Fast Asymmetrical Gates: Galloping

Moving on from slow symmetrical gaits to fast asymmetrical gates, focusing on galloping in horses and dogs. This area is particularly interesting due to its relevance to animals locomoting near their limits and the associated injury risks. Key topics include different types of gallops, the economy of locomotion, injury risk, and links to anatomy and physiology.

Key Concepts

Gallop vs. Canter

Gallop: Used to increase speed beyond a trot.
Canter: A slower gallop with more spacing between the limb contacts of the hind limbs and the forelimbs. Seldomly discussed in biomechanics; preferring the terms slow gallop to fast gallop.

Shift in Support Phases

In a gallop, the support phases shift, with hind limbs and forelimbs working more in pairs.

Increase in Stride Length

A significant increase in stride length facilitates the speed increase from transverse to rotary gallop. Spinal flexion and extension in animals like cheetahs and dogs enable longer aerial phases and greater stride length. Cheetahs can increase their stride length by up to 20% when in pursuit.

Limb Pairing and Power

In galloping, limbs work more as pairs. Greyhounds, for instance, power their gallop through torque, involving rotation around their hips.

Spinal Posture Difference

Dogs and cheetahs exhibit substantial spinal flexion and extension during galloping, visible through differences in spinal posture across different aerial phases.

Bounding Gait

Observed in rodents and rabbits. Two types:

Full Bound: Hind limbs and forelimbs move together.
Half Bound: Forelimbs have an offset in contact.

Many animals using bounding will skip the trot and transition from walk straight to bound at a slow speed. The offset in forelimb contact in a half bound can be subtle and hard to detect without high-speed video.

Horses vs. Dogs: Galloping

Dogs perform transverse gallops at slow speeds and rotary gallops at fast speeds. All dogs can perform a rotary gallop with the footfall sequence: left hind, right hind, right fore, left fore.

Double Suspension Phase: Not all dogs achieve this in the rotary gallop. All dogs get the aerial phase where limbs are outstretched, but not all get the phase where limbs are gathered underneath.
Horses: Only perform transverse gallops. They do not have the outstretched aerial phase but have the grouped underneath phase during gallop.

Cheetahs always achieve two aerial phases (double suspension) in their rotary gallop, with an exaggerated spinal flexion and extension.

Larger, dolichocephalic (long-headed) dogs are more likely to achieve two aerial phases in the rotary gallop, compared to brachycephalic dogs (short-headed) bred for fighting.

Horse Galloping Specifics

In the transverse gallop:

Limb pattern goes across the body; hind limbs and forelimbs work as pairs.
Only an aerial phase where the limbs are gathered underneath the animal. There is no outstretched aerial phase.
Historical paintings often misrepresent the horse galloping with all four legs stretched out.

Ground Reaction Forces During Gallop

Similar to trot, but with differences. The axes are normalized for the body weight of the dog to allow comparision across different sized dogs. Ground reaction force is really similar to what we see for trot. The magnitude of the force would increase to about $600$ Newtons compared to what we see in trot. You can still see the medial lateral cranial caudal forces as well. The limb is on the ground for less time in galloping, and the actual force is higher. A small peak, related to the heel strike, is evident in gallop ground reaction forces.

Challenges in Gathering Data

Force plates are typically hard and built into the ground, making it difficult for animals to maintain footing at galloping speeds. Plates also cannot easily be adjusted to accommodate bigger strides so the animals may only hit one plate. There are not many brands of force plates that can record the force of a galloping horse without bottoming our. To mitigate, matting or turf can be added to provide grip, with possible force exerted by the material subtracted from the data. Some researchers had to bury force plates straight into the race track in order to record the horse data.

Breed Differences & Musculature

Research compares extreme examples. Greyhounds have muscle mass proximally in their limbs for quick limb swing, while fighting breeds have more distal muscle mass for grappling. The apaxial muscles, especially the longissimus dorsi, support spinal flexibility and high-speed locomotion. Greyhounds can augment their hind limb muscle power by 20% due to increased muscle mass in the longissimus dorsi.

Maneuverability Factors

Turning ability depends on factors beyond straight-line speed. Brachycephalic breeds are stable but cannot achieve a high lean angle. Dogs with legs closer together can lean, maintaining speed on bends. Shorter back lengths can be helpful around corners. There are trade-offs between speed and maneuverability, with grip being vital. Claws such as those found on dogs and cheetahs help with grip.

