Anatomical Cross-sectional Area Research Articles

Concentric versus eccentric training: Effect on muscle strength, regional morphology, and architecture

The different architectural adaptations and the regional changes that occur with eccentric (ECC) vs. concentric (CON) muscle actions are not fully understood. The purpose was to investigate regional changes in vastus lateralis muscle (VL) after ECC and CON training. Sixteen males (23 ± 3 y) performed ECC or CON twice weekly over 5 weeks, using a single-leg design. Both training modalities caused similar increases in knee extensor strength (measured with dynamometry) (10-13%) and muscle volume (8%) (measured with 3D ultrasound) after 5-weeks of training. Anatomical cross-sectional area at the mid-point of the muscle was greater after CON training (9%), but greater at the distal end after ECC training (8%). CON training increased fascicle angle at the mid-point (8%), with little change at the distal end (2%). There was a small increase in fascicle length at the mid-point after CON training (3%). Conversely, ECC training caused a greater variation in regional and architectural adaptations. Fascicle length increased at both the mid-point (6%) and distal ends (8%) after ECC training, and similar changes in fascicle angle were also observed in both regions (3-4%). Different region-specific changes are evident after CON and ECC training, with implications for performance and injury risk.

Muscle and Tendon Morphology in Early-Adolescent Athletes and Untrained Peers.

Adolescent athletes can feature significantly greater muscle strength and tendon stiffness compared to untrained peers. However, to date, it is widely unclear if radial muscle and tendon hypertrophy may contribute to loading-induced adaptation at this stage of maturation. The present study compares the morphology of the vastus lateralis (VL) and the patellar tendon between early-adolescent athletes and untrained peers. In 14 male elite athletes (A) and 10 untrained controls (UC; 12–14 years of age), the VL was reconstructed from full muscle segmentations of magnetic resonance imaging (MRI) sequences and ultrasound imaging was used to measure VL fascicle length and pennation angle. The physiological cross-sectional area (PCSA) of the VL was calculated by dividing muscle volume by fascicle length. The cross-sectional area (CSA) of the patellar tendon was measured over its length based on MRI segmentations as well. Considering body mass as covariate in the analysis, there were no significant differences between groups considering the VL anatomical cross-sectional area (ACSA) over its length or maximum ACSA (UC: 24.0 ± 8.3 cm2, A: 28.1 ± 5.3 cm2, p > 0.05), yet athletes had significantly greater VL volume (UC: 440 ± 147 cm3, A: 589 ± 121 cm3), PCSA (UC: 31 ± 9 cm2, A: 46 ± 9 cm2), pennation angle (UC: 8.2 ± 1.4°, A: 10.1 ± 1.3°), and average patellar tendon CSA (UC: 1.01 ± 0.18 cm2, A: 1.21 ± 0.18 cm2) compared to the untrained peers (p < 0.05). However, the ratio of average tendon CSA to VL PCSA was significantly lower in athletes (UC: 3.4 ± 0.1%, A: 2.7 ± 0.5%; p < 0.05). When inferring effects of athletic training based on the observed differences between groups, these results suggest that both muscle and tendon of the knee extensors respond to athletic training with radial growth. However, the effect seems to be stronger in the muscle compared to the tendon, with an increase of pennation angle contributing to the marked increase of muscle PCSA. A disproportionate response to athletic training might be associated with imbalances of muscle strength and tendon stiffness and could have implications for the disposition towards tendon overuse injury.

Regional Hypertrophy, the Inhomogeneous Muscle Growth: A Systematic Review

ABSTRACT A literature search was performed in 2 databases (PubMed and Scopus) on May 22, 2019. From the 14 studies included in the review, 13 found that the anatomical cross-sectional area of some regions of a muscle increased to a greater degree than others. Some studies found increases in the distal region, others reported increases in the middle region, and some found differences between regions but did not report which increased the most. Hypertrophy between and within muscle heads is not homogeneous, confirming that regional hypertrophy actually happens in the quadriceps femoris, triceps brachii, and biceps brachii muscles.

