Immediate effects of myofascial release to the pectoral fascia on posture, range of motion, and muscle excitation: a crossover randomized clinical trial

ABSTRACT

Context

Forward shoulder posture (FSP) is a risk factor for shoulder pathology. Manual therapists often use myofascial release (MFR) to elongate restricted pectoral fascia to reduce FSP and improve shoulder function; however, the effects of this treatment approach remain anecdotal.

Objective

Determine the acute effects of 4-min of MFR, compared to a soft-touch control (CON), to the pectoral fascia on: 1) FSP, 2) shoulder horizontal abduction ROM (HA-ROM), and 3) muscle excitation of the trapezius (upper, middle, lower [UT, MT, LT]) and pectoralis major (PEC).

Methods

Fifty-nine right-handed participants (27 ± 9 years, 30 female) with FSP, but otherwise asymptomatic shoulders participated in a randomized crossover clinical trial by attending two experimental sessions: one MFR and one CON treatment, each administered by a Registered Massage Therapist. FSP, HA-ROM, and muscle excitation during a reaching task, were measured before and after each treatment.

Results

There was a significant interaction between treatment and time for FSP (p = .018, η_p = .093) with FSP decreasing from PRE MFR (128 ± 19 mm) to POST MFR (123 ± 19 mm; p < .001, η_p = .420) and PRE CON (126 ± 19 mm) to POST CON (124 ± 18 mm; p < .001, η_p = .191) interventions. There were no significant differences in HA-ROM or muscle excitation.

Conclusion

Four minutes of MFR or CON to the pectoral fascia acutely reduces FSP.

Pain originating from the shoulder is common, affecting nearly one quarter of adults at any given time [1], and 67% of individuals will experience shoulder pain in their lifetime [2]. Shoulder pain reduces health-related quality of life and increases symptoms of depression [1]. Chronic shoulder pain bears a substantial economic burden, with direct costs equaling ~$7 billion in the United States annually [3]. Efforts to determine the cause of shoulder pathologies have identified a multifactorial etiology, including anatomical structure, age, overuse, tissue compression, postural deviations, and muscular imbalances [4,5]. While the impact of postural deviations on the development of shoulder pathologies is contentious [6–8], available evidence suggests that altered scapular position and forward shoulder posture (FSP) predisposes individuals to shoulder injury [9–14]. Thus, correcting FSP may be important for the prevention of shoulder pathologies.

FSP is found in up to 73% of individuals and is characterized by abduction of the scapula that causes anterior translation of the shoulder from the midline of the body [15]. Clinical indications of FSP include shortened scapular protractors (e.g. pectoralis minor) [9,16], adaptive lengthening of the scapular retractors (e.g. trapezius, rhomboids), greater pectoralis major (PEC) and upper trapezius (UT) muscle excitation, and reduced middle trapezius (MT) excitation [13]. These changes are associated with greater anterior tilt and internal/upward rotation of the scapula [9], thus altering scapulothoracic motion and increasing the risk of shoulder pathology [9–14].

To reduce FSP, therapists aim to lengthen the shortened scapular protractors and their connective tissues, inhibit UT and pectoral excitation, and facilitate MT and lower trapezius (LT) excitation to balance agonist-antagonist excitation and restore neutral posture [8]. For example, UT massage reduces UT excitation [17,18], while stretching and manual therapy to the pectoral muscles increases LT excitation and strength [19,20]. Various massage techniques are proposed to inhibit central motor excitability by activating Golgi tendon organs, muscle spindles, and afferent pathways [21]. Massage to the neck decreased trapezius excitation and α-motoneuron excitability (H reflex) in the brachioradialis, a muscle distal to the treatment site [18]. The latter finding demonstrates that massage can alter muscle excitation in areas removed from the treatment site.

