Abstract
s: Understanding the factors that influence tendon mechanical prop- erties is essential for optimizing performance and preventing injuries in elite athletes. This study aimed to identify the strongest correlates of the biomechanical properties (frequency, stiffness, logarithmic decrement, relaxation, and creep) in the Achilles and patellar ten- dons in elite international athletes. Methods: A cross-sectional study was conducted with 111 elite athletes from 11 sports disciplines assessed at a high-performance training center. Tendon properties were measured bilaterally using MyotonPRO. Anthropometric (height, weight, age), demographic (sex, limb dominance defined as the preferred limb for sport- specific activities), and sport-specific
relaxation, and creep) in the Achilles and patellar ten- dons in elite international athletes. Methods: A cross-sectional study was conducted with 111 elite athletes from 11 sports disciplines assessed at a high-performance training center. Tendon properties were measured bilaterally using MyotonPRO. Anthropometric (height, weight, age), demographic (sex, limb dominance defined as the preferred limb for sport- specific activities), and sport-specific variables were analyzed using correlation, multiple regression, and machine learning approaches. Results: Height showed the strongest corre- lations with tendon frequency and stiffness, particularly for the Achilles tendon (r = 0.52 for frequency; r = 0.53 for stiffness;p≤0.001, large effects). Sex differences were evident across all measures, with men showing higher stiffness and frequency, and women greater relaxation and creep (partialη 2= 0.35–0.48, Cohen’s d = 0.84–1.16). Sports discipline explained substantial variance in tendon properties (η 2> 0.40), and limb dominance influ- enced Achilles stiffness, with left-dominant athletes showing higher values (p< 0.05). Age showed minimal associations (r < 0.10). Conclusions: Height, sex, and sports discipline were the strongest correlates of Achilles and patellar tendon mechanical properties in elite athletes, with large and practically meaningful effects across sports. This comprehensive analysis, utilizing multivariate and machine learning approaches, provides insights that can inform individualized training, injury prevention, and performance optimization strategies in high-performance sports. Keywords:Myoton; tendon biomechanics; elite athletes; stiffness; anthropometry Physiologia2025,5, 56 https://doi.org/10.3390/physiologia5040056
Physiologia2025,5, 56 2 of 21 1. Introduction Tendon mechanical adaptations vary with sport, sex, and anthropometry, yet compar- ative data across elite disciplines remain scarce [1–3]. The Achilles and patellar tendons serve distinct functions: the Achilles primarily stores and releases elastic energy during running and jumping, while the patellar tendon transmits quadriceps forces during knee extension [3,4]. These functional differences lead to sport- and sex-specific adaptations, with males generally exhibiting stiffer tendons and greater adaptation variability across sports [1–3,5,6]. Tendon biomechanical properties critically influence athletic performance and injury risk [7–9]. The Myoton PRO (Myoton AS, Estonia) device provides non-invasive assessment of five complementary parameters: frequency (natural oscillation), stiffness (resistance to deformation), logarithmic decrement (vibration decay), relaxation (tension reduction), and creep (progressive deformation under load) [7,10–12]. While ultrasound elastography remains the gold standard for tendon assessment, Myoton