Effects of Supine Scapular Punch Exercise Combined with the Maximum Abdominal Contraction Maneuver on Abdominal and Shoulder Stabilizer Muscle Activities and Upper Trapezius Muscle Tone

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Abstract

Introduction

The shoulder joint possesses anatomical and functional characteristics that prioritize mobility over stability, making it susceptible to external stresses when exposed to faulty posture and inefficient muscle activation during daily and sporting activities [1]. Repetitive overuse and trauma frequently result in instability or subluxation, which, when persistent, leads to compensatory activation of the cervical and shoulder girdle musculature [2]. This compensatory pattern is often characterized by excessive upper trapezius (UT) activity, accompanied by reduced activation of the serratus anterior (SA) and lower trapezius (LT), thereby creating functional imbalances [3]. The SA, a key muscle for scapular motion and shoulder stability, plays a critical role in controlling scapular kinematics. Insufficient SA activity has been consistently reported in individuals with shoulder impingement, instability, and rotator cuff pathologies, leading to impaired shoulder function [4,5]. Moreover, SA weakness contributes to compensatory UT overactivation, reinforcing the vicious cycle of muscle imbalance and cervicobrachial pain [2]. Given these maladaptive patterns, exercise interventions targeting selective SA activation have been emphasized. Such activation facilitates scapular upward rotation and posterior tilt, reduces the risk of subacromial impingement, and helps maintain appropriate joint spacing [6].

The push-up plus (PUP) exercise is a representative closed kinetic chain (CKC) movement that facilitates selective activation of the serratus anterior (SA) while concurrently reducing upper trapezius (UT) activity. Because of these properties, the PUP has been widely employed in rehabilitation and preventive programs for shoulder dysfunction [7]. In particular, the protraction phase of the PUP promotes SA activation with minimal compensatory UT involvement, thereby contributing to improved shoulder kinematics and function [8]. However, the requirement for weight-bearing limits its applicability in certain populations, and several studies have reported persistent UT overactivity during PUP performance, suggesting that the exercise may not fully achieve selective SA strengthening [9,10]. Recently, the supine scapular punch (SSP) has been introduced as an alternative exercise. When performed in an open kinetic chain (OKC) and under non-weight-bearing conditions, the SSP has been reported to elicit greater SA activation while minimizing compensatory activity of the UT and pectoralis major compared with the PUP [11-13]. These findings indicate that SSP may represent a feasible and effective option, particularly in the early stages of rehabilitation or in experimental settings where control of confounding factors is required. Furthermore, combining SSP with the maximum abdominal contraction maneuve (MACM) has been suggested as a strategy to maximize SA activation while further reducing UT involvement, thereby providing a potential framework for more targeted interventions.

Therefore, this study aimed to investigate the effects of combining MACM with SSP on the activation of the abdominal and shoulder stabilizing muscles, as well as the acute modulation of UT muscle tone in healthy adult men. The findings aim to provide scientific evidence and clinical implications for an effective method to selectively activate the SA while reducing UT tension, thereby contributing to improved shoulder stabilization and preventing injuries.

Methods

Participants

This study referred to previous research [14] and utilized G*Power 3.1.9.7 to calculate the minimum sample size as 11 participants, based on an effect size of 0.83, statistical power of 0.80, and significance level of 0.05. To prevent attrition and maintain statistical power, 25 participants were initially recruited. During the study period, some participants withdrew due to personal reasons or health issues, resulting in a final sample of 21 individuals included in the analysis. Participants were healthy adult men aged between 20 and 40 years, without prior experience of shoulder stabilization exercises within the last six months, and were capable of performing the prescribed exercises without difficulty. The exclusion criteria were as follows: neurological abnormalities, cardiovascular diseases, spinal or pelvic pain and functional impairments, shoulder dysfunction or subluxation, injuries or surgeries to the neck, shoulder, or lumbar regions within the past six months, rib fractures, or other health conditions that could impede exercise performance. This study adhered to ethical standards, including voluntary participation, explanation of the research objectives and methods, and protection of personal information. The general characteristics of the participants are shown in <Table 1>.

