Evidence for repetitive load in the trapezius muscle during a tapping task

• Published in: European journal of applied physiology 2012-08, Vol.112 (8), p.3053-3059
• Main Authors: Tomatis, L., Müller, C., Nakaseko, M., Läubli, T.
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Computers; Electromyography; Ergonomics; Female; Forearm; Fundamental and applied biological sciences. Psychology; Hand; Human Physiology; Humans; Keyboards; Male; Middle Aged; Motor Activity; Muscle Contraction; Muscle function; Muscle, Skeletal - physiology; Occupational Medicine/Industrial Medicine; Original Article; Pain; Posture; Signal Processing, Computer-Assisted; Sports Medicine; Time Factors; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Weight-Bearing; Young Adult
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-011-2290-8

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.