The whole thigh muscles are covered with the fascia lata, which could have morphological and mechanical features that match the underlying muscles' functions. In this study, we investigated the morphological and elastic properties of the human fascia lata taken from four (anterior, medial, lateral, and posterior) sites on the thigh of 17 legs of 12 cadavers (6 males and 6 females, 75-92 years). The thickness of the fascia lata was determined with a caliper. The interwoven collagen fiber's directions were measured and classified into longitudinal, transverse, and diagonal in two opposing directions, relative to the thigh. Tensile strength test along the longitudinal and transverse directions was performed, and the stiffness, Young's modulus, and hysteresis were determined. Fascia lata at the lateral site (0.8 ± 0.2 mm) was significantly thicker compared to other sites (0.2-0.3 mm). Fiber's directions showed substantial variability among sites, and longitudinally directed fibers were higher in proportion (28-32%) than those in other directions (20-27%) at all sites except for the posterior site. The stiffness and Young's modulus in the longitudinal direction (20-283 N/mm; 71.6-275.9 MPa, highest at the lateral site) were significantly higher than in the transverse direction (3-16 N/mm; 3.2-41.9 MPa, lowest at the lateral site). At the medial site, the proportion of the transversely directed fibers was higher in females than males, with higher stiffness and Young's modulus thereof. The present study shows that the fascia lata possesses site- and gender-dependence of the morphological characteristics and elastic properties.

PurposeInstrument-assisted soft tissue mobilization (IASTM) has been reported to improve joint range of motion (flexibility). However, it is not clear whether this change in the joint range of motion is accompanied by any alterations in the mechanical and/or neural properties. This study aimed to investigate the effects of IASTM in plantarflexors and Achilles tendon on the mechanical and neural properties of them.MethodsThis randomized, controlled, crossover study included 14 healthy volunteers (11 men and 3 women, 21–32 yr). IASTM was performed on the skin over the posterior part of the lower leg for 5 min and targeted the soft tissues (gastrocnemii, soleus, and tibialis posterior muscles; overlying deep fascia; and Achilles tendon). As a control condition, the same participants rested for 5 min between pre- and postmeasurements without IASTM on a separate day. The maximal ankle joint dorsiflexion angle (dorsiflexion range of motion), the peak passive torque (stretch tolerance), and the ankle joint stiffness (slope of the relationship between passive torque and ankle joint angle) during the measurement of the dorsiflexion range of motion and muscle stiffness of the triceps surae (using shear wave elastography) were measured before and immediately after the interventions.ResultsAfter IASTM, the dorsiflexion range of motion significantly increased by 10.7% ± 10.8% and ankle joint stiffness significantly decreased by −6.2% ± 10.1%. However, peak passive torque and muscle stiffness did not change. All variables remained unchanged in the repeated measurements of controls.ConclusionIASTM can improve joint range of motion, without affecting the mechanical and neural properties of the treated muscles.

It is unclear whether the superiority of eccentric over concentric training on neuromuscular improvements is due to higher torque (mechanical loading) achievable during eccentric contractions or due to resulting greater total work.PurposeThis study aimed to examine neuromuscular adaptations after maximal eccentric versus concentric training matched for total work.MethodsTwelve males conducted single-joint isokinetic (180°·s−1) maximal eccentric contractions of the knee extensors in one leg (ECC-leg) and concentric in the other (CON-leg), 6 sets per session (3–5 sets in the initial 1–3 sessions), 2 sessions per week for 10 wk. The preceding leg performed 10 repetitions per set. The following leg conducted the equivalent volume of work. In addition to peak torque during training, agonist EMG and MRI-based anatomical cross-sectional area (ACSA) and transverse relaxation time (T2) at midthigh as reflective of neural drive, hypertrophy, and edema, respectively, were assessed weekly throughout the training period and pre- and posttraining. Whole muscle volume was also measured pre- and posttraining.ResultsTorque and EMG (in trained contraction conditions) significantly increased in both legs after week 1 (W1) and week 4 (W4), respectively, with a greater degree for ECC-leg (torque +76%, EMG +73%: posttraining) than CON-leg (+28%, +20%). ACSA significantly increased after W4 in ECC-leg only (+4%: posttraining), without T2 changes throughout. Muscle volume also increased in ECC-leg only (+4%). Multiple regression analysis revealed that changes (%Δ) in EMG solely explained 53%–80% and 30%–56% of the total variance in %Δtorque through training in ECC-leg and CON-leg, respectively, with small contributions (+13%–18%) of %ΔACSA for both legs.ConclusionEccentric training induces greater neuromuscular changes than concentric training even when matched for total work, whereas most of the strength gains during 10-wk training are attributable to the increased neural drive.

