Differences in multi-joint kinematic patterns of repetitive hammering in healthy, fatigued and shoulder-injured individuals

Abstract

Background. Work-related musculo-skeletal disorders have been previously related to movement repetition, inadequate postures, non-ergonomic environments, muscular imbalance and fatigue. However, no direct link between fatigue and injury has been experimentally shown. To address this problem, we compared the effects of fatigue and injury on the kinematics of repetitive hammering.

Methods. Healthy subjects (n = 30) hammered repetitively both before and after fatigue. Fatigue was induced by a combination of static and dynamic procedures. Shoulder-injured subjects (n = 15) hammered for 30 s without fatigue. Kinematics of motion was recorded.

Findings. The movement time and shoulder range of motion during hammering were not affected by either fatigue or shoulder injury. When fatigued, the healthy subjects displayed decreased range of joint motion, peak velocity and peak acceleration of elbow motion during hammering as well as reduced grip strength. Shoulder-injured individuals had a smaller hammer trajectory amplitude than healthy controls with or without fatigue. They also had lower wrist range of motion, elbow peak velocity, and peak wrist and elbow acceleration compared to healthy subjects hammering without fatigue but only lower wrist peak acceleration compared to healthy subjects hammering with fatigue.

Interpretation. Results showed that fatigue affects elbow motion while shoulder injury affects both wrist and elbow motions during hammering. However, shoulder kinematics were not changed by either fatigue or shoulder injury. These changes at the wrist and elbow may reflect strategies used by individuals with shoulder injury to maintain constant movement duration and shoulder kinematics during movement.

Introduction

In the past few decades, the incidence of work-related muscular skeletal disorders (WMSDs) has steadily grown and is now considered to have reached epidemic proportions in industrialized countries (Guidotti, 1992, Ireland, 1998). In the United States, WMSDs have affected approximately 15–20% of the workforce yearly (Melhorn, 1998). The etiology of WMSDs is not well known and is thought to be multi-faceted. Work task characteristics such as a high number of movement repetitions, inadequate or static postures, non-ergonomic environments, muscular imbalances and fatigue have been associated with the development of WMSDs (Viikari-Juntura, 1998). WMSDs most commonly affect the upper limb, with rotator cuff tendinitis, lateral epicondylitis, tenosynovitis or peritendinitis of the wrist or forearm, and carpal tunnel syndrome being the most prevalent diagnoses (Viikari-Juntura, 1998). It has been suggested that repetitive use of the arm above the horizontal level, a regular occurrence in occupational activities such as carpentry and in competitive sports such as swimming and tennis or those involving throwing and pitching, induces fatigue. These activities have a high incidence of injuries involving the impingement of ligaments or tendons at the shoulder level (Hammarskjöld and Harms-Ringdahl, 1992, Hawkins and Hobeika, 1983). In the workplace, a relationship between shoulder injury and the repetitive performance of tasks involving sustained shoulder abduction and flexion has been suggested (Hagberg and Kvarnstrom, 1984, Viikari-Juntura, 1998).

Fatigue has been implicated in the etiology of WMSDs. Enoka and Stuart (1992) define fatigue as a gradual phenomenon that leads to both the inability to maintain the production of force and to an increased perception of task difficulty. The state of fatigue is associated with changes at local as well as central levels of the neuromuscular system. Local aspects of fatigue include decreased force and velocity of muscle contraction, increased amplitude of electromyographic (EMG) activity in a muscle, shifts in frequencies of the EMG signal towards lower levels of the spectrum and, indirectly, decreased range of joint motion (Enoka and Stuart, 1992).

Few studies have tried to establish a link between fatigue and multi-joint coordination. Forestier and Nougier (1998) studied the temporal sequence of peak velocities of arm joints and found that in forceful ball-throwing, a movement reorganization from a proximo-distal sequence to that of a rigidly linked system emerged with fatigue. In a study on repetitive hopping in humans, Bonnard et al. (1994) found that subjects used either of two coordination strategies to adapt to fatigue. One was organized across the leg joints with greater reliance on proximal muscles with fatigue. The other was organized within joints already active in the movement and consisted of earlier activation of fatigued muscles. Another study on repetitive load lifting (Sparto et al., 1997) reported decreased postural stability with fatigue, measured as an increased body center of mass excursion and decreased motion of distal joints (knee and hip) compensated by increased trunk motion. These studies all demonstrate changes in patterns of kinematic or muscular coordination associated with fatigue. Madeleine et al. (1999) measured greater postural muscle EMG and a tendency towards reduced activity in the painful muscle compensated by increased arm and trunk movements during repetitive cutting using a knife in subjects suffering from experimentally induced trapezius muscle pain. In view of the existing literature, we hypothesize that the disruption in multi-muscle and multi-joint coordination due to fatigue and chronic muscle injury would display some similar characteristics, thus suggesting a link between fatigue and the development of injury. We addressed this hypothesis by quantifying both local and global aspects of fatigue in healthy subjects and in patients with chronic shoulder injuries during the performance of a repetitive, multi-joint hammering task. Preliminary results have appeared in abstract form (Côté et al., 2002a).