Variation in the origin of the plantar aponeurosis and its relationship to the origin of the abductor hallucis muscle.

The plantar aponeurosis comprises medial, central, and lateral bands, which arise from the calcaneal tuberosity. Descriptions of the origin of the abductor hallucis vary among different textbooks. The central band and abductor hallucis muscles are related to the windlass mechanism. Given the uncertainties regarding the details of the origins of the central band and the abductor hallucis muscle, we examined those origins in 100 feet of 50 cadavers (25 males and 25 females) by dissection. There were three central band patterns, depending on the attachment sites of the origins of the central and lateral bands: Pattern Ia, the central band covers the lateral band completely; Pattern Ib, the central band covers part of the lateral band; Pattern II, the lateral band covers part of the central band. The origin of the abductor hallucis muscle was confirmed. It showed two types of variation: attachment type, originating from the central band; non-attachment type, not originating from the central band. Central band Patterns Ia, Ib, and II were found in 23 feet (17 males, 6 females), 24 feet (25 males, 28 females), and 24 feet (eight males, 16 females), respectively. Pattern Ia predominated in males and Pattern II in females. The attachment and non-attachment types of abductor hallucis muscle were observed in 28 feet (28%) and 72 feet (72%), respectively. The attachment type with Patterns Ia, Ib, and II was shown in 17 feet, 10 feet, and one foot, respectively. Thus, we revealed variation and sex differences in the central band, which could affect foot morphology and the efficacy of the windlass mechanism.

Regional variations and sex-related differences of stiffness in human tracheal ligaments.

PURPOSE: There have been numerous studies focused on the stiffness of tracheal cartilage. However, no research has been conducted specifically on the annular ligament, nor have any regional differences in the annular ligament been identified. The purpose of this study was to investigate the stiffness of the ligaments present between the thyroid, cricoid and tracheal cartilages. METHODS: The ligaments were identified in the cervical region of living subjects with ultrasonography. The stiffness of the ligaments was measured from the body surface using a digital palpation device (MyotonPRO). Since it is impossible to measure the entire trachea in a living subject, an additional measurement was performed on human cadavers. RESULTS: Both in vivo and cadaveric investigations found that the stiffness of annular ligaments decreased gradually from the superior to inferior parts. There was no difference in the stiffness between males and females in the superior part of the trachea. However, the stiffness of the middle and inferior parts was predominantly higher in females than in males. Furthermore, males showed significant differences in stiffness between the superior and middle parts, while females showed no significant differences. CONCLUSION: These results reveal that there are regional and sex-related differences in the stiffness of human tracheal ligaments.

Assessing site-specificity of the biomechanical properties of hamstring aponeuroses using MyotonPRO: A cadaveric study.

BACKGROUND: Hamstring muscles are the most frequently reported sites of muscle strain injuries, especially near the bi-articular muscles' myotendinous junction, where aponeurosis provides a connective tissue network linking muscle fibers to the tendon. This study aimed to investigate the reliability and site-specific differences of hamstring aponeuroses under different conditions (formalin and urea) using MyotonPRO. METHODS: Eight hamstring muscle groups were dissected from four human cadavers (two males and two females) aged 83-93 years. Measurements of the mechanical properties of the aponeuroses from the superficial and deep regions of biceps femoris long head, semitendinosus, and semimembranosus (after formalin solution immersion) were done using MyotonPRO (intra-rater reliability was examined within a 24-h interval), following which the hamstring aponeuroses were measured using a similar procedure after urea solution immersion. FINDINGS: Test-retest (intra-rater) results revealed that the MyotonPRO measurement of tone, stiffness, relaxation, and creep of cadaveric aponeuroses presented good to excellent reliability (ICC: 0.86 to 0.98). There were no significant differences in tone, stiffness, elasticity, relaxation, and creep among the six sites of hamstring aponeuroses under both formalin and urea conditions. Significant differences between formalin and urea conditions were found in the tone, stiffness, relaxation, and creep of hamstring aponeuroses (P < 0.05). INTERPRETATION: These results suggested that the biomechanical properties of hamstring aponeuroses showed homogeneity between the sites using MyotonPRO. Urea solution could potentially neutralize the effect of formalin on the biomechanical properties of cadaveric muscle-aponeurosis-tendon units. The present findings might influence the design of subsequent cadaveric studies on hamstring muscle strains.

