Abstract
Hoffmann (H‐) reflex amplitudes in plantar flexor soleus muscle are modulated by posture, yet dorsiflexor tibialis anterior (TA) H‐reflex parameters have sparingly been studied. The purpose was to investigate modulation of the TA H‐reflex when postural demands are increased from sitting to standing. In this study, data from 18 participants (Age: 25 ± 4 years, Height: 170.9 ± 9.5 cm, Weight: 75.9 ± 17.2 kg) allowed comparison of two experimental conditions involving different postures (i.e. sitting and standing). Maximal amplitude of the TA H‐reflex (H max) as a percent of the maximal M‐wave amplitude (M max) (H max (% M max)) during sitting and standing was compared using ANOVA. Modulation of TA H‐reflex amplitude was found: Eleven participants showed facilitation and seven showed no change of reflex amplitudes. Only participants in the facilitation group showed modulation related to changes in posture (sitting: 8.7 ± 2.9%; standing: 14.8 ± 6.7%, P = 0.005). These data provide evidence of the sensitivity to posture of TA H‐reflexes. As with task‐dependent changes in soleus H‐reflexes, presynaptic regulation of Ia afferent transmission is a possible mechanism. Further investigations into causes of modulation are warranted.
Highlights
IntroductionPresynaptic inhibition is an important mechanism modulating the H-reflex amplitude, and it changes with alterations in posture (McNeil et al, 2013)
Hoffmann (H-) reflex amplitude modulation has been used to study the relationship between Ia afferent feedback and postural control (Chen and Zhou, 2011).Presynaptic inhibition is an important mechanism modulating the H-reflex amplitude, and it changes with alterations in posture (McNeil et al, 2013)
tibialis anterior (TA) H-reflexes were undetectable without a background contraction
Summary
Presynaptic inhibition is an important mechanism modulating the H-reflex amplitude, and it changes with alterations in posture (McNeil et al, 2013). Presynaptic inhibition is positively correlated with increases in postural demand, such as lying to standing, and standing to a 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society. Changes in presynaptic inhibition as inferred from modulation of H-reflex amplitude when background electromyography (EMG) and other factors are controlled, suggest a shift in the central nervous system (CNS) to increase voluntary control over the body and reduce fall risk (Huang et al, 2009). Postactivation depression disynaptic inhibitory pathways, such as Ib inhibitory interneurons and Renshaw cells, allow inhibitory postsynaptic potentials to suppress motorneurons (Pierrot-Deseilligny and Mazevet, 2000)
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