Biomechanics
Randomized Controlled Trial
2013
Effects of bench press inclination on upper body pressing muscle activation
By Atle Hole Saeterbakken and Roland van den Tillaar
Journal of Sports Science and Medicine, 12(2), pp. 232-236
<h2>Abstract</h2>
<p>The incline bench press is widely used to develop the upper portion of the pectoralis major, yet the optimal inclination angle for maximizing clavicular head activation while minimizing excessive anterior deltoid recruitment has not been definitively established. This study examined <a href="/terms/electromyography/" class="term-link" data-slug="electromyography" title="EMG">EMG</a> activation of the pectoralis major (clavicular and sternal heads), anterior deltoid, and triceps brachii during flat, 30-degree, 45-degree, and 60-degree incline bench press conditions in resistance-trained men. Fifteen participants performed each angle at 70% of their flat bench <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> with EMG recorded from each target muscle. The 30-degree incline produced peak clavicular pectoralis major activation (78.2 ± 13.1% MVIC), significantly exceeding the flat bench and higher incline conditions. At 45 degrees and above, anterior deltoid activation increased markedly and progressively, while pectoralis major activation declined. The flat bench elicited the highest sternal pectoralis major activation. These findings challenge the common belief that steep inclines are necessary for upper chest development and suggest that 30 degrees represents a biomechanically optimal inclination for targeting the clavicular head.</p>
<h2>Introduction</h2>
<p>The pectoralis major is a large, fan-shaped muscle with two anatomically distinct heads: the clavicular head (upper pectoralis) originating from the medial clavicle, and the larger sternal head originating from the sternum and costal cartilages [1]. These regions have different fiber orientations and, critically, different mechanical functions. The sternal head is the primary contributor to shoulder adduction and horizontal flexion across a wide range of positions, while the clavicular head makes its largest contribution when the arm moves in a more superior direction — a distinction that has motivated the widespread use of inclined pressing angles in bodybuilding and chest development programs [2].</p>
<p>The incline bench press modifies the direction of the pressing force by elevating the torso relative to horizontal. This changes the orientation of the humerus during the pressing movement and, theoretically, increases the contribution of the clavicular pectoralis relative to the sternal head and increases the mechanical arm of the anterior deltoid. The concept is mechanically sound: because the clavicular head has fibers that pull the humerus upward and forward (as opposed to the more directly horizontal pull of the sternal fibers), a press performed in a more upward direction should preferentially recruit it [3].</p>
<p>However, the assumption underlying many training recommendations — that steeper inclines produce progressively greater upper chest activation — may be overly simplistic. As bench angle increases, the direction of pressing approaches vertical, and the exercise transitions biomechanically from a pectoralis-dominant movement to one that is increasingly shoulder-dominant. The anterior deltoid, whose primary action is shoulder flexion, becomes progressively more active as the pressing direction becomes more vertical [4]. This transition means that at sufficiently steep incline angles, the anterior deltoid may overtake the pectoralis as the primary mover, fundamentally changing the nature of the exercise.</p>
<p>The practical question — which inclination angle maximizes clavicular pectoralis major activation without excessively diverting load to the anterior deltoid — is directly relevant to exercise selection for chest <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>. Despite its practical importance, relatively few studies have systematically compared <a href="/terms/electromyography/" class="term-link" data-slug="electromyography" title="EMG">EMG</a> activation across multiple inclination angles in a single well-controlled experiment. This study addresses this gap by comparing flat, 30°, 45°, and 60° bench press conditions.</p>
<h2>Methods</h2>
<p><strong>Participants</strong></p>
<p>Fifteen resistance-trained men (mean age 23.8 ± 3.2 years; mean bench press <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> 97.4 ± 18.3 kg; minimum 2 years continuous resistance training) participated. Participants were required to have regular experience with both flat and incline bench pressing. Those with shoulder, elbow, or pectoral injuries in the previous 6 months were excluded. All participants provided written informed consent.</p>
<p><strong>Exercise Protocol</strong></p>
<p>Each participant attended a familiarization session followed by two testing sessions separated by 48 hours. The familiarization session established 1RM on the flat barbell bench press. Subsequent testing sessions examined <a href="/terms/electromyography/" class="term-link" data-slug="electromyography" title="EMG">EMG</a> activation during four bench angle conditions:</p>
