Spinal AMP kinase activity differentially regulates phrenic motor plasticity.

Acute intermittent hypoxia (AIH) elicits phrenic motor plasticity via multiple distinct cellular mechanisms. With moderate AIH, phrenic motor facilitation (pMF) requires G protein-coupled serotonin type 2 receptor activation, ERK MAP kinase activity, and new synthesis of brain-derived neurotrophic factor. In contrast, severe AIH elicits pMF by an adenosine-dependent mechanism that requires exchange protein activated by cAMP, Akt, and mammalian target of rapamycin (mTOR) activity, followed by new tyrosine receptor kinase B protein synthesis; this same pathway is also initiated by G protein-coupled serotonin 7 receptors (5-HT).

The slope of the oxygen pulse curve does not depend on the maximal heart rate in elite soccer players.

Introduction: It is unknown whether an extremely high heart rate can affect oxygen pulse profile during progressive maximal exercise in healthy subjects.

Objective: Our aim was to compare relative oxygen pulse (adjusted for body weight) curves in athletes at their maximal heart rate during treadmill cardiopulmonary exercise testing.

Methods: A total of 180 elite soccer players were categorized in quartiles according to their maximum heart rate values (n = 45).