Caffeine does not influence persistent inward current contribution to motoneuron firing
- Mackay, Karen, Orssatto, Lucas, Polman, Remco, Van der Pols, Jolieke, Trajano, Gabriel
- Authors: Mackay, Karen , Orssatto, Lucas , Polman, Remco , Van der Pols, Jolieke , Trajano, Gabriel
- Date: 2023
- Type: Text , Journal article
- Relation: Journal of Neurophysiology Vol. 130, no. 6 (2023), p. 1529-1540
- Full Text: false
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- Description: The purpose of this study was to investigate whether caffeine consumption would change persistent inward current (PIC) contribution to motoneuron firing at increased contraction intensities and after repetitive sustained maximal contractions. Before and after the consumption of 6 mg·kg-1 of caffeine or placebo, 16 individuals performed isometric triangular-shaped ramp dorsiflexion contractions (to 20% and 40% of peak torque), followed by four maximal contractions sustained until torque production dropped to 60% of maximum, and consecutive 20% triangular-shaped contractions. Tibialis anterior motor unit firing frequencies were analyzed from high-density surface electromyograms. PIC contribution to motor unit firing was estimated by calculating the delta frequency (DF) using the paired motor unit technique. Motoneuron peak firing frequencies at 20% and 40% contractions and total torque-time integral during the repetitive sustained maximal contractions were also assessed. DF increased 0.69 peaks per second (pps) (95% CI ¼ -0.98, -0.405; d ¼ -0.87) from 20% to 40% contraction intensities and reduced 0.85 pps (95% CI ¼ 0.66, 1.05; d ¼ 0.99) after the repetitive sustained maximal contractions, regardless of caffeine consumption. Participants produced 337 Nm·s (95% CI ¼ 49.9, 624; d ¼ 0.63) more torque integral during the repetitive sustained maximal contractions after caffeine consumption. A strong repeated-measures correlation (r ¼ 0.61; 95% CI ¼ 0.49, 0.69) was observed between reductions of DF and peak firing frequencies after the repetitive sustained maximal contractions. PIC contribution to motoneuron firing increases from 20% to 40% contraction intensities, with no effect of caffeine (on rested tibialis anterior). Repetitive sustained maximal contractions reduced PIC contribution to motoneuron firing, regardless of caffeine or placebo consumption, evidencing that changes in intrinsic motoneuron properties contributed to performance loss. Caffeine-attenuated reduction of torque production capacity was unlikely mediated by PICs. © 2023 American Physiological Society. All rights reserved.
Effects of α-lactalbumin on strength, fatigue and psychological parameters: a randomised double-blind cross-over study
- Mackay-Phillips, Karen, Orssatto, Lucas, Polman, Remco, Van der Pols, Jolieke, Trajano, Gabriel
- Authors: Mackay-Phillips, Karen , Orssatto, Lucas , Polman, Remco , Van der Pols, Jolieke , Trajano, Gabriel
- Date: 2023
- Type: Text , Journal article
- Relation: European Journal of Applied Physiology Vol. 123, no. 2 (2023), p. 381-393
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- Reviewed:
- Description: Purpose: The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as
- Description: Purpose: The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as α-lactalbumin) is of interest because this amino acid is the only precursor for brain serotonin synthesis. Therefore, the purpose of this study was to determine the effects of α-lactalbumin supplementation on neuromuscular performance. Methods: Using a randomised double-blind cross-over design, 16 healthy participants performed plantar flexor and handgrip maximal voluntary contractions, a 30-s submaximal handgrip contraction, and a plantar flexor fatigue protocol before and 90 min after consuming either 40 g of α-lactalbumin, an isonitrogenous beverage (Zein) or an isocaloric beverage (corn-starch). Sleepiness, mood, and cognition were assessed to evaluate any psychological effects. Results: α-Lactalbumin decreased force steadiness by 25% during the sustained submaximal handgrip contraction (p < 0.01) and induced greater fatigue (15% reduction in total torque–time integral, p = 0.01) during the fatigue protocol. These effects were not observed for the other control beverages. No effects were found for maximal or explosive strength, or psychological measurements. Conclusions: 40 g of α-lactalbumin increased handgrip force variability and reduced performance during fatiguing muscle contractions but did not influence brief maximal contractions or psychological parameters in healthy individuals. These findings support the hypothesis that the consumption of α-lactalbumin can increase motor neurone input–output gain and exacerbate central fatigue during sustained maximal exercise. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
