Anatomical Cross-sectional Area Research Articles

Specific force of the vastus lateralis in adults with achondroplasia

Achondroplasia is a clinical condition defined by shorter stature and disproportionate limb length. Force production in able-bodied individuals (controls) is proportional to muscle size, but given the disproportionate nature of achondroplasia, normalizing to anatomical cross-sectional area (ACSA) is inappropriate. The aim of this study was to assess specific force of the vastus lateralis (VL) in 10 adults with achondroplasia (22 ± 3 yr) and 18 sex-matched controls (22 ± 2 yr). Isometric torque (iMVCτ) of the dominant knee extensors (KE) and in vivo measures of VL muscle architecture, volume, activation, and patella tendon moment arm were used to calculate VL physiological CSA (PCSA), fascicle force, and specific force in both groups. Achondroplasic muscle volume was 53% smaller than controls (284 ± 36 vs. 604 ± 102 cm3, P < 0.001). KE iMVCτ was 63% lower in achondroplasia compared with controls (95 ± 24 vs. 256 ± 47 N⋅m, P < 0.001). Activation and moment arm length were similar between groups ( P > 0.05), but coactivation of bicep femoris of achondroplasic subjects was 70% more than controls (43 ± 20 vs. 13 ± 5%, P < 0.001). Achondroplasic subjects had 58% less PCSA (43 ± 10 vs. 74.7 ± 14 cm2, P < 0.001), 29% lower fascicle force (702 ± 235 vs. 1704 ± 303 N, P < 0.001), and 29% lower specific force than control subjects (17 ± 6 vs. 24 ± 6 N⋅cm-2, P = 0.012). The smaller VL specific force in achondroplasia may be attributed to infiltration of fat and connective tissue, rather than to any difference in myofilament function. NEW & NOTEWORTHY The novel observation of this study was the measurement of normalized force production in a group of individuals with disproportionate limb length-to-torso ratios.

Lower limb muscle volume estimation from maximum cross-sectional area and muscle length in cerebral palsy and typically developing individuals

BackgroundDeficits in muscle volume may be a significant contributor to physical disability in young people with cerebral palsy. However, 3D measurements of muscle volume using MRI or 3D ultrasound may be difficult to make routinely in the clinic. We wished to establish whether accurate estimates of muscle volume could be made from a combination of anatomical cross-sectional area and length measurements in samples of typically developing young people and young people with bilateral cerebral palsy. MethodsLower limb MRI scans were obtained from the lower limbs of 21 individuals with cerebral palsy (14.7±3years, 17 male) and 23 typically developing individuals (16.8±3.3years, 16 male). The volume, length and anatomical cross-sectional area were estimated from six muscles of the left lower limb. FindingsAnalysis of Covariance demonstrated that the relationship between the length*cross-sectional area and volume was not significantly different depending on the subject group. Linear regression analysis demonstrated that the product of anatomical cross-sectional area and length bore a strong and significant relationship to the measured muscle volume (R2 values between 0.955 and 0.988) with low standard error of the estimates of 4.8 to 8.9%. InterpretationThis study demonstrates that muscle volume may be estimated accurately in typically developing individuals and individuals with cerebral palsy by a combination of anatomical cross-sectional area and muscle length. 2D ultrasound may be a convenient method of making these measurements routinely in the clinic.

Estimating medial gastrocnemius muscle volume in children with spastic cerebral palsy: a cross-sectional investigation.

