1. In human pennate muscle, changes in anatomical cross-sectional area (CSA) or volume caused by training or inactivity may not necessarily reflect the change in physiological CSA, and thereby in maximal contractile force, since a simultaneous change in muscle fibre pennation angle could also occur. 2. Eleven male subjects undertook 14 weeks of heavy-resistance strength training of the lower limb muscles. Before and after training anatomical CSA and volume of the human quadriceps femoris muscle were assessed by use of magnetic resonance imaging (MRI), muscle fibre pennation angle (theta(p)) was measured in the vastus lateralis (VL) by use of ultrasonography, and muscle fibre CSA (CSA(fibre)) was obtained by needle biopsy sampling in VL. 3. Anatomical muscle CSA and volume increased with training from 77.5 +/- 3.0 to 85.0 +/- 2.7 cm(2) and 1676 +/- 63 to 1841 +/- 57 cm(3), respectively (+/- S.E.M.). Furthermore, VL pennation angle increased from 8.0 +/- 0.4 to 10.7 +/- 0.6 deg and CSA(fibre) increased from 3754 +/- 271 to 4238 +/- 202 microm (2). Isometric quadriceps strength increased from 282.6 +/- 11.7 to 327.0 +/- 12.4 N m. 4. A positive relationship was observed between theta(p) and quadriceps volume prior to training (r = 0.622). Multifactor regression analysis revealed a stronger relationship when theta(p) and CSA(fibre) were combined (R = 0.728). Post-training increases in CSA(fibre) were related to the increase in quadriceps volume (r = 0.749). 5. Myosin heavy chain (MHC) isoform distribution (type I and II) remained unaltered with training. 6. VL muscle fibre pennation angle was observed to increase in response to resistance training. This allowed single muscle fibre CSA and maximal contractile strength to increase more (+16 %) than anatomical muscle CSA and volume (+10 %). 7. Collectively, the present data suggest that the morphology, architecture and contractile capacity of human pennate muscle are interrelated, in vivo. This interaction seems to include the specific adaptation responses evoked by intensive resistance training.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7793.2001.t01-1-00613.x

A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in muscle architecture.

Muscle ultrasound is a useful tool in the diagnosis of neuromuscular disorders, as these disorders result in muscle atrophy and intramuscular fibrosis and fatty infiltration, which can be visualized with ultrasound. Several prospective studies have reported high sensitivities and specificities in the detection of neuromuscular disorders. Although not investigated in large series of patients, different neuromuscular disorders tend to show specific changes on muscle ultrasound, which can be helpful in differential diagnosis. For example, Duchenne muscular dystrophy results in a severe, homogeneous increase of muscle echo intensity with normal muscle thickness, whereas spinal muscular atrophy shows an inhomogeneous increase of echo intensity with severe atrophy. A major advantage of muscle ultrasound, compared to other imaging techniques, is its ability to visualize muscle movements, such as muscle contractions and fasciculations. This study reviews the possibilities and limitations of ultrasound in muscle imaging and its value as a diagnostic tool in neuromuscular disorders.

Muscle ultrasound in neuromuscular disorders.

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2 = 0.13), knee flexion (r2 = 0.18), and knee extension (r2 = 0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r = ?0.37), knee flexion (r = ?0.43), and knee extension (r = ?0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.

Relationship between Hip and Knee Strength and Knee Valgus during a Single Leg Squat

The purpose of this study was to investigate the differences in the viscoelastic properties of human tendon structures (tendon and aponeurosis) in the medial gastrocnemius muscle between men (n=16) and women (n=13). The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle was measured directly by ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) and tendon elongation (L) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the Fm- L loop to the area beneath the curve during the ascending phase was calculated as hysteresis. The L values at force production levels beyond 50 N were significantly greater for women than for men. The maximum strain (100xDeltaL/initial tendon length) was significantly greater in women [9.5 (1.1)%] than in men [8.1 (1.6)%]. The stiffness and Young's modulus were significantly lower in women [16.5 (3.4) N/mm, 277 (25) MPa] than in men [25.9 (7.0) N/mm, 356 (32) MPa]. Furthermore, the hysteresis was significantly lower in women [11.1 (5.9)%] than in men [18.7 (8.5)%, P=0.048]. These results suggest that there are gender differences in the viscoelastic properties of tendon structures and that these might in part account for previously observed performance differences between the genders.

