Don't worry about pump. I haven't got pump in a long time. Some of my body parts never get a pump unless I workout in very high rep ranges. The only thing you should be focused on is whether you are making progress.

I've been training for almost a year now and recently (maybe 10 days ago) I lost my pump. For 4/5 sessions I haven't been able to get any kind of pump at all just sore arms. I always used to get it and literally couldn't even shower without moving like a robot as my arms were so pumped
A friend of mine told me to incorporate a 4-0-2/3-0-2 tempo which I have started (as best as I can as gym is quite loud). This seemed to work short term but about 4/5 mins after I finished, my arms just felt sore and the pump had already gone.
I do regularly change my routine and recently started german volume training. So my question is how can i get my pump back?

Don't worry about pump. I haven't got pump in a long time. Some of my body parts never get a pump unless I workout in very high rep ranges. The only thing you should be focused on is whether you are making progress.
“I used to do drugs. I still do drugs. But I used to, too.”
Have you changed your diet? I notice that when I drop my calories and carbs I don't get a full pump like when I lift while bulking. Have you changed your pre workout meal? I also find it hard to get a pump if I don't have a solid meal 30 min. prior to working out. Have you stopped using any supplemets that may have added a pump (L-arginine,Beta alinine)? I know some say pumps don't matter, but I feel like I had a bad workout if I don't get that pump rush, ruins the rest of my day.

i know i feel the exact same. Feels like i havent done anything, especially when as recently as a few weeks ago I was getting it.
I haven't changed my diet at all, if anything i'm eating better since I've finished university and I am back home. The only supplements I take is creatine and I'm currently off that (could be it?) and as for pre workout meal, I usually go gym mornings and I never NOT have a solid breakfast.
I guess if it doesn't really matter then I shouldnt worry about it, but doesn't it help muscle growth?
There is your answere!! CREATINE...
When I am not on creatine my pumps are flat. Get back on creatine and the pumps will come back. I like ON micronized creatine. It's creapure so you know you are getting good stuff not bunk from china. And it's cheap.
No matter what anyone says I say pumps matter. Even if it's just phycological it just makes my entire day when I have a huge pump. It's very euphoric. I also get better pumps and my veins come out more with caffein pre workout. 100mg-200mg should do it.
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