title: Discharge behaviors of trapezius motor units during exposure to low and high levels of acute psychosocial stress.
abstract: This study investigated the effects of acute psychosocial stress on trapezius single motor unit discharge behaviors. Twenty-one healthy women performed feedback-controlled isometric contractions under conditions of low and high psychosocial stress in the same experimental session. Psychosocial stress was manipulated using a verbal math task combined with social evaluative threat that significantly increased perceived anxiety, heart rate, and blood pressure (P < 0.001). Motor unit discharge behaviors including the threshold and discharge rate at recruitment [7.7% (5.7%) maximal voluntary isometric contraction and 7.3 pulses per second (pps) (6.8 pps), P > 0.121, N = 103] and derecruitment [6.0% (4.4%) maximal voluntary isometric contraction and 6.5 pps (4.1 pps), P > 0.223, N = 99], the mean [11.3 pps (2.3 pps), P = 0.309, N = 106] and variability [2.5 pps (0.91 pps), P = 0.958, N = 106] of discharge rate, and the proportion of motor units exhibiting double discharges (21%, P = 0.446) did not change across stress conditions. Discharge rate modulation with changes in contraction intensity was highly variable and similar across stress conditions (P > 0.308, N = 89). Rate-rate modulation of concurrently active motor units was also highly variable (r = -0.84 to 1.00, N = 75). Estimates of DeltaF for motor unit pairs with rate-rate modulation >or=0.7 were positive and similar across stress conditions [4.7 pps (2.0 pps), P = 0.405, N = 16]. The results indicate that acute psychosocial stress does not alter trapezius motor unit discharge behaviors during a precisely controlled motor task in healthy women.
authors.affiliation: Clinical Science Program, University of Colorado Denver, Aurora, Colorado 80045, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Stephenson
authors.forename: Katrina S
authors.initials: KS
authors.lastname: Maluf
mesh_terms: D000208:Acute Disease; D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology*; D009483:Neuropsychological Tests; D012919:Social Behavior; D013315:Stress, Psychological / Q000503:physiopathology*; D055815:Young Adult