Ryota Akagi

Muscle volume compared to cross-sectional area is more appropriate for evaluating muscle strength in young and elderly individuals

OBJECTIVE the present study examined which of muscle volume (MV) and cross-sectional area (CSA) is appropriate for evaluating the relation with elbow flexor muscle strength in young and elderly individuals. METHODS the subjects were 52 young (20-34 year; 30 men and 22 women) and 51 elderly individuals (60-77 year, 19 men and 32 women). The MV and maximal anatomical CSA (ACSA) of elbow flexors were determined by magnetic resonance imaging. The torque developed during maximal voluntary contraction of isometric elbow joint flexion was converted to force by dividing it by the forearm length of each subject. RESULTS torque was significantly correlated with MV in young and elderly individuals (r = 0.564-0.926). Similarly, force was also significantly correlated with ACSA in each of them (r = 0.637-0.906). However, the y-intercepts of the regression lines for the ACSA-force relationship in young men and women were significantly higher than zero. There was no age effect on torque per MV, whereas force per ACSA was significantly higher in young adults than in elderly individuals. CONCLUSION for elbow flexors, MV compared to ACSA is appropriate for evaluating the size-strength relationship and the existence of age-related difference in muscle strength per size.

Reliability and Validity of Quantifying Absolute Muscle Hardness Using Ultrasound Elastography

Muscle hardness is a mechanical property that represents transverse muscle stiffness. A quantitative method that uses ultrasound elastography for quantifying absolute human muscle hardness has been previously devised; however, its reliability and validity have not been completely verified. This study aimed to verify the reliability and validity of this quantitative method. The Young’s moduli of seven tissue-mimicking materials (in vitro; Young’s modulus range, 20–80 kPa; increments of 10 kPa) and the human medial gastrocnemius muscle (in vivo) were quantified using ultrasound elastography. On the basis of the strain/Young’s modulus ratio of two reference materials, one hard and one soft (Young’s moduli of 7 and 30 kPa, respectively), the Young’s moduli of the tissue-mimicking materials and medial gastrocnemius muscle were calculated. The intra- and inter-investigator reliability of the method was confirmed on the basis of acceptably low coefficient of variations (≤6.9%) and substantially high intraclass correlation coefficients (≥0.77) obtained from all measurements. The correlation coefficient between the Young’s moduli of the tissue-mimicking materials obtained using a mechanical method and ultrasound elastography was 0.996, which was equivalent to values previously obtained using magnetic resonance elastography. The Young’s moduli of the medial gastrocnemius muscle obtained using ultrasound elastography were within the range of values previously obtained using magnetic resonance elastography. The reliability and validity of the quantitative method for measuring absolute muscle hardness using ultrasound elastography were thus verified.

Establishing a new index of muscle cross-sectional area and its relationship with isometric muscle strength

The present study aimed i) to establish an index of muscle cross-sectional area (CSA) based on muscle thickness and circumference through a comparison with muscle CSA determined by magnetic resonance imaging (MRI), and ii) to examine the relationships between muscle strength and the index determined at rest and during the maximal isometric contraction. The muscle CSA of elbow flexors at 60% of the upper arm length (CSA60) and the maximal CSA of elbow flexors (CSAmax) were measured using MRI in 26 men and 8 women. The muscle thickness (MT) of elbow flexors and the circumference (C) of upper arm at 60% of the upper arm length were measured using ultrasonography and anthropometry, respectively, in 29 men and 9 women. The measurements of MT and C were performed in the resting (MTr and Cr) and contracted condition (MTm and Cm), where the subjects performed maximal voluntary contraction (MVC) of isometric elbow joint flexion. The torque developed during MVC was converted into the muscle force (F) of elbow flexors. The MTr × Cr was significantly correlated both with CSA60 and CSAmax (P < 0.001). The F was significantly correlated with MTm × Cm (r = 0.847, P < 0.001) and MTr × Cr (r = 0.839, P < 0.001). However, stepwise multiple regression analysis selected only MTm × Cm as a significant contributor for estimating F. The present study indicates that MT × C reflects muscle CSA, and can be an index for assessing muscle CSA. In addition, the findings obtained here showed a possibility that MT × C during MVC is more closely related to F than that at rest.

