Abstract
Background
TRX suspension push-ups enable adjustment of body angle to manipulate loading and neuromuscular demand. However, the effects of extreme inclinations, particularly declined positions where the hands are lower than the feet, on upper-body muscle activation remain unclear. This study aimed to examine how different body angles influence upper-body activation during TRX push-ups compared with those performed on a stable surface.
Methods
Nineteen trained men performed push-ups at five body angles (+ 30°, + 15°, 0°, − 15°, − 30°) under TRX and stable-surface conditions. Surface EMG was recorded from the pectoralis major (PM), anterior deltoid (AD), triceps brachii (TRI), upper trapezius (UT), and serratus anterior (SA). EMG data were normalized to maximal voluntary isometric contraction (%MVIC), and two-way repeated-measures ANOVA was used to compare activation differences between conditions and angles. The significance level was determined as p < .05.
Results
TRX push-ups elicited medium to extremely high activation in the PM, AD, and TRI. PM activation was significantly greater with TRX compared with stable-surface push-ups (p < .05), particularly at + 30°, + 15°, and 0° compared with lower angles (p < .05). Both TRX and stable-surface push-ups produced greater AD, TRI, UT, and SA activation at − 30° than at higher angles.
Conclusion
TRX push-ups at higher inclinations (+ 30° to 0°) effectively target the pectoralis major, while lower angles (− 30°) preferentially increase activation of the anterior deltoid, triceps brachii, upper trapezius, and serratus anterior. These findings provide angle-specific recommendations for suspension training push-ups to optimize muscle activation patterns.
Keywords: Functional training, Angle of movement, Electromyography
Background
TRX suspension training serves as a functional exercise method that utilizes an unstable environment created by suspension straps to alter the body’s center of mass and base of support. These changes enhance muscle activation and motor control capabilities [1, 2]. This training approach has been widely applied for improving strength, stability, and movement coordination [3, 4]. By supporting the body through suspended straps, TRX exercises increase stability challenges and require coordinated activation among primary movers, assisting, and stabilizing muscles to maintain proper control [5]. Although TRX exercises offer functional advantages, the unstable environment also imposes notable biomechanical constraints. In particular, changes in joint loading, elevated requirements for neuromuscular stabilization, and alterations in movement mechanics become more pronounced when the feet are positioned above shoulder height. These factors suggest that suspension system does not uniformly increase muscle activation across all angles, underscoring the need to examine how instability interacts with specific body positions.
The push-up, a prevalent exercise within TRX suspension training, serves to effectively engage the pectoralis major (PM), anterior deltoid (AD), triceps brachii (TRI), and the muscle groups responsible for shoulder stabilization (including serratus anterior, SA) [6, 7]. Previous research indicated that the instability characteristic of this suspension modality elevates the muscular demands for maintaining stable movement, thereby significantly enhancing coordination and presenting an increased challenge [8]. Additionally, engaging in push-ups on a suspension apparatus, as opposed to conventional stable surfaces, has been shown to elicit heightened muscle activation [5], especially within the PM, AD and TRI [9–11]. Moreover, the inherent instability of the suspension apparatus compels the muscular groups to perpetually modify load distribution throughout the exercise, further augmenting coordination and stability of movement.
Changes in body angle significantly influence load adjustment and stability during TRX push-up. The TRX system modulates intensity via angle and height adjustments of the suspension strap [12]. This modulation is grounded in principles of stability, vector resistance, and pendulum dynamics [1]. However, this modulation entails important biomechanical considerations. As the body angle shifts toward decline positions (feet elevated), loading on the upper extremities and shoulder complex increases, requiring greater neuromuscular control and activation of stabilizing muscles such as the SA and upper trapezius (UT) to maintain proper scapular kinematics and glenohumeral integrity. Indeed, studies showed that instability conditions enhanced the activity of shoulder stabilizers (e.g., SA, UT) while reducing activation of primary movers (e.g., PM) [2]. Additionally, the interaction of suspension strap dynamics and angle variations profoundly affected load distribution and cooperative muscle activation, particularly with elevated foot height. Near-horizontal body angles result in significant activation increases in the triceps and serratus anterior; conversely, raising the foot above shoulder height may altered the activation patterns of the AD and UT [13, 14]. However, the evidence regarding muscle activity at different angles remains insufficient. Nevertheless, the specific activation characteristics of these muscle groups under extreme angle conditions, such as when foot height exceeds shoulder height, remain inadequately explored.
