School of Human Kinetics and Recreation, and Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
J Physiol. 2024 Nov;602(21):5699-5711. doi: 10.1113/JP285049. Epub 2024 Jul 26.
Acute intermittent hypoxia (AIH) is an emerging technique for enhancing neuroplasticity and motor function in respiratory and limb musculature. Thus far, AIH-induced improvements in strength have been reported for upper and lower limb muscles after chronic incomplete cervical spinal cord injury (iSCI), but the underlying mechanisms have been elusive. We used high-density surface EMG (HDsEMG) to determine if motor unit discharge behaviour is altered after 15 × 60 s exposures to 9% inspired oxygen, interspersed with 21% inspired oxygen (AIH), compared to breathing only 21% air (SHAM). We recorded HDsEMG from the biceps and triceps brachii of seven individuals with iSCI during maximal elbow flexion and extension contractions, and motor unit spike trains were identified using convolutive blind source separation. After AIH, elbow flexion and extension torque increased by 54% and 59% from baseline (P = 0.003), respectively, whereas there was no change after SHAM. Across muscles, motor unit discharge rates increased by ∼4 pulses per second (P = 0.002) during maximal efforts, from before to after AIH. These results suggest that excitability and/or activation of spinal motoneurons is augmented after AIH, providing a mechanism to explain AIH-induced increases in voluntary strength. Pending validation, AIH may be helpful in conjunction with other therapies to enhance rehabilitation outcomes after incomplete spinal cord injury, due to these enhancements in motor unit function and strength. KEY POINTS: Acute intermittent hypoxia (AIH) causes increases in muscular strength and neuroplasticity in people living with chronic incomplete spinal cord injury (SCI), but how it affects motor unit discharge rates is unknown. Motor unit spike times were identified from high-density surface electromyograms during maximal voluntary contractions and tracked from before to after AIH. Motor unit discharge rates were increased following AIH. These findings suggest that AIH can facilitate motoneuron function in people with incomplete SCI.
急性间歇性低氧（AIH）是一种增强呼吸和肢体肌肉神经可塑性和运动功能的新技术。迄今为止，在慢性不完全性颈脊髓损伤（iSCI）后，AIH 已被报道可增强上肢和下肢肌肉的力量，但潜在机制尚不清楚。我们使用高密度表面肌电图（HDsEMG）来确定与仅呼吸 21%空气（SHAM）相比，在 9%吸入氧、21%吸入氧（AIH）之间穿插 15 次 60 秒暴露后，运动单位放电行为是否会发生变化。我们在 7 名 iSCI 个体进行最大肘部屈伸收缩期间记录肱二头肌和肱三头肌的 HDsEMG，并使用卷积盲源分离识别运动单位尖峰序列。AIH 后，肘部屈伸扭矩分别比基线增加了 54%和 59%（P=0.003），而 SHAM 后没有变化。在肌肉之间，运动单位放电率在最大努力期间增加了约 4 脉冲/秒（P=0.002），从 AIH 之前到之后。这些结果表明，在 AIH 后兴奋性和/或脊髓运动神经元的激活增强，为解释 AIH 诱导的自愿力量增加提供了机制。在不完全性脊髓损伤后，AIH 可能有助于与其他治疗方法相结合，增强康复效果，因为它增强了运动单位功能和力量。关键点：急性间歇性低氧（AIH）可引起慢性不完全性脊髓损伤（SCI）患者的肌肉力量和神经可塑性增加，但它如何影响运动单位放电率尚不清楚。在最大自主收缩期间，从高密度表面肌电图中识别出运动单位尖峰时间，并从 AIH 之前跟踪到之后。AIH 后运动单位放电率增加。这些发现表明，AIH 可以促进不完全性 SCI 患者的运动神经元功能。
