Acute Intermittent Hypoxia (AIH) is a rehab approach attributed to serotonin. AIH signaling also occurs via adenosine, and the pathways inhibit each other. Increased neural adenosine in aging may stymie AIH plasticity. The hypothesis is pre-treatment with adenosine 2A receptor inhibition (A2AI) enhances AIH effects on motor plasticity in unaffected adults. AIH exposures will be paired with A2AI or placebo, with a 4-week washout. Primary outcome measures include inspiratory and grip strength.

Inclusion Criteria:

• Aged 40-79 years Non-smokers Ambulatory in the community Do not require assistance to complete activities of daily living

Exclusion Criteria:

• Restrictive or obstructive lung conditions Pregnancy Active respiratory infections Use of antibiotics in the last 4 weeks Symptomatic cardiac disease BMI >35 kg/m2 Seizure disorder or progressive neurological condition Uses positive pressure mechanical ventilation when awake and upright, or oxygen assistance at any time