In push-up-related research, comparisons between upper and lower limb elevation have been conducted, with most studies focusing on differences between stable and unstable surfaces [15, 16]. While some investigations have examined the effects of the push-up angle [17] and upper limb elevation [6], the majority of these studies focused on scenarios where the hands and feet were positioned at similar elevations. Limited findings address decline push-ups. In training practice, lower limb elevation is often used as a practical method to increase intensity or introduce variation. However, previous study designs have primarily focused on angles where the shoulder joints are positioned above the lower limbs. Although some studies explored lower limb elevation during push-ups, the designs of these studies did not involve TRX system. Hence, the aim of the present study was to determine the muscle activity during push-ups at all possible angles between the torso and ground. Based on previous findings, it was hypothesized that (1) decline positions would elicit greater activation of the AD, TRI, UT, and SA due to higher stabilization demands; (2) incline positions would result in relatively greater activation of the PM; and (3) overall muscle activation would be higher during TRX suspension push-ups than during stable-surface push-ups, regardless of body angle.
Methods
Experimental approach to the problem
The present study employed a within-participant repeated-measure design to investigate muscle activity differences during push-ups performed on stable surface and TRX system. Push-ups were executed at five different angles: the shoulder joints positioned higher (+ 30° and + 15°), lower (− 15° and − 30°), and parallel (0°) to the ankle joints. Muscle activity of the PM, AD, TRI, SA, and UT was recorded throughout the experimental procedure using a surface EMG system (TeleMyo 2400T G2, Noraxon USA). The order in which the exercise conditions were implemented was counterbalanced. Prior to the experimental trials, maximum voluntary isometric contraction (MVIC) test were performed for each muscle, and the EMG signals were normalized to the respective MVIC values for comparisons across different exercise conditions.
Participants
Power analysis (GPower, 3.1.9) indicated that a sample size of 14 was required to perform a two-way repeated-measures ANOVA (2*5) with the following input parameters: effect size f = 0.25, alpha = 0.05, power = 0.80, and measurements = 10. This study recruited nineteen healthy male university students in physical education (age: 21.1 ± 1.2 years; height: 174.1 ± 4.9 cm; weight: 70.7 ± 7.2 kg). The sample consisted of athletes with at least six years of training experience in handball, volleyball, or track and field, and all participants were right-hand dominant. Each participant had at least six months of consistent resistance training experience (three sessions per week) that regularly included push-up exercises and prior experience with TRX suspension training. None of the participants had sustained injuries within the previous six months that could affect their normal physical performance, and all were free from cardiovascular, musculoskeletal, pulmonary, or arthritic disorders. This study was approved by the National Tsing Hua University Institutional Review Board (No. 10711HS080) and conducted in accordance with the Declaration of Helsinki.
Procedures
Participants completed two sessions: a familiarization session and an experimental session, both conducted at the same time of day in the morning. The familiarization session took place 48–72 h before the experimental session to ensure consistency. Participants were required to adhere to specific pre-session guidelines, including refraining from consuming food, beverages, or stimulants (e.g., caffeine) within 2 h of each session and avoiding vigorous physical activity beyond routine daily activities for at least 24 h prior to the exercises.
Familiarization sessions
Each participant was required to participate in two familiarization sessions in which they were shown how to perform TRX push-up at + 30º, + 15º, 0º, − 15º, and − 30º (Fig. 1). The angle was defined as that between the straight line from the shoulder joint to the ankle joint and the ground. A horizontal body line represents 0º; +30° and + 15° indicate that the shoulder joints were higher than the ankle joints; and − 30° and − 15° indicate that the shoulder joints were lower than the ankle joints. The purpose of familiarization sessions was to ensure the participants were fully aware of how to perform all movements and capable of performing these movements without any assistance.
Fig. 1.
Illustration of TRX and stable-surface push-up angle settings
The TRX strap length and height of the aerobic steps (which were used to elevate the feet; Fig. 1) were also recorded to determine the appropriate settings for the formal experiment. If a participant was unable to master the push-up movements within the two familiarization sessions, three or more sessions were held until the participant had fully mastered the movements.