Gender differences in the viscoelastic properties of tendon structures

In the general population, an estimated one in 3000 individuals sustains an anterior cruciate ligament injury per year in the United States, corresponding to an overall injury rate of approximately 100,000 injuries annually. This national estimate is low for women because anterior cruciate ligament injury rates are reported to be two to eight times higher in women than in men participating in the same sports, presenting a sizable health problem. With the growing participation of women in athletics and the debilitating nature of anterior cruciate ligament injuries, a better understanding of mechanisms of injury in women sustaining anterior cruciate ligament injuries is essential. Published studies strongly support noncontact mechanisms for anterior cruciate ligament tears in women, which make these injuries even more perplexing. Speculation on the possible etiology of anterior cruciate ligament injuries in women has centered on anatomic differences, joint laxity, hormones, and training techniques. Investigators have not agreed on causal factors for this injury, but they have started to profile the type of athlete who is at risk. In the current study the most recent scientific studies of intrinsic and extrinsic risk factors thought to be contributing to the high rate of female anterior cruciate ligament injuries will be reviewed, important differences will be highlighted, and recommendations proposed to alleviate or minimize these risk factors among female athletes will be reported where appropriate.

Anterior cruciate ligament injuries in the female athlete: Potential risk factors

The cross-sectional areas (CSA) of fat, muscle and bone tissues of the limb as well as maximal voluntary isokinetic strength were measured in untrained men (n = 27) and women (n = 26) aged 18-25 years. Anatomical CSA of the three tissues were determined by ultrasound on the upper arm and thigh. The isokinetic strength of the elbow and knee extensor and flexor muscles were measured by an isokinetic dynamometer (Cybex II) at 1.05 rad.s-1. The women had significantly (P 0.05) and the elbow flexors of the women (r = 0.388, P > 0.05). No significant difference between sexes was observed when strength was expressed per unit of muscle CSA (F.CSA-1) for the elbow flexors and extensors. However, the men showed significantly higher F.CSA-1 than the women for the knee flexors and extensors (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of muscle cross-sectional area and strength between untrained women and men

The influences of age and sex on the cross-sectional area (CSA) and isometric strength of the ankle dorsiflexors and plantarflexors (PF) were investigated in four age groups of 121 boys and 121 girls aged: 7–9, 10–12, 13–15, and 16–18 years. A single anatomical cross-section was determined at 30% of the distance from the articular cleft between the femur and tibiacondyles by using an ultrasonic apparatus. In both sexes, the increase in age was associated with significant increases in the CSA and strength (ST) of these opposing muscle groups. The sex differences became apparent in the 13–15 year group for CSA and in the 16–18 year group for ST but the differences reduced considerably when CSA and ST were expressed per unit of the second power of the lower leg length (CSA·LL
−2) and the product of CSA and the lower leg length (ST·CSA
−1·LL
−1), respectively. However,CSA·LL
−2 of both muscles had a tendency to be increased at and over the age of 10–12 years, and was the highest at 16–18 years, andST·CSA
−1·LL
−1 of PF showed higher values in the older boys than in the younger. Thus, it appeared that, at least in the reciprocal muscle groups of the ankle joint, the sex differences in muscle CSA and ST during growth could be accounted for by differences in LL and muscle mass, respectively. However, other factors must also be involved to explain completely the age differences in these variables.

