Having sculpted abs is usually one of the main aesthetic goals of all those who train in the gym.
Over the years, an infinite number of strategies, techniques, and exercises have been proposed to train this area, creating and spreading false myths and illusory promises in many cases.
The crunch is perhaps the most famous exercise for training the abdomen.
For a long time, in fact, it was considered the king of exercises for this muscle area, considered by many to be indispensable in any self-respecting training program.
In recent years, however, the fame of this exercise has gradually faded, unlike the plank, whose popularity has grown exponentially.
This is probably due to factors such as the spread of functional training, the widespread fear of the risks associated with flexing the spine (which occurs during the crunch), and the general idea that the plank trains the abdominal muscles better than the crunch.
But is it really so? Is the plank really better than the crunch in all respects? What exercise is best for training the abdominal muscles? Which of the two activates these muscles the most? Which is safer and less risky?
Let’s analyze the question, basing ourselves as always on the most recent scientific literature.
Analysis And Biomechanics Of The Crunch And Plank
Let’s start by analyzing these two exercises. At first glance, they look very different:
In the crunch, we are lying on our stomach, typically with the knees bent and the arms held behind the head, crossed over the shoulders or stretched forward, and from here the trunk is partially raised through a flexion movement of the spine, and then return to the starting position.
On the contrary, in the plank exercise, we are on our stomach with the elbows and toes resting on the floor, to unload the weight of the body, kept in a horizontal position.
While they may seem so different, both exercises target the rectus abdominis, internal obliques, external obliques, and transverse abdominis. Other muscles will also be activated, such as the rectus femoris, iliopsoas, and spinal erectors.
If we take a step back and look at these two basic exercises, we are actually faced with two very similar exercises, one isotonic and the other one isometric.
In fact, in the crunch, we witness a concentric and eccentric muscle contraction, with repeated shortening and lengthening of the muscles, while in the plank (isometric exercise) the length of the muscle is kept the same during the duration of the exercise, while this remains in any case in contraction.
It must be said that there are an infinite number of variations of these two exercises, capable of modifying the type of contraction chosen, the degree of difficulty, and the level of muscle activation.
For educational purposes, the two classic variants of crunch and plank will be analyzed in this article.
Rectus Abdominis And Obliques: Which One Is More Active?
Let’s analyze the results of the studies that compared these two exercises, and in particular how much the individual abdominal muscles are activated in one and the other. Starting with an important premise: greater muscle activation does not necessarily mean greater hypertrophic stimulus.
Starting from the rectus abdominis (by far the most famous abdominal muscle), whose main action is that of flexion of the trunk (bringing the sternum towards the pelvis and vice versa) and the retroversion of the pelvis (which during the plank it must be actively maintained, as gravity would lead to anteversion).
Some recent studies have compared the activity of the rectum in these two exercises, concluding that the rectus abdominis is more active in the crunch than in the plank (54% of maximum voluntary contraction vs 30%).
These results can vary widely based on the variation of plank and crunch that takes place (also in this context we are referring to the standard executions of plank and crunch).
Based on these results, if our goal is to target the rectus abdominally as much as possible, the crunch would seem more effective than the plank.
Let’s now move on to the internal and external oblique muscles of the abdominals.
These muscles are commonly associated with the action of lateral inclination and rotation of the trunk, but in fact, in addition to these functions, they also assist the rectus abdominis in flexion and retroversion of the pelvis.
Studies have shown that the oblique muscles are more active in the plank than in the crunch. In fact, in the plank, it has been seen that these have a degree of activation of 45% (of the maximum voluntary contraction), while in the crunch only 32%. The rectus femoris is also more active in the plank, as it is forced by gravity to maintain isometric knee extension.
In conclusion, it seems that the rectus abdominis is more active in the crunch, while the other muscles (obliques, rectus femoris, paraspinal) are more active in the plank. Let’s now analyze the issue from a rehabilitation and accident risk point of view.
Crunch, Plank, And Back Pain: Which Is More Effective?
Consulting the literature that analyzed the role of these two exercises in the rehabilitation of back pain, it emerged that neither seems to be superior to the other.
This conclusion is certainly sensible and predictable since back pain is a highly subjective and variable problem, multifactorial and dependent on many variables, including both purely biomechanical and psycho-social factors.
It would be reductive to think only about which is the most effective of these two exercises in this context.
Not surprisingly, therefore, studies have found no substantial differences between these two exercises in cases of back pain.
Crunch, Plank, And Back Pain: Which Is Less Risky?
And speaking of the risk factor? Which of the two is safer for our back health?
There is currently no quality evidence that the crunch has a higher risk of injury than the plank, although it has often been demonized in this respect.
The spine has in fact been for years the subject of myths and concepts that looked at this structure as if it were “crystal”, while we know today that the spine is extremely strong and adaptable.
In any case, both exercises have a very low level of risk (also considering that the loads and forces involved are very low).
Many think that the crunch is by default a harmful movement for the back, but if we analyze this issue in the literature we find that the results are extremely variable, heterogeneous, and inconsistent (based on the structure of the articles and the parameters analyzed in the latter).
For this reason, we can say that at the moment no quality evidence proves that the crunch is a harmful exercise for the back.
Which Improves Performance The Most?
Moving from a “performance” perspective, the results are similar between the two exercises: both bring improvements, which in the studies analyzed were measured with the sit-up test.
The plank test (essentially in these tests the parameters recorded during a sit were compared. -up and a plank), and with the sprint to 20 meters. From this point of view, therefore, we cannot say which of the two exercises is more effective.
In conclusion, we can say that the most sensible strategy to optimize the training of the abdominal muscles is to structure training programs that include both isometric exercises and isotonic exercises.
Possibly inserting both the plank and the crunch, according to the needs, at the functional level, and to the tastes of the subject, thus providing training stimuli of various types to the muscles of this much-desired area.