MVIC determination
For normalization of the EMG data, each participant was required to perform MVIC for each muscle, and EMG responses were collected from the skin surface. Before the electrodes were attached, the skin at the electrode attachment sites was shaved using a razor and cleaned with alcohol to ensure accurate electrode placement and minimize impedance. The MVIC test of the PM, AD, TRI, UT, and SA was three MVIC each lasting 5 s. A two-minute interval of rest was allotted between the MVIC test of different muscles. Verbal feedback was provided for each subject for the MVIC procedures. Positions for the MVICs were performed according to standardized procedures, the specific experimental procedures were as follows: (1) PM: the shoulder abducted to 90° and the elbow flexed at 90°, and shoulder horizontal adduction was performed [18]; (2) AD: the shoulder joint was flexed 90°, and shoulder joint flexion was performed [18]; (3) TRI: sitting position. the shoulder and elbow joints were flexed 90°, and the forearm pronated, and elbow extension was performed [18]; (4) UT: the shoulder abducted to 90° with the neck side-bent, rotated to the opposite side, and extended [19]; (5) SA: supine position. the shoulder flexed to 125°, and the scapula was upwardly rotated with the shoulder flexed [19].
Exercise sessions and applications
In the formal experiment, the TRX strap was connected to an anchor point and was perpendicular to the ground. Each participant was required to perform push-ups at five angles (+ 30°, + 15°, 0°, − 15°, and − 30°). For each angle, five repetitions were performed. The participant had a 3–5-minute recovery interval between sets for each angle. The amplitude of the EMG root mean square (RMS) for the PM, AD, TRI, UT, and SA was recorded during the entire procedure. In all trials, the greatest RMS value recorded during push-ups was averaged and normalized to the MVIC (%MVIC). A previous study’s categorization of muscle activation into four levels was adopted in this study to compare muscle activity levels under different conditions: low (L) = 0–20% MVIC; mid-level (M) = 21–40% MVIC; high (H) = 41–60% MVIC; and very high (VH) = ≥ 61% MVIC [20].
Instrumentation and data processing
The muscle activity of the right-side PM, AD, TRI, SA, and UT was recorded using an EMG system (TeleMyo 2400T G2, Noraxon USA) with a sampling rate of 1,000 Hz. Following the recommendations of the Surface EMG for the Non-Invasive Assessment of Muscles (SENIAM) [21], pairs of bipolar surface electrodes were aligned along the muscle midline and oriented parallel to the muscle fibers. The center-to-center distance between electrodes was set at 2.5 cm. Electrodes were placed on the muscle belly of each target muscle as follows: PM at the midpoint between the sternal notch and the anterior axillary line along the sternocostal fibers; AD at approximately 2 cm distal to the anterior acromion; TRI at 50% of the distance between the posterior acromion and the olecranon; SA on the lateral thoracic wall at the level of the 5th–7th ribs just inferior to the axilla; and UT at the midpoint between the C7 spinous process and the acromion. Electrode placements followed SENIAM guidelines and were consistent with previous push-up EMG studies [16, 21]. Prior to electrode placement, the skin was prepared by shaving and cleaning with alcohol wipes to reduce impedance. A reference electrode was affixed to the acromioclavicular joint, and interelectrode resistance was verified to remain below 10 kΩ for all participants. The collected EMG signals were digitized using the TeleMyo 2400T G2 system and subsequently processed with Myoresearch XP 1.07 software (Noraxon USA Inc.). Signal processing included rectification, band-pass filtering, and integration. EMG amplitude was determined as follows: (1) during MVIC tests, the root mean square (RMS) of the signal was calculated over a 500-millisecond window centered on the peak force; (2) during push-up exercises, the RMS was calculated for each repetition within a 500-millisecond window centered on the highest signal value. For visualization purposes, time-normalized EMG profiles were also generated across the entire push-up cycle (Fig. 2). For each repetition, the processed EMG amplitude was resampled to 0–100% of the push-up cycle and then averaged across the five repetitions for each condition and angle. Group curves are presented as the mean, and the shaded area indicates one standard deviation.
Fig. 2.
Time-normalized EMG profiles of the pectoralis major, anterior deltoid, triceps brachii, serratus anterior, and upper trapezius during TRX and stable-surface push-ups performed at five body angles (+ 30°, + 15°, 0°, − 15°, − 30°). EMG amplitudes are expressed as %MVIC and time-normalized to 0–100% of the push-up cycle
Data analysis and statistics
Statistical analyses were performed using SPSS version 27.0 for Windows. All data are presented as a mean (M) and standard deviation (SD). The Shapiro–Wilk test was used to assess the normality of the variables. A two-way repeated-measures analysis of variance (ANOVA) was used to compare the differences in muscle activity during push-ups performed on two surfaces (stable surface vs. TRX) and fives angles (+ 30º, + 15º, 0º, -15º, and − 30º). If an interaction approached significance, Tukey’s post hoc test and paired t-test was used. The significance level was set at 0.05.