A cross-sectional study of the size and strength of the lower leg muscles during growth

Isokinetic strength and cross-sectional area (CSA) of knee extensor muscles were examined in 60 boys and girls, aged 6-9 years, and in 71 young adult men and women to investigate the influences of age and gender on the strength capabilities in relation to muscle size. A single anatomical CSA of quadriceps femoris at the right mid-thigh was measured by using a B-mode ultrasonic apparatus. Isokinetic strength produced at three kinds of constant velocity, 1.05, 3.14, and 5.24 rad.s-1, was significantly correlated to the product of CSA and thigh length (TL) in separate samples by age and gender. In both genders, however, young adults had significantly higher ratios of strength to CSA.TL (ST.CSA-1.TL-1) than children at all measurement velocities. Relative differences in ST.CSA-1.TL-1 between children and young adults became larger with increasing test velocity. Within the same generation, men had significantly higher ST.CSA-1.TL-1 than women at all measurement velocities except for the ratio in children at 1.05 rad.s-1. These results indicate that the ability to produce strength proportional to muscle size is lower in children than in young adults, regardless of gender, and lower in women than in men within the same generation.

Strength and cross-sectional area of knee extensor muscles in children

The force generation capacity, during 50 repeated maximal knee extensions with a constant velocity of 3.14 rad.s-1, and cross-sectional area (CSA) of the quadriceps femoris muscles were determined for untrained women (n = 36) and men (n = 27) aged from 18 to 25 years. As force scores in the maximal repetitions, the mean values of force (F) of every 5 consecutive and all trials and the percentage of decline of F (%D) with 50 contractions were calculated. The CSA was measured by using a B-mode ultrasound technique at the midpoint of the thigh length. The F decreased from 303 (SEM 13) N at the 1st-5th trial to 155 (SEM 9) N at the 46th-50th trial for the men, and from 202 (SEM 9) N to 94 (SEM 4) N for the women. The F of every 5 consecutive and all trials were significantly correlated to muscle CSA: for the men r = 0.552-0.872 (P < 0.01) and for the women r = 0.609-0.857 (P < 0.01). The men showed significantly higher F at every 5 consecutive trials than the women even when calculated per unit muscle CSA (F.CSA-1). There were significant correlations between %D and F.CSA-1 at the 1st-5th trial: r = 0.538 (P < 0.01) for the men and r = 0.631 (P < 0.01) for the women, respectively. The average values of %D were almost the same in both sexes: for the men 48 (SEM 3) % and for the women 52 (SEM 2) %, respectively. However, an ANCOVA calculation on %D, using F.CSA-1 at the 1st-5th trial as the covariate, indicated that the women had significantly higher %D than the men. Thus, the force output during the maximal repetitions was significantly correlated to the CSA of quadriceps femoris in both sexes. The force output was lower in the women than in the men even when the difference in the muscle CSA was allowed for. The women had higher %D than the men when force output per unit muscle CSA during the initial 5 repetitions was compared.

Sex difference in force generation capacity during repeated maximal knee extensions

The purpose of this study was to investigate the force-producing characteristics of boys aged 13 years in relation to fatigue of elbow flexor muscles. Maximal voluntary force in elbow flexion was measured before and after a muscle endurance test (MET) by using an isokinetic dynamometer isometrically, concentrically and eccentrically at three velocities, i.e. 0.21, 0.52, and 1.05 rad · s−1. The MET consisted of maximal concentric and eccentric muscle actions performed alternately at 0.52 rad · s−1 for 50 consecutive trials. Muscle cross-sectional area (CSA) of elbow flexor muscles (biceps brachii and brachialis) was measured by a B-mode ultrasound apparatus. Although eccentric force showed significantly higher values than concentric force during MET, there was no significant difference in the rate of decline in force between the two actions. There was no significant difference in the rate of decline in force after MET for each velocity and muscle action. Isometric, concentric and eccentric force before MET was significantly related to muscle CSA whereas, after MET, concentric force significantly correlated with muscle CSA but there was no significant correlation between muscle CSA and isometric or eccentric force. From our study, it is therefore suggested that in development to maturity, isometric, concentric and eccentric force decrease at the same rate with advancing muscle fatigue; however, there might be differences among muscle actions in facors affecting force development.

S Ikegawa

Papers

Comparison of muscle cross-sectional area and strength between untrained women and men

A cross-sectional study of the size and strength of the lower leg muscles during growth

Strength and cross-sectional area of knee extensor muscles in children

Sex difference in force generation capacity during repeated maximal knee extensions

Concentric and eccentric muscle strength before, during and after fatigue in 13 year-old boys