PURPOSE: Planning tennis sessions accentuating physical development requires an understanding of training load (TL). The aims were to describe the external and internal TL of drills and analyze relationships between ratings of perceived exertion (RPE), TL, and other measures. METHODS: Fourteen elite-level junior tennis athletes completed 259 individual drills. Six coaches helped devise classifications for all drills: recovery/defensive, open pattern, accuracy, 2-on-1 open, 2-on-1 net play, closed technical, point play, and match play. Notational analysis on stroke and error rates was performed postsession. Drill RPE and mental exertion were collected postdrill, while heart rate (HR) was recorded continuously. RESULTS: Recovery/defensive, open pattern, and point play were significantly greater than closed technical drills (P < .05) for RPE and mental exertion, as were accuracy drills and match play (P < .05). Recovery/defensive, open-pattern, accuracy, and 2-on-1 open drills had higher stroke rates than match play (P < .05). Error rates of closed technical drills were significantly higher than for open pattern, 2-on-1 drills, point play, and match play (P < .05). No HR differences were observed (P > .05) between categories. Substantial correlations existed for drill RPE and TL with mental exertion (r > .62) for several categories. TL was substantially correlated with total strokes (r > .65), while HR and stroke and error rates were in slight to moderate agreement with RPE and TL (r < .51). CONCLUSIONS: Recovery/defensive drills are highest in physiological stress, making them ideal for maximizing physicality. Recovery/defensive drills compromised training quality, eliciting high error rates. In contrast, 2-on-1 net-play drills provided the lowest error rates, potentially appropriate for error-amelioration practice. Open-pattern drills were characterized by significantly higher stroke rates, suggesting congruence with high-repetition practice. Finally, with strong relationships between physical and mental perception, mental exertion may complement currently used monitoring strategies (TL and RPE).