Question: How many hours of equestrian experience has shown a significant decline in risk of injury?
About the article "Equestrianism", section "Health issues".

Candidate passages:
Handling, riding, and driving horses has a number of health risks.
Riding has some inherent risks, as when mounted, the rider's head may be up to from the ground, and the horse may travel at a speed of up to .
The injuries observed range from very minor injuries to fatalities.
A recent study in Germany reported that the relative risk of injury from riding a horse, compared to riding a bicycle, was 9 times higher for adolescents and 5.6 times higher for younger children, but that riding a horse was less risky than riding a moped.
In Victoria, Australia, a search of state records found that equestrian sports had the third highest incidence of serious injury, after motor sports and power boating.
In Greece, an analysis of a national registry estimated the incidence of equestrian injury to be 21 per 100,000 person-years for farming and equestrian sports combined, and 160 times higher for horse racing personnel.
Other findings were that use of spurs may contribute to ankle fractures and dislocations, and helmets likely prevent traumatic brain injuries.
In the United States each year an estimated 30 million people ride horses, resulting in 50,000 emergency room visits (1 visit per 600 riders per year).
A survey of 679 equestrians in Oregon, Washington, and Idaho estimated that at some time in their equestrian career one in five will be seriously injured, resulting in hospitalization, surgery, or long-term disability.
Among survey respondents, novice equestrians had an incidence of any injury that was threefold over intermediates, fivefold over advanced equestrians, and nearly eightfold over professionals.
Approximately 100 hours of experience are required to achieve a substantial decline in the risk of injury.
The survey authors conclude that efforts to prevent equestrian injury should focus on novice equestrians.
Virtually all organ systems experience a progressive decline in function as a result of the aging process.
One example is a decline in circulatory system function caused in part by thickening of the cardiac muscle.
This can lead to congestive heart failure or pulmonary edema.
Atrophy of the brain begins to accelerate at around seventy years of age, which leads to a significant reduction in brain mass.
Since the skull does not decrease in size with the brain, there is significant space between the two when this occurs which puts the elderly at a higher risk of a subdural hematoma after sustaining a closed head injury.
The reduction of brain size can lead to issues with eyesight, cognition and hearing. 
Inflammation can cause further damage to the spinal cord, and patients are sometimes treated with drugs to reduce swelling.
Corticosteroid drugs are used within 8 hours of the injury.
This practice is based on the National Acute Spinal Cord Injury Studies (NASCIS) I and II, though other studies have shown little benefit and concerns about side effects from the drug have changed this practice.
High dose methylprednisolone may improve outcomes if given within 6 hours of injury.
However, the improvement shown by large trials has been small, and comes at a cost of increased risk of serious infection or sepsis due to the immunosuppressive qualities of high-dose corticosteroids.
Methylprednisolone is not longer recommended in the treatment of acute spinal cord injury. 
Tranexamic acid has been found to decrease the risk of death in people who have significant bleeding due to trauma.
However, it may actually "increase" the risk of death due to bleeding if administered more than 3 hours after the injury. 
Spending many hours sitting each day is related to raised mortality and CVD risk regardless of total physical activity.
Inflammatory and metabolic risk factors partly explain this relationship.
Our whole body is put at risk with prolonged sitting.
When an individual is kept in an unnatural seated position for extended periods of time, their body starts to wear.
Furthermore, the longer they remain in the upright position, the more at risk they are for injury.
However, individuals can lower their risk by changing the way they sit, what they’re sitting on, and giving their body additional support with something as simple as a footrest.
Some physical effects that computer users can experience are restricted blood flow to their muscles, such as neck, shoulders, upper limbs, and lower back.
The concerns of overusing the computer are becoming so real that studies show just how the body deteriorates with prolonged sitting.
The five major areas that have been studied are organ damage, muscle degeneration, leg disorders, unclear mindset, and bad back.
Prolonged sitting can cause organ damage because diseases such as heart disease have an easier way to penetrate your body.
With limited movement, muscles burn less fat; furthermore the blood flows more sluggishly during the prolonged period, then giving fatty acids even more opportunity to easily clog the heart.
Moreover, it has been shown that prolonged sitting has been linked to high blood pressure and raised cholesterol, and people with the most inactive time are more than twice as likely to have cardiovascular disease than others with the least.
Muscle degeneration is at also risk with prolonged sitting.
One of the most underrated parts of your body are your hips.
The hips allow you to keep balanced, however in the case of prolonged sitting, there is no available time to stretch your hip flexors.
Rather, the hip flexors become shorter and tighter.
Your future can be affected by this “action” of prolonged sitting because studies have shown that decreased hip mobility is one of the main reasons elderly people fall.
Leg disorders come with lack of movement during prolonged sitting.
When individuals do not partake in activities such as walking and running, they lose the chance to engage hip and lower-body bones to grow thicker, denser, and stronger.
These three factors can prevent diseases such as osteoporosis, which has been on the rise, and doctors credit this fact to the prolonged sitting at a computer.
Additionally, brain functioning can be increased with more activity.
The foggier and unclear your mind is, the less active the individual is.
With breaks of running or walking or anything that gets your heart rate up and blood flowing with aid your brain to function at its highest level.