Various therapeutic approaches addressing the length and extensibility of the shortened scapular protractors tissue have demonstrated improvements in FSP [22–24], range of motion (ROM) [24], and pectoralis minor length [24,25]. One such treatment is myofascial release (MFR); a group of widely practiced techniques where mechanical pressure is applied to fascia until elongation and softening occurs [26]. MFR increases flexibility, reduces muscle soreness, improves local blood flow, and aides in post-exercise recovery, including blood lactate removal, and power, speed and strength [21,27–29]. For example, one study demonstrated that 3 min of MFR induced changes in fascial fibrosis and increased tissue mobility, as determined by experienced clinical judgment [30]. Self and instrument-assisted MFR techniques to the pectoral region improve ROM, pectoralis minor length, and FSP [24,31], while a single session combining self-MFR and stretching of infraspinatus acutely improved the ratio of agonist (infraspinatus) to antagonist (PEC and latissimus dorsi) muscle excitation [32]. However, it is not known if a therapist-administered MFR alters FSP, horizontal abduction range of motion (HA-ROM), or muscle excitation of the scapular protractors and retractors.

The purpose of this study was to determine the acute effects of 4-min of MFR, compared to a soft-touch control (CON; no pressure), to the pectoral fascia in individuals with FSP on: 1) FSP, 2) HA-ROM, and 3) muscle excitation of the trapezius (UT, MT, LT) and PEC. As self-MFR decreases FSP [24], and other pectoral lengthening techniques increase shoulder range of motion [23–25], we hypothesized that MFR would: 1) decrease FSP; and 2) increase HA-ROM, compared to CON. Additionally, given that plantarflexor lengthening promotes autoinhibition [33], and that self-MFR and stretching of the infraspinatus improves agonist to antagonist excitation [32], we hypothesized that MFR would 3) increase MT and LT excitation and decrease UT and PEC excitation, compared to CON.

Methods

Experimental design

A within-subjects, repeated measures single-blinded crossover design study was conducted. Participants attended two 1-hexperimental sessions in a laboratory separated by at least 48 h. Session order was randomized and counterbalanced (Research Randomizer v4.0, Social Psychology Network, USA). All experimental procedures were approved by the University of Manitoba’s Education/Nursing Research Ethics Board and were conducted in accordance with the Declaration of Helsinki [34]. Participants provided informed consent upon receiving written and verbal details of the experimental procedures. This study was registered with the U.S. National Library of Medicine ClinicalTrials.gov database [NCT04944745].

FSP and HA-ROM were measured, followed by muscle excitation during a reaching task immediately before (PRE) and after (POST) MFR and CON. All measurements were taken on the right side in order to keep the experimental set-up consistent. The same researcher performed all measurements for a given participant, and all treatments were performed by the same registered massage therapist (RMT). An a priori power analysis using G*Power ($\mathit{\alpha }=.05,$ β = .8) and a moderate effect size yielded a required sample size of 60 participants.

Participants

A convenience sample of 66 individuals was recruited from the University of Manitoba and surrounding community between September 2020 and November 2021. Eligibility criteria included: between 18–60 years old; right-hand dominant; had not experienced recent (<6 months) pain, injury, or orthopedic disorders to the shoulders, upper back, or neck (e.g. rotator cuff tear); no previously diagnosed neurological or musculoskeletal disorder (e.g. muscular dystrophy). Eligible participants were required to have at a minimum of 1 cm of anterior deviation of the acromion process from the lateral plum line [22]. Sixty participants (n = 60, 27 ± 9 years old, 30 female) were included (Figure 1). Participants were asked to refrain from physical activity of the upper body for 48-h prior to each session.

Figure 1.

CONSORT diagram.

a) 66 individuals were recruited, 6 were excluded due to not meeting inclusion criteria. b) 60 participants were randomized to receive myofascial release (MFR) or soft-touch control (CON) for their first visit. c) 31 of the 60 received the MFR intervention at their first visit and 29 received CON. d) 59 of the 60 participants attended a second session where they received the second intervention: 28 of the 29 participants who initially received CON completed their second session by receiving MFR and all of the participants who initially received MFR completed their second session by receiving CON. e) Electromyographic data errors occurred for 1 (UT and LT) and 2 (MT and PEC) participants during the maximal voluntary contraction and were thus discarded.

Forward Shoulder Posture (FSP) measurement

FSP was measured using the double-square method, where participants stood in a relaxed position against a wall (Supplemental Figure S1). A modified combination square (Swanson Tool Company 12-in Combo Square, Frankfurt, IL, United States) was used to measure the distance from the wall to their anterior acromion [35]. The mean of three separate measurements was used for analysis. Between each measurement, participants took a step forward, shook their arms and returned to the wall.

