diff --git a/bionc/vizualization/pyorerun_interface.py b/bionc/vizualization/pyorerun_interface.py
index 09f461bd..dd49f323 100644
--- a/bionc/vizualization/pyorerun_interface.py
+++ b/bionc/vizualization/pyorerun_interface.py
@@ -1,7 +1,7 @@
 import numpy as np
 
 from pyorerun.biorbd_components.model_display_options import DisplayModelOptions
-from ..bionc_numpy import NaturalVector
+from ..bionc_numpy import NaturalVector, NaturalCoordinates
 from ..bionc_numpy.joints import Joint
 from ..protocols.biomechanical_model import GenericBiomechanicalModel
 
@@ -51,6 +51,10 @@ def nb_segments(self) -> int:
     def segments(self) -> tuple["BioncSegment", ...]:
         return tuple(BioncSegment(s, i) for i, s in enumerate(self.model.segments.values()))
 
+    @property
+    def segment_names_with_mass(self) -> tuple[str, ...]:
+        return tuple([segment.name for segment in self.model.segments.values() if segment.mass > 0])
+
     def segment_homogeneous_matrices_in_global(self, q: np.ndarray, segment_index: int) -> np.ndarray:
         """
         Returns a biorbd object containing the roto-translation matrix of the segment in the global reference frame.
@@ -63,11 +67,12 @@ def segment_homogeneous_matrices_in_global(self, q: np.ndarray, segment_index: i
 
         return transform
 
-    def center_of_mass(self, q: np.ndarray) -> np.ndarray:
+    def centers_of_mass(self, q: np.ndarray) -> np.ndarray:
         """
         Returns the position of the center of mass in the global reference frame
         """
-        pass
+        Q = NaturalCoordinates(q[:, None])
+        return self.model.center_of_mass_position(Q).squeeze().T
 
     @property
     def nb_ligaments(self) -> int:
diff --git a/examples/play_with_joints/two_constant_length.py b/examples/play_with_joints/two_constant_length.py
index 89a7218c..1b452d2f 100644
--- a/examples/play_with_joints/two_constant_length.py
+++ b/examples/play_with_joints/two_constant_length.py
@@ -173,6 +173,16 @@ def main(initial_pose: str = "hanged", show_results: bool = True):
             all_states=all_states,
             dynamics=dynamics,
         )
+
+        # animation
+        from pyorerun import PhaseRerun
+        from bionc.vizualization.pyorerun_interface import BioncModelNoMesh
+
+        prr = PhaseRerun(t_span=time_steps)
+        model_interface = BioncModelNoMesh(model)
+        prr.add_animated_model(model_interface, NaturalCoordinates(all_states[: (12 * model.nb_segments), :]))
+        prr.rerun()
+
         # plot results
 
         import matplotlib.pyplot as plt
@@ -196,15 +206,6 @@ def main(initial_pose: str = "hanged", show_results: bool = True):
         plt.legend()
         plt.show()
 
-        # animation
-        from pyorerun import PhaseRerun
-        from bionc.vizualization.pyorerun_interface import BioncModelNoMesh
-
-        prr = PhaseRerun(t_span=time_steps)
-        model_interface = BioncModelNoMesh(model)
-        prr.add_animated_model(model_interface, NaturalCoordinates(all_states[: (12 * model.nb_segments), :]))
-        prr.rerun()
-
 
 if __name__ == "__main__":
     # main("hanged", show_results=True)
diff --git a/pyproject.toml b/pyproject.toml
index 0709e30e..f008ac53 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,20 +20,31 @@ classifiers = [
          "Operating System :: OS Independent",
      ]
 dependencies = [
-    - numpy
-    - packaging
+    "numpy",
+    "packaging",
     # "ezc3d", # Not yet available on pypi, use `conda install -c conda-forge ezc3d`
-    - plotly
-    - pyorerun
-    - python >=3.9
-    - casadi
-    - dill
-    - mesa-libgl-devel-cos7-x86_64
-    - pyomeca
-    - numba
+    "plotly",
+    "pyorerun",
+    "python >=3.9",
+    "casadi",
+    "dill",
+    "mesa-libgl-devel-cos7-x86_64",
+    "pyomeca",
+    "numba",
     # "biorbd" # Not yet available on pypi, use `conda install -c conda-forge biorbd`
-    ]
-keywords = ["inverse-kinematics", "biomechanics", "multibody-dynamics", "mechanics motion-analysis", "kinesiology", "inverse-dynamics, "cartesian-coordinates", "forward-dynamics", "holonomic-constraints", "natural-coordinates"]
-
+]
+keywords = [
+    "inverse-kinematics",
+    "biomechanics",
+    "multibody-dynamics",
+    "mechanics",
+    "motion-analysis",
+    "kinesiology",
+    "inverse-dynamics",
+    "cartesian-coordinates",
+    "forward-dynamics",
+    "holonomic-constraints",
+    "natural-coordinates"
+]
 [project.urls]
 homepage = "http://github.com/Ipuch/bionc"