diff --git a/backend/app/services/garmin_connect_sync.py b/backend/app/services/garmin_connect_sync.py
index a1f9bb6..04c3e05 100644
--- a/backend/app/services/garmin_connect_sync.py
+++ b/backend/app/services/garmin_connect_sync.py
@@ -69,15 +69,20 @@ def authenticate_garmin(email: str, password_enc: str, token_store: Optional[str
 def sync_activities(garmin, user_id: int, since: Optional[datetime],
                     db, file_store_path: str) -> int:
     """
-    List activities since `since` from Garmin Connect, skip any already in the
-    DB, download FIT ZIPs for new ones, and queue them for processing.
+    List activities from Garmin Connect, skip any already in the DB, download
+    FIT ZIPs for new ones, and queue them for processing.
+
+    On first sync (since=None) fetches the full account history back to 2010.
+    On incremental syncs fetches from one day before last_sync_at.
     Returns the number of new activities queued.
     """
+    import time
     from app.workers.tasks import process_activity_file
     from app.models.user import Activity
-    from sqlalchemy import select
+    from sqlalchemy import select, func
 
-    start_date = (since - timedelta(days=1)).date() if since else (date.today() - timedelta(days=30))
+    # First sync: fetch everything; incremental: one day overlap to catch late uploads
+    start_date = (since - timedelta(days=1)).date() if since else date(2010, 1, 1)
     end_date = date.today()
 
     try:
@@ -94,14 +99,35 @@ def sync_activities(garmin, user_id: int, since: Optional[datetime],
         if not garmin_id:
             continue
 
-        # Skip if already imported (garmin_activity_id unique index)
+        # Fast path: already imported via Garmin Connect sync
         existing = db.execute(
             select(Activity).where(Activity.garmin_activity_id == garmin_id)
         ).scalar_one_or_none()
         if existing:
             continue
 
-        # Download original FIT (wrapped in a ZIP by Garmin)
+        # Slow-path dedup: activity imported via bulk export (no garmin_activity_id).
+        # Check by start_time; stamp the ID so future syncs skip it in the fast path.
+        act_start_str = act.get("startTimeLocal") or act.get("startTimeGMT") or ""
+        if act_start_str:
+            try:
+                from datetime import datetime as _dt
+                act_start = _dt.fromisoformat(act_start_str.replace("Z", "+00:00"))
+                time_match = db.execute(
+                    select(Activity).where(
+                        Activity.user_id == user_id,
+                        func.date(Activity.start_time) == act_start.date(),
+                    )
+                ).scalar_one_or_none()
+                if time_match:
+                    if not time_match.garmin_activity_id:
+                        time_match.garmin_activity_id = garmin_id
+                        db.commit()
+                    continue
+            except Exception:
+                pass  # couldn't parse time — fall through to download
+
+        # Download original FIT (Garmin wraps it in a ZIP)
         try:
             zip_bytes = garmin.download_activity(
                 int(garmin_id),
@@ -111,7 +137,7 @@ def sync_activities(garmin, user_id: int, since: Optional[datetime],
             logger.warning("Failed to download activity %s: %s", garmin_id, exc)
             continue
 
-        # Extract the FIT file from the ZIP
+        # Extract the FIT from the ZIP
         try:
             with zipfile.ZipFile(io.BytesIO(zip_bytes)) as zf:
                 fit_names = [n for n in zf.namelist() if n.lower().endswith(".fit")]
@@ -132,6 +158,9 @@ def sync_activities(garmin, user_id: int, since: Optional[datetime],
         process_activity_file.delay(str(dest), user_id, "fit", garmin_id)
         queued += 1
 
+        # Brief pause to avoid hammering the Garmin API
+        time.sleep(0.5)
+
     return queued
 
 
@@ -145,7 +174,8 @@ def sync_wellness(garmin, user_id: int, since: Optional[datetime], db) -> int:
     """
     from sqlalchemy import text
 
-    start_date = since.date() if since else (date.today() - timedelta(days=7))
+    # First sync: 90 days of wellness history; incremental: from last sync
+    start_date = since.date() if since else (date.today() - timedelta(days=90))
     days = (date.today() - start_date).days + 1
     processed = 0
 
diff --git a/backend/app/workers/tasks.py b/backend/app/workers/tasks.py
index afc0ae9..da33b71 100644
--- a/backend/app/workers/tasks.py
+++ b/backend/app/workers/tasks.py
@@ -93,6 +93,11 @@ def process_activity_file(self, file_path: str, user_id: int, source_type: str,
         ).scalar_one_or_none()
 
         if existing:
+            # Stamp garmin_activity_id if this came from a Garmin Connect sync
+            # so future syncs skip the fast-path dedup and don't re-download.
+            if garmin_activity_id and not existing.garmin_activity_id:
+                existing.garmin_activity_id = garmin_activity_id
+                db.commit()
             return {"activity_id": existing.id, "status": "duplicate"}
 
         # Get user max HR for zone calculation