Results
The muscle activation during push-ups on a stable surface and with TRX at five angles is shown in Table 1. For PM muscle activation, no significant interaction was found (F = 1.069, p = .364, partial η² =0.056). Significant main effects were observed for surface (F = 20.782, p < .001, partial η² = 0.536) and angles (F = 19.109, p < .001, partial η² = 0.515). Post hoc analysis revealed that PM activation was significantly greater during TRX push-ups than stable-surface push-ups. PM activation at + 30°, + 15°, 0°, and − 15° was significantly greater than at − 30°, and at 0° was significantly greater than at − 15°.
Table 1.
Differences in muscle activity during push-ups with TRX and on a stable surface
| Methods | Angles | PM | AD | TRI | UT | SA |
|---|---|---|---|---|---|---|
|
TRX Push-up |
+ 30° | 50.4 ± 21.3¢£ | 41.1 ± 21.5 | 33.6 ± 10.9£ | 16.3 ± 6.4£ | 17.3 ± 6.6 |
| + 15° | 52.4 ± 19.8¢£ | 46.7 ± 25.8 | 31.5 ± 10.4 | 15.5 ± 5.7£ | 27.5 ± 11.2* | |
| 0° | 54.6 ± 19.5¥¢£ | 58.1 ± 35.1*‡ | 33.0 ± 12.0 | 14.2 ± 4.6£ | 37.2 ± 11.9*‡ | |
| -15° | 51.7 ± 19.2¢£ | 63.2 ± 38.6*‡† | 35.2 ± 13.2 | 18.1 ± 7.4† | 45.7 ± 15.4*‡† | |
| -30° | 41.5 ± 13.8£ | 64.5 ± 35.3*‡† | 37.1 ± 12.5‡ | 20.4 ± 7.3‡† | 55.2 ± 18.2*‡†¥ | |
|
Stable Push-up |
+ 30° | 40.6 ± 17.9¢ | 41.1 ± 21.1 | 29.5 ± 10.0 | 05.0 ± 2.8 | 22.5 ± 11.6 |
| + 15° | 39.2 ± 16.0¢ | 44.3 ± 20.8 | 32.0 ± 11.5 | 07.0 ± 4.7* | 30.6 ± 12.4* | |
| 0° | 40.8 ± 15.3¥¢ | 49.1 ± 23.2*‡ | 34.5 ± 12.4*‡ | 10.1 ± 6.5*‡ | 34.2 ± 12.5*‡ | |
| -15° | 35.8 ± 15.2¢ | 55.5 ± 27.1*‡† | 37.8 ± 16.2*‡ | 18.0 ± 12.4*‡† | 44.6 ± 14.7*‡† | |
| -30° | 27.2 ± 13.1 | 59.5 ± 27.6*‡† | 41.4 ± 18.2*‡†¥ | 25.3 ± 18.2*‡†¥ | 55.2 ± 16.2*‡†¥ |
Values are mean ± SD. Body angles represent the inclination of the shoulder relative to the ankle (+ 30°, + 15°, 0°, -15°, -30°)
Significant differences compared with *+30° push-ups; ‡+15° push-ups; †0° push-ups; ¥−15° push-ups; ¢−30° push-ups; £stable-surface push-ups
Abbreviations: PM Pectoralis major, AD Anterior deltoid, TRI Triceps brachii, UT Upper trapezius, SA Serratus anterior, %MVIC Percentage of maximal voluntary isometric contraction
For AD muscle activation, no significant interaction was observed between surface and angles (F = 1.581, p = .218, partial η² =0.081). No significant main effect was found for surface (F = 1.637, p = .217, partial η² =0.083). A significant main effect for angle was observed (F = 17.831, p < .001, partial η² =0.498). Post hoc analysis indicated that AD at 0°, − 15°, and − 30° was significantly greater than at + 30° and + 15°, while at − 15° and − 30° was significantly greater than at 0°.
