What structural elements of zone 3 workouts can be adjusted to avoid interfering with base fitness development, and are there any particular types of interval patterns, work-to-rest ratios, or training block configurations that can be optimized to achieve this balance effectively. Specifically, how can endurance athletes fine-tune the duration and frequency of zone 3 sessions to stimulate significant physiological adaptations without inducing excessive fatigue or detraining of low-intensity endurance capabilities. Are there any data-driven guidelines or coaching strategies that can be applied to resolve potential conflicts between building high-intensity fitness and maintaining base fitness, and if so, what are the key performance indicators that should be monitored to ensure a harmonious integration of these two training objectives.