title: Evidence for repetitive load in the trapezius muscle during a tapping task.
abstract: Many studies describe the trapezius muscle activation pattern during repetitive key-tapping focusing on continuous activation. The objectives of this study were to determine whether the upper trapezius is phasically active during supported key tapping, whether this activity is cross-correlated with forearm muscle activity, and whether trapezius activity depends on key characteristic. Thirteen subjects (29.7 ± 11.4 years) were tested. Surface EMG of the finger's extensor and flexor and of the trapezius muscles, as well as the key on-off signal was recorded while the subject performed a 2-min session of key tapping at 4 Hz. The linear envelopes obtained were cut into single tapping cycles extending from one onset to the next onset signal and subsequently time-normalized. Effect size between mean range and maximal standard deviation was calculated to determine as to whether a burst of trapezius muscle activation was present. Cross-correlation was used to determine the time-lag of the activity bursts between forearm and trapezius muscles. For each person the mean and standard deviation of the cross-correlations coefficient between forearm muscles and trapezius were determined. Results showed a burst of activation in the trapezius muscle during most of the tapping cycles. The calculated effect size was ≥0.5 in 67% of the cases. Cross-correlation factors between forearm and trapezius muscle activity were between 0.75 and 0.98 for both extensor and flexor muscles. The cross-correlated phasic trapezius activity did not depend on key characteristics. Trapezius muscle was dynamically active during key tapping; its activity was clearly correlated with forearm muscles' activity.
authors.affiliation: Institute of Human Movement Sciences and Sport, Swiss Federal Institute of Technology, Zurich, Switzerland. tomatisl@ethz.ch
authors.forename: L
authors.initials: L
authors.lastname: Tomatis
authors.forename: C
authors.initials: C
authors.lastname: Müller
authors.forename: M
authors.initials: M
authors.lastname: Nakaseko
authors.forename: T
authors.initials: T
authors.lastname: Läubli
mesh_terms: D000328:Adult; D003201:Computers; D004576:Electromyography; D006804:Ergonomics; D005260:Female; D005542:Forearm; D006225:Hand; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D016474:Weight-Bearing; D055815:Young Adult