Lunges are a great workout for your lower body. But have you done them over a long distance?

Sometimes, you have to go drastic lengths to get the workout you need, when you need it.

Once, when I was teaching a fitness seminar in England, my good friend George had invited me to stay with him at his country home just outside of London.

The solution: A road near his home that was exactly one mile (or, since we were in the UK and they’re confused about proper units of measurement, 1.60934 kilometers). I casually asked George one day if he had ever lunged the full length of the road. He looked at me and said, “you’re bloody insane.”

Challenge accepted.

One of my most basic exercise principles is that you don’t need a lot of leg exercises to get a great leg workout. I told George to go put his workout clothes on. Together, we lunged the entire road without resting.

To this day, George says he can’t drive on that path without feeling some kind of post-traumatic stress disorder. The workout is as tough mentally as it is physically.

WATCH: The No Weights Killer Leg Workout

But the physical benefit is huge: Lunging for distance is one of the smartest things you can do to protect your knees from injury. There’s just something about the lunge that stabilizes the knee joint. Done often, this workout can relieve the pain of people whose knees ache when running or squatting.

But it also builds you stronger, more efficient legs. Runners will be able to power up hills quicker. And lifters will notice more reps and quicker recovery.

As always, listen to your body. If you can’t handle that volume at this point in your training, try for a shorter distance, or set a timer and lunge in place for as many reps as possible (AMRAP). Whatever you do, make sure you challenge yourself without pushing too far beyond your limits.

The Maximus One Mile Leg Masher

Directions: Do bodyweight lunges for one mile straight.

Perform the move just like the video below — but instead of alternating legs to stay in one spot, lunge to step forward with each leg.

This can be done on a track (four total laps), or inside a gym (if you’re especially masochistic. Just measure the distance and divide it by 5,280. The result is the number of “laps” you have to do.

Goal time: