Biomedical subjects

N Guissard

Publications and source records attributed to N Guissard.

3 recordsLinked to original sources

PubMed1992

EMG and mechanical changes during sprint starts at different front block obliquities.

The effect of decreased front block obliquity on start velocity was studied during sprint starts. The electromyographic (EMG) activity of the medial gastrocnemius (MG), the soleus (Sol), and the vastus medialis (VM) was recorded and analyzed at a 70 degrees, a 50 degrees, and a 30 degrees angle between the foot plate surface and the horizontal. Integrated EMGs (IEMG) were compared with muscle length changes in the MG and Sol in relation to foot and knee movements. The results indicate that decreasing front block obliquity significantly (P < 0.05) increases the start velocity without any change to the total duration of the pushing phase and the overall EMG activity. This improvement in sprint start performance is associated with the enhanced contribution of the MG during eccentric and concentric phases of calf muscles contraction. In the "set position" the initial length of MG and Sol is increased at 50 degrees and 30 degrees as compared with 70 degrees. The subsequent stretch-shortening cycle is improved and contributes more effectively to the speed of the muscle shortening. Moreover, lengthening these muscles during the eccentric phase stretches the muscle spindles, and the reflex activities that contribute to the observed increase in the MG IEMG, are present when the slope of the block is reduced. The results indicate that decreasing front block obliquity induces neural and mechanical modifications that contribute to increasing the sprint start velocity without any increase in the duration of the pushing phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Decrease of motoneuron excitability during stretching of the human soleus.

Changes of motoneuron (MN) excitability was studied during the basic modalities of slow or static stretching of the human soleus muscle (Sol). Tendon (T) and Hofmann (H) reflexes were recorded during slow passive (assisted) stretching (SS). The H response was analysed in SS, in SS preceded by a maximal isometric contraction of the muscle or contraction-relaxation (CR) and during stretching of the muscle by contracting the antagonistic muscle (AC). The maximal joint mobilization during SS, CR and AC appears to be closely related to the decrease of the H response. It is suggested that the joint mobilization during slow stretching is closely controlled by the level of inhibition of the MN pool excitability, which lasts only as long as the stretching manoeuvre is maintained.

Adult↗

PubMed1988

Muscle stretching and motoneuron excitability.

Change of motoneuron excitability has been studied during the three basic modalities of slow or static stretching of the human soleus muscle. Tendon (T) and Hoffmann (H) reflexes were analyzed during static stretching (SS). The H response was compared in SS, in SS preceded by a maximal isometric contraction of the muscle or contraction-relaxation (CR) and during stretching of the muscle by contracting the antagonistic muscles (AC). During progressive dorsiflexion of the foot there is a significant difference (p less than 0.05) between T and H reflexes during SS, although the amplitude of direct motor (M) response, evoked by a maximal stimulation of the motor nerve, is not changed. The maximal joint mobilization during SS, CR and AC modalities appears to be closely related to the decrease in the H response during stretching. This decrease is significantly (p less than 0.05) smaller in SS than in AC or CR. In this last method, the duration of the maximal isometric contraction does not affect the results. In these three basic stretching procedures, the H reflex quickly recovers as soon as the manoeuvre is interrupted. It is suggested that changes in muscle motoneuron pool excitability closely control joint mobilization during slow or static stretching. The inhibition of the motoneurons observed during SS, CR and AC modalities is limited to the duration of the stretching manoeuvre.

Adult↗