Punching is a fundamental human movement that is the defining action of many combat sports, most of all boxing where it is the primary method of attack. This thesis investigated the biomechanics and determinants of punching to answer the question, “What defines effective punching in boxing?” The first chapter of the thesis expanded on these themes, as well as identifies current gaps in the literature relating to the analysis of punching in boxing. Chapter two was a narrative review of methods used to assess impact kinetics and the contributors to impact kinetics in combat sports. The third chapter was a narrative review on effective mass, an impact variable of interest in the literature. The chapter focused on defining the variable and the methods proposed to maximise effective mass. The review found that effective mass was the inertial contribution of a fighter to impact. Additionally, the review found that double peak muscle activation is currently the only process proposed in the literature to increase effective mass. There is a potential gap in the literature regarding continued force application by the lower body during impact. Chapter four, a qualitative study of experienced boxing coaches exploring their views on effective punching performance. The results of the study are in agreement with Chapter two in that the lower body’s contribution was key to producing an effective punch. Chapter five presents an original method to measure impact kinetics using practical, simple, affordable, and relevant equipment. Reliability test statistics determined that all measures had acceptable reliability (CV ≤ 4.6%). Validity was determined via linear regression of a spectrum of loads and coefficient of determination. All variables were found to have a good fit to the model (r^2 ≥ 0.92) except for rate of force development (r^2 ≥ 0.57). Chapter six, assessed the reliability of the method described in Chapter five on a cohort of experienced boxers and untrained participants tested intra and intersession. Reliability statistics were small (ICC < 0.67 and CV < 10%) to moderate (ICC < 0.67 or CV < 10%) and technical error of measurement was moderate (TEM = 0.60 – 1.19). Chapter seven was a mixed method analysis of ground reaction forces, electromyography, and high-speed video to define the phases of straight and hook punches. The definition of phases was a novel contribution to the punching literature, identifying three phases for straight punches (initiation, execution, and impact) and four for hook punches (wind-up, initiation, execution and impact). The chapter used qualitative and quantitative methods to discover the uniqueness of each punch type and the differences between lead and rear hand punches of the same punch type. Chapter eight, the final experimental study of the thesis, used the findings from throughout this research to identify the determinants of impact kinetics in straight and hook punches. Findings from the study further reinforce the uniqueness of each punch type as no individual variable determined impact kinetics across them. There were general commonalities, as the majority of determinants were found in the lower body (19 of the 28), confirming the findings of Chapter Two, and those related to the upper body indicated that relaxation of the musculature was key to optimising impact kinetics. Results relating to effective mass found that double peak muscle activation had no correlation, while the lower body had meaningful correlations. This finding confirms the theory introduced in Chapter Three regarding the lower body’s continued force application during impact, but conflicts with current theories relating to double peak muscle activation. The final chapter (nine) is a summary of findings, areas for future research, and practical applications. This PhD has contributed knowledge regarding the understanding of effective mass in punching, the role of ground reaction forces as a key to punching, the kinematic and kinetic events of punching in a phase model, and the determinants of impact kinetics in straight and hook punching.