Running backs have long been known as the work horses of the NFL, playing hard, fast and dirty for a relatively short period of time

These five former Broncos are the best of the best at what is arguably the most brutal position in the league. While their career statistics are perhaps unequal, it’s important to keep in mind the evolution of the running back from the inception of the league to now.

Still, at some point in their career, each of these guys were the best in the league. If you would have picked someone different, let me know.

(To check out the rest of our rankings, click here)

5. Otis Armstrong

Years with Broncos: 1973-80 (8 seasons)

Career Stats: 4,453 rushing yards; 131 receptions; 1,302 receiving yards; 32 total touchdowns

Career Accolades: 2-time Pro Bowler; 1-time First-Team All-Pro

Armstrong’s statistics may not be eye-catching, stretched across eight seasons, but keep in mind, NFL rushers in the 1970s played a different game than running backs today. Armstrong led the league in yards in 1974 with 1,407, and he did while simultaneously blocking for his backfield partner, Hall of Famer Floyd Little.

For much of his career, Armstrong was moved to fullback and charged with finding holes for Little to explode through. After Little’s snaps were reduced due to a November injury, Armstrong moved back to tailback and averaged 150 ypg in the final four weeks. Only OJ Simpson, Lawrence McCutcheon and Franco Harris broke the 1,000 yard barrier that season.

In Armstrong’s 1976 season, he compiled 1,008 yards and became a part of history as the Broncos reached their first Super Bowl.

Perhaps it was his grueling time as a fullback, but Armstrong was forced to retire at age 30, when his recurring spinal and neck pain became too much.

“It’s the life of a running back,” Armstrong said after his Colorado Hall of Fame Induction in 2014. “I don’t know a running back who doesn’t feel that way in the morning. Floyd (Little) and I have talked about it. But if we had it to do over again, we’d go right back out there.”