Horizontal Abduction Range of Motion (HA-ROM) measurement

Pectoralis major length was measured indirectly via HA-ROM (Supplemental Figure S2). Participants laid supine on a plinth set at a standardized height and horizontally abducted their right shoulder with their elbow flexed at 90°, mimicking a pectoral stretch. A meter stick was used to measure the distance from the participant’s olecranon to the ground. The mean of three separate measurements was used for analysis. Between each measurement, participants returned their arm to the starting position.

Muscle excitation: surface electromyography

Bipolar surface electromyography (sEMG) was collected from the UT, MT, LT, and PEC horizontal fibers during a reaching task (Figure 2). Electrode locations were landmarked, and the skin was prepared by shaving, buffing with an abrasive paste (Nuprep, Weaver and Company, Aurora, CO, USA), and cleaning with a 70% isopropyl alcohol swab. Bipolar electrodes (CDE-C, OT Bioelettronica, Torino, Italy) were applied running approximately parallel to the direction of the muscle fibers. A grounding electrode was placed on the participant’s C7 spinous process, and a grounding strap around their left wrist.

Figure 2.

sEMG bipolar electrode setup for pectoralis major, upper, middle, and lower trapezius in reaching task.

Four pairs of bipolar electrodes were applied parallel to the muscle fibres of each participant’s right pectoralis major, upper trapezius, middle trapezius, and lower trapezius, according to SENIAM recommendations. Pectoralis major a) the bipolar electrodes were applied to the sternal head of the pectoralis major between the right edge of the sternum and costal cartilages of ribs 1–6 and the greater tubercle (GT) of the right humerus. Upper trapezius b) the electrodes were applied midway between the right acromion (AC) and C7, where a grounding electrode was placed. Middle Trapezius c) the electrodes were placed half of the distance from the medial border of the scapula to T3, in the direction of T5 to the acromion. Lower Trapezius d) the electrodes were placed 2/3 of the distance from the superior angle (SA) of the scapula to T8. A ground electrode was placed on C7 (e) and around the participant’s left wrist (f)

Maximal Voluntary Contractions (MVCs)

Participants completed three maximal voluntary contractions (MVCs) for the trapezius then PEC in the same order during each visit to use as a reference contraction. Participants completed a familiarization repetition in the first experimental session.

For the trapezius MVC, participants laid prone on a plinth with their shoulder abducted to 120° and pulled up on an inextensible handle toward the ceiling. This position elicits the greatest excitation for all three regions of the trapezius compared to individual test positions for the UT and MT, and was therefore used for the trapezius MVC [36]. For the PEC MVC, participants laid supine on the plinth with their shoulder abducted at 90°, elbow extended and palm facing the ceiling and attempted to horizontally adduct the handle. Participants were counted down from 5-s, directed to contract as hard as possible for 5-s while being verbally encouraged, and given 2-min of rest between the three repetitions.

Reaching task

Participants sat at a height adjustable workstation with a touchscreen monitor (NEC EX241UN-PT-H, Sharp NEC Display Solutions Ltd., USA). The table height was adjusted so that their elbows were flexed ~ 80° with their hands flat on the table. The monitor was set at a distance from the participant so their elbow was flexed ~ 20° when they reached to touch the screen. This reaching task was chosen to evaluate the effect of MFR on a common, functional task with practical implications to activities of daily living and workplace environments that would include computer usage and reaching for small items.

A custom-written program was designed using E-prime (v3.0 Psychology Software Tools Inc., Pittsburgh, PA, United States), where participants reached from a ‘home’ button (a consistent position on the tabletop) to a target on the monitor. One of five black squares appeared in the center or corners of the monitor. Target presentation was pseudorandomized; each target appeared 12 times for a total of 60 targets/testing block, lasting ~ 4-min.

