Big movement is not a blessing, it's a disability
Modern sports horses tend to have a large range of motion of their joints due to their specific connective tissue properties.
You could probably say that most modern sports horses fall into the hypermobile spectrum. This means that, put simply, thier connective tissue is basically more loose. Their ligaments are not as tight, their fascia allows more movement than in the average body and their joints have a greater than average range of motion. This creates the extravagant movement that seems to be praised in today's dressage ring, but apart from bringing high scores, it actually causes a lot of problems.
There has not been a lot of research done on hypermobility in horses, but the data from human studies suggests that hypermobile bodies have a lot of problems. The greater range of motion puts them at risk of back problems and arthritis, they are more prone to anxiety, have poorer body awareness and they are more likely to suffer from chronic pain at some point in their lives. Some studies also suggest that their sympathetic nervous system is more easily triggered (hence the risk for anxiety) which can cause sleeping issues as well. As if all that isn't enough hypermobile people tend to have issues with their digestive systems as well.
Hypermobile horses need slow, controlled work and time to strengthen the muscles stabilizing their spines.
All these symptoms sound very familiar to anyone who's been around sport horses for a while. How many of them are so anxious that you risk your life everytime you lead them from their stall to the arena? How many of them have stomach ulcers or have trouble gaining muscle mass? How many of them suffer from chronic pain? All of these problems have become so very common in the modern horse, we don't even see them as unusual anymore. This is the price they pay for showy movement and high scores in the dressage ring.
The hypermobile horse won't do well in a »normal« traning setting. His body has special needs and those need to be met in training. We need to take into consideration that they have very bendy bodies that they have poor control over, they are highly strung and prone to digestive upset. Our mission then is to calm them down, put the nervous system in a relaxed enough state to learn, teach them how to control their bodies and at the same time strengthen their stabilizing muscles. Easy peasy. These horses are not easy to work with. They need an experienced and patient teacher and they need time. Lots of it. The key to keeping them healthy is to focus on slow, controlled movement in hand. They will need time to develop good body awareness, they will need time to build enough stabilizing muscles to be able to control their bendy spine. Avoid working in faster gaits, especially on the lunge, until they have enough control to use their bodies properly. This slow, systematic work needs to be coupled with support from their living environment. Encourage free movement, reduce stress levels and make sure to consult an expert regarding the best diet. You can't control the properties of their connective tissue, but you can make sure everything else in their bodies is functioning as well as possible. Make sure the hooves are balanced, never skip a dentist appointment, get the bodyworker out on a regular basis and be sure to tackle any health issues as early as possible. Prevention is key.
Providing an appropriate living environment with free movement and low stress levels is key to keeping hypermobile horses healthy.
While they look pretty, big Warmblood horses are not easy to keep healthy. If you are in the process of getting a horse, think twice if you want to go for that gorgeous giant with incredible movement. Think about whether you have the knowledge, patience and resources for working with a hypermobile horse. If trained according to their specific needs, they can truly become amazing athletes, but the road is long.