Comparative ultrasonographic assessment of supraspinatus, infraspinatus, and biceps tendon thickness in bodybuilders and non-sportsperson.

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Learn more: PMC Disclaimer | PMC Copyright Notice J Ultrasound . 2025 Mar 9;28(2):405–412. doi: 10.1007/s40477-025-01004-z Comparative ultrasonographic assessment of supraspinatus, infraspinatus, and biceps tendon thickness in bodybuilders and non-sportsperson Najmeh Pirasteh 1 , Hamid reza Farpour 2, 3, ✉ , Parisa Najafi 4 , Mohammad Hossein Jabbedari 1 Author information Article notes Copyright and License information 1 Student Research Committee, Department of physical medicine and rehabilitation, Shiraz University of Medical Sciences, Shiraz, Iran 2 Orthopedic & rehabilitation research center, Department of physical medicine and rehabilitation, Shiraz University of Medical Sciences, Shiraz, Iran 3 Shiraz Geriatric Research Center, School of medicine, Shiraz University of Medical Sciences, Shiraz, Iran 4 Faculty of Sports and Exercise Science, Universiti Malaya, Kuala Lumpur, 50603 Malaysia ✉ Corresponding author. Received 2024 Jul 27; Accepted 2024 Dec 2; Collection date 2025 Jun. © Società Italiana di Ultrasonologia in Medicina e Biologia (SIUMB) 2025. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law. PMC Copyright notice PMCID: PMC12145356  PMID: 40059249 This article has been corrected. See J Ultrasound. 2025 Apr 5;28(3):779 . Abstract Background Healthy tendons are crucial for sportspersons to prevent injuries. While resistances exercise is known to increase muscle size and composition, its impact on tendon thickness remains unclear. This study investigated potential differences in tendon thickness between bodybuilders and non-sportsperson control group and their association with training intensity/duration in bodybuilders. Methods Forty men in the age range 18 to 40 were included in the study. Fifteen bodybuilders (2–3 weekly upper body resistance training sessions, moderate-to-high intensity, > 6 months) and 25 non-sportsperson controls participated. All were free of tendon injuries in the studied muscles (biceps, supraspinatus, infraspinatus). Two independent physiatrists measured tendon thickness using ultrasound. Results No significant differences in tendon thickness were found between bodybuilders and non-sportsperson controls (dominant/non-dominant sides). However, within the bodybuilding group, tendon thickness showed strong positive correlations with both training intensity ( r = 0.59–0.84) and exercise duration ( r = 0.71–0.88). Conclusion This study found no overall group differences in tendon thickness between bodybuilders and non-sportsperson controls. However, for bodybuilders, increased training intensity and duration were associated with thicker tendons. Further research with larger samples and advanced techniques is warranted to understand the complex relationship between resistance training and tendon adaptations. Keywords: Exercise, Tendons thickness, Bodybuilders, Ultrasound, Supraspinatus, Infraspinatus, Biceps Introduction In recent years, new sports like functional fitness, jumping fitness, and wearable technologies such as electrical muscle stimulation (EMS) have emerged. However, bodybuilding has remained popular and has become one of the most prominent fitness activities, especially through its presence on social media platforms. This has resulted in more people engaging in bodybuilding to improve their self-perception and body image [ 1 , 2 ]. Bodybuilding primarily involves systematic resistance training exercises targeting most major muscle groups. These exercises are performed over an extended period, with varying frequency and intensity, aiming to induce muscle hypertrophy [ 3 ]. It is noteworthy that some bodybuilders employ anabolic hormones and rigorous dietary regimens to optimize muscle growth [ 4 ]. Supraspinatus and infraspinatus, as a part of rotator cuff muscles, assist in the abduction and external rotation of the arm, stabilizing the glenohumeral joint by compressing the head of the humerus during this action [ 5 ]. In