Acute effect of static stretching on hardness of the gastrocnemius muscle

PURPOSE The objective of this study is to investigate the acute effects of static stretching (SS) on muscle hardness of the gastrocnemius medialis (MG) and gastrocnemius lateralis (LG). METHODS Twenty young men participated in this study. MG and LG hardness was measured using shear wave ultrasound elastography before and after three bouts of 2-min SS. The measurement site of muscle hardness was at 30% of the lower leg length from the popliteal crease to the lateral malleolus. Similarly, the passive range of motion (ROM) of dorsiflexion, musculotendinous unit (MTU) stiffness determined by the slope of the portion of the passive torque-angle curve from 15° to 25°, and joint torque developed during isometric maximal voluntary plantarflexion at 0° of ankle joint angle were also measured before and after SS. RESULTS SS increased ROM and decreased MTU stiffness significantly but did not change joint torque. The main effects of test time and muscle group on muscle hardness were significant without a significant interaction of these variables. Both differences between the relative changes in the MG and LG hardness and between the muscle hardness ratios before and after SS were not significant. A significant correlation between the muscle hardness ratios before and after SS was found. CONCLUSION The results of this study suggest that three bouts of 2-min SS of the plantar flexors is useful for preventing muscle injury, improving muscle condition, and maintaining muscle strength, and that the acute effects of SS on the muscle hardness of MG and LG are of the same degree.

Effect of a 5-week static stretching program on hardness of the gastrocnemius muscle.

This study investigated the effects of a static stretching (SS) program on muscle hardnesses of the gastrocnemius medialis (MG) and gastrocnemius lateralis (LG). Nineteen young men participated in this study. Either the right or left leg was randomly selected to conduct three bouts of 2‐min SS of the plantar flexors 6 days a week for 5 weeks in each subject (the SS group), and the other leg was assigned to a control group. Before (pretest) and after (posttest) conducting the SS program, MG and LG hardnesses were measured using shear wave ultrasound elastography. The SS program was found to decrease muscle hardnesses, but not to change the ratio of MG hardness to LG hardness. There were no significant differences between the relative changes in the MG and LG hardnesses from pretest to posttest in both the SS and control groups. Significant correlations between the muscle hardness ratios at pretest and posttest were found in both groups. The results of this study suggest that the current SS program is useful for improving muscle condition in the plantar flexors, and that its long‐term effects on the MG and LG hardnesses are of the same degree.

Longitudinal and transverse deformation of human Achilles tendon induced by isometric plantar flexion at different intensities

The present study determined in vivo deformation of the entire Achilles tendon in the longitudinal and transverse directions during isometric plantar flexions. Twelve young women and men performed isometric plantar flexions at 0% (rest), 30%, and 60% of the maximal voluntary contraction (MVC) while a series of oblique longitudinal and cross-sectional magnetic resonance (MR) images of the Achilles tendon were taken. At the distal end of the soleus muscle belly, the Achilles tendon was divided into the aponeurotic (ATapo) and the tendinous (ATten) components. The length of each component was measured in the MR images. The widths of the Achilles tendon were determined at 10 regions along ATapo and at four regions along ATten. Longitudinal and transverse strains were calculated as changes in relative length and width compared with those at rest. The ATapo deformed in both longitudinal and transverse directions at 30%MVC and 60%MVC. There was no difference between the strains of the ATapo at 30%MVC and 60%MVC either in the longitudinal (1.1 and 1.6%) or transverse (5.0∼11.4 and 5.0∼13.9%) direction. The ATten was elongated longitudinally (3.3%) to a greater amount than ATapo, while narrowing transversely in the most distal region (-4.6%). The current results show that the magnitude and the direction of contraction-induced deformation of Achilles tendon are different for the proximal and distal components. This may be related to the different functions of Achilles tendon, i.e., force transmission or elastic energy storage during muscle contractions.

Relationships between muscle size and hardness of the medial gastrocnemius at different ankle joint angles in young men

Background Measurement of muscle hardness is important for objective evaluation of the muscle condition. Muscle hardness may be related to muscle size, but this relationship has not yet been examined. Purpose To examine the relationship between the size and hardness of the medial gastrocnemius muscle (MG) at different ankle joint angles. Material and Methods Twelve young male subjects comprised the present study. Muscle thickness of the right MG (MTMG) was measured by ultrasonography as an index of muscle size. The MTMG was determined at 30% of the lower leg length from the popliteal crease to the lateral malleolus. At the same site, muscle hardness of the right MG (MHMG) was measured with ultrasound real-time tissue elastography. Both measurements were taken while each subject was instructed to lie in a prone position on a test bench. The right ankle was secured to a handmade apparatus by a non-elastic belt, with the hip and knee joints fully extended and the ankle positioned at +30°, 0° and –20° (0°: neutral position, positive values indicating plantar flexion). Results There were no significant differences in the MTMG among the ankle joint angles whereas the MHMG significantly increased as the ankle was moved from plantar flexion to dorsiflexion. As a result, there was a difference in the MTMG-MHMG relationship between the angles. The MTMG significantly correlated with the MHMG only at +30° (r = 0.635, P < 0.05) where passive torque around the ankle has been shown to be near zero in previous studies. Conclusion The hardness of the relaxed MG with no passive tension appears to depend on its size.

