title: Actions of β2-adrenoceptor agonist drug on human soleus muscle contraction.
abstract: OBJECTIVE
  The effects of β(2)-agonists on human skeletal muscle contractile properties, particularly on slow fibers, are unclear. Moreover, it remains to be ascertained whether central motor drive (CMD) during voluntary contractions could counter for eventual contractile alterations induced by β(2)-agonists. This study investigated central and peripheral neuromuscular adjustments induced by β(2)-agonist terbutaline on a predominantly slow human muscle, the soleus.
  
  
  METHODS
  Ten recreationally active men ingested either a single dose of 8 mg of terbutaline or placebo in a randomized double-blind order (two experimental sessions). Isometric plantarflexion torque was measured during single and tetanic (10 and 100 Hz) stimulations as well as during submaximal and maximal voluntary contractions (MVC). Twitch peak torque and half-relaxation time were calculated. CMD was estimated via soleus electromyographic recordings obtained during voluntary contractions performed at approximately 50% MVC.
  
  
  RESULTS
  MVC and twitch peak torque were not modified by terbutaline. Twitch half-relaxation time was 28% shorter after terbutaline administration compared with placebo (P < 0.001). Tetanic torques at 10 and 100 Hz were significantly lower after terbutaline intake compared with placebo (-40% and -24% respectively, P < 0.001). Despite comparable torque of submaximal voluntary contractions in the two conditions, CMD was 7% higher after terbutaline ingestion compared with placebo (P < 0.01).
  
  
  CONCLUSIONS
  These results provide evidence that terbutaline modulates the contractility of the slow soleus muscle and suggest that the increased CMD during submaximal contractions may be viewed as a compensatory adjustment of the central nervous system to counter the weakening action induced by terbutaline on the contractile function of slow muscle fibers.
authors.affiliation: Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland. Giacomo.Crivelli@unil.ch
authors.forename: Giacomo
authors.initials: G
authors.lastname: Crivelli
authors.forename: Fabio
authors.initials: F
authors.lastname: Borrani
authors.forename: Romain
authors.initials: R
authors.lastname: Capt
authors.forename: Gérald
authors.initials: G
authors.lastname: Gremion
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Maffiuletti
mesh_terms: D000284:Administration, Oral; D058666:Adrenergic beta-2 Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D004311:Double-Blind Method; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology; D013177:Sports; D013726:Terbutaline / Q000008:administration & dosage / Q000494:pharmacology*; D019415:Torque
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D013726:Terbutaline