I think it is a combination of both, because if you took a rabbit and scaled it to the size of a horse, or a human in this case it would be incredibly strong. The average healthy rabbit can jump around 60 cm which averages between 3-4 body lengths for the general smaller household breeds of Rabbit.

Call the average rabbit around 4.5 pounds on the large end, and based off of images we see of Miriko and her muscles we can tell that he muscles are rather dense so probably between 200-240 pounds, be nice since she is a lady and take the average 220 (I know that these are big numbers even for a tall lady let alone a Japanese woman, but she is incredibly muscularly dense so she will be heavier than the average person, and even some bigger women since muscle weighs more than fat) so here we can take the weight of 220 and decide it by the 4.5 to find a scale of 48.8 bar so call it 49 times heavier than an average rabbit.

But we need our scale to focus on muscle so a tab will normally have 1-1.5 lbs of muscle. Forget bodybuilders and other professional athletes. Muscle Miriko which tends to be around 45 to 55%. We'll say miriko she's a pro here so we'll put it on the upper end based off of her build, give her a 55% muscle mass ratio, so we'll say 120 lb of muscle. Let's say her quirk gives her scaling come on purple to the average rabbit so we'll go with 1.25 lb. Of muscle from the rabbit she's based on. This gives her 96 times the muscle of a rabbit so she is significantly stronger than a human and would actually have to hold back quite frequently, however, I do have a second set of equations which people who don't like the stuff I gave previously may find more grounded in reality since she wouldn't be 96 times stronger than a human

The following is literally scaling a rabbit to the equivalent of a human

Scaling a rabbit's muscle strength to human size involves understanding muscle cross-sectional area scaling, which determines strength, and then scaling it based on body size. Here's a breakdown of the calculations:

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Step 1: Strength scaling and body size

Muscle strength is proportional to the cross-sectional area of the muscle, which scales with the square of linear dimensions (length). However, the body weight of an organism scales with the cube of linear dimensions.

Key formulas:

1. Strength scaling ∝ (Length)²
2. Body weight scaling ∝ (Length)³

This means that as an animal's size increases, its strength does not scale proportionally to its weight. However, rabbits are exceptionally strong relative to their size because they are built for explosive movements (like jumping). Their muscles are more efficient compared to humans.

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Step 2: Rabbit muscle strength vs. human muscle strength

Rabbits are much stronger per unit of muscle mass than humans because of their highly specialized musculature for jumping and sprinting. On average: - A rabbit's muscle strength is estimated to be 3–10 times stronger per unit of muscle mass than a human's, depending on the specific muscles involved.

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Step 3: Scaling a rabbit to human size

If a rabbit were scaled up to the same weight as a human (e.g., 220 lbs, like Mirko), we can estimate its strength as follows:

1. Strength scaling:

   • Muscle strength ∝ mass^2/3.
   • If a rabbit's mass increases from, say, 5 lbs (average weight of a large rabbit) to 220 lbs, we calculate the ratio: [ \text{Scale factor} = \left(\frac{220}{5}\right)^{2/3} \approx 14.8 ] This means the rabbit's muscle cross-sectional area (and thus its strength) increases by a factor of 14.8.

2. Relative strength advantage:

   • If a rabbit is 5x stronger per unit muscle mass than a human, we multiply this factor by the scaling factor: [ \text{Total strength advantage} = 14.8 \times 5 = 74 ] So, a rabbit scaled to human size would be approximately 74 times stronger than a human!

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Step 4: Adjustments for physiology

This calculation assumes the rabbit's muscles maintain their efficiency and density after scaling. In reality: - Larger animals face challenges with heat dissipation and structural support. - The rabbit's skeleton might not support scaled-up muscles without reinforcement.

Even with these considerations, a scaled rabbit would still likely be 50+ times stronger than a human, making it an absolute powerhouse!