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Through observation and empirical evidence, a lot of strength trainers and bodybuilders have found that 5-6 reps is ideal for building strength, while 10-12 reps is ideal for building size.

I've noticed in my own experience that it's a lot easier for me to add 10lbs to a lift at the 5 rep range, than it is for me to keep the weight for my previous 5RM and go up to 8 or 10 reps.

An obvious answer might be that increasing the reps significantly increases the total load (8 reps at 100lbs is 800lbs total, while 5 reps at 110lbs is 550lbs total), but I'm wondering if there's also something else. Football players are tested for the 40 yard dash because that's about the distance that can be maintained at top speed, around the 5-7 second range, while a 100 meter sprint would have even the best sprinters slowing down slightly at the finish compared to their top speed at any point on the stretch.

Is there something similar going on with lifts? Such as muscle glycogen stores being exhausted in the 5-6 rep range, and the body having to switch to breaking down lactate for energy in the 10-12 rep range?

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I don't actually know anything on this topic, but I've seen a test: "take 80% of your one-rep max and do as many repetitions as you can. If you only get five reps or less then you fall into the fast twitch world. If you get ten reps or more, than you are a slow twitch rider." (I can't vouch for its validity.) Maybe you're just a slow-twitch guy? (Also, I've heard 1-3 reps for strength; 5-6 is a nice Goldilocks zone between strength and hypertrophy, as I understand it.) –  Dave Liepmann Jul 25 '12 at 2:01
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@DaveLiepmann dude! that is an awesome assessment which you have gathered. Although mildy true repetition maxes based on a percentage scale just doesn't work IMO. BUT it is a good scale to measure for the amateur lifter. When we would have an athlete who needed to gain mass we would always take his last set in a set of 3-5, take 80% of that and tell him to do 10 reps of that. Insane increase in hypertrophy was seen by a lot of the athletes, not to mention a mental challenge. We would also do 20rep maxes every now and then for awesome hypertrophy results (squats, bench, etc.) –  Andreas Jul 25 '12 at 6:08
    
I'm sorry @DaveLiepmann but that makes no sense. According to my 1 rep max formula I train with, I have to (and can) lift 8 reps of 180kg (80% of my 1 rep max) to reach 225kg (my 1 rep max) on deadlifts. I don't think that means I'm a "slow-twitch guy" - it merely means the formula I use for deadlifts is quite accurate! –  Mike S Aug 1 '12 at 1:12

1 Answer 1

It goes without saying (?) that these rep ranges are to some kind of failure. The idea is that failure occurs because some system is depleted/damaged and with rest it will be repaired and eventually strengthened. 1-3 reps is thought to stress out your neurotransmitters so you fail and the body's response is improved nerves and muscle recruitment that increases speed-strength (think Olympic lifting). The next system to go is internal to the muscle fibers (4-6). The body needs more strength. Then the energy stores within the cell are taxed at 7-12 - you need bigger cells (hypertrophy). Over 12, failure is lack of capillaries to remove waste products and bring in oxygen - you need more vessels maybe even bigger lungs. Of course there is overlap. 10 solid reps followed by 1 not so solid, followed by puking (not really necessary) will hit all the systems - some of that failure will be neuro, some a drained fiber etc. Thus the popularity of 8-12. The take-away is that at some point you'll start "programming" - spending time at each rep range to support the next. That's another topic. Is there a lot of hard science behind this? That's also another topic.

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