Participants completed a short familiarization block in their first session. The microswitch (Submini Snap Action Switch, Philmore Manufacturing, Rockford, USA) home button embedded on the table was pressed and held, triggering a fixation screen for a short, random fore period (2000 to 2500 ms). One of five targets appeared, prompting participants to release the home button, reach to, and press the center of the target ‘as quickly and accurately as possible’ using their right arm. Once pressed, the participant was prompted to return to the home position. E-prime recorded participant reaction and movement times via the microswitch and touchscreen. Given that muscle excitation patterns would likely differ between target locations, only movements to the top-right target were analyzed. Additional target locations were included to prevent repetitive and anticipated movements.

Interventions

Both interventions were administered to the right pectoral fascia by the same RMT (18 years’ experience) with training in MFR (Supplemental Figure S3). The RMT was the only individual with access to the randomization schedule and delivered interventions accordingly. To reduce variability in positioning and impedance between measurements, electrode locations were outlined before removal. Researchers were blinded to the treatment intervention and exited the laboratory prior to the intervention.

Both interventions were performed identically apart from the application of different pressures. Participants laid supine with their arms resting by their sides and a bolster under their knees. Participants were told that they would receive one of two MFR interventions that had different pressure but were not told which intervention they would receive that session. The RMT informed patients to notify them if their discomfort or burning sensation surpassed a perceived 7 out of 10 so pressure could be modified; however, no participant reported this.

Given that ~3.3 min of MFR modifies fascial fibrosis [30], each intervention was 4-min. A cross-hand technique was applied to the superficial right pectoral fascia. One hand (anchoring hand) was placed on the right edge of the sternum (ribs 3 to 6), and the other hand (mobilizing hand) was placed over the anterior aspect of the humerus at the insertion point of the PEC. For MFR, a gentle posterior pressure was applied to the anchoring hand to ‘hold’ the fascia in place, and a moderate posterolateral pressure was applied to the mobilizing hand to take up the slack within the fascial tissue without gliding, allowing for mechanical stretch of the pectoral fascia. For CON, the RMT applied no pressure ‘light-touch’. After each intervention, the therapist slowly released any pressure applied from the mobilizing hand first. The RMT carefully reapplied the PEC electrodes and provided a modified t-shirt that visually concealed the treatment area but allowed access to the electrode wiring.

Surface electromyography data processing

Data processing was performed by a blinded investigator. sEMG signals were recorded and processed using OT BioLab+ (v1.3.2, OT Bioelettronica, Torino, Italy). Data were sampled at 2,048 in bipolar configuration with a gain of 500, band-pass filtered (−3 dB bandwidth, 10–500 Hz), and digitally converted by a 16-bit A/D converter (Quattrocento, OT Bioelettronica, Torino, Italy). Signals were digitally band-pass Butterworth filtered at 30–500 Hz post-collection to remove electrocardiogram contamination [37]. The root-mean-square (RMS) was calculated for each pair of electrodes. Data was exported from OT BioLab+ as a.csv file in 0.001 epochs.

A one-second period surrounding the peak of each muscle’s MVC was taken (0.5 s before/after). Muscle excitation during the reaching task was calculated during the movement time of each top-right target (i.e. release of microswitch to touch of target), as movement onset for each target was timestamped on the sEMG recording. The mean RMS of the 12 movement times was divided by the respective MVC to yield a percentage of excitation for each muscle, which was used for analysis.

Statistical analysis

Statistical analyses were performed using SPSS (v25, IBM, New York, USA). Normality was assessed using Shapiro-Wilk where data were considered normally distributed if p > .05. Outliers were defined as values greater than ± 3 standard deviations. A two-way (intervention*time) repeated measures ANOVA was conducted on PRE and POST values of MFR and CON on all dependent variables. Post-hoc Bonferroni corrected t-tests were conducted on significant interactions to determine simple main effects. Data were considered statistically significant if p < .05. Small, medium and large effect size (ηp² was interpreted as: 0.01, 0.06, and 0.14, respectively [38].

Intrasession reliability of FSP and HA-ROM measurements were determined by a two-way mixed model absolute agreement intraclass correlation (ICC) using participants’ individual PRE measurements from the first visit. ICC values of < 0.5, 0.5–0.75, 0.75 – 0.9, and > 0.9 indicated poor, moderate, good, and excellent reliability, respectively.

