Fig 1.
(A) Ratcheting Task. Subjects stood in front of a board placed at 60% of arm length in front of the toes, and rotated a bolt placed through the board at eye level using a ratcheting socket wrench. The torque required to rotate the bolt clockwise was ~ 4 Nm. (B) Experimental Session. Subjects performed three trials of a repetitive ratcheting task pre and post fatigue. Two different fatigue protocols (Proximal/Distal) were performed on separate days at least one week apart. Subjects performed the fatigue task during minutes 2 and 4 of the post-test to prevent recovery in the targeted muscle group. The order of test days was randomized. (C) Illustration of the wrench coordinate system.
Fig 2.
Perceived exertion and strength.
(A) Average ratings of perceived exertion (RPE), (B) shoulder flexion maximum voluntary contraction (MVC), and (C) grip MVC for the proximal (squares) and distal (circles) fatigue sessions after the pre-test, fatigue, and post-test on each day. MVCs are reported as a percentage of the initial MVC. Error bars represent 95% confidence intervals. * indicates a difference from baseline strength.
Fig 3.
(A) Average position and angular velocity of the wrench pre (blue) and post (red) fatigue across all subjects are shown for proximal and distal fatigue. Data are normalized to 100% of the movement cycle (top position to top position). (B) The average range of motion (top) and movement duration (middle) of the wrench cycles did not change, but wrench rotation variability (MeanSD) increased after both fatigue protocols (bottom). Error bars show 95% confidence intervals.
Fig 4.
Average joint angles across subjects for the ratcheting motion pre (blue) and post (red) two different fatigue protocols. Angles are normalized to 100% of the movement cycle (top position to top position). The angles shown represent those most affected by fatigue.
Table 1.
Maximum joint angles (degrees) are given as mean (standard deviation) across subjects.
Fig 5.
Changes in wrench-hand coordination post fatigue.
The change (post—pre fatigue) in the peak angular velocity of the wrench relative to the hand about the wrench Z axis and the timing of peak wrist extension velocity for proximal and distal fatigue. Positive values indicate an increase after fatigue.
Table 2.
Peak joint angular velocities.
Maximum joint angular velocities (degrees/second) are given as mean (standard deviation) across subjects. Probability statistics are for univariate ANOVAs.
Fig 6.
Changes in movement variability post fatigue.
Change in MeanSD (post—pre fatigue) at the trunk (A), shoulder (B), elbow and wrist (C), and hand and wrench (D) after proximal (squares) and distal (circles) fatigue. Positive values indicate that variability increased after fatigue. Error bars represent the 95% confidence interval. * indicates PROX/DIST × PRE/POST interaction effect.
Table 3.
MeanSD for each joint angles is given as the mean (standard deviation across subjects. Probability statistics are for univariate ANOVAs.