Table 1.

General characteristics of the subjects.

Experimental Design and Procedures

This study was designed based on the hypothesis that the SSP+MACM condition would increase serratus anterior (SA) activation and decrease upper trapezius (UT) muscle tone compared to the SSP-only condition. To enhance exercise accuracy, a 10-minute practice session was conducted, followed by a 10-minute rest period before measurements. Prior to testing, surface electromyography (sEMG) electrodes were applied to measure maximum voluntary isometric contraction (MVIC), and a MyotonPRO device was used to assess baseline UT muscle tone. Participants performed the SSP and SSP+MACM exercises in a randomized order while EMG data were recorded. The order of conditions was assigned by random numbering; odd-numbered participants performed SSP followed by SSP+MACM, whereas even-numbered participants performed the reverse sequence. Exercises were performed verbally cued at 60 beats/min using a metronome, with three repetitions, each held for 5 s. Rest intervals of 5 s between repetitions and 3 min between conditions were provided to minimize muscle fatigue. The overall experimental procedure is illustrated in <Figure 1>.

Figure 1.

Research design.

Measurement Instruments and Procedures

Surface Electromyography

Muscle activity was recorded using the Delsys Trigno Wireless System (Delsys Inc., USA). Trigno Avanti sensors (AgAgCl electrodes, 11×1 mm diameter, 10 mm inter-electrode distance) collected data at 1,000 Hz. Noise was filtered with a bandpass filter of 20-450 Hz, and signals were processed using root mean square (RMS) analysis over 125 ms epochs. Prior to electrode placement, the skin was shaved and disinfected with alcohol to maintain skin impedance below 5 kΩ. Electrode placement followed the SENIAM guidelines <Figure 2>. Muscle activity was recorded for 5 s during exercise performance, with the middle 3-second window used for analysis and expressed as %MVIC.

Figure 2.

Surface electromyography sensor locations.

Maximum Voluntary Isometric Contraction

To normalize the EMG data, MVIC measurements were performed for the dominant side muscles of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), serratus anterior (SA), and upper trapezius (UT). Each muscle was tested three times for 5 s, and RMS values were calculated from the middle 3 s. A 3-minute rest period was provided between trials. Manual muscle testing was performed as follows [15].

• RA: Hook-lying position, arms crossed in an X over the chest, maximal resistance during trunk flexion

• EO: Hook-lying, maximal resistance during trunk flexion toward the contralateral knee

• IO: Hook-lying, maximal resistance during trunk flexion toward the ipsilateral knee

• SA: Supine position, shoulder flexed at 90°, maximal resistance during protraction

• UT: Seated position, dominant side lateral neck flexion with contralateral rotation, maximal resistance during shoulder elevation

Muscle Tone Measurement

UT muscle tone was assessed with the MyotonPRO (Myoton AS, Estonia). The probe was vertically applied to the spinous process of C7 and the midpoint of the acromion, delivering a 0.58 N mechanical impulse for 15 ms to elicit muscle oscillations. The participants were seated with their backs supported in a relaxed position. Measurements were taken three times and averaged. The measurement postures and sites are illustrated in <Figure 3>.

Figure 3.

MyotonPRO probe location (a. Measurement location, b. MyotonPRO placement)

Exercise Intervention

Supine Scapular Punch (SSP)

In the hook-lying position with hips flexed at 45° and knees at 90°, a green Thera-band (medium resistance) was secured at the occiput. The band length was standardized to the resting length and elongated by approximately 20-30% during setup, which corresponds to a light-to-moderate resistance (≈2.3 kg at 100% elongation, based on manufacturer’s specifications). Participants grasped both ends of the band and positioned their hands vertically above the acromioclavicular joint [16]. Following a verbal instruction to “push the hands forward as far as possible”, participants protracted the scapulae against the standardized elastic resistance, maintained the contraction for 5 s, and then returned to the starting position <Figure 4> .