Results

The results are presented in (Table 1). RMS data were not normally distributed as assessed by Shapiro-Wilk’s test (p < .05), and several outliers were identified. Given the robustness of the ANOVA, statistical analyses were conducted without transforming the data. ANOVA’s were run with outliers removed with similar results. Thus, results from the analysis with the full data set are presented.

Table 1.

Summary of the two-way interaction effects between intervention (MFR and CON) and time (PRE and POST) on all outcome variables.

Outcome Variable	MFR		CON		f	p	ηp2	n
	Pre mean (SD)	Post mean (SD)	Pre mean (SD)	Post mean (SD)
FSP (mm)	128 (19)	123 (19)	126 (19)	124 (18)	5.939	.018*	.093	59
HA-ROM (mm)	602 (48)	593 (51)	599 (49)	598 (44)	3.294	.075	.054	59
UT (% MVC)	13.5(14.1)	13.7 (15.8)	13.8 (14.6)	13.1 (13.3)	1.080	.303	.019	58
MT (% MVC)	6.7 (5.3)	7.0 (6.4)	5.8 (3.9)	5.8 (3.7)	.378	.541	.007	57
LT (% MVC)	10.6 (5.8)	10.7 (6.8)	10.5 (5.2)	10.7 (5.1)	.035	.851	.001	58
PEC (% MVC)	12.2 (9.8)	12.9 (10.4)	14.6 (12.7)	14.5 (14.0)	.836	.364	.015	57

CON = “soft-touch” control; %MVC = percentage of maximal voluntary contraction; FSP = forward shoulder posture; HA-ROM = horizontal abduction range of motion; LT = lower trapezius; mm = millimeters; MT = middle trapezius; PEC = pectoralis major; SD = standard deviation; UT= upper trapezius.*Significant interaction.

There was a significant interaction between intervention and time for FSP, F(1, 58) = 5.939, p = .018, 95% CI (2.437 to 4.386), η_p² = .093 (Table 1). Post hoc analysis determined the effect of time (PRE or POST) was dependent on the intervention (MFR or CON). FSP significantly decreased over time in MFR (F(1, 58) = 41.978, p < .001, η_p² = .420) and CON (F(1, 58) = 13.658, p < .001, η_p² = .191) (Figure 3(a); Table 2). There were no differences between MFR and CON at PRE or POST (Table 2). There were no significant interactions for HA-ROM (Figure 3(b)) or muscle excitation of the UT, MT, LT, or PEC (Figure 4(a–d)). ICC values were .99 and .98 for FSP and HA-ROM, respectively.

Figure 3.

a) Forward Shoulder Posture (FSP) and, b) Horizontal Abduction Range of Motion (HA-ROM) before (PRE) and after (POST) 4-Minutes of MFR or Soft-Touch Control (CON) Interventions (individual and group means).

*significant (p <.001) difference pre-post. n = 59. mm = millimeter.

Table 2.

Simple main effects of MFR and CON on FSP.

FSP T-test	f	p	ηp2
MFR PRE to CON PRE	1.933	.170	N/A
MFR POST to CON POST	.368	.546	N/A
MFR PRE to MFR POST	41.978	<.001	.420
CON PRE to CON POST	13.658	<.001	.191

CON = “soft-touch” control; FSP = forward shoulder posture; MFR = myofascial release; PRE = pre-intervention measurement; POST = post-intervention measurement. *Significant interaction.

Figure 4.

Muscle excitation of the a) upper (UT), b) middle (MT), c) lower trapezius (LT) and d) pectoralis major (PEC) before (PRE) and after (POST) 4-minutes of myofascial release (MFR) or soft-touch control (Con)(individual and group means).

n = 58 (UT, LT), 57 (MT, PEC). % MVC = percentage of maximal voluntary contraction

Discussion

The current study determined the acute impact of a 4-min MFR intervention to the pectoral fascia of individuals with FSP on: 1) FSP, 2) HA-ROM, and 3) muscle excitation of UT, MT, LT, and PEC during a reaching task, compared to a 4-min soft-touch CON. In line with our first hypothesis, MFR did reduce FSP; however, CON also reduced FSP. Hypotheses 2–3 were not supported as HA-ROM and muscle excitation were not affected by MFR or CON.

