If you have a lagging muscle group, the cause is more likely neural than physiological. By "lagging" I mean a muscle group that just doesn't seem to grow as fast as the others even though you're training it just as hard as the rest of your body. What are the reasons for limited muscle growth?
A) Hormonal factors: If your natural anabolic hormones (Testosterone, growth hormone, IGF-1) are on the low side, your insulin response is suboptimal (insulin resistance) and your catabolic hormones are chronically elevated, then it'll be next to impossible to add muscle mass.
B) Nutritional factors: If you don't ingest enough nutrients to fuel muscle growth then chances are you won't be able to build new muscle tissue. Digestive problems also fall into this category. If you eat a lot but can't absorb all the nutrients, then it's as if you didn't give your body enough of them to begin with.
C) Metabolic factors: Some people do have a revved up metabolism. This is sometimes due to hyperthyroidism. When someone's metabolic rate is high, then he might require even more food than he should need "in theory." If you don't eat enough for your metabolism, then you won't gain muscle.
D) Improper training: If you neglect a certain muscle group by not training it hard enough or without enough volume, then its growth will be slower.
E) Muscle fiber dominance: The more fast-twitch dominant a muscle is, the better it can grow. So if a muscle group doesn't have a large proportion of fast-twitch fibers, or if your nervous system isn't effective at activating these fast-twitch fibers, then muscle growth will be slower.
Reasons A to C can't explain a lagging muscle group; they can explain lack of overall growth. But if you can develop all your muscles except for one or two stubborn groups then the problem isn't general, so it can't be hormonal, nutritional, or metabolic.
Reason D could explain it. If you're doing little to no biceps work and they aren't growing as fast as the rest of your body, then the training you perform for that muscle group might need to be reevaluated. But if you're training your lagging muscle group just as hard as the rest of the body, then the problem might be elsewhere.
If a muscle is almost devoid of fast-twitch fibers, then it'll be more growth-resistant. However, it's pretty rare to find someone whose major muscle groups have fewer than 30% fast-twitch fibers. And according to the work of professor Tihanyi, a muscle that's 30% fast-twitch can become as strong and grow as much as a muscle that's 70% fast-twitch, if trained properly.
So the real reason for the absence of growth might not be so much the lack of fast-twitch fibers in the muscle, but rather the relative incapacity of the nervous system to recruit the FT fibers that are actually present in the muscle group.
Basically, to make a muscle grow you must be good at activating that muscle! There can be two levels of activation:
Level 1: You have problems recruiting a muscle because it's your weakest link in a chain. For example, if pecs are a weak point when training chest, you recruit more delts and/or triceps. As a result, the delts and triceps grow and get stronger while the pecs are left relatively un-stimulated.
In all fairness, the pectorals are recruited, but since the delts and triceps will do most of the work, the pecs aren't under maximal loading. As a result, you don't recruit the fast-twitch fibers. Over time your nervous system becomes good at recruiting the delts and triceps but less efficient at doing the same for the chest. In that particular case, the more "chest" work you do, the bigger your problem becomes!
You don't need more training volume (at least not right now); you need to work smarter to teach your nervous system how to activate the chest. Once your nervous system is good at recruiting the pectorals, then you can move back to regular chest work and it'll grow optimally.
Level 2: You can recruit a muscle just fine but you have trouble tapping into those high-threshold motor units. Once again, doing more work (volume) isn't the answer. High-threshold motor units/FT fibers are recruited mostly when the tension is high. Tension is maximized either by using heavy loads or explosive movements.
Adding more volume will just create fatigue and will result in an even greater reliance on the slow-twitch fibers. What's worse is that over time the fast-twitch fibers that you're able to recruit could take on slow-twitch properties.
So what can you do? The two strategies are:
Strategy 1: If you have problems recruiting a muscle because it's getting overpowered by others when you perform an exercise, you should use either the pre-fatigue or post-fatigue method. This means supersetting an isolation exercise for the muscle you have problems recruiting with your main training movement.
The isolation exercise is either placed before (pre-fatigue) or after (post-fatigue). Normally I prefer to use the post-fatigue technique, but an activation problem is one of the cases where I actually prefer to use the pre-fatigue method. In that situation, the isolation exercise serves two purposes:
1. It can improve your capacity to activate the target muscle during the main movement via enhanced feedback. By enhanced feedback I mean that the isolation movement will create a localized fatigue and pump that will result in your feeling that muscle group more during the performance of the main movement. Since you can feel that muscle working during your set, it's easier to develop a good mind-muscle link.
2. By creating a certain amount of fatigue with the isolation movement, you make sure that this muscle will be fully stimulated even though it normally doesn't receive maximum stimulation during the multi-joint exercise.
Post-fatigue (performing the isolation exercise after the main movement) does allow you to fully stimulate the target muscle if it hasn't been thoroughly worked with the main, multi-joint exercise. However, you don't get the enhanced feedback effect. That's why when you have problems recruiting a certain muscle, pre-fatigue is a better option: it'll allow you to develop the capacity to recruit that hard-to-target muscle group.
Pre-fatigue isn't as effective as post-fatigue at stimulating maximal growth because you can't use as much weight on the multi-joint movement (because you pre-fatigued a muscle group involved in the lift). That's why you should see pre-fatigue as a "learning tool."
It allows you to become better at recruiting the muscle you want to build. Before being able to fully stimulate growth in a muscle, you must first be able to recruit it optimally! That's the reason why pre-fatigue, which on paper is an inferior muscle-building method, can become very effective for a specific purpose.
Strategy 2: If you can recruit a muscle just fine but it's still stubborn, it can mean that you have problems maximally activating the fast-twitch fibers. Here are a few tips to help you change that:
• Always try to lift the weight with as much acceleration as possible. If the weight is heavy, or fatigue sets in during the last few reps of a set, then the actual speed/acceleration might not be very high. But neurally, the intent to accelerate is the key. This will maximize force production at a given weight which will facilitate FT fiber recruitment.
• Control the weight during the eccentric (lowering) portion and opt for exercises where the target muscle is put in a stretched position. When a muscle is stretched prior to contracting, more fast-twitch fibers will be recruited and it increases force production at high rates of acceleration (which also increases FT recruitment).
• You can combine maximal functional or maximal isometrics with regular lifting movements. You can recruit up to 10% more muscle fibers during a maximal isometric action as during a maximal concentric movement. Performing a maximal isometric action immediately before a regular lifting set will also allow you to recruit more FT fibers during the regular lifting set.
A1. Functional isometric bench press
Use a bar weight that is around 50-60% of your maximum and push it against the pins as hard as humanly possible for 6 seconds.
Rest 60-90 seconds
A2. Bench press
3-5 reps (heavy load)
120 seconds of rest
Perform complex 4-5 times
* Heavier weights can also be used since the more force you have to produce, the more FT fibers you'll recruit. You don't have to shoot for a 1RM; anything in the 4-6 reps range will do, especially if you focus on contracting the muscle as hard as possible during the set.
Hopefully I've given you enough new tricks to motivate you and your stubborn muscles. Now get thee to the gym!