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.

No abstract

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.

BackgroundThe 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.PurposeTo investigate the reliability of ultrasound elastography for the quantification of elasticity of the TrA.Material and MethodsA 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.ResultsThe 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.ConclusionThe reliabilities of the skilled and unskilled operators were high and moderate, respectively.

The aim of this study was to investigate whether accommodating elastic bands with barbell back squats (BSQ) increase muscular force during the deceleration subphase. Ten healthy men (mean ± standard deviation: Age: 23 ± 2 years; height: 170.5 ± 3.7 cm; mass: 66.7 ± 5.4 kg; and BSQ one repetition maximum (RM): 105 ± 23.1 kg; BSQ 1RM/body mass: 1.6 ± 0.3) were recruited for this study. The subjects performed band-resisted parallel BSQ (accommodating elastic bands each sides of barbell) with five band conditions in random order. The duration of the deceleration subphase, mean mechanical power, and the force and velocity during the acceleration and deceleration subphases were calculated. BSQ with elastic bands elicited greater mechanical power output, velocity, and force during the deceleration subphase, in contrast to that elicited with traditional free weight (p < 0.05). BSQ with elastic bands also elicited greater mechanical power output and velocity during the acceleration subphase. However, the force output during the acceleration subphase using an elastic band was lesser than that using a traditional free weight (p < 0.05). This study suggests that BSQ with elastic band elicit greater power output during the acceleration and deceleration subphases.

Takei, S, Hirayama, K, and Okada, J. Comparison of the power output between the hang power clean and hang high pull across a wide range of loads in weightlifters. J Strength Cond Res 35(2S): S84–S88, 2021—The current study compared the peak power output during the hang power clean (HPC) and hang high pull (HHP) across a wide range of external loads in weightlifters. Eight weightlifters completed 1 repetition maximum (1RM) assessment for the HPC (1.59 ± 0.17 kg/body mass) and a power test for the HPC and HHP at relative loads of 40, 60, 70, 80, 90, 95, and 100% 1RM of the HPC. The ground reaction force and 2-dimensional bar position data were recorded to determine the system (barbell + body mass) kinetics and bar height, respectively. System power was calculated as force multiplied by system velocity. The HHP produced significantly greater peak power than the HPC at 40, 60, and 70% 1RM. Conversely, there was no statistical or practical difference in peak power between the exercises at 80, 90, 95, and 100% 1RM. No significant interaction was found in force at peak power, whereas velocity at peak power was significantly greater during the HHP than during the HPC at 40, 60, and 70% 1RM. In addition, significantly greater peak bar height was observed for the HHP than the HPC at 40, 60, and 70% 1RM. From the power output comparisons across loads, the HHP should be used over the HPC at loads of 40–70% 1RM, whereas the HPC and HHP can be interchangeably used at loads of 80–100% 1RM.

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.

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.