Relationship between bilateral differences in single-leg jumps and asymmetry in isokinetic knee strength.

The aims of the study were to investigate the differences in kinematics and kinetics between the dominant and nondominant leg during single-leg jumps without arm swing, and to determine the relationship between bilateral asymmetry in isokinetic knee strength and the single-leg jump. Isokinetic knee strength and single-leg jump kinematics and kinetics were measured in 11 male participants. The bilateral asymmetry index was calculated for each parameter. For isokinetic knee strength, there were no significant differences between the dominant and nondominant legs. Significant correlations were observed for the bilateral asymmetry index for isokinetic knee strength at 180 degrees per second and the bilateral asymmetry indexes for maximum flexion angle and the mean knee joint torque during the single-leg jumps. In conclusion, the findings of the current study suggest an association between knee strength imbalances and the joint angle, as well as the torque produced in single-leg jumps, although no relationship between knee strength and jump height was observed.

Bilateral asymmetry in joint torque during squat exercise performed by long jumpers.

This study aimed to examine the bilateral differences in movement and joint torques during the squat exercise by using kinematic and kinetic analyses. Eighteen long jumpers participated in this study. They performed 3 repetitions of the squat exercise with loads of 50, 70, and 90% of their 3 repetition maximum (3RM). During the exercise, their movement was recorded using a Vicon motion capture system. Ground reaction forces (GRFs) were simultaneously measured by 2 force platforms, one under each foot. On the basis of these position and force data, joint angles and torques for the hip, knee, and ankle were calculated using inverse dynamics. Results showed that the peak vertical and horizontal GRFs did not differ between the takeoff and non-takeoff legs in any loading condition. However, the maximal flexion angle and peak torque at hip showed significant differences between the limbs under all loading conditions (p < 0.05). In addition, the peak ankle torque in the takeoff leg was larger than that in the non-takeoff leg under a load of 90% of 3RM. These results indicate that joint torques may be bilaterally asymmetric when long jumpers perform the squat exercise, which should be considered when attempting to decrease the risk of injury.

Effects of prolonged tendon vibration stimulation on eccentric and concentric maximal torque and emgs of the knee extensors.

The purpose of present study was to compare the effect of Ia afferent attenuation on the activity of alpha motor neuron (MN) during concentric and eccentric action. Eight male subjects were enrolled in the present study. The experiments consisted of two sessions of MVC measurements, since all subjects performed both maximal concentric and eccentric action. EMG signals were simultaneously measured. To establish the baseline of strength, subjects were asked to perform MVC of knee extension in each session. After finishing the measurements, 20 min of vibration stimulation was applied. Immediately after finishing vibration stimulation, the MVC and AEMG were again measured. The means of MVC for concentric knee extension at pre and post- vibration stimulation were 192.2 ± 49.3 Nm and 162.3 ± 47.9 Nm, respectively. The means of MVC for eccentric knee extension at pre and post-vibration stimulation were 299.7 ± 77.0 Nm and 247.3 ± 88. 6 Nm, respectively. Two-factor repeated ANOVA detected significant differences in the MVC. Both main effects for pre-post condition (F(1,7)=, p = 0.0033) and action (F(1,7)=26.35, p = 0.0013) were noted. No interaction effect (action x condition) was noted. The means of AEMG (vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF)) at pre and post -vibration stimulation were decreased. Two-factor repeated ANOVA detected significant differences in AEMG (VM and VL). Both main effects for pre-post condition (VL;F(1,7)=7.27, p = 0.0308, VM; F(1,7)=9.55, p = 0.0175) and action (F(1,7)=12.40, p = 0.0097) were noted in the VL and the VM but not in the RF. Furthermore, significant interaction (action x condition) effect was noted in the VM (F(1,7)=7.03, p = 0.0328) but not in the VL. The MVC and the EMG activity of the VL in response to the prolonged vibration stimulation were significantly reduced in eccentric contraction over concentric contraction. These results represented that a deactivation effect on the alpha MN of the VL during eccentric action was greater than that of concentric action. Key pointsA deactivation effect on the alpha motor neuron of the vastus lateralis during eccentric action was greater than that of maximal concentric action.

Ultrasonographic measurement of tendon displacement caused by active force generation in the psoas major muscle.

The purpose of this study was to examine the validity of using ultrasonography for detecting the force generated by the psoas major muscle, a muscle positioned in the deep trunk. We measured the displacement of central tendon on B-mode ultrasound images of two different longitudinal sections of the muscle during passive hip flexion-extension and isometric hip flexion at varied hip angles. In both tasks, the values of tendon displacement obtained independently from each section coincided well, indicating that tendon displacement took place along a straight trajectory, i.e., close to the nodal line between two scanned planes. It was strongly correlated with both the hip angle (R(2) = 0.98) and the hip-flexion torque (R(2) = 0.83). In the second set of experiment, we measured the tendon displacement during dynamic movements with the combination of ultrasonography and VICON-based motion analysis. From the tendon displacement during dynamic thigh lifting and walking, the force generated by the muscle could be estimated by extracting the force-related component. These results indicate that ultrasonography of the psoas major muscle can measure the displacement of its central tendon accompanied with either length change of the muscle or the elongation of tendon. Although much attention has to be paid to the limitations of this methodology, ultrasonography may be useful for detecting the force generation of the muscle during a variety of dynamic movements.

The development of trunk muscles in male wrestlers assessed by magnetic resonance imaging.