FSP, pectoral length and HA-ROM

FSP was reduced in response MFR, which is consistent with previous reports demonstrating decreased FSP following a variety of techniques aimed at increasing pectoral length [19,22–24]. Most relevant to this work, self-MFR with arm movement [24] and soft-tissue mobilization followed by stretching [19] to pectoralis minor both reduced FSP.

Interestingly, FSP was also reduced in response to CON, a soft-touch intervention with no mechanical pressure applied to lengthen the soft tissue. This finding adds to a growing body of literature demonstrating the positive effects soft-touch has on various psychological and physiological outcomes in adults, such as pain reduction, increased pleasantness, decreased heart rate, and suppression of alpha and beta brain activity [39]. While FSP decreased in both MFR and CON conditions, the effect size for the MFR intervention (η_p² = .420) was more than double the effect size for CON interevention (η_p² = .191), reducing FSP by an average of 5 mm compared to 2 mm, respectively. This demonstrates MFR’s ability to reduce FSP to a greater extent than CON, likely due the mechanical lengthening of the soft-tissue. However, as we could not directly measure tissue length this cannot be confirmed. It is possible that participants became more aware of their posture post-intervention and corrected their posture (subconsciously or otherwise). This response bias may contribute to the decrease in FSP resulting from the CON intervention, as no mechanical tissue lengthening to occurred. These results highlight the continued need for control groups in massage and other therapeutic intervention studies. Given that both 4-min interventions reduced FSP, future studies should explore the benefit(s) of time-efficient preventative therapy as part of employer organized employee health care, particulary for occupations at greater risk of shoulder pathology (e.g. office workers, manual materials handling, etc.). Furthermore, future studies should aim to determine the minimal clinically important change in FSP that would indicate a reduction in the risk of shoulder injury [40].

Collectively, results from the current study and previous work suggest that manual therapy targeting the pectoralis minor and/or major reduce FSP [19,24]. Previous reports demonstrated 3.3 min of MFR results in changes in fascial fibrosis and tissue mobility [30], and that pectoralis minor stiffness is reduced after 30 s of stretching [41]. However, it is not known if the MFR intervention used in the current study altered stiffness of the pectoral fascia and/or muscles. It is possible that both shortened/stiff pectoral fascia and muscles could pull the shoulder complex anteriorly, contributing to a FSP position. Future studies should determine changes in the length and stiffness of both pectoral muscles in response to different interventions aimed at increasing pectoral muscle/fascia length.

Given that our MFR intervention targeted the pectoralis major fascia, and that there is no gold-standard for measuring pectoralis major length, changes in the pectoralis major and its fascia were quantified indirectly using HA-ROM. Despite FSP decreasing in response to both interventions, HA-ROM remined unchanged. While unanticipated, there are several potential factors that may have influenced these results. For example, FSP was measured in a standing position with the shoulders at rest, while HA-ROM brought the glenohumeral joint into end range of motion in a supine position. The contact between the participant’s back and plinth may have placed the scapula in a different position, ultimately influencing mobility of the shoulder. Thus, it is possible changes in pectoral tissue length from MFR altered the resting length of the pectoral fascia/muscle to reduce FSP but did not alter the stretch tolerance of the pectoral tissue. Additionally, multiple MFR interventions may be required to observe changes in HA-ROM. Further, HA-ROM would assess flexibility of all tissues crossing the anterior glenohumeral joint and joint structures; therefore, changes in the length of one structure (e.g. pectoral fascia) may not change the available ROM due to limitations from others. A likely explanation is that the MFR intervention increased the length of the PEC and/or its fascia as evidenced by the change in FSP, yet HA-ROM was unable to detect these changes. It is possible that other factors not measured in the current study were altered that reduced FSP, such as joint articulations, neural tone, or breathing mechanics. A post-hoc Pearson Correlation was conducted to explore the relationship between alterations in FSP and HA-ROM in response to MFR. We found a moderate positive relationship (p = .021; r = .308), suggesting that changes in FSP were associated with changes in HA-ROM. While these results do support the notion that pectoralis major length contributes to FSP, future work should aim to determine a method to quantify pectoralis major length and its fascia more precisely, and their relationship to FSP.