This cross-sectional investigation evaluates the reliability of estimating medial gastrocnemius anatomical cross-sectional area (aCSA) in typically developing and spastic cerebral palsy (SCP) cohorts. It verifies whether muscle volume estimations based on aCSA improve when aCSA is multiplied by muscle-tendon unit (MTU) or muscle length, and whether the resulting errors in volume estimations are smaller than changes after intervention. Fifteen typically developing children (mean age 8y 2mo [SD 1y 5mo], six males, nine females) and 30 children with SCP (mean age 9y 2mo [SD 2y 5mo], 22 males, eight females, Gross Motor Function Classification System [GMFCS] level I=15, II=15) participated in the investigation. The SCP cohort was divided according to GMFCS level. A three-dimensional freehand ultrasound technique was used to estimate medial gastrocnemius aCSA, muscle volume, MTU, and muscle length. Estimated muscle volume (aCSA×MTU or muscle length) was compared with the measured muscle volume. Anatomical cross-sectional area, muscle volume, and muscle length significantly differed between the typically developing and two SCP cohorts (p≤0.050). aCSA multiplied by either MTU or muscle length improved estimations of medial gastrocnemius volume. Leave-one-out cross-validation revealed an absolute difference with measured muscle volume of 3.77 ml (SD 2.90). This investigation revealed that medial gastrocnemius muscle volume can be reliably estimated in a clinically feasible manner in typically developing children and those with SCP. Medial gastrocnemius anatomical cross-sectional area (aCSA) can be reliably estimated in children with spastic cerebral palsy. The location of the anatomical cross-section should be taken with respect to muscle and not bone length. Medial gastrocnemius volume can be reliably estimated by multiplying aCSA and muscle length. The errors in volume estimations are smaller than reported differences after interventions.

Muscle thickness correlates to muscle cross-sectional area in the assessment of strength training-induced hypertrophy.

Muscle thickness (MT) measured by ultrasound has been used to estimate cross‐sectional area (measured by CT and MRI) at a single time point. We tested whether MT could be used as a valid marker of MRI determined muscle anatomical cross‐sectional area (ACSA) and volume changes following resistance training (RT). Nine healthy, young, male volunteers (24 ± 2 y.o., BMI 24.1 ± 2.8 kg/m2) had vastus lateralis (VL) muscle volume (VOL) and ACSA mid (at 50% of femur length, FL) assessed by MRI, and VL MT measured by ultrasound at 50% FL. Measurements were taken at baseline and after 12 weeks of isokinetic RT. Differences between baseline and post‐training were assessed by Student's paired t test. The relationships between MRI and ultrasound measurements were tested by Pearson's correlation. After RT, MT increased by 7.5 ± 6.1% (P < .001), ACSA mid by 5.2 ± 5% (P < .001), and VOL by 5.0 ± 6.9% (P < .05) (values: means ± SD). Positive correlations were found, at baseline and 12 weeks, between MT and ACSA mid (r = .82, P < .001 and r = .73, P < .001, respectively), and between MT and VOL (r = .76, P < .001 and r = .73, P < .001, respectively). The % change in MT with training was correlated with % change in ACSA mid (r = .69, P < .01), but not % change in VOL (r = .33, P > .05). These data support evidence that MT is a reliable index of muscle ACSA mid and VOL at a single time point. MT changes following RT are associated with parallel changes in muscle ACSA mid but not with the changes in VOL, highlighting the impact of RT on regional hypertrophy.

Thigh Muscle Specific‐Strength and the Risk of Incident Knee Osteoarthritis: The Influence of Sex and Greater Body Mass Index

To determine whether lower thigh muscle specific-strength increases the risk of incident radiographic knee osteoarthritis (RKOA), and whether there exists a sex-specific relationship between thigh muscle specific-strength and body mass index (BMI). A total of 161 Osteoarthritis Initiative participants (62% female) with incident RKOA (Kellgren/Lawrence grade 0/1 at baseline, developing an osteophyte and joint space narrowing grade ≥1 by year 4) were matched to 186 controls (58% female) without incident RKOA. Thigh muscle anatomical cross-sectional areas (ACSAs) were determined at baseline using axial magnetic resonance imaging scans. Isometric extensor and flexor muscle strength was measured at baseline, and specific strength (strength ÷ ACSA) was calculated. Logistic regression assessed the risk of incident RKOA associated with muscle specific-strength (with and without adjustment for BMI). Lower knee extensor- and flexor-specific strength significantly increased the risk of incident RKOA in women but not in men (odds ratio 1.47 [95% confidence interval (95% CI) 1.10-1.96] and 1.41 [95% CI 1.06-1.89], respectively). The significant relationship in women was lost after adjustment for BMI. Lower specific strength was associated with higher BMI in women (r = -0.29, P < 0.001), but not in men, whereas absolute strength was associated with BMI in men (r = 0.28, P = 0.001), but not in women. Lower thigh muscle specific-strength predicts incident RKOA in women, with this relationship being confounded by BMI. The sex-specific relationship between muscle specific-strength and BMI provides a possible explanation why women with muscle-strength deficits typically have a poorer prognosis than men with similar strength deficits.

