Cheung, C. K., Hong, Y. Veröffentlicht in coachesinfo.com “...strength and speed sports...”
Goldsmith, W. Veröffentlicht in coachesinfo.com “...strength...”
Persyn, U., Colman, V., Ungerechts, B. Veröffentlicht in coachesinfo.com (2000) “... undulation in butterfly is indicative for the best undulation in breaststroke. Flexibility and strength...”