bodybuilding, these muscles are engaged in various primary and supplementary upper body exercises, such as lateral raises and full can workouts using cables or dumbbells, as well as exercises involving forearm flexion like barbell curls, EZ-bar preacher curls, and hammer curls [ 6 ]. Regular and intense activation of these muscles during bodybuilding exercises may lead to adaptations in muscle and tendon structure. These adaptations are thought to occur in response to the mechanical stress placed on the tissues during resistance training. While changes in muscle size and strength are well-documented, the effects on tendon thickness and properties are less clear, particularly in comparison to non-sportspersons people [ 7 ]. Resistance training is a fundamental component of bodybuilding, essential for increasing muscle mass and reducing body fat to enhance muscle definition. A study by Sukwong et al. demonstrated that elite bodybuilders exhibited lower body fat percentages and greater muscle mass compared to novice practitioners [ 8 ]. While the prevailing hypothesis suggests that exercise induces muscle hypertrophy and alters muscle composition, there is a lack of conclusive evidence regarding the effects on tendon thickness, particularly when comparing bodybuilders to non-sportspersons [ 9 – 11 ]. This gap in knowledge highlights the need for further investigation into the structural adaptations of tendons in response to resistance training. The present study aims to compare the tendon thickness of the biceps, supraspinatus, and infraspinatus muscles between bodybuilders and non-sportspersons. Additionally, it seeks to examine potential associations between tendon thickness and various factors, including demographic characteristics, training intensity, and exercise duration in bodybuilders. Methods Participants This case–control study, conducted at a university-affiliated clinic from August 2021 to January 2022, was approved by the Medical Ethics Committee of the academy (Ethical Code: IR.SUMS.MED.REC.1400.147). A formal sample size calculation determined that a minimum of 14 participants per group was required. Participant recruitment occurred over two months, utilizing a multi-faceted approach including gym flyers, phone calls, social media, and advertisements at the Shiraz Medicine Laboratory. Recruitment materials provided a brief study description, eligibility criteria, and contact information for the research site. Bodybuilders were recruited from gyms in Shiraz, Iran. Eligibility was determined based on inclusion criteria. A total of 63 participants were initially recruited, with 40 meeting the inclusion criteria and subsequently randomized into two groups: 15 bodybuilders and 25 non-sportsperson control group. The study subject gave their informed consent after they were well-informed about the study design, and they were assured that their information would remain confidential. Demographic data, past medical/surgical history, and prior medical status were recorded. In the bodybuilders’ group, the duration of training and intensity of exercises were also recorded. Eligibility criteria Inclusion criteria for bodybuilders were as follows:1) Male, aged 19–40 years; 2) Consistent history of upper extremity resistance training for more than six months; 3) Exercise frequency of 2–3 days per week (75–150 min per week); 4) Moderate to vigorous intensity training, defined as: Moderate: 50–69% of one repetition maximum (1RM), 2–4 sets with 8–12 repetitions, Vigorous: 70–84% of 1RM, 3–6 sets with 6–8 repetitions, Engagement in both multi-joint and single-joint exercises, including chest press, bench press, shoulder press, biceps curls, hammer curls, barbell curls, lat pulldown, incline dumbbell rear lateral raise, military press, deadlifts, and power cleans [ 12 ]. Inclusion criteria for the control group:1) Male, aged 19–40 years; 2) No engagement in regular physical exercise for at least one year [ 12 ]. Exclusion criteria encompassed systemic diseases, rheumatologic disorders, connective tissue disorders, upper extremity trauma or surgery, chronic infections, immune