Being caught in a zombie apocalypse would suck, but most of the time in these scenarios, there are two thing that the surviving humans can count on: being faster and stronger than the zombies. Usually in such tales, the undead/infected move at such a slow pace that the humans can usually keep ahead of them provided that they're staying properly cautious, and due to their decaying bodies, the zombies usually aren't that strong. That's not the case if you're living in the 28 Days Later world, as those zombies are not only swift on their feet, but more powerful than you'd expect. When it comes to their strength levels, 28 Days Later director Danny Boyle actually drew inspiration from a dancer he dated years ago.
While speaking with Yahoo about his latest feature, T2: Trainspotting, Danny Boyle talked about how screenwriter Alex Garland's vision for "running zombies" was enough to bring Boyle aboard, as it was a welcome change from the Night of the Living Dead-style zombies. That segued into the zombie strength levels, which came from a ballet dancer Boyle knew. The director explained:
I'd had a relationship a long, long time ago with a ballet dancer. It was incredible, this body! It was so muscular. It was on a different planet. And I remember thinking, 'If we could put that into the zombies, that would be really scary.' The power in the arms, they can pull you. They can literally tear you apart.
Danny Boyle added that another source of inspiration for 28 Days Later zombies also came from retired athletes and gymnasts who were hired for corporate jobs, noting how if one of those individuals was charging straight at you, there was nothing you could do. They would be too powerful. All these influences led to the kind of zombies moviegoers saw in 28 Days Later. Thanks to the accidental release of a highly contagious virus, the majority of the population was been turned into these monstrous creatures known collectively as The Infected, and the survivors had to be on guard at all times to make sure they weren't killed. Granted, that's the same case in other zombie movies and television shows, but at least with them, there's no need to worry about the zombies running like a track star or having ridiculous muscles. Of all the post-apocalyptic zombie scenarios you could find yourself in, this ranks among the worst, though I'd argue that the World War Z universe is at the top of the list given how those zombie can straight up form gigantic waves.
28 Days Later came out in 2002, and it was followed in 2007 by 28 Weeks Later. There's been talk about another sequel for years, but as of 2015, no significant developments on it have been revealed, although it will mostly likely be called 28 Months Later (duh). In the meantime, if you find yourself in a situation where the 28 Days Later zombies are running at you, don't try to outrun or punch them. You'll at least need a firearm or two to ward them off.