Relationships Between Muscle Strength and Indices of Muscle Cross-sectional Area Determined During Maximal Voluntary Contraction in Middle-aged and Elderly Individuals

Akagi, R, Takai, Y, Kato, E, Fukuda, M, Wakahara, T, Ohta, M, Kanehisa, H, Kawakami, Y, and Fukunaga, T. Relationships between muscle strength and indices of muscle cross-sectional area determined during maximal voluntary contraction in middle-aged and elderly individuals. J Strength Cond Res 23(4): 1258-1262, 2009-The present study examined how muscle cross-sectional area (CSA) indices determined at rest and during maximal voluntary contraction (MVC) are related to muscle strength in middle-aged and elderly individuals (22 men and 36 women, 51-77 years). The muscle thickness (MT) of elbow flexors and circumference (C) at the level 60% distal to the upper arm was measured by ultrasonography and a measuring tape, respectively, both at rest and during isometric MVC of elbow flexion. The muscle strength (F) of elbow flexors was calculated by dividing the torque developed during MVC by the forearm length of each subject. The product of MT and C (MT×C) and the square of MT (MT2) were defined as the muscle CSA indices. The F was significantly correlated with MT×C during MVC (r = 0.905, p ≤ 0.001) and at rest (r = 0.778, p ≤ 0.001), with the former relationship significantly stronger than the latter (p ≤ 0.001). Similarly, F was significantly correlated with MT2 both during MVC (r = 0.896, p ≤ 0.001) and at rest (r = 0.780, p ≤ 0.001), and there was also a significant difference between the correlation coefficients (p ≤ 0.01). These findings show that, in middle-aged and elderly individuals, muscle strength is more closely related to muscle CSA indices during MVC than at rest. It is concluded that the present muscle CSA indices taken during MVC enable easy and practical evaluation of the muscle strength per size of elbow flexors in middle-aged and elderly individuals.

In vivo determination of the Achilles tendon moment arm in three-dimensions

Two-dimensional methods have been applied to determine the Achilles tendon moment arm in previous studies, although the talocrural joint rotates in three-dimension. The purpose of this study was to develop a method for determining the Achilles tendon moment arm in three-dimensions (3DMA). A series of sagittal ankle images were obtained at ankle positions of -20°, -10° (dorsiflexed position), 0° (neutral position), +10°, +20°, and +30° (plantarflexed position). The talocrural joint axis was determined as the finite helical axis of the ankle joint over 20° of displacement, and the 3DMA was determined as the shortest distance from the talocrural joint axis to the line of action of the Achilles tendon force. The corresponding 2DMA was determined with the center of rotation method using the images captured on the sagittal plane passing through the mid-point of the medio-lateral width of the tibia. The 3DMA ranged from 35 to 41 mm across various ankle positions and was, on average, 11 mm smaller than 2DMA. The difference between the two measures was attributable primarily to the deviations of the talocrural joint axis from the anatomical medio-lateral direction. The deviations on the coronal plane (21.4±20.7°) and on the transverse planes (14.8±22.6°) accounted for the errors of 1.3 mm and 3.0 mm, respectively. In addition, selecting either a medially or laterally misaligned sagittal-plane image for determining the 2DMA gave rise to error by 3.5 mm. The remaining difference was accounted for by the random measurement error.

Validity of ultrasound muscle thickness measurements for predicting leg skeletal muscle mass in healthy Japanese middle-aged and older individuals

BackgroundThe skeletal muscle mass of the lower limb plays a role in its mobility during daily life. From the perspective of physical resources, leg muscle mass dominantly decreases after the end of the fifth decade. Therefore, an accurate estimate of the muscle mass is important for the middle-aged and older population. The present study aimed to clarify the validity of ultrasound muscle thickness (MT) measurements for predicting leg skeletal muscle mass (SM) in the healthy Japanese middle-aged and older population.FindingsMTs at four sites of the lower limb and the bone-free lean tissue mass (LTM) of the right leg were determined using brightness-mode ultrasonography and dual-energy X-ray absorptiometry (DXA), respectively, in 44 women and 33 men, 52- to 78-years old. LTM was used as a representative variable of leg skeletal muscle mass. In the model-development group (30 women and 22 men), regression analysis produced an equation with R2 and standard error of the estimate (SEE) of 0.958 and 0.3 kg, respectively: LTM (kg) = 0.01464 × (MTSUM×L) (cm2) - 2.767, where MTSUM is the sum of the product of MTs at four sites, and L is length of segment where MT is determined. The estimated LTM (7.0 ± 1.7 kg) did not significantly differ from the measured LTM (7.0 ± 1.7 kg), without a significant systematic error on a Bland-Altman plot. The application of this equation for the cross-validation group (14 women and 11 men) did not yield a significant difference between the measured (7.2 ± 1.6 kg) or estimated (7.2 ± 1.6 kg) LTM and systematic error.ConclusionThe developed prediction equation may be useful for estimating the lean tissue mass of the lower extremity for the healthy Japanese middle-aged and older population.