diseases, neuromuscular disorders, and the use of hormonal or anabolic steroids. Participants with a history of shoulder pathologies, including pain, instability, dislocation, rotator cuff injuries, tendinopathy, capsulitis, bursitis, active cervical radiculopathy, or brachial plexopathy were also excluded. These criteria were established to minimize potential confounding factors affecting tendon thickness measurements and study results. Procedure Two independent physiatrists conducted comprehensive physical examinations on all participants to ensure the absence of pre-existing shoulder conditions. These examinations included visual inspection, palpation, and assessment of range of motion. Additionally, a series of provocative tests were performed to evaluate glenohumeral conditions and identify potential acromioclavicular or related pathologies. The provocative tests included cross body adduction and active compression tests for acromioclavicular joint; Speed and Yergason tests for bicipital tendinitis; Hawkins and Neer maneuvers for rotator cuff impingement syndrome; apprehension-relocation, O'Brien, and crank tests for glenohumeral instability and labral tears; and lift-off, belly-press, Patte, drop arm, full can, and empty can tests for rotator cuff tendons [ 13 , 14 ].. Participants exhibiting any limitations, pain, tenderness, or positive findings indicative of pathology during these examinations were excluded from the study. This rigorous screening process ensured that only individuals without pre-existing shoulder conditions were included in the study. Subsequently, two physiotherapists conducted ultrasonographic examinations independently using a linear probe with a frequency range of 5–12 MHz, by the protocol recommended by the European Society of Musculoskeletal Radiology. The axial spatial resolution of the ultrasound system was 0.280 mm. This standardized approach ensured consistency and reliability in the imaging process [ 15 ]. Ultrasonographic Assessment of tendon thickness Participants underwent standardized ultrasonographic evaluation in a seated neutral position, with bilateral assessment of shoulders. For long head of the biceps tendon (LHBT) thickness measurement, the arm was positioned adjacent to the trunk, elbow flexed to 90 degrees, and orearm supinated. LHBT thickness was assessed 1 cm distal to the bicipital groove in the long-axis view (Fig. 1 ), adhering to established musculoskeletal ultrasonography guidelines [ 15 , 16 ]. This approach ensured measurement consistency and reproducibility across participants. Fig. 1. Open in a new tab A Biceps tendon (LHBT) ultrasonographic long axis view B Schematic of a longitudinal view of LHBT Subsequently, the participant's arm was positioned posteriorly, with the elbow flexed and the palm placed on the superior aspect of the ipsilateral iliac crest. In this standardized position, the examiner measured the supraspinatus tendon (SST) thickness in the long-axis view. The measurement was taken distal to the anatomical footprint at the sulcus of the greater tuberosity, extending from the articular cartilage to the bursal surface (Fig. 2 ). This technique aligns with established protocols for ultrasonographic assessment of the supraspinatus tendon [ 15 , 16 ]. Fig. 2. Open in a new tab A Supraspinatus tendon (SST) ultrasonographic long axis view B Schematic of a longitudinal view of SST Following the supraspinatus tendon assessment, the examiner repositioned the participant's arm, placing the hand on the contralateral shoulder. In this position, the infraspinatus tendon thickness was measured in the long axis view. The measurement was taken superior to the labrum, at the level of the posterior border of the acromion (Fig. 3 ). This standardized approach for infraspinatus tendon evaluation is consistent with established ultrasonographic protocols [ 15 , 16 ]. Fig. 3. Open in a new tab A Infraspinatus tendon ultrasonographic long axis view of the B Schematic of a longitudinal view of IST Randomization Participants were allocated to the bodybuilder ( n = 15) or non-sportsperson control group ( n = 