Time-varying and speed-matched model for the evaluation of stroke-induced changes in ankle mechanics.

The ankle mechanics (stiffness and moment) are modulated continuously when interacting with the environment during human walking. However, it remains unclear how ankle mechanics vary with walking speeds, and how they are affected by stroke. This study aimed to determine time-varying ankle stiffness and moment in stroke participants during walking, comparing them with healthy participants at matched speeds. A motion capture system, surface electromyography (EMG) system and force plates were used to measure biomechanics of seven healthy participants walking at 5 controlled speeds and ten patients with stroke at self-selected speeds. The ankle moment and stiffness during the stance phase were calculated using an EMG-driven musculoskeletal model. Surface equations of ankle moment and stiffness in healthy participants, with walking speed and stance phase as variables, were proposed based on polynomial fitting. Results showed that as walking speed increased, there was an increase in the ankle stiffness and moment of healthy participants during 77 %-89 % and 63 %-91 % of stance phase, respectively. Patients with stroke had lower ankle stiffness and moment at self-selected walking speed than healthy participants at 1.04 m/s walking speed during 52 %-87 % and 52 %-91 % of stance phase, respectively. At matched walking speed, the peak values of ankle stiffness and moment in patients with stroke were significantly less than those in healthy participants (p = 0.007; p = 0.028, respectively). This study proposes a novel approach to evaluate the ankle mechanics of patients with stroke using the speed-matched model of healthy participants and may provide insights into understanding speed-dependent movement mechanisms of human walking.

Biomechanical assessment of gastrocnemii and Achilles tendon using MyotonPRO: in vivo measurements, and preliminary in situ measurements using formalin-fixed tissues.

PURPOSE: This study aims to evaluate the reliability and validity of using MyotonPRO to quantify the mechanical properties of the muscle-tendon unit through in vivo measurements and preliminary in situ measurements using formalin-fixed tissues. MATERIALS AND METHODS: The mechanical properties of gastrocnemii and the Achilles tendon of 12 healthy adults (six males and six females, 34.9 ± 5.8 years) were examined for in vivo test twice within a day and once post-24 hours using MyotonPRO, while nine human cadavers (formalin-fixed, 3 males and 6 females, 89.9 ± 5.1 years) were assessed for preliminary in situ test with identical time schedule to evaluate the within-day and inter-day reliability and validity. RESULTS: In vivo tests had very high within-day (ICC: 0.96-0.99) and inter-day reliability (ICC: 0.83-0.96), while in situ tests (formalin-fixed tissues) showed high within-day (ICC: 0.87-0.99) and inter-day reliability (ICC: 0.76-0.98) for the results of tone and stiffness. There was no significant difference in the stiffness of the free part of the Achilles tendon between in vivo and in situ conditions. The stiffness of the lateral gastrocnemius (r = 0.55, p = 0.018), proximal part of the Achilles tendon (r = 0.56, p = 0.015), and free part of the Achilles tendon (r = 0.47, p = 0.048) before removing the skin was significantly correlated with that after removing the skin condition. CONCLUSIONS: The findings of the current study suggest that MyotonPRO is reliable and valid for evaluating tendon stiffness both in vivo and in situ (formalin-fixed tissues).

Fatigue-induced changes in hamstrings' active muscle stiffness: effect of contraction type and implications for strain injuries.

PURPOSE: Hamstring strain injuries may occur due to differential fatigue and compromised mechanical properties among the hamstring muscles. We examined (1) the effect of fatigue on hamstrings active muscle stiffness, and (2) whether contraction type affects active muscle stiffness changes during a submaximal fatiguing task. METHODS: Nine healthy males completed 99 submaximal knee flexions in isometric (ISO), concentric (CON), and eccentric (ECC) conditions. We measured the knee flexor maximal voluntary torque (MVT) (pre/post), shear wave velocity (SWV) during contraction and transverse relaxation times (T2) (pre/post) in biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles. RESULTS: MVT decreased substantially after all conditions (- 18.4 to - 33.6%). The average relative torque sustained during the task was lower in CON than ISO and ECC, but absolute torque was similar. SWV interindividual responses were highly variable across muscles and contraction types. On average, BFlh SWV tended to increase in ISO (0.4 m/s, 4.5%, p = 0.064) but decreased in ECC condition (- 0.8 m/s, - 7.7%, p < 0.01). ST SWV decreased in CON (- 1.1 m/s, - 9.0%, p < 0.01), while it remained unchanged in ISO and ECC. SM SWV decreased in CON (- 0.8 m/s, - 8.1%, p < 0.01), but it was unaffected in ISO and variable in ECC. CONCLUSION: Fatigue has a differential effect on the mechanical properties of the constituent hamstring muscles, as measured with shear wave elastography, depending upon contraction type. We found preliminary evidence that BFlh is more fatigued than ST or SM during eccentric contractions, which may explain its susceptibility to strain injuries.

