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In my world there human-animal hybrids. My protagonist is a snow leopard-human girl (outwards looks almost completely human, except for the tail). These hybrids have been created through experiments, so there is no evolution in play.

So I can also play around with sci-fi-ish elements (and/or magic). What would be ways for a cat-human hybrid to achieve more agility?

For example, from what I understand, because the spine has to support the skull, it kinda loses flexibility. If these hybrids would be given implants, could it give some flexibility back?

Interesting question! I have some basic and anatomical considerations that might be of help to you.

Since the hybrids are created using technology (gene editing and so forth), your genewizard scientechs need to do things like these:

• Ensure that the balance centers of her brain derive from cat genes


• Derive her balance, movement and recovery instincts from her cat forebears


• Derive her tail, its musculature and its nervous apparatus from the cat, but see below for specific anatomical considerations


• Apart from genetic manipulation, you'll want to make sure her natural abilities and instincts are well trained.

You don't need implants in the spine, you'd need to remove bone, if anything. The human frame is not built to move like a cat. If you want a catgirl that looks mostly human and has a basically human body, you're going to have to accept some trade-offs. I think if you do the above three points, she'll be considerably more agile by nature than any non-hybrid.

One thing I'd point out, since your catgirl has a tail, is that almost every artist that draws furries gets the tail wrong, from a human-beast hybrid anatomical perspective. Just be aware that a functional and anatomically correct furrygirl won't look like the vast majority of furries you see in art.

Take a look at this furry girl here (cat-human hybrid by mrpersonperson of dA --- Don't worry, totally SFW!) :

And now compare the human skeleton:

with the cat skeleton:

noting the differences between the pelvis and placement of the tail in all three. Notice that the human tail (yeah, we have tails, but they're entirely internal) curves inward and how the gluteus maximus curves outward. Notice how mrpersonperson stuck his furry's tail way up high in the lumbar region of her back. More important than supporting the skull, the spine has to weld the pelvis together to support the whole body! That means she will have no coccyx, no bone to hold the two halves of her pelvis together. She'll collapse, most likely, and certainly not be able to walk let alone leap about gracefully as a cat!

I point this out to bring your focus to the tail. The cat uses its tail quite a lot for balance and agility. Your catgirl will not really be able to do this with a basically human body. This is where her feline tail will end up having to be:

Its bones and musculature will partially push her glutes off to either side, probably giving her a weird gait and certainly making it difficult for her to sit like a human.

Mrpersonperson should have had his furrygirl's tail emerge approximately where her g-string disappears between her glutes.

Scale body size down and metabolism / perceptual speed up.

Small animals with high metabolic rates (e.g. songbirds, chipmunks) process visual stimuli faster than larger, slower metabolizing animals do. It makes sense. What is the point of perceiving what is happening if you are too slow to do anything about it? But if you are able to move fast you have to be able to process sensory stimuli fast or you are literally flying blind. Move your cat woman's size down and metabolism and perceptual speed up.

From:
Metabolic rate and body size are linked with perception of temporal information
Kevin Healy et al

In a broader context, it might be expected that manoeuvrability, a
vital component of an individual’s ability to respond to the
environment, may be one of the main factors determining whether it is
necessary to invest in costly temporal information processing.
Manoeuvrability, as defined by the ability to change body position or
orientation, generally scales negatively with body mass. This negative
scaling emerges primarily through the increased inertia and decreased
limb stroke rate associated with large body size …

These arguments show that, owing to the laws of physics, larger
animals physically respond less quickly to a stimulus. Hence we expect
selection against costly investment in sensory systems with
unnecessarily high temporal resolution in large animals, as
information on such timescales can no longer be utilized effectively.
This may explain why larger vertebrates, along with those with low
metabolic rates, had lower temporal resolution in our study.

Smaller and thinner is always more agile.

Less fat and smaller internal organs also help - at the cost of endurance and ability to use low-energy foods.

Bones should be lightweight and not too easy to break - so fill them with some air, like a bird's bones. Even if that means broken bones require longer treatments.

Some of the brain could go down into the spine (as with birds again) - especially anything related to motoric abilities. Improves reflexes, allows for a smaller head without reducing intelligence and strengthens the spine without adding unnecessary weight.

Stealing photosynthesis from the plants (ideally black, brown or red ones, as green is not a cat-like color) helps to recover strength while resting, even if it only makes a small percentage for a warm-blooded being.

Some animals like Kangurus can 'spring-load' their muscles. This allows jumping around without using a lot of energy.

The larger the frame, the more the bones need to support the muscles - make bones near important muscles across joints extend a little bit for a better angle the muscles can use. Muscles can overlap by splitting the extension into a Y-shape on one side, which also stabilises the joint. Only works for joints limited to one direction, like knees or elbows.

A muscle along the back could help go quickly from a crouch to a jump, or from absorbing a landing on two feet to jumping again. Useful as your 'cat' will usually not use all four paws for movement, I assume.

The hind legs can be a little short for a human - allows switching to running on all fours if needed, for extra-fast sprints. Here, the strengthened back muscle will also add to the speed.

A relatively long neck will help move between upright and quadropedal movement, and also be good for fast jabs - like a snake or a bird.

4 or 6 small boobs are better than 2 large mammaries. However, if you want your cat-woman to be sexy for humans, use the place well - fat, water and oxygen storage, for energy, dry spells and diving, respectively. Similar to some animals expanding their throat, your cat woman could then use her mammaries to signal attraction.

Make your tigress cheat a little - shoes with a blade spring each, an elastic climbing rope with knots for easier climbing (shoes should have a small gap between toe and other digits, to make use of this), knee and elbow protectors for wilder maneuvering, a flight suit for jumping from large heights and other such accessories.

You don't have to do anything

You have already given her the only advantages you can, if she has a tail and claws she can do anything a cat of her size could and likely a lot more. the advantage house cats have is size, smaller animals can move faster. Cats are not more flexible than humans, humans are actually really flexible if they put any effort into it, far more than cats. Humans evolved from primates they are amazing climbers and jumpers and can contort themselves in ways cats could only dream of.

The only other tangible advantage you could give them is better muscle recruitment, which is why large cats can jump so high, but that will cost her fine motor control. So she can jump 18ft but she can't write her own name, not a great tradeoff. Keeping her body mass small is the best thing you can do, mass is the biggest limiting factor for agility.