25) groups using stratified random sampling. Eligible individuals in each stratum were assigned unique identification numbers, and selection was performed using a computer-generated random number sequence. This process, conducted by a researcher not involved in recruitment or data collection, ensured equal selection probability within each group and minimized selection bias. Sample size The sample size was determined based on a comparable study by Leong et al., using a significance level (α) of 0.05 and a power (1-β) of 0.8. This calculation yielded a minimum required sample size of 14 participants per group (bodybuilders and non-sportsperson control group) to detect statistically significant differences between the groups [ 17 ]. Data analysis Data analysis was performed using IBM SPSS Statistics version 26.0 and Microsoft Excel 2007. The Shapiro–Wilk test was employed to assess the normality of distribution for all variables. As the data were normally distributed across bodybuilders, non-sportsperson controls, and sex groups, parametric tests were utilized. One-way ANOVA and independent and paired t-tests were conducted to evaluate between-group differences. Categorical variables were analyzed using Pearson's chi-square test. Relationships between variables were assessed using Pearson's correlation coefficient for normally distributed data and Spearman's rank correlation coefficient for non-normally distributed data. Results are presented as mean ± standard deviation (SD). Statistical significance was set at p < 0.05 for all analyses [ 18 ]. Results Forty participants were recruited during the study period and underwent ultrasound evaluation for tendon thickness measurement. The study included 15 bodybuilders (mean age: 29.53 ± 6.22 years) and 25 non-sportsperson control group (mean age: 31.48 ± 6.55 years). Demographic characteristics, including age, sex, weight, height, and body mass index (BMI), were no significant baseline differences (all p-values > 0.05; detailed data in Table 1 ). Table 1. Demographic data and tendon thickness of the bodybuilder and control groups Variables Total ( n = 40) Bodybuilders ( n = 15) Non-sportsperson ( n = 25) P-value* Gender; n (%) Male 24 (60.0) 10 (66.7) 14 (56.0) 0.50 Female 16 (40.0) 5 (33.3) 11 (44.0) Age (years) (Mean ± SD) 30.75 ± 6.42 29.53 ± 6.22 31.48 ± 6.55 0.36 BMI (kg/m 2 ) (Mean ± SD) 24.47 ± 1.99 23.91 ± 1.52 24.80 ± 2.18 0.17 DS biceps TT (Median [Q1-Q3]) 2.80 [2.80–2.90] 2.80 ± 0.11 2.81 ± 10 0.49 Non-DS biceps TT (Median [Q1-Q3]) 2.80 [2.72- 2.90] 2.82 ± 0.10 2.82 ± 0.11 0.96 DS supraspinatus TT (Mean ± SD) 5.38 ± 0.19 5.38 ± 0.20 5.38 ± 0.18 0.92 Non-DS supraspinatus TT (Mean ± SD) 5.37 ± 0.17 5.38 ± 0.20 5.37 ± 0.16 0.95 DS infraspinatus TT (Mean ± SD) 3.60 ± 0.45 3.68 ± 0.39 3.55 ± 0.48 0.40 Non-DS infraspinatus TT Median [Q1-Q3] 3.60 [3.20–4.00] 3.64 ± 0.35 3.59 ± 0.52 0.68 Open in a new tab DS dominant shoulder, non-DS non-dominant shoulder, TT tendon thickness, BMI Body mass index, SD standard deviation; *Independent sample t -test/Chi-square test Bolded values indicate statistically significant p-values Ultrasound measurements of tendon thickness were performed on both dominant and non-dominant upper limbs in all participants. Moreover, no significant differences in tendon thickness were observed between dominant and non-dominant shoulders across all subgroups (bodybuilders, non-sportsperson control group, and total study population) and genders ( p > 0.05) (Table 2 ). Notably, gender-stratified analysis of tendon thickness revealed no statistically significant differences between male and female participants across all measured variables ( p > 0.05). Table 2. Tendon thickness of dominant and non-dominant shoulders Variables Body Builders (mean ± SD) Non-sportsperson (mean ± SD) DS ( n = 25) Non-DS ( n = 25) p -value* DS ( n = 40) Non-DS ( n = 15) p -value* Biceps tendon thickness 2.82 ± 0.10 2.82 ± 0.11 0.64 2.82 ± 0.10 2.82 ± 0.11 0.50 Supraspinatus tendon thickness 5.38 ± 0.19 5.37 ± 0.17 0.84 5.38 ± 0.19 5.37 ± 0.17 0.84 Infraspinatus tendon thickness 3.60 ± 0.45 3.6 ± 0.46 0.26 3.60 ± 0.45 3.6 ± 0.46 