Influence of continuous inspiratory resistive breathing trials on corticospinal excitability of lower limb muscles during isometric contraction

ABSTRACT

BACKGROUND

Increased work of breathing or fatigue of respiratory muscles has been suggested to reduce exercise performance.

PURPOSE

The present study investigated the effects of continuous inspiratory resistive breathing (IRB) on the responsiveness of corticospinal pathway innervating the vastus lateralis (VL) to determine whether respiratory muscle fatigue affects the central motor output to exercising limb muscles.

METHODS

Eight subjects underwent a 6-min IRB trial three times (IRB1–3) in two experiments. During each IRB trial, the subjects performed voluntary hyperventilation through a mask attached with an inspiratory resistive load (approximately 30% of maximal inspiratory pressure (PImax)). In Experiment 1, PImax was measured at baseline and after each IRB trial. In Experiment 2, VL responses to transcranial magnetic stimulation (motor evoked potentials (MEPs) and cortical silent periods were assessed during 5 s isometric knee extension at an intensity of 15% of the maximal voluntary contraction over the same time course as in Experiment 1.

RESULTS

PImax decreased from baseline after IRB2 and IRB3 (P < 0.05). MEPs increased from baseline after IRB1 and IRB2 (P < 0.05), whereas MEPs after IRB3 were not significantly different from baseline. Cortical silent periods did not change from baseline after IRB1 and IRB2, whereas cortical silent periods after IRB3 increased from baseline (P < 0.05).

CONCLUSION

These results suggest that as inspiratory muscle fatigue progresses, the corticospinal tract controlling the lower limb muscles can shift from excitatory dominance to inhibitory dominance as a whole, affecting the central motor output to working limb muscles.

KEYWORDS:

• Respiratory muscle fatigue
• lower limb muscles
• corticospinal excitability
• transcranial magnetic stimulation

Acknowledgments

This study was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, and Culture (JSPS KAKENHI Grant Number 26350694).

Disclosure statement

No potential conflict of interest was reported by the author(s).

This work was supported by Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, and Culture: [Grant Number 26350694].

Additional information

Funding

This work was supported by JSPS KAKENHI [Grant Number JP26350694].

Notes on contributors

Kei Hatano

Kei Hatano is a prospective PhD student. He has graduated with a Master’s degree from Hokkaido University, Japan. His research interest is in the respiratory-motor interactions.

Zheng Xiao

Zheng Xiao joined this research project to carry out research for his Master’s degree and received his Master’s degree from Hokkaido University, Japan.

Kazuki Shirakawa

Kazuki Shirakawa is a prospective PhD student. He works as an associate professor in the Department of Early Childhood Education of Kushiro Junior College, Japan.

Yoshinori Ohtsuka

Yoshinori Ohtsuka is a doctor and a professor at the Department of Sports and Human Studies, Sapporo International University, Japan.

Takahiro Yunoki

Takahiro Yunoki is an associate professor at the Department of Health and Physical education, Faculty of Education, Hokkaido University, Japan.