After we start strength training , we achieve large strength gains in the exercises we use (and in the exact ways we perform those exercises), and smaller strength gains in *similar* exercises that use the same muscle groups.
This observation has been called the “principle of specificity.”
The principle of specificity is a general strength and conditioning principle, just like the principles of progressive overload, individuality, and variation.
But general principles do not tell us *why* certain adaptations or specific strength gains tend to happen, they only remind us that these things do in fact usually happen.
Following strength and conditioning general principles is therefore a reliable way to ensure that your training programs get you to your intended goal. However, knowing *when* the principles apply will take your programming knowledge from good to great.
It helps to know when you can “break the rules” and when you need to follow them carefully.
So when are strength gains *usually* specific?
When are strength gains *usually* specific?
There are many ways in which we can do a strength training exercise, and most of those ways affect the strength gains that result.
For example, we can choose to lift or lower a weight, move quickly or slowly, lift heavy or light weights, move through full or partial ranges of motion, use stable or unstable environments, use either “weight” or other types of resistance (such as elastic bands), direct force vertically or horizontally relative to the body, and work different muscle groups.
Let’s take a quick look at each of those.
#1. Lifting and lowering weights
In normal strength training, we use both lifting and lowering phases. However, some athletes only do one or the other, because using each phase alone produces very different adaptations from a conventional strength training program.
If we only do the lifting phase (called the concentric), then we might drop the weight under control afterwards, before lifting it again (just like Olympic weightlifters do). This is called “concentric-only” strength training, and it excludes the lowering phase (called the eccentric).
Conversely, we could just do a controlled lowering phase (the eccentric) and have spotters help us return the weight to the top afterwards, before lowering it again (as in a Nordic hamstring curl). This is called “eccentric-only” strength training, and it excludes the lifting phase (the concentric).
Concentric-only and eccentric-only strength training each produce specific adaptations inside the central nervous system and within the muscle itself.
As a result of these specific adaptations, concentric-only strength training produces proportionally greater increases in lifting strength, while eccentric-only strength training causes proportionally greater increases in lowering strength.
#2. Lifting quickly or slowly
When we lift weights, we can choose to either use a slow, controlled tempo, or we can lift the weight as quickly as possible. In addition, we can choose to use a relatively light weight and move very quickly, or we can use a relatively heavy weight and move more slowly.
These possibilities give us three options:
- Lift heavy weights
- Lift light weights slowly
- Lift light weights quickly
Obviously, because muscles have a fairly constant force-velocity relationship, we cannot lift heavy weights quickly.
Lifting light weights quickly produces the greatest increases in high-velocity strength (through a range of unique adaptations that only occur when we contract a muscle very quickly), while lifting heavy weights produces the greatest increases in maximum strength (through a totally different set of adaptations that only occur when we impose a very heavy external load on the muscle).
#3. Using a full or a partial range of motion
When we lift weights, we can choose to either use a full range of motion (like a full squat) where we allow the muscle to lengthen fully, or we use a partial range of motion (like a half squat) where the muscle is only partly lengthened when it reaches the end of the lowering phase.
Strength gains in each case are usually specific to the *longest* muscle length reached in the exercise, because of the adaptations that this triggers within the muscle fiber itself.
This means that the full range of motion exercise produces the greatest increases in strength at a long muscle length, while the partial range of motion exercise produces the greatest increases in strength at a more moderate muscle length.
And this is why strength training using a full squat produces greater gains in 1RM full squat than strength training using a half squat, while strength training using a half squat produces greater gains in 1RM half squat than strength training using a full squat.
#4. Using low reps or high reps
When we lift weights, we can choose either a heavy weight or a light weight, and we can choose to lift to failure, or not to failure. This gives us four options:
- Lift heavy weights to failure
- Lift heavy weights not to failure
- Lift light weights to failure
- Lift light weights not to failure
Lifting to failure allows light weights to recruit more high-threshold motor units, and this seems to be important (perhaps even necessary) for training with light weights to cause muscle growth. And muscle growth is probably the only way that this type of training causes strength gains.
Lifting to failure is less important when using heavy weights, however, as most motor units are recruited in order to lift a weight of 80–90% of 1RM anyway. And using heavy weights causes strength gains through several mechanisms, and not just through muscle growth.
Since lifting to failure has its own set of drawbacks, including a much greater demand on the anaerobic energy system, this means that the options used in practice are (1) lifting a heavy weight not to failure, and (2) lifting a light weight to failure.
Lifting heavy weights produces proportionally greater increases in maximum strength (force produced against a very heavy weight) because of the effects of imposing a very heavy external load on the muscle-tendon unit, while lifting light weights to failure leads to proportionally greater increases in repetition strength (maximum number of repetitions with a given weight), because it involves undergoing high levels of metabolic stress.
