diff --git a/backend/comments/permissions.py b/backend/comments/permissions.py
index b863cc7..4fc1da8 100644
--- a/backend/comments/permissions.py
+++ b/backend/comments/permissions.py
@@ -11,11 +11,32 @@ class IsCommentVisibleToUser(permissions.BasePermission):
     - The comment is on a workout owned by the user
     """
 
+    def has_permission(self, request, view):
+        # For POST requests, check if the user has permission to comment on the workout
+        if request.method == 'POST':
+            workout = request.data.get('workout', None)
+            if not workout:
+                return True  # Let the serializer handle the validation
+            
+            # Extract workout ID from URL
+            workout_id = workout.split('/')[-2]
+            try:
+                from workouts.models import Workout
+                workout = Workout.objects.get(id=workout_id)
+                return (
+                    workout.visibility == "PU"
+                    or workout.owner == request.user
+                    or (workout.visibility == "CO" and workout.owner.coach == request.user)
+                )
+            except:
+                return False
+        return True
+
     def has_object_permission(self, request, view, obj):
         # Write permissions are only allowed to the owner.
         return (
             obj.workout.visibility == "PU"
             or obj.owner == request.user
-            or (obj.workout.visibility == "CO" and obj.owner.coach == request.user)
+            or (obj.workout.visibility == "CO" and obj.workout.owner.coach == request.user)
             or obj.workout.owner == request.user
         )
diff --git a/backend/users/serializers.py b/backend/users/serializers.py
index 321a9ff..add716c 100644
--- a/backend/users/serializers.py
+++ b/backend/users/serializers.py
@@ -7,6 +7,7 @@
 class UserSerializer(serializers.HyperlinkedModelSerializer):
     password = serializers.CharField(style={"input_type": "password"}, write_only=True)
     password1 = serializers.CharField(style={"input_type": "password"}, write_only=True)
+    specialism = serializers.CharField(required=False, allow_blank=True, default="")
 
     class Meta:
         model = get_user_model()
@@ -46,11 +47,13 @@ def create(self, validated_data):
         username = validated_data["username"]
         email = validated_data["email"]
         isCoach = validated_data["isCoach"]
-        if (isCoach):
-            specialism = validated_data["specialism"]
-            user_obj = get_user_model()(username=username, email=email,isCoach=isCoach,specialism=specialism)
-        else:
-            user_obj = get_user_model()(username=username, email=email,isCoach=isCoach)
+        specialism = validated_data.get("specialism", "")
+        user_obj = get_user_model()(
+            username=username,
+            email=email,
+            isCoach=isCoach,
+            specialism=specialism
+        )
         password = validated_data["password"]
         user_obj.set_password(password)
         user_obj.save()
diff --git a/backend/workouts/models.py b/backend/workouts/models.py
index 22bffec..7bfede3 100644
--- a/backend/workouts/models.py
+++ b/backend/workouts/models.py
@@ -7,6 +7,7 @@
 from django.core.files.storage import FileSystemStorage
 from django.conf import settings
 from django.contrib.auth import get_user_model
+from users.validators import FileValidator
 
 
 class OverwriteStorage(FileSystemStorage):
@@ -136,5 +137,14 @@ class WorkoutFile(models.Model):
     owner = models.ForeignKey(
         get_user_model(), on_delete=models.CASCADE, related_name="workout_files"
     )
-    file = models.FileField(upload_to=workout_directory_path)
+    file = models.FileField(
+        upload_to=workout_directory_path,
+        validators=[
+            FileValidator(
+                allowed_extensions=['txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif'],
+                allowed_mimetypes=['text/plain', 'application/pdf', 'image/png', 'image/jpeg', 'image/gif'],
+                max_size=5 * 1024 * 1024  # 5MB
+            )
+        ]
+    )
 
diff --git a/backend/workouts/views.py b/backend/workouts/views.py
index 0387bc6..9d70fa7 100644
--- a/backend/workouts/views.py
+++ b/backend/workouts/views.py
@@ -5,6 +5,8 @@
 
 from rest_framework.parsers import (
     JSONParser,
+    MultiPartParser,
+    FormParser
 )
 from rest_framework.decorators import api_view
 from rest_framework.response import Response
@@ -240,7 +242,7 @@ class WorkoutFileList(
     queryset = WorkoutFile.objects.all()
     serializer_class = WorkoutFileSerializer
     permission_classes = [permissions.IsAuthenticated & IsOwnerOfWorkout]
-    parser_classes = [MultipartJsonParser, JSONParser]
+    parser_classes = [MultiPartParser, FormParser]
 
     def get(self, request, *args, **kwargs):
         return self.list(request, *args, **kwargs)