For TRI muscle activation, a significant interaction between surface and angle was observed (F = 4.894, p = .016, partial η² =0.214). Post hoc comparisons revealed that during TRX push-ups, TRI was significantly greater at − 30° than at + 15° (F = 5.405, p = .007, partial η² =0.231). On a stable surface, TRI at 0°, − 15°, and − 30° was significantly greater than at + 30° and + 15°, and at − 30° was significantly greater than at 0° and − 15° (F = 14.727, p < .001, partial η² =0.450). Moreover, at + 30°, TRI was significantly greater during TRX push-ups than during stable-surface push-ups (p = .023, d = − 0.571, 95% CI [-1.051, − 0.078]).
For UT muscle activation, a significant interaction between surface and angle was observed (F = 10.432, p = .001, partial η² =0.367). Post hoc analysis revealed that during TRX push-ups, UT at − 15° and − 30° was significantly greater than at 0°, and at − 30° was significantly greater than at + 15° (F = 6.043, p < .001, partial η² =0.251). On a stable surface, UT activation differed significantly across angles (F = 23.716, p < .001, partial η² = 0.569). Post hoc comparisons indicated significant differences between all angles (p < .05), with activation highest at − 30°, followed by − 15°, 0°, + 15°, and lowest at + 30°. Moreover, UT activation was significantly greater during TRX push-ups compared to stable-surface push-ups at + 30° (p < .001, d = -1.728, 95% CI [-2.437, -1.001]), + 15° (p < .001, d = -1.692, 95% CI [-2.386, -0.980]), and 0° (p = .031, d = -1.370, 95% CI [-1.993, -0.728]).
For SA muscle activation, a significant interaction between surface and angle was observed (F = 2.913, p = .027, partial η² =0.139). Within-condition analyses revealed that SA activation significantly differed across angles in both TRX push-ups (F = 109.850, p < .001, partial η² = 0.859) and stable-surface push-ups (F = 79.535, p < .001, partial η² = 0.815). Post hoc comparisons showed that SA activation was highest at − 30°, significantly greater than at − 15°, 0°, + 15°, and + 30°. No significant differences between the different surfaces.
Discussion
Previous studies have quantified intensity and load using TRX straps (with a force meter) and the ground reaction force; however, clearly discriminating the loads borne by the upper and lower limbs, respectively, was difficult [22, 23]. To address this limitation, the present study examined how upper-body muscle activation responds to variations in body angle during TRX and stable-surface push-ups. The main findings of this study showed distinct angle-dependent activation patterns: PM activation was greatest at + 30°, + 15°, and 0°, whereas AD, TRI, UT, and SA activation progressively increased in decline positions, peaking at − 30°. These findings support the first two hypotheses regarding the preferential activation of PM in incline positions and increased recruitment of AD, TRI, UT, and SA in decline positions. The third hypothesis was only partially supported, as TRX consistently elevated PM activation but did not uniformly increase activation in the other muscles across all angles. These results indicate that angle manipulation exerts a stronger influence on neuromuscular demand than instability alone. Figure 2 provides a visual depiction of these angle-dependent activation patterns across the push-up cycle.
As the TRX push-up angle decreases, significant changes in upper limb muscle activation patterns are observed. Gulmez et al. [23] quantified that as the body angle approaches horizontal (0°), the proportion of body weight supported by the arms increases substantially. Studies have demonstrated that lower TRX push-up angles shift a greater proportion of body mass load onto the upper limbs, thereby increasing the recruitment of these muscle groups [17, 22]. This corresponds with our findings of markedly higher AD, TRI, UT, and SA activation at the − 30° decline angle. In contrast, the activation pattern of the PM exhibits a different trend. At + 30°, + 15°, and 0°, its activation remains relatively high; however, as the angle decreases to − 15° and − 30°, activation declines. This change may be attributed to increased shoulder flexion with decreasing TRX push-up angles, which alters the primary muscle recruitment pattern and reduces the contribution of the PM. In addition, the increased glenohumeral joint loading under declination conditions may impose a greater posteriorly directed moment on the scapula, thereby elevating the stabilizing demand on the serratus anterior [13]. These findings indicate that variations in suspension push-up angles affect both load distribution and the relative contributions of different muscle groups.
In previous studies, the feet have typically been positioned beneath the anchor point or adjusted relative to the anchor to reach the target angle [6, 16, 22, 23]. However, this study standardized the TRX anchor point and positioned the arms and straps directly beneath it. (Fig. 1). This design reduced potential confounding factors, such as shifting body weight or variations in relative positioning, ensuring that angle variation was the primary factor influencing muscle activation. This design also allowed for a greater range of angle variations in TRX exercises, making it more advantageous for training applications.
