Hope you keep them and keep safe!
I assume it means continuing to be social, helping out, and encouraging the person in question to "get out of their bubble", so to speak.
I haven't had personal experience with the harsher side of depression, so I'm not sure what is effective (on my part).
Depression is a real bitch. It manifests itself differently in everyone. Perhaps coaxing someone to see a therapist, go out or whatever would actually help them. But that's not going to be true for everyone and the coaxing may do more damage than good if it's unprompted. If they express interest in anything (e:g; going to a movie, seeing a therapist, going to the gym), that can be a good time to give them a small nudge. I hope your friends find some light in their tunnels.
Interestingly, it's often exactly the opposite that's needed: just be there and listen.
Once that bond has been made, then one can start to work on improving things.
All of this requires time and a lot of energy.
Verbally expressing your love and support for your friend, and helping them see the positive aspects of their self, their situation, and the world around them can go a long way. If you can get them to talk about their views, and help them see when they're stuck in unproductive negative self-talk, that can be truly eye opening. Help them love themselves. Encourage them to come on a walk or run or other exercise with you; don't force them or over pressure them, but say that you promise they'll feel better.
Sitting alone behind a computer screen every night and weekend is asking for problems.
My understanding is that real clinical depression is not the kind of "feeling down" we all experience at some point or another. That's not something you fix by just having a drink, talk a bit, or go to a party.
It is more like the absence of feelings. Depressive people are more likely to take the least resistance path to everything you try to do. Want them to go out, they will follow you. Want them to talk, they will answer your questions. Leave them alone, they will stay where they are. In fact I know someone with severe depression who didn't even have physical feelings (like hunger, pain, cold, sleepiness, etc...).
Were you diagnosed by a professional psychiatrist ?
As for high intensity, I’m sure that my use of the term isn’t correct, but I do something that raises my heart to 165+ for 30 seconds, keep my heart at 130, do something to spike it after 5 minutes and repeat until tired. I’ve been able to recently accomplish this reliably on an elliptical at the highest resistance level and maintain activity for 60 to 90 minutes.
After longer sessions I feel pretty good and sometimes a bit euphoric.
The most recent depressive bout was probably the most extreme I've gone through, and required a couple close friends to jump in, but again, routine exercise with comfortable bits of a routine mixed in - like making a cup of tea, making sure I have a podcast queued up, a book to read, and a handful of songs I like - has seemed to help pull me from the brink.
Now that I have eclipsed thirty years and I still am over 300 lbs, and some of the recent depression-like feelings, I am making a more of a cognisant action to keep working at this and to journal how I feel before, during, and after the routine.
I look forward to seeing this kind of work being taken a little more seriously as a means to treat depression as opposed to only medication and therapy.