#5. Using “weight” or elastic resistance
Most of the time in the gym, we use “weight” to provide resistance for our muscles, whether it is weight on a barbell, on a machine, or just our own bodyweight.
When we lift a plate-loaded barbell, we exert resistance to overcome two forces. Firstly, there is force exerted on the barbell by gravity, which pulls it constantly towards the earth. Secondly, we exert a force to start the barbell moving, to overcome its inertia. This force applies only when we are accelerating the barbell, at the start of the exercise.
When we squat with a plate-loaded barbell, the force we need to exert on it is therefore greatest at the bottom of the exercise, because we need to overcome *both* inertia and gravity. And as we decelerate towards the end of the exercise, force is at its lowest.
In contrast, if we apply large resistance bands to a barbell squat, there is much less force due to either inertia or gravity, and most of the resistance comes from elongating the elastic. Consequently, the force we need to exert on the barbell is greatest at the top of the exercise, because this is where the elastic band is most elongated.
Using “weight” on the barbell therefore challenges the muscles most when they are at their most lengthened, while using elastic resistance tends to challenge our muscles more when they are short. This produces different effects in each case, because of the adaptations that stimulating a muscle at a certain length triggers within the muscle fiber itself.
This is why strength training using a plate-loaded barbell squat tends to produce proportionally greater gains in 1RM plate-loaded barbell squat, while strength training with a barbell squat against bands produces proportionally greater gains in 1RM barbell squat against bands.
#6. Using “vertical” or “horizontal” force vectors
When we exert force, this can be in any direction relative to our own body, and can be categorized as vertical, horizontal, lateral, and even rotational, depending on the movement.
- Vertical force vectors occur when we exert force upwards, from our feet towards our head (like a vertical jump).
- Horizontal force vectors occur when we exert force forwards, from our back towards our front (like a standing broad jump).
- Lateral force vector occur when we exert force sideways, from our middle towards our side (like a side-step or standing lateral jump).
- Rotational force vectors occur when we turn at the waist.
Each direction involves a different set of joint angles at which peak force is produced, and therefore again involves a different set of muscle lengths in each of the main muscles. And so training with different force vectors causes specific strength gains in each of those force vectors.
#7. Using stable or unstable environments
Most of the time when we lift a weight, we tend to be in either a very stable environment (using a machine) or a moderately stable set-up (using free weights). Rarely, we might be persuaded to do an exercise on an unstable surface, like a Swiss ball.
Under very stable conditions (like a Smith machine bench press), we can lift a heavier weight than we can in moderately stable, or unstable conditions (like a dumbbell bench press on a Swiss ball).
This difference in strength is largely because the need to *balance* in less stable environments requires more involvement from opposing (called antagonist) and supporting (called synergist) muscles. Initially, the activation of these muscles makes it hard to move the weight, which is why we appear to be so much weaker in unstable exercise variations.
Yet, as we practice lifting weights in less stable environments, we learn to move the weight while balancing, and so we appear to gain strength. In reality, much of that gain in strength is an improvement in balance, and so it does not transfer as well as you might expect to strength gains under more stable conditions.
Conversely, no matter how much we gain strength under stable conditions, we will struggle to display that strength under unstable conditions, until we learn to balance as well. And this is why we observe strength gains that are specific to the type of stability used in training.
#8. Muscle group
When we do an exercise, this tends to involve a number of muscles. But there are almost always a range of exercises that can be used to train the same muscle groups.
For example, the squat and the hip thrust both involve the main lower body hip extensors (adductor magnus, gluteus maximus, and hamstrings) and knee extensors (quadriceps), albeit working them hardest at different muscle lengths.
Comparing these exercises, there are important differences in the muscle lengths at which peak muscular contractions occur, and also in the coordination patterns used for each exercise. So strength training with the squat will never produce the same gains in 1RM hip thrust, compared with hip thrust training, and vice versa.
Yet, when a muscle group is trained, it will usually increase in size, and we might expect that this will produce a degree of strength gains in other exercises that use the same muscle groups. And this is exactly what researchers have found, when investigating the hip thrust and squat exercises.
What is the takeaway?
Strength gains are specific for a number of reasons, depending on the key factors that affect force production, such as muscle length, muscle contraction velocity, external load on the muscle, amount of metabolic stress, or need to balance.
Strength gains are therefore specific to whether we lift or lower a weight, move quickly or slowly, lift heavy or light weights, move through full or partial ranges of motion, lift in stable or unstable environments, use “weight” or elastic resistance, direct force vertically or horizontally relative to the body, and to which muscle groups we use in training.