offers distinct advantages for elite athlete populations: (1) field-portable assessment without imaging equipment, (2) rapid bilateral evaluation (<5 min vs. 20–30 min), (3) operator-independent measurements reducing inter-examiner variability, and (4) real-time feedback capability for training environments. Validation studies demonstrate excellent reliability (ICC 0.74–0.99) and strong correlations with elastography (r = 0.72–0.89), supporting its use as a practical alternative for high-performance sports contexts [8,13–15]. The use of this equipment is interesting in high-performance sports, as tendon stiff- ness plays a central role in athletic performance by optimizing the storage and release of elastic energy during movement [10]. In this context, understanding the correlation of tendon biomechanical properties is critically important because of the extreme mechanical demands imposed by high-intensity training and competition [16,17]. However, stiffness is a double-edged characteristic; while adequate stiffness enhances power transmission and performance, excessive stiffness may compromise shock absorption and increase injury risk [18–20]. Thus, optimal tendon behavior represents a balance between performance efficiency and mechanical protection [21]. Sport-specific adaptations illustrate this principle: sprint and power athletes generally display higher tendon stiffness to maximize explosive performance, whereas endurance athletes present more compliant tendon profiles, which favor energy economy over prolonged periods [22,23]. Despite these general trends, the extent to which different sports, sex, and anthropometric characteristics interact to shape tendon mechanics
between performance efficiency and mechanical protection [21]. Sport-specific adaptations illustrate this principle: sprint and power athletes generally display higher tendon stiffness to maximize explosive performance, whereas endurance athletes present more compliant tendon profiles, which favor energy economy over prolonged periods [22,23]. Despite these general trends, the extent to which different sports, sex, and anthropometric characteristics interact to shape tendon mechanics in elite populations remains poorly defined. Deviations from sport-specific tendon mechanical optima increase tendinopathy risk, particularly in the frequently injured Achilles and patellar tendons [9,24,25]. Key correlates include sex (males exhibit greater stiffness, females greater compliance due to hormonal and morphological factors [26,27], anthropometry (taller athletes develop stiffer profiles under greater mechanical demands [28] and age (though elite training may modify typical age-related stiffening patterns [29]. Another understudied correlation is limb dominance, which may lead to asymmetries in tendon properties due to sport-specific unilateral load- ing[30,31] . However, few studies have systematically examined the laterality effects in elite populations across different sports disciplines. A recent study with highly trained athletes demonstrated that a 12-week heavy resistance training program increased Achilles and patellar tendon stiffness by 39% and 16%, respectively, alongside elevated biochemical markers of extracellular matrix remodeling [32]. These findings indicate that high-intensity exercise can promote adaptive tendon stiffening, which may counteract the age-related loss of compliance typically observed in sedentary individuals [22,29]. Nevertheless, the extent to which chronic, sport-specific loading in elite athletes offsets or modifies age- related changes remains unclear, given that their tendons are already exposed to extreme mechanical demands and long-term adaptations.
