diff --git a/backend/data_layer/activity_session_metrics.py b/backend/data_layer/activity_session_metrics.py
index 84fe49c..62783ef 100644
--- a/backend/data_layer/activity_session_metrics.py
+++ b/backend/data_layer/activity_session_metrics.py
@@ -260,15 +260,18 @@ def upsert_session_metrics_from_csv_mapped(
     nur in ``activity_log``-Kernfeldern).
 
     Kernfelder schreibt der Executor nach ``activity_log``; hier keine EAV-Zeilen für Registry-Keys.
-    Bei gesetztem ``training_parameters.source_field`` ist die Spalte kanonisch — kein EAV-Schreiben.
+
+    Hat ein Parameter ``source_field`` (Semantik aus ``activity_log``), wird EAV nur dann **nicht**
+    geschrieben, wenn diese Spalte nach dem Import bereits befüllt ist — sonst gäbe es doppelte
+    Speicherung und der Merge würde ohnehin die Spalte bevorzugen. Ist die Spalte leer (z. B. Feld
+    nur noch über EAV / Custom-Mapping, ohne Registry-Patch), schreibt der Import den Wert aus
+    ``mapped`` nach EAV — analog zum Lesepfad (Spalte zuerst, sonst EAV).
     """
-    cur.execute(
-        "SELECT profile_id FROM activity_log WHERE id = %s",
-        (activity_log_id,),
-    )
+    cur.execute("SELECT * FROM activity_log WHERE id = %s", (activity_log_id,))
     row = cur.fetchone()
     if not row or str(row["profile_id"]) != str(profile_id):
         return
+    header = dict(row)
     schema = resolve_activity_attribute_schema(cur, training_category, training_type_id)
     for spec in schema:
         pkey = spec["key"]
@@ -281,7 +284,9 @@ def upsert_session_metrics_from_csv_mapped(
             continue
         sf_raw = spec.get("source_field")
         if sf_raw is not None and str(sf_raw).strip():
-            continue
+            col = str(sf_raw).strip()
+            if col in header and header[col] is not None:
+                continue
         tid = spec["training_parameter_id"]
         dt = spec["data_type"]
         rules = _validation_rules_dict(spec["validation_rules"])
diff --git a/backend/tests/test_activity_session_metrics.py b/backend/tests/test_activity_session_metrics.py
index 8cb1bdf..21dd2e5 100644
--- a/backend/tests/test_activity_session_metrics.py
+++ b/backend/tests/test_activity_session_metrics.py
@@ -329,7 +329,10 @@ def test_upsert_csv_skips_eav_when_source_field_maps_activity_log(mock_schema):
                 self.asm_inserts += 1
 
         def fetchone(self):
-            return {"profile_id": "00000000-0000-0000-0000-000000000001"}
+            return {
+                "profile_id": "00000000-0000-0000-0000-000000000001",
+                "hr_avg": 130,
+            }
 
     cur = Cur()
     upsert_session_metrics_from_csv_mapped(
@@ -343,6 +346,45 @@ def test_upsert_csv_skips_eav_when_source_field_maps_activity_log(mock_schema):
     assert cur.asm_inserts == 0
 
 
+@patch("data_layer.activity_session_metrics.resolve_activity_attribute_schema")
+def test_upsert_csv_writes_eav_when_source_field_but_column_empty(mock_schema):
+    """source_field gesetzt, activity_log-Spalte leer — Wert aus mapped nur in EAV (kein Registry-Patch)."""
+    mock_schema.return_value = [
+        {
+            "key": "avg_hr",
+            "training_parameter_id": 42,
+            "data_type": "integer",
+            "validation_rules": {"min": 30, "max": 220},
+            "source_field": "hr_avg",
+        }
+    ]
+
+    class Cur:
+        def __init__(self):
+            self.asm_inserts = 0
+
+        def execute(self, sql, params=None):
+            if "INSERT INTO activity_session_metrics" in sql:
+                self.asm_inserts += 1
+
+        def fetchone(self):
+            return {
+                "profile_id": "00000000-0000-0000-0000-000000000001",
+                "hr_avg": None,
+            }
+
+    cur = Cur()
+    upsert_session_metrics_from_csv_mapped(
+        cur,
+        "00000000-0000-0000-0000-000000000001",
+        "00000000-0000-0000-0000-000000000002",
+        {"avg_hr": 130},
+        "cardio",
+        1,
+    )
+    assert cur.asm_inserts == 1
+
+
 @patch("data_layer.activity_session_metrics.resolve_activity_attribute_schema")
 def test_upsert_csv_writes_eav_when_no_source_field(mock_schema):
     mock_schema.return_value = [
@@ -364,7 +406,7 @@ def test_upsert_csv_writes_eav_when_no_source_field(mock_schema):
                 self.asm_inserts += 1
 
         def fetchone(self):
-            return {"profile_id": "00000000-0000-0000-0000-000000000001"}
+            return {"profile_id": "00000000-0000-0000-0000-000000000001", "hr_avg": None}
 
     cur = Cur()
     upsert_session_metrics_from_csv_mapped(
@@ -390,7 +432,7 @@ def test_upsert_csv_skips_eav_when_mapped_key_not_in_profile_schema(mock_resolve
                 self.asm_inserts += 1
 
         def fetchone(self):
-            return {"profile_id": "00000000-0000-0000-0000-000000000001"}
+            return {"profile_id": "00000000-0000-0000-0000-000000000001", "hr_avg": None}
 
     cur = Cur()
     upsert_session_metrics_from_csv_mapped(