Horizontal Eccentric Towing and Its Effects on Sprint Performance
The success of many team sports and track and field athletes can be in part linked with their sprint performance. Therefore, improving sprint performance has been the foci of researchers and practitioners alike. The most commonly used tools that deliver sprint-specific training stimuli are resisted towing devices (RST) (e.g. sleds). RST provides a predominantly concentric (CON) horizontal overload to the musculo-skeletal system, especially in the acceleration phase of the sprint. Perhaps an eccentric (ECC) horizontal overload may be beneficial given the benefits of ECC training; such as, injury prevention and rehabilitation, shift towards faster muscle phenotypes, hypertrophy, strength and power improvements. This resulted in the overarching research question, “Can a novel horizontal ECC towing device improve sprint performance?”. The aim of this thesis was to develop a device that would provide a horizontal ECC stimulus, evaluate the biomechanics of the device and test its effects on sprint performance. A review of existing ECC training devices found limited devices overload in the horizontal plane and none eccentrically overload the musculo-skeletal system in a sprint-specific gait. Therefore, a movement termed horizontal ECC towing (HET) was developed which involves an athlete in a sprint stance trying to move forwards but is being pulled backwards. A device termed the HET device was then developed to automate this movement. The device was powered by a 10 kW electric motor that can tow athletes at velocities up to 3.58 m/s and can tolerate forces up to 2.8 kN. Two familiarisation sessions were found to achieve movement consistency during HET. Biomechanics analysis was conducted to further understand the movement which would help inform training programme development for coaches. Since HET is a novel movement, no research existed. Thus, ECC towing was compared to its opposite, the CON towing direction (CTD). Statistical Parametric Mapping (SPM) analysis of ground reaction force (GRF) profiles found that the two directions were significantly different (p<0.05) and were applying different movement strategies to produce force. This suggested that different lower limb joints were likely responsible for CON and ECC force production. Vertical and horizontal GRFs were lower in the ECC direction (p<0.05), which may be limited by the coefficient of friction and indicated that isokinetic horizontal towing does not follow the contractile-force-velocity relationship. Power and work analysis of the lower limb joints showed that the ankle and hip joints are absorbing energy and likely dissipating it in the ECC towing direction (ETD). ETD has greater ankle and hip joint power absorption and much smaller power production. A four-week intervention of ECC and CON towing in elite female field hockey players (n=10) resulted in no improvements in split times. There is still an opportunity for practitioners and researchers to apply a unique ECC stimulus to their athletes. The intervention study had its limitations as it was based out of the lab in a practical setting. However, no tool provides a similar overload as the HET device. We recommend to those that are interested in overloading the power absorption phase of the ankle and hip joints should incorporate HET. Further research with the HET device involving a larger cohort of athletes could provide more conclusive evidence on the effects on sprint performance.