Although previous studies have reported that TRX instability enhances muscle activation [11, 24, 25]. Snarr and Esco [11] observed greater activation of the PM, AD, and TRI during TRX push-ups. In the present study, only the PM consistently showed higher activation under TRX conditions across angles, whereas no significant surface-related differences were observed for most other muscles at − 15° and − 30°. Borreani et al. [6] demonstrated that at the most demanding position, with the hands positioned approximately 10 cm from the floor, stable push-ups elicited similar PM but greater AD activation, whereas TRX push-ups resulted in greater UT and TRI activation at more inclined positions. Together, these findings indicate that the effect of instability varies with body position and task demand.
The present study demonstrates that push-up angle plays a more dominant role in modulating upper-body muscle activation than TRX instability, with distinct recruitment patterns across different angles (Table 2). At higher angles (+ 30°, + 15°, 0°), PM activation remained high level, while activation of AD, TRI, SA, and UT was relatively stable. In contrast, at lower angles (-15°, -30°), AD and SA activation increased significantly, while TRI activation showed an unexpected pattern, remaining mid-level across all TRX push-ups but increasing to high level only at -30° on the stable surface. These results suggest that the combined effects of body positioning, force distribution, and joint stabilization demands contribute to these activation differences. Analysis of %MVIC variations (Table 3) further supports these findings, revealing that when the push-up angle was less than 0°, activation of AD, TRI, UT, and SA gradually increased, regardless of whether push-ups were performed with TRX or on the stable surface. Notably, PM activation at -30° was 24% and 33% lower compared to 0° in TRX and stable surface push-ups, respectively, confirming that increased shoulder flexion shifts mechanical demands away from PM. Conversely, UT and SA activation were 1.4 and 1.6 times higher at -30° than at 0°, highlighting their critical role in shoulder stabilization at lower angles.
Table 2.
Level of muscle activity during push-ups with TRX and on a stable surface
| Methods | Angles | PM | AD | TRI | UT | SA |
|---|---|---|---|---|---|---|
|
TRX Push-up |
+ 30° | H | H | MID | L | L |
| + 15° | H | H | MID | L | MID | |
| 0° | H | H | MID | L | MID | |
| -15° | H | VH | MID | L | VH | |
| -30° | H | VH | MID | L | VH | |
|
Stable Push-up |
+ 30° | MID | H | MID | L | MID |
| + 15° | MID | H | MID | L | MID | |
| 0° | MID | H | MID | L | MID | |
| -15° | MID | H | MID | L | VH | |
| -30° | MID | H | H | MID | VH |
Angles indicate shoulder-to-ankle inclination (+ 30°, + 15°, 0°, − 15°, − 30°)
Abbreviations: PM Pectoralis major, AD Anterior deltoid, TRI Triceps brachii, UT Upper trapezius, SA Serratus anterior, %MVIC Percentage of maximal voluntary isometric contraction, Muscle activity levels: L: low (0–20%MVIC), MID Mid-level (21–40%MVIC), H High-level (41–60%MVIC), VH Very high-level (≥ 61%MVIC)
Table 3.
Percentage changes in muscle activity in TRX and stable-surface push-ups between the different angles
| Angles | PM | AD | TRI | UT | SA | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| TRX | Stable | TRX | Stable | TRX | Stable | TRX | Stable | TRX | Stable | |
| 0°-+30° | -8 | -1 | -29 | -16 | 2 | -15 | 15 | -50 | -53 | -34 |
| 0°-+15° | -4 | -4 | -20 | -10 | -5 | -7 | 9 | -31 | -26 | -10 |
| 0°--15° | -5 | -12 | 9 | 13 | 6 | 9 | 27 | 78 | 23 | 30 |
| 0°--30° | -24 | -33 | 11 | 21 | 12 | 20 | 44 | 151 | 48 | 61 |
Note: Values represent percentage changes in muscle activity relative to 0°
Abbreviations: PM Pectoralis major, AD Anterior deltoid, TRI Triceps brachii, UT Upper trapezius, SA Serratus anterior
These variations in mechanical demands appear to drive the observed differences in muscle activation. At lower angles (-15°, -30°), greater shoulder flexion likely increases reliance on AD and SA for stabilization, reducing the necessity for TRI to contribute significantly to movement execution, particularly in TRX push-ups where instability further increases postural control demands. The fixed TRX anchor point may have further influenced this redistribution, limiting TRI engagement by promoting compensatory activation of other stabilizers. In contrast, on the stable surface at -30°, the absence of instability may have necessitated greater elbow extension force, leading to increased TRI activation. These findings suggest that TRX instability does not inherently enhance activation across all muscle groups but instead redistributes neuromuscular effort depending on movement constraints.