This study examined localization of muscle damage within the quadriceps femoris induced by different types of eccentric exercises by using transverse relaxation time (T 2 )-weighted magnetic resonance imaging (MRI). Thirty-three young males performed either of the following three exercises: single-joint eccentric contraction of the knee extensors (KE), eccentric squat (S), or downhill walking (DW) (n=11/exercise). KE and S consisted of 5-set×10-lowering of 90% one-repetition maximum load. DW was performed for 60 minutes with −10% slope, 6 km/h velocity, and 20% body mass load carried. At pre-and 24-, 48-, and 72-hours post-exercise, T 2 -MRI was scanned and T 2 values for the rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL), and vastus medialis (VM) at proximal, middle, and distal sites were calculated. Additionally, soreness felt when static pressure was applied to these sites and maximal isometric knee extension torque were measured. Maximal torque significantly (P<.05) decreased (7%-15%) at 24-48 hours after all exercises. T 2 significantly increased (3%-9%) at 24-72 hours after all exercises, with heterogeneities within the muscles found in each exercise. Effect size and peak change of T 2 , as well as soreness, overall indicated that the proximal RF after KE and middle VM after S and DW were most affected by these exercises. The VL did not show any significant T 2 increase after all exercises. These results suggest that muscle damage specifically localizes at the proximal RF by KE and at the middle VM by S and DW, while the VL is least damaged regardless of the exercises. K E Y W O R D Sdownhill walking, knee extension, maximal strength, muscle soreness, squat, T 2 -MRI

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The human triceps surae (two gastrocnemii and soleus) has aponeuroses in the proximal and distal aspects, the latter of which insert into the calcaneus by sharing the common Achilles tendon. These tendinous tissues are known to have elasticity and upon muscle contraction the aponeurosis is stretched both longitudinally (along the muscle’s line of action) and transversely. Higher aponeurosis transverse deformability has been documented, but there is a paucity of information on the morphology and mechanical properties of human aponeurosis. This study aimed to identify morphological and mechanical characteristics of the human triceps surae aponeuroses. Twenty-five triceps surae muscle-tendon units were procured from 13 human donors (formalin fixed, 6 males, 7 females) aged 67–91 years. Specimens of aponeuroses were excised from the eight regions (posterior and anterior regions of the gastrocnemius medialis and lateralis, medial and lateral parts of soleus; proximal, middle, and distal sites each, 2–4 cm × 2–4 cm). Aponeurosis thickness was measured using a digital caliper. Uniaxial tensile tests were implemented to determine the mechanical properties of specimens loaded longitudinally (along the muscle’s line of action) and transversely. The aponeurosis thickness showed significant differences between muscles and sites, while Young’s modulus showed direction-dependent (longitudinal vs. transverse) differences within sites. Results show different morphology and mechanical properties of aponeuroses between synergist muscles. The reason for site-dependent differences in stiffness is due to a reduced aponeurosis thickness rather than a reduction in the material property. The anisotropic elastic feature (differences between longitudinal and transverse directions) of the aponeuroses was more pronounced than previous in vivo findings, suggesting inherent material design of the aponeurosis that matches three-dimensional contractile behavior of muscle fibers.

The main aim was to examine the load bearing of individual hamstring muscles in different contraction types and intensities, through local stiffness measurement by shear wave elastography (SWE). A secondary aim was to examine the relationship between the SWE stiffness measure and hamstrings morphology. Ten healthy males (age 22.1±4.1 years; height 173.7±5.9 cm; body mass 68.6±12.4 kg; mean ± SD) performed knee flexions on an isokinetic dynamometer at different intensities (20–70%MVC, random order) in three separate, randomized conditions: isometric (ISO), concentric (CON) and eccentric (ECC). SWE was used to measure muscle shear wave velocity (SWV) in biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) during contraction. Muscle anatomical cross-sectional area (ACSA) was measured with magnetic resonance imaging and muscle architecture with B-mode ultrasonography. Muscle SWV increased linearly with contraction intensity, but at a varying rate among muscles and contraction types. ST exhibited greater SWV than BFlh and SM in all contraction types, however, there was an upward shift in the SM SWV–torque relationship in ECC compared to ISO and CON. Strong negative correlations were found between peak ISO SWV and ST ACSA (r = -0.81, p = 0.005) and BFlh pennation angle (r = -0.75, p = 0.012). These results suggest that ST has a primary role in hamstrings load bearing in all contraction types, likely due to its morphology; however, there is evidence of increased contribution from SM in eccentric muscle actions.

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