# Validity of smartphone sensors to assess selected kinetic and kinematic outcomes during single-leg landing stabilization tasks

## TL;DR

This study shows that smartphone sensors can reliably measure certain movement and force outcomes during landing tasks, offering a low-cost alternative to specialized equipment.

## Contribution

The study demonstrates the validity of smartphone sensors for assessing kinetics and kinematics during landing stabilization tasks, enabling accessible objective assessments.

## Key findings

- Smartphone sensors showed excellent agreement for time of flight (ICC > 0.94) and good agreement for early balance and trunk orientation.
- Smartphone sensors overestimated all measures compared to specialized equipment (p < 0.001).
- The findings suggest smartphone sensors can be used as a low-cost tool for objective assessment of landing stabilization tasks.

## Abstract

Landing stabilization tasks are a key component of injury prevention and rehabilitation programs. An objective estimation of kinetics and kinematics requires equipment and expertise which are often unavailable outside specialized centres. We investigated whether smartphone sensors, which are widely available to the general population, provide valid estimates of selected body kinematics and kinetics during landing stabilization tasks.

Seventy-six asymptomatic participants (35 females) performed a unilateral landing stabilization task on both legs. Ground reaction forces and trunk orientation were collected using a force platform and an inertial measurement unit, respectively. Participants performed the tasks holding a smartphone on their chest, which collected acceleration and orientation data. We established the validity between estimates obtained with smartphone sensors and specialized equipment using Intraclass Correlation Coefficient (ICC) and paired T-test or Wilcoxon test.

For both legs, agreement was excellent for time of flight (lower bound of the 95% confidence interval of the ICC > 0.94); at least good for early balance (ICC > 0.87), sagittal trunk orientation (ICC > 0.79), and concentric force (ICC > 0.80); and at least moderate for frontal trunk orientation (ICC > 0.58), late balance (ICC > 0.65) and landing impact (ICC > 0.60). Smartphone accelerometers overestimated all measures compared to the force platform (p < 0.001).

Smartphone sensors provide measures similar to those obtained using specialized equipment when used to assess selected kinetics and kinematics outcomes during landing stabilization exercises. Time of flight, concentric force, early balance and trunk orientation in the sagittal plane demonstrated at least good agreement, although smartphone sensors systematically overestimated acceleration-derived measures. This study sets the foundations for the use of smartphone sensors as a simple, inexpensive tool to characterize the performance of landing stabilization tasks objectively.