Initially, the total product curve is typically upward sloping. This reflects the fact that as more units of a variable input (such as labor) are added to a fixed input (like capital or land), the total output or product generally increases.
However, the shape of the total product curve can change over time. Initially, due to the law of increasing returns to scale, the curve rises steeply as efficiencies are discovered. After reaching a certain point, however, the law of diminishing returns sets in, and the curve will begin to rise at a decreasing rate before eventually plateauing or declining if too many inputs are added relative to fixed outputs.
So, the total product curve can be described as initially increasing, subject to diminishing returns as additional inputs are added.