27/07/2020
¡¡¡Muy interesante!!!
WHY WE SHOULD TALK ABOUT RIDER FORCES & NOT RIDER WEIGHT!
For the next discussion on saddles, backs, riders and horses I want to raise one aspect of rider weight! It’s a topic that has been debated extensively in recent years. So let’s first assume that we have sound horses and riders with good core stability riding in appropriately fitted saddles. Does it make a difference if the rider is 50kg or 100kg?
TENDON & JOINT LOADING
A 500kg horse carrying a 50kg rider would be carrying 10% of its own bodyweight. At 100kg that’s 20% of its own bodyweight. Horses evolved over hundreds of thousands of years to carry…..0% their bodyweight. We could argue that in the past few thousand years, we have selectively bred them to carry weight, although perhaps not that successfully. Any weight added on the horse loads the back muscles, which were not designed to carry weight and loads the horse's shock absorbing system in the limbs – the joints and tendons.
BACK LOADING
There is a big difference between sitting on a saddle stationary and moving up and down in the saddle. This is because when in motion the forces on the back are increased due to acceleration. This is why we should talk of FORCE and not WEIGHT.
WEIGHT = mass (kg) x gravity (g). Mass is how much of us there is and weight is what we measure due to our mass being pulled down to the earth by gravity. On the surface of the earth we take gravity to be 1g or 9.8 metres/second/second. CLARIFICATION - Weight is a confusing term because in everyday use we measure it in kg but in scientific terms we refer to it in Newtons (Force). In the context of when there is a static mass on the Earths surface, weight and mass are actually the same. They only become different once the mass starts to move.
FORCE = mass (kg) x acceleration (g). So we also measure acceleration in g, the same as gravity. So a rider sitting still on a non-moving horse applies a Force equal to their mass (equivalent to weight x 1g) but as a rider moves up and down on a horse then the Force on the horses back increases. So if the rider is moving up and down at 2g then the Force on the horse is doubled. In this case we are looking at the total Force on the horses back. We typically measure Force in Newtons. If we want to know what that is per unit of area, then we have to look at Pressure (which we save for another post).
So why is WEIGHT, ACCELERATION & FORCE important?
50kg RIDER at CANTER
Downwards maximum acceleration of 3g
PEAK FORCE on the horses back = 3 x 9.8 x 50
= 1470 Newtons
100kg RIDER at TROT
Downwards maximum acceleration of 1.5g
PEAK FORCE on the horses back = 1.5 x 9.8 x 100
= 1470 Newtons
So the impact on the horses back and limbs is a combination of many factors including...
• MASS (Weight) of Rider
• VERTICAL MOTION OF Rider
WEIGHT (as in common use to mean kg of rider) is therefore only one factor to consider! We should really be discussing FORCE! Not to mention Saddle Contact Area and Pressure which we will save for another day.