title: Observations on force enhancement in submaximal voluntary contractions of human adductor pollicis muscle.
abstract: It has been observed consistently and is well accepted that the steady-state isometric force after active muscle stretch is greater than the corresponding isometric force for electrically stimulated muscles and maximal voluntary contractions. However, this so-called force enhancement has not been studied for submaximal voluntary efforts; therefore, it is not known whether this property affects everyday movements. The purpose of this study was to determine whether there was force enhancement during submaximal voluntary contractions. Human adductor pollicis muscles (n = 17) were studied using a custom-built dynamometer, and both force and activation were measured while muscle activation and force were controlled at a level of 30% of maximal voluntary contraction. The steady-state isometric force and activation after active stretch were compared with the corresponding values obtained during isometric reference contractions. There was consistent and reliable force enhancement in 8 of the 17 subjects, whereas there was no force enhancement in the remaining subjects. Subjects with force enhancement had greater postactivation potentiation and a smaller resistance to fatigue in the adductor pollicis. We conclude from these results that force enhancement exists during submaximal voluntary contractions in a subset of the populations and suggest that it may affect everyday voluntary movements in this subset. On the basis of follow-up testing, it appears that force enhancement during voluntary contractions is linked to potentiation and fatigue resistance and therefore possibly to the fiber-type distribution in the adductor pollicis muscle.
authors.affiliation: University of Calgary, Calgary, Alberta, Canada T2N 1N4.
authors.forename: Ali E
authors.initials: AE
authors.lastname: Oskouei
authors.forename: Walter
authors.initials: W
authors.lastname: Herzog
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D013314:Stress, Mechanical; D013933:Thumb / Q000502:physiology*; D014836:Volition / Q000502:physiology*