Relationship between attachment site of tibialis anterior muscle and shape of tibia: anatomical study of cadavers.

BACKGROUND: Tibialis anterior (TA) muscle is the largest dorsiflexor of the ankle joint and plays an important role during gait movement. However, descriptions of the TA attachment site are inconsistent even among major anatomy textbooks, and its origin, especially the attachment site for the tibia, has not been reported in detail. This study is the first experimental attempt to investigate the origin of the TA in detail, paying particular attention to the relationship with the shape of the tibia, including sex differences. METHODS: Forty legs (20 males, 20 females) from twenty Japanese cadavers were examined. Gross anatomical examination of the TA's attachment site to the tibia and the tibia's shape was performed. RESULTS: The location of the distal end of the TA's attachment on tibia was significantly more distal in males than in females (p < 0.01). The anterior border of the tibia had a gentle S-like curve, with a medially convex curve in the proximal region and a laterally convex curve in the distal region in frontal plane. The most protruding point of the distal curve of the anterior border located significantly more proximal in females than in males (p = 0.02). CONCLUSIONS: There were sex differences in the distal end of the attachment site on tibia of the TA and the shape of the tibia. Consequently, the variations in the attachment site of TA were considered to provide for differences in function of TA. In males, the TA may enable advantageous power exertion, whereas in females it may work efficiently for dorsiflexion of ankle, respectively. Sex differences in TA's attachment site and the shape of the tibia may be involved in gait movement as well as frequency of lower leg disorders such as chronic exertional compartment syndrome.

Investigation of the association between human fascia lata thickness and its neighboring tissues' morphology and function using B-mode ultrasonography.

The fascia lata is a membrane tissue which envelopes all thigh muscles and connects with the subcutaneous adipose tissues through loose connective tissues. It is presumable that the morphology of the fascia lata is strongly affected by the unique properties of underlying thigh muscles and subcutaneous adipose tissues. We aimed to investigate the relationships between characteristics of the fascia lata and adjoining adipose tissues and underlying muscles. Twenty healthy people were recruited (25 ± 3 years, 167.1 ± 8.5 cm, 62.5 ± 13.2 kg). The thickness of the skeletal muscles (rectus femoris, vastus lateralis, biceps femoris, and semitendinosus), and their overlying fascia lata and subcutaneous adipose tissues were measured by B-mode ultrasonography. Isometric knee extension and flexion torque during maximal voluntary contraction were also tested. The fascia lata thickness demonstrated site-dependent differences (vastus lateralis: 0.91 ± 0.20 mm > rectus femoris, biceps femoris, and semitendinosus: 0.56-0.69 mm, p < 0.01). Furthermore, there were large individual variations in the fascia lata thickness even in the same region of the thigh. The fascia lata showed positive simple correlations with height (rectus femoris: r = 0.39 p = 0.01, semitendinosus: r = 0.37 p < 0.05), body mass (rectus femoris: r = 0.59, p < 0.01, vastus lateralis: r = 0.47, p < 0.01, semitendinosus: r = 0.55, p < 0.01), corresponding muscle thickness (rectus femoris: r = 0.39, p < 0.05, semitendinosus: r = 0.74, p < 0.01) and knee extension (rectus femoris: r = 0.52, p < 0.01, vastus lateralis: r = 0.40, p < 0.01) and flexion (semitendinosus: r = 0.41, p < 0.01) torques. After adjusting for the influence of height and/or body mass, the fascia lata thickness showed a partial correlation only with the skeletal muscle thickness at the semitendinosus (r = 0.61, p < 0.01). The present study revealed that the fascia lata has site-specific differences of the thickness, which positively correlates with the underlying muscle thickness and corresponding joint torque. Furthermore, the fascia lata over the semitendinosus is associated with the underlying muscle characteristics independent of the physical constitution. It is assumed that the fascia lata has the plasticity and changes its thickness, which likely corresponds to the morphology of the neighboring tissues and underlying muscle function.

