Accelerated eccentric training: A novel and holistic approach to enhancing physical performance

   

Eccentric training is a method of resistance training that consists of either eccentric only actions during the exercise or eccentric-concentric coupled actions during the exercises, of which typically one of velocity, duration, and mass will be altered during the eccentric phase to create specific adaptations. Eccentric training research has predominantly focused on increasing mass during the eccentric phase or increasing the duration of the eccentric phase in an ambition to enhance muscular hypertrophy and strength at greater rates than conventional training methods. Conversely, there is a dearth of research surrounding increased eccentric velocity or performing eccentric actions as quickly as possible to enhance athletic performance. The purpose of this thesis was to assess the impact of accelerated eccentrics (AE) as a training method. It aimed to critique current knowledge on eccentric training and develop theoretical frameworks incorporating AE. Additionally, the thesis sought to enhance understanding of eccentric training. Chapter 2 provided a critical review analysing fast eccentric actions, highlighting that when eccentric actions are performed at greater velocities, concentric power and velocity increases, as does variables such as jump height. However, the specific adaptions following eccentric velocity as a training method is not validated. Therefore, further research is required to unearth and create a greater understanding into this topic area. Chapter 3 created a theoretical concept into eccentric training, establishing the variety of eccentric training methods that exist. A framework was created to distinguish specific training methods and the intended adaptions they seek to achieve when implemented. The framework established how AE and overspeed eccentrics can increase eccentric velocity, and theorised physical adaptations were established with the addition of how the methods are implemented within practice. 

Chapter 4 determined the reliability of resistance bands, assessing both the tension and retraction velocity they create, this would establish if overspeed eccentrics would create greater eccentric velocity and warrant further investigations. Findings indicated alterations in tension when using resistance bands that would cause incorrect calculations to be made when held at a specific set length, however, a small investigation determined resistance bands create greater downward velocity than just gravity, and thus overspeed eccentrics theoretical concept was proven correct. As band tension alters it was determined that overspeed eccentrics should not be researched further due to inaccuracy in tension and thus raising methodological concerns. 

Chapters 5-7 determined the reliability, acute and chronic effects of AE. Reliability testing (chapter 5) identified during a countermovement jump (CMJ) and land, various metrics were seen as reliable due to > 0.70 interclass corelation, < 10% coefficient of variation and achieving no significant difference between testing sessions. However, various landing metrics were seen as unreliable, either violating one or multiple of the reliability test scores, justifying their exclusion from future testing. Chapter 6 analysed the between condition effects of AE against a control cue, findings indicated the AE cued lead to greater peak and mean braking velocity indicative of greater downward momentum. As a subsequent the AE cue had a significant enhancement in braking mean (p < 0.01) and peak force (p < 0.01), braking impulse (p < 0.01), and a significant reduction in braking phase time (p < 0.01). Findings demonstrated an AE cue creates enhancements in braking (eccentric) strategy and as such this would impact metrics such as braking forces and braking rate of development. Furthermore, a small improvement within propulsion peak and mean force as well as time to take-off being reduced was found, demonstrating AE could yield specific adaptions greater than other training methods. 

As per the findings of chapters 2 and 6 and the theoretical concept created in chapter 3 it was deemed necessary to assess the physical changes in CMJ performance when performing an AE versus 3 s eccentric tempo during an exercise to determine if alterations in physical performance using either training method exist. A rugby academy premiership team completed a 4-week training block to assess alteration in CMJ performance when completing either programme. Findings showed the 3 s eccentric tempo group (3 s) had an increase in body mass (3 s: effect size (ES) = 0.08, AE: ES = 0.03) and jump height (3 s: ES = 0.29, AE: ES = -0.03) than the AE group. However, the AE group reduced time to take-off (AE: ES = -0.02, 3 s: ES = 0.14) and braking phase time (AE: ES = -0.14, 3 s: ES = 0.12), as well as reduction depth displacement (AE: ES = 0.04, 3 s: ES = -0.25). The findings highlight that AE improves braking force production and reducing braking phase time, whereas the 3 s eccentric tempo training method is better suited in increasing jump height and body mass. Results thus confirming the theoretical concept created in chapter 3 for AE theorised adaptations. This solidifies that specific eccentric training methods will yield certain physical adaptations. 

Chapter 8 was comprised of two parts, Chapter 8a undertook a Delphi study with 12 leading expert practitioners and researchers within the field of eccentric training, to provide their opinion on specific matters concerning eccentric training and eccentric muscle lengthening, as deemed an area of interest by the research team. A definition of eccentric training was created within the Delphi study as was a new construct of time in action to provide further information into exercise execution duration. A greater understanding into the definition of eccentric overload was provided, suggesting no consensus was reached with the term and that referring to training methods rather than eccentric overload would provide less confusion. Finally, a greater understanding into muscle lengthening is provided with new construction of passive muscle lengthening, active and forced eccentric actions were proposed, this provides a greater understanding into how muscle lengthening can occur and the subsequent outcomes. Chapter 8b then completed a systematic review into various eccentric training methods, this was completed to introduce the Delphi findings into current literature and provide a new insight into specific findings. Furthermore, the chapter sought to provide greater knowledge to the reader within the various methods that exist within eccentric training to then suggest current known knowledge and how eccentric training should progress in future research.  Finally, the review further aimed to showcase that different eccentric methods would yield different physical responses when they are implemented, justifying the findings of chapter 7. The findings of the thesis support the incorporation of AE as a means to increase rapid force development within the braking phase and provide a greater understanding of the various methods that exist within eccentric training and how these can be used in a strength and conditioning programme to achieve desired responses.