Chelnokov, А¹

Velikiye Luki State Academy of Physical Education and Sports¹, Velikiye Luki, Russia, and-chelnokov@yandex.ru

non-reciprocal inhibition of spinal α-motoneurons at voluntary muscle contraction in teenagers and youths

The purpose of our research was to study the role of non-reciprocal inhibition (NI) of spinal α-motoneurons in regulation of a voluntary muscle contraction in teenagers and youths.

Methods. 14-15 (n=10) and 17-18 year-old teenagers (n=10) took part in the research. NI spinal α-motoneurons was evaluated according to the degree suppression of a testing m. soleus H-reflex amplitude in conditioning stimulation of afferents m. gastrocnemius med. (Pierrot-Deseilligny, 1979) in rest, during and after static effort. The lower the m. soleus H-reflex suppression is, the stronger is the NI. The interval between the conditioning and testing stimuli in 14-15 year-old teenagers was 1 ms, and in 17-18 year-old teenagers it was 6 ms. The subjects performed a isometric muscle contraction (plantar flexion) with a 5% and 25% of maximal voluntary contraction (МVС) effort within 2 minutes in a sitting position in the dynamographic system Biodex (Biodex Medical System, USA).

Results. In the relative muscular rest condition NI of spinal α-motoneurons is more intense in 14-15 year-old teenagers (64%), than in 17-18 year-old teenagers (83,50%). During a static 5% of MVC effort NI was practically identical in 17-18 year-old teenagers (74,92%) and in 14-15 year-old teenagers (75,11%). At 25 % of MVC in 14-15 year-old teenagers NI was 63,62%, and in 17-18 year-old teenagers it made 125,09 %, i.e. it was non-reciprocal excitation. After the static 5% and 25% of MVC effort NI is more intense in 14-15 year-old teenagers, (57,29% and 21,45%, correspondingly), than in 17-18 year-old teenagers (70,17% and 74,31%, correspondingly) (Fig. 1).

Figure 1. Expressiveness of the NI in 14-15 year-old boys and 17-18 year-old teenagers in rest, during and after a voluntary muscle contraction, %.

Discussion. The presented changes of NI of α-motoneurons at the spinal level specify structural change of neuromuscular systems functional condition in a critical ontogenesis period of the human. The teen age is characterized by intensifying of NI in rest, during and after a voluntary muscle contraction, and the youth age characteristics is weakening of NI in the same conditions. According to Stephens, Yang (1996) the decrease of NI can be caused by of m. triceps surae activation, that also took place at plantar flexion performance in our research. According to Pierrot-Deseilligny et al. (1982) and Gossard et al. (1994), a presynaptic component seems to influence reduction of NI during strong voluntary muscle contractions as the current data about of presynaptic inhibition afferents Ib (Lafleur et al., 1992).

Conclusion. In our opinion, the difference of the NI intensity in teenagers and youth can be connected with morfofunctional spinal and supraspinal interneural pathways maturation, heterochronism interior cortex structures development and the endocrine system central section activities.

References

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