Does resistance training increase aponeurosis width? The current results and future tasks.

The aponeurosis, a sheet of fibrous tissue, is the deep and superficial fascia where muscle fibers attach in pennate muscles. It is quite possible that the aponeurosis size increases in response to resistance training-induced fiber hypertrophy due to an increase in connection area. As a result, it leads to an increase in anatomical muscle cross-sectional area. However, attention has not been paid to aponeurosis area changes. This review sought to determine whether muscle hypertrophy changes aponeurosis width following short-term resistance training using an equation we modified [post/pre changes in aponeurosis width (AWpost/pre) = post/pre changes in anatomical cross-sectional area (CSApost/pre) ÷ post/pre changes in pennation angle (PApost/pre) ÷ post/pre changes in fascicle length (FLpost/pre)]. A search using two electronic databases (PubMed and Google Scholar) was conducted. Nine studies measured CSApost/pre, PApost/pre, and FLpost/pre of the vastus lateralis muscle by ultrasound and magnetic resonance imaging. There was a statistically significant 2.73 [95% CI 1.11, 4.36; p = 0.009] cm2 increase in CSApost/pre along with a statistically significant 1.21° [95% CI 0.44, 1.97; p = 0.002] increase in PApost/pre and a statistically significant 0.36cm [95% CI 0.19, 0.54; p = 0.0002] increase in FLpost/pre. These results yield an estimated 1% reduction in aponeurosis width. Our results suggest that while muscle CSA, pennation angle, and fascicle length all increase following short-term resistance training, the aponeurosis width is not altered.

Intra- and inter-muscular differences in the cross-sectional area of the quadriceps muscles assessed by extended field-of-view ultrasonography.

Τo examine the inter- and intra-muscular differences in the anatomical cross-sectional area (CSA) of the quadricep muscles, using extended - field of view (EFOV) ultrasonography (US). Panoramic transverse US images of the thigh were acquired from 10 young participants at five different locations across the thigh, in two sessions, spaced a week apart. The CSA of the vastus medialis (VM), rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL) and tensor vastus intermedius (TVI) was quantified. The intraclass correlation coefficients ranged from 0.75 to 0.97 and the standard error of measurement ranged from 0.78% to 6.61%, indicating high test-retest reliability. Analysis of the variance indicated that among the 5 quadriceps muscles the VL and the RF displayed the greater CSA proximally, the VI medially and the VM distally across the thigh (p <0.05). No differences in the quadriceps CSA measured with and without including the TVI were found (p >0.05). The EFOV US technique provides transverse scans of the quadriceps muscle in vivo and allowed a reliable and non-invasive determination of CSA at a low cost. Evaluation of CSA along the thigh largely depends on the measurement site. Future studies that examine the quadriceps CSA using EFOV after any form of intervention should consider changes of at least 6.5% as meaningful.

Local fat content and muscle quality measured by a new electrical impedance myography device: correlations with ultrasound variables

The present study investigated the relationship between local fat percentage (SKfat) and muscle quality (MQ) estimated by a new hand-held electrical impedance myography (hEIM) device or derived from ultrasound and strength assessments. The right anterior thigh of 90 healthy participants (mean ± SD; age=22.9 ± 2.9 years; 45 men: BMI = 23.9 ± 2.4 kgm−2; 45 women: BMI = 21.1 ± 1.9 kgm−2) was scanned by hEIM and ultrasound. Correlations between SKfat, local subcutaneous fat (SUBfat), and echo intensity (EIus) were explored. Correlations between MQ, EIus, quadriceps femoris anatomical cross-sectional area (ACSAQF), knee extensors maximum voluntary isometric torque (T), T/ACSAQF, EIus/SUBfat, and ACSAQF/SUBfat were also assessed. SKfat correlated with SUBfat (r = 0.88; p < 0.001) and EIus (r = 0.64; p < 0.001). MQ correlated with EIus (r = −0.66; p < 0.001), ACSAQF (r = 0.37; p < 0.001), EIus/SUBfat (r = 0.37; p < 0.001), and ACSAQF/SUBfat (r = 0.81; p < 0.001). Multiple regression analysis showed that SUBfat, EIus, and sex explained 86% of SKfat variance, whereas ACSAQF/SUBfat, sex and EIus explained 75% of MQ variance. In conclusion, high hEIM local fat percentage relates to greater subcutaneous fat and intramuscular non-contractile tissue content. High hEIM muscle quality relates to greater muscle-size:subcutaneous-fat ratio and contractile tissue content. Sex influences the prediction of both parameters. This hEIM device seems to be useful to estimate local thigh composition.

