Here's a training routine I conjured recently. It's a good compromise between a powerlifting and a bodybuilding program. Let me tell you how I thought about it.
There are two programs I used in the past because of their credibility in the world of barbells. They worked wonders for me, but they did have some drawbacks.
The first program is the famous 5x5, which originated from Reg Park, Arnold Schwarzenegger's idol. This is very popular both in powerlifting and bodybuilding circles because it is very effective in giving people size and strength concurrently. For 5 sets of 5 reps, relatively heavy weights are used for big compound movements like the squat, bench and deadlift, and high intensity and effort is required from the trainee (around 85% of maximal intensity or 5RM). However, such a program is taxing on the nervous system, so you can't effectively use this set-rep scheme more than once in a single workout. Furthermore, the overall volume you can get out of it is only 25 reps, and if you want to increase the volume, you'll have to use lower weights on assistance movements. The end result is that you don't grow as much as in a more bodybuilding-ish program.
The second program is the dreaded 10x10, also known as German Volume Training or GVT. This program is known to make people's muscles grow extremely rapidly. For 10 sets of 10 reps, relatively easy weights are used for two antagonistic compound movements in the same workout, like the bench press and barbell row pairing. That's 100 reps per movement. Believe it or not, despite the lack of a challenging weight, it's the sheer volume and cumulative fatigue that makes this protocol one of the most effective mass-gainers ever invented. However, people have lost strength on this one because of the light weights they were using. The sheer volume also put some people on the injury list because their joints were overused.
This is where the Lucky 7 comes in. You can also call it the 7x7 if you want. With 49 reps, it gives you twice the amount of volume from a 5x5 program and half of that from the 10x10. It also combines the best elements from both programs to produce a profound effect on the body.
The 5x5 definitely has an influence on the Lucky 7. Just like in the 5x5, the trainee would use a relatively heavy weight on a compound movement. However, due to the increased volume, that weight is reduced from 85% to 80% of maximal intensity, or from a 5RM to an 8RM. Like in the 5x5, long rest periods should be used, preferrably 3 minutes in between sets, in order to maximize freshness and strength on each set.
The 10x10 also contributed to the Lucky 7. It also recommends two big compound movements per workout, but instead of a simple antagonistic pairing, an upper/lower push/pull pairing should be used. A Deadlift/Bench and a Squat/Row pairing are good, but a Deadlift/Row and a Bench/Row are not good. This would ensure not only optimal freshness on each exercise, but also the training of as many muscles as possible in a single workout. More importantly, there's the element of cumulative fatigue. 49 reps may only be half of 100, but with heavier weights, the feeling would be similar by the end.
Common to all these three programs is the fact that you DON'T NEED to complete all the reps required. If you can complete 25, 45 or 100 reps, it's time to increase the weight.
Still, there are differences between the Lucky 7 and the other two. Because of the volume and intensity required from the trainee, it's recommended not to use this on the actual powerlifting lifts. Instead, this should be used on their variants. Instead of Back Squats, you should use Front Squats. Instead of Flat BB Bench Presses, you should use Incline Presses or DB Presses. Instead of Competition Deadlifts, you should use Romanian Deadlifts.
The end result is profound. The moderately high volume and intensity would increase your strength and size like never before. You'll see a noticeable increase in your regular Squat, Bench and Deadlift as well as a visible physique improvement.
There is one drawback, though. This program is demanding on the body, so doing additional assistance exercises is not recommended.
It's safe to do this program 3 times a week (M-W-F or T-Th-S). You can have a fourth day wherein you train assistance exercises, though. Just remember to select an upper/lower push/pull pairing, load that barbell with your 8RM, and you're all set to try those 49 reps.