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European Journal of Applied Physiology

Published in:

29-11-2022 | Original Article

The effects of α-lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability

Authors: Karen Mackay Phillips, Lucas B. R. Orssatto, Remco Polman, Jolieke C. Van der Pols, Gabriel S. Trajano

Published in: European Journal of Applied Physiology | Issue 2/2023

Abstract

Introduction

We tested two strategies that hypothetically increase serotonin availability (α-lactalbumin consumption and a remote submaximal handgrip contraction) on estimates of persistent inward currents (PICs) amplitude of soleus muscle in healthy participants.

Methods

With a randomised, double-blind, and cross-over design, 13 healthy participants performed triangular-shaped ramp contractions with their plantar flexors (20% of maximal torque), followed by a 30-s handgrip sustained contraction (40% of maximal force) and consecutive repeated triangular-shaped contractions. This was performed before and after the consumption of either 40 g of α-lactalbumin, an isonitrogenous beverage (Zein) or an isocaloric beverage (Corn-starch). Soleus motor units discharge rates were analysed from high-density surface electromyography signals. PICs were estimated by calculating the delta frequency (ΔF) of motor unit train spikes using the paired motor unit technique.

Results

ΔF (0.19 pps; p = 0.001; d = 0.30) and peak discharge rate (0.20 pps; p < 0.001; d = 0.37) increased after the handgrip contraction, irrespective of the consumed supplement. No effects of α-lactalbumin were observed.

Conclusions

Our results indicate that 40 g of α-lactalbumin was unable to modify intrinsic motoneuron excitability. However, performing a submaximal handgrip contraction before the plantar flexion triangular contraction was capable of increasing ΔF and discharge rates on soleus motor units. These findings highlight the diffused effects of serotonergic input, its effects on motoneuron discharge behaviour, and suggest a cross-effector effect within human motoneurons.

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Title: The effects of α-lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability
Authors: Karen Mackay Phillips
Lucas B. R. Orssatto
Remco Polman
Jolieke C. Van der Pols
Gabriel S. Trajano
Publication date: 29-11-2022
Publisher: Springer Berlin Heidelberg
Published in: European Journal of Applied Physiology / Issue 2/2023
Print ISSN: 1439-6319
Electronic ISSN: 1439-6327
DOI: https://doi.org/10.1007/s00421-022-05101-3

At a glance: The STEP trials

Springer Medicine

The effects of α-lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability

Abstract

Introduction

Methods

Results

Conclusions

At a glance: The STEP trials

Springer Medicine

Abstract

Introduction

Methods

Results

Conclusions

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