Reid, D. A., and J. Kim. “The Frequency of Hamstring Stretches Required to Maintain Knee Extension Range of Motion Following an Initial Six-Week Stretching Programme”. New Zealand Journal of Physiotherapy, vol. 42, no. 1, Mar. 2014, pp. 22–27, https://nzjp.otago.ac.nz/nzjp/article/view/73.