The aim of this thesis was to investigate the use of effort-based intensity prescriptions as a method to reduce individual variability and the occurrence of training non-response. Specifically, this thesis explores the physiological, psychological, and metabolomic responses to the interaction of training duration and effort-based intensity on a single-bout basis, whole session basis, and during chronic training intervention. The first experimental study (Chapter 4) investigated individual variability during self- paced exercise bouts at a rating of perceived exertion (RPE) of either 9, 13, or 17, conducted for either 1, 4, or 8 min. The study found that effort-based intensity prescriptions at higher RPEs and shorter durations result in lower levels of individual variability. The second study (Chapter 5) investigated individual variability during maximal isoeffort training sessions in either short interval (30 sec), long interval (5 min), or continuous exercise matched for total training duration. Long intervals displayed lowest variability in both how the session was performed as well as physiological response compared to short intervals and continuous sessions. The third study (Chapter 6) comprised a 6-week training intervention using maximal isoeffort intensity prescriptions using short (30 sec) or long interval (5 min) session formats, as well as a control group. Whilst short intervals resulted in higher levels of individual variability, a greater training response was found following this session format compared to both the long interval and control groups. The fourth study (Chapter 7) investigated the metabolomic differences between session formats, and between variable and consistent responding participants from Chapter 5. Distinct metabolomic differences were found between all session formats, and key metabolites were found relating to energy turnover, purine metabolism, and amino acid metabolism based on whether individuals were consistent or variable in session performance. The fifth study (Chapter 8) investigated the chronic changes in the urinary metabolome following the training interventions as described in Chapter 6. Several metabolomic markers differentiated between training responders and non-responders, in addition to metabolites associated with increased MMP or V̇O2max across all training groups. The main finding of this thesis was that the use of higher intensity effort-based targets and shorter interval durations has potential in reducing the occurrence of non-response to training.