private function writeTracks(\XMLWriter $xmlWriter, Workout $workout)
    {
        foreach ($workout->tracks() as $track) {
            $xmlWriter->startElement('trk');
            $xmlWriter->writeElement('type', $track->sport());
            $xmlWriter->startElement('trkseg');
            $this->writeTrackPoints($xmlWriter, $track->trackPoints());
            $xmlWriter->endElement();
            $xmlWriter->endElement();
        }
    }