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. Author manuscript; available in PMC: 2021 Jan 23.
Published in final edited form as: J Biomech. 2019 Dec 16;99:109569. doi: 10.1016/j.jbiomech.2019.109569

Table 1:

Description of dependent variables.

Dependent Variables Units Description
Movement time ms The time between the onset of the first burst of EMG activity of the biceps or triceps (described below) and hand contact*
Maximum vertical ground reaction force Percent body weight Maximum vertical ground reaction force following hand contact
Elbow angle at impact Degrees Angle between the vectors connecting the midpoint of the ulnar and radial wrist and the midpoint of the lateral and medial elbow and the midpoint of the elbow and the acromion with 180 degrees representing full extension
Elbow angular velocity at impact Degrees/s Elbow angle was numerically differentiated to determine the elbow angular velocity at impact with positive values for extension and negative values for flexion
Vertical hand velocity at impact m/s The position of the midpoint of the ulnar and radial wrist markers were integrated to determine hand velocity at impact
Vertical neck velocity at impact m/s The position of the midpoint of the right and left acromion was numerically differentiated to determine the vertical neck velocity at impact (vertical neck position represents the position of the torso at shoulder height or the base of the neck)
Initial EMG onset ms The point in time when the linear envelope of the EMG exceeded 3 standard deviations of the average baseline signal measured 100 ms prior to perturbation onset for more than 30 ms following perturbation onset
EMG onset latency ms The period of time between perturbation onset and initial EMG onset
Pre-impact onset ms Pre-impact EMG onset is the largest change in the rate of growth of the rectified, integrated, and normalized EMG signal prior to ground contact (Santello et al., 2001; Santello and McDonagh, 1998)
Pre-impact time ms Period of time between the burst of EMG activity and hand contact
Mean amplitude of EMG activity 50 ms prior to impact Percent Average EMG amplitude 50 ms prior to contact
Mean co-activation index 50 ms prior to impact Percent Calculated following the method of Winter (1990) and averaged over 50 ms prior to impact. Calculated for the biceps with respect to the triceps.
*

Hand contact was defined as the time when the vertical ground reaction force exceeded 10 Newtons.