I've been going to gym for a few months now. I was told that doing low reps with heavy weights builds strength and I've followed this low rep heavy training religiously and seen my strength improve. Now I'm finding that I'm able to lift heavy weights for a few reps 4~5 , but lighter weights also in the same 4~5 reps range. I'm stuck in the 4~5 rep range for 60% ~ 85% of my max. Should I change my training method and start with even lighter weights and go for higher reps?
It makes sense that at 85% of your 1 rep maximum that you'd only be able to do 5 reps. That is close to what a lot of the formulas for predicting your 1 rep maximum based on your 5 rep maximum would say.
For example, if you can do 5 repetitions of 175lbs, the formulas on Wikipedia predict a 1 rep maximum between 197 and 206 (average 202).
So, it looks like you're just about right. 60% seems a bit low, though. Does it differ based on the lift? Maybe that says something about your form on particular lifts, or perhaps you're 'cheating' a bit when you check your 1 rep maximums.
First of all, strength is not for reps but for pushing your body to the limit. If you want power you have to concentrate on the low-rep series for 85% + of your max.
However, it is normal not to make so many reps if you are building strength. It is the key to success as I said earlier in this post.
And for example: before a year or so I wanted to increase the number of my push-ups reps. I was doing strength that time. So, I started doing 50 push ups after my training for a week. And what happened? My PB dropped with 5 kg. That is 5kg just for a week! Imagine if you continue doing this for a month...
So, consider your goals and decide if you want to lift/pull that two times heavier than you weight or stick to high reps and low power.