To get the most results from the work you put in its important to ensure that you you follow a few simple points. The following are the five criteria an exercise must meet to be effective at training a particular muscle.

1) The exercise is a free-weight movement

Focus on free-weight movements are superior to machine-based exercises.

That's ideal because free-weight exercises cause higher muscle activation levels and strength development. Plus, they're more joint friendly, leading to fewer injuries.(1)(2)(3)(4)

Thus, it’s better to do the squat instead of the leg press; the bench press instead of the chest press; and the dumbbell row instead of the machine row.

Now, this doesn’t mean that you should never train with machines. Such movements do have a place in a workout plan. It is hard, for instance, to do a knee flexion isolation movement without the leg extension machine. 

But if you can do a particular movement pattern both with free weights and with a machine, then – all else being equal – the free weight variant will be superior.

2) The exercise has both an eccentric and a concentric phase

There are three main types of muscle contractions:

• Eccentric – a type of muscle activation that produces tension on the muscle while it lengthens. For example, lowering the weight during a bench press. 

• Concentric – a type of muscle activation that produces tension on the muscle while it shortens. For example, lifting the weight during a bench press.

• Isometric – a type of muscle activation that produces tension on the muscle without a change in muscle length. For instance, pushing against an immovable object.

Now, to develop a muscle, the best types of exercises are those that have  clear eccentric and concentric phases. So, you actively control the weight both during the lifting and the lowering part of the movement.(5)(6)(7)

While most exercises are like this, it does exclude some movements from being ideal. Examples are the deadlift and the plank.

During the deadlift, most people don’t control the weight on the way down. Instead, they let the weight drop. That causes them to miss out on the muscle-building benefits of the eccentric phase.

Planks, on the other hand, train your muscles in a static position. That is also suboptimal because such contractions produce lower levels of muscle activation than concentric and eccentric contractions do.(8)

Thus, focus on exercises that have both a clear eccentric and concentric phase.

3) The exercise trains your muscles through a full ROM 

During dynamic exercises, you can train your muscles either through a partial or through a full range of motion (ROM). 

The best of those two ways is to train through a full ROM. Doing so produces the highest muscle activation. This, in turn, causes you to reap the most strength gains and the greatest muscle growth. 

Research shows, for instance, that you can develop your glutes, adductors, and quadriceps better with full squats than with half squats.(9)(10)

As an added benefit, full ROM exercises also place less stress on your connective tissue, making them more joint friendly. That’s why you’ll be less likely to get injured if you train through a full ROM.

4) The exercise allows for micro loading

Progressive overload is the most important training factor to shape an impressive figure. It refers to the fact that you must gradually increase the stimulus you place upon your body.  

It's simple. If you apply progressive overload, there's a reason for your body to improve. But if you fail to apply progressive overload, there won’t be such a reason, which means progress will stall. 

Now, arguably the best way to apply progressive overload is by lifting more weight over time. So, if you did an exercise with 100 pounds last time, you could aim to use 105 pounds during your next workout.

The problem?

Various exercises don't allow for micro progressions. At many gyms, for instance, the weight of the dumbbells goes up in steps of five pounds. Such an increased amount is a lot for many exercises.

If, for example, you use 20 pounds on the dumbbell triceps kickback and the smallest weight progression would be to use 25 pounds, that's a 25% increase in total resistance.

You can compare that jump to upping your squat from 200 pounds to 250 pounds. It's too big an increase.

That's why it's important to select exercises that allow for micro load-ability. Then, you can continue to make progress consistently.

So, instead of doing triceps kickbacks, you could do lying triceps extensions with an EZ bar. That triceps exercise allows for smaller jumps in relative weight.

5) The exercise has the right muscle group as its limiting factor

To train a muscle effectively, the muscle group you want to target should be the limiting factor during the movement – the muscle that gives out first.

For instance, many people deadlift with the motive to build their legs. But besides the fact that the movement doesn't train the legs through its full ROM, there’s another downside. 

For most people, the weakest link during the deadlift is either grip or lower back strength. As a result, they don't train their legs optimally because their grip or lower back gives out first.

That's why, if you're doing an exercise, the muscle you want to target should be the limiting factor. Then, you'll truly train the body part you want to develop.