Short-term landing training attenuates landing impact and improves jump height in landing-to-jump movement.

Landing technique is an important factor influencing jump performance in landing-to-jump (L-J) movement. This study examined the effects of short-term landing training on jump performance in L-J. We hypothesized that landing training without jumping decreases landing impact and increases jump height in L-J. Twenty healthy adult men were randomly assigned to the control (CG: n = 10) or the training (TG: n = 10) group. The TG performed a 2-week landing training (3 times per week, 6 sessions) that aims to decrease impact force. Before and after the training period, both groups performed landing and L-J from a 35-cm height and also squat jumps (SJs). Ground reaction forces and kinematic data were obtained during the landing, L-J, and SJ. The CG showed no significant changes in all measured variables. In the TG, the peak vertical ground reaction force up to 100 mseconds after ground contact in L-J, expressed relative to body mass, significantly decreased (pre: 3.04 [0.77] vs. post: 2.35 [0.37], p < 0.01), and the L-J height significantly increased (pre: 47.2 [5.6] cm vs. post: 48.2 [5.5] cm, p < 0.05) without gain in SJ height. Furthermore, the TG showed significant gains (p < 0.01) in hip joint power during the propulsive phase. The current results support our hypothesis and indicate that short-term landing training improves the technique for absorbing landing impact and increasing L-J height. The increased L-J height may be a result of an increase in power generation around the hip joint.

A biomechanical study of side steps at different distances.

Lateral quickness is a crucial component of many sports. However, biomechanical factors that contribute to quickness in lateral movements have not been understood well. Thus, the purpose of this study was to quantify 3-dimensional kinetics of hip, knee, and ankle joints in side steps to understand the function of lower extremity muscle groups. Side steps at nine different distances were performed by nine male subjects. Kinematic and ground reaction force data were recorded, and net joint torque and work were calculated by a standard inverse- dynamics method. Extension torques and work done at hip, knee, and ankle joints contributed substantially to the changes in side step distances. On the other hand, hip abduction work was not as sensitive to the changes in the side step distances. The main roles of hip abduction torque and work were to accelerate the center of mass laterally in the earlier phase of the movement and to keep the trunk upright, but not to generate large power for propulsion.

Role of the coordinated activities of trunk and lower limb muscles during the landing-to-jump movement.

This study aimed to clarify how the activities of trunk and lower limb muscles during a landing-to-jump (L-J) movement are coordinated to perform the task effectively. Electromyography (EMG) activities of trunk and lower limb muscles as well as kinematic and ground reaction force data were recorded while 17 subjects performed 5 L-Js from a height of 35 cm. The L-J was divided into four phases: PRE phase, 100 ms preceding ground contact; ABSORPTION phase, from ground contact through 100 ms; BRAKING phase, from the end of the ABSORPTION phase to the time of the lowest center of mass position; and PROPULSION phase, from the end of the BRAKING phase to takeoff. The trunk extensor and flexors showed reciprocal activation patterns through the L-J. In the PROPULSION phase, the timings when the EMG activities of the extensor muscles peaked were characterized as a sequential proximal-to-distal pattern. Furthermore, the peak vertical ground reaction force in the ABSORPTION phase relative to body mass negatively correlated to the jump height of the L-J movement and positively correlated with the magnitude of the EMG activities of the soleus in the PRE phase and those of the soleus and rectus abdominis in the ABSORPTION phase. These findings indicate that the intensities and peak timings of muscle activities in the trunk and lower limb are coordinated during the L-J movement and, the coordinated activities would play functional roles such as impact absorption, braking against the descent of body and force generation and direction control for jumping.

Activity modulations of trunk and lower limb muscles during impact-absorbing landing.

This study aimed to investigate the activity patterns of trunk and lower limb muscles during impact-absorbing landing. Electromyogram activities of the trunk and lower limb muscles along with kinematic and ground reaction forces were measured while subjects (n=17) performed 10 landings from a height of 35 cm. Landing motions were divided into three phases: 100 ms preceding ground contact (GC) (PRE phase), from GC through 100 ms (ABSORPTION phase), and from the end of the ABSORPTION phase until the vertical position of the center of mass was minimized (BRAKING phase). During the PRE phase, the rectus abdominis, external oblique, and medial gastrocnemius were highly activated. Upon GC, the hip and knee joints were in a flexed position; the ankle joints, in a plantarflexed position. After GC, peak timings of muscle activities and lower limb joint rotations were characterized by distal-to-proximal sequential patterns. The peak vertical ground reaction force in the ABSORPTION phase relative to body weight positively correlated with the activity levels of the vastus lateralis and gluteus maximus in the PRE phase and that of rectus abdominis in the ABSORPTION phase. These findings indicate that the intensities and peak timings of muscle activities in the trunk and lower limb are coordinated to absorb landing impact.