Though quite a few isolation exercises target the triceps brachii, there are few as effective as the lying tricep extension (also known as skull crushers), a free weight resistance exercise that has earned a mainstay place among the most popular bodybuilding routines.
One point of contention concerning the skull crushers exercise is in regards to the angle of the bench that the exerciser is lying upon, and its effects on the total training stimuli and thus results of the training program itself.
For the most part, performing skull crushers on an incline or flat bench will not alter the results of the exercise to any clinically significant capacity - so long as the exerciser is not performing the movement at a large incline angle, since this will shift the muscular activation to an entirely different muscle group instead.
In more technical terms, the skull crusher exercise is a free weight isolation exercise performed with an EZ curl bar, straight barbell or pair of dumbbells for the purposes of bilateral triceps brachii training.
In terms of mechanics, it primarily utilizes the elbow extension and flexion biomechanic alongside isometric contraction of the deltoids and biceps brachii so as to ensure the weight remains stable enough to move throughout each repetition.
It is most often programmed as an accessory exercise on push or upper body days, wherein its effectiveness is maximized when paired with heavy triceps brachii recruiting compound movements like the bench press or the overhead press.
The terms incline and flat bench refer to the angle that the exercise bench places the lifter’s body in relation to the ground, with an incline-adjusted bench placing the upper torso at a higher elevation than the hips and thus altering a number of factors in whatever exercise is being performed.
In regards to the skull crusher exercise being performed at an incline or on a flat bench, this can equate to certain changes in which muscle group is activated, the extent of said activation and which particular part of a muscle group receives such activation.
Moreover, this difference in elevation will also alter the safety profile and relative risk of injury involved in the exercise, with the flat bench skull crusher exercise presenting a different set of dangers to the incline bench exercise due to the difference in shear force, joint positioning and the object of resistance’s relative angle to that of gravity.
For the most part however, both the incline and flat bench skull crusher exercise are performed in much the same manner and have quite similar form cues, making the choice of which to use up to personal preference and the needs of one’s training program.
The relative angle of resistance imparted by skull crushers is subsequently changed depending on the elevation of the exerciser’s torso in relation to the full extension of their arms, with a flat bench combining with gravity to produce a more downward angle of resistance while an inclined bench skews this to a sideways angle instead.
This is the main source of the albeit minor differences between the two skull crusher variations, with the incline bench allowing for a slightly longer range of motion, wider grip along the bar and reduced pressure on the elbow joints as the angle of resistance does not forcibly compress the tissues therein.
Inversely, the flat bench calls for a more narrow grip along the bar, placing greater pressure on the elbows and reducing the involvement of muscle groups other than the triceps brachii, thereby creating a greater specificity of training stimulus at a muscle group level, though the incline variation exceeds the flat variation in this capacity in certain contexts.
Not only does changing the angle of resistance involved in the exercise also subsequently alter the muscular activation and safety risks of the movement, but so too does it change the more technical aspects of the skull crusher, such as the time under tension, biomechanical compatibility and even the maximal loading potential found therein.
As was previously mentioned in this article, the muscular activation and main focus of the skull crusher exercise can be changed by altering the incline of the exerciser’s body, shifting what muscles specifically are activated to the greatest extent throughout each repetition.
During the flat bench skull crusher, resistance and therefore training stimulus is evenly distributed throughout the three heads of the triceps brachii, creating an even activation across the muscle group and only recruiting other muscles in a stabilizing capacity at most.
This is not the case with the incline bench skull crusher exercise, wherein it is the longer head of the tricep that is activated to a greater extent, with excessive inclines shifting some of the resistance to the anterior deltoid head and thus acting as a sign that the exerciser is performing the movement improperly.
Nevertheless, both the flat bench and incline bench variations of the skull crusher will train the triceps brachii in a highly effective isolationary manner, making this particular point of distinction useless to individuals who are not higher level athletes with a need for highly specific triceps brachii stimulus targeting.
Despite what most exercisers believe, there is in fact very little difference in the range of motion between the incline and the flat bench skull crusher exercise, as both exercises involve lowering the object of resistance (in most cases a barbell) from full elbow extension length until the forearms are approximately parallel to said elbows.
The incline of the exerciser’s torso has no effect on this movement, as the exerciser’s forearms and elbows remain the same length and in relatively the same position regardless - resulting in nearly identical ranges of motion.
The sole difference is in the positioning of the exerciser’s hands along the barbell, with a more narrow grip in the incline bench variation of skull crushers resulting in an ever so slightly longer range of motion depending on an individual’s bodily proportions.
Nonetheless, this difference is minute at best and is generally not factored into the decision on which variation to use, especially since the usage of the decline bench skull crusher variation is far more effective at increasing the exercise’s range of motion.
It is in the risk of injury between the incline and flat bench skull crusher variations that they are most different, as the relative position of the shoulders and upper torso in relation to the elbows during the incline skull crusher is far safer for the elbows than a conventional flat bench skull crusher exercise.
While both exercises can have their risk of elbow injury relatively mitigated through proper loading, programming and the usage of correct form, it is an eventuality that flat bench skull crushers will eventually lead to irritation and damage of the elbow joint and its surrounding connective tissues, making the usage of the incline bench skull crusher exercise a more advisable choice.
In short, it is the incline bench variation of skull crushers that is the more advisable route to take - a piece of advice solely dictated by the relatively greater safety of said exercise in comparison to its flat bench variation.
However, one should be careful to not place the body at too excessive an incline, as this will defeat the entire purpose of the exercise, activating the shoulder muscles instead.
While the flat bench skull crusher exercise is still a perfectly effective and valid triceps isolation exercise, if the lifter has access to an adjustable incline bench and fits it to be more comfortable for their own unique bodily proportions; it is best to use the incline bench variation instead.
1. Stiggins, Chuck; Allsen, Phil Lying barbell triceps extension, National Strength and Conditioning Association Journal: April 1986 - Volume 8 - Issue 2 - p 81-81
2. Sumiaki Maeo, Yuhang Wu, Meng Huang, Hikaru Sakurai, Yuki Kusagawa, Takashi Sugiyama, Hiroaki Kanehisa & Tadao Isaka (2022) Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position, European Journal of Sport Science, DOI: 10.1080/17461391.2022.2100279