The traditional drill-to-game (DTG) approach has been the dominant coaching practice employed by club level Gaelic football (GF) coaches in Ireland. Modified games (MG`s) involve altering normal playing conditions such as the playing area, number of players per team, size and shape of pitch, rules of the game etc., and are a central tenet of the games based approach (GBA). Ideally, MG’s should closely replicate competitive match play demands (MPD). This PhD compared MPD (activity profiles, individual technical skills, team play characteristics and heart rate responses) during 7 and 11-a￾side senior club level GF games with 15-a-side senior championship games while maintaining all other match play conditions. The follow-on study (Physical and physiological predictors of activity profiles during Gaelic football match play) could not be undertaken due to the closure of the exercise physiology laboratories in DCU due to COVID-19. A protocol paper for the study is included as Chapter VI. The final study examined coaching practices of club level GF coaches in relation to the sequencing and time allocation to training and playing form activities, and their rationale for using various modified game formats during training. In general, player activity profiles and technical skills were significantly greater during MG’s than 15-a-side games. Although a similar number of team play opportunities are offered to players competing in 7, 11 and 15 a-side games, the time per team possession and the number of skills per possession was significantly greater in the MG`s. There was very little difference in the maximal and mean HR during MG’s and 15-a-side games. Regardless of the phase of the season, coaches placed a greater emphasis on drills/isolated activities during the first part of training sessions and progressed to game-based activities at the latter part of training sessions. A greater proportion of preseason training sessions was spent in drills/isolated activities than game-based activities. In contrast, significantly more training time was allocated to game-based activities during the competitive season. In summary, MG’s involving reduced player numbers while maintaining all other match play variables closely replicates competitive MPD. Apart from offering valuable insights for senior club level GAA coaches, the research methodology offers a structured framework as a starting point for coaches when altering playing conditions (constraints) during MG`s on MPD. Finally, current coaching practice among senior club level coaches mostly aligns to the traditional DTG approach.