Final answer:
The Atwater calorimeter and Benedict-Roth spirometer are two common direct observation techniques for measurement of physical activity, measuring total heat output and oxygen consumption, respectively.
Step-by-step explanation:
The two common direct observation techniques for measurement of physical activity are the Atwater calorimeter method and the Benedict-Roth spirometer method. The Atwater calorimeter involves a specialized chamber where an individual can live and work for several days while their total heat output is measured, providing an accurate measurement of energy expenditure. Meanwhile, the Benedict-Roth spirometer is a closed-circuit breathing apparatus that measures oxygen consumption, which can be translated into energy expenditure though it is mainly used when an individual is at rest or performing very light exercise.