Turning Considerations

Turning effectively involves multiple variables:

Velocity: High speed increases limb force; slowing down minimizes risk.
Lean Angle: Higher angle allows greater speed; limited in brachycephalic breeds.
Turn Radius: Tighter turns require more grip.

Coefficient of friction of the surface: The two way limb surface interaction is also important.

Cheetahs vs. Greyhounds: A Comparative Study

A study by Penny Hudson compared greyhounds and cheetahs. The cheetahs were safely at the zoo chasing a lure while the greyhounds were running through the lab. Greyhounds reached speeds of about 18 meters per second (their max), while cheetahs can go much faster. The Cheetahs were increasing their stride frequency when the greyhounds had bottomed out. The stride length was increasing in both animals with speed with cheetahs being a little bit bigger due to their size.

Stride frequency is strides per second, and stride length is meters per stride.

Spatio-temporal Kinematic Variables

As speed increases for both cheetahs and greyhounds, stance time reduces, plateauing due to force constraints on the limb. Swing time is reduced as well in Cheetahs due to the swing happening faster. Swing time remains stable in greyhounds due to the limitation of frequency they can swing their legs.

Duty factor, the proportion of the stride in stance phase, follows a similar pattern to stance, limited by force constraints.

Note the duty factor is the porportion of the stride duration spent in contact with the ground.

Fast Asymmetrical Gates: Galloping

Expanding on fast asymmetrical gaits, galloping in horses and dogs presents an intriguing study, particularly relevant to understanding the biomechanics of animals operating near their physiological limits and the consequent risks of injury. Besides horses and dogs, other animals such as cheetahs utilize galloping. This discussion covers various aspects including types of gallops, the economy of locomotion, potential injury risks, and connections to anatomy and physiology.

Key Concepts

Gallop vs. Canter

Gallop: Used to achieve greater speeds than possible with a trot. It involves a specific sequence of footfalls that allows the animal to cover more ground quickly.
Canter: Considered a slower variant of the gallop, characterized by increased spacing between the landing of the hind limbs and forelimbs. This gait is not always distinctly differentiated in biomechanical studies, where the terms slow gallop and fast gallop are preferred to denote speed variations.

Shift in Support Phases

During galloping, the support phases are altered such that hind limbs and forelimbs function more in coordinated pairs, which optimizes propulsion and balance.

Increase in Stride Length

A significant increase in stride length is a key factor in the transition from a transverse to rotary gallop, enabling enhanced speed. Animals like cheetahs and dogs demonstrate substantial spinal flexion and extension, which contribute to extended aerial phases and increased stride length. For example, cheetahs can extend their stride length by as much as 20% during a chase, a crucial adaptation for catching prey.

Limb Pairing and Power

In galloping, the limbs operate more synergistically as pairs. In greyhounds, torque, involving rotation around the hips, is a primary mechanism for powering the gallop, showcasing the efficient conversion of muscle action into forward motion.

Spinal Posture Difference

Significant spinal flexion and extension are observed in dogs and cheetahs during galloping, leading to noticeable differences in spinal posture across various aerial phases. This spinal movement enhances the animal’s ability to increase stride length and frequency.

Bounding Gait

Predominantly seen in rodents and rabbits. It includes two main types:

Full Bound: Both hind limbs and forelimbs move synchronously.
Half Bound: The contact of the forelimbs is offset, providing a slight lead with one limb.

Many animals that use bounding will skip the trot and transition from walk straight to bound at a slow speed. The offset in forelimb contact in a half bound can be subtle and hard to detect without high-speed video.

Horses vs. Dogs: Galloping

Dogs use transverse gallops at slower speeds, transitioning to rotary gallops as speed increases. The typical footfall sequence in a rotary gallop for dogs is left hind, right hind, right fore, left fore.

Double Suspension Phase: This phase is not always achieved by all dogs during the rotary gallop. Although all dogs exhibit an aerial phase with limbs outstretched, not all achieve the phase where limbs are drawn underneath the body.
Horses: Horses exclusively use transverse gallops. They exhibit a grouped underneath phase during the gallop but do not have the outstretched aerial phase.

