A manner of studying human development that stresses the fluctuations and transitions that occur constantly throughout life is referred to as the:

Dynamics-system theory.

Explanation:

Stress may be defined as the mental condition that can cause anxiety, depression or tension. Small stress improves the condition of an individual but high stress can cause long term depression.

The dynamic system theory states that motor development occurs with the changes in the development system and explains the new motor abilities in children. This theory also explains the transitions that might occur in the individual during the stress condition.

Thus, the answer is dynamics system theory.