Achilles Tendon Stiffness: Influence of Measurement Methodology.

OBJECTIVE: Mechanical stiffness derived from force-elongation curves is fundamentally different from shear wave (SW) elastography-based tissue properties. We compared these techniques, with a total of five methods of assessing Achilles tendon (AT) stiffness. METHODS: Seventeen participants (12 male and 5 female) with unilateral AT rupture performed submaximal contractions at 30% and 10% maximal isometric contraction torque of the un-injured limb. SW velocity was acquired at rest. Force-elongation curves were assessed from the free AT and the medial gastrocnemius (MG) tendon. Mechanical stiffness was determined near the end of the linear region of the force-elongation curve and from the toe region. Bivariate correlations between mechanical stiffness and SW velocity, as well as pairwise t-tests between limbs, were computed. RESULTS: In the injured limb, SW velocity correlated with MG tendon and free AT toe-region stiffness during 10% (r = 0.59, p = 0.020 and r = 0.60, p = 0.011, respectively) and 30% of submaximal contractions (r = 0.56, p = 0.018 and r = 0.67, p = 0.004, respectively). The un-injured limb showed no associations. In both limbs pooled together, SW velocity correlated with MG tendon toe-region stiffness in 30% of submaximal contractions (r = 0.43, p = 0.012). Free tendon mechanical stiffness was lower in the injured limb, with a mean difference of 148.5 Nmm⁻¹ (95% CI: 35.6-261.3, p = 0.013), while SW velocity was higher in the injured limb (1.67 m × s⁻¹, 95% CI; -2.4 to -0.9, p < 0.001). CONCLUSION: SW elastography may reflect AT viscoelastic properties at the initial slope of the force-length curve with strains <1% but cannot offer insight into AT mechanics at higher loads. Extended toe regions in the injured limb could have caused the association between mechanical stiffness and SW-based stiffness.

Early Predictors of Recovery From Nonoperatively Treated Achilles Tendon Rupture: 1 Year Follow-Up Study.

PURPOSE: To investigate early structural and mechanical predictors of plantarflexor muscle strength and the magnitude of Achilles tendon (AT) nonuniform displacement at 6 and 12 months after AT rupture. METHODS: Thirty-five participants (28 males and 7 females; mean ± SD age 41.7 ± 11.1 years) were assessed for isometric plantarflexion maximal voluntary contraction (MVC) and AT nonuniformity at 6 and 12 months after rupture. Structural and mechanical AT and plantarflexor muscle properties were measured at 2 months. Limb asymmetry index (LSI) was calculated for all variables. Multiple linear regression was used with the 6 and 12 month MVC LSI and 12 month AT nonuniformity LSI as dependent variables and AT and plantarflexor muscle properties at 2 months as independent variables. The level of pre- and post-injury sports participation was inquired using Tegner score at 2 and 12 months (scale 0-10, 10 = best possible score). Subjective perception of recovery was assessed with Achilles tendon total rupture score (ATRS) at 12 months (scale 0-100, 100=best possible score). RESULTS: Achilles tendon resting angle (ATRA) symmetry at 2 months predicted MVC symmetry at 6 and 12 months after rupture (ß = 2.530, 95% CI 1.041-4.018, adjusted R2 = 0.416, p = 0.002; ß = 1.659, 95% CI 0.330-2.988, adjusted R2 = 0.418, p = 0.016, respectively). At 12 months, participants had recovered their pre-injury level of sports participation (Tegner 6 ± 2 points). The median (IQR) ATRS score was 92 (7) points at 12 months. CONCLUSION: Greater asymmetry of ATRA in the early recovery phase may be a predictor of plantarflexor muscle strength deficits up to 1 year after rupture. TRIAL REGISTRATION: This research is a part of "nonoperative treatment of Achilles tendon rupture in Central Finland: a prospective cohort study" that has been registered in ClinicalTrials.gov (NCT03704532).

Achilles tendon and triceps surae muscle properties in athletes.

PURPOSE: The aim of this study was to investigate internal Achilles tendon (AT) displacement, AT shear wave velocity (SWV), and triceps surae (TS) muscle shear modulus in athletes. METHODS: Internal AT displacement was assessed using ultrasound during isometric contraction. Shear wave elastography was used to assess AT SWV (m × s-1) at rest and TS muscle shear modulus (kPa) during passive ankle dorsiflexion. RESULTS: A total of 131 athletes participated in this study. Athletes who had not exercised within two days had greater AT non-uniformity and mean anterior tendon displacement, and lower SWV at the proximal AT measurement site (mean difference [95% CI]: 1.8 mm [0.6-2.9], p = 0.003; 1.6 mm [0.2-2.9], p = 0.021; - 0.9 m × s-1 [- 1.6 to - 0.2], p = 0.014, respectively). Male basketball players had a lower mean AT displacement compared to gymnasts (- 3.7 mm [- 6.9 to - 0.5], p = 0.042), with the difference localised in the anterior half of the tendon (- 5.1 mm [- 9.0 to - 1.1], p = 0.022). Male gymnasts had a smaller absolute difference in medial gastrocnemius-minus-soleus shear modulus than basketball players (59.6 kPa [29.0-90.2], p < 0.001) and track and field athletes (52.7 kPa [19.2-86.3], p = 0.004). Intraclass correlation coefficients of measurements ranged from 0.720 to 0.937 for internal AT displacement, from 0.696 to 0.936 for AT SWE, and from 0.570 to 0.890 for TS muscles. CONCLUSION: This study provides a reliability assessment of muscle and tendon SWV. The relative differences in passive TS muscle shear modulus suggest sport-specific adaptation. Importantly, in healthy individuals, lower AT displacement after exercise may reflect the time required for tendon recovery.