Longitudinal changes in specific muscle strength but not in muscle anatomical cross-sectional areas is associated with change in knee function - data from the osteoarthritis initiative (OAI)

Purpose: A positive and concurrent association between longitudinal change in knee function (worsening or improvement ≥6 [minimal clinically important difference (MCID)] on the WOMAC function score during Y2→Y4) and change in isometric extensor muscle strength was previously reported. Although muscle anatomical cross-sectional areas (ACSAs) or muscle mass have been shown to be moderately related to muscle strength, it is unknown whether function-related change in muscle strength depends on concordant change in ACSAs or specific strength (e.g.

Влияние “акцентированной эксцентрической нагрузки” на гипертрофию и архитектуру мышц

The purpose of this study was to determine the effects of accentuated eccentric loading vs. traditional strength training on hypertrophy and architecture of vastus lateralis muscle (VL). The main difference between the chosen strength protocol from the conventional strength training protocol that it applies a supramaximal external load during the eccentric phase of the lift, that is, the value exceeding the concentric repetition maximum. The training volume between the experimental groups was equalized. Volunteers that were engaged in strength sports trained two times a week for 13 weeks. Morphological and architectural parameters of the muscles were evaluated using magnetic resonance imaging and ultrasonography. The results of the experiment showed that the most significant increase in anatomical cross-sectional area (ACSA), muscle volume, pennation angle, and physiological cross-sectional area (PCSA) of VL were obtained in the group using an accentuated eccentric loading. This effect can be associated with the use of higher intensity and as a consequence of the greater mechanical strain applied to the muscle, which caused a more pronounced adaptive response. Besides, it was shown that the pennation angle and PCSA increased to a greater extent than ACSA and muscle volume. Our data strongly suggest a close relationship between the pennation angle and muscular hypertrophy. An increase in this parameter that might be driven by space constraints in the hypertrophying muscle can be a reliable indicator of the degree of muscle hypertrophy.

Echo Intensity Reliability for the Analysis of Different Muscle Areas in Athletes.

Lanferdini, FJ, Manganelli, BF, Lopez, P, Klein, KD, Cadore, EL, and Vaz, MA. Echo intensity reliability for the analysis of different muscle areas in athletes. J Strength Cond Res 33(12): 3353-3360, 2019-Skeletal muscles' echo intensity (EI) is used as a parameter to evaluate muscle damage and muscle quality after exercise or training. However, recent muscle EI studies have used regions of interest (ROIs) of different sizes for assessing muscle damage and muscle quality, which may lead to different results if the different ROIs from the same muscle are not reliable. Although a maximum rectangular ROI (RET-ROI), included in the muscles' anatomical cross-sectional area, can be used to represent the maximum muscle ROI (MAX-ROI), no studies were found that investigated the reliability of the evaluations of different ROIs for the EI of superficial vs. deep muscles of the thigh. In addition, no studies have evaluated different ROIs in cyclists, at different days and analyzed by different raters. The aim of this study was to evaluate the EI reliability of rectus femoris (RF) and vastus intermedius (VI) muscles of cyclists. Twenty cyclists visited the laboratory 4 times for the evaluation of RF and VI muscles transversal ultrasound images. Echo intensity was determined from grayscale mean values by 2 examiners who performed the analysis with 3 different ROIs: MAX-ROI, RET-ROI, and 1-cm ROI (1CM-ROI). The between-ROI EI data reliability showed a strong correlation in both RF (r ≥ 0.79) and VI (r ≥ 0.87) muscles. Bland-Altman tests demonstrated high agreement among RF ROI muscle areas (p > 0.05), with no agreement between the VI areas (p < 0.05). Only the RF muscle MAX-ROI, RET-ROI, and 1CM-ROI areas are similar for EI analysis, with no similarities for the same VI muscle areas.

