Effect of
muscle metaboreflex activation on pupil diameter in
humans
Naoyuki Hayashi and Nami Someya
The pupil
diameter is increased by sympathetic activation. However, it remains unclear
whether activation by metabolically sensitive skeletal muscle afferents (i.e.,
the muscle metaboreflex) dilates the pupil. We
investigated the influence of muscle metaboreflex
activation on the pupil diameter. Eight healthy subjects performed 2 min of
isometric hand-grip exercise at 30 % maximal voluntary contraction, which was
followed by either 2 min of postexercise muscle ischemia (PEMI) in the
forearm (experimental trial) or no PEMI (control trial). The pupil diameter and
blood pressure were continuously recorded. The mean blood pressure increased significantly
from rest during exercise in both trials, and this increase was maintained
during the PEMI period in the experimental trial but not during the recovery
period in the control trial. Hand-grip exercise significantly increased the
pupil diameter by 7 ± 1 % (mean ± SE) and 5 ± 1 % from the resting
baseline in the control and experimental trials, respectively. This increase
was maintained during the PEMI period in the experimental trial while it
decreased by half during the recovery period in the control trial. These
findings suggest that the muscle metaboreflex
contributes to dilation of the pupil.
Key words: Exercise,
Pupil, Muscle metaboreflex