\begin{tikzpicture}[->,auto,x=3cm, y=1.5cm]

  \node (EEG) at (1.5,3) {EEG};
  \node (EMG) at (3.5,-0.5) {EMG};
  \node (Syn) at (2.5,0.5) {Synergies};

  \node (kin) at (0.5,0.5) {Velocities};
  \node (pos) at (-0.5,-0.5) {Positions};

  \draw[->,very thick] (EMG) -- (Syn);
  \draw[->,very thick] (pos) -- (kin);

  \draw[->] (EEG) -- (EMG);
  \draw[->] (Syn) -- (kin);
  \draw[->] (Syn) -- (pos);
  \draw[->] (EEG) -- (kin);
  \draw[->] (EEG) -- (pos);
  \draw[->] (EEG) -- (Syn);
  \draw[->] (EMG) edge[bend left,distance=1cm] (kin);
  \draw[->] (EMG) edge[bend left,distance=1.5cm] (pos);

  \draw[->,dashed] (EEG) .. controls (2.3,0.7) .. (pos);
  \draw[->,dashed] (EEG) .. controls (2.3,0.7) .. (kin);


  %legend
  \node (pred) at (0,3) {predicted};
  \node (comp) at (0,2.5) {computed};
  \node (via) at (-0.1,2) {predicted via};

  \draw[->, very thick] (comp) -- ++(0.5,0);
  \draw[->] (pred) -- ++(0.5,0);
  \draw[->, dashed] (via) -- ++(0.6,0);


\end{tikzpicture}