Ryoichi Ema

In vivo measurement of human rectus femoris architecture by ultrasonography: Validity and applicability

The architectural feature of the rectus femoris (RF) has been scarcely investigated despite its substantial contribution to knee extension torque and large plasticity in the muscularity. This study aimed to examine the reproducibility and validity of ultrasound measurements of RF architecture and interrelationships among the architectural parameters. After confirming the measurement accuracy of an examiner (measurement errors <1%), in vivo and cadaveric measurements of fascicle lengths and pennation angles of RF were performed. Day‐to‐day reproducibility of measurements was investigated in vivo including muscle thickness measurement. Validity of measurements was investigated by comparing the values between direct and ultrasound measurements for the cadaver. The intraclass correlation coefficients were 0·984, 0·960 and 0·932, and root mean square difference between measured values on 2 days was 0·8 mm, 3·1 mm and 1·4° for muscle thickness, fascicle length and pennation angle, respectively. The validity of measurements was similar or better than those of previous reports on other muscles. We also confirmed a positive correlation between the muscle thickness and the pennation angle as has been shown in other muscles. The current results warrant the use of B‐mode ultrasonography for examining the architectural characteristics of RF in vivo.

Non‐uniform muscle oxygenation despite uniform neuromuscular activity within the vastus lateralis during fatiguing heavy resistance exercise

Previous studies have reported for the vastus lateralis (VL) that the extent of muscle hypertrophy in response to resistance training is greater in the distal than in the middle region, despite uniform muscle fibre composition within VL along its length. In the present study, to investigate mechanism(s) for such non‐uniform muscle hypertrophy, we simultaneously measured neuromuscular activity and muscle oxygenation state at the middle and distal regions of VL during fatiguing heavy resistance exercise. Twelve males performed unilateral knee extension exercise which consisted of 4 sets of 8 repetitions at intensity of 80% of the individual one repetition maximum. During the resistance exercise, neuromuscular activities and muscle oxygenation status at the middle and distal regions (50% and 70% of the thigh length, respectively) of VL were measured by using electromyography and near‐infrared spectroscopy, respectively. Neuromuscular activities were similar between the distal and middle regions of VL, whereas muscle tissue oxygenation saturation was significantly lower at the distal than at the middle region of VL. These results suggest a possibility that the regional difference in muscle oxygenation but not in neuromuscular activity during fatiguing heavy resistance exercise is responsible for the regional difference in hypertrophy within a muscle.

Unique muscularity in cyclists' thigh and trunk: A cross-sectional and longitudinal study

This study examined the influence of regular training in competitive cycling on individual muscle volume of the thigh and psoas major cross‐sectionally and longitudinally. T1‐weighted magnetic resonance (MR) images of the trunk and right thigh were obtained from eight experienced varsity male cyclists (experience: > 4 years) and 10 untrained men (experiment 1), and from 12 (10 males, two females) varsity cyclists before and after competitive cycling training for 6 months (experiment 2). From the MR images, the volumes of each of the quadriceps femoris and hamstrings, total adductors, gracilis, sartorius, and psoas major were determined. The volumes of the monoarticular thigh muscles, semitendinosus, and psoas major muscles were significantly greater in the experienced cyclists than in the untrained men (experiment 1), and increased significantly after the competitive training for 6 months (experiment 2). In contrast, the volumes of the other biarticular thigh muscles were similar among the experienced cyclists and untrained men (experiment 1), and did not change by competitive cycling training (experiment 2). The results indicate that competitive cycling training induces muscle‐specific hypertrophy of the synergistic muscles, especially between the monoarticular and biarticular muscles, leading to quantitative profiles of the musculature in experienced cyclists.

Further potentiation of dynamic muscle strength after resistance training

PURPOSE One bout of 5-6 s of maximal voluntary isometric contraction (MVC) is known to enhance subsequent dynamic joint performance such as dynamic joint torque and power with maximal voluntary effort. On the other hand, such a muscle contraction can also induce muscle fatigue. It is then possible that individual differences in fatigue resistance is a factor that affects the balance between potentiation and fatigue. Here, we examined the effect of chronic heavy-resistance training on the extent and time course of the potentiation of maximal voluntary dynamic torque. METHODS Before and after a 12-wk intervention, maximal voluntary concentric knee extension torque at 210° · s(-1) was measured in the following sequence: before and immediately after a 5-s MVC of knee extension and 1, 3, and 5 min thereafter. The training group performed heavy-resistance training exercise of knee extension consisting of five sets of eight repetitions with 80% of one-repetition maximum, three sessions a week during the intervention period. RESULTS Before the resistance training intervention, maximal voluntary concentric torque was significantly enhanced only at 1 and 3 min post-MVC. After the 12-wk resistance training, the maximal voluntary concentric torque was potentiated also immediately after the conditioning MVC and was further increased at 1-min point. CONCLUSION These findings indicate that the contraction-induced potentiation of maximal voluntary dynamic torque is pronounced in strength-trained individuals.

Inferior Muscularity of the Rectus Femoris to Vasti in Varsity Oarsmen

The purpose of this study was to examine the morphological profiles of 4 constituents (vastus lateralis, vastus medialis, vastus intermedius and rectus femoris) of the quadriceps femoris in oarsmen through comparison with non-athletes. T1-weigheted magnetic resonance (MR) images of the thigh were obtained from 14 oarsmen and 19 non-athlete men. From the MR images, serial anatomical cross-sectional areas (ACSAs) and muscle volume of each muscle were determined. The muscle volume of the total quadriceps femoris, vastus lateralis, vastus medialis and vastus intermedius were significantly larger in the oarsmen than in the non-athlete men, whereas that of the rectus femoris was comparable for the 2 groups. The portion of the rectus femoris as a percentage of total quadriceps femoris volume was significantly higher in the non-athlete men than in the oarsmen, and vice versa for the vastus lateralis. The proximal-to-distal and middle-to-distal ACSA ratios in each muscle did not differ between the 2 groups. The present results indicate inferior muscular hypertrophy of the rectus femoris compared to the vasti in oarsmen, and that the vasti are equally hypertrophied along their lengths. This may be due to muscle-specific adaptation to the rowing exercise.