Physiologia2025,5, 56 3 of 21 Current literature limitations include the scarcity of multi-sport elite athlete data and the lack of comprehensive multivariate analyses of tendon mechanical correlates [33], highlighting the need for systematic investigation across diverse elite sporting pop- ulations. While previous Myoton studies in elite athletes have focused on single sports [4,34,35] or limited parameter sets, no study has comprehensively examined all five Myoton parameters across multiple elite sports with a systematic analysis of anthro- pometric and demographic correlates. Therefore, this study aimed to: (1) provide the first comprehensive multivariate analysis of Myoton-derived tendon properties across diverse elite sporting disciplines, (2) establish sport-specific and anthropometric correlates using advanced statistical modeling, including machine learning approaches, and (3) differenti- ate mechanical property patterns between Achilles and patellar tendons in elite athletes. We hypothesized that sport type would explain the largest variance in tendon properties (particularly for the Achilles tendon), with secondary effects of anthropometry (height, weight) and sex, while age and limb dominance would show minimal associations in this elite athlete population. 2. Results There was no missing data for the analyzed variables because the assessment protocol was completed for all recruited participants. According to Supplementary Table S1, males had significantly higher height, weight, and BMI than females (p< 0.05), while age was higher in females (Fisher’s exact test;p= 0.706). Table by sport. Table 1.Anthropometric and demographic characteristics of athletes by sport modality. Sport n Height (m) [95%CI] BMI (kg/m 2 ) [95%CI] Weight (kg) [95%CI] Age (Years) [95%CI] TL (h/wk) % Right Athletics * 7 1.76±0.08 [1.70, 1.82] ab 24.2±1.6 [22.9, 25.5] ab 74.1±11.2 [64.8, 83.4] ab 25.1±4.2 [21.6, 28.6] 16±2.5 85.7 Archery * 8 1.69±0.09 [1.62, 1.76] a 24.8±2.7 [22.7, 26.9] ab 70.6±10.2 [62.5, 78.7] a 27.6±6.3 [22.6, 32.6] 14±3.0 100 Boxing * 7 1.69±0.11 [1.60, 1.78] a 22.9±1.9 [21.3, 24.5] a 65.3±11.6 [55.0, 75.6] a 23.7±3.2 [21.0, 26.4] 15±2.0 100 Cycling 15 1.68±0.08 [1.64, 1.72] a 23.4±1.8 [22.4, 24.4] a 66.1±9.2 [61.1, 71.1] a 22.5±5.1 [19.8, 25.2] 18±4.0 93.3 Handball 15 1.77±0.07 [1.73, 1.81] b 25.6±3.3 [23.8, 27.4] b 80.5±11.8 [74.1, 86.9] b 25.9±4.7 [23.3, 28.5] 16±3.0 86.7
14±3.0 100 Boxing * 7 1.69±0.11 [1.60, 1.78] a 22.9±1.9 [21.3, 24.5] a 65.3±11.6 [55.0, 75.6] a 23.7±3.2 [21.0, 26.4] 15±2.0 100 Cycling 15 1.68±0.08 [1.64, 1.72] a 23.4±1.8 [22.4, 24.4] a 66.1±9.2 [61.1, 71.1] a 22.5±5.1 [19.8, 25.2] 18±4.0 93.3 Handball 15 1.77±0.07 [1.73, 1.81] b 25.6±3.3 [23.8, 27.4] b 80.5±11.8 [74.1, 86.9] b 25.9±4.7 [23.3, 28.5] 16±3.0 86.7 Judo 10 1.72±0.08 [1.67, 1.77] ab 29.4±5.0 [25.9, 32.9] c 83.0±20.4 [68.9, 97.1] b 25.7±4.3 [22.7, 28.7] 15±2.5 100 Karate 13 1.72±0.06 [1.69, 1.75] ab 24.1±2.6 [22.6, 25.6] ab 71.5±9.4 [66.0, 77.0] ab 25.5±5.0 [22.5, 28.5] 14±2.0 92.3 Volleyball 14 1.90±0.09 [1.85, 1.95] c 24.7±1.8 [23.7, 25.7] ab 89.6±11.6 [83.0, 96.2] c 25.6±3.3 [23.8, 27.4] 17±3.5 92.9 Statistics <0.001 0.002 <0.001 0.381 0.381 0.682 Note: equal letters indicate no statistically significant difference in the post hoc test. TL—training load. * Should be interpret with caution due to small sample size (n< 8). Training load is reported as mean±SD in hours per week. Volleyball athletes were significantly taller and heavier than athletes of other sports, while judo athletes had the highest BMI. Athletes in sports such as boxing and archery have lower anthropometric profiles. No significant differences were observed in age or lateral dominance between the different sports, indicating that these factors were not correlates of sports specialization in this sample. Table Achilles and patellar tendons according to limb dominance and sex. Significant bilateral