Cheetahs consistently achieve two aerial phases (double suspension) in their rotary gallop, characterized by pronounced spinal flexion and extension.

Larger, dolichocephalic (long-headed) dogs are more prone to achieving two aerial phases in the rotary gallop compared to brachycephalic dogs (short-headed), which are often bred for fighting. The skull shape influences their agility and galloping efficiency.

Horse Galloping Specifics

In the transverse gallop:

The limb pattern is such that limbs move across the body, with hind limbs and forelimbs working in pairs to maximize thrust and efficiency.
There is only an aerial phase where the limbs are gathered underneath the animal’s body; an outstretched aerial phase is absent.
It is a common error in historical paintings to depict horses galloping with all four legs stretched out, which is biomechanically incorrect.

Ground Reaction Forces During Gallop

While similar to those in a trot, ground reaction forces during a gallop exhibit some key differences. Forces are normalized to the body weight of the dog to allow comparison across different sizes. The magnitude of the force can increase to approximately $600$ Newtons, higher than observed in a trot. Medial-lateral and cranial-caudal forces are also present. The time the limb spends on the ground is shorter during a gallop, leading to a higher actual force. A small peak, related to the heel strike, can be seen in gallop ground reaction forces.

Challenges in Gathering Data

Force plates, typically hard and embedded in the ground, pose challenges for animals maintaining footing at galloping speeds. The fixed size of these plates can also be problematic, as they may not accommodate larger strides, potentially resulting in animals only hitting one plate per stride. Furthermore, only a few brands of force plates can accurately record the force exerted by a galloping horse without reaching their maximum recording capacity. To address these issues, researchers often add matting or turf to enhance grip, though the force exerted by these materials must be subtracted from the data. In some instances, researchers have had to embed force plates directly into racetracks to gather horse data.

Breed Differences & Musculature

Research often juxtaposes extreme examples to highlight specific adaptations. Greyhounds, bred for speed, have muscle mass concentrated proximally in their limbs to facilitate rapid limb swing, while fighting breeds have more distal muscle mass to aid in grappling. The apaxial muscles, especially the longissimus dorsi, play a critical role in supporting spinal flexibility and high-speed locomotion. Greyhounds can increase their hind limb muscle power by 20% due to the enhanced muscle mass in the longissimus dorsi.

Maneuverability Factors

Turning ability depends on factors beyond straight-line speed. For example, while stable, brachycephalic breeds cannot achieve a high lean angle. Conversely, dogs with legs positioned closer together can lean more effectively, maintaining speed through bends. Shorter back lengths can also be advantageous around corners. There are inherent trade-offs between speed and maneuverability, with grip being a vital factor. Claws, such as those found on dogs and cheetahs, help grip.

Turning Considerations

Effective turning involves a combination of variables:

Velocity: Maintaining low speed is key to minimizing limb force and potential injury; reducing speed minimizes risk.
Lean Angle: A higher lean angle allows for greater speed but is limited in brachycephalic breeds due to their body structure.
Turn Radius: Tighter turns necessitate greater grip to maintain control.
Coefficient of friction of the surface: The two way limb surface interaction is also important for effective turning.

Cheetahs vs. Greyhounds: A Comparative Study

A study by Penny Hudson compared greyhounds and cheetahs to understand the biomechanics of speed. The cheetahs were observed safely at the zoo chasing a lure, while the greyhounds ran in a controlled lab setting. Greyhounds reached speeds of approximately 18 meters per second (their maximum), whereas cheetahs can achieve much greater speeds. Cheetahs demonstrated an increase in stride frequency, while greyhounds approached their physical limits. Stride length increased with speed in both animals, though cheetahs generally had a larger stride length due to their size.

Stride frequency is strides per second, and stride length is meters per stride. These variables are crucial in determining the overall speed and efficiency of locomotion.

Spatio-temporal Kinematic Variables

As speed increases for both cheetahs and greyhounds, stance time reduces, plateauing due to force constraints on the limb. The swing time is also reduced in cheetahs, attributed to faster leg movements. In contrast, swing time remains relatively stable in greyhounds, limited by their maximum leg swing frequency.

Duty factor, which represents the proportion of the stride spent in the stance phase, follows a pattern similar to stance time, constrained by force limitations