Training is just an attack on muscle fiber. We go in the gym and "attack" our muscles in an effort to make them grow bigger and stronger. What many people don't realize is that by attacking your muscle in many different ways they will respond by growing in different manners.
Even though any type of training leads to a muscle size increase the way that size comes about is not the same. The 2 most popular forms of musclar attack can be illustrated if you compare the training of a powerlifter to that of a bodybuilder.
Powerlifters like to train with heavy loads, long rest-intervals, and less volume than a bodybuilder. It is obvious that they do build a significant amount of muscle growth from this approach even though the level of hypertrophy they build may not surpass the ultimate hypertrophy of the elite bodybuilding.
But powerlifters are after strength first and size is secondary. The strength to bodyweight ratio of a powerlifter is usually very high and the type of muscle they do build tends to be functional. Basic movements like squats, bench presses, deadlifts, and rows build strong and thick muscle that sticks around around and doesn't dissipate with a 2 week lay-off from training. I'll explain why in a minute.
The classical bodybuilding approach on the other hand calls for way more sets, higher reps, less rest between sets, and more total volume overall. The strength built with this type of training does not approach that of a powerlifter, but bodybuilders are after muscle growth, not strength.
One scientific explanation of the classical "bodybuilding" type of training is that the repeated muscular contractions in a semi-state of fatigue produce a disruption of the electrochemical homeostasis of the muscle cells. This is characterized by an accumulation of sodium, calcium and other ions inside the muscle cell.
This ultimately results in the activation of increased protein synthesis and fiber hypertrophy. The muscle grows bigger in an effort to deal with this ionic disruption. This type of training also leads to a greater than normal storage of glycogen and fluid within the muscle.
The extra glycogen and fluid build-up is termed non-functional hypertrophy because it causes growth of the non-contractile tissue, or sarcoplasmic hypertrophy. Sarcomeres are the actual contractile elements of the muscle cells, or protein structures, whereas sarcoplasm is the fluid in and around the cell.
Growth of the sarcoplasm is largely the reason for the superior muscle growth that classical bodybuilding approaches give. An easier way to think of sarcoplasmic hypertrophy is to think of it as the "pump". You can do pump training with lighter weights and get bigger alright, but the bad thing about this type of training is it doesn't lead to much an increase in tension overload or strength, and it also can be very temporary.
If you're a high volume pumper you can probably take a week off training and piss away 10 lbs of muscle! If you want to maximize hypertrophy, you also need high-tension overload to place stress on the sarcomeres and increase the actual protein content of the muscle cell. Training with short rests and light to moderate weights is not consistent with sarcomeric hypertrophy. High-tension overload through heavy weights causes damage of the actual contractile elements of the muscle, the sarcomeres. Because heavy training damages these structures, they repair themselves a little bit bigger each time, in an effort to deal with the stress.
Muscle subjected to tension overload mobilizes the satellite cells, or pre-cursor muscle cells that hover above each muscle cell. This in turn increases the myonuclei number of the recipient muscle cells and facilitates muscle growth, an adaptation that will allow the enlarged muscles to undergo more forceful contractions and lift heavier loads.
Lifting a heavy weight or especially emphasizing eccentric training causes lots of tension overload and thus damage to the contractile elements, the sarcomeres. However, there is more to the anabolic muscle growth response than muscle damage. If muscle damage was the only factor then all we would have to do is go in the gym and do really heavy supramaximal eccentrics (lowering a very heavy weight).
You also must consider the benefits of the other type of growth stimulus as well, the growth that comes from the classical bodybuilding approach of using light to moderate weights, shorter rest intervals, and more volume. Other than stimulating the "pump", this type of training induces substrate uptake so that nutrients are partitioned into the lean (muscular) compartment and away from the fat compartment, so bodybuilders who train like this tend to develop a leaner physique. As mentioned, this type of training also induces metabolite build-up and ion transport, all of which are involved in the hypertrophy response and which too much fiber damage can interfere with.
A good way to look at and separate the 2 approaches is like this. Classical bodybuilding training that targets ionic movement through higher volume, moderate weight and short rest intervals stimulates one type of muscle growth; whereas using very heavy weights and overloading mechanical tension stimulates another. They both offer advantages and disadvantages but when you combine both approaches together you get the best of both worlds and results that will surpass what you could get by using either method alone.
