy, while 4 indicates severe muscle atrophy. The system was developed to provide a practical way to monitor skeletal muscle loss because more technical methods of measuring muscle mass can require specialized expertise, equipment, or expense. 

Learn more about muscle anatomy with Horse Muscle Anatomy Explained: Major Muscle Groups, What They Do, And Why They Matter

Why Muscle Scoring Matters

Muscle loss can be gradual, subtle, and easy to overlook. A horse may continue eating normally and may even appear generally well while losing muscle over the topline, neck, or hindquarters. Regular muscle scoring helps identify these changes before they become severe.

A professional muscle score can help:

• Establish a baseline for each horse

• Monitor aging horses

• Evaluate response to nutrition and exercise programs

• Track rehabilitation after injury or illness

• Identify muscle loss associated with pain, disuse, or disease

• Detect asymmetry that may suggest lameness, neurologic disease, or uneven use

• Improve communication between owners, veterinarians, farriers, trainers, and nutrition professionals

Loss of skeletal muscle mass may compromise both performance and welfare, which is why routine monitoring has practical value in horse management. In the MASS research, evaluations of the neck, back, and hindquarter regions showed acceptable reliability among trained raters, while the abdominal region was less reliable and is generally less useful as a primary scoring region. 

The Overall Scoring System

The equine body muscle score is best understood as a regional scoring system, not simply one whole-horse number.

The most useful regions to assess are:

1. Neck

2. Back

3. Hindquarters

Each area is scored separately on a 1 to 4 scale: 

This scoring approach allows the evaluator to describe where muscle loss is occurring, how severe it is, and whether it is symmetrical. A horse may score normally in the neck but show moderate loss through the back and hindquarters. Another horse may show severe loss on one side of the hindquarters only. These patterns are clinically important and should not be hidden by a single average score.

How Scores Are Achieved

Professional muscle scoring combines visual assessment and palpation. The evaluator looks at the horse, feels the muscle groups with a flat hand, compares both sides of the body, and assigns the score that best matches the observed shape, tone, and tissue depth.

1. Prepare the Horse

The horse should be standing square on level ground in good lighting. The coat should be clean enough to allow the evaluator to see surface contours. Thick winter hair, heavy blankets, poor lighting, uneven footing, or a tense posture can all make scoring less accurate.

The horse should be viewed from:

• Both sides

• The front

• The rear

• Slightly above or along the topline when appropriate

Photographs are helpful, but they should not replace palpation.

2. Evaluate Muscle Shape

A key principle of muscle scoring is the distinction between convex, flat, and concave muscle shape.

Convex

Convex muscle curves outward. This usually indicates normal or well-maintained muscle mass.

Flat

Flat muscle has lost some fullness. This may indicate mild or moderate muscle reduction, depending on the region and firmness.

Concave

Concave muscle curves inward. This is a stronger indicator of significant muscle loss, especially when paired with prominent bones or a rigid, soft, or poorly developed feel.

Current scoring guides advise evaluators to assess whether muscles are flat, concave, or convex, and to use a flat hand with light pressure when palpating the scored areas. 

3. Palpate Muscle Tone

Muscle should not be judged by appearance alone. Palpation helps determine whether the tissue feels firm and elastic, soft, rigid, reduced, or uneven.

When palpating:

• Keep the hand flat

• Use light, consistent pressure

• Feel both sides of the horse

• Compare left and right muscle mass

• Avoid digging with the fingertips

• Note pain, tension, heat, or flinching

Firm, elastic muscle is generally a positive finding. Soft, rigid, or markedly reduced tissue may indicate poor muscle quality or muscle loss.

4. Score Each Region Separately

The neck, back, and hindquarters should each receive their own score. In professional recording, the score should be written by region, for example:

Neck: 1Back: 2Hindquarters: 3

This is more useful than writing only “overall score 2,” because it shows the distribution of muscle loss.

When left and right sides differ, record the asymmetry clearly:

Hindquarters: Left 4, Right 2

Marked asymmetry should be discussed with a veterinarian, particularly if it is new, progressive, or associated with weakness, lameness, poor coordination, or loss of performance.