Age-related changes in the effects of strength training on lower leg muscles in healthy individuals measured using MRI

BackgroundWe previously measured the rate of regaining muscle strength during rehabilitation of lower leg muscles in patients following lower leg casting. Our primary aim in this study was to measure...

Associations of maximal voluntary isometric hip extension torque with muscle size of hamstring and gluteus maximus and intra-abdominal pressure.

Muscle size of the hamstring and gluteus maximus (GM) as well as intra-abdominal pressure (IAP) are considered as factors affecting the torque development during hip extension. This study examined the associations of torque development during maximal voluntary isometric hip extension with IAP and muscle size of the hamstring and GM. Anatomical cross-sectional area (ACSA) of the hamstring and thickness of GM were determined in 20 healthy young males using an ultrasonography apparatus (Experiment 1). Torque and IAP were simultaneously measured while subjects performed maximal voluntary isometric hip extension. The IAP was measured using a pressure transducer placed in the rectum and determined at the time at which the developed torque reached to the maximal. In Experiment 2, torque and IAP were measured during maximal voluntary isometric hip flexion in 18 healthy young males. The maximal hip extension torque was significantly correlated with the IAP (r=0.504, P=0.024), not with the ACSA of the hamstring (r=0.307, P=0.188) or the thickness of GM (r=0.405, P=0.076). The relationship was still significant even when the ACSA of the hamstring and the thickness of GM were adjusted statistically (r=0.486, P=0.041). The maximal hip flexion torque was not significantly correlated with the IAP (r=-0.118, P=0.642). The current results suggest that IAP can contribute independently of the muscle size of the agonists to maximal voluntary hip extensiontorque.

Hind limb extensor muscle architecture reflects locomotor specialisations of a jumping and a striding quadrupedal caviomorph rodent

Muscle architecture is an important factor in determining muscle function. The physiological cross-sectional area (PCSA) is directly proportional to the force-generating capacity of a muscle, while fibre length determines the capacity for a muscle’s length change. For a given muscle volume, both parameters cannot be maximised at the same time, and therefore, specialisation in accordance with specific functional demands is widely accepted. Building on this, the architecture of selected hind limb extensor muscles of two caviomorph rodent species of similar body size but with differing locomotor modes were analysed and compared. Individual fascicles of fixed cadavers were carefully removed during stepwise dissection. After removal of each fascicle, the left-behind groove within the muscle belly was digitised to capture the length and orientation of the removed fascicle. Pennation angle, muscle volume, and anatomical cross-sectional area were determined, and finally, PCSA and force-generating capacity were approximated for a hip extensor (M. biceps femoris), a knee extensor (M. vastus lateralis), and an ankle extensor (M. triceps surae). Muscle architecture appeared to reflect locomotor specialisation of a jumping (Chinchilla chinchilla) in comparison with a striding quadrupedal (Cavia porcellus) species, but considerable variability of the limited specimens analysed was found. With the biceps femoris as an exception, analysed specimens of Chinchilla had relatively more voluminous and thus metabolically expensive hind limb extensors with both a greater capacity for length change and for force generation. These results are in agreement with a greater demand for powerful hind limb extension during launches and provide further evidence that muscle architecture is adapted to differing functional demands in closely related species.

Resting Energy Expenditure in Adults with Becker's Muscular Dystrophy.