<ul>
<li>Flat (0 degrees)</li>
<li>Low Incline (30 degrees)</li>
<li>Moderate Incline (45 degrees)</li>
<li>High Incline (60 degrees)</li>
</ul>
<p>All conditions used a barbell with the same absolute load, set at 70% of the flat bench press 1RM. This approach held load constant across conditions rather than establishing separate 1RMs for each angle, which would confound changes in <a href="/terms/muscle-activation/" class="term-link" data-slug="muscle-activation" title="muscle activation">muscle activation</a> with differences in relative effort. Three repetitions per condition were performed, with conditions presented in counterbalanced order and separated by 3-minute rest periods.</p>
<p><a href="/terms/grip-width/" class="term-link" data-slug="grip-width" title="Grip width">Grip width</a> was standardized to 1.5x biacromial width and maintained across all conditions. A metronome ensured consistent tempo (2-second descent, 1-second pause, 1-second ascent). <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="Range of motion">Range of motion</a> was standardized to barbell contact with the chest at the bottom and full elbow extension at the top.</p>
<p><strong>EMG Data Collection</strong></p>
<p>Surface electrodes were placed on: the clavicular head of the pectoralis major (approximately 2 cm below the mid-clavicle, following fiber direction toward the humerus), sternal head of the pectoralis major (approximately at the level of the fourth rib, at the lateral margin), anterior deltoid (anterior aspect of the shoulder, approximately 3 cm below the lateral clavicle), and triceps brachii long head (posterior aspect of the upper arm, midpoint between acromion and olecranon).</p>
<p>EMG signals were amplified, bandpass filtered (20–500 Hz), and normalized to MVIC values obtained from standardized <a href="/terms/isometric-contraction/" class="term-link" data-slug="isometric-contraction" title="isometric contraction">isometric contraction</a> positions for each muscle group. Mean and peak EMG amplitude were quantified during the <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="concentric phase">concentric phase</a> of each repetition.</p>
<p><strong>Statistical Analysis</strong></p>
<p>One-way repeated-measures ANOVA with Bonferroni post hoc testing compared EMG across the four angle conditions for each muscle. Significance was set at p 0.05; partial eta-squared (η²p) was calculated as a measure of <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a>.</p>
<h2>Results and Discussion</h2>
<p><strong>Clavicular Pectoralis Major Activation</strong></p>
<p>Bench angle significantly affected clavicular pectoralis major <a href="/terms/electromyography/" class="term-link" data-slug="electromyography" title="EMG">EMG</a> activation (F(3,42) = 12.7; p 0.001; η²p = 0.48). The 30-degree incline produced the highest clavicular head activation (78.2 ± 13.1% MVIC), which was significantly greater than the flat bench (61.4 ± 10.8% MVIC; p = 0.009), the 45-degree incline (70.3 ± 11.7% MVIC; p = 0.031), and the 60-degree incline (58.6 ± 10.2% MVIC; p = 0.002). The 45-degree condition was not significantly different from the flat bench, while the 60-degree condition produced the lowest clavicular head activation of all four angles.</p>
<table>
<thead>
<tr>
<th>Condition</th>
<th>Clavicular PMaj (%MVIC)</th>
<th>Sternal PMaj (%MVIC)</th>
<th>Ant. Deltoid (%MVIC)</th>
<th>Triceps (%MVIC)</th>
</tr>
</thead>
<tbody>
<tr>
<td>Flat (0°)</td>
<td>61.4 ± 10.8</td>
<td>89.3 ± 14.2</td>
<td>31.4 ± 7.8</td>
<td>68.7 ± 11.3</td>
</tr>
<tr>
<td>30° Incline</td>
<td>78.2 ± 13.1</td>
<td>74.1 ± 12.8</td>
<td>42.3 ± 8.6</td>
<td>61.2 ± 10.4</td>
</tr>
<tr>
<td>45° Incline</td>
<td>70.3 ± 11.7</td>
<td>63.2 ± 11.4</td>
<td>58.7 ± 10.1</td>
<td>57.8 ± 9.9</td>
</tr>
<tr>
<td>60° Incline</td>
<td>58.6 ± 10.2</td>
<td>52.1 ± 9.6</td>
<td>72.4 ± 12.8</td>
<td>54.3 ± 9.1</td>
</tr>
</tbody>
</table>
<p><strong>Sternal Pectoralis Major Activation</strong></p>
<p>As expected, the flat bench produced the highest sternal head activation (89.3 ± 14.2% MVIC), with activation declining progressively and significantly at each higher inclination angle. The 60-degree incline produced sternal head activation of only 52.1 ± 9.6% MVIC — a reduction of approximately 42% relative to the flat bench. This finding confirms that elevated bench angles reduce overall pectoralis major sternal involvement, a consideration for individuals whose goal is general chest mass rather than regional specialization.</p>
<p><strong>Anterior Deltoid Activation</strong></p>