Regional Scoring Guide 

Neck

The neck is scored by looking at muscle fullness from the poll to the shoulder and by feeling the muscle along both sides of the neck.

The horse’s neck muscles can be thought of in three main groups:

1. Topline muscles, such as the splenius and semispinalis capitis, which lift and stabilize the neck.

2. Underside muscles, such as the sternomandibularis, longus colli, and longus capitis, which flex and lower the head and neck.

3. Side and shoulder-support muscles, such as the brachiocephalicus, trapezius, rhomboideus, and serratus ventralis cervicis, which help turn the neck, move the forelimb, and support the shoulder.

Study the Horse's Muscles with our Free Interactive Horse Muscles Tool

A healthy horse needs these muscles to work together so the neck can be strong, flexible, balanced, and comfortable.

Score 1: No Atrophy

The neck muscles are rounded and firm. The transition from neck to shoulder appears smooth. There is no obvious shelf, hollow, or loss of fullness.

Example: A mature riding horse in regular work has a smooth, rounded neck. The muscles feel firm and even on both sides. There is no depression where the neck meets the shoulder.

Score 2: Mild Atrophy

The neck begins to look flatter. A slight shelf may appear where the neck joins the shoulder. Muscle is still present but has lost some roundness.

Example: A horse returning from several weeks of reduced exercise has a slightly flatter neck than usual. The muscles still feel firm, but the transition into the shoulder is less smooth.

Score 3: Moderate Atrophy

The neck muscles are clearly reduced. They may appear flat or slightly concave. The neck may look narrower, and the shelf near the shoulder becomes more apparent.

Example: An older horse has a narrow neck with reduced muscle on both sides. The shoulder-neck junction is angular, and the muscles feel less elastic.

Score 4: Severe Atrophy

The neck appears hollow, thin, or sharply reduced. The muscle may feel rigid, very soft, or poorly developed. A prominent shelf may be visible where the neck meets the shoulder.

Example: A horse with progressive muscle wasting has deep concavity along the neck and a sharply defined shoulder junction. One side may be smaller than the other.

Back

The back is scored by assessing the muscles alongside the spine. These muscles are important for carrying posture, supporting the rider, transferring power from the hindquarters, and maintaining topline strength.

The main muscles of the horse’s back include the longissimus dorsi, illocostalis, spinalis, multifidus, latissimus dorsi , and the deep stabilizing muscles between the vertebrae. The abdominal muscles are also essential because they support the back from underneath.

A healthy horse’s back is not just strong. It must be flexible, stable, coordinated, and able to work with the neck, abdomen, pelvis, and limbs.

Score 1: No Atrophy

The back muscles are firm and full. The topline appears smooth. The muscles on either side of the spine are convex or flat but not hollow.

Example: A horse in steady work has a broad, firm back. The topline is smooth, and the muscles beside the spine are even.

Score 2: Mild Atrophy

The back muscles are slightly reduced. There may be mild flattening or early concavity. The top of the spine may become more visible, but the back still has reasonable muscle coverage.

Example: A horse after a short rest period shows mild loss of topline fullness. The muscles are slightly flatter than before but not deeply hollow.

Score 3: Moderate Atrophy

The back muscles are clearly reduced. Concavity may be visible alongside the spine. The bony structures of the topline become easier to see or feel.

Example: A horse that has been out of regular work for several months has a visible groove along the back, reduced muscle on both sides of the spine, and less ability to lift through the topline.

Score 4: Severe Atrophy

The back is deeply hollow. The spine is prominent, and the muscles on either side are markedly reduced. This score indicates significant muscle wasting.

Example: A chronically ill or severely deconditioned horse has a narrow, sunken back with very little muscle fullness along the spine.

Hindquarters

The hindquarters are among the most important areas to score because they contain large propulsive muscles. Loss here may affect power, balance, ability to rise, engagement, and athletic performance.

The major muscles of the horse’s hindquarters include the gluteal muscles, hamstrings, quadriceps, inner thigh muscles, deep hip stabilizers, iliopsoas, gastrocnemius, and digital flexor muscles.

A simple way to think about them is:

• Gluteals and hamstrings create power.

• Quadriceps stabilize and extend the stifle.

