Final answer:
The specific intensity level for stage 2 is not provided, but it should increase to bring the heart rate into the recommended aerobic target range of 120-160 bpm, considering the individual's age and fitness level.
Step-by-step explanation:
The intensity level for stage 2 of an exercise protocol when the average steady state heart rate is less than 80 bpm at the end of the 1st stage isn't explicitly provided within the context of the question. However, in exercise physiology, it's understood that individuals should exercise within a target heart rate range to maintain optimal cardiac output (CO). This range is generally between 120 bpm and 160 bpm for healthy individuals during aerobic exercise.
Considering that the resting heart rate for adults is typically between 60 bpm to 100 bpm, and well-trained athletes can have lower resting rates, a heart rate less than 80 bpm after the 1st stage suggests that the individual is well below their target heart rate range for aerobic exercise. Therefore, to progress safely and effectively, the intensity set for stage 2 would likely be adjusted upwards to bring the heart rate into the lower end of the target range, but this should be done gradually and under supervision.
It is important to note that maximum heart rates can be broadly estimated by subtracting one's age from 220 bpm. Therefore, the age of the individual and their fitness level should be considered when determining exercise intensity levels to avoid the risk of abnormal heart rates like bradycardia or tachycardia.