Theoretical contribution of the upper extremities to reducing trunk extension following a laboratory-induced slip

Abstract

Slips are frequently the cause of fall-related injuries. Identifying modifiable biomechanical requirements for successful recovery is a key prerequisite to developing task-specific fall preventive training programs. The purpose of this study was to quantify the biomechanical role of the upper extremities during the initial phase of a slip resulting in trunk motion primarily in the sagittal plane. Two groups of adults were examined: adults over age 65 who fell and adults age 18-40 who avoided falling after slipping. We hypothesized that rapid shoulder flexion could significantly reduce trunk extension velocity, that adults who slipped would implement this as a fall avoidance strategy, and that younger adults who avoided falling would use this strategy more effectively than older adults who fell. The kinematics of the 12 younger adults and eight older adults were analyzed using a threesegment conservation of momentum model developed to represent the trunk, head and upper extremities. The model was used to estimate the possible contribution of the upper extremities to reducing trunk extension velocity. The model showed that upper extremity motion can significantly reduce trunk extension velocity. Although the upper extremities significantly reduced the trunk extension velocity of both young and older adults (p<0.027), the reduction found for the young adults, 13.6±11.4%, was significantly larger than that of the older adults (5.8±3.4%, p=0.045). Given the potential for trunk extension velocity to be reduced by rapid shoulder flexion, fall prevention interventions focused on slip-related falls may benefit from including upper extremity motion as an outcome whether through conventional or innovative strategies.

Older adults who have previously fallen due to a trip walk differently than those who have fallen due to a slip

“…The use of upper extremity motion to reduce trunk extension during slipping may be more beneficial for avoiding a fall than the positioning of the COM to the base of support at slip onset 24 . As slips are explosive and ballistic in nature 25 , other factors such as muscle strength and onset latencies may be of greater importance than COM positioning for whether a recovery is successful or not.…”

Use of a cane for recovery from backward balance loss during treadmill walking

“…The backward motion of the C7 marker represents trunk extension. Because the ability to limit trunk extension is crucial for preventing falls (Grabiner et al 2008;Troy et al 2009), it appears that a cane may have negative effects on balance recovery from backward balance loss.…”

“…First, arm elevation moves the COM anteriorly and, second, rapid shoulder flexion may reduce trunk extension velocity (Troy et al 2009). An individual holds a cane out in front of the body, and the cane itself has mass (albeit quite small); therefore, the body weight is transferred anteriorly.…”

“…Therefore, C7 backward velocity and acceleration were faster when holding a cane than when not holding a cane. Arm elevation provides the most meaningful and beneficial contribution to balance recovery if it occurs rapidly, but only up until the arms are parallel to the ground (Troy et al 2009). When using a cane, however, the right hand was elevated only 187 SD 98 mm, which was not enough to restore dynamic stability.…”

Experimental studies and model development for individual-specific fall detection

“…The slip recovery attempt involved musculoskeletal coordinate, neuromuscular control, and their interaction with the environment (Redfern et al, 2001). A wide range of reactive recovery strategy was studied (Parijat and Lockhart, 2008;Troy et al, 2009). Among those responses, compensatory stepping was the irreplaceable important recovery strategy, especially in response to a large disturbance (Bhatt et al, 2005).…”