Client of mine has trouble going upstairs? Suggestions for workout corrective exercises and why this may be happening?

Without many details given about the client, I’d say a basic closed chain movement with very natural mechanics, large range of motion and low injury risk to develop strength, balance and mobility without leaning too heavily on any single one of those criteria. The best movement in that category, in my opinion, that’s easy to teach and has high accessibility, is the goblet squat, done with progressively larger range of motion. Maybe I’m oversimplifying the issue, but sometimes a simple answer works best, at least as a starting place. If this isn’t helpful, share some more details about the client and any imbalances and/or specific weaknesses and/or areas of excessively poor flexibility. Here’s a primer on the goblet squat: http://formfromfunction.com/blog/the-squat-starting-at-the-begining-with…