Temporal Muscle-specific Disuse Atrophy during One Week of Leg Immobilization.

Musculoskeletal injuries necessitate periods of disuse (i.e., limb immobilization) during which rapid skeletal muscle atrophy occurs. The relative susceptibility of different muscles of the thigh to disuse atrophy remains uninvestigated. We assessed muscle disuse atrophy of individual thigh muscles throughout 1 wk of unilateral knee immobilization. Thirteen healthy, young (20.2 ± 0.6 yr) men underwent 7 d of unilateral leg immobilization via knee bracing. Magnetic resonance imaging scans were performed bilaterally prior to, and following 2 and 7 d of immobilization to determine the volume and anatomical cross-sectional area of the individual muscle groups of the upper legs. In contrast to the control leg, total thigh muscle volume had decreased by 1.7% ± 0.3% (P < 0.01) and 5.5% ± 0.6% (P < 0.001) in the immobilized leg after 2 and 7 d of disuse, respectively. Muscle loss was significantly greater in the Musculus quadriceps (day 2; 1.7% ± 0.3% (P < 0.05) and day 7; 6.7% ± 0.6%) when compared with the Musculus hamstrings (day 2; 1.4% ± 0.2% (P < 0.01) and day 7; 3.5% ± 0.3%) after 7 d of disuse (P < 0.001). Individual muscles of the thigh exhibited different atrophy rates with the Musculus vastus lateralis anatomical cross-sectional area showing the greater (2.6% ± 0.4% and 7.2% ± 0.8%), and the Musculus gracilis the lesser (1.1% ± 0.7% and 2.3% ± 1.0%) decline following 2 and 7 d of immobilization, respectively (P < 0.01). Thigh muscle disuse atrophy occurs rapidly and is already evident within 2 d of leg immobilization and progresses at a similar rate over the next 5 d (~0.8% muscle loss per day). M. quadriceps muscle shows more atrophy when compared with the M. hamstrings.

Reliability and Validity of Ultrasonography for Measurement of Hamstring Muscle and Tendon Cross-Sectional Area

The purpose of this study was to determine the reliability and validity of ultrasonography for measurement of hamstring muscle and semitendinosus (ST) tendon cross-sectional area (CSA). On two consecutive days, muscle anatomical CSA (ACSA) and ST tendon CSA were measured at standardized positions (30%–80% of thigh length; half the distance from the distal muscle-tendon junction to the popliteal crease) on 12 legs using ultrasonography and compared with corresponding magnetic resonance imaging measures. Inter-day intraclass correlation coefficients were good-to-excellent (0.882–0.996) for all assessed muscle and tendon sites. The limits of agreement widths were narrowest (range: 17%–52%) when muscle ACSA was large but were wide at sites with relatively small ACSA (≤184%) and for ST tendon CSA (range: 72%). Results suggest ultrasound-based measures of individual hamstring muscle maximal ACSA are reliable and valid and ST tendon CSA measures are reliable but require comparison with cadaveric or intra-operative measurements to verify validity.

