As I grow older, my running speed gets slower. I know that first hand.
Here is an article that goes into details of how the researches concluding the same thing: older runners’ biomechanics changes. Meaning the legs lose its muscular power as one gets older, and as a result, running efficiency decreases.
Hence, the old wo/man shuffle. It sounds bad, I know. Visualize it as the opposite of what you would see in running magazines where young models with impressive midriffs running with their feet airborne. Yeah, hard to squeeze those vertical lift from an old pair legs like mine.
But all is not lost. If you want delay the muscle power lost, the article suggests weight training (particularly after the age fifty) to retard the atrophy. Even in the inevitable case when the shuffle does become a reality, at least it helps to minimize running injury.
Do you feel like you’re losing your bounce?