Test-retest reliability of the FALL FIT system for assessing and training protective arm reactions in response to a forward fall

Abstract

The use of the hands and arms is an important protective mechanism in avoiding fall-related injury. The aim of this study was to evaluate the test-retest reliability of fall dynamics and evokd protective arm response kinematics and kinetics in forward falls simulated using the FALL simulator For Injury prevention Training and assessment system (FALL FIT). Fall FIT allows experimental control of the fall height and acceleration of the body during a forward fall. Two falls were simulated starting from 4 initial lean angles in Experiment 1 and with 4 different fall accelerations in Experiment 2. Fourteen younger adults (25.1±3.5 years) and 13 older adults (71.3±3.7 years) participated in Experiment 1 and 13 younger adults (31.8±5.7 years) participated in Experiment 2. Intraclass correlation coefficients (ICC) were used to the evaluate absolute agreement of single measures at each condition and averages across conditions. Average measures of fall dynamics and evoked kinematics and kinetics exhibited excellent reliability (ICC(A,4)>0.86). The reliability of single measures (ICC(A,1) > 0.59) was good to excellent, although 18% of single measures had a reliability (ICC(A,1)) between 0.00 and 0.57. The FALL FIT was shown to have good to excellent reliability for most measures. FALL FIT can produce a wide range of fall dynamics through modulation of initial lean angle and body acceleration. Additionally, the range of fall velocities and evoked kinematics and kinetics are consistent with previous fall research.•The FALL FIT can be used to gain further insight into the control of protective arm reactions and may provide a therapeutic tool to assess and train protective arm reactions.

Keywords: Falls; Injury; Upper extremity.

Graphical abstract

Fig. 1

Illustration of the FALL simulator For Injury prevention Training and assessment system (FALL FIT). Participants lay on top of the support platform. At an unpredictable time, the support platform and the participant are released from a leaning position (panel A). Following perturbation onset, the participant rapidly orients their hands and arms to prepare to absorb the impact energy following impact with the landing surface (panel B). The device is held in position using an electromagnet. The initial lean angle is controlled by varying the distance between the anchor point and the electromagnet (panel C). A counterweight system is used to reduce the angular acceleration of the support platform. A schematic diagram of the FALL FIT with a counterweight system is shown in panel D. The participant is modeled as an inverted pendulum with mass m₁ and height L. When the system is released, the angle θ increases, pulling point B downward. The counterweight m₂ moves upward at a rate that is 4 times greater than point B moves downward. Four pulleys, P₁, P₂, P₃, and P₄, were used to effectively multiply the counterweight m₂. The pulley system was an effort to compensate for the relatively small moment arm the counterweight load acts through compared to the inverted pendulum, r versus L respectively. Physical constraints limited the maximum allowable radius r of the counterweight pulley (P_c). The cable system needed to be sufficiently far from the area where the arms could move during the trials. Additionally, the pivot point A had to be higher above the ground than the radius of the counterweight pulley. Adapted from Borrelli, Creath, and Rogers (2020) with permission from Elsevier.