PurposeThe purpose of this study was: 1) To compare Resting energy expenditure (REE) in adult males with Becker’s Muscular Dystrophy (BeMD, n = 21, 39 ±12 years) and healthy controls (CTRL, n = 12, 37 ±12 years) 2) Determine whether other physiological parameters correlate with REE in BeMD, and 3) Compare current prediction methods of REE with measured REE.MethodsREE was calculated via indirect calorimetry using continuous, expired gas analysis following an overnight fast. Fat free mass (FFM) and fat mass were measured by bioelectrical impedance. B-mode ultrasound measured Tibialis Anterior (TA) and Gastrocnemius Medialis (GM) anatomical cross sectional area (ACSA). The Bone Specific Physical Activity Questionnaire measured physical activity.ResultsNo difference in REE was found between CTRL and BeMD groups (1913 ±203 & 1786 ±324 Kcal respectively). Other physiological comparisons showed increased fat mass (+54%), decreased TA ACSA (-42%), increased GM ACSA (+25%) as well as reduced respiratory function (FVC -28%; FEV1−27%) in BeMD adults compared to controls. REE estimated from prediction equations (Schofield’s) in Muscular Dystrophy were different from measured REE (P<0.05, bias = -728kcal), while the Mifflin equation was no different from measured REE (r2 = 0.58, Bias = -8kcal). Within the present BeMD, REE predicted from FFM (REE = FFM x 34.57–270; r2 = 0.85) and body mass (REE = BM x 15.65 + 421.5; r2 = 0.66), were not different from measured REE (bias equals 0 and 0.2kcals, respectively)ConclusionsDespite no differences in REE between CTRL and BeMD adults, increased fat masses highlights the requirement for explicit nutritional guidelines, as well as maintenance of physical activity levels, where possible. Prediction equations are frequently used in clinical settings, however these have been shown to be less accurate in BeMD; therefore, the equations proposed here should be used where possible.

Sex differences in the effect of fish-oil supplementation on the adaptive response to resistance exercise training in older people: a randomized controlled trial

Background: Resistance exercise increases muscle mass and function in older adults, but responses are attenuated compared with younger people. Data suggest that long-chain n–3 polyunsaturated fatty acids (PUFAs) may enhance adaptations to resistance exercise in older women. To our knowledge, this possibility has not been investigated in men.Objective: We sought to determine the effects of long-chain n–3 PUFA supplementation on resistance exercise training–induced increases in muscle mass and function and whether these effects differ between older men and women.Design: Fifty men and women [men: n = 27, mean ± SD age: 70.6 ± 4.5 y, mean ± SD body mass index (BMI; in kg/m2): 25.6 ± 4.2; women: n = 23, mean ± SD age: 70.7 ± 3.3 y, mean ± SD BMI: 25.3 ± 4.7] were randomly assigned to either long-chain n–3 PUFA (n = 23; 3 g fish oil/d) or placebo (n = 27; 3 g safflower oil/d) and participated in lower-limb resistance exercise training twice weekly for 18 wk. Muscle size, strength, and quality (strength per unit muscle area), functional abilities, and circulating metabolic and inflammatory markers were measured before and after the intervention.Results: Maximal isometric torque increased after exercise training to a greater (P < 0.05) extent in the long-chain n–3 PUFA group than in the placebo group in women, with no differences (P > 0.05) between groups in men. In both sexes, the effect of exercise training on maximal isokinetic torque at 30, 90, and 240° s−1, 4-m walk time, chair-rise time, muscle anatomic cross-sectional area, and muscle fat did not differ (P > 0.05) between groups. There was a greater (P < 0.05) increase in muscle quality in women after exercise training in the long-chain n–3 PUFA group than in the placebo group, with no such differences in men (P > 0.05). Long-chain n–3 PUFAs resulted in a greater decrease (P < 0.05) than the placebo in plasma triglyceride concentrations in both sexes, with no differences (P > 0.05) in glucose, insulin, or inflammatory markers.Conclusion: Long-chain n–3 PUFA supplementation augments increases in muscle function and quality in older women but not in older men after resistance exercise training. This trial was registered at clinicaltrials.gov as NCT02843009.

Differential Effects of 2 Rehabilitation Programs Following Anterior Cruciate Ligament Reconstruction.

