Normobaric hypoxia does not influence the sural nerve cutaneous reflex during standing

Debenham, Mathew I. B.; Bruce, Christina D.; Rancier, Juliana M.; McNeil, Chris J.; Dalton, Brian H.

doi:10.1007/s00221-023-06711-9

Exp Brain Res

2023

DOI: 10.1007/s00221-023-06711-9

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Normobaric hypoxia does not influence the sural nerve cutaneous reflex during standing

Mathew I. B. Debenham,

Christina D. Bruce,

Juliana M. Rancier

et al.

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2024

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Cited by 3 publications

References 42 publications

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The effects of four hours of normobaric hypoxia on the vestibular control of balance

Debenham,

Bruce,

McNeil

et al. 2024

Exp Brain Res

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The effects of four hours of normobaric hypoxia on the vestibular control of balance

Debenham,

Bruce,

McNeil

et al. 2024

Exp Brain Res

View full text Add to dashboard Cite

Acute normobaric hypoxia causes a rightward shift in the torque-frequency relationship but has no effect on postactivation potentiation

Bruce,

Debenham,

Dalton

et al. 2024

Journal of Applied Physiology

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Low fractions of inspired oxygen (FIO2; i.e., hypoxia) affect aspects of skeletal muscle contractility in humans, but it remains unclear if post-activation potentiation (PAP) and the torque-frequency (T-F) relationship are altered. We investigated the effects of two (H2) and four hours (H4) of normobaric hypoxia (FIO2=0.11±0.47) on the magnitude of PAP of the knee extensors (KE) and the T-F relationship of the dorsiflexors (DF) in 13 and 12 healthy participants, respectively. To assess PAP, a resting twitch was evoked via femoral nerve stimulation before, and 2-300 s following a 10-s maximal voluntary contraction (MVC). A T-F relationship was obtained by stimulating the common fibular nerve with a single pulse and 1-s trains between 5-100 Hz. During hypoxia, peripheral oxygen saturation decreased by ~18% from 98.0±0.8% at baseline (P<0.001). MVC force and voluntary activation (VA) of the KE were lower than baseline throughout hypoxia (e.g., ~8 and ~5%, respectively at H2; P≤0.027); however, the magnitude of PAP was not altered by hypoxia (P≥0.711). Surprisingly, PAP did increase with time across the control day (P≤0.012). MVC torque and VA of the DF were unaffected by hypoxia (P≥0.127), but the estimated frequency required to evoke 50 % of 100-Hz torque increased by ~1.2 Hz at H2 (P≤0.021). These results imply that two hours of normobaric hypoxia were sufficient to: i) impair neural drive to the KE but not the mechanism(s) responsible for PAP, and ii) lead to a rightward shift of the T-F relationship for the DF.

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Four hours of normobaric hypoxia reduces Achilles tendon reflex inhibition

Debenham,

Bruce,

McNeil

et al. 2024

Journal of Applied Physiology

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Acute exposure to hypoxia increases postural sway, but the underlying neurophysiological factors are unclear. Golgi tendon organs (GTOs), located within the musculotendinous junction (MTJ), provide inhibitory signals to plantar flexor muscles that are important for balance control; however, it is uncertain if GTO function is influenced by hypoxia. The aim of this study was to determine how normobaric hypoxia influences lower limb tendon-evoked inhibitory reflexes during upright stance. We hypothesized that tendon-evoked reflex area and duration would decrease during hypoxia, indicating less inhibition of postural muscles compared to normoxia. At baseline (BL; 0.21 fraction of inspired oxygen, FIO2) and at ~2 (H2) and 4 (H4) hours of normobaric hypoxia (0.11 FIO2) in a normobaric hypoxic chamber, sixteen healthy participants received electrical musculotendinous stimulation (MTstim) to the MTJ of the left Achilles tendon. The MTstim was delivered as two sets of 50 stimuli while the participant stood on a force plate with their feet together. Tendon-evoked inhibitory reflexes were recorded from the surface electromyogram of the ipsilateral medial gastrocnemius, and center of pressure (CoP) variables were recorded from the force plate. Normobaric hypoxia increased CoP velocity (p ≤ 0.002) but not CoP standard deviation (p ≥0.12). Compared to BL, normobaric hypoxia reduced tendon-evoked inhibitory reflex area by 45% at H2 and 53% at H4 (p ≤ 0.002). In contrast, reflex duration was unchanged during hypoxia. The reduced inhibitory feedback from the GTO pathway could likely play a role in the increased postural sway observed during acute exposure to hypoxia.

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Normobaric hypoxia does not influence the sural nerve cutaneous reflex during standing

Cited by 3 publications

References 42 publications

The effects of four hours of normobaric hypoxia on the vestibular control of balance

The effects of four hours of normobaric hypoxia on the vestibular control of balance

Acute normobaric hypoxia causes a rightward shift in the torque-frequency relationship but has no effect on postactivation potentiation

Four hours of normobaric hypoxia reduces Achilles tendon reflex inhibition

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