FSP and muscle excitation

Contrary to our hypothesis, muscle excitation of the UT, MT, LT and PEC during a reaching task did not differ in response to MFR or CON. Literature examining the impact of various massage techniques on changes in muscle excitation are equivocal [17,18,32,42,43]. Our results are consistent with previous reports that massage does not alter excitation of treated muscles, such as 30-min of massage to the legs [42] or back [43]. Conversely, several authors report changes in excitation of treated muscles in response to various massage techniques [17,18,32]. For example, 5- and 20-min of massage to the neck/shoulder decreases UT excitation [17,18] and self-MFR and stretching of the infraspinatus increased infraspinatus excitation during isometric strength testing [32]. Changes in muscle excitation in response to massage indicate an alteration in the voluntary descending drive to skeletal muscles from the primary motor cortex (central motor drive).

Many investigators propose that massage techniques inhibit central motor excitability by activating a combination of Golgi tendon organs, muscle spindles, and group III and IV afferent pathways [21]. Fascial experts suggest MFR stimulates fascial mechanoreceptors, which alters gamma motor tone and central motor drive [44]. Given that the MFR intervention in this study did not alter muscle excitation, it is possible that the intensity and/or duration of the intervention was not sufficient to stimulate mechanoreceptors to alter central motor drive. However, self-MFR and stretching to the shoulder with a comparable duration (cumulative 3.5-min between interventions) and intensity (tender or uncomfortable) reported altered excitation, that may be due to the combined treatment, stretching or the self-MFR treatment [32].

Literature has not determined the impact of severity of FSP, and the minimum threshold needed for clinically significant FSP. As such, it is unknown what magnitude of FSP increases the shoulder pathology risk. Previous research has used a variety of FSP inclusion criteria, including 3 cm from plinth to acromion in supine position [13], or 7 cm of distance from the wall to acromion while standing [16]. Similar to our study, 1 cm of anterior deviation of the acromion from the lateral plumb line was used to include participants with moderate [22] or severe [15] FSP. Thus, while the present study included participants with a minimum of 1 cm of anterior deviation of the acromion, the minimum threshold for clinically relevant FSP remains unknown. Further, our use of 1 cm of deviation was a minimum, with most participants having substantially greater FSP as measured using the double-square method (mean: 127 mm, 78 mm to 171 mm). This surpassed the inclusion criteria by Lee [16] that used a minimum of 7 cm (or 70 mm) to indicate FSP. Yoo [13] reported those with FSP (minimum 3 cm between plinth and acromion), had increased UT and PEC, and decreased MT excitation compared to those without FSP. Given the differences in FSP classification technique, it is uncertain if participants in the current study had the same degree of FSP to exhibit similar alterations in excitation. We conducted a post-hoc Pearson Correlation between baseline FSP and excitation change scores to explore the relationship between FSP severity and excitation. Interestingly, increased magnitude of FSP was not associated with greater alterations of excitation in any muscle (UT: p = .167, r = .187; MT: p = .847, r = .026; LT: p = .208, r = .171; PEC: p = .764, r = .041).

Limitations

There are limitations to the current study that can guide future research. First, the generalizability is limited to healthy, younger, right-handed individuals with FSP. Secondly, while a reduction in FSP was observed after both interventions, it is unknown how long this reduction would last as follow-up measurements were not performed.

While HA-ROM was reliable, changes to passive HA-ROM may not be related to changes in resting or stretch length of PEC due to other structures that can limit HA-ROM. Umehara et al. investigated changes in pectoralis minor stiffness using shear wave elastography following stretching at varying degrees of shoulder abduction, finding that 90° and 150° of horizontal abduction elongated and decreased tissue stiffness of pectoralis minor [41,45]. These results suggest that our HA-ROM measurement would also target the pectoralis minor. Future studies should use shear wave elastography to quantify stiffness of the pectoralis major and minor in response to a pectoral MFR.

