Torque-onset determination: Unintended consequences of the threshold method.
BACKGROUND
Compared with visual torque-onset-detection (TOD), threshold-based TOD produces onset bias, which increases with lower torques or rates of torque development (RTD).


OBJECTIVE
To compare the effects of differential TOD-bias on common contractile parameters in two torque-disparate groups.


METHODS
Fifteen boys and 12 men performed maximal, explosive, isometric knee-extensions. Torque and EMG were recorded for each contraction. Best contractions were selected by peak torque (MVC) and peak RTD. Visual-TOD-based torque-time traces, electromechanical delays (EMD), and times to peak RTD (tRTD) were compared with corresponding data derived from fixed 4-Nm- and relative 5%MVC-thresholds.


RESULTS
The 5%MVC TOD-biases were similar for boys and men, but the corresponding 4-Nm-based biases were markedly different (40.3±14.1 vs. 18.4±7.1ms, respectively; p<0.001). Boys-men EMD differences were most affected, increasing from 5.0ms (visual) to 26.9ms (4Nm; p<0.01). Men's visually-based torque kinetics tended to be faster than the boys' (NS), but the 4-Nm-based kinetics erroneously depicted the boys as being much faster to any given %MVC (p<0.001).


CONCLUSIONS
When comparing contractile properties of dissimilar groups, e.g., children vs. adults, threshold-based TOD methods can misrepresent reality and lead to erroneous conclusions. Relative-thresholds (e.g., 5% MVC) still introduce error, but group-comparisons are not confounded.
Faculty of Applied Health Sciences, Brock University, St Catharines, ON, Canada. Electronic address: rdotan@brocku.ca.
Raffy
R
Dotan
Faculty of Applied Health Sciences, Brock University, St Catharines, ON, Canada.
Glenn
G
Jenkins
Research Institute for Sport and Exercise Sciences, Faculty of Science, Liverpool John Moores University, Liverpool, UK.
Thomas D
TD
O'Brien
Physical & Health Education, Schulich School of Education, Nipissing University, North Bay, ON, Canada.
Steve
S
Hansen
Faculty of Applied Health Sciences, Brock University, St Catharines, ON, Canada.
Bareket
B
Falk
D001696:Biomechanical Phenomena; D002648:Child; D004576:Electromyography / Q000379:methods / Q000592:standards*; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000254:growth & development / Q000502:physiology; D011930:Reaction Time; D015203:Reproducibility of Results; D019415:Torque; D055815:Young Adult
Children; EMD; Onset bias; RFD; RTD; Torque kinetics