Exploration of muscle-tendon biomechanics one year after Achilles tendon rupture and the compensatory role of flexor hallucis longus.

Achilles tendon (AT) rupture leads to long-term structural and functional impairments. Currently, the predictors of good recovery after rupture are poorly known. Thus, we aimed to explore the interconnections between structural, mechanical, and neuromuscular parameters and their associations with factors that could explain good recovery in patients with non-surgically treated AT rupture. A total of 35 patients with unilateral rupture (6 females) participated in this study. Muscle-tendon structural, mechanical, and neuromuscular parameters were measured 1-year after rupture. Interconnections between the inter-limb differences (Δ) were explored using partial correlations, followed by multivariable linear regression to find associations between the measured factors and the following markers that indicate good recovery: 1) tendon length, 2) tendon non-uniform displacement, and 3) flexor hallucis longus (FHL) normalized EMG amplitude difference between limbs. Δmedial gastrocnemius (MG) (ß = -0.12, p = 0.007) and Δlateral gastrocnemius (ß = -0.086, p = 0.030) subtendon lengths were associated with MG tendon Δstiffness. MG (ß = 11.56, p = 0.003) and soleus (ß = 2.18, p = 0.040) Δsubtendon lengths explained 48 % of variance in FHL EMG amplitude. Regression models for tendon length and non-uniform displacement were not significant. Smaller inter-limb differences in Achilles subtendon lengths were associated with smaller differences in the AT stiffness between limbs, and a smaller contribution of FHL muscle to the plantarflexion torque. In the injured limb, the increased contribution of FHL appears to partially counteract a smaller contribution from MG due to the elongated tendon, however the role of FHL should not be emphasized during rehabilitation to allow recovery of the TS muscles.

In vivo localized gastrocnemius subtendon representation within the healthy and ruptured human Achilles tendon.

The Achilles tendon (AT) is composed of three distinct in-series elastic subtendons, arising from different muscles in the triceps surae. Independent activation of any of these muscles is thought to induce sliding between the adjacent AT subtendons. We aimed to investigate displacement patterns during voluntary contraction (VOL) and selective transcutaneous stimulation of medial (MGstim) and lateral (LGstim) gastrocnemius between ruptured and healthy tendons and to examine the representative areas of AT subtendons. Twenty-eight patients with unilateral AT rupture performed bilateral VOL at 30% of the maximal isometric uninjured plantarflexion torque. AT displacement was analyzed from sagittal B-mode ultrasonography images during VOL, MGstim, and LGstim. Three-way ANOVA revealed a significant two-way interaction of contraction type × location on the tendon displacement [F(10-815) = 3.72, P < 0.001]. The subsequent two-way analysis revealed a significant contraction type × location interaction for tendon displacement [F(10-410)=3.79, P < 0.001] in the uninjured limb only, where LGstim displacement pattern was significantly different from MGstim (P = 0.008) and VOL (P = 0.005). When comparing contraction types between limbs, there were no difference in the displacement patterns, but displacement amplitudes differed. There was no significant difference in the location of maximum or minimum displacement between limbs. The displacement pattern was not different in nonsurgically treated compared with uninjured tendons 1 yr after rupture. However, free tendon stiffness seems to be lower in the injured AT, leading to more displacement during electrically induced contractions compared with the uninjured. Our results suggest that near the calcaneus, LG subtendon is located in the most anterior region adjacent to medial gastrocnemius.NEW & NOTEWORTHY Using selective electrical stimulation, we report the distributions of medial and lateral gastrocnemius subtendon representations within the healthy and ruptured Achilles tendon. In the majority of our sample, lateral gastrocnemius subtendon was found in the most anterior region adjacent to medial gastrocnemius both in the healthy and ruptured, nonsurgically treated tendon. The tendon internal displacement pattern does not seem to differ, but displacement amplitude and nonuniformity differed between healthy and ruptured tendons 1 yr after rupture.

Muscle-tendon morphomechanical properties of non-surgically treated Achilles tendon 1-year post-rupture.

