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Vasoconstrictor responsiveness in contracting human muscle: influence of contraction frequency, contractile work, and metabolic rate

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Abstract

Purpose

The aim of this study was to examine whether independent effects exist between contractile work and metabolic demand (VO2m) on vasoconstrictor responsiveness (i.e., functional sympatholysis) under different contraction durations matched for total contractile work in exercising human skeletal muscle.

Methods

Ten young men performed rhythmic forearm contractions at 10 and 15% of maximum voluntary contraction (MVC) which consisted of muscle contractions using the same duty cycle but altering the duration of the contraction–relaxation cycles of exercise and included: 1) fast frequency contractions at 10% MVC (FFC10%) using a contraction relaxation cycle at 1:2 s; 2) slow frequency contractions at 10% MVC (SFC10%) at 2:4 s; and 3) SFC at 15% MVC (SFC15%) at 2:4 s. Lower body negative pressure (LBNP) was applied to increase sympathetic vasoconstriction during forearm exercise. Brachial artery diameter and blood velocities (measured via Doppler ultrasound) determined forearm blood flow (FBF), and forearm vascular conductance (FVC) was calculated from FBF (ml min−1) and mean arterial blood pressure.

Results

Results revealed that steady-state indices of FBF, FVC, and VO2m were greater (P < 0.05) in FFC10% and SFC15% vs. SFC10%. In addition, the magnitude of vasoconstriction (percent reduction in FVC) in response to reflex increases in sympathetic activity during LBNP was greater with SFC10% vs. FFC10% (−20.6 ± 3.0 vs. −11.1 ± 2.0%; P < 0.05), whereas there was no difference with FFC10% vs. SFC15% (−11.1 ± 2.0 vs. −11.8 ± 1.8%; P = 0.91).

Conclusions

Our data indicate that faster work-matched muscle contractions increase blood flow and metabolism, leading to improved functional sympatholysis as compared to slower work-matched muscle contractions in humans.

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Abbreviations

ATP:

Adenosine triphosphate

CtvO2 :

Venous oxygen content

ECG:

Electromyography

FBF:

Forearm blood flow

FFC10% :

Fast frequency contractions at 10% MVC

FVC:

Forearm vascular conductance

LBNP:

Lower body negative pressure

MAP:

Mean arterial pressure

MVC:

Maximal voluntary contraction

NO:

Nitric oxide

O2 :

Oxygen

PvO2:

Partial pressure of venous oxygen

SFC10% :

Slow frequency contractions at 10% MVC

SFC15% :

Slow frequency contractions at 15% MVC

SNS:

Sympathetic nervous system

SS:

Steady state

SvO2 :

Oxygen saturation

VO2m :

Muscle oxygen consumption

%ΔFVC:

Percent change in forearm vascular conductance

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Acknowledgements

The authors are grateful for the subjects who volunteered to participate in this study. Extended appreciation goes out to Charles Ganger IV, Samuel Norton, and Aaron Schneider for their valuable technical assistance during experimental data collection.

Author contributions

Performed experiments (NTK, WEH, KU, and DPC), analyzed data (NTK), interpreted results of experiments (NTK, WEH, and DPC), prepared figures (NTK), drafted manuscript (NTK), edited/revised manuscript (NTK, WEH, KU, and DPC), approved final version (NTK, WEH, KU, and DPC), and conception and design of research (NTK and DPC).

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Authors

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Correspondence to Nicholas T. Kruse.

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Grants

This research was supported by National Heart, Lung, and Blood Institute Research Grant HL-105467 (to D.P. Casey) and T32HL-007121 (to N.T. Kruse).

Conflict of interest

No conflicts of interest, financial or otherwise, are declared by the authors.

Additional information

Communicated by Massimo Pagani.

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Kruse, N.T., Hughes, W.E., Ueda, K. et al. Vasoconstrictor responsiveness in contracting human muscle: influence of contraction frequency, contractile work, and metabolic rate. Eur J Appl Physiol 117, 1697–1706 (2017). https://doi.org/10.1007/s00421-017-3660-7

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  • DOI: https://doi.org/10.1007/s00421-017-3660-7

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