0.26 Open in a new tab DS dominant shoulder, non-DS non-dominant shoulder, TT tendon thickness, SD Standard deviation; *Paired Sample T -test Bolded values indicate statistically significant p-values As shown in Table 3 , no significant differences were observed in tendon thickness of the biceps, supraspinatus, and infraspinatus muscles in the dominant shoulder between bodybuilders and the non-sportsperson control group (all p > 0.05). Similarly, tendon thickness in the non-dominant shoulder did not differ significantly between the two groups for all measured muscles (all p > 0.05). Table 3. Comparison of tendon thickness in dominant and non-dominant shoulders between bodybuilders and non-sportsperson control group Variables DS (mean ± SD) Non-DS (mean ± SD) Body builders ( n = 15) Non-sportsperson ( n = 25) p - value* Body builders ( n = 15) Non-sportsperson ( n = 25) p - value* Biceps TT 2.84 ± 0.11 2.82 ± 0.11 0.50 2.82 ± 0.11 2.82 ± 0.11 0.94 Supraspinatus TT 5.39 ± 0.21 5.37 ± 0.18 0.91 5.39 ± 0.20 5.37 ± 0.16 0.94 Infraspinatus TT 3.68 ± 0.49 3.55 ± 0.49 0.40 3.64 ± 0.36 3.59 ± 0.52 0.75 Open in a new tab DS dominant shoulder, non-DS non-dominant shoulder, TT tendon thickness, SD Standard deviation; *Paired Sample T -test Bolded values indicate statistically significant p-values In bodybuilders, higher exercise intensity was significantly associated with increased tendon thickness in the dominant biceps ( p = 0.04), supraspinatus ( p < 0.001), and infraspinatus ( p < 0.001) muscles (Table 4 ). Additionally, bodybuilders with more than 3 years of exercise experience demonstrated significantly greater tendon thickness in the dominant biceps ( p = 0.04), supraspinatus ( p = 0.001), and infraspinatus ( p < 0.001) muscles. Similar significant improvements in tendon thickness related to exercise intensity and duration were observed in the non-dominant biceps, supraspinatus, and infraspinatus muscles of bodybuilders (all p = 0.05) (Table 4 ). Table 4. Demographic data and tendon thickness according to the intensity and duration of bodybuilders' exercises (n = 15) Variables Intensity (mean ± SD) Duration (mean ± SD) Moderate ( n = 9) Vigorous ( n = 6) p -value* < 1 year ( n = 5) 1–3 years ( n = 6) > 3 years ( n = 4) p -value* Age (years) 29.22 ± 6.85 30.00 ± 5.73 0.82 31.00 ± 7.65 27.67 ± 5.35 30.50 ± 6.56 0.67 BMI (kg/m 2 ) 23.95 ± 1.64 23.84 ± 1.48 0.90 24.40 ± 0.99 23.29 ± 1.75 24.22 ± 1.75 0.46 Gender; n (%) Male 6 (66.7) 4 (66.7) 1.00 3 (60.0) 4 (66.7) 3 (75.0) 0.89 Female 3 (33.3) 2 (33.3) 2 (40.0) 2 (33.3) 1 (25.0) DS biceps TT 2.78 ± 0.10 2.91 ± 0.07 0.04 2.74 ± 0.11 2.86 ± 0.08 2.92 ± 0.05 0.04 Non-DS biceps TT 2.75 ± 0.07 2.93 ± 0.05 < 0.001 2.72 ± 0.08 2.85 ± 0.08 2.92 ± 0.05 0.01 DS supraspinatus TT 5.26 ± 0.15 5.56 ± 0.15 < 0.001 5.18 ± 0.10 5.40 ± 0.10 5.62 ± 0.15 0.001 Non-DS supraspinatus TT 5.25 ± 0.10 5.56 ± 0.16 0.001 5.20 ± 0.10 5.41 ± 0.16 5.55 ± 0.19 0.01 DS infraspinatus TT 3.46 ± 0.30 4.00 ± 0.30 < 0.001 3.28 ± 0.22 3.80 ± 0.25 4.00 ± 0.36 < 0.001 Non-DS infraspinatus TT 3.44 ± 0.31 3.93 ± 0.16 < 0.001 3.28 ± 0.30 3.73 ± 0.20 3.95 ± 0.19 0.01 Open in a new tab DS dominant shoulder, non-DS non-dominant shoulder, TT tendon thickness, BMI Body mass index, SD standard deviation; *Independent sample t -test/One-Way analysis of variance test or Chi-square test Bolded values indicate statistically significant p-values Pearson correlation analysis revealed significant moderate to high positive correlations ( r = 0.59 to 0.84) between tendon thickness and exercise intensity for the dominant and non-dominant biceps, supraspinatus, and infraspinatus muscles in bodybuilders (all p ≤ 0.001). Similarly, categorized exercise duration showed significantly high positive correlations ( r = 0.67 to 0.87) with tendon thickness in these muscles (all p ≤ 0.001). Continuous exercise duration (in months) also demonstrated significant high positive correlations ( r = 0.71 to 0.88) with tendon thickness across all measured muscles (all p ≤ 0.001). As detailed in Table 5 , all correlation analyses were performed. Table 5. The correlation between exercise