The muscular function restoration related to the type of physical rehabilitation followed after anterior cruciate ligament reconstruction (ACLR) using autologous hamstring tendon graft in terms of strength and cross-sectional area (CSA) remain controversial. To analyze the CSA and force output of quadriceps and hamstring muscles in subjects following either an Objective Criteria-Based Rehabilitation (OCBR) algorithm or the usual care (UCR) for ACL rehabilitation in Spain, before and 1 year after undergoing an ACLR. Longitudinal clinical double-blinded randomized controlled trial. Sports-medicine research center. 40 recreational athletes (30 male, 10 female [24 ± 6.9 y, 176.55 ± 6.6 cm, 73.58 ± 12.3 kg]). Both groups conducted differentiated rehabilitation procedures after ACLR. Those belonging to OCBR group were guided in their recovery according to the current evidence-based principles. UCR group followed the national conventional approach for ACL rehabilitation. Concentric isokinetic knee joint flexor-extension torque assessments at 180°/s and Magnetic Resonance Imaging (MRI) evaluations were performed before and 12 months after ACLR. Anatomical muscle CSA (mm2) was assessed, in Quadriceps, Biceps femoris, Semitendinous, Semimembranosus, and Gracilis muscles at 50% and 70% femur length. Reduced muscle CSA was observed in both treatment groups for Semitendinosus and Gracilis 1 year after ACLR. At 1-year follow-up, subjects allocated to the OCBR demonstrated greater knee flexor and extensor peak torque values in their reconstructed limbs in comparison with patients treated by UCR. Objective atrophy of Semitendinosus and Gracilis muscles related to surgical ACLR was found to persist in both rehabilitation groups. However, OCBR after ACLR lead to substantial gains on maximal knee flexor strength and ensured more symmetrical anterior-posterior laxity levels at the knee joint.

Anatomical cross-sectional area of the quadriceps femoris and sit-to-stand test score in middle-aged and elderly population: development of a predictive equation

BackgroundAlthough the sit-to-stand (STS) test score has been shown to relate to the strength and size of the quadriceps femoris (QF) for elderly population, it is unknown whether this relationship is influenced by a posture (i.e., the trunk being allowed to stoop or not) during the STS test. The present study investigated the relationship between STS test score and QF anatomical cross-sectional area (ACSA) in the middle-aged and elderly population with regard to the difference in the posture during STS test, and aimed to develop an accurate predicting equation of the QF ACSA from the STS test score.Methods105 males (40–81 years) and 113 females (41–79 years) participated in the present study, then the subjects were divided at random as validation and cross-validation groups. Mid-thigh QF ACSA was determined by magnetic resonance imaging. Subjects performed a 10-repeated STS as fast as possible in two conditions: (1) with the trunk being allowed to stoop during the sitting phases, and (2) kept upright throughout the test. A power index of the STS test score was calculated based on an equation obtained in a previous study using the time taken for each test condition, the thigh and shank lengths, and body mass. In the validation group (n = 109), a stepwise multiple linear regression analysis was performed to create a predictive model of the ACSA with sex, age, the STS time, and power for both conditions as independent variables. The formulated predictive equation was examined in the cross-validation group (n = 109).ResultsIn the validation group, a stepwise regression analysis revealed that STS power with upright trunk condition, sex, and age but not with the stooping condition, were selected as variables to predict QF ACSA (R2 = 0.64, P < 0.001). There was no systematic error for the relationship between predicted and measured values in the cross-validation group.ConclusionsThese results indicate that STS test score with upright trunk condition is one of the indices of QF muscle size of the middle-aged and elderly population. The estimated predicting equation should be useful in clinical and practical settings for the health promotion.

Sex differences in the response to resistance exercise training in older people.

Resistance exercise training is known to be effective in increasing muscle mass in older people. Acute measurement of protein metabolism data has indicated that the magnitude of response may differ between sexes. We compared adaptive responses in muscle mass and function to 18 weeks resistance exercise training in a cohort of older (>65 years) men and women. Resistance exercise training improved knee extensor maximal torque, 4 m walk time, time to complete five chair rises, muscle anatomical cross‐sectional area (ACSA) and muscle quality with no effect on muscle fat/water ratio or plasma glucose, insulin, triacylglycerol, IL‐6, and TNF‐α. Differences between sexes were observed for knee extensor maximal torque and muscle quality with greater increases observed in men versus women (P < 0.05). Maximal torque increased by 15.8 ± 10.6% in women and 41.7 ± 25.5% in men, whereas muscle quality increased by 8.8 ± 17.5% in women and by 33.7 ± 25.6% in men. In conclusion, this study has demonstrated a difference in the magnitude of adaptation, of some of the outcome measures employed, in response to 18 weeks of resistance exercise training between men and women. The mechanisms underlying this observation remain to be established.

Two-dimensional assessment of the nasal valve area cannot predict minimum cross-sectional area or airflow resistance.

