Understanding Rotational Overload Effects of Thigh Wearable Resistance on Kinematic and Kinetic Properties of Sprint-running
Advancements in technology enable loads to be attached on the body, creating wearable resistance (WR) which athletes can wear during sport-specific movements, such as sprint-running. Measurements of sprint-running mechanics are often linear in quantification, despite being the result of joint rotations. Therefore, quantifying rotational movement, especially with the emergence of WR limb loading is important. One measurement tool that can collect rotational movement data is an inertial measurement unit (IMU) which allows sprint performance to be measured within its natural context. This research aimed to assess the kinematic and kinetic effects of a sprint-specific rotational form of resistance through thigh attached WR and sought to determine whether IMUs could quantify rotational kinematics of sprint-running. A review into the effects of leg attached WR on sprint-running performance found WR of ≤5% body mass (BM), provided a significant overload to step frequency while having minimal impact on step length. However, no studies had assessed the rotational work of the thighs and limited research had investigated kinetic changes. A review investigating the use of inertial sensors during sprint-running found mixed levels of agreement, mainly due to the methodological differences. Moreover, the use of inertial sensors to quantify rotational kinematics had not been investigated. The identified gaps and limitations from the reviews set the framework for the thesis. The first study determined if IMUs could quantify thigh rotational kinematics during sprint-running. The IMU derived thigh angular displacement and velocity were reproducible between trials (coefficient of variation 6.7-9.7%, intraclass correlation coefficient: 0.95-0.96). Compared to a motion capture system, moderate to high levels of agreement were found, with the IMU underestimating thigh angular displacement (-6.7% to -9.0%) and angular velocity (-5.3% to -16.4%). Study two determined the load effects of thigh WR on kinematics and kinetics during non-motorised treadmill sprinting. Thigh WR ≥2% BM resulted in moderate to large effect size (ES) changes (-7.0% to -12.0%) in angular kinematics with trivial to small ES changes (-3.6% to 5.0%) found in linear kinematic and kinetic sprint-running properties. Given greater changes found with WR ≥2% BM, studies three to five used 2% BM. Study three assessed changes in kinematics and kinetics, and study four quantified mechanical rotational changes, both during 50 m over ground sprint-running. The WR condition resulted in small ES increases (<2%) in sprint times, moderate ES changes in net anterior-posterior impulses (-4.8%), vertical stiffness (-5.7%), and step frequency (-2.8%) while step length was unaffected. The rotational changes were trivial to small ES increases in thigh angular displacement (0.6-3.4%), a significant decrease in thigh angular velocity (-2.5% to -8.0%), and rotational work was significantly increased (9.8-19.0%). The fifth study measured the effects of thigh WR on sprint-running performance following a 5 week training period using a single-subject design. Thigh WR resulted in increased horizontal force (7.1%), vertical stiffness (12.9%) and rotational thigh velocity (4.5%) resulting in faster times (2.4-3.4%) over 40 m sprint-running. In summary, thigh WR provided similar effects to previous WR research in linear kinematic and kinetic properties. By utilising IMUs to investigate rotational movement specific loading, this thesis provided original research into the significant changes in rotational kinematics and work from thigh WR which provided a more ecological valid measure of sprint-specific rotational training. As such, rotational overloading of the hip musculature can be achieved in a progressive and planned manner, which assists with WR programming for improved sprint performance.