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Prior research has highlighted the therapeutic benefits of acute intermittent hypoxia (AIH) in enhancing motor performance after motor incomplete spinal cord injury and in able-bodied individuals. Although studies in rodents and humans indicate that AIH may facilitate motor excitability, the relationship between excitability changes and functional performance remains unclear. In addition, discrepancies in the effects of AIH on excitability in able-bodied individuals merit further investigation. Understanding the concurrent impact of repetitive AIH on voluntary activation and spinal reflex excitability may clarify the functional implications of AIH for muscle force production. High voluntary activation is vital for sustaining torque production during activities that require repeated muscle contractions. We hypothesized that repetitive AIH would attenuate decreases in both voluntary activation and maximum torque production typically observed during fatiguing contractions. To test this hypothesis, we examined the effects of four consecutive days of AIH on voluntary activation and torque generation during repeated maximal plantar flexion contractions. We assessed changes in voluntary activation using the central activation ratio by calculating the ratio of voluntary torque to the torque produced with supramaximal electrical stimulation. Consistent with our hypothesis, we show that repetitive AIH significantly increases both voluntary activation and peak torque during fatiguing contractions. We did not observe any changes in resting spinal reflex excitability or antagonist muscle coactivation during fatiguing contractions post-AIH. Together, these findings suggest that repetitive AIH reduces performance fatigability through enhanced descending neural drive. Optimizing voluntary activation is critical for facilitating the recovery of functional walking skills after neurological injury. NEW & NOTEWORTHY: This study shows that repetitive acute intermittent hypoxia (AIH) significantly increases both voluntary activation and peak torque during fatiguing lower limb contractions. However, resting spinal reflex excitability and antagonist muscle coactivation during fatiguing contractions did not change following repetitive AIH. Together, these observations indicate that repetitive AIH reduces performance fatigability through enhanced descending neural drive. These findings underscore the therapeutic potential of AIH for promoting motor recovery after neurological injury. [ABSTRACT FROM AUTHOR]

Breathing mild bouts of low oxygen air (i.e. acute intermittent hypoxia, AIH) has been shown to improve locomotor function in humans after a spinal cord injury. How AIH‐induced gains in motor performance are achieved remains unclear. We examined the hypothesis that AIH augments motor learning and motor retention during a locomotor adaptation task. We further hypothesized that gains in motor learning and retention will be associated with reductions in net metabolic power, consistent with the acquisition of energetically favourable mechanics. Thirty healthy individuals were randomly allocated into either a control group or an AIH group. We utilized a split‐belt treadmill to characterize adaptations to an unexpected belt speed perturbation of equal magnitude during an initial exposure and a second exposure. Adaptation was characterized by changes in spatiotemporal step asymmetry, anterior–posterior force asymmetry, and net metabolic power. While both groups adapted by reducing spatial asymmetry, only the AIH group achieved significant reductions in double support time asymmetry and propulsive force asymmetry during both the initial and the second exposures to the belt speed perturbation. Net metabolic power was also significantly lower in the AIH group, with significant reductions from the initial perturbation exposure to the second. These results provide the first evidence that AIH mediates improvements in both motor learning and retention. Further, our results suggest that reductions in net metabolic power continue to be optimized upon subsequent learning and are driven by more energetically favourable temporal coordination strategies. Our observation that AIH facilitates motor learning and retention can be leveraged to design rehabilitation interventions that promote functional recovery. Key points: Brief exposures to low oxygen air, known as acute intermittent hypoxia (AIH), improves locomotor function in humans after a spinal cord injury, but it remains unclear how gains in motor performance are achieved.In this study, we tested the hypothesis that AIH induces enhancements in motor learning and retention by quantifying changes in interlimb coordination, anterior–posterior force symmetry and metabolic cost during a locomotor adaptation task.We show the first evidence that AIH improves both motor learning and savings of newly learned temporal interlimb coordination strategies and force asymmetry compared to untreated individuals.We further demonstrate that AIH elicits greater reductions in metabolic cost during motor learning that continues to be optimized upon subsequent learning.Our findings suggest that AIH‐induced gains in locomotor performance are facilitated by enhancements in motor learning and retention of more energetically favourable coordination strategies. [ABSTRACT FROM AUTHOR]

The article is an author response to Panza et al. regarding the effects of acute intermittent hypoxia (AIH) on motor learning and metabolic cost. The authors address concerns about statistical approaches, metabolic adaptations, and future research directions related to AIH protocols. They discuss the importance of within-group analyses to identify phase-dependent changes in motor patterns and metabolic power. The study conducted at a higher altitude in Boulder, Colorado, utilized 90-second hypoxic bouts, resulting in lower oxygen saturation levels compared to other studies. The authors also consider the potential benefits of hypercapnic AIH on motor plasticity and emphasize the need for standardized dosing parameters to advance understanding of AIH effects on human motor performance. [Extracted from the article]

Acute intermittent hypoxia (AIH) enhances human motor function after incomplete spinal cord injury. Although the underlying mechanisms in humans are unknown, emerging evidence indicates that AIH facilitates corticospinal excitability to the upper limb. However, the functional relevance of this plasticity remains unexplored, and it is unclear whether similar plasticity can be induced for lower limb motor areas. We recently demonstrated that AIH improves motor learning and metabolic efficiency during split-belt walking. Thus, we hypothesized that AIH increases lower limb excitability and that these enhancements would predict the magnitude of motor learning and the corresponding reductions in net metabolic power. We assessed tibialis anterior (TA) excitability using transcranial magnetic stimulation and quantified changes in spatiotemporal asymmetries and net metabolic power in response to split-belt speed perturbations. We show that AIH enhances TA excitability, and that the magnitude of this facilitation positively correlates with greater spatiotemporal adaptation. Notably, we demonstrate a novel association between increased excitability and reduced net metabolic power during motor learning and savings. Together, our results suggest that AIH-induced gains in excitability predict both the magnitude of motor learning and the associated metabolic efficiency. Determining indices of AIH-induced improvements in motor performance is critical for optimizing its therapeutic reach., Competing Interests: Additional information The authors declare no competing financial interests.

The development of EMG based controllers for automated gait orthosis is a promising intervention for post-stroke gait rehabilitation and assistive device applications. However, the integration of stroke specific modular neuromuscular patterns for the design of active gait assistance controller is largely unexplored. To this end, this work presents preliminary evidence of the associated variability between lower limb muscle activation patterns underlying discrete isometric control objectives and the analogous dynamic subtask during treadmill gait using matrix factorization algorithms. We find that common muscle coordination patterns underlying both isometric and dynamic gait submovements can be used to reconstruct relevant spatio-temporal patterns for healthy locomotion. We propose that synergies extracted isometrically may be sufficient to tune adaptive controller assistance for disruptive linkages in the EMG control signal to impact gait dysfunction.