When carrying a heavy weapon, like a rocket launcher or fuel rod gun (maybe snipers), it would slightly slow you down when compared to a person carrying a normal non heavy weapon. Sprint would then only be for carrying a heavy weapon which, when sprinting, would allow you to sprint(run) at the same speed of someone with a normal gun.
This would add skill to using power weapons by making you an easier target if caught in the open and knowing when to sprint or not because it would stop you from shooting.
It would also add more realism seeing as a rocket launcher is usually heavier than a normal gun.
Thoughts?