Reactive Strength is a physical quality that strength and conditioning practitioners aim to develop in athletic populations due to its positive relationships with locomotor performance. This quality is developed through the implementation of plyometrics training, typically starting with low intensity exercises such as the 10/5 repeated jump (RJ) before progressing to high intensity exercises such as the drop jump (DJ). However, in some settings, this linear approach has been questioned as the most time efficient method of training. Furthermore, previous research has shown low commonality between the RJ and DJ, suggesting that reactive strength (via reactive strength index (RSI)), of the RJ and DJ may not be the same. Therefore, exposing cohorts to the RJ training may not transfer to DJ performance. However, there has been no literature to further explore these differences and the ability to quantify holistic reactive strength performance. Consequently, a new metric for measuring reactive strength, the reactive quality ratio (RQR), has been presented in this thesis to compare relative differences in DJ and RJ RSI. Therefore, the aim of this thesis was to determine the validity and practical application of the RQR to holistically quantify reactive strength. This can then be used by practitioners to highlight whether an individual or team is proficient or inefficient in high or low amplitude reactive strength tasks. This allows the prescription of specific resistance and plyometric exercises to focus on areas of development.First, a systematic review of the literature (Chapter 3) was first conducted to determine whether RSI was sensitive to population differences. Population sensitivity is important as it determines whether RSI is a worthwhile strength quality to benchmark cohorts and highlights the potential underlying anthropometrical and morphological reasons behind it. Results concluded that RSI from a DJ was a differentiating factor among populations with a common theme being cohorts with a higher RSI, were stronger or exhibited greater lean muscle mass allowing for them to have higher relative force output. Furthermore, this review found no comparisons of RJ RSI in any previous study, highlighting gaps in the literature and the need for original investigation. Therefore, comparing the RSI in both the DJ and the RJ was identified as a crucial next step to validate the use of the RQR.The following original investigations (Chapter 4 & 5) explored the differences in DJ and RJ and to determine whether they were unique to each other as a determining factor for the use of the RQR. Results found that low commonality between RJ and DJ RSI (r²=32%). Additionally, the DJ had a higher relationship to maximal isometric strength than the RJ. This was potentially reflective of the significantly larger impulse and landing rate of force development (RFD) in the DJ from 45cm than the RJ, representative of a larger eccentric demand in the DJ, thus intensity. This resulted in stronger elite male australian football cohorts having a higher DJ RSI output than elite female australian footballers, yet not RJ RSI output.It was also determined that the RQR had good levels of reliability (ICC = 0.76; 0.52-0.89) with a low-level coefficient of variation (<4.02%). This meant that the RQR could be used longitudinally to determine effects of training interventions on reactive strength. Results of a single-case experimental design (SCED) study (chapter 6) showed a significant increase in trend in RQR (1.02; IQR: 0.89-1.06 to 1.08; IQR: 1.03-1.10) following intervention, indicating differing responses in DJ and RJ reactive strength. These results concur with the narrative of the thesis that DJ and RJ RSI should be examined together if wanting to holistically monitor reactive strength. Whilst further exploration is needed and population specific, optimal ranges determined by mean population results discussed in the thesis suggest a RQR of 1.00 ± 0.10 for males and 0.80 ± 0.10 for females. Lower RQR indicates a focus on maximal strength and high-amplitude plyometrics, whereas higher RQR suggests targeting low-amplitude plyometrics for repeated jump strategies.