- Authors: Mackay-Phillips, Karen , Orssatto, Lucas , Polman, Remco , Van der Pols, Jolieke , Trajano, Gabriel
- Date: 2023
- Type: Text , Journal article
- Relation: European Journal of Applied Physiology Vol. 123, no. 2 (2023), p. 381-393
- Full Text:
- Reviewed:
- Description: Purpose: The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as
- Description: Purpose: The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as α-lactalbumin) is of interest because this amino acid is the only precursor for brain serotonin synthesis. Therefore, the purpose of this study was to determine the effects of α-lactalbumin supplementation on neuromuscular performance. Methods: Using a randomised double-blind cross-over design, 16 healthy participants performed plantar flexor and handgrip maximal voluntary contractions, a 30-s submaximal handgrip contraction, and a plantar flexor fatigue protocol before and 90 min after consuming either 40 g of α-lactalbumin, an isonitrogenous beverage (Zein) or an isocaloric beverage (corn-starch). Sleepiness, mood, and cognition were assessed to evaluate any psychological effects. Results: α-Lactalbumin decreased force steadiness by 25% during the sustained submaximal handgrip contraction (p < 0.01) and induced greater fatigue (15% reduction in total torque–time integral, p = 0.01) during the fatigue protocol. These effects were not observed for the other control beverages. No effects were found for maximal or explosive strength, or psychological measurements. Conclusions: 40 g of α-lactalbumin increased handgrip force variability and reduced performance during fatiguing muscle contractions but did not influence brief maximal contractions or psychological parameters in healthy individuals. These findings support the hypothesis that the consumption of α-lactalbumin can increase motor neurone input–output gain and exacerbate central fatigue during sustained maximal exercise. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
The effects of α-lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability
- Mackay-Phillips, Karen, Orssatto, Lucas, Polman, Remco, Van der Pols, Jolieke, Trajano, Gabriel
- Authors: Mackay-Phillips, Karen , Orssatto, Lucas , Polman, Remco , Van der Pols, Jolieke , Trajano, Gabriel
- Date: 2023
- Type: Text , Journal article
- Relation: European Journal of Applied Physiology Vol. 123, no. 2 (2023), p. 395-404
- Full Text:
- Reviewed:
- Description: Introduction: We tested two strategies that hypothetically increase serotonin availability (
- Description: 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. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. Erratum: Correction to: The effects of α‑lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability - The original version of this article unfortunately contained a mistake. The corrected details are given below for your reading. The author’s name Karen Mackay-Phillips was incorrectly written as Karen Mackay Phillips. In section “Overview”, first sentence should read as “The current study was part of an experiment that has been divided in two parts, where some variables are presented in a companion paper (https:// doi. org/ 10. 1007/ s00421- 022- 05103-1).”. © 2022 Springer-Verlag GmbH Germany, part of Springer Nature.
- Authors: Mackay-Phillips, Karen , Orssatto, Lucas , Polman, Remco , Van der Pols, Jolieke , Trajano, Gabriel
- Date: 2023
- Type: Text , Journal article
- Relation: European Journal of Applied Physiology Vol. 123, no. 2 (2023), p. 395-404
- Full Text:
- Reviewed:
- Description: Introduction: We tested two strategies that hypothetically increase serotonin availability (
- Description: 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. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. Erratum: Correction to: The effects of α‑lactalbumin supplementation and handgrip contraction on soleus motoneuron excitability - The original version of this article unfortunately contained a mistake. The corrected details are given below for your reading. The author’s name Karen Mackay-Phillips was incorrectly written as Karen Mackay Phillips. In section “Overview”, first sentence should read as “The current study was part of an experiment that has been divided in two parts, where some variables are presented in a companion paper (https:// doi. org/ 10. 1007/ s00421- 022- 05103-1).”. © 2022 Springer-Verlag GmbH Germany, part of Springer Nature.
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