While TRX push-ups increased PM activation across all angles, they did not significantly alter TRI, SA, or UT activation compared to stable push-ups. Higher-angle TRX push-ups (+ 30°, + 15°, 0°) primarily target PM, whereas lower angles (-15°, -30°) shift activation toward AD and SA. Given that no single push-up variation maximizes activation across all muscle groups, training programs should adjust angles to target specific muscles rather than relying solely on TRX instability. Future research should examine how joint loading strategies, muscle coordination, and external support conditions interact to optimize neuromuscular control in suspension training.
The present study has several strengths and inherent methodological constraints. A primary strength is the examination of upper-body muscle activation across a wide range of body angles under both TRX and stable-surface conditions using a standardized EMG protocol. Regarding methodological constraints, muscle activation was characterized across the entire push-up cycle to reflect overall neuromuscular demand, consistent with prior TRX and push-up EMG studies. This analytical approach does not allow for differentiation between concentric and eccentric phases of movement; therefore, the present findings should be interpreted in terms of activation magnitude rather than detailed temporal characteristics of muscle activity.
Conclusions
The present findings indicate that body angle is the primary mechanical factor governing upper-body muscle activation during suspension push-ups, whereas the effect of suspension-induced instability is muscle-specific. Across both TRX and stable-surface conditions, higher angles (+ 30°, + 15°, and 0°) preferentially increased activation of the PM, whereas lower angles (− 15° and − 30°) progressively increased activation of the AD, TRI, UT, and SA. These angle-dependent activation patterns provide a quantitative basis for selecting push-up configurations to emphasize specific upper-limb muscle groups in trained individuals. TRX selectively augmented PM activation across angles without uniformly increasing activation of AD, TRI, UT, or SA. In contrast, declining body positions were the primary determinant for elevating activation of the shoulder and scapular stabilizers regardless of surface condition. Accordingly, manipulation of push-up angle appears to be a more effective strategy than suspension instability alone for modulating neuromuscular demand during push-up variations in physically trained young adults.
Acknowledgements
We thank all participants from the Department of Physical Education at National Tsing Hua University for their time and effort in this study, as well as the research team of the Exercise Physiology Laboratory at Chinese Culture University for their assistance with data collection and support.
Abbreviations
- AD
Anterior Deltoid
- ANOVA
Analysis of Variance
- EMG
Electromyography
- H
High-Level
- L
Low-Level
- MID
Mid-Level
- MVIC
Maximum Voluntary Isometric Contraction
- PM
Pectoralis Major
- SA
Serratus Anterior
- SD
Standard Deviation
- SENIAM
Surface Electromyography for the Non-Invasive Assessment of Muscles
- TRI
Triceps Brachii
- TRX
Total Resistance Exercises
- UT
Upper Trapezius
- VH
Very High-Level
Authors’ contributions
Y.-C. Lin designed the study methodology, supervised data collection, analyzed and interpreted the data, drafted sections of the manuscript, and critically revised and finalized the manuscript. T.-L. Chiang conceptualized the study, supervised experimental implementation, analyzed and interpreted the data, drafted the initial manuscript, and critically revised and finalized the manuscript. S.-H. Chan collected data, performed data processing and visualization, and critically revised the manuscript. K.-F. Lin contributed to study design, assisted with data analysis, and critically revised the manuscript. C.-H. Hsu designed the study, interpreted the data, critically revised the manuscript, and provided expertise in exercise physiology and resistance training research. All authors have read and approved the final version of the manuscript and agree on the order of authorship.
Funding
The author(s) reported there is no funding associated with the work featured in this article.
Data availability
The datasets analyzed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
The study protocol was developed in accordance with the guidelines proposed in the Declaration of Helsinki and was approved by National Tsing Hua University Institutional Review Board (No. 10711HS080). All participants gave informed consent before their inclusion in the study.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Yu-Chin Lin and Tsung-Lin Chiang contributed equally as co-first authors.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets analyzed during the current study are available from the corresponding author on reasonable request.