Figure 4.

SSP (a. Starting position, b. Exercising position).

SSP Combined with Maximum Abdominal Contraction Maneuver (SSP + MACM)

Using the same position and Thera-band setup as SSP, a 22 cm diameter Redondo ball was placed between the knees. Upon verbal cue (“Exhale maximally while pushing your hands forward and squeezing the ball tightly between your knees”), participants performed maximal expiration with co-contraction of the abdominal and hip adductor muscles, protracting the scapulae, and holding for 5 s before returning [17] <Figure 5>.

Figure 5.

SSP + MACM (a. Starting position, b. Exercising position).

Data Analysis

Statistical analyses were conducted using SPSS for Windows (version 30.0). Descriptive statistics, including means (M) and standard deviations (SD), were calculated for all variables. Normality was assessed using the Shapiro-Wilk test. For comparisons of muscle activation (%MVIC) between conditions, paired t-tests were used for normally distributed data (p > 0.05), and Wilcoxon signed-rank tests were applied when normality was violated (p < 0.05). Upper trapezius muscle tone differences among baseline, post-SSP, and post-SSP+MACM were analyzed using one-way repeated- measures analysis of variance for normal data and the Friedman test for non-normal data. The significant effects were further examined using Bonferroni-corrected post hoc analyses. Effect sizes were reported as Cohen’s d for t-tests, rank effect size r for Wilcoxon tests, and η² (eta-squared) for ANOVA. Statistical significance was set at p < 0.05.

Results

This study analyzed 21 healthy adult men to compare the effects of SSP combined with maximum abdominal contraction maneuve on abdominal and shoulder muscle activation and UT muscle tone.

RA, IO and EO Muscle Activation

Abdominal muscle activation data for the RA and IO satisfied the normality assumption (p > 0.05) and were analyzed using paired t-tests. EO violated the normality assumption (p < 0.05) and was analyzed using the Wilcoxon signed-rank test. As shown in <Table 2>, muscle activation of the RA (t = -3.509, p = 0.002), IO (t = -5.206, p = 0.004), and EO (z = -4.015, p < 0.001) were significantly greater in the SSP+MACM condition than in the SSP alone condition. The effect sizes indicated moderate to large effects: RA (d = 0.77), IO (d = 1.14), and EO (r = 0.88).

Table 2.

Comparison of the muscle activities of RA, EO, IO.

SA and UT Muscle Activation

SA activation met normality (p > 0.05) and was analyzed using paired t-tests, whereas UT activation did not (p < 0.05) and was analyzed using Wilcoxon signed-rank test. <Table 3> indicates that SA activation was significantly higher under SSP+MACM than under SSP (t = -3.160, p = 0.005; d = 0.69), whereas UT activation was significantly lower in SSP+MACM (z = -4.015, p < 0.001; r = 0.88).

Table 3.

Comparison of the muscle activities of SA, UT.

UT Muscle Tone

UT muscle tone satisfied normality assumptions (p > 0.05) and was analyzed using a one-way repeated measures ANOVA. As presented in <Table 4>, significant differences were observed among the three conditions (F = 24.98, p < 0.001), with a moderate effect size (η = 0.055). Post hoc analysis revealed that the UT tone at baseline and post-SSP was significantly higher than that at post-SSP+MACM.

Table 4.

Comparison of the muscle tone of UT.

Discussion

This study compared the effects of SSP and SSP+MACM on abdominal and shoulder stabilization muscle activation and UT muscle tone in healthy adult men. The results demonstrated that the combined SSP+MACM condition elicited significantly greater activation in the RA, EO, IO, and SA, while decreasing UT activation and muscle tone, with immediate reductions observed after exercise. The findings are discussed in the following section.