• Iliopsoas and hip flexors bring the hind limb forward.

• Adductors and deep hip muscles control limb position and stabilize the pelvis.

• Gastrocnemius and flexor muscles help with hock action, push-off, and lower-limb support.

Together, these muscles allow the horse to move forward, carry weight, balance, turn, stop, jump, and perform athletic work.

Score 1: No Atrophy

The hindquarters are rounded, firm, and symmetrical. The croup and gluteal muscles are well filled. Bones of the pelvis are not unusually prominent.

Example: A fit horse has rounded hindquarters with even muscle development on both sides. The muscles feel firm and elastic.

Score 2: Mild Atrophy

The hindquarters begin to lose roundness. There may be slight flattening at the top or sides of the croup. Bony landmarks may be mildly easier to identify.

Example: A horse recovering from mild lameness has slightly flatter hindquarters, but the muscles are still present and gener

ally symmetrical.

Score 3: Moderate Atrophy

The hindquarters are visibly reduced. Muscles may be concave below the point of hip or over the croup. Pelvic bones become more noticeable.

Example: A horse with reduced work due to chronic soreness has flatter, narrower hindquarters. The croup lacks fullness, and the point of hip is more apparent.

Score 4: Severe Atrophy

The hindquarters are deeply concave or markedly wasted. Pelvic bones are prominent. There may be obvious asymmetry between left and right sides.

Example: A horse with neurologic disease or severe disuse has one hindquarter much smaller than the other, with deep hollowing and loss of muscle mass.

How to Determine the Overall Result

Because muscle loss may be regional, the best professional approach is to report both regional scores and an overall interpretation.

Regional Score

Each area receives its own score:

Neck: 2

Back: 3

Hindquarters: 3

This tells the owner, veterinarian, or trainer where the problem is most evident.

Highest-Score Method

The highest regional score identifies the most severe area of muscle loss.

Example:

Neck: 1

Back: 2

Hindquarters: 4

Overall interpretation: Severe regional muscle loss, because one area scores 4.

This method is useful because it prevents serious localized muscle loss from being minimized.

Total-Score Method

For tracking progress over time, the three regional scores may also be added together:

• Minimum total: 3

• Maximum total: 12

Example:

Neck: 2 + Back: 2 + Hindquarters: 3 = Total 7

This can help monitor trends, especially when the same evaluator scores the same horse every 30 to 60 days. However, the total score should never replace the regional notes, because the pattern of muscle loss is often more important than the number alone.

Practical Scoring Examples

Example 1: Normal Muscle

Horse: 9-year-old gelding in regular work

Neck: Rounded and firm

Back: Smooth and well filled

Hindquarters: Symmetrical and muscular

Scores: Neck 1, Back 1, Hindquarters 1

Total: 3

Interpretation: No evident muscle atrophy.

Example 2: Mild Generalized Muscle Loss

Horse: 16-year-old mare returning from a period of reduced exercise

Neck: Slight flattening

Back: Mild topline reduction

Hindquarters: Slightly less rounded than previous photographs

Scores: Neck 2, Back 2, Hindquarters 2

Total: 6

Interpretation: Mild generalized muscle loss. This may reflect reduced workload, aging, early nutritional inadequacy, or a combination of factors.

Example 3: Moderate Topline and Hindquarter Loss

Horse: Mature riding horse after several months out of work

Neck: Normal

Back: Concavity along both sides of the spine

Hindquarters: Flattened croup and reduced gluteal fullness

Scores: Neck 1, Back 3, Hindquarters 3

Total: 7

Interpretation: Moderate regional muscle loss, most evident through the back and hindquarters. A progressive strengthening program and veterinary review for pain or lameness may be appropriate.

Example 4: Severe Asymmetrical Muscle Loss

Horse: Senior horse with declining coordination

Neck: Mild loss

Back: Moderate loss

Left Hindquarter: Severe wasting

Right Hindquarter: Mild to moderate loss

Scores: Neck 2, Back 3, Hindquarters Left 4 / Right 2

Interpretation: Severe asymmetrical muscle loss. This pattern warrants veterinary evaluation because uneven wasting may suggest neurologic disease, chronic lameness, or another significant medical issue.

