Liu Fang, Jones Alice Y M, Tsang Raymond C C, Yam Timothy T T, Tsang William W N
Department of Physiotherapy, School of Nursing and Health Sciences, Hong Kong Metropolitan University, Hong Kong, China; Department of Rehabilitation, Shenzhen Second People's Hospital, The First Affiliated Hospital of Shenzhen University Health Science Centre, Shenzhen, China.
School of Health and Rehabilitation Sciences, The University of Queensland, Queensland, Australia.
Respir Physiol Neurobiol. 2025 Jan;331:104365. doi: 10.1016/j.resp.2024.104365. Epub 2024 Nov 1.
Inspiratory muscle training (IMT) is often employed to enhance improvement in inspiratory muscle strength. However, the relationship between inspiratory muscle recruitment patterns and increasing inspiratory load remains unclear. Furthermore, the effect of breathing instructions on diaphragm activity at various inspiratory loads is unknown.
To investigate the recruitment activity of the diaphragm and sternocleidomastoid (SCM) muscle under increased inspiratory pressure loading, with and without diaphragmatic breathing instructions, in healthy young adults.
Participants were invited to breathe, in random order, 6 sets of 10 breaths at inspiratory loads of 30 % to 80 % maximal inspiratory pressure (MIP), in 10 % increments. The measurement process was repeated with a specific focus of diaphragmatic descent during inspiration. During each targeted breath, recordings of surface electromyography of the right SCM muscle and thickness of the right hemi-diaphragm measured by ultrasonography were undertaken concurrently.
Sixty-two adults (31 males, age: 23±3 years) participated in the study. Irrespective of breathing instructions, computed diaphragm thickening fraction (DTf) increased with increasing inspiratory load but peaked at 50 % MIP and declined with increasing load to 80 % MIP. SCM recruitment increased with increasing inspiratory load to 80 % MIP. Forced inspiration with diaphragmatic breathing was associated with a higher DTf and lower SCM muscle activity. The above pattern was similar for both male and female participants. Female participants produced higher SCM activity compared with males but only at inspiration loads below 50 % MIP.
In a cohort of young healthy adults, magnitude of diaphragmatic effort was greatest at 50 % MIP but declined with increasing inspiratory load to 80 % MIP. Forced inspiration combined with focused diaphragmatic breathing accentuated diaphragm contraction and reduced SCM muscle contribution. Our findings show that diaphragmatic muscle recruitment is non-linear and that the generic clinical prescription of an IMT program may need to be reconfigured.
吸气肌训练（IMT）常用于增强吸气肌力量的改善。然而，吸气肌募集模式与吸气负荷增加之间的关系仍不清楚。此外，呼吸指令对不同吸气负荷下膈肌活动的影响尚不清楚。
研究健康年轻成年人在有或无膈肌呼吸指令的情况下，吸气压力负荷增加时膈肌和胸锁乳突肌（SCM）的募集活动。
邀请参与者以随机顺序在吸气负荷为最大吸气压力（MIP）的30%至80%下进行6组，每组10次呼吸，每次增加10%。测量过程重复进行，特别关注吸气时的膈肌下降情况。在每次目标呼吸期间，同时记录右侧SCM肌肉的表面肌电图和通过超声测量的右侧半膈肌厚度。
62名成年人（31名男性，年龄：23±3岁）参与了该研究。无论呼吸指令如何，计算得出的膈肌增厚分数（DTf）随吸气负荷增加而增加，但在50%MIP时达到峰值，并随负荷增加至80%MIP而下降。SCM的募集随吸气负荷增加至80%MIP而增加。膈肌呼吸的强制吸气与较高的DTf和较低的SCM肌肉活动相关。上述模式在男性和女性参与者中相似。女性参与者在低于50%MIP的吸气负荷下比男性产生更高的SCM活动。
在一组年轻健康成年人中，膈肌用力程度在50%MIP时最大，但随吸气负荷增加至80%MIP而下降。强制吸气结合专注的膈肌呼吸可增强膈肌收缩并减少SCM肌肉的贡献。我们的研究结果表明，膈肌募集是非线性的，IMT计划的一般临床处方可能需要重新配置。