Quadriceps and Gastrocnemii Anatomical Cross-Sectional Area and Vastus Lateralis Fascicle Length Predict Peak-Power and Time-To-Peak-Power

ABSTRACTPurpose: The current study investigated the role of quadriceps and gastrocnemii size and vastus lateralis and gastrocnemius medialis muscle architecture in peak-power and time-to-peak-power exerted in an all-out Wingate test. Twenty-one amateur cyclists were recruited. Methods: Quadriceps and gastrocnemii anatomical cross-sectional area (ACSA), and vastus lateralis and gastrocnemius medialis pennation angle and fascicle length were measured using ultrasound. Relative peak-power (normalized per body mass) and time-to-peak-power were measured during a 30s all-out test. Results: Relative peak-power was correlated with quadriceps ACSA (r = 0.896, p < .001), gastrocnemii ACSA (r = 0.811, p < .001), vastus lateralis (r = 0.787, p < .001) and gastrocnemius medialis pennation angle (r = 0.638, p < .003). Multiple regression revealed that quadriceps and gastrocnemii ACSA accounted for 85% (R2= 0.85) of peak-power variance. Time-to-peak-power showed very large (r = −0.868, p < .001) and large correlation (r = −0.680, p = .001) with VL and GM fascicle length, respectively. Multiple regression analysis revealed that VL fascicle length explained 75% (R2= 0.75) of the time-to-peak-power variance. Conclusions: Quadriceps and gastrocnemii ACSA largely explained relative peak-power in an all-out Wingate test. Vastus lateralis fascicle length was the main predictor of the time-to-peak-power. Muscle architecture characteristics seem to be involved in the power generating capacity.

Simplified Triceps Surae Muscle Volume Assessment in Older Adults.

Triceps surae (TS) muscle volume can be estimated in young adults by only considering the maximal anatomical cross-sectional area (ACSAmax) and the length of the muscle due to the presence of a constant muscle-specific shape factor. This study aimed to investigate if this simplified muscle volume assessment is also applicable in older adults or if muscle-specific shape changes with aging. MRI sequences were taken from the dominant leg of 21 older female adults. The boundaries of all three TS muscles (SOL, soleus; GM, gastrocnemius medialis; GL, gastrocnemius lateralis) were manually outlined in transverse image sequences, and muscle volume for each muscle was calculated as the integral of the obtained cross-sectional areas of the contours along the whole length of the muscle (measured volume) and, in addition, by using the average muscle-specific shape factors of each muscle obtained from the ratio of the measured volume and the product of ACSAmax and the muscle length (estimated volume). There were no differences in the measured and estimated muscle volumes (SOL: 357.7 ± 61.8 vs. 358.8 ± 65.3 cm3; GM: 179.5 ± 32.8 vs. 179.8 ± 33.3 cm3; GL: 90.2 ± 15.9 vs. 90.4 ± 14.8 cm3). However, when using the reported shape factors of younger adults instead, we found a significant (p < 0.05) overestimation of muscle volume for SOL and GM with average RMS differences of 6.1 and 7.6%, respectively. These results indicate that corrections of muscle-specific shape factors are needed when using the previously proposed simplified muscle volume assessment as aging may not only be accompanied with muscle atrophy but also changes in the shape of skeletal muscle.

Effects of High-Intensity Interval Training and Isoinertial Training on Leg Extensors Muscle Function, Structure, and Intermuscular Adipose Tissue in Older Adults.

