Towards prevention of overuse lower limb injury with a smart wearable for military use

Abstract

This thesis explains the research into and implementation of overuse lower-limb injury prediction among military recruits, using wearable plantar-pressure sensing and biomechanical gait algorithms. The research has been done with the purpose of designing a usable, affordable and accurate injury-prevention tool, increasing both military wellbeing and operability. For years, researchers have gathered evidence of correlations between specific gait biomechanics of individuals and their influence on injury incidence. Using various types of laboratory equipment, such as pressure plates, walkways and treadmills, researchers found a strong correlation between parameters like cadence, vertical loading, (time to peak) heel rotation and local peak pressure values and different types of common overuse injuries in the lower limbs. However, laboratory tests often neglect the influence of footwear, distraction and fatigue. In addition, they are expensive and time-consuming tasks. One specific user group that suffers from a high incidence of overuse injuries is the military. About 3000 recruits follow basic military training each year, of which about 13% end up with one of three most common injuries: MTSS, iliotibial band syndrome and tibial stress fractures. Of those injured recruits, about 8% gets discharged from the military. This high rate is caused by the intensity of training, often accompanying high carried loads and pressure to perform. Specifically, the cumulation of repeated smaller impacts during marches is bound to cause overuse injury. The ability of commercially-used pressure-sensitive insoles to measure abnormality in injury-predictive gait parameters was tested in a series of studies. First, measurements from the insoles were compared to a commonly used gait-analysis tool: a GAITRite walkway (n=20). This study found no statistical agreement in sample-to-sample predictability. To validate whether those results could be caused by methodical differences, a second study was performed comparing the insole measurements of injured soldiers to those of control subjects (n=10). This test did result in significant between-group differences for all measured parameters. Furthermore, significant differences in parameters were found between walking on military boots and running shoes. A strategic study revealed that the product could find a competitive advantage in service and software innovation, with a focus on (a) accuracy while maintaining usability for specific user groups and (b) multi-diagnostic ability and spread market targeting (both b2b and b2c). Specific user demands were found and defined as a reduction in insecurity at various levels (e.g. where a soldier wants to be reassured about their personal fitness, a commander wants to ensure operation-readiness). A design proposal was created (Figure 1), based on research insights. The concept insole not only meets military-specific embodiment, hardware needs and improved sensor placement, but a service-design proposal enables both direct users and important stakeholders to use the data for injury prevention, rehabilitation, adaptation of footwear, operational management, training customization and general overuse-injury research. Besides meeting the needs within a military context, the product could be adjusted to meet the needs of other (occupational) overuse-injury sensitive users, such as police, hospital staff and factory workers. Clinical applications include automation of insole orthosis customization and prevention of ulceration among diabetic patients.