diff --git a/rowers/dataprep.py b/rowers/dataprep.py
index e73bc863..42efff8f 100644
--- a/rowers/dataprep.py
+++ b/rowers/dataprep.py
@@ -415,7 +415,7 @@ def resample(id, r, parent, overwrite='copy'):
 def calculate_goldmedalstandard(rower, workout, recurrance=True):
     cpfile = 'media/cpdata_{id}.parquet.gz'.format(id=workout.id)
     try:
-        df = pd.read_parquet(cpfile)
+        df = pl.read_parquet(cpfile)
     except:
         background = True
         if settings.TESTING:
@@ -423,11 +423,13 @@ def calculate_goldmedalstandard(rower, workout, recurrance=True):
         df, delta, cpvalues = setcp(workout, background=background)
         if df.empty:
             return 0, 0
+        df = pl.from_pandas(df)
 
-    if df.empty and recurrance:  # pragma: no cover
+    if df.is_empty() and recurrance:  # pragma: no cover
         df, delta, cpvalues = setcp(workout, recurrance=False, background=True)
         if df.empty:
             return 0, 0
+        df = pl.from_pandas(df)
 
     age = calculate_age(rower.birthdate, today=workout.date)
 
@@ -490,9 +492,10 @@ def calculate_goldmedalstandard(rower, workout, recurrance=True):
     scores = 100.*powers/wcpowers
 
     try:
-        indexmax = scores.idxmax()
-        delta = int(df.loc[indexmax, 'delta'])
-        maxvalue = scores.max()
+        df = pl.DataFrame({'times': times, 'scores': scores})
+        df = df.filter(pl.col("scores") == pl.col("scores").max())
+        delta = df[0, "times"]
+        maxvalue = df[0, "scores"]
     except (ValueError, TypeError, KeyError):  # pragma: no cover
         indexmax = 0
         delta = 0