Contributions of exercise-induced fatigue versus intertrial tendon vibration on visual-proprioceptive weighting for goal-directed movement

Abstract

It has been argued that exercise-induced muscle fatigue and tendon vibration can alter proprioceptive estimates of limb position. While exercise-induced muscle fatigue may also affect central efferent processes related to limb position sense, tendon vibration specifically targets peripheral afferent signals. It is unclear, however, whether either of these perturbations (i.e., muscle fatigue or tendon vibration) can alter the multisensory weighting processes preceding goal-directed movements. The current study sought to specifically explore visual-proprioceptive weighting before or after eccentric exercise-induced antagonist muscle fatigue (experiment 1) versus with or without intertrial simultaneous agonist-antagonist tendon vibration (experiment 2). To assess sensory weighting, a visual-proprioceptive mismatch between the participant's actual initial starting position and the associated visual cursor position was employed. This method provides an estimate of the participant's reliance on the proprioceptive or visual starting limb position for their aiming movements. Although there was clear evidence of muscle fatigue, there was no systematic alteration of proprioceptive weighting after eccentric exercise and no relationship between sensory weighting and the level of fatigue. On the other hand, participants' reliance on their actual (proprioceptive) limb position was systematically reduced when exposed to agonist-antagonist tendon vibration before each aiming movement. These findings provide seminal evidence that intertrial tendon vibration, but not exercise-induced fatigue, can alter the reliability of proprioceptive estimates and the relative contributions of visual and proprioceptive information for goal-directed movement.NEW & NOTEWORTHY Previous work has used muscle fatigue or tendon vibration to perturb proprioceptive limb position estimates. This study sought to determine whether exercise-induced muscle fatigue versus intertrial tendon vibration can alter multisensory weighting for upper limb-aiming movements. By introducing a discrepancy between participants' actual proprioceptive and visual finger position, this study provides seminal evidence for the reduction of proprioceptive-to-visual weighting using intertrial tendon vibration but no evidence for a systematic reduction following exercise-induced fatigue.

Keywords: action; multisensory; muscle fatigue; proprioception; tendon vibration; visual.

Fig. 1.

A: the 4 aiming conditions. The cursor is depicted with a black circle, and the limb was not visible. The dotted white circle is a placeholder for the other start position. The aligned conditions are depicted in the top left and bottom right corners in which the starting cursor and starting finger position were in the same location (i.e., F1C1 and F2C2). The misaligned conditions are depicted in the bottom left and top right corners (i.e., F1C2 and F2C1), in which the starting finger position was displaced from the starting cursor position which represented their finger. Note that participants did not have cursor feedback during the movement. B: experimental setup. When the participant’s arm was underneath the half-silvered mirror setup, the participant did not have vision of the limb. The black square underneath the participants arm was Velcro and allowed for a custom positioning of the elbow rest. The 2 cursor starting positions and the target positions are displayed. Note that only 1 cursor starting position was displayed for each trial.

Fig. 2.

A: experimental setup used for the exercise session. The participant sat in the Biodex System 4 Pro with their arm in the horizontal plane. During the eccentric contraction, participants were applying force in the flexion direction while the manipulandum was extending their elbow joint. B: online visual feedback available to the participant. This is the force output of 1 set of eccentric contractions from an exemplar participant. During the eccentric contractions, participants were given a target line (dotted line) and asked to reach the goal line with their force. During the protocol, this was continuously updated.

Fig. 3.

A: mean force before and after the exercise session. B: proprioceptive weight before and after the exercise session; a.u., arbitrary units. See Fig. 4 for the process of calculating proprioceptive weight. Error bars depict means ± SE, and gray lines depict individual data (n = 15). *P < 0.05; ns, not significant.

Fig. 4.

A: mean trajectories for the preexercise aiming conditions. Left: aligned conditions (i.e., F1C1 and F2C2); middle: different cursor positions with the same finger position (i.e., F1C1 and F1C2); right: different finger positions with the same cursor position (i.e., F1C1 and F2C1). Each dot represents the position at every 5% of the movement time. B: mean movement distances in the different finger and cursor positions. The Δ value describes the difference in mean movement distance between the conditions in the associated bar graphs. To calculate proprioceptive weight, the differences in movement distance (Δ = 30.2) between the 2 finger starting positions conditions (i.e., F1 and F2) were collapsed across cursor positions and divided by the difference in movement distance (Δ = 45.1) in the aligned conditions (i.e., F1C1 and F2C2). Error bars depict means ± SE.

Fig. 5.

A: mean trajectories for the postexercise aiming conditions. Left: aligned conditions (i.e., F1C1 and F2C2); middle: different cursor positions with the same finger position (i.e., F1C1 and F1C2); right: different finger positions with the same cursor position (i.e., F1C1 and F2C1). Each dot represents the position at every 5% of the movement time. B: mean movement distances in the different finger and cursor positions. The Δ value describes the difference in mean movement distance between the conditions in the associated bar graphs. Error bars depict means ± SE.

Fig. 6.

Proprioceptive weight in the no vibration and vibration conditions. See Fig. 4 for the process of calculating proprioceptive weight. Error bars depict means ± SE, and gray lines depict individual data (n = 10). *P < 0.05.

Fig. 7.

A: mean trajectories for the no vibration aiming conditions. Left: aligned conditions (i.e., F1C1 and F2C2); middle: different cursor positions with the same finger position (i.e., F1C1 and F1C2); right: different finger positions with the same cursor position (i.e., F1C1 and F2C1). Each dot represents the position at every 5% of the movement time. B: mean movement distances in the different finger and cursor positions. The Δ value describes the difference in mean movement distance between the conditions in the associated bar graphs. Error bars depict means ± SE.

Fig. 8.

A: mean trajectories for the vibration aiming conditions. Left: aligned conditions (i.e., F1C1 and F2C2); middle: different cursor positions with the same finger position (i.e., F1C1 and F1C2); right: different finger positions with the same cursor position (i.e., F1C1 and F2C1). Each dot represents the position at every 5% of the movement time. B: mean movement distances in the different finger and cursor positions. The Δ value describes the difference in mean movement distance between the conditions in the associated bar graphs. Error bars depict means ± SE.