Hamstrings load bearing in different contraction types and intensities: A shear-wave and B-mode ultrasonographic study.

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.

Inhomogeneous and anisotropic mechanical properties of the triceps surae muscles and aponeuroses in vivo during submaximal muscle contraction.

This study aimed to identify characteristics of the triceps surae muscles and aponeuroses stiffness in vivo, during graded isometric submaximal plantarflexion efforts. A total of twelve healthy male subjects (age: 27 ± 4 years) participated and were required to stay at rest (0% MVC) and perform isometric submaximal plantar flexion contractions (20%, 40%, 60% of MVC) on a dynamometer. Young's modulus of triceps surae muscles and the adjoining aponeuroses between gastrocnemii and soleus at the proximal and distal sites were obtained in the longitudinal direction (along muscle's line of action) during at rest and submaximal plantar flexions. Additionally, Young's modulus of adjoining aponeuroses in the transverse direction at the distal sites was also calculated. Young's modulus of LG (lateral gastrocnemius), SOL-lat (lateral part of soleus) and LPS (superficial aponeurosis of LG) at the proximal site showed significant (p < 0.001) graded increase response to the submaximal contraction levels. Besides, in the lateral side, significant differences in the Young's modulus of aponeuroses were observed between longitudinal and transverse directions at rest and during contractions (p < 0.002). Changes of aponeuroses length were significantly correlated with Young's modulus changes of the proximal gastrocnemii muscle bellies (r = 0.43-0.45, p = 0.006-0.008) and superficial aponeuroses (r = 0.49-0.60, p < 0.002). The results further indicate that the triceps surae muscles and aponeuroses showed inhomogeneous and anisotropic mechanical properties during submaximal muscle contractions, and the stiffening effect of muscle belly possibly make influence on the mechanical properties of aponeuroses during muscle contractions, especially for the lateral gastrocnemius.

Inhomogeneous and Anisotropic Mechanical Properties of the Triceps Surae Aponeuroses in Older Adults: Relationships With Muscle Strength and Walking Performance.

This study investigated (a) site- and direction-dependent variations of passive triceps surae aponeurosis stiffness and (b) the relationships between aponeurosis stiffness and muscle strength and walking performance in older individuals. Seventy-nine healthy older adults participated in this study. Shear wave velocities of the triceps surae aponeuroses at different sites and in two orthogonal directions were obtained in a prone position at rest using supersonic shear imaging. The maximal voluntary isometric contraction torque of the plantar flexors and normal (preferred) and fast (fastest possible) walking speeds (5-m distance) were also measured. The shear wave velocities of the adjoining aponeuroses were weakly associated with plantar flexion torque (r = .23-.34), normal (r = .26), and fast walking speed (r = .25). The results show clear spatial variations and anisotropy of the triceps surae aponeuroses stiffness in vivo, and the aponeurosis stiffness was associated with physical ability in older adults.

Site dependent elastic property of human iliotibial band and the effect of hip and knee joint angle configuration.

The iliotibial band (ITB) is the lateral thickening of the fascia lata. The ITB has been extensively studied for its relevance to injury, but not much is known about its elastic properties. We aimed to investigate the site- and joint angle-dependence of ITB elasticity. We tested twelve healthy males (22-30 years; in vivo) and twelve male cadavers (69-93 years; cadaver). The Young's modulus of the ITB was measured in the longitudinal direction at five sites (over the proximal, middle, and distal bellies of the vastus lateralis (VL), superior border of the patella, and between femur and tibia) of the right limb, by ultrasound shear wave elastography (in vivo) and the tensile test (cadaver). Joint angle-dependence was also studied for nine different positions (knee angles at 0, 25, 90˚ x hip angles at 0, 40, 90˚) (in vivo). Over VL, the ITB was more compliant at the distal (17.6-190.1 kPa; in vivo, 219.4 ± 68.8 MPa; cadaver, mean ± SD) than other sites (24.2-221.4 kPa, 337.9-362.7 MPa). The ITB at the superior border of the patella and between femur and tibia was stiffer in vivo (31.8-271.8 and 50.9-208.8 kPa), while it was more compliant in cadavers (113.4 ± 63.7 and 130.4 ± 73.7 MPa), compared to other sites. The ITB became stiffer associated with increasing hip extension angle and knee flexion angle, and the hip remarkably affecting the values regardless of site (in vivo). Our findings have clinical significance with respect to the site- and joint angle-dependence of ITB-related overuse injury.