Physiologia2025,5, 56 4 of 21 differences in the Achilles tendon properties were observed, with right limb dominance demonstrating a higher frequency (t = 2.54,p= 0.012, d = 0.18) and stiffness (t = 2.32, p= 0.021, d = 0.16) than left limb dominance. Sex-based analysis showed that males exhib- ited significantly greater Achilles stiffness (t = 5.87,p< 0.001, d = 1.04), higher frequency (t = 4.92,p< 0.001,d = 0.83), and lower values for logarithmic decrement, relaxation time, and creep (allp< 0.01,d = 0.60–1.03), indicating stiffer and less viscous tendons. Signifi- cant sex differences were found for the patellar tendon in stiffness, relaxation, and creep (p< 0.01, d = 0.53–0.81), while no lateral asymmetry was detected for any parameter. Table 2.Descriptive analysis by limb dominance and sex for Achilles and patellar tendons. Variable Group Mean ±SD [95% CI] p-Value (Effect Size) Achilles tendon Frequency (Hz) Left 28.5 ±3.2 a [27.9–29.1] 0.012 (d = 0.18) Right 29.1 ±3.5 [28.4–29.8] Male 29.8 ±3.4 a [29.1–30.5] ≤0.001 (d = 0.83) Female 27.2 ±2.8 [26.5–27.9] Stiffness (N/m) Left 720 ±120 a [695–745] 0.021 (d = 0.16) Right 740 ±130 [715–765] Male 780 ±135 a [752–808] ≤0.001 (d = 1.04) Female 650 ±110 [625–675] Logarithmic decrement Left 0.98 ±0.25 [0.93–1.03] 0.154 Right 0.95 ±0.28 [0.89–1.01] Male 0.89 ±0.22 a [0.85–0.93] 0.008 (d = 0.60) Female 1.05 ±0.3 [0.98–1.12] Relaxation (ms) Left 7.2 ±1.5 [6.9–7.5] 0.089 Right 7.0 ±1.6 [6.7–7.3] Male 6.5 ±1.4 a [6.2–6.8] ≤0.001 (d = 0.92) Female 8.2 ±1.5 [7.8–8.6] Creep (mm) Left 0.48 ±0.1 [0.46–0.50] 0.102 Right 0.46 ±0.11 [0.44–0.48] Male 0.43 ±0.09 a [0.41–0.45] ≤0.001 (d = 1.03) Female 0.55 ±0.12 [0.52–0.58] Patellar tendon Frequency (Hz) Left 21.8 ±3.1 [21.1–22.5] 0.243 Right 21.5 ±3.4 [20.8–22.2] Male 21.2 ±3.5 a [20.5–21.9] 0.035 (d = 0.34) Female 22.3 ±2.8 [21.6–23.0] Stiffness (N/m) Left 580 ±135 [552–608] 0.187 Right 590 ±140 [561–619] Male 610 ±145 a [580–640] 0.009 (d = 0.53) Female 540 ±120 [515–565] Logarithmic decrement (dimensionless) Left 0.96 ±0.11 [0.94–0.98] 0.421 Right 0.95 ±0.12 [0.93–0.97] Male 0.94 ±0.1 [0.92–0.96] 0.112 Female 0.98 ±0.13 [0.95–1.01] Relaxation (ms) Left 9.3 ±2.1 [8.9–9.7] 0.305 Right 9.1 ±2.3
0.34) Female 22.3 ±2.8 [21.6–23.0] Stiffness (N/m) Left 580 ±135 [552–608] 0.187 Right 590 ±140 [561–619] Male 610 ±145 a [580–640] 0.009 (d = 0.53) Female 540 ±120 [515–565] Logarithmic decrement (dimensionless) Left 0.96 ±0.11 [0.94–0.98] 0.421 Right 0.95 ±0.12 [0.93–0.97] Male 0.94 ±0.1 [0.92–0.96] 0.112 Female 0.98 ±0.13 [0.95–1.01] Relaxation (ms) Left 9.3 ±2.1 [8.9–9.7] 0.305 Right 9.1 ±2.3 [8.7–9.5] Male 8.7 ±2.0 a [8.3–9.1] ≤0.001 (d = 0.81) Female 10.1 ±2.2 [9.6–10.6]
