The effect of divided attention on gait stability following concussion

Abstract

Background. The need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance, relatively little information on gait and dynamic stability is available on motor task performance for young adults following concussion. This study was performed to investigate the effect of divided attention following concussion on various gait variables. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability.

Methods. Ten subjects with Grade 2 concussion completed testing within 48 h of injury as well as 10 age-, height-, weight-, and activity-matched controls. The gait protocol consisted of level walking under two conditions: (1) undivided attention (single-task) and (2) while simultaneously completing simple mental tasks (dual-task). Whole-body motion data were collected using a six-camera motion analysis system. A 13-segment biomechanical model was used to compute whole body center of mass motion and velocity.

Findings. Walking with a concurrent cognitive task resulted in significant changes in gait and center of mass measurements for both groups. Concussed subjects were found to be able to conservatively adjust their whole body center of mass motion to maintain dynamic stability while walking without divided attention. However, while walking with divided attention, subjects with concussion demonstrated a significantly greater medio-lateral center of mass sway.

Interpretation. These data suggest that the ability to control and maintain stability in the frontal plane during walking is diminished under divided attention in individuals following a concussion.

Introduction

The brain is a highly complex organ that coordinates all functions of the body from intelligence and consciousness to automatic responses such as breathing and circulation. Injuries to the brain, such as concussion, and the resulting symptoms have been recognized since the 16th century (Maroon et al., 2000). Difficulties in definition, recognition, and assessment of concussion have made epidemiological study difficult. However, the yearly incidence of football-related concussions was estimated at 40,000 in 1.1 million high school football players, or 3.6% (Powell and Barber-Foss, 1999). In a study of 141 high school and college football players followed for two years (McCrea et al., 1997), 4.3% experienced mild traumatic brain injury (MTBI). While the high impact nature of football lends itself to high incidences of concussion, the potential for injury to the brain is present in all sports.

According to the Centers for Disease Control and Prevention (1999) it is estimated that 5.3 million Americans live with disabilities associated with traumatic brain injury (TBI) at a cost of $56.3 billion annually. Many of these injuries fall under the category of MTBI (Bailes and Hudson, 2001). While no injury to the brain should be considered minor (Cantu, 1997) there is a prevailing notion that one concussion results in little permanent neurological damage (Maroon et al., 2000). However, rate of recovery, even from a single concussion, is highly individual, and standardized recovery curves are not readily available to physicians and certified athletic trainers to make objective return-to-play decisions (McCrory et al., 2000). Given the potentially serious consequences of concussions, the need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance (Wojtys et al., 1999), relatively little information is available on dynamic motor task performance following concussion. Some patients report symptoms long after the injury even though their cognitive deficits are small (Alves et al., 1986).

Most biomechanical studies on MTBI to date have largely been limited to postural sway during quiet standing or during standing with altered sensory inputs (Geurts et al., 1996; Geurts et al., 1999; Guskiewicz et al., 1996; Ingersoll and Armstrong, 1992; Lahat et al., 1996; Lehmann et al., 1990; Rubin et al., 1995; Wade et al., 1997; Wober et al., 1993). Guskiewicz et al. (1996) concluded that participants with MTBI demonstrated impaired postural stability for one to three days following injury. Guskiewicz et al. (2001) also reported no relationship between symptoms, performance on tests of cognitive function, and static postural stability. The data suggested that recovery of motor function, as demonstrated by static postural control following MTBI, might be independent of cognitive recovery.

Recent studies have reported effects of moderate to severe TBI on gait and dynamic stability (Basford et al., 2003; McFadyen et al., 2003; Chou et al., 2004). Such post-TBI individuals, even with a normal neurological and musculoskeletal examination, were found to walk with increased caution, demonstrating a significantly slower walking speed and shorter stride length. Compared to matched controls, patients with TBI also displayed a significantly greater and faster medio-lateral center of mass (CoM) motion, which has been demonstrated to be a sensitive measure of dynamic stability (Basford et al., 2003; Chou et al., 2004). However, most of the participants included in these studies suffered a moderate to severe TBI (initial Glasgow Coma Scale ⩽ 12) and complained of instability during gait at the time of testing (duration of injury: 2–22 months). Similar information on gait and dynamic stability is currently not available for young adults following a concussion.

Maintenance of balance and limb coordination during locomotion or sport activities requires a complex interaction of sensory input and motor output. Sensory systems monitor the location of the whole body CoM relative to the foot-ground center of pressure (CoP), provide orientation in space, and monitor the environment. Motor systems provide appropriate coordinated muscular activation and force generation. When the brain is engaged the effect is synchronized movement. This dynamic interaction is vividly portrayed in athletics. But when a person is required to perform synchronized movement with divided attention, the effect is not as well understood. Previous studies have found that attentional demands increase as physical requirements increase. Lajoie et al. (1993) found that response time to an auditory stimulus were shortest when physical demands were less (sitting) and increased as the task demands increased (standing and walking). They also found that the response times were greater in the more unstable single-stance phase of gait compared to double-stance. It has been reported further that divided attention reduced obstacle avoidance performance while walking (Weerdesteyn et al., 2003). Ebersbach et al. (1995) also demonstrated that mean digit recall was greater during quiet stance than during walking. However, to date little is known about the effect of divided attention on gait in persons with recent brain injury.

A functionally challenging dual task, such as varying conditions of mental concentration while walking, may prove to be related to post-concussion status and provide more pertinent information regarding the optimal time for return to play. The overall goal of this study was to determine the effect of divided attention on balance control during gait in persons who have recently suffered a concussion. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability, as indicated by an increased frontal plane CoM motion, while performing a concurrent cognitive task during walking.