intensity, duration, and tendon thickness in bodybuilders based on Pearson correlation/ Spearman correlation Variables DS biceps Non-DS biceps DS supraspinatus Non-DS supraspinatus DS infraspinatus Non-DS infraspinatus Intensity (P-value; CC) 0.02 ; 0.59 < 0.001 ; 0.89 0.001 ; 0.76 < 0.001 ; 0.84 < 0.001 ; 0.66 0.001 ; 0.77 Duration (categorized) (P-value; CC) 0.001 ; 0.67 < 0.001 ; 0.79 < 0.001 ; 0.87 0.001 ; 0.78 0.001 ; 0.74 < 0.001 ; 0.79 Duration (months) (P-value; PC) < 0.001 ; 0.71 < 0.001 ; 0.88 < 0.001 ; 0.83 < 0.001 ; 0.80 0.001 ; 0.77 < 0.001 ; 0.84 Open in a new tab DS dominant shoulder, non-DS non-dominant shoulder, CC correlation coefficient, PC Pearson correlation Bolded values indicate statistically significant p-values Discussion Tendons play a vital role in transmitting force between muscles and bones, and their health is essential for optimal performance and injury prevention. While bodybuilding is known to promote muscle hypertrophy (growth), its impact on tendon size and potential implications have remained unclear. This study used ultrasound (a reliable method, [ 15 , 16 ]) to assess tendon thickness in bodybuilders compared to non-sportsperson controls group. While no significant differences were found in overall thickness, interestingly, exercise intensity and duration within the bodybuilding group correlated with increased tendon thickness. These findings contribute to understanding tendon adaptations in response to bodybuilding. To our knowledge, this study is the first to examine the effects of bodybuilding on biceps, supraspinatus, and infraspinatus tendon thickness, limiting direct comparisons with existing literature. In contrast to our findings, Wang et al. reported significant differences in biceps and supraspinatus tendon thickness between baseball athletes and non-athlete controls [ 19 ]. The absence of significant differences in our study may be attributed to sport-specific adaptations, training duration, sample size limitations, or variations in measurement techniques. Bodybuilding, unlike baseball, may not induce the same degree of tendon hypertrophy due to differences in mechanical loading patterns. Additionally, our participants' training history (duration) may not have been sufficient to elicit measurable tendon adaptations, or our sample size may have limited statistical power to detect subtle differences. Further research with larger samples and longitudinal designs is needed to clarify the potential effects of bodybuilding on tendon morphology. Malanga et al. investigated supraspinatus tendon thickness differences between dominant and non-dominant arms in young baseball players [ 20 ]. Their study, involving twelve asymptomatic players, utilized ultrasound measurements. Results revealed significant differences in supraspinatus tendon thickness (in both long-axis and short-axis views) for the dominant side of right-handed players, but not for left-handed players. The discrepancy between these findings and our results may be attributed to the nature of the sports examined. Baseball pitching predominantly involves unilateral arm use, whereas bodybuilding typically requires bilateral, symmetrical muscle contractions. This fundamental difference in movement patterns and force distribution likely accounts for the contrasting outcomes observed in tendon adaptations between the two sports. In our study, high-intensity resistance exercise performed for more than 3 years demonstrated a significant correlation with tendon thickness of the biceps, supraspinatus, and infraspinatus muscles in both dominant and non-dominant shoulders of bodybuilders. This finding aligns with research by Seynnes et al., who observed increased patellar tendon cross-sectional area after just 9 weeks of resistance training [ 21 ]. They attributed these rapid changes to the high mechanical loads associated with resistance exercise, which stimulate tendon adaptation. The longer duration of our study (> 3 years) compared to Seynnes et al.'s 9-week intervention may explain the more pronounced tendon adaptations observed in our participants. These results suggest that