In story I'm considering writing, a branch of hominid that had been trapped on another alternate earth after being crossing over through rifts are able to return to our earth after these rifts started appearing again.
These hominids which split from homo sapiens 200,000 to 100,000 years ago are descended from a founder population that had migrated through a rift before it closed. In overall appearance, you would not be blamed for mistaking one of these humans as being apart of our species...
...if not for the fact that they are much stronger than we are.
Some feats that these humans have displayed are:
Much higher muscular strength, allowing a single person to toss steel trash can 5 to 10 meters with relatively little effort.
Flip a car onto its roof or with a buddy do the same thing with large truck.
Carry heavy objects like 100 kg dumbbells around with ease.
Have a much higher level of endurance than we do.
Be able to run faster and for a longer period of time than we can.
Jump and leap three times further than we can.
Survive accidents unscathed that would have severally crippled or even kill human from our world. Such a very bad car or train crashes, or falling from a height that would have broken our bones.
Take large amounts of punishment in a fight that would have left a human from our from world out of commission, either from pain, inability to get up due to injuries, or sheer exhaustion.
Overall, the thing you would expect to see happen to characters in a action movie or anime.
Additionally, these feats are displayed by individuals who otherwise look like your average street joe who is moderately fit and healthy, and not someone who looks like a brickhouse. Variation exists of course but above is the standard.
Now these changes do have a physiological bases, though at the cost of very active metabolism that these humans need to maintain by consuming large amounts of calories to keep running. So much in fact that when times are lean, they can enter a state of torpor to conserve energy and prevent starvation for a time.
Some of these physiological changes are:
An increase in muscle density per cm3 and a much higher count of muscular mitochondria than we do.
Increased amounts of intracellular ATP
Thicker and denser bones that appears to originate from a variation of a mutation in the Lpr5 gene.
Large amount of blood capillary beds that act as blood revisors for extended periods of activity.
A more efficient respiratory system.
The front portion of the skull i.e face, is much thicker than ours with a appropriate reduction in brain size. Though curiously it has appeared to compensate for this by being more complex than our brains, resulting in comparable levels of intellect.
Enzymes in the blood that breaks down lactic acid far better than our bodies can.
An immune system more resistant to prion disease than your typical human, take that as you will.
Wiring from the nerves that affect musculature that allow both fine precision and stimulation so that they can have both strength and precision.
A retention of stem cell production.
Thicker and larger tendons than ours.
And several others that help contribute to making sure these humans don't break themselves. It should be noted however that the natural lifespan is shorter by as much as decade when compared to homo sapiens, caused most likely from the metabolic strain caused by their bodies.
In short, the question I have is what sort evolutionary path did they take on there hellhole of a world to come to this!?
The only explanation I can think of is that they had to both simultaneously fight off, and run away from, much more deadly predators while also hunting either much faster or larger and tougher prey.
Is this a reasonable explanation? Or are the characteristics described are to extreme and excessive to naturally occur?
Some additional tidbits.
While they are omnivores and will eat fruits and vegetables, even enjoy it, they do have a preference for meat.
They have larger and pointer incisors and piercing molars. Nothing to big, though noticeable when they flash a friendly smile towards you.
A larger nasal cavity, its only noticeable when you compare skulls as the nose does not appear any different form ours.
A larger ocular orbit that houses a slightly larger eye that collects more light during the evening and dawn. Again, nothing too noticeable at first glance though after inspection you could make a slight difference in size.