Sprint Running With Lower-limb Wearable Resistance: Acute Mechanical Responses and Training Outcomes
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Sprint running, and in particular one’s ability to perform maximal acceleration over short distances, is a key component of performance for many sports. Thus, the best methods to develop an athlete’s sprint running capabilities is of interest to many coaches. Lower-limb wearable resistance (WR) is a movement- and speed-specific training method for sprint running that allows close adherence to the principle of training specificity. Therefore, lower-limb WR could be well suited for producing adaptations that transfer to unloaded sprint running. This thesis aimed to answer the overarching question, “What are the effects of lower-limb WR on short distance sprint running?” A review of the literature (Chapter 2) found that lower-limb WR loading schemes of 0.6−5% body mass (BM) significantly increased contact time (2.9−8.9%), decreased step frequency (−1.4 to −3.7%), and slowed total sprint times (0.6−7.4%). However, minimal kinetic and joint kinematic information had been published which limited the understanding of the underlying mechanics associated with sprint running with lower-limb WR. Also, no prior investigations had employed a shank- or thigh-only load configuration. Further, there was no research-based evidence detailing how an athlete population might respond to lower-limb wearable resistance training (WRT) for sprint running. These important gaps and limitations provided a framework for the research undertaken in this thesis. The first study (Chapter 3) investigated the effects of 2% BM thigh and shank WR on joint kinematics during early acceleration. It was found that significant differences in maximal joint angles between loaded and unloaded sprint running were small (ES = 0.23–0.38), limited to the hip and knee joints, and < 2° on average. Also, average hip flexion and extension velocity were significantly overloaded with the thigh and shank WR, which suggested a specific application for lower-limb WR to target the hip flexion and extension actions associated with fast sprint running. In study two (Chapter 4), it was found that athletes were largely able to maintain propulsive and net anterior-posterior impulse values using 2% BM thigh and shank WR. However, greater increases to braking and vertical impulses were observed with shank WR (2.72−26.3% compared to unloaded) than with thigh WR (2.17−12.1% compared to unloaded). Considering these findings and the greater practitioner interest in shank WR for training applications due to practical utility, a third study (Chapter 5) was undertaken to compare the force waveforms between unloaded and 2% BM shank WR sprint running to better understand the underlying cause(s) for increased horizontal braking and vertical impulses and determine if there are significant differences in the magnitude of forces around impact. Significant differences in the anterior-posterior component of the ground reaction force (i.e. greater levels of braking force) between unloaded and shank WR occurred between 20.8−28.3% of ground contact at 10 m, 20 m, and 30 m. Thus, there was no indication that greater horizontal braking or vertical forces occur during the impact portion of ground contact. These studies identified specific underlying mechanisms that may render thigh and shank WR as effective training tools for sprint acceleration performance. Two training studies were subsequently undertaken in this thesis to investigate the longitudinal effects of shank WRT for sprint running in field-based sports athletes. Six weeks of WRT was found to be superior to unloaded training in maintaining the technical ability to produce horizontal force at low velocities and maintaining a horizontally oriented ground reaction force with increasing speed in collegiate/semi-professional rugby athletes (Chapter 6). Nine weeks of WRT in high school American football athletes did not result in significant post-training differences between the WR and unloaded training (Chapter 8). Detailed inspection of the training protocols employed and athlete responses provided evidence that shank-placed WR can be used to amplify the nuances of a sprint running training protocol. Prior to Chapter 8, a study was completed to establish the level of agreement between the horizontal F-v profile variables obtained from two field-based velocity measurement devices, a 1080 Sprint and a Stalker ATS II radar gun (Chapter 7). This provided the necessary information to determine if the two devices could be used interchangeably to inform device selection, and thus, number of testing time points to be included in the training study that followed (Chapter 8). The research presented in this thesis has identified the mechanical determinants that are overloaded by lower-limb WR, and thus, may be influenced over time to produce positive speed adaptations. Also, this thesis has identified lower-limb WRT as a time-efficient method to retain mechanical characteristics of sprint performance, which may have beneficial implications for sports with constrained schedules. In conclusion, it is suggested that this method of resistance training could be used concurrently with other resistance training methods in a mixed-method training approach to provide a unique stimulus to encourage continued improvement in speed development or further target velocity-based individual weaknesses.