\begin{table}[h!]
  \begin{center}
    \begin{tabular}{| l c r |}
    \hline
    1 & 2 & 3 \\
    4 & 5 & 6 \\
    7 & 8 & 9 \\
    \hline
    \end{tabular}
  \end{center}
  \caption{Sources of Workload}
\end{table}


\begin{table}[h!]
  \begin{center}
    \begin{tabular}{| l c r |}
    \hline
    Effort or Performance & Temporal Demand or Frustration & Temporal Demand or Effort \\
    \hline
    Physical Demand or Frustration & Performance or Frustration & Physical Demand or Temporal Demand \\
    \hline
    7 & 8 & 9 \\
    \hline
    10 & 11 & 12\\
    \hline
    \end{tabular}
  \end{center}
  \caption{Sources of Workload}
\end{table}