The purpose of this study was to compare the development of trunk musculature among Elite, Sub-elite, and Elite junior wrestlers. The performance level of these groups, ordered highest to lowest, is as follows: Elite (n = 20), Sub-elite (n = 25), and Elite junior (n = 39). A magnetic resonance imaging device was used to measure the cross-sectional area (CSA) of the trunk muscles. The whole trunk muscle cross-sectional area (t-MCSA) of the Elite group was significantly larger than that of the Elite junior group (p < 0.05). The rectus abdominis muscle CSA of the Elite group was significantly larger than that of the Elite junior group (p < 0.01). The psoas major muscle CSA of the Elite group was significantly larger than that of the Elite junior group (p < 0.05). There were no significant differences in the CSA of any of the trunk muscles between the Elite and Sub-elite groups. In conclusion, compared with Elite junior wrestlers, it is conceivable that a greater CSA of trunk flexors of Elite wrestlers is one factor which supports increased performance.

Physiological responses to interval training sessions at velocities associated with VO2max.

Previous research has indicated that short-duration, high-intensity work intervals performed at velocities associated with maximal oxygen uptake (vVO2max) combined with active recovery intervals may be effective in eliciting improvements in endurance performance. This study was designed to characterize selected physiological responses to short-duration (< or = 60 seconds) interval work performed at velocities corresponding to 100% of vVO2max. Twelve men participated in 3 randomized trials consisting of treadmill running using work (W)/recovery (R) intervals of 15 seconds W/15 seconds R (15/15); 30 seconds W/15 seconds R (30/15); and 60 seconds W/15 seconds R (60/15). Work intervals were performed at 100% of vVO2max, whereas R intervals were performed at 50% of vVO2max. A fourth trial consisting of continuous work (C) at 100% of vVO2max was also performed. All subjects completed the 15/15 and 30/15 trials; however, only 5 of the 12 completed the 60/15 trial. The percentage of VO2max (mean +/- SD) during 15/15 (71.6 +/- 4.2%) was significantly lower (p < or = 0.05) than the percentages during 30/15 (84.6 +/- 4.0%), 60/15 (89.2 +/- 4.2%), or C (87.9 +/- 5.0%). Similar results were found for heart rate and perceived exertion. Blood lactate concentrations following exercise were significantly lower (p < or = 0.05) in 15/15 (7.3 +/- 2.4 mmol x L(-1)) than in the other trials. No significant differences (p > 0.05) existed among 30/15 (11.5 +/- 1.8 mmol x L(-1)), 60/15 (12.5 +/- 1.8 mmol x L(-1)) or C (12.1 +/- 1.8 mmol x L(-1)). High intensity, short-duration 2:1 W/R intervals appear to produce responses that may benefit both aerobic and anaerobic energy system development. A 4:1 W/R ratio may be an upper limit for individuals in the initial phases of interval training.

Differences in fat-free mass and muscle thicknesses at various sites according to performance level among judo athletes.

The purpose of this study was to investigate differences in fat-free mass and thicknesses of various muscles among judo athletes of different performance levels. The subjects were 69 male judo athletes of 3 different performance levels. Group A was composed of athletes who participated in the Olympic Games or Asian Games (n = 13). Groups B (n = 21) and C (n = 35) were composed of judo athletes at a university who did or did not participate in intercollegiate competitions (including qualifying matches), respectively. Muscle and fat thicknesses were measured by B-mode ultrasound at 9 sites. Fat percentage was calculated from fat thicknesses using a previously reported equation. Fat-free mass was calculated from fat percentage and body weight. Muscles thicknesses were normalized to the height of the individual. Group A had significantly larger fat-free mass than Group C (p < 0.05). The normalized thicknesses of the elbow extensor and flexor muscles were significantly larger in Group A than in Group C. The normalized thickness of the elbow flexor muscle was significantly larger in Group A than in Group B. The results of this study showed that judo athletes with low performance levels such as those in Group C had lower fat-free mass, and the degree of development of the brachialis muscles differed according to performance level.

Resistance training during unweighting maintains muscle size and function in human calf.

PURPOSE: A 20-d 6 degrees head-down tilt bed rest project was conducted to evaluate the effect of dynamic leg press and plantar flexion resistance training on muscle size and function in human plantar flexors (PF) throughout the prolonged bed rest. METHODS: Twelve healthy men participated in this study and were divided two groups: resistance training (BR-Tr group: N = 6, age: 23 +/- 2 yr, height: 170 +/- 3 cm, weight: 66 +/- 7 kg) and nontraining (BR-Cont group: N = 6, age: 23 +/- 1 yr, height: 170 +/- 3 cm, weight: 67 +/- 6 kg) during the bed rest. Physiological cross-sectional area (PCSA) and peak torque of the PF muscle group was determined. Spin-spin relaxation times (T2) of the medial (MG) and lateral gastrocnemius (LG) and soleus (Sol) muscle was measured at rest and immediately after unilateral calf-raising exercise (5 sets of 10 reps). RESULTS: PCSA of the PF muscle group did not show any significant change in BR-Tr group; however, for the BR-Cont group, PCSA decreased by 13% after bed rest (P < 0.05). There was no significant change in exercise-induced T2 change of the MG, LG, or Sol muscles between before and after the bed rest in BR-Tr group; however, in the BR-Cont group, significant increases in T2 were found in these three muscles after the bed rest (P < 0.05 to 0.01). CONCLUSION: We conclude that dynamic leg press and plantar flexion resistance training during bed rest maintains muscle size and function (torque and T2), and that this training could be useful for prevention of progressive muscle deconditioning during spaceflight.