We compared the effects of aerobic high-intensity training (HIT) and isoinertial resistance training (IRT) on the strength, mass, architecture, intermuscular adipose tissue (IMAT) quality, and neuromuscular activation of the quadriceps in elderly subjects. Twelve healthy men (69.3 ± 4.2 years; 77.8 ± 10.4 kg; 1.72 ± 0.05 m) were exposed to 8 weeks of HIT (7 × 2-min cycling repetitions at 90% of O2peak, 3 times/week) and, after 4 months (detraining), to IRT (4 × 7 maximal concentric–eccentric knee extensions, 3 times/week). Before and after trainings, we measured knee extension isometric (TMVC) and dynamic (TC) maximal concentric torque, anatomical cross-sectional area (ACSA) at 25, 50, and 75% of femur length, quadriceps volume (Vol), IMAT, pennation angle (θp) of the fibers from the vastus lateralis, and voluntary activation (%Act). TMVC and TC were significantly larger only after IRT (P = 0.008); IRT was able to elicit a greater increase of ACSA than HIT; Vol increases similarly and significantly after HIT and IRT (P = 0.003–0.001); IMAT at 50% of femur length decreased after both HIT and IRT (P = 0.001–0.003); physiological cross-sectional area (PCSA) was larger after IRT than before (P = 0.025); specific torque did not change throughout the study (45.5 N cm–2 ± 12.0); %Act of the quadriceps was significantly affected only by IRT (P = 0.011). Both HIT and IRT are able to elicit beneficial modifications of muscular mass, architecture, and quality (reducing IMAT) in elderly subjects in connection with an amelioration of strength. HIT and IRT caused a homogeneous increase of ACSA and of Vol of the quadriceps. PCSA increases, but specific strength per unit of PCSA did not change. The increases of functional torque seemed to be attributed to a parallel increase of %Act and muscle hypertrophy only after IRT. Data suggest that IMAT may be a prominent indicator to track metabolic-dependent activity and skeletal muscle quality.

Moderate Intensity Resistive Training Reduces Oxidative Stress and Improves Muscle Mass and Function in Older Individuals.

An innovative moderate-intensity resistive exercise-training (RT) program was tested in thirty-five sarcopenic elders (SAR). The subjects were randomized into two groups: SAR training (SAR-RT), n = 20, 73.0 ± 5.5 years, or SAR non-training (SAR-NT), n = 15, 71.7 ± 3.4 years. The training consisted of 12-week progressive RT, thrice/week, at 60% one-repetition maximum (1RM), 3 sets, 14–16 repetitions for both upper and lower limbs. The pre and post intervention measurements included: the skeletal muscle index (SMI%); strength (1RM); stair-climbing power (SCP); muscle thickness (MT) of vastus lateralis (VL) and elbow flexors (EF), VL pennation angle (PA), rectus femoris (RF) anatomical cross-sectional area (ACSA); reactive oxygen species (ROS), total antioxidant capacity (TAC), protein carbonyls (PC), thiobarbituric acid-reactive substances (TBARS), 8-isoprostane (8-iso-PGF2-α), 8-OH-2-deoxyguanosine (8-OH-dG), as markers of oxidative stress/damage (OxS). In SAR-RT, SCP increased by 7.7% (P < 0.01), MT increased by 5.5% for VL, 10.4% for EF and PA increased by 13.4% for VL (P < 0.001 for all). The RF ACSA increased by 14.5% (P < 0.001). 1RM significantly increased by at least 67% for all muscles tested. Notably muscle strength (1RM) positively correlated (P < 0.001) with TAC and negatively with PC (P < 0.001). In conclusion, moderate intensity RT is an effective strategy to increase muscle mass and strength in SAR, while minimizing OxS.

Effects of Lengthening Velocity During Eccentric Training on Vastus Lateralis Muscle Hypertrophy.

Eccentric loading is an effective stimulus for muscle hypertrophy and strength gains, however, the effect of lengthening velocity is under debate. The purpose of the current study was to investigate the influence of muscle lengthening velocity during eccentric training on muscle hypertrophy and strength gains at a given overall loading volume. Forty-seven participants were randomly assigned to a control (n = 14, age: 26.9 ± 4.1 years) and an experimental group (n = 33, age: 27.1 ± 4.4 years). Each leg of the participants in the experimental group was randomly assigned to one of the four eccentric training protocols with different angular velocities (i.e., 45, 120, 210, and 300°/s). Both the magnitude of loading (100% of the isometric maximum) and overall time under tension was matched between the protocols. The training was performed for 33 sessions, 3 times per week with 5 training sets per session. Before and after the intervention, the maximum isometric knee extension moments were measured in all groups using dynamometry, vastus lateralis (VL) muscle anatomical cross-sectional area, and VL muscle volume were measured in the experimental group using magnetic resonance imaging. Data was analyzed in a mixed-design analysis of variance. After the training intervention, the maximum knee joint moments increased in the experimental group (14.2%, p < 0.05) but not the control group. VL anatomical cross-sectional area and VL muscle volume increased significantly (p < 0.05) in the experimental group (5.1 and 5.7%, respectively), but we did not find any significant differences between the four training protocols in all investigated parameters (p > 0.05). The present study provides evidence that muscle hypertrophy and strength gains after eccentric exercise is velocity-independent when load magnitude and overall time under tension are matched between conditions. This is likely due to the similar mechanical demand for the muscle induced by the loading conditions of all four training protocols. The better control of motion and the potentially decreased joint loading compared to high lengthening velocity contractions support the application of slow eccentric exercises in special populations like elderly and people with neurological and musculoskeletal diseases.