<p>The most striking finding was the progressive and substantial increase in anterior deltoid activation as bench angle increased. From 31.4 ± 7.8% MVIC at flat to 72.4 ± 12.8% MVIC at 60 degrees, anterior deltoid activation more than doubled. At 45 degrees, the anterior deltoid activation (58.7% MVIC) was already approaching the clavicular pectoralis activation (70.3% MVIC), indicating that the anterior deltoid was a near-equal contributor to the pressing movement. At 60 degrees, the anterior deltoid activation (72.4% MVIC) actually exceeded the clavicular pectoralis activation (58.6% MVIC), effectively reclassifying the 60-degree incline as a shoulder-dominant pressing exercise.</p>
<p><strong>Mechanistic Interpretation</strong></p>
<p>The optimal activation of the clavicular pectoralis at 30 degrees reflects the confluence of two mechanical factors. First, the 30-degree incline orients the pressing vector more closely with the line of pull of the clavicular fibers, which insert on the humerus at an angle that aligns better with a slightly upward pressing direction than a pure horizontal direction. Second, at this moderate incline the anterior deltoid moment arm has not yet grown sufficiently to overtake the pectoralis as the dominant mover, preserving pectoralis-dominant mechanics [5].</p>
<p>The steep decline in clavicular activation at 60 degrees, paradoxically, suggests that the popular training belief that "steeper angles = more upper chest" is incorrect above approximately 30–45 degrees. Beyond this range, the exercise transitions toward a shoulder press pattern that is far more effective as an anterior deltoid developer than a pectoral one.</p>
<h2>Practical Applications</h2>
<p><strong>Optimal Angle Selection for Upper Chest Development</strong></p>
<p>Based on the <a href="/terms/electromyography/" class="term-link" data-slug="electromyography" title="EMG">EMG</a> evidence from this study, the 30-degree incline represents the optimal bench angle for selectively targeting the clavicular head of the pectoralis major. Practitioners who have been using 45-degree or steeper inclines with the intention of developing the "upper chest" should consider reducing the angle, as steeper settings increasingly shift load to the anterior deltoid rather than increasing pectoralis activation.</p>
<p>Key angle recommendations:</p>
<ul>
<li><strong>30 degrees</strong>: Optimal for clavicular pectoralis major development; maximizes upper chest activation while maintaining pectoralis-dominant mechanics</li>
<li><strong>0 degrees (flat)</strong>: Optimal for overall pectoralis mass (highest sternal head activation); should remain a cornerstone of chest training</li>
<li><strong>45 degrees</strong>: Transitional zone — meaningful pectoralis and deltoid co-stimulation; suitable for general upper pressing development</li>
<li><strong>60 degrees and above</strong>: Functions primarily as an anterior deltoid exercise; appropriate when shoulder development is the goal, not upper chest</li>
</ul>
<p><strong>Combining Angles for Complete Chest Development</strong></p>
<p>A complete pectoralis major development program should incorporate both flat and low-incline pressing to adequately stimulate both regional portions of the muscle:</p>
<ul>
<li><strong>Flat bench press</strong>: 3–5 sets of 4–8 repetitions (primary strength/mass movement)</li>
<li><strong>30-degree incline press</strong>: 3–4 sets of 8–12 repetitions (upper chest specialization)</li>
<li><strong>Decline press or dips</strong>: 2–3 sets of 10–15 repetitions (lower chest / sternal emphasis, optional)</li>
</ul>
<p>Training programs that use only flat pressing may underdev the clavicular head, while programs relying primarily on moderate-to-steep inclines may develop the anterior deltoid disproportionately relative to the pectoralis.</p>
<p><strong>Equipment Considerations</strong></p>
<p>Adjustable bench settings in commercial gyms are often available at 30-degree increments (30, 45, 60, or similar). <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="If">If</a> a 30-degree setting is unavailable, a 15–30-degree range is still preferable to 45+ for upper chest emphasis. Dumbbell incline press variations may allow finer angle adjustments than fixed barbells.</p>
<p><strong>Technique for 30-Degree Incline Press</strong></p>
<ol>
<li>Set the bench to 30 degrees and position the body so the bar touches the upper sternum / collarbone area at the bottom</li>
<li>Maintain scapular retraction and depression throughout to stabilize the shoulder girdle</li>
<li>Use a grip approximately 1.5x shoulder width — too narrow reduces pectoralis stretch, too wide increases shoulder stress</li>
<li>Lower the bar under control (2–3 seconds) and press explosively, focusing on squeezing the upper chest at the top</li>
<li>Avoid letting the elbows flare excessively (greater than 75 degrees from the torso) to reduce anterior shoulder stress</li>
</ol>
<p><strong>Special Consideration for Anterior Shoulder Overuse</strong></p>
<p>Athletes with a heavy bench pressing background or those experiencing anterior shoulder discomfort should be aware that any incline pressing increases anterior deltoid demand relative to flat pressing. Individuals with anterior capsule or rotator cuff issues may find that even 30-degree inclines produce discomfort and should work within pain-free ranges under clinical guidance.</p>