Last spring with the Walk It Challenge, we talked about walking a lot, and with good reasons. It's an easy activity that is not only very effective, but low cost.
Still many people confided in me that they thought walking was not enough of a challenge for them. They couldn't figure out how to add intensity to their daily walks. Really? In San Francisco?
Incline:
The first obvious suggestion is find a few good hills and go to town. Walking uphill will add intensity. We are lucky you can find all grades, all heights, we have it all in SF!
Surface:
There isn't much difference in intensity between walking on pavement or on gravel really, but soft sand? Try walking on the beach away from the water. After a while you really start feeling it!
Weight:
You can buy vest that are made to add weight. Those are a good way to add weight to your walk without compromising your posture and/or your joints. There are also ankle and wrist weights that you can get. Honestly, with a bad knee, I would not use those, but it's between you and your doctor to know if it's ok for you to use them. Remember that any weight you chose to carry on your walks, you have to walk back with. :o)
Speed:
Sounds obvious, but if you don't have any hill nearby (hum..) or beaches, and weights are not happening, go for speed! You usually do your loop in 45 minutes? Shoot for 40 next time. Or keep the same time, but add a few blocks to your walk.
Walking can be a challenging activity if you want it to be, you can take it outside the city too! Go hiking! Just remember that it's generally much hotter outside of San Francisco, so plan adequately for clothing, sunscreen and water!