The great thing about strength training is that it works.

Want to lift heavier things? Strength training is the only way you can do that. Want bigger muscles? Lifting weights does that. Are you rehabbing a musculoskeletal injury? Resistance training of some sort will probably be involved. Want to improve your general health? Try out those weird machines at the gym. Want to live longer, while looking younger? You guessed it, you need more strength training in your life.

As you can see from the above list, strength training plays a particularly important role in the fitness industry. 

In fact, it is not exaggerating to say that strength training is the single most valuable tool used by strength and conditioning coaches and personal trainers. Without strength training, we would find it hard to bring real value to our clients.

For bodybuilders and other people seeking improved body composition, strength training is essential. It is the only natural way to increase muscle size, and the only way to avoid losing lean body mass when dieting. For team sports athletes, targeted strength training can improve sprinting ability, enhance jumping performance, and increase speed when changing direction.

Indeed, as fitness professionals, we are very fortunate that one of our primary tools is so amazingly effective and useful to people. Few other industries have this luxury.

But if we already know that strength training works, why do we need so much more research into it?

I think the answer to that question is very simple.


The great thing about strength training is that it works. The annoying thing is that we don't fully understand how. 

Generations of strength training experts have formulated four principles to guide us, which are (1) progressive overload, (2) individuality, (3) specificity, and (4) variety. However, these are practical guidelines and not scientific laws, and we actually know very little about why they apply. 

Let me explain.

#1. Progressive overload

When we start strength training regularly, we find that we can put the weight up, or increase the number of reps in each set, nearly every workout. As time goes on, this becomes harder. And after a few years, it is very challenging.

Even so, this gradual increase in load or reps is important for our progress to continue. If we lift the same weight for the same number of reps every time we go to the gym, we will not achieve the same improvements.

We call this the principle of progressive overload, but although we can name it, we don't know exactly why it happens. 

It seems likely that if we lift the same weight for the same number of reps in a second workout, the effective load is lighter relative to our new maximum capacity, compared to in the first workout. So the stimulus is smaller. If we repeat this process a couple of times, the workout we once found hard is no longer challenging, and provides no further incentive for our body to adapt. However, this is theoretical, and has not been tested.

Similarly, we do not know why it is easy to add weight or reps at the beginning of a training program, but much harder later on. It is likely related to the rate at which increases in neural drive, muscle size, lateral attachments between muscle fibers, tendon stiffness, and coordination occur. However, the speed at which each of these adaptations happen over time is still unknown.

We need research into this area, so that we can figure out new ways to help advanced athletes continue improving.

#2. Individuality

We have all had the experience of using the same strength training program for two different people, and getting completely different results. Even when two people have broadly the same training history (or lack thereof), one can see amazing gains, and the other achieve very little.

We call this the principle of individuality, but again, we don't really know why it happens. We can attribute the effect to genetics or previous exposure to different types of loading, but we don't know which genetic variations or training experiences lead to one individual increasing muscle size far more than all the others, while a different person gains far more strength.

We need research to figure this out, so that we can better tailor strength training programs to each person.


We all know that different strength training programs produce slightly different results. If you lift mainly very heavy weights (1 – 5RM), your maximum strength tends to jump upwards. If you do lots of reps with lighter loads, your repetition strength (muscular endurance) improves. And if you do a block of power training with light loads and fast bar speeds, you start being able to move the bar much more quickly.

We call this the principle of specificity, but we don't understand completely why it happens. Even so, we are now starting to understand that each type of strength training causes slightly different adaptations from the others, and that these differing adaptations are what brings about its unique effects.

We need more research to understand what triggers each of these specific adaptations, so that we can better tailor strength training programs to achieve each goal.


Following the same strength training program for a long time without changing it eventually leads to stagnation, and improvements come to a halt. 

We call this the principle of variety, but we have literally no idea why it happens. Various frameworks have been proposed, but they are totally theoretical, and we have no hard science to help explain it. The phenomenon could be physiological, or it could be psychological.

We need research to understand what stops us from improving when continuing with the same strength training program for a long period of time, without changing it. Since variety tends to reduce our ability to use the principles of progressive overload and specificity, this would help us use the minimal required dose of variety, and maximize gains.



The great thing about strength training is that it works. However, much remains to be learned about how it works. We have a framework of four principles that can guide us when we write strength training programs, but there are many unanswered questions that prevent us from implementing these principles as effectively as we might want. 

Fortunately, more research into how strength training works is already filling some of these gaps. As it comes out, we will gradually be able to write better programs that help athletes progress for longer, that are more tailored to each individual, that are better targeted at the overall goal, and that use the optimum amount of variety required to avoid stagnation.


Research that fills in the gaps between our key strength training principles is coming out all the time. In the S&C Research Review, I write about ten of these new studies every month. 

When writing about each study, I explain what it tells us about how strength training works, and how it can help us fill in the gaps between each of the four principles, and enable us to write better training programs.

The review is divided into three areas:

  1. Strength training and biomechanics
  2. Athletic performance (sprinting, jumping, and changing direction)
  3. Hypertrophy (muscle growth)

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