As we did not include a control group without FSP, it is unknown if participants from the current study had preexisting altered excitation compared to those without FSP. Additionally, future work should consider if using a within-participant, between shoulder design with those who have unilateral FSP is feasible to more holistically define the relationship between shoulder posture, muscle excitation and length. Further, our reaching task, meant to represent activities of daily living and repeated work-related tasks, may not have elicited enough muscular force to reveal differences in excitation. It is possible that altered excitation may only be present in higher intensity tasks requiring greater muscular force. For example, Yoo (2013) assessed excitation in those with and without FSP during an arm raising task with a 2 kg wrist weight. The use of a 2 kg weight may have increased the task intensity, and thus muscular force, enough to observe the differences in excitation that we were not able to observe in our unloaded reaching task. Lastly, while the RMT was experienced, intervention intensity was applied subjectively. Thus, it is not known how uniform pressure was across interventions. Future research should aim to quantify and standardize applied pressure of different manual interventions.

Conclusion

A 4-min MFR and CON to the pectoral fascia reduces FSP, but neither influenced HA-ROM or muscle excitation. Despite the large effect both MFR and CON had on decreasing FSP, MFR elicited a greater decrease compared to CON, demonstrating MFR’s superior ability to reduce FSP, likely due to the mechanical lengthening of the pectoral soft-tissue. It is likely that multiple intervention sessions may be needed for changes in HA-ROM and muscle excitation to appear. However, given that MFR was found to acutely reduce FSP, it is worth pursuing the possibility that 4-min of MFR may indeed reduce an individual’s risk for the development of shoulder pathology. Taken together, there is initial evidence for the benefits of MFR and CON in reducing FSP, which may reduce shoulder pathology risk. Future research should employ a course of interventions that more closely resembles a course of care in a rehabilitation context.

Biographies

Sarah Bohunicky is a Certified Athletic Therapist and PhD candidate at the University of Manitoba in Applied Health Sciences. Her research investigates various shoulder rehabilitation strategies and the impact they have on posture, range of motion, muscle excitation, and muscle stiffness. Sarah is also an instructor at Acadia University where she teaches in the School of Kinesiology.

Lindsey Rutherford grew up in a small town in Manitoba where her love of sports and activity brought her to the University of Manitoba to study Kinesiology, majoring in Athletic Therapy. As an undergraduate student, Lindsey was the recipient of two Undergraduate Research Awards that exposed her to research and broadened her skillset that was especially applicable to her experience as a healthcare professional. Now a Certified Athletic Therapist, Lindsey is continuing her education by pursuing a doctorate in chiropractic in Minneapolis, Minnesota.

Kara-Lyn Harrison received her Honours Bachelor of Kinesiology and Masters of Science in Kinesiology and at Lakehead University. Kara is currently a PhD candidate in Applied Health Sciences. Her research focuses on sex differences in myoelectric manifestations of fatigue.

Quinn Malone received his Bachelor of Science and his Master of Science degrees from the University of Manitoba in 2016 and 2021, respectively. He is currently completing his PhD in Kinesiology at the University of British Columbia: Okanagan, investigating the effects of acute cannabis intoxication on motor behaviour. He has been involved in a number of research projects since 2014, covering a variety of subjects including; non-surgical spine care, opioids in healthcare, exercise measurement methodology, motor control, and electronic healthcare device development.

Dr. Cheryl M. Glazebrook is Professor at the University of Manitoba. Her research program seeks to understand how the nervous system integrates information from different senses (e.g., sight, sound) to perform precise movements. She manipulates the accuracy and availability of visual, auditory, and somatosensory information in order to develop principles for using multisensory information to improve motor skill learning and performance.

Dr. Trisha D. Scribbans is Certified Athletic Therapist and Associate Professor at the University of Manitoba. Her research program focuses on understanding the neuromuscular mechanisms that control of force production and movement of the upper extremity, with a particular emphasis on the role of scapular position and movement in shoulder and scapulothoracic mechanics/pathomechanics. She is also interested in identifying novel treatment/prevention strategies to reduce the incidence and duration chronic shoulder pathologies, individual responses to rehabilitative exercise strategies and skeletal and neurological adaptations to exercise training and other therapies.

Funding Statement

This research study was registered with the U.S. National Library of Medicine ClinicalTrials.gov database [NCT04944745].

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/10669817.2024.2316414