Skeletal Muscle Fiber Adaptations Following Resistance Training Using Repetition Maximums or Relative Intensity.

The purpose of the study was to compare the physiological responses of skeletal muscle to a resistance training (RT) program using repetition maximum (RM) or relative intensity (RISR). Fifteen well-trained males underwent RT 3 d·wk−1 for 10 weeks in either an RM group (n = 8) or RISR group (n = 7). The RM group achieved a relative maximum each day, while the RISR group trained based on percentages. The RM group exercised until muscular failure on each exercise, while the RISR group did not reach muscular failure throughout the intervention. Percutaneous needle biopsies of the vastus lateralis were obtained pre-post the training intervention, along with ultrasonography measures. Dependent variables were: Fiber type-specific cross-sectional area (CSA); anatomical CSA (ACSA); muscle thickness (MT); mammalian target of rapamycin (mTOR); adenosine monophosphate protein kinase (AMPK); and myosin heavy chains (MHC) specific for type I (MHC1), type IIA (MHC2A), and type IIX (MHC2X). Mixed-design analysis of variance and effect size using Hedge’s g were used to assess within- and between-group alterations. RISR statistically increased type I CSA (p = 0.018, g = 0.56), type II CSA (p = 0.012, g = 0.81), ACSA (p = 0.002, g = 0.53), and MT (p < 0.001, g = 1.47). RISR also yielded a significant mTOR reduction (p = 0.031, g = −1.40). Conversely, RM statistically increased only MT (p = 0.003, g = 0.80). Between-group effect sizes supported RISR for type I CSA (g = 0.48), type II CSA (g = 0.50), ACSA (g = 1.03), MT (g = 0.72), MHC2X (g = 0.31), MHC2A (g = 0.87), and MHC1 (g = 0.59); with all other effects being of trivial magnitude (g < 0.20). Our results demonstrated greater adaptations in fiber size, whole-muscle size, and several key contractile proteins when using RISR compared to RM loading paradigms.

Sex Differences in Correlations Between Muscle Architecture and Impulse in a Heterogenous Group of Athletes

BACKGROUND: Previous investigations have identified moderate to strong relationships between skeletal muscle architecture (SMA) and performance measures in athletes, however differences between males and females in this regard are not well known. A better understanding of relationships between task-specific impulse windows and SMA in males and females may allow coaches to direct training stimuli toward improving specific morphological underpinnings of sport performance for the athletes under their care. PURPOSE: The purpose of this analysis was to determine relationships between components of SMA and isometric impulse in male and female athletes. METHODS: Pennation angle (PA), fascicle length (FL), and anatomical cross-sectional area (ACSA) were determined for the vastus lateralis muscle via β-mode ultrasonography in a group of male (n = 94) and female (n = 61) collegiate, club, and international athletes. Net isometric impulse at 50, 90, 200, and 250 ms was measured during an isometric mid-thigh pull (IMTP) test administered pre-season as part of an ongoing athlete monitoring program. RESULTS: Pearson product-moment correlation revealed weak correlations between FL and impulse in males (r = 0.33 to 0.36, p < 0.05) but not in females, weak correlations between CSA and impulse in males (r = 0.39 to 0.48, p < 0.05), and weak to moderate correlations between CSA and impulse in females (r = 0.55 to 0.62, p < 0.05). CONCLUSIONS: These results indicate that there may be sex-based differences in the physiological underpinnings of impulse generation in trained athletes, particularly in relation to both muscle size and fascicle length of the vastus lateralis. Further research should investigate changes in these relationships over time and consider contributions from neuromuscular components.

