Author/Editor		Gollhofer, A; Strojnik, V; Rapp, W; Schweizer, L
Title		Behaviour of triceps surae muscle-tendon complex in different jump conditions
Type		članek
Source		Eur J Appl Physiol
Vol. and No.		Letnik 64
Publication year		1992
Volume		str. 283-91
Language		eng
Abstract		The force-length relationship of the human muscle-tendon complex (MTC) of the triceps surea 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 forcelentht relationship was calculated from the signals of the components of the groung 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-lenght 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-lenght 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 shotening phase. it was concluded that segmental stretch reflex activation represented the predominant activation process during the isometric loading phase, to meet the adequte stiffness properties of the MTC.
Descriptors		EXERTION MUSCLE, SKELETAL ACHILLES TENDON MOVEMENT ADULT BIOMECHANICS MUSCLE CONTRACTION ELASTICITY ELECTROMYOGRAPHY LEG