The effect of integrating micro spring technology into running shoes to influence biomechanical parameters and knee pain/comfort scores in recreational runners with knee pain

Abstract

The continued popularity of recreational running and an ever-increasing focus on injury prevention and pain reduction has led to a significant recent expansion in the sports technology market. Many new technologies put forward claims around reducing the risk of injury, but very few offer detailed supporting evidence to substantiate these claims. As injury levels in recreational runners remain high it would seem the technologies currently used in running shoes are not effectively addressing this problem. This thesis focused on exploring the potential of a new and unique pocketed micro spring technology to influence biomechanical and clinical measures in a multi-faceted interdisciplinary investigation.
The two main aims of this piece of work were to identify whether pocketed micro spring technology could be viably and effectively integrated into a commercial branded running shoe and to explore the efficacy and effectiveness of such technology on recreational runners with and without knee pain.
Firstly, an iterative process was followed to establish the most effective mass-spring-damper solution that could be created with the resources available and that was also technically feasible to mass produce. This stage of the research comprised of a number of small studies exploring the effect of pocketed micro spring technology on impact loading rates in a laboratory-based setting using primarily kinetic analysis. In total 35 healthy recreational runners were tested through the iteration process. During detailed analysis of human trials, important biomechanical variances were highlighted specifically within the first 5% of stance phase, leading to a more detailed exploration of the instantaneous loading rate principle than has been outlined in previous published literature.
Work also included technical modifications to the technology itself in an attempt to engineer a performance driven solution capable of improving the shock absorption characteristics exhibited by running shoes currently on the market. From the impact data of the healthy subjects, key loading parameters which reflected the mechanics of foot impacts during running were used to develop a new drop rig testing machine. Although not an original aim of this thesis, this development was seen as an opportunity to attempt to eliminate the intra and inter subject variability of human running trials. This machine aimed to replicate both rearfoot and forefoot impact loading during running to determine the effects of subtle differences in the design and materials used in running shoes. Results from these studies established that it was possible to develop a pocketed micro spring capable of reducing initial vertical loading rates, more effectively than popular branded market leading running shoe technology.
Once a running shoe with a mass-spring-damper system in the midsole capable of reducing impact forces experienced when running had been developed, a second phase larger study was carried out to examine the influence of pocketed micro spring technology on biomechanical parameters, and pain and comfort scores, in recreational runners with and without knee pain. As part of this study, the runners took part in outdoor running trials in both their regular running shoes and running shoes integrating pocketed micro spring technology. Inertial Measurement Units or IMUs (Delsys inc) were used to measure biomechanical variables and Numeric Comfort Rating Scale (NCRS) questionnaires were used to collect comfort data from both groups. The IMUs allowed this study to investigate angular velocity parameters alongside deceleration parameters to explore impact loading and stability during initial foot contact, also enabling the use of such data as proxy measures to the force plates used in the first stage of this research. Knee Injury and Osteoarthritis Outcome Score (KOOS) and Numeric Pain Rating Scale (NPRS) questionnaires were also used to collect pain data from those individuals knee pain.
Results demonstrated clear and significant reductions in both vertical impact jerk and internal tibial rotation velocity in both participant groups when wearing the new technology, this included 16.0% (knee pain group) and 11.7% (healthy group) reductions respectively for vertical impact jerk, and 19.1% (knee pain group) and 32.6% (healthy group) reductions respectively for internal tibial rotation velocity. Grouped and individual analysis showed a strong link between biomechanical changes and comfort, with the recreational runners with knee pain experiencing lower levels of pain and greater levels of comfort when wearing and training in the shoes with the pocketed micro spring technology.
This thesis has provided information not previously available regarding the enhancement and integration of a mass-spring-damper system into a running shoe. This work offers a unique and novel insight into the potential of pocketed micro spring technology to reduce key biomechanical parameters, increase comfort and reduce pain across healthy and knee pain recreational runners.