long-term, high-intensity resistance training can induce significant structural changes in shoulder tendons, potentially as an adaptive response to increased mechanical loads over time. This study had several limitations, primarily due to the COVID-19 pandemic, which restricted participant recruitment and follow-up assessments. The resulting small sample size and cross-sectional design limited our ability to assess longitudinal changes in tendon thickness among bodybuilders. Additionally, ultrasound was not performed before the exercise program, preventing comparisons of tendon thickness before and after training. Future research should aim to include larger cohorts of professional athletes with extended training histories and utilize advanced imaging techniques such as MRI. Incorporating tendon elastography could also provide a more comprehensive evaluation of training-induced adaptations. Future studies should implement longitudinal designs with baseline measurements to better understand the temporal dynamics of tendon adaptation. These studies could explore the optimal timing, dosage, and duration of exercise protocols to maximize tendon healing and recovery. Additionally, examining the cellular and molecular mechanisms underlying tendon adaptations to resistance training would provide valuable insights. Such research would enhance our understanding of the relationship between resistance training and tendon morphology, as well as identify potential factors influencing tendon thickness changes over time. Conclusion This study provides novel insights into the effects of long-term, high-intensity bodybuilding on tendon morphology in the shoulder region. While no significant differences in overall tendon thickness were observed between bodybuilders and non-athlete controls, our findings reveal a positive correlation between exercise intensity and duration with increased tendon thickness within the bodybuilding group. This suggests that prolonged, vigorous resistance training may induce adaptive changes in tendon structure, potentially as a response to increased mechanical loading. However, the complex relationship between resistance training and tendon morphology warrants further investigation. Future longitudinal studies with larger sample sizes, advanced imaging techniques, and consideration of molecular mechanisms are necessary to elucidate the full extent of tendon adaptations in response to bodybuilding. Acknowledgements This manuscript was the subject of the dissertation of Najmeh Pirasteh (NO.23420), which was approved by the vice-chancellor of research at Shiraz University of Medical Sciences, Shiraz, Iran. The authors would like to thank the center for developing clinical research at Nemazi hospital and Dr. Nasrin Shokrpour for editorial assistance. The authors would also thank Mr. Ali Kamali for arrangement of cases. Abbreviations EMS Eclectic muscle stimulation 1RM One repetition maximum LHBT Long head of the biceps tendon SST Supraspinatus tendon SPSS Statistical Package for Social Sciences Authors' contributions All authors contributed equally to the manuscript preparation and read and approved the final manuscript. Funding No financial support was received for this report. Data availability All data regarding this study has been reported in the manuscript. Please contact the corresponding author if you are interested in any further information. Declarations Conflict of interest None. Consent for publication Written informed consent was obtained from the patients in our study. Footnotes The online version of this article was revised to update the fourth author affiliation as "Faculty of Sports and Exercise Science, Universiti Malaya, Kuala Lumpur 50603, Malaysia". Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Change history 4/5/2025 A Correction to this paper has been published: 10.1007/s40477-025-01016-9 References 1. Magee K. (2018) Understanding the Social Media Fandom of the Mr. Olympia Bodybuilding Show. 2. Ţifrea C, Cristian V, Manescu D (2015) Improving fitness through bodybuilding workouts. 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