Plyometric Training Favors Optimizing Muscle–Tendon Behavior during Depth Jumping

The purpose of the present study was to elucidate how plyometric training improves stretch–shortening cycle (SSC) exercise performance in terms of muscle strength, tendon stiffness, and muscle–tendon behavior during SSC exercise. Eleven men were assigned to a training group and ten to a control group. Subjects in the training group performed depth jumps (DJ) using only the ankle joint for 12 weeks. Before and after the period, we observed reaction forces at foot, muscle–tendon behavior of the gastrocnemius, and electromyographic activities of the triceps surae and tibialis anterior during DJ. Maximal static plantar flexion strength and Achilles tendon stiffness were also determined. In the training group, maximal strength remained unchanged while tendon stiffness increased. The force impulse of DJ increased, with a shorter contact time and larger reaction force over the latter half of braking and initial half of propulsion phases. In the latter half of braking phase, the average electromyographic activity (mEMG) increased in the triceps surae and decreased in tibialis anterior, while fascicle behavior of the gastrocnemius remained unchanged. In the initial half of propulsion, mEMG of triceps surae and shortening velocity of gastrocnemius fascicle decreased, while shortening velocity of the tendon increased. These results suggest that the following mechanisms play an important role in improving SSC exercise performance through plyometric training: (1) optimization of muscle–tendon behavior of the agonists, associated with alteration in the neuromuscular activity during SSC exercise and increase in tendon stiffness and (2) decrease in the neuromuscular activity of antagonists during a counter movement.

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 12 weeks 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 CSA were 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.

Muscle size-strength relationship including ultrasonographic echo intensity and voluntary activation level of a muscle group

This study aimed to investigate the relationship between muscle volume (MV) and joint torque for the plantar flexors (PF) in 40 young (20 men and 20 women) and 33 elderly (19 men and 14 women) individuals in consideration of the voluntary activation (VA) of PF and ratio of intramuscular adipose tissue within PF assessed by ultrasonographic echo intensity (EI). MV was estimated from the thickness of PF on ultrasonography and the lower leg length using a prediction equation previously reported. The maximal voluntary contraction torque of isometric plantar flexion was measured as TQMVC. VA (%) was assessed using the twitch interpolation technique, and maximal joint torque calculated by TQMVC/VA × 100 was adopted as TQ100%. The correlation coefficients between MV and TQMVC (r = 0.518) and between MV and TQ100% (r = 0.602) were both significant, with the latter being significantly higher than the former. When a stepwise multiple regression analysis using MV and EI as independent variables and TQ100% as the dependent variable was performed, MV (β = 0.554) and EI (β = -0.203) were both selected as significant contributors for estimating TQ100%. Additionally, the residual errors of TQ100% using the multiple regression equation (independent variables: MV and EI; 18.6 ± 14.4 Nm) were significantly lower than those using the simple regression equation (independent variable: MV; 36.6 ± 28.0 Nm). These results suggest that the consideration of VA and EI with muscle size results in a closer muscle size-strength relationship than previously achieved.

Effect of knee alignment on the quadriceps femoris muscularity: Cross-sectional comparison of trained versus untrained individuals in both sexes

Knee alignment is suggested to be a factor affecting each quadriceps femoris muscle size, and knee alignment such as Q-angle differs between men and women. Also, training can induce inhomogeneous hypertrophy among the quadriceps femoris, thereby leading to different component characteristics of the muscles. If Q-angle is a major determinant of the quadriceps femoris muscularity, it is hypothesized that the sex-related difference in the quadriceps femoris muscularity, if any, is further highlighted in trained individuals, being associated with Q-angle. We tested this hypothesis. Magnetic resonance images of the right thigh were obtained from 26 varsity rowers as trained subjects (13 for each sex) and 34 untrained individuals as controls (17 for each sex). From the images, muscle volume of each constituent of the quadriceps femoris (vastus lateralis, VL; medialis, VM; intermedius; rectus femoris) was determined. The Q-angle was measured during quiet bilateral standing with hand support as needed. Percent volume of VM to the total quadriceps femoris was greater in female rowers than male rowers and female controls, and that of VL was greater in male rowers than male controls. There were no correlations between Q-angle and percent muscle volume in any muscles regardless of rowing experience or sex. The current study revealed that well-trained rowers have sex-related quadriceps femoris muscularity but no significant correlations between percent muscle volume in any muscles and Q-angle. Our findings suggest that Q-angle is not a major determinant of the quadriceps femoris muscularity in either well-trained or untrained individuals.

Effect of calf-raise training on rapid force production and balance ability in elderly men

Calf-raise training with the intent to move rapidly, without special equipment or venue, induces an improvement of explosive plantar flexion force, which is attributable to neuromuscular rather than musculotendinous adaptations. Although the training effect on balance performance was trivial, we found a sign of improvement (i.e., neuromuscular adaptations during standing). In conclusion, functional neuromuscular capacity can be enhanced by home-based calf-raise exercise in elderly men, which may protect against mobility loss with aging.