Clinicians who manage nasal obstruction often comment on the shape and size of the nasal valve (NV) area. However, correlation of the symptoms of obstruction, nasal airflow dynamics, and the endoscopic appearance of the anatomic cross-sectional area of the NV is poorly understood. Endoscopic imaging and calculation of the NV area is investigated as a tool for either clinical or research use. To describe and evaluate a two-dimensional measurement of the minimum cross-sectional area (MCA) of the NV by using endoscopic imaging. A cross-sectional study of patients with symptoms of nasal obstruction who were undergoing nasal assessment was performed. The NV was measured with digital imaging taken from the endoscopy. Adobe Photoshop was used to calculate the digital MCA of the NV based on pixel count and a reference marker placed in the image field. Airway parameters were assessed by using a nasal obstruction visual analog scale, nasal airway resistance via rhinomanometry, and acoustic rhinometry derived MCA (acoustic MCA). Correlation of the digital MCA and airway parameters was made and interobserver correlation of the MCA measures was calculated. Thirty-three nasal airways were assessed: mean (standard deviation) digital MCA (0.28 ± 0.13 cm(2)) and mean (standard deviation) acoustic MCA (0.51 ± 0.15 cm(2)). Correlation of the digital MCA with visual analog scale was poor (Pearson r = 0.10, p = 0.56). Similar finding between digital and acoustic MCA was poor (Pearson r = 0.50, p = 0.56, respectively) despite a moderately strong interobserver correlation for the digital MCA (Pearson r = 0.79, p < 0.001). Qualitative endoscopic assessment of the NV may help clinicians predict NV dysfunction but simple two-dimensional measures seemed to be of limited value in accurately assessing the three-dimensional NV quantitatively.

Muscle Damage following Maximal Eccentric Knee Extensions in Males and Females.

AimTo investigate whether there is a sex difference in exercise induced muscle damage.Materials and MethodVastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage.ResultsPatella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p<0.05). There was no sex difference in isometric torque loss and muscle soreness post exercise induced muscle damage (p>0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05).ConclusionBased on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage.

Effects of neuromuscular electrical stimulation and low-level laser therapy on neuromuscular parameters and health status in elderly women with knee osteoarthritis: A randomized trial.

To determine the effects of neuromuscular electrical stimulation and low-level laser therapy on neuromuscular parameters and health status in elderly subjects with knee osteoarthritis. A randomized evaluator-blinded clinical trial. Forty-five elderly women with knee osteoarthritis. Subjects were randomized into 1 of the following 3 intervention groups: electrical stimulation group (18-32 min pulsed current, stimulation frequency 80 Hz, pulse duration 400 μs, stimulation intensity 40% of maximal isometric voluntary contraction), laser group (dose 4-6 J per point, 6 points at the knee joint) or combined group (electrical stimulation plus laser therapy). The outcomes included muscle thickness and anatomical cross-sectional area (ultrasonography), knee extensors' electrical activity (electromyography), torque (dynamometry) and health status (Western Ontario and McMaster Universities Osteoarthritis Index). All groups underwent a 4-week control period (without intervention) followed by an 8-week intervention period. Muscle thickness and anatomical cross-sectional area increased in the electrical stimulation and combined groups. All groups presented similar improvements in torque, electrical activity and health status. Electrical stimulation alone or in combination with laser therapy generated positive effects on all evaluated parameters. Laser therapy increased health status and electrical activity, but had no effect on muscle mass.

Relationships of ultrasound measures of intrinsic foot muscle cross-sectional area and muscle volume with maximum toe flexor muscle strength and physical performance in young adults.

[Purpose] To investigate the relationships between toe flexor muscle strength with (TFS-5-toes) and without (TFS-4-toes) the contribution of the great toe, anatomical and physiological muscle cross-sectional areas (CSA) of intrinsic toe flexor muscle and physical performance were measured. [Subjects] Seventeen men (82% sports-active) and 17 women (47% sports-active), aged 20 to 35 years, volunteered. [Methods] Anatomical CSA was measured in two intrinsic toe flexor muscles (flexor digitorum brevis [FDB] and abductor hallucis) by ultrasound. Muscle volume and muscle length of the FDB were also estimated, and physiological CSA was calculated. [Results] Both TFS-5-toes and TFS-4-toes correlated positively with walking speed in men (r=0.584 and r=0.553, respectively) and women (r=0.748 and r=0.533, respectively). Physiological CSA of the FDB was significantly correlated with TFS-5-toes (r=0.748) and TFS-4-toes (r=0.573) in women. In men, physiological CSA of the FDB correlated positively with TFS-4-toes (r=0.536), but not with TFS-5-toes (r=0.333). [Conclusion] Our results indicate that physiological CSA of the FDB is moderately associated with TFS-4-toes while toe flexor strength correlates with walking performance.