BACKGROUND: Achilles tendon rupture appears to alter stiffness and length of the tendon. These alterations may affect the function of tendon in force transmission and in energy storage and recovery. We studied the mechanical properties of the Achilles' tendon post-rupture and their association with function. METHODS: Twenty-four (20 males, 4 females) participants (mean age: 43 y, 176 cm, 81 kg) were recruited. Ultrasonography and dynamometry were used to assess the muscle-tendon unit morphological and mechanical properties of non-surgically treated patients 1-year post rupture. FINDINGS: Injured tendons were longer with difference of 1.8 cm (95%CI: 0.5-1.9 cm; P < 0.001), and thicker by 0.2 mm (0.2-0.3 mm; P < 0.01). Medial gastrocnemius cross-sectional area was 1.0 cm2 smaller (0.8-1.1 cm2; P < 0.001), fascicles were 0.6 cm shorter (0.5-0.7 cm; P < 0.001) and pennation angle was 2.5° higher (1.3-3.6°; P < 0.001) when compared to the uninjured limb. We found no differences between injured and uninjured tendon stiffness 1-year post-rupture (mean difference: 29.8 N/mm, -7.7-67.3 N/mm; P = 0.170). The injured tendon showed 1.8 mm (1.2-2.4 mm; P < 0.01) lower elongation during maximal voluntary isometric contractions. Patient-reported functional outcome was related to the tendon resting length (ß = 0.68, r(10) = 4.079, P = 0.002). Inter-limb differences in the medial gastrocnemius fascicle length were related to inter-limb differences in maximum contractions (ß = 1.17, r(14) = 2.808, P = 0.014). INTERPRETATION: Longer Achilles tendon resting length was associated with poorer self-evaluated functional outcome. Although the stiffness of non-surgically treated and uninjured tendons was similar 1-year post rupture, plantar flexion strength deficit was still present, possibly due to shorter medial gastrocnemius fascicle length.

Warm-Up and Hamstrings Stiffness, Stress Relaxation, Flexibility, and Knee Proprioception in Young Soccer Players.

CONTEXT: Nerves or fascia may limit motion in young soccer players, thereby contributing to frequent hamstrings injuries. Nerve-gliding exercises and self-myofascial release techniques may enhance range of motion (ROM). OBJECTIVE: To compare the immediate effect of foam rolling (FR) and neurodynamic nerve gliding (NDNG) on hamstrings passive stiffness, viscoelasticity, flexibility, and proprioception during the warm-up of soccer players. DESIGN: Crossover study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 15 male soccer players (age = 18.0 ± 1.4 years, height = 183.1 ± 6.0 cm, mass = 76.9 ± 7.8 kg) on the same team. INTERVENTION(S): The FR and NDNG consisted of 6 sets of 45 seconds with a 15-second rest between sets. Over a 2-week period, participants performed FR and NDNG on 2 separate occasions. MAIN OUTCOME MEASURE(S): Stiffness (between 50% and 80%, and 85% and 95% [STFmax] of maximal knee-extension ROM), viscoelasticity (stress-relaxation test), knee-extension ROM, hamstrings passive-resistance torque (PRT), hip-flexion angle (straight-leg raise test), and active knee-joint position sense. RESULTS: We observed an interaction between time and intervention for STFmax (F1,17 = 5.024, P = .042), knee-extension ROM (F1,17 = 7.371, P = .02), and PRT (F1,17 = 4.876, P = .044). The NDNG technique induced increases in STFmax (t17 = 2.374, P = .03), ROM (t17 = 2.843, P = .01), and PRT (t17 = 2.982, P = .008). Both NDNG and FR led to improved performance on the straight-leg raise test (F1,17 = 87.514, P < .001). No interaction or main effect was found for the stress-relaxation test or active knee-joint position sense. CONCLUSIONS: Adding NDNG to the warm-up routine increased ROM more than FR and may benefit soccer players.

Immediate effects of neurodynamic nerve gliding versus static stretching on hamstring neuromechanical properties.

PURPOSE: We investigated the immediate effects of neurodynamic nerve gliding (ND) on hamstring flexibility, viscoelasticity, and mechanosensitivity, compared with traditional static stretching (ST). METHODS: Twenty-two physically active men aged 21.9 ± 1.9 years were divided randomly into two equal intervention groups using ST or ND. An isokinetic dynamometer was used to measure the active knee joint position sense, perform passive knee extension, record the passive extension range of motion (ROM) and the passive-resistive torque of hamstrings. Stiffness was determined from the slope of the passive torque-angle relationship. A stress relaxation test (SRT) was performed to analyze the viscoelastic behavior of the hamstrings. The passive straight leg raise (SLR) test was used to evaluate hamstring flexibility. RESULTS: A significant interaction was observed for ROM and passive ultimate stiffness, reflected by an increase in these indicators after ND but not after SD. SLR increased significantly in both groups. After ST, a significantly faster initial stress relaxation was observed over the first 4 s. than after ND. There was no significant change in the active knee joint position sense. CONCLUSIONS: ND provided a slightly greater increase in hamstring extensibility and passive stiffness, possibly by decreasing nerve tension and increasing strain in connective tissues than ST. The ST mostly affected the viscoelastic behavior of the hamstrings, but neither intervention had a significant impact on proprioception.