Recovery of upper extremity sensorimotor system acuity in baseball athletes after a throwing-fatigue protocol

Abstract

Context: Research indicates that upper extremity fatigue hampers sensorimotor system acuity. However, no investigators have observed recovery of upper extremity acuity after fatigue.

Objective: To observe recovery of active position reproduction acuity in overhead throwers after a throwing-fatigue protocol.

Design: Single-session, repeated-measures design.

Setting: University musculoskeletal laboratory.

Patients or other participants: Sixteen healthy collegiate baseball players (age = 21.0 +/- 1.6 years, height = 175.8 +/- 10.2 cm, mass = 82.8 +/- 4.3 kg).

Intervention(s): Subjects threw a baseball with maximum velocity (every 5 seconds) from a single knee. Every 20 throws, subjects rated their upper extremity exertion on a Borg scale until reporting a level of more than 14.

Main outcome measure(s): We used an electromagnetic tracking system to measure active multijoint position reproduction acuity at 5 intervals: prefatigue; immediately postfatigue; and after 4, 7, and 10 minutes of recovery. Blindfolded subjects reproduced their arm-cocked and ball-release positions. Dependent variables were 3-dimensional variable errors of scapulothoracic, glenohumeral, elbow, and wrist joints; endpoint (ie, hand) position error represented overall upper extremity acuity. The independent variable was time (measured prefatigue and at 4 postfatigue intervals).

Results: Fatigue significantly affected acuity of scapulothoracic, glenohumeral, and elbow joints and endpoint error for both positions (P < .001). Fatigue significantly affected wrist acuity only for ball release (P < .001). For arm-cocked reproduction, each measure of acuity, except that of the glenohumeral joint, recovered by 7 minutes; for ball release, each measure of acuity recovered within 4 minutes (P > .05).

Conclusions: The sensorimotor system deficits that we observed after fatigue recovered within 7 minutes in most upper extremity joints. Glenohumeral arm-cocked position reproduction acuity failed to recover within 10 minutes. Research indicates that overhead throwers are vulnerable in this position to the capsulolabral injuries commonly observed in throwing athletes. Future researchers should explore this relationship and the effectiveness of exercises aimed at enhancing sensorimotor system acuity and endurance.

Keywords: joint position sense; multijoint position reproduction.

Figure 1. An overhead throwing athlete reproduces his arm-cocked position during the active multijoint position reproduction test. Reprinted with permission..

Figure 2. An overhead throwing athlete reproduces his ball-release position during the active multijoint position reproduction test. Reprinted with permission..

Figure 3. Analysis for recovery of individual upper extremity joint acuity (3-dimensional variable error [mean ± SD]) for arm-cocked position reproduction after the throwing-fatigue protocol. Comparisons of prefatigue with postfatigue and each recovery test are presented. *Indicates significantly greater error than the respective joint's prefatigue value (P < .001).

Figure 4. Analysis for recovery of individual upper extremity joint acuity (3-dimensional variable error [mean ± SD]) for ball-release position reproduction after the throwing-fatigue protocol. Comparisons of prefatigue with postfatigue and each recovery test are presented. *Indicates significantly greater error than the respective joint's prefatigue value (P < .001).

Figure 5. Analysis for recovery of upper extremity endpoint acuity (3-dimensional variable error [mean ± SD]) for reproduction of arm-cocked and ball-release positions after the throwing-fatigue protocol. Comparisons of prefatigue with postfatigue and each recovery test are presented. *Indicates significantly greater error than the respective measure's prefatigue value (P < .001).