Muscle and tendon adaptation in adolescent athletes: Alongitudinal study.

There is evidence that a non-uniform adaptation of muscle and tendon in young athletes results in increased tendon stress during mid-adolescence. The present longitudinal study investigated the development of the morphological and mechanical properties of muscle and tendon of volleyball athletes in a time period of 2 years from mid-adolescence to late adolescence. Eighteen elite volleyball athletes participated in magnetic resonance imaging and ultrasound-dynamometry sessions to determine quadriceps femoris muscle strength, vastus lateralis, medialis and intermedius morphology, and patellar tendon mechanical and morphological properties in mid-adolescence (16±1years) and late adolescence (18±1years). Muscle strength, anatomical cross-sectional area (CSA), and volume showed significant (P<0.05) but moderate increases of 13%, 6%, and 6%, respectively. The increase of patellar tendon CSA (P<0.05) was substantially greater (27%) and went in line with increased stiffness (P<0.05; 25%) and reduced stress (P<0.05; 9%). During late adolescence, a pronounced hypertrophy of the patellar tendon led to a mechanical strengthening of the tendon in relation to the functional and morphological development of the muscle. These adaptive processes may compensate the unfavorable relation of muscle strength and tendon loading capacity in mid-adolescence and might have implications on athletic performance and tendon injury risk.

Biomechanical implications of skeletal muscle hypertrophy and atrophy: a musculoskeletal model.

Muscle hypertrophy and atrophy occur frequently as a result of mechanical loading or unloading, with implications for clinical, general, and athletic populations. The effects of muscle hypertrophy and atrophy on force production and joint moments have been previously described. However, there is a paucity of research showing how hypertrophy and atrophy may affect moment arm (MA) lengths. The purpose of this model was to describe the mathematical relationship between the anatomical cross-sectional area (ACSA) of a muscle and its MA length. In the model, the ACSAs of the biceps brachii and brachialis were altered to hypertrophy up to twice their original size and to atrophy to one-half of their original size. The change in MA length was found to be proportional to the arcsine of the square root of the change in ACSA. This change in MA length may be a small but important contributor to strength, especially in sports that require large joint moments at slow joint angular velocities, such as powerlifting. The paradoxical implications of the increase in MA are discussed, as physiological factors influencing muscle contraction velocity appear to favor a smaller MA length for high velocity movements but a larger muscle MA length for low velocity, high force movements.

Inter- and intramuscular differences in training-induced hypertrophy of the quadriceps femoris: association with muscle activation during the first training session.

The purpose of this study was to examine whether inter- and intramuscular differences in hypertrophy induced by resistance training correspond to differences in muscle activation during the first training session. Eleven young men completed 12weeks of training intervention for knee extension. Before and after the intervention, T1-weighted magnetic resonance (MR) images were recorded to determine the volume and anatomical cross-sectional area (CSA) along the length of the individual muscles of the quadriceps femoris. The T2-weighted MR images were also acquired before and immediately after the first training session. The T2 was calculated for each pixel within the quadriceps femoris, from which the muscle activation was evaluated as %activated volume and area. The results showed that the %activated volume after the first training session was significantly higher in the vastus intermedius than the vastus medialis. However, the relative change in muscle volume after the training intervention was significantly greater in the rectus femoris than the vasti muscles (vastus lateralis, intermedius and medialis). Within the rectus femoris, both the %activated area and relative increase in CSAwere significantly greater in the distal region than the proximal region. In contrast, the %activated area and relative increase in CSA of the vasti were nearly uniform along each muscle. These results suggest that the muscle activation during the first training session is associated with the intramuscular difference in hypertrophy induced by training intervention, but not with the intermuscular difference.