The maximum abdominal contraction maneuve (MACM) employed in this study integrates key components: abdominal drawing-in maneuver (ADIM), maximal expiration (ME), and isometric hip adduction (HA). This combination effectively induces co-contraction of both deep (TrA and IO) and superficial (RA and EO) abdominal muscles, enhancing core stability. The significant increase in RA, EO, and IO activation under SSP+MACM suggests that this combination effectively recruits both deep (TrA and IO) and superficial (RA and EO) abdominal muscles. This partially contrasts with prior findings indicating that ADIM alone more effectively increases TrA and IO thickness and activity [17]. Hence, SSP+MACM appears to compensate limitations of ADIM in superficial abdominal muscle activation. HA contributes to the co-contraction of the pelvic floor and abdominal muscles, increasing intra-abdominal pressure and enhancing core dynamic stability [11-13]. Reports of the HA facilitating trunk muscle activation [18-20] are consistent with our findings. Collectively, SSP+MACM maximized the activation of both superficial and deep muscles, enhancing trunk stabilization beyond what ADIM alone could achieve.

SA activation was significantly enhanced, whereas UT activation decreased with SSP+MACM. This aligns with previous evidence that strengthening SA activity can reduce compensatory UT overactivation, a mechanism frequently associated with scapular dyskinesis and impingement [2,4,6,9,10]. Umehara et al. [19] noted that SA fatigue negatively impacts scapular kinematics and shoulder stability. The UT/SA activation ratio, known to predict rehabilitation outcomes [7], was improved in the present study, empirically supporting the relevance of MACM in selective SA recruitment. In this study, UT muscle tone decreased significantly immediately after SSP+MACM. However, this effect was limited to acute observations, and no direct measures of neuromuscular control were assessed. Elevated baseline UT tone is consistent with known compensatory overactivity when the SA is weak [2]. These findings suggest that SSP+MACM can acutely modulate muscle tone. Because the present study involved a single-session design, conclusions regarding long-term benefits, such as sustained reductions in UT tone or improvements in overall shoulder stability, cannot be drawn. Future longitudinal studies are warranted to determine whether repeated SSP+MACM practice produces persistent adaptations in neuromuscular coordination and shoulder function.

Previous studies have highlighted the limitations of SSP in adequately activating SA [11-13]. By incorporating MACM, this study demonstrated enhanced abdominal co-contraction via ME and HA, which, in turn, facilitated selective SA activation and reduced UT tone [17,20]. These findings provide preliminary evidence for the acute utility of SSP+MACM in addressing muscle imbalance; however, the interpretation should be limited to immediate effects measured by EMG and muscle tone rather than long-term functional outcomes.

Therefore, SSP+MACM may be considered a time-efficient exercise option for healthy young adult men, particularly for short-term interventions targeting reductions in shoulder and neck muscle tension and selective SA activation. However, this study assessed only acute responses following maximal contractions, and does not provide evidence of long-term effects. Future longitudinal studies are needed to determine whether repeated SSP+MACM practice can produce sustained improvements in shoulder stability, UT muscle tone, and core muscle co-activation. Moreover, while the present study focused on UT, SA, and core muscles, incorporating additional rotator cuff muscles and a broader range of shoulder movements could further clarify the role of core activation in foundational shoulder rehabilitation. Investigations in clinical populations, including individuals with shoulder pain or functional deficits, as well as older adults and females, would provide critical insights into the practical applicability of SSP+MACM as a rehabilitation program.

Conclusion

This study compared the effects of SSP and SSP+MACM on abdominal and shoulder stabilizer muscle activation and UT muscle tone in healthy adult men. The results revealed that SSP+MACM significantly increased the activation of the RA, EO, IO, and SA muscles while decreasing UT activation and muscle tone, thereby addressing the limitations of SSP alone in selectively activating the SA and suppressing UT compensation. These findings suggest that SSP+MACM is a practical exercise strategy that can simultaneously improve shoulder stability and reduce muscle tone within a short period. Further research is warranted to verify its applicability and long-term benefits in diverse populations and settings.

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