To build the ultimate muscular physique you should have dualistic goals in training. You need to increase your strength and train heavy like a powerlifter, but you also need to train light, fast, and "for the pump". Out of all the hundreds of training methods out there I have yet to hear anyone say that in order to grow bigger over time you should lift gradually lighter weights! So you should always pay attention to increasing your weights on whatever movement you're doing.
Even if you're doing an exercise for 15 repetitions per set with 30-second rest intervals in an effort to "get a pump", you should still pay attention to how much load you're working with and try to gradually increase that load. Progressive resistance is the name of the game here. To build muscle that lasts you should ALWAYS be increasing your poundages in all movements.
Many bodybuilders recommend sets of 8-10 reps with weight as heavy as you can to target tension overload, but this is inefficient. The problem with trying to increase strength when using 8 or more reps per set is this usually will cause you to use a load somewhere between 60-80% of your 1 rep maximum. Tension overload and strength can be more effectively attained by executing heavy weight, low rep sets, in the 3-5 rep range.
Also, the lower repetition sets stimulate a different type and quality of muscle fiber. As your loading in a given movement approaches your 1 repetition maximum you use more of the more powerful type II muscle fibers that are responsible for the majority of long lasting muscle size and strength.
Training at 80% or more of your 1rm builds strength more effectively, which will carry-over into any other types of training and therefore make that training more effective. When targeting sarcomeric hypertrophy, any training that requires you to use less than 70% of your 1-rep maximum for a given movement is quite ineffective.
I know you're probably saying to yourself: "But low reps are only for strength and higher reps are for size. I've used low reps in the past and I got stronger but not any bigger". Maybe, but that's probably because you kept doing the same number of sets when using low reps as you did when you were using high reps so you greatly diminished the total volume of the workout and this led to the decreased growth response. If you train with low reps you need to increase the sets to get the same amount of volume.
What Does This Mean?
If one keep using the same number of sets:
High reps: 3 sets of 10 reps with 120lbs for the chest, each rep lasts 4 seconds, the "workout" lasts 12 minutes (total volume: 30 reps, total tonnage lifted 3600lbs)
Low reps: 3 sets of 3 reps for the chest with 200lbs, each rep lasts 4 seconds, the "workout" lasts 12 minutes (total volume: 9 reps, total tonnage lifted: 1800lbs)
Total volume: -21reps
Total tonnage: -1800lbs
So in this case using heavier weights will lead to less gain. However if you were to adjust the sets to keep the same volume:
High reps: 3 sets of 10 reps with 120lbs for the chest, each rep lasts 4 seconds, the "workout" lasts 12 minutes (total volume: 30 reps, total tonnage 3600lbs)
Low reps: 10 sets of 3 reps for the chest with 200lbs, each rep lasts 4 seconds, the "workout" lasts 20 minutes (total volume: 30 reps, total tonnage: 6000lbs)
Total volume: equal
Total tonnage: +2400lbs
In this case the second workout will obviously be more effective. In fact due to the extra tonnage lifted it will be at least 1/3 more effective. When all other things are equal, the workout with the heaviest average weight will always stimulate more growth. This is why it's key to always increase your poundages.
Now to illustrate how both types of training can work together, lets say you like to do several burnout sets at the end of your arm workout with short rest intervals and fairly light weights. This gives you a good "pump" and stimulates the 2nd type of muscle growth I talked about. The problem with this is you're not going to be building much strength with this approach so there's a limit how effective it's going to be.
Now if you changed your approach and started each workout off with a heavy movement done for low reps in powerlifting style and focused on increasing your poundage in that movement and kept the rest of your workout the same, after a few weeks you'd likely find that you're able to handle more weight at the end of your workout in your burnout sets, so you get more results from that type of training.
So to accomplish both of these goals in one training session you'd start off training like a powerlifter with very heavy weights, long rests, and multiple sets. As you progress through the workout you end up training like a typical pump artist, using multiple sets of moderate weight with higher repetitions and short rest intervals.
The latter can be accomplished for example by performing say 5-10 sets of 6-10 reps using short 30-45 second rest intervals between sets, or by using strip-sets, or supersets.
A sample workout for chest might look like this:
A.Incline Bench Press- 5x5 (5 sets of 5 repetitions with 5 repetition maximum