The force-length relationship of the human muscle-tendon complex (MTC) of the triceps surae and the achilles tendon was investigated in various stretch load conditions. Six male subjects performed various vertical jumps with maximal effort: squat jumps (SJ), counter movement jumps (CMJ) and drop jumps (DJ) from a height of 24 cm, 40 cm and 56 cm. The force-length relationship was calculated from the signals of the components of the ground reaction forces and the kinematic data obtained from the high-speed film records. Surface electromyograms (EMG) of the soleus, gastrocnemius and tibialis anterior muscles were also recorded. The force-length diagrams showed individually high sensitivity to the imposed stretch load. In conditions with relatively low stretch load requirements there was a counter-clockwise direction observable, indicating that the energy absorbed during the eccentric, or lengthening phase was lower than the energy delivered during the concentric, or shortening phase. In high load conditions this relationship was reversed indicating a negative energy balance. The EMG-length diagrams of SJ and CMJ consisted of an initial isometric loading of the muscle, followed by a shortening phase with only slightly reduced EMG amplitudes. In DJ, however, the diagrams showed an initial lengthening of the MTC with fairly constant activation amplitudes. After 40 ms an isometric loading of the muscle, lasting for approximately 80 ms, was followed by a shortening phase. It was concluded that segmental stretch reflex activation represented the predominant activation process during the isometric loading phase, to meet the adequate stiffness properties of the MTC.

The purpose of this study was to investigate whether the stretch-shortening cycle (SSC) contraction is integrated in neuromuscular activation in upper body muscles during double poling in cross-country skiing. Thirteen elite skiers performed double poling roller-skiing at increasing treadmill velocities of 9, 15, 21, 27 km h(-1) and their individual maximal velocity. Elbow angle, axial pole force and surface EMG in the triceps brachii, pectoralis major, latissimus dorsi and teres major muscle were recorded. Increases in peak pole force, rate of force development and elbow flexion angular velocities were identified (P < 0.05). The mean MVC-normalized EMG amplitudes increased during the pre-activation phase before pole plant, elbow flexion and the reflex-mediated phase between 30 and 120 ms after pole plant due to velocity increases (P < 0.05). It is thus suggested that elite cross-country skiers use SSC during double poling, particularly in the triceps muscle in order to generate high forces.

Introduction Leg length inequalities (LLI) are a common finding. Rasterstereography offers a non-invasive, contactfree and reliable method to detect the effects of LLIs on spinal posture and pelvic position. Materials and methods A total of 115 subjects were rasterstereographically examined during different artificially created leg length inequalities (5-15 mm) using a platform. The pelvic obliquity and torsion and the lateral and frontal deviation of the spine, as well as the surface rotation, were measured. Results Changes in platform height led to an increase of the pelvic tilt and torsion. Only minor changes in the spinal posture were found by different simulated leg length inequalities. Conclusions Our study showed that there was a correlation between an artificial leg length inequality up to 15 mm and pelvic tilt or torsion, but only minor changes in the spinal posture were measured. Further studies should investigate the effects of greater leg length inequalities on spine and pelvis.

Purpose Leg length inequalities (LLIs) can result in an increased energy consumption, abnormal gait or osteoarthritis of the hip. In a previous study we simulated different LLIs of up to 15 mm and evaluated their effects on the pelvic position and spinal posture. We found a correlation between LLIs and resulting changes of the pelvic position. Despite suggestions in the literature we were not able to detect significant changes of the spinal posture. Therefore, the purpose of this study was to determine the amount of LLI that would in fact alter the spinal posture. Methods The subjects were placed on a simulation platform, whose height could be precisely controlled by the measuring device, to simulate different LLIs of up to 20 mm. For LLIs [20 mm, additional precision-cut wooden blocks were used under one foot. After an adaptation period the resulting changes of the pelvis and spine were measured with a rasterstereographic device. ResultsWe found a significant correlation between platform height changes and changes of the pelvic position. The frontal spinal parameters surface rotation and lateral deviation changed significantly when simulating differences greater than 20 mm. No changes of the sagittal spinal curvature were measured, however, a trend to decreasing kyphotic angles was noted. Conclusions Our study has shown for the first time that LLIs [20 mm will lead to significant changes in the spinal posture of healthy test subjects. However, these changes were only found in frontal (surface rotation and lateral flexion) spinal parameters, but not in sagittal parameters. Here for the kyphotic angle only a tendency to decreasing angles was noted. We have also found a significant correlation between different leg lengths and changes of the pelvic position. Further, females and males seem to react in the same way to LLIs.

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