What the Scores Mean Clinically

Score 1: No Atrophy

This is the desired finding. Muscle mass appears appropriate for the individual horse’s age, use, and management. Continue routine monitoring.

Score 2: Mild Atrophy

Mild atrophy is an early warning sign. It may reflect a recent decrease in exercise, early aging changes, poor protein intake, subtle pain, or recovery from illness. This score is often reversible when the cause is identified early.

Score 3: Moderate Atrophy

Moderate atrophy is clinically important. It suggests that muscle loss is no longer subtle. The horse may have reduced strength, reduced topline support, reduced hindquarter power, or impaired performance. A score of 3 should prompt a careful review of diet, workload, soundness, saddle fit, dental status, and overall health.

Score 4: Severe Atrophy

Severe atrophy indicates significant muscle wasting. It may be associated with chronic disease, pain, neurologic dysfunction, prolonged inactivity, malnutrition, or advanced age-related decline. A score of 4 should be treated as a serious finding, especially if the change is rapid or asymmetrical.

Rationale Behind the System

The rationale for equine body muscle scoring is based on three principles.

First, muscle loss affects function. A horse with reduced muscle may struggle to carry itself correctly, stabilize joints, generate power, or recover from work. Muscle loss may also affect welfare by making ordinary movement more difficult.

Second, muscle loss is often regional. A horse may lose muscle mainly through the back, one hindquarter, or one side of the neck. This pattern can provide valuable clues about use, pain, compensation, or disease.

Third, a practical scoring system allows repeated monitoring. Even when advanced imaging or laboratory testing is not available, a consistent visual and hands-on scoring method can identify trends over time. The MASS study found reliable scoring agreement for the neck, back, and hindquarter regions among evaluators, supporting the practical use of these areas for monitoring muscle atrophy in horses. 

Best Practices for Accurate Scoring

For the most consistent results:

• Score the horse in the same location each time.

• Use good lighting.

• Stand the horse square.

• Evaluate both sides.

• Palpate with a flat hand and light pressure.

• Record each region separately.

• Take photographs from consistent angles.

• Recheck every 30 to 60 days when monitoring change.

• Use the same evaluator whenever possible.

• Record recent exercise, illness, lameness, diet changes, and medications.

If two evaluators disagree, they should review the horse together and discuss the specific region causing disagreement. Differences often occur when one person relies too heavily on visual appearance and the other places more emphasis on palpation.

Common Causes of Reduced Muscle Score

A declining muscle score may be associated with:

• Reduced exercise or stall rest

• Inadequate high-quality protein intake

• Insufficient calories

• Dental disease

• Chronic pain

• Lameness

• Back pain

• Poor saddle fit

• Aging

• Neurologic disease

• Endocrine disease such as PPID

• Chronic inflammatory or systemic illness

• Recovery from injury or surgery

The score itself does not diagnose the cause. It identifies the presence, location, and severity of muscle loss so that the underlying reason can be investigated.

When to Seek Veterinary Evaluation

Veterinary evaluation is recommended when:

• Muscle loss is rapid

• A score increases from 1 or 2 to 3 or 4

• Muscle loss is asymmetrical

• The horse shows weakness or stumbling

• The horse has difficulty rising

• Performance declines unexpectedly

• The horse appears painful during palpation

• The topline or hindquarters deteriorate despite appropriate exercise

• Muscle loss occurs with weight loss, dullness, fever, or abnormal behavior

A professional muscle score is most valuable when combined with a broader health assessment, soundness evaluation, nutrition review, and history of the horse’s workload.

Equine Body Muscle Scoring provides a structured, practical way to evaluate muscle mass and muscle loss in horses. By scoring the neck, back, and hindquarters separately on a 1 to 4 scale, owners and professionals can identify early changes, monitor trends, and recognize patterns that may point to disuse, pain, aging, nutritional problems, or disease.

The most important principle is consistency. The same method, the same regions, the same scoring scale, and careful written records allow subtle changes to become visible over time. A muscle score is not a diagnosis, but it is a valuable clinical and management tool that helps protect performance, comfort, and long-term health.