Effects of 8 weeks of moderate-intensity resistance training on muscle changes in postmenopausal women with different angiotensin-converting enzyme insertion/deletion polymorphisms of interest

The aim of the study was to explore the association between angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism and muscle adaptations to moderate-intensity resistance training in postmenopausal women. Forty healthy postmenopausal Chinese women (aged 53-66 years) were recruited and grouped by ACE I/D polymorphism (the homozygous deletion genotype [DD], n = 12; the I allele carriers [II/ID], n = 28). All participants performed an 8-week full-body resistance training program at moderate intensity with 15-repetition maximum. Upper- and lower-limb muscle mass, grip and back strength, anatomical cross-sectional area of the rectus femoris (ACSARF), isokinetic knee extension strength (MVCKE) and knee flexion strength were measured before and after training. Our results showed significant genotype × time interaction in ACSARF and MVCKE (P = 0.007 and P = 0.03, respectively) with the DD group having greater changes in corresponding parameters than the I-allele carriers (P = 0.012 and P = 0.018, respectively). Multivariate linear regression results showed that the ACE DD genotype was positively related to the grip strength adaptation (r = 0.48, P = 0.05). This study improves our understanding of the association between the ACE I/D polymorphism and muscular responses to moderate intensity resistance training among postmenopausal women and revealed that the DD genotype has predominant adaptations in grip strength, rectus femoris size, and knee extensor strength.

Hamstring muscle activation and morphology are significantly altered 1-6years after anterior cruciate ligament reconstruction with semitendinosus graft.

Harvest of the semitendinosus (ST) tendon for anterior cruciate ligament reconstruction (ACLR) causes persistent hypotrophy of this muscle even after a return to sport, although it is unclear if hamstring activation patterns are altered during eccentric exercise. It was hypothesised that in comparison with contralateral control limbs, limbs with previous ACLR involving ST grafts would display (i) deficits in ST activation during maximal eccentric exercise; (ii) smaller ST muscle volumes and anatomical cross-sectional areas (ACSAs); and (iii) lower eccentric knee flexor strength. Fourteen athletes who had successfully returned to sport after unilateral ACLR involving ST tendon graft were recruited. Median time since surgery was 49months (range 12-78months). Participants underwent functional magnetic resonance imaging (MRI) of their thighs before and after the Nordic hamstring exercise (NHE) and percentage change in transverse (T2) relaxation time was used as an index of hamstring activation. Muscle volumes and ACSAs were determined from MRI and distal ST tendons were evaluated via ultrasound. Eccentric knee flexor strength was determined during the NHE. Exercise-induced T2 change was lower for ST muscles in surgical than control limbs (95% CI - 3.8 to - 16.0%). Both ST muscle volume (95% CI - 57.1 to - 104.7cm3) and ACSA (95% CI - 1.9 to - 5.0cm2) were markedly lower in surgical limbs. Semimembranosus (95% CI 5.5-14.0cm3) and biceps femoris short head (95% CI 0.6-11.0cm3) volumes were slightly higher in surgical limbs. No between-limb difference in eccentric knee flexor strength was observed (95% CI 33N to - 74N). ST activation is significantly lower in surgical than control limbs during eccentric knee flexor exercise 1-6years after ACLR with ST graft. Lower levels of ST activation may partially explain this muscle's persistent hypotrophy post ACLR and have implications for the design of more effective rehabilitation programs. IV.