I am kinda new to pull-ups and i am having a problem. So right now I can do 8 pull-ups in a row but if I try to do another set after some rest, I can only get 4 to 5 reps. Is there something I can change with my pull-up training?
I find controlled negatives help a lot with pull-ups. Start at the top of the bar, and slowly lower yourself down. Basically a pull up in reverse. You can aim for a specific number of seconds before you are fully extended.
That's normal. Rest longer, keep going. Do 8 then 5 then 3 then 1. You'll see progress fairly quickly and soon you'll get to 9 then 10 etc. When I first started about a year ago, I could barely manage 5 pull ups, and maybe 10 pushups. Now I can bang out multiple sets of 10 pull-ups, and a set of ~100 push ups. Also worth noting that some people, depending on body type, have a harder time with pull ups. I think arm length possibly becomes a factor. Not a scientist. Every pull up is progress (:
How long are you resting between sets? The simple answer could very well be that you just need to rest longer between sets. As Dr. Mike Israetel explains in this video, there's no magic number for how long you need to rest.
https://youtu.be/0FZf6nv_aGg
There's a lot of great advice here! You've got multiple suggestions here that are well worth a try. In addition to the controlled negatives, monitoring rest between sets, and continuing good sets even as you get down to only being able to do one rep a set, I'll add two thoughts.
Different grips for increased assistance as you go along - when your lats start to fatigue during your sets, you can throw in some chin-ups to get some assistance from your biceps or some close side-grip pull ups to shift some of the focus to other muscles for help.
Do a form check! It's not a mark of shame -- even after years of pumping out pull ups with ease I recently realized I'd gotten complacent and stopped activating my lats for too many sets to count. Make sure you're not hunching your shoulders up, make sure your grip width is right (I overfocused on wide grip pull ups to the point where the muscles above my lats have taken over and made it harder to activate those big lats I should be using to further increase my numbers/effectiveness, resulting in an odd stall that's forced me into doing more lat focused exercises so my body gets used to relying on them as the primary force for pull ups), etc.
On top of that, sometimes we use too much momentum near the top and end up doing some decent metabolic work but take away the strength building we need to increase the full range of the muscles we're working effectively. Sometimes we barely get our chin over the top of the bar instead of fighting to push our chest up to it, etc.
You can do assisted pull-ups to increase your number of reps. If you have a gym membership, many have an assisted pullup machine. They also sell straps and bungee cords that can be used on regular pullup bar
8 pullups is great. To get to high rep counts you need more overall weekly volume. One thing you can do is don't think just about how many you can do in 1 session, but instead per day or week. For example, when I was specializing to get to 20 in a row, my preparation would simply be 5-6 sets of 10+ reps, but the progressive overload is that the total for the day's work started at 60, then I would add 5 reps to the total quota for the next week's working sets. That achieves the "progressive overload" requirement to stimulate growth. It is MUCH easier to add 5 reps at some point in the day than to add 5 reps right after the end of the last set. The progression is stronger if you cluster your work together, but if you can't progress in clusters, then you space it out until you can progress. Eventually around 85 reps per day, the 20 in a row became feasible. So by this point most of my sets were 14-17 reps.
This is similar to how you progress in body building or strength training, at an advanced level you can't progress every workout, so you may add an extra work day elsewhere in the week. Or you just add an extra set to one of those days, the spacing gives you more window for progressive overload and thus progress over 2 weeks or cycles instead of every week. The growth isn't as rapid when spaced, but growth will still happen.
Also if you aren't lean, get lean. Pullup reps scale very strongly with weight loss, so if you're packing excess bodyfat, your reps will be pretty significantly depressed.