Spatial variation and inconsistency between estimates of onset of muscle activation from EMG and ultrasound.
Delayed onset of muscle activation can be a descriptor of impaired motor control. Activation onset can be estimated from electromyography (EMG)-registered muscle excitation and from ultrasound-registered muscle motion, which enables non-invasive measurements in deep muscles. However, in voluntary activation, EMG- and ultrasound-detected activation onsets may not correspond. To evaluate this, ten healthy men performed isometric elbow flexion at 20% to 70% of their maximal force. Utilising a multi-channel electrode transparent to ultrasound, EMG and M(otion)-mode ultrasound were recorded simultaneously over the biceps brachii muscle. The time intervals between automated and visually estimated activation onsets were correlated with the regional variation of EMG and muscle motion onset, contraction level and speed. Automated and visual onsets indicated variable time intervals between EMG- and motion onset, median (interquartile range) 96 (121) ms and 48 (72) ms, respectively. In 17% (computed analysis) or 23% (visual analysis) of trials, motion onset was detected before local EMG onset. Multi-channel EMG and M-mode ultrasound revealed regional differences in activation onset, which decreased with higher contraction speed (Spearman ρ ≥ 0.45, P < 0.001). In voluntary activation the heterogeneous motor unit recruitment together with immediate motion transmission may explain the high variation of the time intervals between local EMG- and ultrasound-detected activation onset.
Pain Clinic, Anaesthesiology, University Medical Center, Göttingen, Germany.
Angela V
AV
Dieterich
Laboratory of Engineering of the Neuromuscular System and Motor Rehabilitation, Department of Electronics, Politecnico di Torino, Torino, Italy.
Alberto
A
Botter
Laboratory of Engineering of the Neuromuscular System and Motor Rehabilitation, Department of Electronics, Politecnico di Torino, Torino, Italy.|School of Physical Education and Sports, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
Taian Martins
TM
Vieira
Department of Medical and Health Sciences, Physiotherapy, Linköping University, Linköping, Sweden.
Anneli
A
Peolsson
Pain Clinic, Anaesthesiology, University Medical Center, Göttingen, Germany.
Frank
F
Petzke
School of Physiotherapy and Exercise Science, Faculty of Health Sciences, Curtin University, Perth, Australia.
Paul
P
Davey
Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
Deborah
D
Falla
D000328:Adult; D004576:Electromyography / Q000379:methods*; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D014463:Ultrasonography / Q000379:methods*; D055815:Young Adult