The great thing about strength training is that it works for a wide range of goals.

It improves sports performance, enhances body composition, prevents losses in muscle mass during a diet or periods of immobilization, and makes us more flexible.

The challenging thing about strength training is that it is very hard to figure out which training program works best for each goal.

We have this problem because of two reasons.

Firstly, when we test performance-related outcomes, such as maximum strength, jumping height, sprinting speed, or flexibility, there are many environmental factors that can change the result we record. This makes it difficult to tell whether there has been an improvement, or whether we just changed the test. 

Secondly, the improvements in each of these desirable outcomes varies a great deal, both between individuals, and also between training programs. 

Let's take a look at each of those problems in turn, and see how we can fix them.


When we test strength, jumping height, or flexibility, or in fact any performance-related outcome, there are many things that can influence the outcome.

Here are some examples (thanks to Israel Halperin):

  • Mental fatigue – our physical performance is reduced, when we have recently been thinking hard, whether at work or in school.
  • Attentional focus – when we direct our focus to the goal of the movement, our performance improves, but when we direct our focus towards a part of our body (as many coaching cues tend to encourage), our performance gets worse.
  • Autonomy – when we feel like we have little control over our environment, we become demotivated, and perform badly. In contrast, when we are allowed to make choices, our performance improves.
  • Time of day - when we test our performance in the morning, it is often worse than in the afternoon.
  • Supplement usage - both caffeine and creatine improve performance in many anaerobic activities, so either starting or ceasing to use either of these can affect the result on a performance test.
  • Music - when upbeat music is playing, our performance on physical tests tends to get better.
  • Number and nature of observers - performance tends to improve when there are more observers in the room, but the exact effects are also sex-specific. For males, performance is enhanced by opposite-sex observers. For females, performance is enhanced by same-sex observers and reduced by opposite-sex observers.
  • Encouragement and feedback - loud, repetitive, and positive feedback enhances performance, but negative feedback reduces performance.
  • Knowledge of exercise end-point - when we know how much further we have to go, we can hang on. When the nature of the test is more open-ended, such as "as many reps as possible" then we tend to stop earlier than we should.
  • Content of warm-up - some types of warm-up can improve performance in strength tests (such as ballistic exercises for the prime mover muscle groups), whereas some types of warm-up have sometimes reduced performance (such as lengthy static stretching).

What is the problem?

The problem is that if any of these environmental factors differ between the tests done at the start and end of a training program, then the changes recorded could be caused *either* by the training program itself, *or* by the change in environmental factors.

So the fewer of these factors that you control, the harder it is to convince other people that the results you recorded after a program were caused by the program itself. 

In fact, if you are not controlling any these factors, it is very likely that a large proportion of the changes you record are caused by changes in your testing conditions.

How do we fix the problem?

Environmental factors as so important, that when researchers carry out a study, they have a long checklist of things like this, and this helps to make sure that the exact same environmental conditions are present for all tests. 

Unless you are working in elite sport, you are probably not already using a similar checklist. So the improvements you record after a training program will be altered either positively or negatively by these factors.

In practice, a checklist is a great idea, because it allows us to fix most of these items. Things like the time of day of the test, the content of the warm-up before a test, the number and nature of observers, the music that is playing, the attentional focus cues, and the content of the verbal feedback can all be written down and controlled perfectly every time, if you are disciplined.

To provide a personal point of view: I always ask people if they control these factors when they tell me about the effects of their training programs. If they say no, I usually dismiss their results as being untrustworthy. It is a quick (but admittedly unpopular) way to triage out unreliable data.


We have all seen the same training program have different effects when followed by either two different people, or by the same person on two different occasions.

And research supports our observations. 

In fact, studies have shown that gains in muscular strength and size after the *exact* same strength training program can vary massively between people.

Famously, Hubal et al. (2005) carried out a study in 585 subjects who did 12 weeks of biceps curl strength training. Changes in muscle size ranged from -2 to +59%, and the increases in 1RM biceps curl ranged from 0 to +250%. 

These are staggeringly big differences!

We still do not know why some people achieve such great improvements in strength and size after a training program, while others do not (and it is worth noting that the high-responders for strength or size are not necessarily the same people).

Why does this happen?

Several hypotheses have been suggested, such as:

  • Differences in baseline training status – those individuals who have already become accustomed to using their muscles to produce high levels of force will probably achieve smaller gains. 
  • Genetic qualities – some people may just be capable of adapting more quickly to a given stimulus, or may experience a lot of muscle damage early in the training program and thereby lose muscle mass, which then takes time to replace.
  • Behaviors that the subjects display in the training period - some people may display eating habits that are more well-suited to increasing muscle size (calories and protein), or may exert a greater amount of effort in each set during training.

However, the truth is that we do not yet know.

What is the problem?

The problem is that this variability in the responses of different people to the exact same training program makes it very difficult to compare the effects of two template training programs that we have written. 

We might assume that because our program A worked well in a group of clients, while program B worked less well in a different group, that program A was better than program B. However, the clients who did program A could have been high responders, while the clients who did program B may have been low responders.

How do we fix the problem?

Researchers fix this problem by finding a group of subjects, and then either (1) randomly allocating them into two groups who do program A or program B, or (2) randomly allocating them to do either program A first, and then program B.

By randomly allocating the subjects to each group, they make it likely that the number of high responders and low responders who are following each training program are similar. This makes it possible for us to learn whether program A is better on average than program B.

While it is highly unlikely that many strength coaches or personal trainers will use this method for learning from experience, there are physiotherapists who have taken this route, especially when carrying out post-surgical rehabilitation. They allocate cases alternately to one treatment or another, as they come in, and then analyze the speed of recovery at a later date to see which approach is better. 

To provide a personal point of view: I would always be excited to see any data collected by a strength coach using this approach, although I have not yet seen it done. Combined with a checklist for controlling environmental factors, I think the data collected would be just as valuable as the results published by researchers.


The great thing about strength training is that it works. However, learning what works best from our experience is very, very difficult.

Learning from experience is difficult for two reasons. 

Firstly, many environmental factors can influence performance in a progress test (such as 1RM bench press). So unless we keep a checklist of things to do the same, every time we do that progress test, we could be measuring the effects of the environment, rather than of our training program, which is not that helpful.

Secondly, some people achieve large gains after training, while others fail to improve at all after the exact same program. While research corrects for this, our own experience typically does not. So unless we randomly allocate people to one training program or another, and compare them at a later date, we could be measuring the ability of a person to respond to training, rather than of our training program, which is not that helpful.

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 write better 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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