Soft tissue injuries can be career-threatening, or even career ending, for many performance horses. Understanding how and why they happen can help riders, trainers, and owners take preventative steps before small problems turn into catastrophic injuries.
As horsemen, we need to understand the mechanics and biology behind tendon and ligament damage, from the microscopic fiber changes to the environmental and training factors that make horses more vulnerable.
The Role of Tendons and Ligaments in Movement
Knowing the difference between tendons and ligaments is the key to fully understanding how and why injuries happen, and how we can help prevent them.
Tendons connect muscle to bone. They act like springs, storing and releasing energy with each stride.
Ligaments connect bone to bone. They stabilize joints, and prevent excessive movement.
In performance horses, tendons (particularly the superficial digital flexor tendon and the deep digital flexor tendon) are subjected to extreme forces during galloping, jumping, and sudden stops. Ligaments like the suspensory ligament absorb high levels of strain to prevent the fetlock from overextending.
These structures are made primarily of collagen fibers arranged in parallel bundles for maximum tensile strength. Unfortunately, this structure has limits, and when forces exceed their capabilities, they become damaged.
Microtears
Soft tissue damage often starts at a microscopic level. Each fiber in a tendon or ligament can only stretch so far before its collagen bonds start to break. When horses train or compete at high intensity, repetitive loading causes tiny tears in the fibers, and impact forces (jumping, turning, galloping) increase strain on already stressed fibers.
In early stages, microtears are not always visible or detectable, but they weaken the structure. If rest and recovery aren't adequate, the damage accumulates, making the tissue more prone to major lesions or ruptures.
Lesions
If microtears progress, they can form lesions. These are localized areas of fiber disruption that are often visible on ultrasound. Lesions mean that sections of tendon or ligament have lost their structural integrity, reducing their ability to store and release energy efficiently.
The body attempts to repair these lesions by laying down scar tissue, but scar tissue is significantly less elastic and more brittle than healthy collagen fibers. This makes reinjury far more likely.
How Overheating Damages Soft Tissue
During intense exercise, tendons and ligaments generate heat from friction as fibers slide over one another. In horses, tendon core temperatures can exceed 110ºF (43ºC) during intense exercise.
At around 108ºF (42ºC), tendon cells (tenocytes) begin to suffer heat stress and die. This cell death impairs the tendon's ability to maintain and repair collagen fibers. Repeated overheating can lead to chronic microdamage.
Unfortunately, protective boots can actually worsen the problem by trapping heat. Cooling the legs immediately after intense work is critical to maintaining cellular integrity.
Overstretching Beyond the Safe Limit
Tendons and ligaments are viscoelastic, meaning they can stretch and return to shape, but only within certain limits.
The superficial digital flexor tendon can naturally stretch up to 16% of its length during high-intensity exercise. Beyond that point, collagen fibers begin to break.
Overstretching can happen in a single traumatic event (landing awkwardly from a jump, slipping, or misstepping), or cumulative strain from repetitive overextension during training without enough recovery.
When overstretching occurs, the damage is immediate and often severe, and can lead to full or partial ruptures.
Why Recovery is So Slow
Tendons and ligaments have limited blood supply, which means fewer nutrients and oxygen reach the injured area. This makes healing slower than in muscles or skin.Â
Even after months of rehabilitation, the repaired tissue contains less organized collagen, scar tissue remains weaker and less elastic, and the injured area is permanently more vulnerable to future damage. The reinjury rates for tendon and ligament damage are so high, often 40-60% or more in performance horses.
Because soft tissue injury recovery is so challenging, prevention is always better than treatment. Key steps include:
- Evidence-based training with gradual increases in workload
- Varied exercise surfaces to avoid repetitive strain
- Regular leg inspections to detect heat, swelling, or changes early
- Post-work cooling to combat heat-related damage
- Nutritional support to collagen synthesis and reduce inflammation, such as targeted joint and tendon supplements
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The Science Behind Soft Tissue Injuries
Soft tissue injuries can be career-threatening, or even career ending, for many performance horses. Understanding how and why they happen can help riders, trainers, and owners take preventative steps before small problems turn into catastrophic injuries.
As horsemen, we need to understand the mechanics and biology behind tendon and ligament damage, from the microscopic fiber changes to the environmental and training factors that make horses more vulnerable.
The Role of Tendons and Ligaments in Movement
Knowing the difference between tendons and ligaments is the key to fully understanding how and why injuries happen, and how we can help prevent them.
Tendons connect muscle to bone. They act like springs, storing and releasing energy with each stride.
Ligaments connect bone to bone. They stabilize joints, and prevent excessive movement.
In performance horses, tendons (particularly the superficial digital flexor tendon and the deep digital flexor tendon) are subjected to extreme forces during galloping, jumping, and sudden stops. Ligaments like the suspensory ligament absorb high levels of strain to prevent the fetlock from overextending.
These structures are made primarily of collagen fibers arranged in parallel bundles for maximum tensile strength. Unfortunately, this structure has limits, and when forces exceed their capabilities, they become damaged.
Microtears
Soft tissue damage often starts at a microscopic level. Each fiber in a tendon or ligament can only stretch so far before its collagen bonds start to break. When horses train or compete at high intensity, repetitive loading causes tiny tears in the fibers, and impact forces (jumping, turning, galloping) increase strain on already stressed fibers.
In early stages, microtears are not always visible or detectable, but they weaken the structure. If rest and recovery aren't adequate, the damage accumulates, making the tissue more prone to major lesions or ruptures.
Lesions
If microtears progress, they can form lesions. These are localized areas of fiber disruption that are often visible on ultrasound. Lesions mean that sections of tendon or ligament have lost their structural integrity, reducing their ability to store and release energy efficiently.
The body attempts to repair these lesions by laying down scar tissue, but scar tissue is significantly less elastic and more brittle than healthy collagen fibers. This makes reinjury far more likely.
How Overheating Damages Soft Tissue
During intense exercise, tendons and ligaments generate heat from friction as fibers slide over one another. In horses, tendon core temperatures can exceed 110ºF (43ºC) during intense exercise.
At around 108ºF (42ºC), tendon cells (tenocytes) begin to suffer heat stress and die. This cell death impairs the tendon's ability to maintain and repair collagen fibers. Repeated overheating can lead to chronic microdamage.
Unfortunately, protective boots can actually worsen the problem by trapping heat. Cooling the legs immediately after intense work is critical to maintaining cellular integrity.
Overstretching Beyond the Safe Limit
Tendons and ligaments are viscoelastic, meaning they can stretch and return to shape, but only within certain limits.
The superficial digital flexor tendon can naturally stretch up to 16% of its length during high-intensity exercise. Beyond that point, collagen fibers begin to break.
Overstretching can happen in a single traumatic event (landing awkwardly from a jump, slipping, or misstepping), or cumulative strain from repetitive overextension during training without enough recovery.
When overstretching occurs, the damage is immediate and often severe, and can lead to full or partial ruptures.
Why Recovery is So Slow
Tendons and ligaments have limited blood supply, which means fewer nutrients and oxygen reach the injured area. This makes healing slower than in muscles or skin.Â
Even after months of rehabilitation, the repaired tissue contains less organized collagen, scar tissue remains weaker and less elastic, and the injured area is permanently more vulnerable to future damage. The reinjury rates for tendon and ligament damage are so high, often 40-60% or more in performance horses.
Prevention is Key
Because soft tissue injury recovery is so challenging, prevention is always better than treatment. Key steps include:
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