diff --git a/supirfactor_dynamical/models/biophysical_model.py b/supirfactor_dynamical/models/biophysical_model.py
index f246d28..a92435e 100644
--- a/supirfactor_dynamical/models/biophysical_model.py
+++ b/supirfactor_dynamical/models/biophysical_model.py
@@ -422,10 +422,7 @@ def _training_step(
         :rtype: float, float, float
         """
 
-        if (
-            self.separately_optimize_decay_model and
-            self._decay_optimize(epoch_num)
-        ):
+        if self.separately_optimize_decay_model:
 
             # Call the training step and compare the negative velocity
             # to the decay output data
@@ -450,14 +447,24 @@ def _training_step(
 
             decay_loss = 0.
 
+        # Call the main training step and compare velocity to the
+        # expected output velocity
         loss = super()._training_step(
             epoch_num,
             train_x,
-            optimizer[2] if self._decay_optimize(epoch_num) else
-            optimizer[0],
-            loss_function
+            None,
+            loss_function,
+            optimizer_step=False
         )
 
+        if self._decay_optimize(epoch_num):
+            _optimizer = optimizer[2]
+        else:
+            _optimizer = optimizer[0]
+
+        _optimizer.step()
+        _optimizer.zero_grad()
+
         return loss, decay_loss
 
     def _calculate_all_losses(