Nsenga Leunkeu, A., R. Shephard, and S. Ahmaidi. “A Brief History of Exercise Clearance and Prescription: 1. The Era of Heart Rate Recovery Curves”. The Health & Fitness Journal of Canada, Vol. 7, no. 1, Jan. 2014, pp. 26-35, doi:10.14288/hfjc.v7i1.155.