The Effects of Extracorporeal Shock Wave Therapy on Spastic Muscle of the Wrist Joint in Stroke Survivors: Evidence From Neuromechanical Analysis.

Background: This study combined neuromechanical modeling analysis, muscle tone measurement from mechanical indentation and electrical impedance myography to assess the neural and peripheral contribution to spasticity post stroke at wrist joint. It also investigated the training effects and explored the underlying mechanism of radial extracorporeal shock wave (rESW) on spasticity. Methods: People with first occurrence of stroke were randomly allocated to rESW intervention or control group. The intervention group received one session of rESW therapy, followed by routine therapy which was the same frequency and intensity as the control group. Outcome measures were: (1) NeuroFlexor method measured neural component (NC), elastic component (EC) and viscosity component (VC), and (2) myotonometer measured muscle tone (F) and stiffness (S), (3) electrical impedance myography measured resistance (R), reactance (X) and phase angle (θ); (4) modified Asworth scale; (5) Fugl Meyer Upper limb scale. All outcome measures were recorded at baseline, immediately post rESW and at 1-week follow-up. The differences between the paretic and non-paretic side were assessed by t-test. The effectiveness of rESW treatment were analyzed by repeated-measures one-way analysis of variance (ANOVA) at different time points. Results: Twenty-seven participants completed the study. NC, EC, and VC of the Neuroflexor method, F and S from myotonometer were all significantly higher on the paretic side than those from the non-paretic side. R, X, and θ from electrical impedance were significantly lower on the paretic side than the non-paretic side. Immediately after rESW intervention, VC, F, and S were significantly reduced, and X was significantly increased. The clinical scores showed improvements immediate post rESW and at 1-week follow-up. Conclusions: The observed changes in upper limb muscle properties adds further support to the theory that both the neural and peripheral components play a role in muscle spasticity. ESW intervention may be more effective in addressing the peripheral component of spasticity in terms of muscle mechanical properties changes. The clinical management of post stroke spasticity should take into consideration of both the neural and non-neural factors in order to identify optimal intervention regime.

Dependence of muscle and deep fascia stiffness on the contraction levels of the quadriceps: An in vivo supersonic shear-imaging study.

In the present study we investigated muscle contraction-driven changes in deep fascia mechanical property, to reveal mechanical interactions between them. Fourteen males (22-37 yr) performed isometric knee extension at 20, 40, 60% of the maximal voluntary contraction (MVC). During each contraction and at rest, shear wave velocities (SWV) of the rectus femoris (RF) and vastus lateralis (VL) and fascia lata were measured in both longitudinal and transverse ultrasound transducer directions relative to the thigh. Surface electromyogram was recorded from RF and VL and root mean square (RMS) values were determined. The slopes of the linear correlations between normalized SWV (%SWV: relative to rest) and RMS (%RMSEMG: relative to MVC) were calculated for different sites and directions. Both muscles and fascia lata became stiffer as the muscle activation level increased to comparable degrees, with the slopes of those changes being 4-9 times higher in the longitudinal than transverse direction. The fascia lata showed lower slopes than those of muscles in the longitudinal direction while in the transverse direction neither parts showed significant differences. These results suggest that the force produced by the muscles partly transmitted to the fascia lata in the longitudinal and transverse directions, causing anisotropic changes in musculofascial entity.

Morphological and mechanical properties of the human triceps surae aponeuroses taken from elderly cadavers: Implications for muscle-tendon interactions.

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.

Neuromuscular Adaptations to Work-matched Maximal Eccentric versus Concentric Training.

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. PURPOSE: This study aimed to examine neuromuscular adaptations after maximal eccentric versus concentric training matched for total work. METHODS: Twelve males conducted single-joint isokinetic (180°·s) 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. RESULTS: Torque 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. CONCLUSION: Eccentric 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.