There aren't too many activities that generate those two lines. Inline skating around gates on a declining road and aggressive MTB on technical trails are the closest I can think of. Trail running is a distant second. Gym work doesn't address this issue at all. I use weight lifting to address strength deficiencies that trail running misses.
Actually, I like the "bag hop" part of this video with Kit Deslauriers: https://www.youtube.com/watch?v=zBXSEPosKYE which I think gives a pretty good proprioceptive workout. It has helped my bump skiing quite a lot. Particularly in getting my knees/feet closer together and getting that feeling ingrained in muscle memory. However, I can't manage to hop quite as large an obstacle as Kit does in the video: I kind of have to use an orange cone laid on its side to jump over. But hey, she's a good 20 years younger than me! (Not to mention that she's light years ahead of how I might ski even in my wildest dreams) Click on the link for details of how much and how long to do each part. Essentially, it is 20 sec per activity with a minute between cycles, to be repeated 6 times.
That video is part of a 4-part, two day cycle of exercises by the Mountain Athletics gym in Jackson, who also authored the video linked by @tonyplush in Post #8 above. The two day cycle was released by The North Face as a iPhone app a couple of years ago that I have used, along with other gym activities, to get into/stay in skiing shape for the last two seasons, and leading up to next season. The video in Post #8 was well known to me as a corollary to that app, which had stoked an interest in Mountain Athletics. I searched yesterday for a link to the app, but it has apparently been taken down. That's a real shame, because I greatly credit it with what I consider to be the humble improvements I have experienced on the slopes in the last two years. Later tonight I will try to emulate the two day cycle of exercises within the app by stringing together videos by Kit and others at Mountain Athletics that I now know continue to exist in the YouTube cloud.
Edited by cosmoliu - 8/7/16 at 2:08pm