Kuniaki Hirayama

Acute Effects of an Ascending Intensity Squat Protocol on Vertical Jump Performance

Abstract Hirayama, K. Acute effects of an ascending intensity squat protocol on vertical jump performance. J Strength Cond Res 28(5): 1284–1288, 2014—The purpose of this study was to examine the acute effects of an ascending intensity squat protocol consisting of single-repetition exercises on subsequent vertical jump performance. Fourteen college weightlifters attended 2 testing sessions: squat (SQ) and control (CON) conditions. In the SQ condition, squat exercises with incremental loads (20% 1 repetition maximum [RM], 40% 1RM, 60% 1RM, 80% 1RM, and maximal isometric [MI] half-squat exercise) were performed with a time interval of 3 minutes after submaximal cycling and static stretching. Maximum vertical jump height was measured at the beginning of the session and after cycling, static stretching, and each squat exercise in the SQ condition. In the CON condition, vertical jump height was measured at the same times with the subject resting on a chair after cycling and stretching. Vertical jump height gradually increased after 60% 1RM, 80% 1RM, and MI half-squat exercises compared with baseline values (i.e., first trial of vertical jump), whereas no change was observed in the CON condition. These results suggest that an ascending intensity squat protocol consisting of single-repetition exercises of sufficient intensity can be useful for athletes who require high muscular power.

Neural modulation of muscle-tendon control strategy after a single practice session.

PURPOSE The purpose of the present study was to examine a hypothesis that the musculotendinous behavior during a propelling action with a countermovement can be altered by a single practice session through modulation of neuromuscular activities. METHODS Eight males performed unilateral maximal plantarflexion with (CMJ) and without (noCMJ) countermovement before and after a practice consisting of six sets of three repetitions of unilateral CMJ exercises. Measurements included EMG activities of the triceps surae and tibialis anterior muscles and the fascicle behavior of the gastrocnemius by ultrasonography, and impulse was calculated from the force-time data. The change in tendon length was also estimated. RESULTS The impulse in CMJ increased after the practice, but that in noCMJ did not. After the practice, the magnitude of fascicle lengthening and shortening in CMJ decreased, which was accompanied by an increase in tendon shortening without change in the ankle joint range of motion. The time lag from the onset of reaction force to that of EMG activities of the triceps surae muscles was shortened after the practice. CONCLUSIONS The results support the hypothesis and indicate that, as a neural modulation through a single practice, the muscle-tendon unit behavior during CMJ can be optimized to improve the performance.

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.

Reliability of ultrasound elastography for the quantification of transversus abdominis elasticity.

Background The transversus abdominis (TrA), which is considered to be involved in controlling spinal stability, is covered by two muscles (i.e. the external and internal oblique muscles) as well as subcutaneous fat. Therefore, there were doubts about whether it was possible to perform highly reliable measurements of muscle elasticity. Purpose To investigate the reliability of ultrasound elastography for the quantification of elasticity of the TrA. Material and Methods A skilled and an unskilled operator of ultrasound elastography measured TrA elasticity in 10 healthy men (age, 24 ± 4 years; height, 172.0 ± 5.2 cm; weight, 72.3 ± 12.0 kg) in the supine position. The tests were repeated six times; of the six measured values, a group of four measurements showing the lowest coefficient of variation (CV) was adopted and the mean values were used for further analysis. This procedure was repeated twice on each participant on two different days. Results The intra-class correlation coefficients (ICCs) between days for skilled and unskilled operators were 0.86 (P < 0.00) and 0.59 (P = 0.02), respectively, and the CVs were 8.7% and 13.8%, respectively. The ICCs between operators and CVs were in the range of 0.56–0.57 (P = 0.02–0.03) and 13.5–15.5%, respectively. No systematic error was found for any comparison. Conclusion The reliabilities of the skilled and unskilled operators were high and moderate, respectively.

Relationship of pectoralis major muscle size with bench press and bench throw performances

Abstract Akagi, R, Tohdoh, Y, Hirayama, K, and Kobayashi, Y. Relationship of pectoralis major muscle size with bench press and bench throw performances. J Strength Cond Res 28(6): 1778–1782, 2014—This study examined the relationship of muscle size indices of the pectoralis major muscle with bench press and bench throw performances in 18 male collegiate athletes. The maximal cross-sectional area (MCSAMAx) and volume (MV) of the pectoralis major muscle were determined by magnetic resonance imaging. First, subjects were tested for their one repetition maximum bench press strength (1RMBP) using a Smith machine. At a later date, subjects performed bench throws using the Smith machine with several different loads ranging from 30.0 kg to 90% of 1RMBP. Barbell positions were measured by a linear position transducer, and bench throw power was calculated using a dynamic equation. Three trials were performed for each load. In all the trials, the maximal peak power was adopted as bench throw peak power (PPBT). The 1RMBP was significantly correlated with MCSAMAx. Similarly, the correlation coefficient between MV and PPBT was significant. In contrast to the y-intercept of the MV-PPBT regression line, that of the MCSAMAx-1RMBP regression line was not significantly different from 0. These results suggested that, although the dependence on pectoralis major muscle size is slightly different between bench press strength and bench throw power, the pectoralis major muscle size has a significant impact on bench press and throw performances. Greater muscle size leads to heavier body weight, which can be a negative factor in some sports. We therefore recommend that athletes and their coaches develop training programs for improving sports performance by balancing the advantage of increased muscle size and the potential disadvantage of increased body weight.

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.

Jump Performance Enhancement Induced by Countermovement

The execution of a countermovement prior to the main movement, during which the agonist muscles experience a stretch–shortening cycle (shortening after being lengthened) enhances the exercise performance outcome (countermovement effect). During the stretch–shortening cycle, the fascicles and tendons exhibit a unique behavior; much of the length changes of skeletal muscle occur in tendons while fascicles contract almost isometrically. The countermovement effect varies among individuals and changes through training (or practice). The dynamics of muscle fascicles and tendons may underlie the effects of interindividual differences and training on the countermovement effect.

EFFECT OF EXPLOSIVE-TYPE STRENGTH TRAINING AND SHORT-TERM DETRAINING ON RATE OF TORQUE DEVELOPMENT DURING ISOMETRIC KNEE EXTENSION

Rate of torque development (RTD) is considered important for improving the performance in sports requiring explosive strength. Although RTD was reported to be increased after explosive-type strength training (Tillin et al. Exp Physiol 2012;97:630–41.), the effect of subsequent detraining on the increased RTD remains unclear. Therefore, this study aimed to investigate the effect of explosive-type strength training and subsequent short-term detraining on RTD during isometric knee extension. Ten male subjects participated in this study. They underwent explosive-type strength training for 6 weeks (3 days per week) and detraining for 3 weeks. The training consisted of four sets of 10 repetitions of explosive contractions of less than 1 s. At the pre- and post-training phases (PRE and POST, respectively) and after the detraining phase (DE), we measured the quadriceps femoris muscle thickness using ultrasonography. In addition, we measured the maximum voluntary torque (MVT) during maximum voluntary isometric knee extension of 3–5 s and RTD during explosive isometric knee extension of less than 1 s. In PRE, POST and DE, quadriceps femoris muscle thickness did not change. In POST, MVT and RTD increased compared with those in PRE (p<0.05). In DE, no change was observed in MVT compared with that in POST. However, in DE, RTD decreased compared with that in POST (p<0.05). In addition, no difference was observed between PRE and DE. These findings suggest that RTD increased after the 6-week explosive-type strength training but returned to the pre-training level after the 3-week short-term detraining. It is necessary to take into account the time point at which we evaluate the effect of training after explosive-type strength training.