Physiologia2025,5, 56 5 of 21 Table 2.Cont. Variable Group Mean ±SD [95% CI] p-Value (Effect Size) Creep (mm) Left 0.59 ±0.14 [0.56–0.62] 0.188 Right 0.57 ±0.15 [0.54–0.60] Male 0.55 ±0.13 a [0.52–0.58] 0.002 (d = 0.65) Female 0.65 ±0.15 [0.61–0.69] Note: The supraindex a indicates a difference between limbs (right/left), as well as between sexes (male/female). Table After applying the Bonferroni correction for multiple comparisons, all significant differences in the Achilles tendon parameters remained (p< 0.05), whereas only relaxation time and creep retained significance for the patellar tendon. These results confirm that the sport- related effects were particularly robust for the Achilles tendon. Table 3.Biomechanical properties by sport discipline. Sport nFrequency (Hz) Stiffness (N/m) Logarithmic Decrement Relaxation (ms)Creep (mm) Achilles Cycling 15 27.8 ±2.9 a 675±85 a,b 1.02±0.18 a 7.8±1.1 a 0.51±0.08 a Roller Hockey12 30.2±1.8 b,c 805±75 c 0.89±0.2 b,c 6.5±0.8 b,c 0.43±0.07 b,c Karate 14 30.5±3.2 b,c 785±95 c 0.82±0.15 c 6.7±1.0 b 0.44±0.08 b,c Athletics 8 31.2 ±2.5 c 820±110 c 0.79±0.22 c 6.3±1.2 c 0.41±0.09 c Volleyball 13 32.1 ±3.8 c 865±130 d 0.75±0.19 c 5.9±1.3 c 0.39±0.1 c Taekwondo 8 26.8 ±3.5 a 645±120 a 0.98±0.25 a,b 8.2±1.5 a 0.53±0.11 a Judo 10 27.2 ±3.8 a 665±140 a 1.12±0.3 a 7.9±1.4 a 0.52±0.12 a p-value (η 2 ) <0.001 (0.24) <0.001 (0.29) <0.001 (0.22) <0.001 (0.27) <0.001 (0.25) Patellar Cycling 15 21.2 ±2.5 565 ±90 0.97 ±0.1 9.4 ±1.2 a 0.6±0.09 a Roller Hockey12 21.5 ±2.8 590 ±110 0.94 ±0.11 9.1 ±1.5 a 0.58±0.1 a,b Karate 14 21.8 ±3.5 610 ±125 0.93 ±0.12 8.8±1.8 a,b 0.56±0.11 a,b Athletics 8 22.1 ±3.1 625 ±135 0.91 ±0.13 8.5±1.6 b,c 0.54±0.1 b,c Volleyball 13 22.5 ±2.9 595 ±115 0.89 ±0.14 8.2 ±1.4 c 0.52±0.09 c Taekwondo 8 21.3 ±4.2 610 ±145 0.95 ±0.15 9.1 ±1.7 a 0.59±0.12 a Judo 10 22.8 ±3.7 630 ±135 0.99 ±0.16 9.8 ±1.9 a 0.63±0.13 a p-value (η 2 ) 0.325 (0.09) 0.215 (0.11) 0.418 (0.07) 0.012 (0.18) 0.008 (0.2) Note: Sports with different letters are significantly different (p< 0.05). The Achilles tendon showed significant differences across all five parameters (p≤0.001for all comparisons,
±4.2 610 ±145 0.95 ±0.15 9.1 ±1.7 a 0.59±0.12 a Judo 10 22.8 ±3.7 630 ±135 0.99 ±0.16 9.8 ±1.9 a 0.63±0.13 a p-value (η 2 ) 0.325 (0.09) 0.215 (0.11) 0.418 (0.07) 0.012 (0.18) 0.008 (0.2) Note: Sports with different letters are significantly different (p< 0.05). The Achilles tendon showed significant differences across all five parameters (p≤0.001for all comparisons, partialη 2= 0.22–0.29), with high-impact sports such as Volleyball and Athletics exhibiting significantly higher stiffness and frequency, along with lower logarithmic decrement, relaxation time, and creep. In contrast, combat sports (Judo and Taekwondo) displayed a more compliant tendon profile with greater elasticity. Signifi- cant differences for the patellar tendon were only observed in relaxation time (p= 0.012, η 2 = 0.18) and creep (p= 0.008,η 2= 0.2), with similar patterns across sports. Post hoc analyses confirmed that Volleyball and Athletics differed significantly (p< 0.05) from mar- tial arts across most Achilles tendon parameters, highlighting a clear spectrum of tendon adaptation based on mechanical demands. Height showed the strongest association with Achilles tendon properties. Robust positive correlations were observed between height and right Achilles stiffness (r = 0.532, 95% CI: 0.378–0.658,p< 0.001) and frequency (r = 0.521, 95% CI: 0.365–0.650,p< 0.001), with similar strong correlations for the left tendon (stiffness: r = 0.432, 95% CI: 0.267–0.575;
Physiologia2025,5, 56 6 of 21 frequency: r = 0.354, 95% CI: 0.178–0.511; bothp< 0.001). The non-overlapping confidence intervals between height-Achilles correlations (r > 0.35) and height-patellar correlations (all r < 0.3, 95% CIs:−0.089 to 0.275) confirm that height effects are significantly stronger for the Achilles tendon. Conversely, height was strongly negatively correlated with Achilles relaxation (r =−0.445, 95% CI:−0.585 to−0.284) and creep (r =−0.398, 95% CI:−0.548 to−0.228), indicating that taller athletes possess stiffer, less compliant Achilles tendons. Figure biomechanics in this study. Figure 1.Correlations between height (cm) and biomechanical properties of Achilles and patellar tendons.Y-axes show frequency (Hz), stiffness (N/m), logarithmic decrement (dimensionless), relaxation (ms), and creep (mm). Sample size:n= 111 elite athletes. Scatter plots show individual data points colored by sex (blue = male, red = female) with regression lines (black). Gray area represents the confidence interval of the regression line. Correlation coefficients (r) andp-values are displayed for each relationship. Sex showed the second strongest association with tendon properties, with effect sizes demonstrating clear practical significance. Males exhibited significantly stiffer Achilles tendons with large effect sizes: stiffness (Cohen’s d = 1.12, 95% CI: 0.68–1.56), frequency (d = 0.83, 95% CI: 0.42–1.24), and reduced compliance parameters including relaxation (d =−1.16, 95% CI:−1.61 to−0.71) and creep (d =−1.08, 95% CI:−1.52 to−0.64). The non-overlapping confidence intervals for Achilles sex effects (all |d| > 0.6) versus patellar sex effects (|d| < 0.5) confirm that sex differences are significantly more pronounced in the Achilles tendon. For the patellar tendon, only moderate effects were observed for stiffness (d = 0.53, 95% CI: 0.13–0.93) and relaxation (d =−0.81, 95% CI:−1.23 to−0.39), with overlapping confidence intervals indicating similar magnitude effects. Figure summarizes the sex-based differences in tendon biomechanics.
Physiologia2025,5, 56 7 of 21 Figure 2.Sex differences in biomechanical properties of Achilles and patellar tendons.Y-axes show frequency (Hz), stiffness (N/m), logarithmic decrement (dimensionless), relaxation (ms), and creep (mm). Sample sizes: malesn= 76, femalesn= 35. Box plots show median (center line), interquartile range (box), and whiskers extending to 1.5 times the interquartile range. Statistical comparisons show p-values and Cohen’s d effect sizes. Light blue = male, light coral = female. Sports disciplines showed substantial variance in Achilles tendon properties with very large effect sizes: frequency (F = 9.478,p< 0.001, partialη 2= 0.487, 95% CI:0.32–0.61), stiffness (F = 12.672,p< 0.001, partialη 2= 0.559, 95% CI: 0.41–0.68), logarithmic decrement (F = 8.552,p< 0.001, partialη 2 = 0.461, 95% CI: 0.30–0.59), relaxation (F = 11.099,p< 0.001, partialη 2= 0.526, 95% CI: 0.37–0.65), and creep (F = 9.016,p< 0.001, partialη 2= 0.474, 95% CI: 0.31–0.61). These effect sizes indicate that sport type explains 46–56% of Achilles tendon variance, representing very large practical effects (partialη 2> 0.40). In contrast, patellar tendon sport effects were significantly smaller with moderate effect sizes: frequency (F = 2.510,p= 0.010, partialη 2= 0.201, 95% CI: 0.08–0.35), stiffness (F = 2.362,p= 0.015, partialη 2= 0.191, 95% CI: 0.07–0.34), relaxation (F = 4.167,p< 0.001, partialη 2= 0.294, 95% CI: 0.15–0.45), and creep (F = 3.666,p< 0.001, partialη 2= 0.268, 95% CI: 0.13–0.42), with non-overlapping confidence intervals confirming that sport effects are significantly stronger for Achilles versus patellar tendons. Among the sports analyzed, volleyball players consistently exhibited the highest stiffness values. Cyclists demonstrated intermediate stiffness values with relatively high relaxation, and combat sports (judo, karate, and taekwondo) showed considerable variability. Figure in tendon properties.
Description
This study identifies correlates of tendon stiffness in elite athletes.